Cathode material, preparation method thereof, cathode sheet, secondary battery, and electric device

Abstract

The present application provides a positive electrode material, a method for preparing a positive electrode material, a positive electrode sheet, a secondary battery, and an electric device, the positive electrode material comprising: 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, the coating layer comprising Na x M y O2, wherein M comprises at least one of B, Si, and P, x is greater than 0, and y is greater than 0.

Description

Technical Field

[0001] This application belongs to the field of electrochemical technology, and in particular relates to a positive electrode material and its preparation method, a positive electrode sheet, a secondary battery, and an electrical device. Background Technology

[0002] In recent years, the application of secondary batteries, represented by sodium-ion batteries, has become increasingly widespread. These batteries are widely used in energy storage systems for hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. Due to the significant development of secondary batteries, higher requirements have been placed on their energy density, cycle performance, and safety performance. However, currently, traditional sodium-ion batteries generally suffer from poor cycle performance, failing to meet practical application needs. Summary of the Invention

[0003] The purpose of this application is to provide a positive electrode material and its preparation method, a positive electrode sheet, a secondary battery, and an electrical device, which can improve the cycle performance of the secondary battery.

[0004] To achieve the aforementioned objectives, this application provides a cathode material comprising: 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 contains Na. x M y O2, wherein M includes at least one of B, Si and P, x>0, y>0, and Na x M y The net charge of O2 is zero.

[0005] The cathode material provided in this application includes a sodium-containing cathode material matrix and a material containing Na. x M y The O2 coating layer, wherein Na in the coating layer x M y The formation of O2 can consume residual alkali (Na2CO3 and NaOH) on the surface of the sodium-containing cathode material matrix, reducing the content of surface residual alkali (Na2CO3 and NaOH), reducing irreversible capacity loss of the cathode material caused by surface residual alkali, and improving cycle performance. Furthermore, the coating layer can isolate the sodium-containing cathode material matrix from the air, preventing exposure and inhibiting continuous reaction between the material and air components (water and carbon dioxide), thereby suppressing the continuous formation of surface residual alkali and maintaining the integrity of the material's crystal structure, further improving the cycle performance of the cathode material.

[0006] In some embodiments of this application, the coating layer includes: a transition layer relatively close to the sodium-containing cathode material substrate, wherein the transition layer contains a doped region of element M; and an oxide layer relatively far from the sodium-containing cathode material substrate, the oxide layer containing Na. x M y O2.

[0007] The coating layer can include a transition layer and an oxide layer. The transition layer effectively enhances the bonding force between the coating layer and the sodium-containing cathode material substrate, preventing coating layer detachment during long-term cycling and improving the structural stability of the cathode material surface. Furthermore, the doping region of element M in the coating layer is a shallow doping layer close to the sodium-containing cathode material substrate. This shallow doping allows the element M to form chemical bonds with the substrate, further enhancing the bonding force and structural stability of the cathode material surface, thus improving its cycle stability. The formation of the oxide layer consumes residual alkali (Na2CO3 and NaOH) on the surface of the sodium-containing cathode material substrate, reducing the content of residual alkali (Na2CO3 and NaOH) and minimizing irreversible capacity loss caused by residual alkali, further improving cycle performance.

[0008] The cathode material satisfies at least one of the following conditions:

[0009] (1) The surface residual alkali content of the positive electrode material is 0.5 wt.% to 5.5%, optionally 0.8 wt.% to 4.5%; and

[0010] (2) Based on the total mass of the coating layer, the mass percentage of element M in the doped region is greater than the mass percentage of element M in the oxide layer. Optionally, the mass percentage of element M in the doped region is 0.05% to 0.3%.

[0011] The mass percentage of M element in the doped region is greater than that in the oxide layer, which is conducive to the formation of more chemical bonds between M element and the sodium-containing cathode material matrix, thereby further enhancing the bonding force between the coating layer and the sodium-containing cathode material matrix and improving cycle stability.

[0012] In some embodiments of this application, the positive electrode material satisfies at least one of the following conditions:

[0013] (1) The sodium-containing cathode material matrix includes one or more of layered oxides, Prussian blue compounds, and polyanionic compounds.

[0014] Optionally, the layered oxide has the chemical formula Na. x Mn a Fe b Nic L d O 2-e Where 0.7<x≤1, 0<a, 0≤b, 0.1<c≤0.3, 0≤d, a+b+c+d+e=1, -0.1≤e≤0.1, and L is selected from one or more of Cu, Li, Ti, Zr, K, Nb, Mg, Ca, Mo, Zn, Cr, W, Bi, Sn, Ge, Al, Si, La, Ta, P and B;

[0015] Further optionally, the sodium-containing cathode material matrix is ​​an O3-type layered oxide;

[0016] (2) The sodium-containing cathode material matrix is ​​made of micron particles, and the average particle size of the micron particles is from 1 μm to 25 μm, and can be selected from 1 μm to 15 μm;

[0017] (3) The coating layer comprises 0.001% to 3% by mass in the cathode material, optionally 0.01% to 2%, and more preferably 0.01% to 1%; and

[0018] (4) The thickness of the coating layer is 0.5 nm to 30 nm, and can be selected as 1 nm to 5 nm.

[0019] By controlling the thickness of the coating layer and its mass percentage in the cathode material within an appropriate range, it is possible to ensure the bonding force between the coating layer and the sodium-containing cathode material matrix, prevent the coating layer from falling off during long cycles, and improve the structural stability of the cathode material surface. Furthermore, it can effectively isolate the sodium-containing cathode material matrix from air, preventing the continuous reaction between the material and components in the air (water and carbon dioxide), thereby inhibiting the continuous generation of residual alkali on the surface, maintaining the integrity of the material's crystal structure, and improving the cycle performance of the cathode material. It also facilitates the effective insertion and extraction of active ions in the cathode material, enabling the cathode material to function stably in the secondary battery.

[0020] A second aspect of this application provides a method for preparing a cathode material, comprising: providing a sodium-containing cathode material matrix; and performing surface heat treatment on the sodium-containing cathode material matrix using vapor coated with a modifier to form a Na-containing matrix on at least a portion of the surface of the sodium-containing cathode material matrix. x M y An O2 coating layer is used to obtain a positive electrode material, wherein M includes at least one of B, Si, and P, x>0, y>0, and the Na... x M y The net charge of O2 is zero.

[0021] The method provided in this application utilizes the vapor of a coating modifier to perform surface heat treatment on a sodium-containing cathode material substrate. This allows the vapor of the coating modifier to react with residual alkali on the surface of the sodium-containing cathode material substrate, generating a product containing Na.x M y A coating layer of the O2 oxidation component can reduce the residual alkali on the surface of the sodium-containing cathode material matrix, and can also isolate the sodium-containing cathode material matrix from air through the coating layer to prevent its exposure in the air, thereby preventing the continuous generation of residual alkali on the surface, reducing the irreversible capacity loss of the sodium-ion secondary battery, and improving the cycling performance.

[0022] In some embodiments of the present application, the surface heat treatment of the sodium-containing cathode material matrix using the vapor of the coating modifier includes: sintering the sodium-containing cathode material matrix and the coating modifier to make the sodium-containing cathode material matrix contact and react with the vapor of the coating modifier, and forming a transition layer relatively close to the sodium-containing cathode material matrix and an oxidation layer relatively far from the sodium-containing cathode material matrix on at least a part of the surface of the sodium-containing cathode material matrix. Among them, the transition layer contains a doping region of element M, and the oxidation layer contains Na x M y O2 oxidation component.

[0023] In the above steps, by sintering the sodium-containing cathode material matrix and the coating modifier, the coating modifier can be continuously volatilized to form vapor, and continuously contact and react with the sodium-containing cathode material matrix to form Na x M y O2 oxidation component, thereby reducing the residual alkali substances on the surface of the cathode material through the reaction. At the same time, during the sintering process, the elements in the coating modifier will also spontaneously diffuse to the surface layer of the sodium-containing cathode material matrix under the action of thermodynamics, forming a transition layer with shallow doping between the sodium-containing cathode material matrix and the coating layer, and forming a doping region of element M in the transition layer. In the doping region of element M, element M can form a chemical bond with the sodium-containing cathode material matrix, which can effectively enhance the binding force between the coating layer and the sodium-containing cathode material matrix, avoid the shedding of the coating layer during long cycling of the cathode material, and is beneficial to improving the surface stability, and further improving the cycling stability.

[0024] In some embodiments of the present application, the method satisfies at least one of the following conditions:

[0025] (1) The coating modifier includes one or more of boric acid, boron oxide, silicic acid, and ammonium dihydrogen phosphate;

[0026] (2) The sodium-containing cathode material matrix includes one or more of layered oxides, Prussian blue compounds, and polyanionic compounds, and can be an O3-type layered oxide; and

[0027] (3) The mass ratio of the coating modifier to the sodium-containing cathode material matrix is m, 0 < m < 2, and can be 0.05 ≤ m ≤ 1;

[0028] (4) When performing the sintering treatment, the coating modifier is in solid or liquid phase, and can be optionally in solid phase.

[0029] The mass ratio m of the coating modifier to the sodium-containing cathode material matrix is within a suitable range, which can not only achieve a good coating effect on the sodium-containing cathode material matrix, but also keep the capacity of the material at a relatively high level, thus achieving a balance between capacity performance and coating effect. In addition, the coating modifier is in solid or liquid phase and does not contain moisture, and the steam formed after the sintering treatment also does not contain water vapor, which can avoid the contact between the sodium-containing cathode material matrix and moisture, effectively reduce the residual alkali substances on the surface, and at the same time maintain the integrity of the crystal structure of the material, thereby being beneficial to improving the cycle performance of the cathode material.

[0030] In some embodiments of the present application, the sintering treatment of the sodium-containing cathode material matrix and the coating modifier includes: providing a first container, wherein the first container contains the coating modifier and a second container, and the second container contains the sodium-containing cathode material matrix, and the gas phases in the first container and the second container are connected; and sintering the first container.

[0031] By sintering the first container containing the second container and the coating modifier, the coating modifier can be volatilized to form steam. Since the gas phases in the first container and the second container are connected, the formed steam can diffuse into the second container and react with the sodium-containing cathode material matrix in the second container, and gradually form a coating layer through continuous reactions during the continuous sintering process.

[0032] In some embodiments of the present application, providing the first container includes: providing the second container; placing the second container in the first container; and laying the coating modifier in at least part of the area between the outer walls of the first container and the second container. Optionally, the laying thickness of the coating modifier is not higher than 2 cm.

[0033] The laying thickness of the coating modifier not being higher than 2 cm is beneficial to the full and continuous volatilization of the coating modifier during the sintering process, so that it can fully react with the residual alkali on the surface of the sodium-containing cathode material matrix and form a good coating effect on the sodium-containing cathode material matrix.

[0034] In some embodiments of the present application, the method satisfies at least one of the following conditions:

[0035] (1) The temperature of the sintering is T1, 0 < T1 < 2000 °C, and can be optionally 200 °C ≤ T1 ≤ 800 °C;

[0036] (2) The time of the sintering is t1, 0 < t1 < 36 h, and can be optionally 1 h ≤ t1 ≤ 18 h; and

[0037] (3) The first container and the second container can each independently be a crucible.

[0038] The sintering temperature T1 and time t1 are controlled within a suitable range, which can not only make the reaction between the vapor of the coating modifier and the sodium-containing cathode material matrix proceed sufficiently, but also ensure that the sodium-containing cathode material matrix does not suffer Na loss and damage the crystal structure of the material, which helps to further improve the cycle performance.

[0039] In some embodiments of the present application, the sintering treatment of the sodium-containing cathode material matrix and the coating modifier includes: performing heat treatment on the coating modifier to form the vapor of the coating modifier; introducing the vapor of the coating modifier into a rotary kiln containing the sodium-containing cathode material matrix; and sintering the vapor of the coating modifier introduced into the rotary kiln and the sodium-containing cathode material matrix.

[0040] In the above steps, first perform heat treatment on the coating modifier to continuously volatilize the coating modifier to form vapor; at the same time, introduce the vapor into a rotary kiln containing the sodium-containing cathode material matrix, and the vapor of the coating modifier can contact and react with the sodium-containing cathode material matrix, and a coating layer is gradually formed through continuous reaction during the continuous sintering process. Among them, during the continuous rotation of the rotary kiln, the sodium-containing cathode material matrix can be dispersed, making the coating layer formed on its surface more uniform.

[0041] In some embodiments of the present application, the method satisfies at least one of the following conditions:

[0042] (1) The sintering temperature is T2, 0 < T2 < 1000 °C, and it can be selected as 200 °C ≤ T2 ≤ 800 °C; and

[0043] (2) The sintering time is t2, 0 < t2 < 36 h, and it can be selected as 1 h ≤ t2 ≤ 18 h.

[0044] The sintering temperature T2 and time t2 are controlled within a suitable range, which can not only make the reaction between the vapor of the coating modifier and the sodium-containing cathode material matrix proceed sufficiently, but also ensure that the sodium-containing cathode material matrix does not suffer Na loss and damage the crystal structure of the material, which helps to further improve the cycle performance.

[0045] In some embodiments of the present application, the method satisfies at least one of the following conditions:

[0046] (1) The temperature of the heat treatment is T3, 300 < T3 < 2000 °C, and it can be selected as 400 °C ≤ T3 ≤ 1800 °C;

[0047] (2) The rotational speed of the rotary kiln is R, where 0 r / min < R ≤ 15 r / min, and optionally 3 r / min ≤ R ≤ 8 r / min; and

[0048] (3) The flow rate of the vapor of the coating modifier is v, where 0 ml / min < v ≤ 5 ml / min, and optionally 0.5 ml / min ≤ v ≤ 2 ml / min.

[0049] Controlling the temperature T3 of the heat treatment within a suitable range can cause the coating modifier to continuously volatilize, continuously form vapor, and react more fully with the residual alkali substances on the surface of the sodium-containing cathode material matrix.

[0050] The third aspect of the present application provides a positive electrode sheet, including the positive electrode material described in the first aspect of the present application or the positive electrode material prepared by the method described in the second aspect of the present application.

[0051] The fourth aspect of the present application provides a secondary battery, including the positive electrode sheet described in the third aspect of the present application.

[0052] The fifth aspect of the present application provides an electrical device, including the secondary battery described in the fourth aspect of the present application.

[0053] Details of one or more embodiments of the present application are set forth in the following drawings and description. Other features, objects, and advantages of the present application will become apparent from the specification, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 is a schematic structural diagram of an embodiment of the device for preparing the positive electrode material of the present application.

[0055] Figure 2 is a schematic structural diagram of another embodiment of the device for preparing the positive electrode material of the present application.

[0056] Figure 3 is the first-cycle charge-discharge capacity curve graph of the sodium-ion batteries in Example 1 and Comparative Example 1 of the present application.

[0057] Figure 4 is the cycle performance curve graph of the sodium-ion batteries in Example 1 and Comparative Example 1 of the present application.

[0058] Figure 5 is the SEM graph of the positive electrode materials in Example 1 and Comparative Example 1 of the present application.

[0059] Figure 6 is a schematic diagram of an embodiment of the secondary battery of the present application.

[0060] Figure 7 is an exploded schematic diagram of an embodiment of the secondary battery of the present application.

[0061] Figure 8 This is a schematic diagram of yet another embodiment of the secondary battery of this application.

[0062] Figure 9 This is a schematic diagram of another embodiment of the secondary battery of this application.

[0063] Figure 10 yes Figure 9 The exploded diagram.

[0064] Figure 11 This is a schematic diagram of one embodiment of the power-consuming device that uses a secondary battery as a power source according to this application. Detailed Implementation

[0065] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with embodiments. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. The embodiments described herein are illustrative in nature and are used to provide a basic understanding of this application. The embodiments of this application should not be construed as limiting this application.

[0066] For the sake of brevity, this article only discloses a few specific numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0067] In this description, unless otherwise stated, "above" and "below" include the stated number.

[0068] Unless otherwise stated, the terms used in this application have their common meanings as commonly understood by those skilled in the art. Unless otherwise stated, the 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).

[0069] The list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms can mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another instance, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

[0070] Currently, due to the limitations of the manufacturing process, the surface of traditional sodium-ion secondary battery cathode materials, especially layered oxide cathode materials, often retains residual alkali (Na2CO3 and NaOH). This residual alkali makes the material highly susceptible to moisture absorption and deterioration, reduces compatibility with binders, and causes a decrease in slurry dispersion and stability, which is detrimental to subsequent coating processes. More importantly, the inventors discovered that when the aforementioned cathode materials are exposed to air for extended periods, they continuously react with components in the air (water and carbon dioxide), continuously forming residual alkali on the surface of the cathode material. This residual alkali increases the irreversible capacity loss of sodium-ion secondary batteries, leading to a continuous deterioration in their cycle performance.

[0071] Currently, conventional methods for reducing residual alkali on the surface of sodium-ion cathode materials mainly include water washing or coating, or a combination of both. While water washing can reduce surface alkali, the inventors have found that sodium-ion cathode materials are extremely sensitive to moisture. Simple washing exposes more active surfaces to air, leading to the formation of more residual alkali and irreversible damage, thus deteriorating the material's cycle performance. Furthermore, the inventors have discovered that water washing not only removes surface alkali but also washes away sodium from the material's crystal lattice, resulting in sodium loss and damage to the crystal structure, thus failing to achieve a satisfactory washing effect. Conventional coating methods typically involve dry-mixing the sodium-ion cathode material with a coating agent. However, the inventors have found that traditional dry-mix coating is limited by the size of the coating agent particles, and the coating method is often point-based, resulting in an uneven coating layer and failing to achieve a good coating effect. In addition, when the washing method is combined with the coating method, not only will the disadvantages of each method be present, but the entire process will also be longer, thereby increasing production costs.

[0072] To address the aforementioned problems, the inventors, through extensive research, proposed a method for preparing cathode materials. This method ingeniously utilizes the vapor of a coating modifier to perform surface heat treatment on a sodium-containing cathode material substrate. This allows the vapor of the coating modifier to react with residual alkali on the surface of the sodium-containing cathode material substrate, generating a product containing Na. x M y The O2 coating layer can reduce the surface residual alkali of the sodium-containing cathode material matrix and isolate the sodium-containing cathode material matrix from the air, preventing its exposure to the air and thus preventing the continuous generation of surface residual alkali, reducing the irreversible capacity loss of sodium-ion secondary batteries, and improving their cycle performance.

[0073] A first aspect of this application provides a 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 containing Na. x M y O2, wherein M includes at least one of B, Si and P, x>0, y>0, and Na x M y The net charge of O2 is zero.

[0074] In the embodiments of this application, Na x M y The net charge of O2 is zero, meaning that in the case of Na... x M y In a system composed of O2, the algebraic sum of the total charge of sodium ions and the total negative charge of M ions and oxygen ions is zero. x M y The net charge of O2 can be characterized by X-ray photoelectron spectroscopy (XPS).

[0075] The cathode material provided in this application includes a sodium-containing cathode material matrix and a material containing Na. x M y The O2 coating layer, wherein Na in the coating layer x M y The formation of O2 can consume residual alkali (Na2CO3 and NaOH) on the surface of the sodium-containing cathode material matrix, reducing the content of surface residual alkali (Na2CO3 and NaOH), reducing irreversible capacity loss of the cathode material caused by surface residual alkali, and improving cycle performance. Furthermore, the coating layer can isolate the sodium-containing cathode material matrix from the air, preventing exposure and inhibiting continuous reaction between the material and air components (water and carbon dioxide), thereby suppressing the continuous formation of surface residual alkali and maintaining the integrity of the material's crystal structure, further improving the cycle performance of the cathode material.

[0076] In some embodiments, the surface residual alkali content of the positive electrode material is from 0.5 wt.% to 5.5%. For example, the surface residual alkali content of the positive electrode material can be 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, or within any range of the above values. Optionally, the surface residual alkali content of the positive electrode material is from 0.8 wt.% to 4.5%.

[0077] In this embodiment, the surface residual alkali content of the cathode material refers to the mass percentage of Na2CO3, NaOH, and other trace alkaline substances (if present) contained on the surface of the cathode material. This can be quantitatively characterized by acid-base titration. As a non-limiting example of acid-base titration, a certain amount of sodium-containing cathode material matrix can be dissolved in water to obtain a sample solution. A mixed solution of methyl orange and phenolphthalein is used as an indicator for the sample solution. A standard hydrochloric acid solution is added to the sample solution until the solution changes from purple to red, which is the titration endpoint. The surface residual alkali content of the cathode material can be calculated from the concentration of the standard hydrochloric acid solution and the volume consumed during titration.

[0078] In some embodiments, the coating layer includes a transition layer relatively close to the sodium-containing cathode material substrate, wherein the transition layer contains a doped region of element M; and an oxide layer relatively far from the sodium-containing cathode material substrate, the oxide layer containing Na. x M y O2.

[0079] The coating layer can include a transition layer and an oxide layer. The transition layer effectively enhances the bonding force between the coating layer and the sodium-containing cathode material substrate, preventing coating layer detachment during long-term cycling and improving the structural stability of the cathode material surface. Furthermore, the doping region of element M in the coating layer is a shallow doping layer close to the sodium-containing cathode material substrate. This shallow doping allows the element M to form chemical bonds with the substrate, further enhancing the bonding force and structural stability of the cathode material surface, thus improving its cycle stability. The formation of the oxide layer consumes residual alkali (Na2CO3 and NaOH) on the surface of the sodium-containing cathode material substrate, reducing the content of residual alkali (Na2CO3 and NaOH) and minimizing irreversible capacity loss caused by residual alkali, further improving cycle performance.

[0080] In this embodiment, the reduction in the residual alkali content on the surface of the sodium-containing cathode material substrate can be qualitatively measured using SEM (scanning electron microscopy). Specifically, under SEM, the residual alkali on the surface of the sodium-containing cathode material substrate usually appears as dense dots or fine debris on the particle surface; and when the residual alkali decreases, the dense dots or fine debris on the particle surface can be clearly seen to be significantly reduced.

[0081] In some embodiments, the mass percentage of element M in the doped region is greater than the mass percentage of element M in the oxide layer, based on the total mass of the coating layer. Optionally, the mass percentage of element M in the doped region is from 0.05% to 0.3%. For example, the mass percentage of element M in the transition layer can be 0.1%, 0.15%, 0.2%, 0.25%, or within any range of the above values.

[0082] In this embodiment of the application, the doped region of element M refers to a specific doped region distributed in the transition layer, in which the content of element M is significantly higher than that of other elements, and the content of element M contained in the specific doped region is also significantly higher than that in other regions of the transition layer.

[0083] The mass percentage of element M in the doped region is a well-known concept in the art and can be determined using instruments and methods known in the art. For example, an EDS spectrometer can be used to measure the mass percentage of element M in the doped regions of the coating layer and transition layer, thereby quantitatively analyzing the mass percentage of element M in the doped region.

[0084] The mass percentage of M element in the doped region is greater than that in the oxide layer, which is conducive to the formation of more chemical bonds between M element and the sodium-containing cathode material matrix, thereby further enhancing the bonding force between the coating layer and the sodium-containing cathode material matrix and improving cycle stability.

[0085] In some embodiments, the sodium-containing cathode material matrix may include one or more of layered oxides, Prussian blue compounds, and polyanionic compounds. However, this application is not limited to these materials, and other conventionally known materials that can be used as cathode active materials for sodium-ion batteries may also be used as the sodium-containing cathode material matrix.

[0086] In some embodiments, the layered oxide may be Na. x M1 yO2, x>0, y>0; wherein M1 can be one or more elements selected from Li, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Fe, Ni, Co, Mn, Cu, Zn, Sr, Y, Zr, Nb, Mo, Bi, La, etc. Optionally, based on the significant residual alkali problem in the sodium-containing cathode material matrix, the layered oxide described in this application can be an O3-type layered oxide.

[0087] In some embodiments, the layered oxide has the chemical formula Na. x Mn a Fe b Ni c L d O 2-e Where 0.7<x≤1, 0<a, 0≤b, 0.1<c≤0.3, 0≤d, a+b+c+d+e=1, -0.1≤e≤0.1, and L is selected from one or more of Cu, Li, Ti, Zr, K, Nb, Mg, Ca, Mo, Zn, Cr, W, Bi, Sn, Ge, Al, Si, La, Ta, P and B.

[0088] In this embodiment, O3 type represents a face-centered cubic crystal structure with stacked layers in an ABCABC periodic pattern. In O3 type layered oxide, "O" represents the octahedral coordination environment of sodium ions (O represents octahedron); the number "3" represents the number of TMO2 plates in a single unit cell (TM represents transition metal elements); that is, sodium layers and transition metal layers are stacked alternately on both sides of the oxygen layer, Na occupies the 3a position in the unit cell, O occupies the 6a position in the unit cell, and the transition metal occupies the 3b position in the unit cell.

[0089] In some embodiments, the polyanionic compound may be a compound containing sodium ions, transition metal ions, and tetrahedral (YO4). n- A class of compounds with anionic units. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si; n represents (YO4). n- The price state.

[0090] In some embodiments, the polyanionic compound may also be a sodium ion, transition metal ion, or tetrahedral (YO4) compound. n- A class of compounds containing anionic units and halide anions. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si, and n represents (YO4). n- The valence state; the halogen can be at least one of F, Cl and Br.

[0091] In some embodiments, the polyanionic compound may also be a tetrahedral (YO4) compound containing sodium ions. n- Anionic unit, polyhedral unit (ZO) y ) m+ And a class of compounds with optional halide anions. Y can be at least one of P, S, and Si, and n represents (YO4). n- The valence state; Z represents a transition metal, which can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; m represents (ZO) y ) m+ The valence state; the halogen can be at least one of F, Cl and Br.

[0092] As specific examples, polyanionic compounds can be NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2(P2O7), NaM'PO4F (M' is one or more of V, Fe, Mn and Ni), and Na3(VO4)2(PO4)3 ... y )2(PO4)2F 3-2y At least one of (0≤y≤1).

[0093] In some embodiments, the Prussian blue compounds may contain sodium ions, transition metal ions, and cyanide ions (CN). - A class of compounds. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Prussian blue compounds can be, for example, Na. a Me b Me' c (CN)6, wherein Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co and Zn, 0 < a ≤ 2, 0 < b < 1, 0 < c < 1.

[0094] In some embodiments, the sodium-containing cathode material matrix is ​​composed of micron-sized particles with an average particle size of 1 μm to 25 μm. For example, the average particle size of the micron-sized particles can be 3 μm, 5 μm, 7 μm, 9 μm, 11 μm, 13 μm, 15 μm, 17 μm, 19 μm, 21 μm, 23 μm, or within any range of the above values. Optionally, the average particle size of the micron-sized particles is 1 μm to 15 μm.

[0095] The average particle size of micron-sized particles in a sodium-containing cathode material matrix is ​​a term known in the art and can be determined using instruments and methods known in the art. For example, it can be conveniently determined using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK, according to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method.

[0096] The average particle size of the micron-sized particles in the sodium-containing cathode material matrix affects the average particle size of the cathode material particles obtained. By controlling the average of the micron-sized particles within a suitable range, the average particle size of the cathode material particles can also be within a suitable range. This is beneficial for the close contact arrangement of the cathode material particles when forming the cathode film, thereby increasing the content of cathode material per unit volume of the cathode film and thus improving the energy density of the secondary battery.

[0097] In some embodiments, the coating layer comprises 0.001% to 3% of the cathode material by mass. For example, the coating layer may comprise 0.005%, 0.01%, 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, or any range thereof. Optionally, the coating layer comprises 0.01% to 2% of the cathode material by mass, and more preferably 0.01% to 1%.

[0098] The mass percentage of the coating layer in the cathode material is a well-known concept in the art and can be determined using instruments and methods known in the art. For example, the proportion of coating elements within the micro-region of the cathode material can be measured using a combination of TEM (transmission electron microscopy) and EDS (energy dispersive spectroscopy), and the percentage of the coating layer can be calculated from this. Alternatively, the total amount of coating elements in the cathode material can first be measured using ICP (inductively coupled plasma) and then the proportion of coating elements in the portion of the cathode material within the coating layer can be measured using XPS (X-ray photoelectron spectroscopy). Subtracting the two values ​​will give the percentage of the coating layer.

[0099] In some embodiments, the thickness of the coating layer is from 0.5 nm to 30 nm. For example, the thickness of the coating layer can be 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, or within any range of the above values. Optionally, the thickness of the coating layer is from 1 nm to 5 nm.

[0100] The thickness of the coating layer has a meaning known in the art and can be measured using instruments and methods known in the art; for example, it can be measured using a transmission electron microscope (TEM).

[0101] By controlling the thickness of the coating layer and its mass percentage in the cathode material within an appropriate range, it is possible to ensure the bonding force between the coating layer and the sodium-containing cathode material matrix, prevent the coating layer from falling off during long cycles, and improve the structural stability of the cathode material surface. Furthermore, it can effectively isolate the sodium-containing cathode material matrix from air, preventing the continuous reaction between the material and components in the air (water and carbon dioxide), thereby inhibiting the continuous generation of residual alkali on the surface, maintaining the integrity of the material's crystal structure, and improving the cycle performance of the cathode material. It also facilitates the effective insertion and extraction of active ions in the cathode material, enabling the cathode material to function stably in the secondary battery.

[0102] A second aspect of this application provides a method for preparing a cathode material, comprising:

[0103] S10, Provide a sodium-containing cathode material matrix;

[0104] S20. Perform surface heat treatment on the sodium-containing cathode material substrate using vapor coated with a modifier to form a Na-containing layer on at least a portion of the surface of the sodium-containing cathode material substrate. x M y An O2 coating layer is used to obtain a positive electrode material, wherein M includes at least one of B, Si, and P, x>0, y>0, and the Na... x M y The net charge of O2 is zero.

[0105] The method provided in this application utilizes the vapor of a coating modifier to perform surface heat treatment on a sodium-containing cathode material substrate. This allows the vapor of the coating modifier to react with residual alkali on the surface of the sodium-containing cathode material substrate, generating a product containing Na. x M y The O2 coating layer can reduce the surface residual alkali of the sodium-containing cathode material matrix and isolate the sodium-containing cathode material matrix from the air, preventing its exposure to the air. This can prevent the continuous generation of surface residual alkali, reduce the irreversible capacity loss of sodium-ion secondary batteries, and improve cycle performance.

[0106] In addition, compared with the traditional water washing method, this application uses the vapor of the coating modifier to perform surface heat treatment on the sodium-containing cathode material matrix to reduce surface residual alkali, which can avoid direct contact between the sodium-containing cathode material matrix and water. This can avoid the water washing process from damaging the crystal structure of the cathode material, avoid irreversible damage to the cathode material, and further improve the cycle performance of the secondary battery.

[0107] Furthermore, compared to the traditional dry-mix coating method, this application utilizes the vapor of the coating modifier to react with the sodium-containing cathode material matrix, eliminating the need for a dry-mixing step between the cathode material and the coating agent, shortening the contact time between the cathode material and air, and reducing the formation of residual alkali. Moreover, dry-mix coating, limited by the size of the coating agent particles, typically involves point coating, resulting in an uneven coating layer and poor air isolation. In contrast, the vapor-phase coating process of this application allows for sufficient contact and reaction between the coating modifier and the cathode material surface, forming a more uniform coating layer, thereby achieving better air isolation.

[0108] Furthermore, compared with the traditional method of combining water washing and coating, the method provided in this application can reduce the residual alkali on the surface of the cathode material while forming a coating layer. That is, the reduction of residual alkali on the surface of the cathode material and the formation of the coating layer can be achieved by a single surface heat treatment process, thereby shortening the process flow and reducing the impact of the entire process on the performance of the cathode material.

[0109] In some embodiments, step S20 involves performing surface heat treatment on the sodium-containing cathode material substrate using vapor coated with the modifier, including the following steps:

[0110] S200: The sodium-containing cathode material substrate and the coating modifier are sintered, causing the vapors of the sodium-containing cathode material substrate and the coating modifier to react in contact, forming a transition layer relatively close to the sodium-containing cathode material substrate and an oxide layer relatively far from the sodium-containing cathode material substrate on at least a portion of the surface of the substrate. The transition layer contains a doped region of element M, and the oxide layer contains Na. x M y O2.

[0111] In step S200, by sintering the sodium-containing cathode material matrix and the coating modifier, the coating modifier can continuously volatilize to form vapor, and continuously react with the sodium-containing cathode material matrix to form Na. x M y O2 is released, thereby reducing residual alkali on the surface of the cathode material through a reaction. Simultaneously, during sintering, elements in the coating modifier spontaneously diffuse to the surface of the sodium-containing cathode material substrate under thermodynamic forces, forming a shallow-doped transition layer between the substrate and the coating layer. Within this transition layer, M-element doping regions are formed. In these M-element doping regions, M-element can form chemical bonds with the sodium-containing cathode material substrate, effectively enhancing the bonding force between the coating layer and the substrate. This prevents the coating layer from detaching during long-term cycling, improving surface stability and ultimately enhancing cycle stability.

[0112] In some embodiments, the sodium-containing cathode material matrix may include one or more of layered oxides, Prussian blue compounds, and polyanionic compounds. However, the present application is not limited to these materials, and the sodium-containing cathode material matrix may also use other conventionally known materials that can be used as the positive electrode active material of a sodium-ion battery. Optionally, considering the significance of the residual alkali problem on the surface of the sodium-containing cathode material matrix, the layered oxide in the present application may be an O3-type layered oxide.

[0113] In some embodiments, the type of the coating modifier is not specifically limited, as long as it has good volatility during the sintering process, can form steam, and can react with the residual alkali substances on the surface of the sodium-containing cathode material matrix. For example, the coating modifier may be one or more of boric acid, boron oxide, silicic acid, and ammonium dihydrogen phosphate.

[0114] In some embodiments, during the sintering process, the coating modifier is in a solid phase or a liquid phase, and may be selected as the solid phase. The coating modifier is in a solid phase or a liquid phase and does not contain moisture, and the steam formed after the sintering process also does not contain water vapor, which can avoid the contact between the sodium-containing cathode material matrix and moisture, effectively reduce the residual alkali substances on the surface, and at the same time maintain the integrity of the crystal structure of the material, thereby being beneficial to improving the cycle performance of the cathode material.

[0115] In some embodiments, the mass ratio of the coating modifier to the sodium-containing cathode material matrix is m, where 0 < m < 2. For example, the mass ratio of the coating modifier to the sodium-containing cathode material matrix may be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or within the range composed of any of the above values. Optionally, the mass ratio of the coating modifier to the sodium-containing cathode material matrix is 0.05 ≤ m ≤ 1.

[0116] When the mass ratio m of the coating modifier to the sodium-containing cathode material matrix is within a suitable range, it can not only achieve a good coating effect on the sodium-containing cathode material matrix, but also keep the capacity of the material at a relatively high level, that is, a balance between the capacity performance and the coating effect can be achieved. When m is relatively large, it is easy to cause the amount of the coating modifier to be relatively large, and the proportion of the sodium-containing cathode material matrix will decrease, and the capacity will decrease; when m is relatively small, it may be difficult to achieve a good coating effect.

[0117] In some embodiments, in step S200, the sintering process of the sodium-containing cathode material matrix and the coating modifier may include the following steps:

[0118] S2010. Provide the second container, wherein the second container contains the sodium-containing cathode material matrix;

[0119] S2020: Place the second container inside the first container, and connect the gas in the first container and the second container.

[0120] S2030. The coating modifier is applied to at least a portion of the area between the outer walls of the first container and the second container.

[0121] S2040, Sinter the first container.

[0122] In steps S2010 to S2040 above, sintering the first container containing the second container and the coating modifier allows the coating modifier to volatilize and form vapor. Since the first container and the second container are connected in terms of gas phase, the vapor formed can diffuse into the second container and react with the sodium-containing cathode material matrix in the second container. During the continuous sintering process, the coating layer is gradually formed through continuous reaction.

[0123] In some embodiments, the types of the first container and the second container are not specifically limited, as long as the first container can contain the second container, the two can be connected in a gas phase, and both can withstand high-temperature sintering. For example, the first container and the second container can each be an independent crucible.

[0124] As a non-limiting example of a cathode material preparation device, see attached... Figure 1 The diagram shows the structure of the apparatus used to prepare the cathode material in steps S2010 to S2040 above. The sodium-containing cathode material substrate 8 can be placed in the second crucible 6 first, and then the second crucible 6 can be placed in the first crucible 7. The coating modifier 9 is evenly spread in the area between the outer walls of the first crucible 7 and the second crucible 6, and then the first crucible 7 is covered. Finally, it is sintered.

[0125] In some embodiments, the thickness of the coating modifier is not specifically limited and can be adjusted according to the actual height and volume of the container used. Optionally, to continuously obtain vapor from the coating modifier, the thickness of the coating modifier should not exceed 2 cm. For example, the thickness of the coating modifier can be 2 cm, 1.9 cm, 1.8 cm, 1.7 cm, 1.6 cm, 1.5 cm, 1.4 cm, 1.3 cm, 1.2 cm, 1.1 cm, 1.0 cm, 0.9 cm, 0.8 cm, 0.7 cm, 0.6 cm, 0.5 cm, 0.4 cm, 0.3 cm, 0.2 cm, 0.1 cm, or within any range of the above values.

[0126] In some embodiments, the sintering temperature is T1, where 0 < T1 < 2000 °C. For example, T1 can be 50 °C, 100 °C, 200 °C, 300 °C, 400 °C, 500 °C, 600 °C, 700 °C, 800 °C, 900 °C, 1000 °C, 1100 °C, 1200 °C, 1300 °C, 1400 °C, 1500 °C, 1600 °C, 1700 °C, 1800 °C, 1900 °C or within the range composed of any of the above values. Optionally, the sintering temperature is 200 °C ≤ T1 ≤ 800 °C. Controlling the sintering temperature T1 within a suitable range can not only cause the coating modifier to volatilize to form steam, but also ensure that the sodium-containing cathode material matrix does not undergo Na loss and damage the crystal structure of the material, which helps to improve the cycling performance.

[0127] In some embodiments, the sintering time is t1, where 0 < t1 < 36 h. For example, t1 can be 1 h, 2 h, 8 h, 12 h, 16 h, 20 h, 24 h, 28 h, 32 h, 35 h or within the range composed of any of the above values. Optionally, the sintering time is 1 h ≤ t1 ≤ 18 h. Controlling the sintering time t1 within a suitable range can not only allow the reaction between the steam of the coating modifier and the sodium-containing cathode material matrix to proceed充分, but also ensure that the sodium-containing cathode material matrix does not undergo Na loss and damage the crystal structure of the material, which helps to further improve the cycling performance.

[0128] In some embodiments, in step S200, the sintering treatment of the sodium-containing cathode material matrix and the coating modifier may also include the following steps:

[0129] S2100. Heat-treat the coating modifier to form steam of the coating modifier;

[0130] S2200. Pass the steam of the coating modifier into a rotary kiln containing the sodium-containing cathode material matrix;

[0131] S2300. Sinter the steam of the coating modifier passed into the rotary kiln and the sodium-containing cathode material matrix.

[0132] In the above steps S2100 to S2300, first heat-treat the coating modifier to continuously volatilize the coating modifier to form steam; at the same time, pass the steam into a rotary kiln containing the sodium-containing cathode material matrix, and the steam of the coating modifier can contact and react with the sodium-containing cathode material matrix, and gradually form a coating layer through continuous reactions during the continuous sintering process. Among them, during the continuous rotation of the rotary kiln, the sodium-containing cathode material matrix can be dispersed, making the coating layer formed on its surface more uniform.

[0133] As a non-limiting example of the cathode material preparation device, as shown in the appendix Figure 2 As shown, it is a schematic structural diagram of the device for preparing the positive electrode material in the above steps S2100 to S2300. Compressed air can be introduced into the heating device 10. The coating modifier forms steam after being heat-treated in the heating device 10. The compressed air carries the steam of the coating modifier into the rotary kiln 11 and reacts with the sodium-containing positive electrode material matrix in the rotary kiln 11. During the continuous sintering of the rotary kiln 11, a coating layer is gradually formed through continuous reactions. Among them, the concentration of the steam introduced into the rotary kiln can be adjusted by controlling the flow rate of the compressed air.

[0134] In some embodiments, the filling amount of the sodium-containing positive electrode material matrix in the rotary kiln is not specifically limited, as long as the sodium-containing positive electrode material matrix can be evenly dispersed. Optionally, to obtain a better dispersion effect, the loading amount of the sodium-containing positive electrode material matrix in the rotary kiln may not exceed 1 / 2 of the volume of the rotary kiln furnace tube.

[0135] It can be understood that the operations in the above steps S2100 to S2300 of the present application occur simultaneously. Therefore, the sequence of steps S2100, S2200, and S2300 is not specifically limited.

[0136] In some embodiments, the temperature of the heat treatment is T3, where 300 < T3 < 2000 °C. For example, T3 can be 400 °C, 500 °C, 600 °C, 700 °C, 800 °C, 900 °C, 1000 °C, 1100 °C, 1200 °C, 1300 °C, 1400 °C, 1500 °C, 1600 °C, 1700 °C, 1800 °C, 1900 °C or within the range composed of any of the above values. Optionally, the temperature of the heat treatment is 400 °C ≤ T3 ≤ 1800 °C. Controlling the temperature of the heat treatment within a suitable range can cause the coating modifier to continuously volatilize, continuously form steam, and react more fully with the residual alkali substances on the surface of the sodium-containing positive electrode material matrix.

[0137] In some embodiments, the flow rate of the steam of the coating modifier is v, where 0 ml / min < v ≤ 5 ml / min. For example, the flow rate of the steam of the coating modifier can be 0.5 ml / min, 1.0 ml / min, 1.5 ml / min, 2.0 ml / min, 2.5 ml / min, 3.0 ml / min, 3.5 ml / min, 4.0 ml / min, 4.5 ml / min or within the range composed of any of the above values. Optionally, the flow rate of the steam of the coating modifier is 0.5 ml / min < v ≤ 2 ml / min.

[0138] By adjusting the flow rate of the vapor of the coating modifier within a suitable range, the concentration of the vapor of the coating modifier that contacts and reacts with the sodium-containing cathode material matrix can be controlled within a suitable range, so that the total amount of the coating modifier used during the reaction can be controlled, which is conducive to a more sufficient reaction between the coating modifier and the residual alkali substances on the surface of the sodium-containing cathode material matrix.

[0139] In some embodiments, the rotation speed of the rotary kiln is R, 0 r / min < R ≤ 15 r / min. For example, R can be 1 r / min, 3 r / min, 5 r / min, 7 r / min, 9 r / min, 11 r / min, 13 r / min or within the range composed of any of the above values. Optionally, R is 0.5 r / min to 2 r / min.

[0140] By controlling the rotation speed R of the rotary kiln within a suitable range, the sodium-containing cathode material matrix can contact the vapor of the coating modifier under the action of a suitable dispersing force, which is conducive to achieving a more uniform coating effect.

[0141] In some embodiments, the sintering temperature is T2, 0 < T2 < 1000 °C. For example, T2 can be 50 °C, 100 °C, 150 °C, 200 °C, 250 °C, 300 °C, 350 °C, 400 °C, 450 °C, 500 °C, 550 °C, 600 °C, 650 °C, 700 °C, 750 °C, 800 °C, 850 °C, 900 °C, 950 °C or within the range composed of any of the above values. Optionally, the sintering temperature is 200 °C ≤ T2 ≤ 800 °C. Controlling the sintering temperature T2 within a suitable range can not only enable the coating modifier to volatilize to form vapor, but also ensure that the sodium-containing cathode material matrix does not suffer Na loss and damage the crystal structure of the material, which helps to improve the cycle performance.

[0142] In some embodiments, the sintering time is t2, 0 < t2 < 36 h. For example, t2 can be 1 h, 2 h, 8 h, 12 h, 16 h, 20 h, 24 h, 28 h, 32 h, 35 h or within the range composed of any of the above values. Optionally, the sintering time is 1 h ≤ t2 ≤ 18 h. Controlling the sintering time t2 within a suitable range can not only enable the reaction between the vapor of the coating modifier and the sodium-containing cathode material matrix to proceed sufficiently, but also ensure that the sodium-containing cathode material matrix does not suffer Na loss and damage the crystal structure of the material, which helps to further improve the cycle performance.

[0143] The third aspect of the present application provides a secondary battery, including any device in which an electrochemical reaction occurs to mutually convert chemical energy and electrical energy, for example, a sodium-ion secondary battery.

[0144] In some embodiments, the secondary battery of this application includes a positive electrode, a negative electrode, a separator, and an electrolyte. During the charging and discharging process, 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, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0145] [Positive electrode plate]

[0146] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, said positive electrode film layer comprising the positive electrode material of the first aspect of this application or the positive electrode material prepared by the method of the second aspect of this application. As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0147] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material on the polymer material substrate. The metal material includes, but is not limited to, aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The polymer material substrate may be a substrate such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0148] In some embodiments, the positive electrode film layer does not exclude other positive electrode active materials besides the positive electrode material of the first aspect of this application or the positive electrode material prepared by the method of the second aspect of this application. For example, in some embodiments, the positive electrode film layer of this application may also include other conventionally known materials that can be used as positive electrode active materials for sodium-ion batteries. As specific examples, other positive electrode active materials may include at least one of sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds.

[0149] As an optional technical solution in this application, the transition metal in the sodium transition metal oxide can be at least one selected from Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. For example, the sodium transition metal oxide is Na. x MO2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0 < x ≤ 1.

[0150] As an optional technical solution in this application, the polyanionic compound can be a compound containing sodium ions, transition metal ions, or a tetrahedral (YO4) structure. n- A class of compounds with anionic units. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si; n represents (YO4). n- The price state.

[0151] Polyanionic compounds can also contain sodium ions, transition metal ions, or tetrahedral (YO4) ions. n- A class of compounds containing anionic units and halide anions. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si, and n represents (YO4). n- The valence state; the halogen can be at least one of F, Cl and Br.

[0152] Polyanionic compounds can also be sodium-containing tetrahedral (YO4) compounds. n- Anionic unit, polyhedral unit (ZO) y ) m+ And a class of compounds with optional halide anions. Y can be at least one of P, S, and Si, and n represents (YO4). n- The valence state; Z represents a transition metal, which can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; m represents (ZO) y ) m+ The valence state; the halogen can be at least one of F, Cl and Br.

[0153] Polyanionic compounds include, for example, NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2(P2O7), NaM'PO4F (where M' is one or more of V, Fe, Mn and Ni), and Na3(VOy)2(PO4)2F. 3-2y At least one of (0≤y≤1).

[0154] Prussian blue compounds can be a class of compounds containing sodium ions, transition metal ions, and cyanide ions (CN-). The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Examples of Prussian blue compounds include Na. a Me b Me' c(CN)6, wherein Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co and Zn, 0 < a ≤ 2, 0 < b < 1, 0 < c < 1.

[0155] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0156] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0157] The positive electrode sheet in this application can be prepared according to conventional methods in the art. For example, the positive electrode film layer is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode material, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP), but is not limited to it.

[0158] The positive electrode sheet of this application does not exclude other additional functional layers besides the positive electrode film layer. For example, in some embodiments, the positive electrode sheet of this application further includes a conductive undercoat layer (e.g., composed of a conductive agent and a binder) sandwiched between the positive current collector and the positive electrode film layer and disposed on the surface of the positive current collector. In other embodiments, the positive electrode sheet of this application further includes a protective layer covering the surface of the positive electrode film layer.

[0159] [Negative electrode plate]

[0160] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer comprising a negative electrode material. As an example, the negative current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the opposite surfaces of the negative current collector.

[0161] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material on the polymer material substrate. The metal material includes, but is not limited to, copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc., and the polymer material substrate includes, but is not limited to, polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0162] In some embodiments, the negative electrode material may be a negative electrode active material known in the art for use in secondary batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0163] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0164] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0165] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0166] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as negative electrode material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0167] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0168] The negative electrode sheet of this application does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of this application further includes a conductive undercoat layer (e.g., composed of a conductive agent and an adhesive) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector. In other embodiments, the negative electrode sheet of this application further includes a protective layer covering the surface of the negative electrode film layer.

[0169] Electrolyte

[0170] The electrolyte acts as a conductor of active ions between the positive and negative electrodes. The electrolyte used in the secondary battery of this application can be any electrolyte known in the prior art.

[0171] In some embodiments, the electrolyte includes an organic solvent, a sodium salt, and optional additives. The types of organic solvent, sodium salt, and additives are not specifically limited and can be selected as needed.

[0172] In some embodiments, as examples, the sodium salt includes, but is not limited to, at least one of NaPF6, NaClO4, NaBCl4, NaSO3CF3, and Na(CH3)C6H4SO3. One of the above sodium salts may be used alone, or two or more may be used simultaneously.

[0173] In some embodiments, as examples, the organic solvent includes, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), 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). One of the above organic solvents may be used alone, or two or more may be used simultaneously. Optionally, two or more of the above organic solvents may be used simultaneously.

[0174] In some embodiments, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0175] As an example, the additives include, but are not limited to, at least one of fluoroethylene carbonate (FEC), 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).

[0176] The electrolyte can be prepared according to conventional methods in the art. For example, an organic solvent, a sodium salt, and optional additives can be mixed evenly to obtain an electrolyte. There are no particular restrictions on the order of addition of the materials; for example, the sodium salt and optional additives can be added to the organic solvent and mixed evenly to obtain an electrolyte; or, the sodium salt can be added to the organic solvent first, and then the optional additives can be added to the organic solvent and mixed evenly to obtain an electrolyte.

[0177] [Isolation membrane]

[0178] The separator is positioned between the positive and negative electrodes, 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 restriction on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0179] In some embodiments, the material of the separator can be selected from one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride, but is not limited to these. 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. In some embodiments, a ceramic coating or a metal oxide coating may also be provided on the separator.

[0180] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0181] In some embodiments, the secondary battery cell may include an outer packaging. This outer packaging can be used to encapsulate the aforementioned electrode assembly and electrolyte.

[0182] In some implementations, the outer packaging of the secondary battery cell can be a rigid shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging of the secondary battery cell can also be a soft pack, such as a pouch. The soft pack can be made of plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0183] This application does not impose any particular limitation on the shape of the secondary battery cell; it can be cylindrical, square, or any other arbitrary shape. Figure 6 This is an example of a square-structured secondary battery 5.

[0184] In some implementations, refer to Figure 7 The outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity. Positive electrode sheets, negative electrode sheets, and a separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be adjusted according to requirements.

[0185] In some implementations, the secondary battery may also be a battery module assembled from multiple battery cells. The number of battery cells in the battery module may be multiple, and the specific number may be adjusted according to the application and capacity of the battery module.

[0186] Figure 8 This is battery module 4, used as an example. (See reference...) Figure 8 In battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0187] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0188] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0189] In some implementations, the aforementioned battery cells can also be directly assembled into a battery pack, and the number of battery cells contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0190] Figure 9 and Figure 10This is battery pack 1 as an example. (See reference...) Figure 9 and Figure 10 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3. The upper body 2 covers the lower body 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0191] A fifth aspect of this application provides an electrical device comprising at least one of the secondary battery, battery module, or battery pack described in this application. The secondary battery, battery module, or battery pack can be used as a power source for the device or as an energy storage unit for the device. The device can be, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. For example, it can be a laptop computer, pen input computer, mobile computer, e-book player, portable telephone, portable fax machine, portable copier, portable printer, stereo headset, video recorder, LCD TV, portable cleaner, portable CD player, mini CD, transceiver, electronic notebook, calculator, memory card, portable recorder, radio, backup power supply, motor, automobile, motorcycle, electric bicycle, bicycle, lighting fixture, toy, game console, clock, power tool, flashlight, camera, large household storage battery, etc.

[0192] The device can be configured to use a secondary battery, battery module, or battery pack, depending on its usage requirements.

[0193] Figure 11 This is an example device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0194] Example

[0195] The following examples describe the disclosure of this invention in more detail. These examples are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of this disclosure. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on mass, and all reagents used in the examples are commercially available or synthesized by conventional methods and can be used directly without further processing. The instruments used in the examples are also commercially available.

[0196] Example 1

[0197] Preparation of cathode materials

[0198] First, the metal oxide and sodium salt are mixed evenly in a certain proportion. Then, the mixture is placed in a sagger in a box furnace and sintered according to a specific sintering regime. After sintering is completed and cooled to room temperature, it is crushed to obtain O3-type layered oxide, which can be used as the substrate for sodium-containing cathode materials.

[0199] 20g of the above-mentioned O3-type layered oxide (NaFe) 0.5 Mn 0.5 O2 is evenly spread in the second crucible, and then the second crucible is placed in the middle of the first crucible. Boron oxide, the coating modifier, is evenly spread around the blank area of ​​the first crucible, and then the crucible lid is placed on top. Finally, the first crucible is placed in a muffle furnace for high-temperature sintering at 500℃ for 6 hours. After sintering and cooling, the modified sample is obtained, namely 0.004NaBO2·0.996NaFe. 0.5 Mn 0.5 O2 cathode material.

[0200] Preparation of positive electrode sheet

[0201] The above-mentioned positive electrode material, conductive carbon black, and binder PVDF were mixed in a mass ratio of 96.7:1.7:1.6, and an appropriate amount of solvent NMP was added. The mixture was stirred in a vacuum mixer to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated on both surfaces of the positive electrode current collector aluminum foil. After vacuum drying at 70°C for 12 hours, the positive electrode sheet was obtained by slitting and cutting into sheets.

[0202] Preparation of negative electrode sheet

[0203] Hard carbon as the negative electrode material, sodium carboxymethyl cellulose as the thickener, styrene-butadiene rubber as the binder, and acetylene black as the conductive agent are mixed in a mass ratio of 97:1:1:1. Deionized water is added, and the mixture is stirred in a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry is then uniformly coated onto copper foil. After the copper foil is dried at room temperature, it is transferred to a 120°C oven to dry for 1 hour. Then, it is cold-pressed and slit to obtain a negative electrode sheet.

[0204] Preparation of electrolyte

[0205] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent; NaPF6 was dissolved in the above organic solvent, and then fluoroethylene carbonate (FEC) was added and mixed evenly to obtain an electrolyte; wherein the concentration of NaPF6 was 1 mol / L.

[0206] Preparation of the separating membrane

[0207] PE porous film is used as the separator.

[0208] Preparation of sodium-ion batteries

[0209] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrode assembly is then wound up to obtain the electrode assembly. The electrode assembly is placed in an outer package, injected with the prepared electrolyte, and then sealed. After processes such as formation, degassing, and edge trimming, a sodium-ion battery is obtained.

[0210] Examples 2 to 43

[0211] The preparation method of the sodium-ion battery is similar to that in Example 1, except that the cathode material and related parameters in its preparation process were adjusted. Specific parameters are detailed in Table 1 below. " / " indicates that the corresponding parameter does not exist.

[0212] In Examples 32 to 39, the preparation method of the cathode material is as follows: O3-type layered oxide is placed in a rotary furnace, and the modifier is placed in the front heating device. The rotary furnace and heating device are started, and compressed air is introduced. The heating device and sintering device are sintered according to the set speed and temperature. After the sintering is completed and cooled to room temperature, the modified sample can be obtained, that is, the cathode material is obtained.

[0213] Comparative Example 1

[0214] The method used to prepare the cathode material in Comparative Example 1 is similar to that in Example 1, except that no coating modifier is added during the preparation process.

[0215] Comparative Example 2

[0216] Comparative Example 2 uses a traditional water washing method to treat O3-type layered oxides to obtain cathode materials.

[0217] Comparative Example 3

[0218] Comparative Example 3 uses a traditional acid washing method to treat O3-type layered oxides to obtain a cathode material.

[0219] Comparative Example 4

[0220] Comparative Example 4: A cathode material was obtained by dry mixing and coating O3-type layered oxide with boric acid as a coating modifier, wherein the amount of boric acid added was 3000 ppm.

[0221] Comparative Example 5

[0222] The method used to prepare the cathode material in Comparative Example 5 is similar to that in Example 32, except that the sintering temperature is 2500℃.

[0223] Comparative Example 6

[0224] The method used to prepare the cathode material in Comparative Example 6 is similar to that in Example 40, except that no coating modifier is added during the preparation process.

[0225] Comparative Example 7

[0226] The method used to prepare the cathode material in Comparative Example 7 is similar to that in Example 41, except that no coating modifier is added during the preparation process.

[0227] Table 1

[0228]

[0229]

[0230] Test section

[0231] (1) Test of surface residual alkali content of cathode material

[0232] Weigh 20.000g of the sample, transfer it to 100mL of deionized water, stir for 30min and filter. Transfer 60mL to a 250mL conical flask, add 10 drops of indicator (methyl orange and phenolphthalein) and shake well. The solution turns purple. Titrate with 0.1103mol / L hydrochloric acid as a standard solution. Titrate until bright green (record V1), and continue titrating until magenta (record V2).

[0233] Surface residual alkali content % = C × V² / 2 / 1000 × m² / m³ / m¹ × 73.89 × 100

[0234] Na2CO3 content % = C × (V2 - V1) / 1000 × m2 / m3 / m1 × 73.89 × 100

[0235] NaOH content % = C × (2V1 - V2) / 1000 × m2 / m3 / m1 × 23.95 × 100

[0236] Where m1 is the sample mass, m2 is the mass of water removed, and m3 is the mass of the filtrate after filtration.

[0237] (2) Test of the mass percentage of M element in the doped region

[0238] XPS (X-ray photoelectron spectroscopy) can distinguish between doped regions and coating thickness, as well as the proportion and content of element M in the corresponding regions. The mass percentage content can be calculated by measuring the proportion of element M inside the region using XPS. Alternatively, the mass percentage content of element M in the doped region can be measured by combining TEM (transmission electron microscopy) and EDS (energy dispersive spectroscopy).

[0239] (3) Testing of M element content in cathode materials

[0240] The content of element M in cathode materials has a well-known meaning in the art and can be determined using instruments and methods well-known in the art. For example, the total content of element M in cathode materials can be determined by ICP (inductively coupled plasma).

[0241] (4) Surface morphology testing (SEM) of cathode materials

[0242] The surface morphology of the cathode material was tested using a JEOL JSM-6510 scanning electron microscope.

[0243] (5) Sodium-ion battery discharge specific capacity test

[0244] At 25°C, the sodium-ion battery is charged to 4.3V at a constant current density of 10mA / g, and then discharged to 1.5V at a constant current density of 10mA / g to obtain the discharge specific capacity.

[0245] (6) Sodium-ion battery cycle performance test

[0246] The cycle test temperature is 25℃. The battery is charged at a constant current of 1C to 4.3V, left to stand for 5 minutes, and then discharged at 1C to 1.5V. The capacity obtained in this step is used as the initial capacity. The 1C charge / 1C discharge cycle test is carried out until the sodium-ion battery cycle capacity retention rate is 80%. The capacity after 100 cycles and the number of cycles corresponding to the capacity retention rate of 80% are recorded.

[0247] Table 2 presents the performance test results of Examples 1 to 43 and Comparative Examples 1 to 7.

[0248] Table 2

[0249]

[0250]

[0251] Through append Figure 5 SEM images of the cathode materials in Example 1 (right side) and Comparative Example 1 (left side) show that the cathode material in Example 1 has achieved surface coating. Comparative analysis of Example 1 with Comparative Example 1, Example 40 with Comparative Example 6, and Example 41 with Comparative Example 7 reveals that when no coating modifier is added during the preparation process, the residual alkali content of the cathode material is significantly higher, and the discharge specific capacity, capacity retention rate, and cycle number of the sodium-ion battery are significantly lower. This indicates that adding the coating modifier of this application during the preparation process can effectively reduce the residual alkali content and improve the cycle performance of the sodium-ion battery.

[0252] Comparative analysis of Example 1 and Comparative Example 2 shows that although the traditional water washing method in Comparative Example 2 can reduce the residual alkali to a certain extent, the discharge specific capacity, capacity retention rate and cycle number of the sodium-ion battery are significantly lower than those in Example 1. This indicates that the method of this application can reduce the residual alkali while maintaining the high cycle performance of the sodium-ion battery, which is significantly better than the traditional water washing method.

[0253] Comparative analysis of Example 1 and Comparative Example 3 shows that although the traditional acid washing method in Comparative Example 3 can reduce the residual alkali content to a certain extent, the discharge specific capacity, capacity retention rate and cycle number of the sodium-ion battery are significantly lower than those in Example 1. This indicates that the method of this application can reduce the residual alkali content while maintaining the high cycle performance of the sodium-ion battery, which is significantly better than the traditional acid washing method.

[0254] Comparative analysis of Example 1 and Comparative Example 4 shows that in Comparative Example 4, after dry mixing and coating O3-type layered oxide with the coating modifier boric acid, the residual alkali content of the cathode material is significantly higher than that in Example 1, while the discharge specific capacity, capacity retention rate, and cycle number of the sodium-ion battery are significantly lower than those in Example 1. This indicates that the method of this application can more effectively reduce the residual alkali content and also ensure that the sodium-ion battery has high cycle performance, which is significantly better than the dry mixing and coating method.

[0255] Comparative analysis of Example 32 and Comparative Example 5 shows that when the sintering temperature is outside the range provided in this application, the residual alkali content of the cathode material is significantly higher, and the discharge specific capacity, capacity retention rate and cycle number of the sodium-ion battery are significantly lower. This indicates that when preparing cathode materials using the method of this application, the sintering temperature needs to be controlled within the range provided in this application. This can effectively reduce the residual alkali content and improve the cycle performance of the sodium-ion battery.

[0256] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0257] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims, and the specification and drawings can be used to interpret the scope of protection of the claims.

Claims

1. A positive electrode material, characterized in that, include: Sodium-containing cathode material matrix; and A coating layer covering at least a portion of the surface of the sodium-containing cathode material substrate, the coating layer containing Na x M y O2, wherein M includes at least one of B, Si and P, x>0, y>0; The coating layer includes: A transition layer relatively close to the sodium-containing cathode material substrate, wherein the transition layer contains a doped region of element M; and The oxide layer, located relatively far from the sodium-containing cathode material substrate, contains the Na... x M y O2; Based on the total mass of the coating layer, the mass percentage of the M element in the doped region is 0.05% to 0.3%.

2. The cathode material according to claim 1, characterized in that, The cathode material satisfies at least one of the following conditions: (1) The residual alkali content on the surface of the positive electrode material is 0.5 wt.% to 5.5 wt.%; and (2) Based on the total mass of the coating layer, the mass percentage of element M in the doped region is greater than the mass percentage of element M in the oxide layer.

3. The cathode material according to claim 1 or 2, characterized in that, The residual alkali content on the surface of the cathode material is from 0.8 wt.% to 4.5 wt.%.

4. The cathode material according to any one of claims 1 to 3, characterized in that, The cathode material satisfies at least one of the following conditions: (1) The sodium-containing cathode material matrix includes one or more of layered oxides, Prussian blue compounds, and polyanionic compounds; (2) The sodium-containing cathode material matrix is ​​composed of micron particles, and the average particle size of the micron particles is 1 μm to 25 μm; (3) The coating layer accounts for 0.001% to 3% of the mass of the cathode material; and (4) The thickness of the coating layer is 0.5 nm to 30 nm.

5. The positive electrode material according to claim 4, characterized in that, At least one of the following conditions must be met: (1) The layered oxide has the chemical formula Na x Mn a Fe b Ni c L d O 2-e , where 0.7 < x ≤ 1, a > 0, b ≥ 0, 0.1 < c ≤ 0.3, d ≥ 0, a + b + c + d + e = 1, -0.1 ≤ e ≤ 0.1, and L is selected from one or more of Cu, Li, Ti, Zr, K, Nb, Mg, Ca, Mo, Zn, Cr, W, Bi, Sn, Ge, Al, Si, La, Ta, P, and B; (2) The average particle size of the micron particles is 1 μm to 15 μm.

6. The cathode material according to claim 4 or 5, characterized in that, The sodium-containing cathode material matrix is ​​an O3-type layered oxide.

7. The cathode material according to any one of claims 1 to 6, characterized in that, At least one of the following conditions must be met: (1) The coating layer accounts for 0.01% to 2% of the mass of the cathode material; (2) The thickness of the coating layer is 1 nm to 5 nm.

8. The cathode material according to any one of claims 1 to 7, characterized in that, The coating layer accounts for 0.01% to 1% of the mass of the cathode material.

9. A method for preparing a cathode material, characterized in that, include: Provide a sodium-containing cathode material matrix; and The sodium-containing cathode material substrate is subjected to surface heat treatment using vapor coated with a modifier to form a Na-containing layer on at least a portion of the surface of the sodium-containing cathode material substrate. x M y The O2 coating layer yields the positive electrode material, wherein M includes at least one of B, Si and P, x>0, y>0; The coating layer includes: A transition layer relatively close to the sodium-containing cathode material substrate, wherein the transition layer contains a doped region of element M; and The oxide layer, located relatively far from the sodium-containing cathode material substrate, contains the Na... x M y O2; Based on the total mass of the coating layer, the mass percentage of the M element in the doped region is 0.05% to 0.3%.

10. The method according to claim 9, characterized in that, The surface heat treatment of the sodium-containing cathode material matrix using vapor coated with a modifier includes: The sodium-containing cathode material matrix and the coating modifier are sintered to allow the vapors of the sodium-containing cathode material matrix and the coating modifier to react in contact, thereby forming a transition layer relatively close to the sodium-containing cathode material matrix and an oxide layer relatively far away from the sodium-containing cathode material matrix on at least a portion of the surface of the sodium-containing cathode material matrix.

11. The method according to claim 10, characterized in that, The method satisfies at least one of the following conditions: (1) The coating modifier includes one or more of boric acid, boron oxide, silicic acid and ammonium dihydrogen phosphate; (2) The sodium-containing cathode material matrix includes one or more of layered oxides, Prussian blue compounds, and polyanionic compounds; (3) The mass ratio of the coating modifier to the sodium-containing cathode material matrix is ​​m, 0 <m<2; and (4) When the sintering process is carried out, the coating modifier is a solid phase or a liquid phase.

12. The method according to claim 10 or 11, characterized in that, At least one of the following conditions must be met: (1) The sodium-containing cathode material matrix is ​​an O3-type layered oxide; (2) The mass ratio of the coating modifier to the sodium-containing cathode material matrix is m, where 0.05 ≤ m ≤ 1; (3) When performing the sintering treatment, the coating modifier is in a solid phase.

13. The method according to any one of claims 10 to 12, characterized in that, The sintering treatment of the sodium-containing cathode material matrix and the coating modifier includes: Providing a first container, wherein the first container contains the coating modifier and a second container, and the second container contains the sodium-containing cathode material matrix, and the gas phases in the first container and the second container are connected; and Sintering the first container.

14. The method according to claim 13, characterized in that, The providing of the first container includes: Providing the second container; Placing the second container inside the first container; and Laying the coating modifier in at least a partial area between the outer walls of the first container and the second container.

15. The method according to claim 14, characterized in that, The laying thickness of the coating modifier is not higher than 2 cm.

16. The method according to any one of claims 13 to 15, characterized in that, The method satisfies at least one of the following conditions: (1) The temperature of the sintering is T1, where 0 < T1 < 2000 °C; (2) The time of the sintering is t1, where 0 < t1 < 36 h; and (3) The first container and the second container can each independently be crucibles.

17. The method according to any one of claims 13 to 16, characterized in that, The method satisfies at least one of the following conditions: (1) The temperature of the sintering is T1, where 200 °C ≤ T1 ≤ 800 °C; (2) The time of the sintering is t1, where 1 h ≤ t1 ≤ 18 h.

18. The method according to any one of claims 10 to 17, characterized in that, The sintering treatment of the sodium-containing cathode material matrix and the coating modifier includes: Performing heat treatment on the coating modifier to form the vapor of the coating modifier; Passing the vapor of the coating modifier into a rotary kiln containing the sodium-containing cathode material matrix; and Sintering the vapor of the coating modifier and the sodium-containing cathode material matrix passed into the rotary kiln.

19. The method according to claim 18, characterized in that, The method satisfies at least one of the following conditions: (1) The temperature of the sintering is T2, where 0 < T2 < 1000 °C; and (2) The time of the sintering is t2, where 0 < t2 < 36 h.

20. The method according to claim 18 or 19, characterized in that, Satisfies at least one of the following conditions: (1) The temperature of the sintering is T2, where 200 °C ≤ T2 ≤ 800 °C; (2) The time of the sintering is t2, where 1 h ≤ t2 ≤ 18 h.

21. The method according to any one of claims 18 to 20, characterized in that, The method satisfies at least one of the following conditions: (1) The temperature of the heat treatment is T3, where 300 < T3 < 2000 °C; (2) The rotation speed of the rotary kiln is R, where 0 r / min < R ≤ 15 r / min; and (3) The flow rate of the vapor of the coating modifier is v, where 0 ml / mi < v ≤ 5 ml / min.

22. The method according to any one of claims 18 to 21, characterized in that, Satisfies at least one of the following conditions: (1) The temperature of the heat treatment is T3, where 400 °C ≤ T3 ≤ 1800 °C; (2) The rotation speed of the rotary kiln is R, where 3 r / min ≤ R ≤ 8 r / min; (3) The flow rate of the vapor of the coating modifier is v, where 0.5 ml / min ≤ v ≤ 2 ml / min.

23. A positive electrode plate, characterized in that, Includes the cathode material according to any one of claims 1 to 8 or the cathode material prepared by the method according to any one of claims 9 to 22.

24. A secondary battery, characterized in that, Includes the cathode electrode sheet according to claim 23.

25. An electrical appliance, characterized in that, Includes the secondary battery according to claim 24.

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