Sodium-ion battery positive electrode material, preparation method thereof, positive electrode sheet, battery and electric device

Abstract

The application belongs to the technical field of batteries, and provides a sodium-ion battery positive electrode material, a preparation method thereof, a positive electrode sheet, a battery and an electric device. The sodium-ion battery positive electrode material comprises a sodium-containing positive electrode material base body and a coating layer coated on at least part of the surface of the sodium-containing positive electrode material base body; wherein the coating layer comprises a metal phosphate containing at least sodium and aluminum elements. The battery prepared from the sodium-ion battery positive electrode material has the characteristics of high battery capacity and good cycle stability.

Description

Technical Field

[0001] This application belongs to the field of battery technology, specifically relating to a sodium-ion battery positive electrode material and its preparation method, positive electrode sheet, battery, and power-consuming device. Background Technology

[0002] Sodium-ion batteries are rechargeable batteries that primarily rely on the movement of sodium ions between the positive and negative electrodes. Rechargeable batteries, represented by sodium-ion batteries, have been applied in various fields, including energy storage systems (such as hydropower, thermal power, wind power, and solar power plants), electric vehicles, and aerospace. Compared to lithium-ion batteries, sodium-ion batteries have a significant cost advantage in raw materials, especially for the cathode material, which accounts for a large portion of the cost. Sodium salts, the main component of sodium-ion battery cathode materials, are more abundant, and their price is much lower than that of lithium salts used in lithium-ion battery cathode materials, making sodium-ion battery cathode materials less expensive than lithium-ion batteries. However, the poor electrochemical performance of sodium-ion batteries in terms of capacity, rate capability, and stability limits their practical applications. Summary of the Invention

[0003] To address the aforementioned problems, the purpose of this application is to provide a sodium-ion battery cathode material, its preparation method, a cathode sheet, a battery, and an electrical device. Batteries prepared using the aforementioned sodium-ion battery cathode material exhibit high capacity and good cycle stability.

[0004] In a first aspect, this application provides a sodium-ion battery cathode material, comprising: a sodium-containing cathode material matrix, and a coating layer covering at least a portion of the surface of the sodium-containing cathode material matrix; wherein the coating layer comprises a metal phosphate, and the metal phosphate contains at least sodium and aluminum. In the sodium-ion battery cathode material of this application, the metal phosphate containing at least sodium and aluminum is distributed on the matrix as a coating layer component, which not only reduces the residual alkali content on the matrix surface but also makes the coating layer conductive, stabilizing the interface while promoting the migration of sodium ions.

[0005] In some embodiments of this application, the chemical formula of the metal phosphate is Na. x1 Al y1 L y2 P z O sThe L element comprises at least one of Ca, Mg, Fe, Ti, V, Cr, Mn, Ni, La, Ce, Sr, Cu, Zn, Y, Zr, Nb, and Mo; x1 > 0, y1 > 0, y2 ≥ 0, z > 0, and s > 0. The coating layer comprises a metal phosphate containing aluminum, sodium, and optionally the aforementioned metal element L, transforming the poorly conductive residual alkali on the substrate into a conductive network of metal oxide-phosphorus oxide, thereby improving the conductivity of the cathode material. Optionally, the chemical formula of the metal phosphate is NaAl. y1 L y2 P z O2, and 0 < y1 < 1, 0 ≤ y2 < 1, 0 < z < 1.

[0006] In some embodiments of this application, the molar ratio of aluminum to phosphorus in the metal phosphate in the coating layer can be 0.1-10, which can improve the stability of the coating layer on the substrate surface. Optionally, the molar ratio of aluminum to phosphorus is 0.1-0.6, thereby giving the coating layer high stability while further improving the conductivity of the cathode material.

[0007] In some embodiments of this application, the thickness of the coating layer can be 1 nm to 100 nm. Optionally, the thickness of the coating layer is 5 nm to 25 nm, thereby reducing the migration path of sodium ions and improving rate performance while ensuring the coating effect.

[0008] In some embodiments of this application, the sodium-containing cathode material matrix may include a layered oxide, the chemical formula of which is Na. x2 Mn a Fe b M c A d O 2-e+f Q e Wherein, M includes at least one of Cu, Ni, Li, Ti, Zr, K, La, Ce, Sr, Sb, Nb, Mg, Ca, Mo, Zn, Cr, W, Bi, Sn, Ge and Al; A includes at least one of Si, P, B, S and Se; Q includes at least one of F, Cl and N; a > 0, b > 0, c ≥ 0, d ≥ 0, and a + b + c + d = 1, x² ≥ 0.66, 0 ≤ e ≤ 0.1, -0.1 ≤ f ≤ 0.

[0009] In some embodiments of this application, the layered oxide is an O3-type layered oxide. During the preparation of the cathode material, the surface of the O3 layered oxide contains more residual alkali. Sufficient residual alkali can provide a sodium source for the coating layer during sintering, thereby forming a sodium-containing coating layer and converting the poorly conductive residual alkali into a coating layer with better conductivity, which can improve the rate performance of the material.

[0010] In some embodiments of this application, the mass ratio of the coating layer to the sodium-containing cathode material can be (0.1-10):100. Optionally, the mass ratio of the coating layer to the sodium-containing cathode material substrate is (0.2-2):100. This, while ensuring the coating effect, can further improve the migration efficiency of sodium ions and enhance the rate performance of the material.

[0011] Secondly, this application provides a method for preparing the sodium-ion battery cathode material, the method comprising: mixing coating raw materials, including an aluminum source and a phosphorus source, with a sodium-containing cathode material matrix and sintering. This method can reduce the residual alkali generated in the sodium-containing cathode material matrix. During sintering, the residual alkali is converted into a conductive network containing Na2O-P2O5, and Na2O-P2O5 is combined with aluminum-containing metal oxides to form a metal phosphate containing at least sodium and aluminum elements coated on the matrix surface, thereby obtaining the sodium-ion battery cathode material.

[0012] In some embodiments of this application, the aluminum source includes at least one of aluminum oxide and aluminum hydroxide.

[0013] In some embodiments of this application, the phosphorus source includes at least one of ammonium dihydrogen phosphate and ammonium metaphosphate.

[0014] In some embodiments of this application, the aluminum source is alumina, and the median particle size of the alumina is 10 nm-50 nm; the phosphorus source is ammonium dihydrogen phosphate, and the median particle size of the ammonium dihydrogen phosphate is 1 μm-15 μm. Therefore, the material of the resulting coating layer can be more uniformly dispersed on the substrate surface, improving the electrochemical performance of the cathode material.

[0015] In some embodiments of this application, the coating material further includes at least one of titanium dioxide (TiO2) and calcium oxide (CaO). The addition of CaO can further form NaCaPO4 in the coating layer. The presence of NaCaPO4 allows it to effectively remove water from the electrolyte and suppress the influence of HF during battery cycling. The specific reaction is as follows:

[0016] NaCaPO4 + HF → CaHPO4 + NaF

[0017] 2NaCaPO4+H2O→2CaHPO4+Na2O;

[0018] The introduction of TiO2 can form NaTi2(PO4)3 solid electrolyte on the substrate surface, which not only has high ionic conductivity but also excellent thermal stability.

[0019] In some embodiments of this application, the sintering temperature can be 100℃-1000℃. Optionally, the sintering temperature is 300℃-600℃, thereby promoting the reaction between the phosphorus source and the residual alkali in the matrix, and making the formed coating layer more tightly bonded to the matrix.

[0020] In some embodiments of this application, the sintering time is 1 hour to 24 hours. Optionally, the sintering time is 3 hours to 10 hours, thereby ensuring the coating effect while further preventing the diffusion of lattice sodium to the surface.

[0021] In some embodiments of this application, the mixing includes: first mixing the components in the coating layer raw material to obtain a composite coating agent; and then second mixing the composite coating agent with a sodium-containing cathode material matrix.

[0022] Optionally, the conditions for the first mixing include: a rotation speed of 800 rpm to 1200 rpm and a mixing time of 20 min to 60 min. This results in a composite coating agent with uniformly dispersed components, improving the coating effect.

[0023] Optionally, the conditions for the second mixing include: a rotation speed of 800 rpm to 1000 rpm and a time of 20 min to 30 min.

[0024] Thirdly, this application provides a positive electrode sheet comprising the sodium-ion battery positive electrode material described in the first aspect of this application or the sodium-ion battery positive electrode material prepared by the method described in the second aspect of this application.

[0025] Fourthly, this application provides a battery comprising the sodium-ion battery positive electrode material described in the first aspect of this application or the sodium-ion battery positive electrode material prepared by the method described in the second aspect of this application, or comprising the positive electrode sheet described in the third aspect of this application.

[0026] Fifthly, this application provides an electrical device including the battery described in the fourth aspect of this application.

[0027] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0028] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. In the drawings:

[0029] Figure 1 This is a scanning electron microscope image of the sodium-ion battery cathode material prepared in Example 1;

[0030] Figure 2 This is a scanning electron microscope image of the sodium-containing cathode material in Comparative Example 1;

[0031] Figure 3 Comparison of cycle performance of sodium-ion batteries prepared using the cathode materials of Example 1 and Comparative Example 1;

[0032] Figure 4 This is a schematic diagram of the structure of a battery according to one embodiment of this application;

[0033] Figure 5 This is a schematic diagram of the structure of a battery module according to one embodiment of this application;

[0034] Figure 6 This is a schematic diagram of the structure of a battery pack according to one embodiment of this application;

[0035] Figure 7 for Figure 6 Exploded view;

[0036] Figure 8 A schematic diagram of one embodiment of an electrical device that uses a battery as a power source.

[0037] Explanation of reference numerals in the attached figures:

[0038] 1: Battery; 2: Battery module; 3: Battery pack; 4: Upper casing; 5: Lower casing. Detailed Implementation

[0039] The present application will be further described below with reference to specific embodiments. It should be understood that these specific embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0040] In this application, the term "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this application can be combined with other embodiments.

[0041] The "range" disclosed in this application is defined in the form of a lower limit and / or an upper limit. A given range is defined by selecting a lower limit and / or an upper limit, which defines the boundary of the particular range. Ranges defined in this way may or may not include endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form an undefined range, and any lower limit can be combined with other lower limits to form an undefined range. Similarly, any upper limit can be combined with any other upper limit to form an undefined range. Furthermore, each individually disclosed point or single value can itself serve as a lower limit or upper limit, combined with any other point or single value, or combined with other lower limits or upper limits to form an undefined range.

[0042] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0043] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0044] Unless otherwise specified, the terms "comprising," "including," "containing," "containing," and "having" as used in this application can be open-ended or closed-ended. For example, "comprising," "including," "containing," and "having" can mean that other unlisted components may also be included, or that only the listed components may be included. Furthermore, in this application, the terms "multiple," "at least one," and "amount" refer to two or more. "Above" and "below" include the stated number. For example, "two or more" includes two of themselves, such as two, three, four, or more.

[0045] Unless otherwise specified, in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0046] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit this application; the terms "comprising" and "having," and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion. Unless otherwise stated, the terms used in this application have their commonly understood meanings as understood by one of ordinary skill in the art. Unless otherwise stated, the numerical values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0047] Although sodium-ion battery cathode materials have similar performance to lithium-ion cathode materials, their interfaces are more sensitive to air and electrolytes during both storage and use. Currently, in the sodium battery field, sodium-ion cathode materials have high interfacial impedance, severely hindering the exchange of sodium ions (Na₂O₃). + The migration of sodium ion cathode materials leads to a decrease in the electrochemical performance of the battery, and the residual alkali on the surface of sodium ion cathode materials (especially layered oxides) also causes a significant decrease in capacity. Therefore, it is necessary to modify sodium ion cathode materials.

[0048] Accordingly, a first aspect of this application provides a sodium-ion battery cathode material, comprising: a sodium-containing cathode material matrix, and a coating layer covering at least a portion of the surface of the sodium-containing cathode material matrix. The coating layer comprises a metal phosphate containing at least sodium and aluminum. In the sodium-ion battery cathode material of this application, the coating layer containing the metal phosphate can shield against air and electrolyte. This coating layer not only reduces the residual alkali content on the matrix surface but also has conductivity, stabilizing the interface while promoting sodium ion migration and improving the rate performance of the battery. In this application, "metal phosphate" refers to a complex containing a metal element, phosphorus element, and oxygen element. The elements in the complex can exist in various component forms. Due to differences in the coating agent ratio, the alkali content of the substrate surface, and the preparation conditions, these components may include, but are not limited to, oxides of metal elements (such as Al2O3, TiO2), oxyacid salts of metal elements (such as Na2TiO3), oxides of phosphorus (such as P2O5), and various inorganic substances composed of metal elements, phosphorus, and oxygen elements (such as NaPO3, NaTi2(PO4)3, NaAl). 0.4 Ti 0.2 PO4).

[0049] In some embodiments, the chemical formula of the metal phosphate is Na. x1 Al y1 L y2 P z O sWherein, L includes at least one of Ca, Mg, Fe, Ti, V, Cr, Mn, Ni, La, Ce, Sr, Cu, Zn, Y, Zr, Nb, and Mo; x1 > 0, y1 > 0, y2 ≥ 0, z > 0, s > 0. The coating layer includes a metal phosphate containing aluminum, sodium, and optionally the aforementioned metal element L, which transforms the poorly conductive residual alkali on the substrate into a conductive network of metal oxide (including aluminum oxide compounds and optionally metal L oxides)-phosphorus oxide, thereby improving the conductivity of the cathode material. Na x1 Al y1 L y2 P z O s The net charge is zero. A net charge of zero means that the Na... x1 Al y1 L y2 P z O s In this system, the algebraic sum of the positive charges of sodium ions, aluminum ions, phosphorus ions, and metallic L ions, and the negative charges of oxygen ions, is zero. For example, when y2 = 0, a net charge of zero indicates that x1, y1, z, and s satisfy the relationship x1 + 3y1 + 5z = 2s; when y2 > 0, a net charge of zero indicates that x1, y1, y2, z, and s satisfy the relationship x1 + 3y1 + my2 + 5z = 2s, where m represents the number of positive charges carried by metallic L ions. For example, when L is Mg, the number of positive charges of L ions is m = 2. The net charge can be measured using X-ray photoelectron spectroscopy (XPS).

[0050] In some embodiments, the molar ratio of aluminum to phosphorus in the metal phosphate in the coating layer is 0.1-10, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 3.5, 4, 5, 8, 9, etc.; thus, the coating layer located on the substrate surface has high stability. Optionally, the molar ratio of aluminum to phosphorus in the metal phosphate is 0.1-0.6, which can further improve the conductivity of the cathode material while ensuring coating stability.

[0051] In this application, when the metal phosphate is represented by the relevant chemical formula, the molar ratio of aluminum to phosphorus is equivalent to the ratio of y1 to z in the corresponding subscripts of Al and P.

[0052] In some specific embodiments, the chemical formula of the metal phosphate is NaAl. y1 L y2 P zO2, where 0 < y1 < 1, 0 ≤ y2 < 1, 0 < z < 1. In this embodiment, Na is used as the reference to represent the relative molar amounts of Al, L, and P; where y1 can optionally satisfy the relationship 0.01 < y1 < 0.9, or more preferably 0.05 < y1 < 0.3; y2 can optionally satisfy the relationship 0 ≤ y2 < 0.5, or more preferably 0 ≤ y2 < 0.3; z can optionally satisfy the relationship 0.1 < z < 0.9, or more preferably 0.2 < z < 0.6.

[0053] In some embodiments, the thickness of the coating layer can be 1 nm to 100 nm, such as 1 nm, 2 nm, 3 nm, 5 nm, 10 nm, 11 nm, 15 nm, 18 nm, 20 nm, 25 nm, 30 nm, 40 nm, 45 nm, 50 nm, 60 nm, etc. Optionally, the thickness of the coating layer is 5 nm to 25 nm. This reduces the migration path of sodium ions while ensuring the coating effect, thus improving rate performance. The thickness of the coating layer can be obtained by transmission electron microscopy analysis.

[0054] This application does not specifically limit the sodium-containing cathode material matrix, and it can be any sodium-ion cathode material well known in the art, such as at least one of layered oxides, Prussian blue compounds, and polyanionic compounds. Furthermore, this application is particularly suitable for improving the electrochemical performance of sodium-containing cathode materials with high residual alkali content. From this perspective, optionally, the sodium-containing cathode material is a layered oxide. The layered oxide typically includes sodium-containing transition metal layered oxides.

[0055] In some embodiments, the chemical formula of the layered oxide is Na. x2 Mn a Fe b M c A d O 2-e+f Q e, a>0, b>0, c≥0, d≥0, and a+b+c+d=1, x2≥0.66, 0≤e≤0.1; wherein, M includes at least one of Cu, Ni, Li, Ti, Zr, K, La, Ce, Sr, Sb, Nb, Mg, Ca, Mo, Zn, Cr, W, Bi, Sn, Ge and Al, and may be selected as at least one of Ni, Cu, Zn, Ti, Zr, Ca and Al; A includes at least one of Si, P, B, S and Se; Q includes at least one of F, Cl and N; a>0, may be selected as 0.1<a≤0.6; b>0, may be selected as 0.1<b≤0.6; c≥0, may be selected as 0≤c≤0.9, d≥0, and a+b+c+d=1; x2≥0.66, may be selected as 0.66≤x2≤1; 0≤e≤0.1, -0.1≤f≤0. It should be understood that when the O site in the layered oxide is doped with Q, during the high-temperature synthesis process, lattice oxygen release will occur, making the sum of the subscripts of O and Q in the chemical formula 2+f less than 2.

[0056] In some embodiments, the layered oxide is an O3-type layered oxide. During the preparation of the sodium-ion battery cathode material, the surface of the O3 layered oxide contains more residual alkali, which has poor conductivity. However, sufficient residual alkali can be transformed into a coating layer with better conductivity during sintering, thereby improving the rate performance of the material.

[0057] In some embodiments, the particle size D of the sodium-containing cathode material matrix V 50 is 1μm-15μm, such as 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, etc. Matrix particle size D V 50 can be measured using a laser particle size analyzer.

[0058] In this application, the mass of the coating layer can be determined based on the mass of the sodium-containing cathode material substrate. In some embodiments, the mass ratio of the coating layer to the sodium-containing cathode material substrate in the sodium-ion battery cathode material is (0.1-10):100, for example, 0.1:100, 0.2:100, 0.3:100, 0.4:100, 0.5:100, 0.6:100, 0.7:100, 0.8:100, 0.9:100, 1:100, 1.1:100, 1.2:100, 1.5:100, 1.8:100, 2:100, 3:100, 4:100, 5:100, 6:100, 7:100, 8:100, 9:100, etc. Optionally, the mass ratio of the coating layer to the sodium-containing cathode material matrix is ​​(0.2-2):100, which can further improve the migration efficiency of sodium ions and improve the rate performance of the material while ensuring the coating effect.

[0059] A second aspect of this application provides a method for preparing the sodium-ion battery cathode material, the method comprising: mixing coating raw materials, including an aluminum source and a phosphorus source, with a sodium-containing cathode material matrix and sintering. This method can reduce the residual alkali generated in the sodium-containing cathode material matrix. During the sintering process, the residual alkali is first converted into a conductive network with Na2O-P2O5, and the Na2O-P2O5 combines with aluminum-containing metal oxides to form a metal phosphate containing at least sodium and aluminum elements coated on the matrix surface, thereby obtaining the sodium-ion battery cathode material.

[0060] According to the method of this application, the sodium-containing cathode material matrix can be commercially available or prepared using methods well-known in the art; this application does not impose any particular limitation on this. In some embodiments, the sodium-containing cathode material matrix is ​​Na. x2 Mn a Fe b M c A d O 2-e+f Q eThe precursor is prepared by a method comprising the following steps: uniformly mixing a transition metal source (including a manganese source, an iron source, and optionally an M source and an A source) and a sodium source according to the component ratio of the chemical formula to obtain a sodium-containing cathode material precursor; and then calcining, cooling, and crushing the precursor. It should be understood that, to avoid sodium volatilization at high temperatures, the relative amounts of the sodium source and each transition metal source may be slightly higher than the ratio shown in their chemical formulas, for example, 3% higher. The transition metal source may include oxides of transition metals. As an example, the transition metal source includes iron oxide, manganese oxide, nickel oxide, etc., and the sodium source includes one or more of Na₂CO₃, NaHCO₃, NaOH, and Na₂O₂. The calcination temperature may be 500℃-1300℃, for example, 500℃, 600℃, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃, etc. The calcination time can be 5h-20h, for example 5h, 6h, 7h, 8h, 9h, 10h, 12h, 14h, 15h, 18h, 20h, etc. The crystal phase structure of the prepared sodium-containing cathode material matrix can be determined by X-ray diffraction (XRD), and the elemental composition can be determined by inductively coupled plasma atomic emission spectrometry (ICP).

[0061] According to the method of this application, the aluminum source in the coating material may include a solid aluminum source, which is typically selected from various aluminum-containing compounds that can be converted into aluminum oxide during sintering. In some embodiments, for the sake of raw material availability, the aluminum source includes at least one of alumina and aluminum hydroxide.

[0062] According to the method of this application, the phosphorus source in the coating material may include a solid phosphorus source, which is typically selected as a phosphorus-containing compound capable of being converted into phosphorus oxides during sintering. As an example, the phosphorus source includes one or more of acidic solid phosphorus sources and neutral solid phosphorus sources. Optionally, the phosphorus source includes at least one of ammonium dihydrogen phosphate and ammonium metaphosphate.

[0063] In some specific embodiments, the aluminum source is alumina, and the phosphorus source is ammonium dihydrogen phosphate. The median particle size of the alumina can be 10nm-50nm, such as 10nm, 15nm, 20nm, 22nm, 25nm, 30nm, 35nm, 40nm, 45nm, etc.; the median particle size of the ammonium dihydrogen phosphate can be 1μm-15μm, such as 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 12μm, 13μm, 14μm, 15μm, etc. The nano-sized alumina and micron-sized ammonium dihydrogen phosphate are uniformly mixed with the matrix. As an example, during the low-temperature sintering stage, ammonium dihydrogen phosphate readily undergoes the following reaction:

[0064] 190℃: NH4H2PO4→H3PO4+NH3↑

[0065] 215℃: 2H3PO4 → H4P2O7 + H2O

[0066] 300℃: H4P2O7 → 2HPO3 + H2O

[0067] HPO3 + Na2O → Na x3 (PO) y +H2O↑

[0068] HPO3 + NaOH → Na x3 (PO) y +H2O

[0069] HPO3 + Na2CO3 → Na x3 (PO) y +CO2+H2O↑;

[0070] Through the aforementioned decomposition and acid-base neutralization reactions, the poorly conductive residual alkalis (including Na₂O, NaOH, and Na₂CO₃) on the matrix are transformed into a Na₂O-P₂O₅ conductive network. Furthermore, the Na₂O-P₂O₅ further complexes with Al₂O₃, forming metal phosphates that coat the matrix surface, stabilizing the interface and improving the material's electrochemical performance. In addition, using ammonium dihydrogen phosphate as a raw material, which decomposes into phosphoric acid upon heating, exhibits stronger reactivity with residual alkalis, thus more effectively removing them.

[0071] In some embodiments, the coating material is composed of the aluminum source and the phosphorus source. In other embodiments, the coating material is composed of the aluminum source, the phosphorus source, and an L source. The L source can be a solid L source, such as an oxide containing element L.

[0072] In some embodiments, the coating material further includes at least one of titanium oxide and calcium oxide.

[0073] As an example, the median particle size of titanium dioxide is 20μm-50μm, such as 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, etc.

[0074] As an example, the median particle size of calcium oxide is 20μm-50μm, such as 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, etc.

[0075] In some embodiments, the mixing process includes: first mixing the components (aluminum source, phosphorus source, and optionally L source) in the coating material to obtain a composite coating agent; and second mixing the composite coating agent with the sodium-containing cathode material matrix. This two-stage mixing improves the uniformity of the coating material's dispersion in the matrix.

[0076] In some embodiments, the first mixing can be carried out on a ball mill. Optionally, the conditions for the first mixing include: a rotation speed of 800 rpm to 1200 rpm and a time of 20 min to 60 min. This yields a composite coating agent with uniformly dispersed components.

[0077] In some embodiments, the second mixing can be carried out on a mixer (e.g., a mechanical fusion machine). Optionally, the conditions for the second mixing include: a rotation speed of 800 rpm to 1000 rpm and a time of 20 min to 30 min. This reduces energy consumption while ensuring the dispersion of the composite coating agent in the sodium-containing cathode material matrix.

[0078] According to the method of this application, the sintering of the precursor obtained after mixing can be carried out in an oxygen-containing atmosphere, such as oxygen or air, to obtain a phosphate coating layer comprising at least aluminum (Al) and sodium (Na). The elemental composition of the coating layer can be obtained by XPS elemental valence state analysis combined with ICP analysis.

[0079] In some embodiments, the sintering temperature is 100℃-1000℃, for example, 100℃, 150℃, 190℃, 200℃, 210℃, 215℃, 280℃, 300℃, 350℃, 400℃, 500℃, 600℃, 700℃, 750℃, 800℃, 900℃, 1000℃, etc. Optionally, the sintering temperature is 300-600℃, thereby promoting the reaction between the phosphorus source and the residual alkali in the matrix, and making the formed coating layer more tightly bonded to the matrix. In particular, when the phosphorus source is ammonium dihydrogen phosphate, controlling the sintering temperature within this range can, on the one hand, control the volatilization rate of ammonium dihydrogen phosphate, allowing it to react effectively with the residual alkali, and on the other hand, avoid the crystallization of Al2O3-P2O5 formed due to excessively high reaction temperature (the performance of crystalline coating layers is inferior to that of amorphous coating layers). In addition, controlling the sintering temperature within this range can further prevent the coating agent from being doped into the matrix due to excessively high temperatures, which would reduce the coating effect (this problem leads to increased Na volatilization and capacity loss).

[0080] In some embodiments, the sintering time is 1 hour to 24 hours, for example, 1 hour, 2 hours, 2.5 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, 20 hours, 22 hours, 24 hours, etc. Optionally, the sintering time is 3 hours to 10 hours, which can ensure the coating effect while minimizing the diffusion of sodium from the matrix lattice to the surface due to its own instability, thus preventing the formation of new residual alkali.

[0081] In some specific implementations, the method includes the following steps:

[0082] S1: Provides sodium-containing cathode materials;

[0083] S2: The coating material, including nano-sized alumina, micron-sized ammonium dihydrogen phosphate and optional micron-sized L source, is mixed evenly in a ball mill to obtain a composite coating agent;

[0084] S3: The sodium-containing cathode material and composite coating agent are mixed evenly using a mechanical fusion machine, placed in a muffle furnace for sintering, and air is introduced during the sintering process. After sintering, the mixture is cooled to room temperature.

[0085] A third aspect of this application provides a positive electrode sheet comprising the sodium-ion battery positive electrode material described in the first aspect of this application or the sodium-ion battery positive electrode material prepared by the method described in the second aspect of this application.

[0086] In some embodiments, the positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector, the positive electrode film layer containing the sodium-ion battery positive electrode material.

[0087] In this application, the positive current collector can be, for example, a metal foil or a composite current collector. The metal foil is, for example, aluminum foil. The composite current collector can include a polymer base layer and a metal layer formed on at least one side of the polymer base layer. The material of the metal layer includes, but is not limited to, aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, silver alloys, etc.; the polymer material of the polymer base layer can be, for example, polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0088] In some embodiments, the sodium-ion battery positive electrode material serves as the positive electrode active material in the positive electrode film layer. In addition to this positive electrode material, the positive electrode film layer may optionally include a conductive agent and / or a binder. As examples, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers; the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0089] This application does not specifically limit the preparation method of the positive electrode sheet, and it can be prepared by referring to existing methods. For example, the positive electrode slurry is coated on the positive electrode current collector, and then dried and cold-pressed to form the positive electrode sheet. The positive electrode slurry can be formed by dispersing sodium-ion battery positive electrode material, optional conductive agent, optional binder and other components in a solvent (e.g., N-methylpyrrolidone) and stirring evenly.

[0090] Furthermore, the positive electrode sheet of this application does not exclude other additional functional layers besides the positive electrode film layer. For example, the positive electrode sheet may also include a conductive undercoat layer (e.g., composed of a conductive agent and a binder) disposed between the positive current collector and the positive electrode film layer. As another example, the positive electrode sheet may also include a protective layer covering the surface of the positive electrode film layer.

[0091] The fourth aspect of this application provides a battery comprising the sodium-ion battery positive electrode material described in the first aspect of this application or the sodium-ion battery positive electrode material prepared by the method described in the second aspect of this application, or comprising the positive electrode sheet described in the third aspect of this application.

[0092] In this application, the battery can be a secondary battery. It is understood that the secondary battery can be a sodium-ion battery. In some embodiments, the secondary battery further includes a negative electrode, a separator, and an electrolyte. During battery charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, disposed between the positive and negative electrodes, prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0093] [Negative electrode plate]

[0094] In some embodiments, the negative electrode sheet may include a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector, the negative electrode film layer comprising a negative electrode material.

[0095] In some embodiments, the negative electrode current collector may include a metal foil or a composite current collector. The metal foil may be, for example, copper foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one side of the polymer substrate. The materials of the metal layer include, but are not limited to, copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, silver alloys, etc., and the polymer materials of the polymer substrate include, but are not limited to, polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0096] In this application, the negative electrode material may include negative electrode active materials well known in the art for use in secondary batteries. For example, the negative electrode active material includes at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may include at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may include at least one of elemental tin, tin oxide compounds, and tin alloys.

[0097] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may include, for example, at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), carboxymethyl cellulose (CMC), and carboxymethyl chitosan (CMCS).

[0098] In some embodiments, the negative electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0099] In some embodiments, the negative electrode film layer may optionally contain other additives, such as thickeners. Specific examples of thickeners include, but are not limited to, sodium carboxymethyl cellulose (CMC-Na).

[0100] This application does not specifically limit the preparation method of the negative electrode sheet, and it can be prepared by referring to existing methods. For example, the negative electrode material, conductive agent, binder and other negative electrode components are dispersed in a solvent (e.g., deionized water) to form a negative electrode slurry; then the negative electrode slurry is coated on a negative electrode current collector, and after drying, cold pressing, etc., a negative electrode sheet is obtained.

[0101] Electrolyte

[0102] In this application, the electrolyte can be selected from existing secondary batteries. In some embodiments, the electrolyte comprises an organic solvent, a sodium salt, and optional additives. The sodium salt includes, but is not limited to, at least one selected from NaPF6, NaClO4, NaBCl4, NaSO3CF3, and Na(CH3)C6H4SO3. The organic solvents include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0103] In some embodiments, the additives in the electrolyte may include negative electrode film-forming additives and positive electrode film-forming additives; they may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc. As an example, the additives may include, but are not limited to, at least one of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), vinyl sulfate (DTD), propylene sulfate, vinyl sulfite (ES), 1,3-propanesulfonate lactone (PS), 1,3-propenesulfonate lactone (PST), sulfonate cyclic quaternary ammonium salts, succinic anhydride, succinic anhydride (SN), adiponitrile (AND), tris(trimethylsilane) phosphate (TMSP), and tris(trimethylsilane) borate (TMSB).

[0104] [Isolation membrane]

[0105] In this application, the separator is disposed between the positive and negative electrode plates, primarily serving to prevent short circuits between the positive and negative electrodes while allowing active ions to pass through. This application does not impose any particular limitation on the type of separator; various porous structures well-known in the art can be used. In some embodiments, the separator material may include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. Furthermore, the separator can be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0106] In some embodiments, a ceramic coating and / or a metal oxide coating are also provided on the separator.

[0107] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0108] This application does not impose any particular restrictions on the shape of the battery; it can be cylindrical, square, or any other arbitrary shape. Figure 4 Here is an example of a square-structured battery 1. The number of electrode components contained in the battery can be one or more, and can be adjusted as needed.

[0109] In some embodiments, the battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0110] In some embodiments, the outer packaging may include a housing and a cover. The housing may include a base plate and side plates attached to the base plate, the base plate and side plates enclosing a receiving cavity. The housing has an opening communicating with the receiving cavity, and the cover plate is capable of covering the opening to close the receiving cavity. The electrode assembly may be encapsulated within the receiving cavity.

[0111] In some implementations, the battery is packaged in a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell.

[0112] In other embodiments, the battery is packaged in a pouch, such as a bag-type pouch. The pouch can be made of plastic, such as polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0113] In some implementations, batteries can be assembled into battery modules, and the number of batteries contained in a battery module can be multiple, with the specific number adjustable according to the application and capacity of the battery module.

[0114] Figure 5 This is battery module 2 as an example. (See reference...) Figure 5 In battery module 2, multiple batteries 1 can be arranged sequentially along the length of battery module 2. Of course, they can also be arranged in any other manner. Furthermore, these multiple batteries 1 can be fixed in place using fasteners.

[0115] The battery module 2 may also include a housing with a receiving space in which a plurality of batteries 1 are received.

[0116] In some implementations, the battery modules can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0117] Figure 6 and 7 This is battery pack 3 as an example. (See reference...) Figure 6 and 7The battery pack 3 may include a battery box and multiple battery modules 2 disposed within the battery box. The battery box includes an upper body 4 and a lower body 5, with the upper body 4 covering the lower body 5 to form a closed space for accommodating the battery modules 2. The multiple battery modules 2 can be arranged in any manner within the battery box.

[0118] The fifth aspect of this application provides an electrical device including the battery described in the fourth aspect of this application.

[0119] In this application, the electrical device may include, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. The battery of the electrical device can be selected according to its usage requirements.

[0120] Figure 8 This is an example of an electrical device. The device can be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0121] In other specific examples, the power device may be a mobile phone, tablet, or laptop. This device typically requires a slim and lightweight design and may use a battery cell as its power source.

[0122] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0123] Example 1

[0124] 1) Preparation of sodium-containing cathode materials

[0125] MnO, Fe2O3, NiO, and Na2CO3 were mixed thoroughly at a molar ratio of Mn / Fe / Ni / Na of 1 / 3:1 / 3:1 / 3:1.03. The mixture was then placed in a sagger within a box furnace and sintered at 900℃ for 15 hours. After sintering and cooling to room temperature, the mixture was crushed to obtain NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 Sodium-containing cathode material containing O2.

[0126] 2) Alumina (D50 = 20 nm) and ammonium dihydrogen phosphate (D50 = 5 μm) were mixed in a ball mill at a molar ratio of Al to P of 0.4. The mixture was ball-milled at a speed of 1000 rpm for 1 h to obtain a composite coating agent.

[0127] 3) Take 1 kg of sodium-containing cathode material and 5 g of composite coating agent (coating amount of 0.5%) and mix them in a mechanical fusion machine. Control the mixing speed at 800 rpm and the mixing time at 0.5 h. Place the resulting mixture in a muffle furnace and sinter at 350 °C for 8 h, with dry air introduced during the sintering process. After sintering, allow it to cool naturally to room temperature to obtain a sodium-ion battery cathode material with a surface coating of sodium and al phosphate metal salts. The morphology of this sodium-ion battery cathode material is as follows: Figure 1 As shown, the morphology of the sodium-containing cathode material (uncoated) is represented by [data / image / image]. Figure 2 In comparison, the sodium-ion battery cathode material of Example 1 has more and smaller particles dispersed on its surface, resulting in a higher surface roughness, while the uncoated sodium-containing cathode material has a relatively smooth surface.

[0128] Examples 2-6

[0129] Sodium-ion battery cathode materials were prepared according to the method in Example 1, except that in Examples 2-6, the amounts of alumina and ammonium dihydrogen phosphate were adjusted according to Al / P molar ratios of 0.1, 0.3, 0.6, 1 and 8, respectively.

[0130] Examples 7-10

[0131] Sodium-ion battery cathode materials were prepared according to the method of Example 1, except that in Examples 7-10, the coating amount (the percentage of the composite coating agent mass to the matrix mass) was adjusted to 0.1%, 0.2%, 2%, and 5%, respectively.

[0132] Examples 11-14

[0133] Sodium-ion battery cathode materials were prepared according to the method of Example 1, except that in Examples 11-14, the sintering temperatures were adjusted to 100°C, 300°C, 600°C and 900°C, respectively.

[0134] Examples 15-18

[0135] Sodium-ion battery cathode materials were prepared according to the method of Example 1, except that in Examples 15-18, the sintering time was adjusted to 1h, 3h, 10h and 20h respectively.

[0136] Comparative Example 1

[0137] The sodium-containing cathode material prepared in Example 1 was used as a comparative sample.

[0138] Comparative Example 2

[0139] Sodium-ion battery cathode material was prepared according to the method in Example 1, except that aluminum oxide was not used and 5g of ammonium dihydrogen phosphate was used as a coating agent.

[0140] Comparative Example 3

[0141] Sodium-ion battery cathode materials were prepared according to the method in Example 1, except that ammonium dihydrogen phosphate was not used, and 5g of alumina was used as a coating agent.

[0142] Example 19

[0143] Alumina (D50 = 20 nm), ammonium dihydrogen phosphate (D50 = 5 μm), and titanium oxide (D50 = 30 μm) were mixed in a ball mill at an Al / P / Ti molar ratio of 0.4 / 1 / 0.2. The mixture was ball-milled at 1000 rpm for 1 h to obtain a composite coating agent.

[0144] 1 kg of sodium-containing cathode material (same as in Example 1) and 5 g of composite coating agent were mixed in a mechanical fusion machine at a mixing speed of 800 rpm for 0.5 h. The resulting precursor was placed in a muffle furnace and sintered at 350 °C for 9 h, with dry air introduced during the sintering process. After sintering, the material was naturally cooled to room temperature to obtain a sodium-ion battery cathode material with a surface coating of phosphate metal salts containing Na, Al and Ti.

[0145] Example 20

[0146] Alumina (D50 = 20 nm), ammonium dihydrogen phosphate (D50 = 5 μm), and calcium oxide (D50 = 50 μm) were mixed in a ball mill at an Al / P / Ca molar ratio of 0.4 / 1 / 0.2. The mixture was ball-milled at 1000 rpm for 1 h to obtain a composite coating agent.

[0147] 1 kg of sodium-containing cathode material (same as in Example 1) and 5 g of composite coating agent were mixed in a mechanical fusion machine at a mixing speed of 800 rpm for 0.5 h. The resulting precursor was placed in a muffle furnace and sintered at 400 °C for 8 h, with dry air introduced during the sintering process. After sintering, the material was naturally cooled to room temperature to obtain a sodium-ion battery cathode material with a surface coating of phosphate metal salts containing Na, Al and Ca.

[0148] The composite coating agents, their dosages, and sintering conditions in Examples 1-20 and Comparative Examples 1-3 are shown in Table 1.

[0149] Test section

[0150] 1. Material Characterization

[0151] (1) Matrix crystal structure testing

[0152] A Brucker D8A_A25 X-ray diffractometer from Brucker AxS GmbH, Germany, was used with CuKα rays as the radiation source, and the wavelength of the rays was... The sodium-containing cathode material was tested by scanning a 2θ angle range of 10°-90° at a scanning rate of 2° / min.

[0153] (2) Particle size (Dv50) test

[0154] Particle size was tested using a Malvern laser particle size analyzer, with reference to the standard GB / T19077-2016.

[0155] Pretreatment: Add an appropriate amount of the sample to be tested and water to a beaker, and add a dispersant (sodium hexametaphosphate). Sonicate the sample at 120W for 5 minutes to ensure that the sample is completely dispersed in the dispersant.

[0156] Test: After the sample is poured into the injection tower, it circulates with the solution to the test optical path system. Under the illumination of the laser beam, the particle size distribution characteristics are obtained by receiving and measuring the energy distribution of the scattered light (shading degree: 8-12%).

[0157] (3) Element content test of coating layer

[0158] First, the elemental binding energy and chemical shift of the sample surface are measured by XPS to obtain the elemental composition and chemical state of the sample surface. Then, the elemental content is determined by inductively coupled plasma atomic emission spectroscopy.

[0159] (4) Testing of coating thickness

[0160] The thickness of the coating layer was measured using a high-resolution transmission electron microscope (HR-TEM JEM-2100F).

[0161] (5) Scanning electron microscopy (SEM) test

[0162] The tests were performed using a field emission scanning electron microscope (Zeiss Gemini 360) according to the JY / T010-1996 standard.

[0163] The material characterization results are shown in Table 1.

[0164] 2. Performance Testing

[0165] (1) Preparation of button sodium-ion batteries

[0166] 1) Preparation of positive electrode sheet

[0167] The sodium-ion battery cathode materials prepared in the examples and comparative examples were mixed with conductive carbon black SuperP, binder PVDF and solvent NMP in a mass ratio of 80:15:5:100 and stirred evenly to obtain cathode slurry. The cathode slurry was then uniformly coated on one surface of the cathode current collector (aluminum foil), and then dried, cold-pressed and cut to obtain cathode sheet.

[0168] 2) Preparation of negative electrode sheet

[0169] The negative electrode material hard carbon, conductive agent carbon black SuperP, binder CMC and solvent water are mixed and stirred evenly in a mass ratio of 8:1:1:10 to obtain a negative electrode slurry; the negative electrode slurry is then uniformly coated on one surface of the negative electrode current collector (copper foil); after drying, cold pressing and slitting, a negative electrode sheet is obtained.

[0170] 3) Preparation of electrolyte

[0171] Sodium hexafluorophosphate (NaPF6) was dissolved in solvent EC / DEC (1∶1, v / v) to obtain a NaPF6 electrolyte with a concentration of 1 mol / L.

[0172] 4) Cut the obtained positive electrode, separator (porous polyethylene film) and negative electrode into round pieces and arrange them in order so that the separator is between the positive electrode and the negative electrode to play a role in isolation. The separator is impregnated with the electrolyte and then compacted to obtain a button sodium-ion battery.

[0173] (2) Performance testing of sodium-ion batteries

[0174] 1) Ratio Performance Test

[0175] The rate performance test process is as follows: At 25℃, within a voltage range of 1.5-4.2V, the coin cell sodium-ion battery is charged and discharged at rates of 1C and 5C respectively to obtain the capacity of the material at 1C and 5C rates. The nominal specific capacity is 140mAh / g.

[0176] 2) Capacity retention rate over 400 laps

[0177] The cycle performance test process is as follows: At 25℃, the coin cell sodium-ion battery is charged to 4.2V at a rate of 0.1C, and then discharged to 1.5V at a rate of 0.1C. This process is repeated once to complete the battery activation. After activation, the coin cell sodium-ion battery is charged to 4.2V at a rate of 1C, and then discharged to 1.5V at a rate of 1C. This yields the initial cycle capacity. The above 1C charge-discharge cycle is repeated 400 times. The capacity retention rate after 400 cycles is obtained by dividing the discharge capacity after 400 cycles by the initial 1C discharge capacity.

[0178] 3) Electrochemical impedance spectroscopy (EIS) test

[0179] The tests were conducted using a German Zahner electrochemical workstation and Zview software. Impedance information from the high-frequency, mid-frequency, and low-frequency regions was fitted based on the equivalent circuit to determine the Rct and R of the battery sample. s The impedance value is set to a frequency of 100kHz-0.01Hz, and the voltage amplitude is set to 10mV.

[0180] The EIS test procedure is as follows: Charge and discharge the coin cell sodium-ion battery at a rate of 0.1C for one cycle within the voltage range of 1.5-4.2V, then charge it at a rate of 1C to 4.2V and keep the voltage constant until the current is less than or equal to 0.05C. After standing for 6 hours, perform the EIS test.

[0181] 4) Na + Diffusion coefficient test

[0182] Na + The diffusion coefficient test procedure is as follows: At 25℃, the coin cell sodium-ion battery is charged to 4.2V at a constant current density of 10mA / g, and then discharged to 1.5V at a constant current density of 10mA / g. The sodium ion diffusion coefficient (DNa+) is calculated using the following formula:

[0183] D Na+ =R 2 T 2 / (2A 2 n 4 F 4 C 2 σ 2 Formula 1

[0184] Z′=R s +R ct +σw -1 / 2 Formula 2

[0185] Where R is the gas constant, R = 8.314 J / (mol·K). T = 298 K, and A is the electrode area (1.54 cm²). 2 ), where n is the number of electrons transferred during the reaction (n=1), F is the Faraday constant, C is the bulk concentration of sodium ions, C=ρ / M (ρ is the density of the cathode material, M is the molar mass of the material), and σ is the slope of the impedance fitting in Formula 2. Substituting these values ​​into Formula 1 will allow you to calculate the Na. + Diffusion coefficient;

[0186] In Formula 2, Z' represents the Warburg impedance, Rct represents the charge transfer impedance, and R... s ω represents the interfacial membrane impedance, and w represents the angular frequency.

[0187] The test results of the button cells prepared above are shown in Table 2.

[0188] Table 1

[0189]

[0190]

[0191] Table 2

[0192]

[0193]

[0194] Comparing Examples 1-20 with Comparative Example 1, it can be seen that the batteries prepared with the sodium-ion battery cathode materials of Examples 1-20 have higher 5C capacity, capacity retention, and Na+. + Diffusion coefficient. It can be seen that, compared to sodium-containing electrode materials without a coating layer (Comparative Example 1), the co-coating of cathode materials prepared in Examples 1-20 with coating materials containing solid phosphorus and solid aluminum sources improves the rate performance, cycle stability, and Na+ diffusion coefficient of the battery. + Diffusion coefficient. In Comparative Examples 2 and 3, although the sodium-containing cathode materials were coated with phosphorus and aluminum sources respectively, the rate performance of the prepared cathode materials was poor. + The diffusion coefficient is low.

[0195] Figure 3 The figure shows the capacity retention rate changes of the batteries of Example 1 and Comparative Example 1 during 400 cycles. As can be seen from the figure, the capacity retention rate of the battery of Example 1 is always higher than that of Comparative Example 1, and the rate of decrease in capacity retention rate is much lower than that of Comparative Example 1 as the number of cycles increases, indicating that the battery of Example 1 has higher stability.

[0196] In summary, this application modifies sodium-containing cathode materials using coating materials containing phosphorus and aluminum sources. The phosphates containing at least sodium and aluminum formed on the substrate surface simultaneously improve the conductivity and cycle stability of the cathode material.

[0197] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A sodium-ion battery cathode material, characterized in that, include: A sodium-containing cathode material substrate, and a coating layer covering at least a portion of the surface of the sodium-containing cathode material substrate; wherein the coating layer comprises a metal phosphate, and the metal phosphate contains at least sodium and aluminum. The sodium-containing cathode material matrix comprises a layered oxide, the chemical formula of which is Na. x2 Mn a Fe b M c A d O 2-e+f Q e Wherein, M includes at least one of Cu, Ni, Li, Ti, Zr, K, La, Ce, Sr, Sb, Nb, Mg, Ca, Mo, Zn, Cr, W, Bi, Sn, Ge and Al; A includes at least one of Si, P, B, S and Se; Q includes at least one of F, Cl and N; a > 0, b > 0, c ≥ 0, d ≥ 0, and a + b + c + d = 1, x² ≥ 0.66, 0 < e ≤ 0.1, -0.1 ≤ f ≤ 0.

2. The sodium-ion battery cathode material according to claim 1, characterized in that, The chemical formula of the metal phosphate is Na. x1 Al y1 Ly2P z O s L includes at least one of Ca, Mg, Fe, Ti, V, Cr, Mn, Ni, La, Ce, Sr, Cu, Zn, Y, Zr, Nb, and Mo; x1 > 0, y1 > 0, y2 ≥ 0, z > 0, and s > 0.

3. The sodium-ion battery cathode material according to claim 2, characterized in that, The chemical formula of the metal phosphate is NaAl. y1 Ly2P z O2, and 0 < y1 < 1, 0 ≤ y2 < 1, 0 < z < 1.

4. The sodium-ion battery cathode material according to claim 1 or 2, characterized in that, In the metal phosphate, the molar ratio of aluminum to phosphorus is 0.1-10.

5. The sodium-ion battery cathode material according to claim 4, characterized in that, In the metal phosphate, the molar ratio of aluminum to phosphorus is 0.1-0.

6.

6. The sodium-ion battery cathode material according to claim 1 or 2, characterized in that, The thickness of the coating layer is 1nm-100nm.

7. The sodium-ion battery cathode material according to claim 6, characterized in that, The thickness of the coating layer is 5nm-25nm.

8. The sodium-ion battery cathode material according to claim 1 or 2, characterized in that... The layered oxide is an O3-type layered oxide.

9. The sodium-ion battery cathode material according to claim 1 or 2, characterized in that, The mass ratio of the coating layer to the sodium-containing cathode material matrix is ​​(0.1-10):

100.

10. The sodium-ion battery cathode material according to claim 9, characterized in that, The mass ratio of the coating layer to the sodium-containing cathode material matrix is ​​(0.2-2):

100.

11. A method for preparing the sodium-ion battery cathode material according to any one of claims 1-10, characterized in that, include: The coating material, including aluminum and phosphorus sources, is mixed with a sodium-containing cathode material matrix and then sintered.

12. The method according to claim 11, characterized in that, The aluminum source includes at least one of aluminum oxide and aluminum hydroxide; and / or The phosphorus source includes at least one of ammonium dihydrogen phosphate and ammonium metaphosphate.

13. The method according to claim 11 or 12, characterized in that, The aluminum source is alumina, and the median particle size of the alumina is 10nm-50nm; the phosphorus source is ammonium dihydrogen phosphate, and the median particle size of the ammonium dihydrogen phosphate is 1μm-15μm.

14. The method according to any one of claims 11-12, characterized in that, The sintering satisfies at least one of the following conditions: (1) The sintering temperature is 100℃-1000℃; (2) The sintering time is 1h-24h.

15. The method according to claim 14, characterized in that, (1) The sintering temperature is 300℃-600℃; (2) The sintering time is 3h-10h.

16. The method according to any one of claims 11-12, characterized in that, The mixing process includes the following steps: The components in the coating material are first mixed to obtain a composite coating agent; The composite coating agent is mixed with the sodium-containing cathode material matrix in a second process; The conditions for the first mixing include: a rotation speed of 800 rpm to 1200 rpm and a time of 20 min to 60 min; The conditions for the second mixing include: a rotation speed of 800 rpm to 1000 rpm and a time of 20 min to 30 min.

17. The method according to any one of claims 11-12, characterized in that, The coating material also includes at least one of titanium oxide and calcium oxide.

18. A positive electrode plate, characterized in that, The sodium-ion battery cathode material comprises any one of claims 1-10 or a sodium-ion battery cathode material prepared by any one of claims 11-17.

19. A battery, characterized in that, It comprises the sodium-ion battery positive electrode material according to any one of claims 1-10 or the sodium-ion battery positive electrode material prepared by the method according to any one of claims 11-17, or includes the positive electrode sheet according to claim 18.

20. An electrical appliance, characterized in that, Includes the battery as described in claim 19.

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