Cathode material and method of manufacturing the same, positive electrode plate and sodium ion battery

Abstract

The present application belongs to the field of batteries and provides a positive electrode material, a method for manufacturing the same, a positive electrode plate, and a sodium ion battery. The positive electrode material comprises a core, said core contains sodium iron phosphate pyrophosphate and optional sodium iron phosphate, and the mass ratio of said sodium iron phosphate to said sodium iron phosphate pyrophosphate in said positive electrode material is (0 to 0.15): (99.85 to 100). The present application improves the capacity and cycle performance of the positive electrode material and the sodium ion battery.

Description

Technology Field

[0001] The present invention relates to the field of battery technology, specifically to a positive electrode material, a method for manufacturing the same, a positive electrode plate, and a sodium ion battery. This application claims priority to a Chinese patent application filed on October 8, 2024, with application number 2024113981023 and titled "positive electrode material and method for manufacturing the same, positive electrode plate and sodium ion battery," all of which are used by reference. Background Technology

[0002] Sodium-ion batteries (SIBs) are secondary batteries with the next-largest application prospects after lithium-ion batteries (e.g., applicable to the new energy vehicle sector), and their electrochemical performance is primarily determined by the performance of the cathode. Among cathode materials, sodium iron pyrophosphate has become one of the widely used materials in sodium-ion batteries due to its excellent theoretical electrochemical performance. Although its theoretical electrochemical performance is relatively excellent, sodium iron pyrophosphate currently manufactured in practice still suffers from poor capacity and cycle performance.

[0003] Taking into account the technical problems existing in the background technology, the present application provides a positive electrode material, a method for manufacturing the same, a positive electrode plate, and a sodium ion battery that can solve the problem of reduced capacity and cycle performance of sodium iron phosphate pyrophosphate currently manufactured in practice.

[0004] In a first aspect, the anode material provided in an embodiment of the present application comprises a core, wherein the core contains sodium iron phosphate pyrophosphate and optional sodium iron phosphate, and the mass ratio of the sodium iron phosphate to the sodium iron phosphate pyrophosphate in the anode material is (0 to 0.15): (99.85 to 100).

[0005] The anode material provided by the present application controls the mass ratio of the sodium iron phosphate (NaFePO4) impurity phase and the sodium iron phosphate pyrophosphate (Na4Fe3(PO4)2P2O7) main phase to the above range, thereby controlling the mass ratio of the sodium iron phosphate impurity phase to a low range, improving the purity of the sodium iron phosphate pyrophosphate main phase, and effectively reducing the adverse effect of the sodium iron phosphate impurity phase on the capacity and cycle performance of the anode material, so that the capacity and cycle performance of the material are greatly improved.

[0006] In some embodiments, it further comprises a carbon-containing coating layer covering at least a portion of the surface of the core;

[0007] Optionally, the thickness of the carbon-containing coating layer is 2 nm to 5 nm;

[0008] Optionally, the carbon-containing coating layer covers the surface of the core with a coating rate of 97% to 100%.

[0009] The carbon-containing coating layer is uniformly distributed on the core surface, which is advantageous for increasing the compaction density and capacity of the anode material while ensuring the electronic conductivity and corrosion resistance to the electrolyte of the anode material.

[0010] In some embodiments, the anode material is,

[0011] (1) Condition in which the compaction density of the anode material is 2.25 g / mL to 2.45 g / mL;

[0012] (2) The specific surface area of ​​the anode material is 10 m 2 / g~15.5m 2 Condition for / g;

[0013] (3) One or more of the following conditions are satisfied: the powder resistivity of the anode material is 14 Ω·cm to 45 Ω·cm.

[0014] When the positive electrode material satisfies the above conditions, the sodium ion battery manufactured using it has excellent electrochemical performance, such as energy density.

[0015] In a second aspect, the method for manufacturing an anode material provided in the embodiment of the present application is.

[0016] A step of obtaining a first mixed solution by mixing a phosphate source, a ferrous source, a pyrophosphate source, a sodium source, a first reducing agent, and a solvent;

[0017] A step of obtaining a precursor by drying the first mixed solution;

[0018] The method comprises the step of obtaining an anode material by calcining the above precursor; wherein the anode material includes a core, the core contains sodium iron phosphate pyrophosphate and optional sodium iron phosphate, and the mass ratio of the sodium iron phosphate to the sodium iron phosphate in the anode material is (0~0.15):(99.85~100).

[0019] The above manufacturing method of the present application adopts a solution method to produce sodium iron phosphate pyrophosphate. Compared to the conventional solid-state method, it is possible to achieve a uniform mixture of pyrophosphate groups, phosphate groups, ferrous ions, sodium ions, etc., and during calcination, the solid diffusion path is shorter, reaction fusion is better, the formation of sodium iron phosphate impurity phases is reduced, the particle density of the manufactured anode material is higher, and the performance of the manufactured anode material in terms of capacity and cycle performance is effectively improved.

[0020] In some embodiments,

[0021] (1) The above sodium source includes an organic sodium salt, and

[0022] Optionally, the organic sodium salt comprises one or more of sodium citrate, sodium acetate, sodium malate, and sodium lactate, optionally comprises sodium citrate and / or sodium acetate, and also optionally comprises sodium citrate and sodium acetate.

[0023] Optionally, if the organic sodium salt comprises sodium citrate and sodium acetate, the molar ratio of sodium citrate to sodium acetate is (0.1–0.6):(0.4–0.9);

[0024] (2) The above first reducing agent comprises one or more of titanium trichloride, ammonium sulfite, and ascorbic acid;

[0025] (3) The above iron source includes one or more of ferrous acetate and ferrous phosphate;

[0026] (4) The above phosphate source includes one or more of ferrous phosphate and phosphoric acid;

[0027] (5) The above pyrophosphate source comprises pyrophosphate and / or pyrophosphate, optionally the pyrophosphate comprises sodium pyrophosphate and / or ammonium pyrophosphate;

[0028] (6) The molar ratio of iron element, phosphorus element and first reducing agent in the first mixed solution is 3:(4.04~4.1):(0.05~0.1), and

[0029] Optionally, a condition in which the molar ratio of the phosphorus element in the pyrophosphate source and the phosphorus element in the first mixed solution is (2.04~2.1):(4.04~4.1);

[0030] (7) Condition in which the molar ratio of sodium ions to ferrous ions in the first mixed solution is (1~1.08):1, optionally (1.02~1.05):1;

[0031] (8) The above solvent includes one or more of purified water, deionized water, and distilled water;

[0032] (9) One or more of the following conditions are satisfied: the average particle size of the above precursor is 5 μm to 20 μm.

[0033] The present application uses an organic sodium salt to simultaneously provide a sodium source and a carbon source. Compared to a method of introducing a carbon source and a sodium source separately, this is advantageous for a more uniform distribution of the carbon source, thereby further enhancing the effect of improving the corresponding electrochemical performance of the anode material by the carbon-containing coating layer.

[0034] In some embodiments, the ferrous iron source is selected from ferrous phosphate, and the method for producing the ferrous phosphate is,

[0035] A step of obtaining a sol containing ferrous hydroxide by adding a first pH adjuster to a second mixed solution containing a ferrous salt and a second reducing agent to adjust the pH value of the second mixed solution to 7.2 to 7.5;

[0036] The method comprises the step of adding a second pH adjuster to the sol to adjust the pH value of the sol to 3.5 to 4.5 to obtain the ferrous phosphate;

[0037] Optionally, the first pH adjuster comprises ammonia water and / or sodium hydroxide, and optionally comprises ammonia water; and when the first pH adjuster comprises ammonia water, the concentration of the first pH adjuster is 5 mol / L to 10 mol / L;

[0038] Optionally, the second reducing agent comprises one or more of sodium borohydride, phosphoric acid, and hydrazine hydrate;

[0039] Optionally, the second pH adjuster comprises phosphoric acid;

[0040] Optionally, the molar ratio of the iron element in the first iron salt and the second reducing agent in the second mixed solution is 1:(0.01~0.1).

[0041] When ferrous phosphate is manufactured using the above manufacturing method, the primary particles of the manufactured ferrous phosphate can be made finer, and in the subsequent process of manufacturing an anode material using ferrous phosphate as a raw material, the ferrous phosphate can dissolve more quickly in the solvent, so the dissolution rate is faster and the dissolution is more effective, so the final chemical composition ratio of the core of the anode material is closer to the theoretical value (i.e., Na4Fe3(PO4)2P2O7) and the formation of sodium iron phosphate impurity phase can be further suppressed.

[0042] In some embodiments, after the step of adjusting the pH value of the sol to 3.5 to 4.5, the method further includes the step of raising the temperature of the sol to 80°C to 95°C and stirring for 30 to 60 minutes.

[0043] In the technical means according to the embodiment of the present application, heating the sol and then stirring the reaction is advantageous for the precipitation of ferrous phosphate.

[0044] In some embodiments, the calcination treatment includes raising the precursor to a preset temperature and maintaining it at the preset temperature;

[0045] Optionally, the preset temperature is 600°C to 700°C;

[0046] Optionally, the above-mentioned warming time is 4h to 8h;

[0047] Optionally, the calcination treatment is performed under a protective atmosphere;

[0048] Additionally, optionally, the protective atmosphere includes a nitrogen atmosphere and / or an argon atmosphere.

[0049] If the preset temperature or holding time of the calcination treatment is kept within the respective ranges mentioned above, not only can the density of the carbon-containing coating layer be improved, but the purity of sodium iron pyrophosphate in the anode material can also be improved.

[0050] In a third aspect, the positive electrode plate provided in the embodiment of the present application comprises a positive material according to the first aspect of the present application or a positive material manufactured by a manufacturing method according to the second aspect of the present application.

[0051] In this embodiment, the positive electrode plate includes the aforementioned positive material, thus having a higher capacity and better cycle performance.

[0052] In a fourth aspect, the sodium ion battery provided in the embodiment of the present application includes a positive electrode plate according to the third aspect of the present application.

[0053] In this embodiment, the sodium ion battery includes the aforementioned positive electrode plate, thus having a higher capacity and better cycle performance.

[0054] In a fifth aspect, the electric device provided in an embodiment of the present application includes a sodium ion battery according to the fourth aspect of the present application.

[0055] The electric device of the present application includes a sodium ion battery provided in the present application, and thus has at least the same advantages as a sodium ion battery.

[0056] The above description is merely an overview of the technical solution of the present application. To understand the technical means of the present application more thoroughly, it may be implemented in accordance with the contents of the specification. Furthermore, to enable a clearer understanding of the purpose, features, and advantages of the present application, specific embodiments of the present application are described below. Brief explanation of the drawing

[0057] Hereinafter, to more clearly explain the technical means of the present application, the drawings used in the description of the present application are briefly introduced. The drawings described below are merely some embodiments of the present application, and it is obvious to those skilled in the art that other drawings can be obtained based on these drawings without creative work. FIG. 1 is a diagram showing the manufacturing process flow of the anode material provided in the present application. Figure 2 is a scanning electron microscope (SEM) image of the anode material prepared in Example 1 of the present application. Figure 3 is a scanning electron microscope (SEM) image of the anode material prepared in Example 2 of the present application. Specific details for implementing the invention

[0058] Hereinafter, embodiments of the technical means of the present application will be described in detail with reference to the attached drawings. The following embodiments are used merely to more clearly explain the technical means of the present application and are therefore illustrative; the scope of protection of the present application is not to be limited thereto.

[0059] All technical and scientific terms used in this specification have the same meaning as generally understood by those skilled in the art to which the present invention pertains, unless otherwise defined; terms used in this specification are intended to specifically describe embodiments and are not to be interpreted as limiting the scope of this application; and terms "comprising," "having," and all variations thereof as used in the description of the invention, claims, and drawings in this application are interpreted to cover non-exclusive inclusions.

[0060] In the embodiments of this application, terms such as "first," "second," etc. are used merely to distinguish different objects and should not be interpreted as indicating or implying relative importance, or as implicitly indicating the number of technical features being modified, a specific order, or a subject-object relationship. In the embodiments of this application, "plural" means two or more unless specifically defined otherwise.

[0061] In this specification, "Examples" means that specific features, structures, or characteristics described in combination with the Examples may be included in at least one Example of this application. As stated in various places in this specification, this phrase does not necessarily refer to the same Example, nor are they independent or alternative Examples mutually exclusive from other Examples. Those skilled in the art will understand clearly and implicitly that the Examples described in this specification may be combined with other Examples.

[0062] In the embodiments of this application, the term "and / or" merely describes the association between related objects and indicates that three relationships may exist; for example, “A and / or B” may represent three cases: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, in this specification, the symbol " / " generally indicates that the related objects before and after it have an "or" relationship.

[0063] In the embodiments of the present application, the term “plural” means two or more (including two), likewise, “plural group” means two or more groups (including two groups), and “plural piece” means two or more pieces (including two pieces).

[0064] In the description of the embodiments of the present application, the directional or positional relationships indicated by technical terms such as “center,” “longitudinal,” “transverse,” “length,” “width,” “thickness,” “top,” “bottom,” “front,” “back,” “left,” “right,” “vertical,” “horizontal,” “top,” “bottom,” “inside,” “outside,” “clockwise,” “counterclockwise,” “axial,” “radial,” and “circular” are based on the directional or positional relationships illustrated in the attached drawings and are merely intended to easily and briefly explain the embodiments of the present application. They do not indicate or imply that the mentioned devices or components must have a specific direction or be configured and operated in a specific direction, and therefore should not be interpreted as limiting the present application.

[0065] Unless otherwise specifically stated in the description of the embodiments of this application, technical terms such as “mounting,” “connecting to each other,” “connecting,” and “fixing” should be interpreted in a broad sense, for example, they may be fixedly connected, detachably connected, or integrally formed; or they may be mechanically connected or electrically connected; or they may be directly connected or indirectly connected through an intermediate element; or the interiors of two components may be in communication or there may be an interaction relationship between two components. A person skilled in the art to which this application pertains will be able to readily understand the specific meaning that the said terms have in the embodiments of this application depending on the specific circumstances.

[0066] Currently, sodium iron phosphate cathode materials being manufactured generally contain a certain amount of impurity phases, such as sodium iron phosphate, in addition to the sodium iron phosphate main phase. The presence of such impurity phases can easily degrade the capacity and cycle performance of the cathode material. Furthermore, the higher the content of these impurity phases in the cathode material, the more severe the degradation of capacity and cycle performance becomes, resulting in a decline in the cathode material's capacity and cycle performance.

[0067] In order to solve the technical problem of reduced capacity and cycle performance of the currently existing sodium iron phosphate, the present application provides a positive electrode material and a method for manufacturing the same, a positive electrode plate, a sodium ion battery, and an electric device. By improving the current sodium iron phosphate positive electrode material and the method for manufacturing the same, a technical effect of improving capacity and cycle performance can be obtained, and accordingly, the capacity and cycle performance of the positive electrode plate, the secondary battery, and the electric device can also be improved.

[0068] In a first aspect, the anode material according to the present application comprises a core, wherein the core contains sodium iron phosphate pyrophosphate and optional sodium iron phosphate, and the mass ratio of the sodium iron phosphate to the sodium iron phosphate in the anode material is (0 to 0.15): (99.85 to 100).

[0069] The anode material provided by the present application controls the mass ratio of the sodium iron phosphate (NaFePO4) impurity phase and the sodium iron phosphate pyrophosphate (Na4Fe3(PO4)2P2O7) main phase to the above range, thereby controlling the mass ratio of the sodium iron phosphate impurity phase to a low range, improving the purity of the sodium iron phosphate pyrophosphate main phase, and effectively reducing the adverse effect of the sodium iron phosphate impurity phase on the capacity and cycle performance of the anode material, so that the capacity and cycle performance of the material are greatly improved.

[0070] In some embodiments, the mass ratio of the sodium iron phosphate pyrophosphate in the anode material is 99.85% to 100%. For example, the mass ratio may be 99.85%, 99.86%, 99.87%, 99.88%, 99.89%, 99.9%, 99.91%, 99.92%, 99.93%, 99.4%, 99.95%, 99.96%, 99.97%, 99.98%, 99.99%, 100%, or may be within a range consisting of any of the above figures.

[0071] In the technical means according to the embodiment of the present application, sodium iron phosphate pyrophosphate occupies a relatively high mass ratio in the anode material, that is, the purity of the sodium iron phosphate pyrophosphate column in the anode material is relatively high, so the capacity and cycle performance of the anode material can be effectively improved.

[0072] In some embodiments, the mass ratio of the sodium iron phosphate in the anode material is 0 to 0.15%. For example, the mass ratio may be 0, 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, or may be within a range consisting of any of the above values.

[0073] In the technical means according to the embodiment of the present application, when the mass ratio of sodium iron phosphate in the anode material is within the above range, sodium iron phosphate pyrophosphate in the anode material occupies a relatively high mass ratio, that is, the purity of the sodium iron phosphate pyrophosphate column in the anode material can be relatively high. This allows for the effective improvement of the capacity and cycle performance of the anode material.

[0074] In some embodiments, the mass fraction of sodium element in the anode material is 14% to 16%, the mass fraction of iron element is 25% to 26%, and the mass fraction of phosphorus element is 17% to 21%. For example, the mass fraction of sodium element in the anode material may be 14%, 14.5%, 15%, 15.5%, or 16%, or may be within a range consisting of any of the above values; the mass fraction of iron element may be 25%, 25.5%, or 26%, or may be within a range consisting of any of the above values; and the mass fraction of phosphorus element may be 17%, 18%, 19%, 20%, or 21%, or may be within a range consisting of any of the above values.

[0075] In some embodiments, the anode material further comprises a carbon-containing coating layer covering at least some surface of the core.

[0076] In some embodiments, the mass ratio of the carbon-containing coating layer in the anode material is 1.2% to 4.5%. For example, the mass ratio may be 1.2%, 1.25%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or may be within a range consisting of any of the above values.

[0077] In the technical means according to the embodiment of the present application, the carbon-containing coating layer of the anode material can effectively improve the electronic conductivity of sodium iron phosphate pyrophosphate, thereby further improving the electrochemical performance of the anode material in terms of rate capability.

[0078] In some embodiments, the thickness of the carbon-containing coating layer is 2 nm to 5 nm. For example, the thickness of the carbon-containing coating layer may be 2 nm, 2.3 nm, 2.5 nm, 2.7 nm, 3 nm, 3.3 nm, 3.5 nm, 3.7 nm, 4 nm, 4.3 nm, 4.5 nm, 4.7 nm, or 5 nm, or may be within a range consisting of any of the above values, which is advantageous for simultaneously ensuring the electronic conductivity of the anode material and corrosion resistance to the electrolyte.

[0079] In some embodiments, the carbon-containing coating layer covers the surface of the core with a coating rate of 97% to 100%. For example, the coating rate may be 97%, 98%, 99%, or 100%, or may be within a range consisting of any of the above values, and accordingly, the carbon-containing coating layer is uniformly distributed on the surface of the core, which is advantageous for increasing the compaction density of the anode material and increasing the capacity of the anode material while simultaneously ensuring the electronic conductivity of the anode material and corrosion resistance to the electrolyte.

[0080] It can be understood that the "coverage rate" described in this application refers to the ratio of the area of ​​the core surface covered by the carbon-containing coating layer to the surface area of ​​the core.

[0081] In some embodiments, the compaction density of the anode material is 2.25 g / mL to 2.45 g / mL. For example, the compaction density may be 2.25 g / mL, 2.27 g / mL, 2.3 g / mL, 2.32 g / mL, 2.35 g / mL, 2.37 g / mL, 2.4 g / mL, 2.41 g / mL, 2.43 g / mL, 2.45 g / mL, or may be within a range consisting of any of the above values.

[0082] For reference, the compaction density of the anode material refers to the compaction density of the anode material measured under a pressure of 3 tons.

[0083] In the technical means according to the embodiment of the present application, since the compaction density of the anode material is relatively high, the sodium ion battery can have a higher energy density.

[0084] In some embodiments, the specific surface area (BET specific surface area) of the anode material is 10 m 2 / g~15.5m 2 It is / g. For example, the above specific surface area is 10m² 2 / g, 11m 2 / g, 12m 2 / g, 13m 2 / g, 14m 2 / g, 15m 2 / g, 15.5m 2 It may be / g, or may be within a range consisting of any of the values ​​above. This is advantageous for further improving the capacity and cycle performance of sodium-ion batteries.

[0085] In some embodiments, the powder resistivity of the anode material is 14Ω·cm to 45Ω·cm. For example, the powder resistivity may be 14Ω·cm, 20Ω·cm, 25Ω·cm, 27Ω·cm, 30Ω·cm, 33Ω·cm, 35Ω·cm, 37Ω·cm, 40Ω·cm, 42Ω·cm, 45Ω·cm, or may be within a range consisting of any of the above values, which is advantageous for improving the cycle performance of the sodium-ion battery.

[0086] In a second aspect, the method for manufacturing an anode material provided by the present application can be used to manufacture an anode material according to the first aspect of the present application, and

[0087] (S1) A step of obtaining a first mixed solution by mixing a phosphate radical source, a ferrous iron source, a pyrophosphate source, a sodium source, a first reducing agent, and a solvent;

[0088] (S2) A step of obtaining a precursor by drying the first mixed solution;

[0089] (S3) A step of obtaining an anode material by calcining the precursor; the anode material may include a core, the core contains sodium iron phosphate pyrophosphate and optional sodium iron phosphate, and the mass ratio of the sodium iron phosphate to the sodium iron phosphate in the anode material is (0~0.15):(99.85~100).

[0090] The above manufacturing method of the present application adopts a solution method to produce sodium iron phosphate pyrophosphate. Compared to the conventional solid-state method, it is possible to achieve a uniform mixture of pyrophosphate groups, phosphate groups, ferrous ions, sodium ions, etc., and the solid diffusion path during calcination is shorter, thus improving reaction fusion, reducing the formation of sodium iron phosphate impurity phases, increasing the particle density of the manufactured anode material, and effectively improving the performance of the manufactured anode material in terms of capacity and cycle performance.

[0091] In some embodiments, the pyrophosphate group source comprises pyrophosphate and / or pyrophosphate, and optionally the pyrophosphate comprises sodium pyrophosphate and / or ammonium pyrophosphate.

[0092] In some embodiments, the sodium source includes an organic sodium salt.

[0093] For reference, the "organic sodium salt" described in this application means a salt formed by combining a sodium ion and an acid radical ion, wherein the number of carbon atoms contained in the acid radical ion is two or more.

[0094] In some embodiments, the organic sodium salt comprises one or more of sodium citrate, sodium acetate, sodium malate, and sodium lactate.

[0095] In the technical means according to the embodiment of the present application, an organic sodium salt is used to simultaneously provide a sodium source and a carbon source. Compared to a method of introducing a carbon source and a sodium source separately, this is advantageous for a more uniform distribution of the carbon source, thereby further enhancing the effect of improving the corresponding electrochemical performance of the anode material by the carbon-containing coating layer.

[0096] In some embodiments, the organic sodium salt comprises sodium citrate and / or sodium acetate, and optionally comprises sodium citrate and sodium acetate.

[0097] In the technical means according to the embodiment of the present application, when the organic sodium salt includes sodium citrate and sodium acetate, a synergistic effect occurs between sodium citrate and sodium acetate, which is advantageous for improving the density of the carbon-containing coating layer, and thus the electronic conductivity and corrosion resistance to the electrolyte of the anode material are improved, while the compaction density of the anode material is also increased.

[0098] In some embodiments, when the organic sodium salt comprises sodium citrate and sodium acetate, the molar ratio of sodium citrate to sodium acetate is (0.1 to 0.6):(0.4 to 0.9), which is advantageous for further improving the density of the carbon-containing coating layer, thereby increasing the compaction density of the anode material. For example, the molar ratio of sodium citrate to sodium acetate may be 0.1:0.9, 0.1:0.4, 0.2:0.7, 0.3:0.8, 0.6:0.9, 0.5:0.5, 0.5:0.4, 0.6:0.4, or may be within a range consisting of any of the above values.

[0099] In some embodiments, the first reducing agent comprises one or more of titanium trichloride, ammonium sulfite, and ascorbic acid. The first reducing agent can prevent the ferrous ion from being oxidized during the precipitation process.

[0100] In some embodiments, the ferrous source comprises one or more of ferrous acetate and ferrous phosphate.

[0101] In some embodiments, the phosphate group source comprises one or more of ferrous phosphate and phosphoric acid.

[0102] In some embodiments, the molar ratio of the iron element, the phosphorus element, and the first reducing agent in the first mixed solution is 3:(4.04 to 4.1):(0.05 to 0.1). For example, the molar ratio may be 3:4.04:0.1, 3:4.05:0.09, 3:4.06:0.08, 3:4.07:0.07, 3:4.08:0.06, 3:4.09:0.05, 3:4.1:0.05, or may be within a range consisting of any of the above values.

[0103] In some embodiments, the molar ratio of the phosphorus element in the pyrophosphate source and the phosphorus element in the first mixed solution is (2.04 to 2.1):(4.04 to 4.1). For example, the molar ratio of the phosphorus element in the pyrophosphate source and the phosphorus element in the first mixed solution may be 2.04:4.1, 2.05:4.09, 2.06:4.08, 2.07:4.07, 2.08:4.06, 2.09:4.05, 2.1:4.04, or may be within a range consisting of any of the above values.

[0104] In some embodiments, when the phosphate source and the ferrous source are selected from ferrous phosphate, the molar ratio of the phosphorus element in the ferrous phosphate, the iron element in the ferrous phosphate, the phosphorus element in the pyrophosphate source, and the first reducing agent is 2:3:(2.04~2.1):(0.05~0.1). For example, the molar ratio may be 2:3:2.04:0.1, 2:3:2.05:0.09, 2:3:2.06:0.08, 2:3:2.07:0.07, 2:3:2.08:0.06, 2:3:2.09:0.05, 2:3:2.1:0.05, or may be within the range consisting of any of the above values.

[0105] Conventional methods for manufacturing sodium iron phosphate pyrophosphate generally use phosphate as a raw material and convert the phosphate into pyrophosphate at high temperatures; however, since it is generally impossible to control the molar ratio of phosphate groups to pyrophosphate groups within the converted sodium iron phosphate pyrophosphate, a large amount of sodium iron phosphate impurity phase is present. On the other hand, in this application, by controlling the molar ratio of the iron element, the phosphorus element in ferrous phosphate, the phosphorus element in the pyrophosphate group source, and the first reducing agent to the above range, the molar ratio of pyrophosphate groups to phosphate groups within the final product, sodium iron phosphate pyrophosphate, is controlled. Since there is no need to convert the phosphate into pyrophosphate at high temperatures, the formation of sodium iron phosphate impurity phase is effectively reduced.

[0106] In some embodiments, the molar ratio of sodium ions to ferrous ions in the first mixed solution is (1 to 1.08):1, optionally (1.02 to 1.05):1. For example, the molar ratio may be 1:1, 1.02:1, 1.03:1, 1.04:1, 1.05:1, 1.06:1, 1.07:1, 1.08:1, or may be within a range consisting of any of the above values.

[0107] The present application uses ferrous ions as an iron source, thereby avoiding the need for reduction during the calcination process compared to using trivalent iron ions as a raw material, which is advantageous for lowering the calcination temperature of sodium iron pyrophosphate, improving the uniformity of crystal grains and particles of the anode material, and reducing energy consumption.

[0108] In some embodiments, the solvent comprises one or more of purified water, deionized water, and distilled water.

[0109] In some embodiments, when preparing the first mixed solution, the pyrophosphate group source, pyrophosphate, and the solvent are first prepared into a pyrophosphate solution, and then the phosphate group source, the ferrous source, the sodium source, and the first reducing agent are dissolved in the pyrophosphate solution to obtain the first mixed solution.

[0110] In some embodiments, the concentration of the pyrophosphate solution may be 1 mol / L to 2 mol / L.

[0111] In some embodiments, the average particle size of the precursor is 5 μm to 20 μm. For example, the average particle size of the precursor may be 5 μm, 7 μm, 9 μm, 11 μm, 13 μm, 15 μm, 17 μm, 19 μm, 20 μm, or may be within a range consisting of any of the above values.

[0112] In some embodiments, the drying in step S2 may be spray drying.

[0113] In some embodiments, during the spray drying process, the inlet gas temperature is 200°C to 350°C, the average particle size of the prepared precursor is 5μm to 20μm, and the moisture content of the material is 1.0wt% or less (i.e., the mass fraction of H2O in the precursor is 1.0% or less). For example, the inlet gas temperature may be 200°C, 210°C, 230°C, 250°C, 270°C, 290°C, 310°C, 330°C, or 350°C, or may be within a range consisting of any of the above values; and the average particle size of the precursor may be 5μm, 8μm, 10μm, 12μm, 14μm, 16μm, 18μm, or 20μm, or may be within a range consisting of any of the above values.

[0114] In some embodiments, the method for producing the ferrous phosphate is,

[0115] (S10) A step of adding a first pH adjuster to a second mixed solution containing a ferrous salt and a second reducing agent to adjust the pH value of the second mixed solution to 7.2 to 7.5, thereby obtaining a sol containing ferrous hydroxide;

[0116] (S10) A second pH adjuster is added to the sol to adjust the pH value of the sol to 3.5 to 4.5, thereby obtaining the ferrous phosphate; the method includes the step of adding a second pH adjuster to the sol to adjust the pH value of the sol to 3.5 to 4.5.

[0117] In the process of manufacturing ferrous phosphate according to steps S10 to S20, in step S10, a sol containing ferrous hydroxide precipitate is first manufactured, and then ferrous phosphate is obtained through the precipitation conversion process of step S20, thereby making the primary particles of the manufactured ferrous phosphate finer. In the subsequent process of manufacturing an anode material using ferrous phosphate as a raw material, ferrous phosphate can be dissolved more quickly in the solvent, so the dissolution rate is faster and the dissolution is more effective. Consequently, the final chemical composition ratio of the core of the anode material becomes closer to the theoretical value (i.e., Na4Fe3(PO4)2P2O7) and the formation of sodium iron phosphate impurity phase can be further suppressed.

[0118] In some embodiments, at step S10, the pH value of the second mixed solution may be 7.2, 7.3, 7.4, or 7.5, or may be within a range consisting of any of the above values, which is advantageous for the formation of a sol containing ferrous hydroxide.

[0119] In some embodiments, at step S20, the pH value of the sol may be 3.5, 3.7, 3.9, 4.1, 4.3, 4.5, or may be within a range consisting of any of the above values, which can promote the conversion of ferrous hydroxide into ferrous phosphate precipitate.

[0120] In some embodiments, the first pH adjuster comprises ammonia water and / or sodium hydroxide, and optionally comprises ammonia water.

[0121] In some embodiments, when the first pH adjuster includes ammonia water, the concentration of the first pH adjuster is 5 mol / L to 10 mol / L. For example, the concentration may be 5 mol / L, 6 mol / L, 7 mol / L, 8 mol / L, 9 mol / L, 10 mol / L, or may be within a range consisting of any of the above values.

[0122] In the technical means according to the embodiment of the present application, when the first pH adjuster includes ammonia water, it is advantageous not only for the formation of ferrous hydroxide but also for the volatilization of ammonium ions in the form of ammonia gas during the subsequent calcination process, so that other impurity elements are not introduced, which is advantageous for improving the purity of sodium iron phosphate pyrophosphate in the manufactured anode material.

[0123] In some embodiments, the ferrous salt comprises one or more of ferrous sulfate, ferrous chloride, and ferrous acetate.

[0124] In some embodiments, the second reducing agent comprises one or more of sodium borohydride, phosphoric acid, and hydrazine hydrate.

[0125] In some embodiments, the molar ratio of the first iron salt to the second reducing agent is 1:(0.01 to 0.1), and for example, the molar ratio may be 1:0.01, 1:0.02, 1:0.03, 1:0.04, 1:0.05, 1:0.06, 1:0.07, 1:0.08, 1:0.09, 1:0.1, or may be within a range consisting of any of the above values.

[0126] In some embodiments, the molar ratio of the iron element in the first iron salt and the second reducing agent in the second mixed solution is 1:(0.01 to 0.1), and for example, the molar ratio may be 1:0.01, 1:0.02, 1:0.03, 1:0.04, 1:0.05, 1:0.06, 1:0.07, 1:0.08, 1:0.09, 1:0.1, or may be within a range consisting of any of the above values.

[0127] In some embodiments, the second pH adjuster includes phosphoric acid to adjust the pH value without introducing other impurities.

[0128] In some embodiments, after the step of adjusting the pH value of the sol to 3.5 to 4.5, the method further includes the step of raising the temperature of the sol to 80°C to 95°C and then stirring for 30 to 60 minutes. For example, the raised temperature may be 80°C, 81°C, 83°C, 85°C, 87°C, 89°C, 91°C, 93°C, or 95°C, or may be within a range consisting of any of the above values; and the time of the stirring reaction may be 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes, or 60 minutes, or may be within a range consisting of any of the above values.

[0129] In the technical means according to the embodiment of the present application, heating the sol and then stirring the reaction is advantageous for the precipitation of ferrous phosphate.

[0130] In some embodiments, the calcination treatment includes raising the precursor to a preset temperature and maintaining it at the preset temperature.

[0131] In some embodiments, the heating rate of the precursor in the calcination treatment is 80°C / h to 120°C / h. For example, the heating rate of the precursor may be 80°C / h, 90°C / h, 100°C / h, 110°C / h, 120°C / h, or may be within a range consisting of any of the above values.

[0132] In some embodiments, the preset temperature is 600°C to 700°C. For example, the preset temperature may be 600°C, 610°C, 620°C, 630°C, 640°C, 650°C, 660°C, 670°C, 680°C, 690°C, or may be within a range consisting of any of the above values.

[0133] In some embodiments, in the calcination process, the holding time at a preset temperature is 4h to 8h. For example, the holding time at a preset temperature may be 4 hours, 5 hours, 6 hours, 7 hours, or 8 hours, or may be within a range consisting of any of the above values.

[0134] In the technical means according to the embodiment of the present application, if the preset temperature or holding time of the calcination treatment is set within the respective ranges, it is advantageous to improve the density of the carbon-containing coating layer while simultaneously improving the purity of sodium iron phosphate pyrophosphate in the anode material.

[0135] In some embodiments, the calcination treatment is performed under a protective atmosphere.

[0136] In some embodiments, the protective atmosphere includes a nitrogen atmosphere and / or an argon atmosphere.

[0137] In some embodiments, humidity is controlled to 0.2% or less and oxygen content to less than 1 ppm during heat retention; after heat retention, the material is cooled to extract the material, and the extracted material is crushed, sieved, iron removed, and packaged to obtain an anode material.

[0138] In a third aspect, the positive electrode plate provided in the present application comprises a positive material according to the first aspect of the present application or a positive material manufactured by a manufacturing method according to the second aspect of the present application.

[0139] The positive electrode plate comprises a positive material according to the first aspect of the present application or a positive material manufactured by the manufacturing method according to the second aspect of the present application, thereby having a higher capacity and better cycle performance.

[0140] In a fourth aspect, the sodium ion battery provided in the present application comprises a positive electrode plate according to the third aspect of the present application.

[0141] The sodium ion battery includes a positive electrode plate according to the third aspect of the present application, and thus has a higher capacity and better cycle performance.

[0142] In a fifth aspect, the electric device provided in the present application includes a sodium ion battery according to the fourth aspect of the present application.

[0143] The electric device includes a sodium ion battery according to the fourth aspect of the present application, and thus has at least the same advantages as a sodium ion battery.

[0144] In some embodiments, the electric device may be, but is not limited to, a mobile phone, tablet, laptop computer, electric toy, electric tool, electric cart vehicle, electric automobile, ship, spacecraft, etc. Here, electric toys may include stationary or mobile electric toys, and may include, for example, game consoles, electric vehicle toys, electric ship toys, and electric aircraft toys, and spacecraft may include airplanes, rockets, space shuttles, spacecraft, etc.

[0145] Some specific embodiments are listed below. It should be noted that the embodiments described below are illustrative and used merely to explain the present application, and should not be construed as limiting the application. Where specific techniques or conditions are not specified in the embodiments, the invention shall be performed in accordance with the techniques or conditions described in literature of the art to which the invention pertains or in product descriptions. Unless the manufacturer is specified, all reagents or equipment used are ordinary products available on the market.

[0146] I. Manufacturing Method

[0147] [Example 1]

[0148] 1. Preparation of Ferrous Phosphate

[0149] (1) Ferrous sulfate is added to hydrazine hydrate and stirred to mix uniformly. Then, ammonia water with a concentration of 8 mol / L is added, the temperature is set to 25°C and the time for adding ammonia water is set to 25 minutes. The pH of the mixed solution is adjusted to 7.35, and then the mixed solution is stirred until it changes from a gel to a sol, thereby forming a uniform sol containing ferrous hydroxide. Here, the molar ratio of ferrous sulfate to hydrazine hydrate is 1:0.1.

[0150] (2) Add phosphoric acid to the sol and adjust the pH value to 4; raise the temperature to 90°C and stir the reaction at this temperature for 50 minutes; then filter and wash to obtain ferrous phosphate precipitate.

[0151] 2. Manufacturing of cathode materials

[0152] (1) Ferrous phosphate and ascorbic acid are dissolved in a pyrophosphate solution, sodium citrate and sodium acetate are added to the resulting solution and stirred to dissolve them, thereby obtaining a mixed solution.

[0153] Here, the molar ratio of pyrophosphate and ascorbic acid in the added ferrous phosphate and pyrophosphate solution is 1:1.035:0.07, the molar ratio of added sodium citrate and sodium acetate is 0.4:0.6, the concentration of the pyrophosphate solution is 1.5 mol / L, and the molar ratio of sodium ions to ferrous ions in the mixed solution is 1.03:1.

[0154] (2) The mixed solution is spray-dried, and the inlet gas temperature during the spray-drying process is set to 280°C to obtain a precursor, and the average particle size of the prepared precursor is 12 μm, and the moisture content of the material is 1.0 wt% or less.

[0155] (3) Calcin the precursor, create a protective atmosphere using nitrogen, raise the temperature to 650°C at a heating rate of 100°C / h, maintain the temperature at this temperature for 6 hours, control the humidity of the maintenance section to 0.2% and the oxygen content to less than 1 ppm, and cool to extract the material; the extracted material is crushed, sieved, iron removed and packaged to obtain an anode material.

[0156] [Example 2]

[0157] 1. Preparation of Ferrous Phosphate

[0158] (1) Ferrous chloride and sodium borohydride are mixed and stirred uniformly, then ammonia water with a concentration of 5 mol / L is added, the temperature is set to 20℃ and the time for adding ammonia water is 15 minutes, and the pH of the mixed solution is adjusted to 7.2, then the mixed solution is stirred until it changes from a gel to a sol to form a uniform sol. Here, the molar ratio of ferrous chloride to sodium borohydride is 1:0.08.

[0159] (2) Add phosphoric acid to the sol and adjust the pH value to 3.5; then raise the temperature to 80°C and stir the reaction at this temperature for 30 minutes; then filter and wash to obtain ferrous phosphate precipitate.

[0160] 2. Manufacturing of cathode materials

[0161] (1) Ferrous phosphate and titanium trichloride are dissolved in a pyrophosphate solution, sodium citrate and sodium acetate are added to the resulting solution and stirred to dissolve them, thereby obtaining a mixed solution.

[0162] Here, the molar ratio of pyrophosphate and titanium trichloride in the added ferrous phosphate and pyrophosphate solution is 1:1.02:0.05, the molar ratio of added sodium citrate and sodium acetate is 0.1:0.9, the concentration of the pyrophosphate solution is 1 mol / L, and the molar ratio of sodium ions to ferrous ions in the mixed solution is 1.02:1.

[0163] (2) The mixed solution is spray-dried, and the temperature of the incoming gas during the spray-drying process is set to 200°C to obtain a precursor, and the average particle size of the prepared precursor is 5 μm, and the moisture content of the material is 1.0 wt% or less.

[0164] (3) Calcin the precursor, using nitrogen to create a protective atmosphere, and raise the temperature to 600°C at a heating rate of 80°C / h, then maintain the temperature at this temperature for 4 hours, control the humidity of the heat section to 0.2% and the oxygen content to less than 1 ppm, and cool to extract the material; the extracted material is crushed, sieved, iron removed, and packaged to obtain an anode material.

[0165] [Example 3]

[0166] 1. Preparation of Ferrous Phosphate

[0167] (1) Ferrous sulfate and phosphoric acid are mixed and stirred uniformly, then ammonia water with a concentration of 10 mol / L is added, the temperature is set to 30°C and the time for adding ammonia water is set to 30 minutes, and the pH of the mixed solution is adjusted to 7.5, then the mixed solution is stirred until it changes from a gel to a sol to form a uniform sol. Here, the molar ratio of ferrous sulfate to phosphoric acid is 1:0.03.

[0168] (2) Add phosphoric acid to the sol and adjust the pH value to 4.5; then raise the temperature to 95°C and stir the reaction at this temperature for 60 minutes; then filter and wash to obtain ferrous phosphate precipitate.

[0169] 2. Manufacturing of cathode materials

[0170] (1) Ferrous phosphate and ammonium sulfite are dissolved in a pyrophosphate solution, sodium citrate and sodium acetate are added to the resulting solution and stirred to dissolve them, thereby obtaining a mixed solution.

[0171] Here, the molar ratio of pyrophosphate and ammonium sulfite in the added ferrous phosphate and pyrophosphate solution is 1:1.05:0.1, the molar ratio of added sodium citrate and sodium acetate is 0.6:0.4, the concentration of the pyrophosphate solution is 2 mol / L, and the molar ratio of sodium ions to ferrous ions in the mixed solution is 1.05:1.

[0172] (2) The mixed solution is spray-dried, and the inlet gas temperature during the spray-drying process is set to 350°C to obtain a precursor, and the average particle size of the prepared precursor is 20 μm, and the moisture content of the material is 1.0 wt% or less.

[0173] (3) Calcin the precursor, create a protective atmosphere using nitrogen, raise the temperature to 700°C at a heating rate of 120°C / h, maintain the temperature at this temperature for 8 hours, control the humidity of the maintenance section to 0.2% and the oxygen content to less than 1 ppm, and cool to extract the material; the extracted material is crushed, sieved, iron removed and packaged to obtain an anode material.

[0174] [Example 4]

[0175] The manufacturing process is similar to Example 1, the main difference being that in step 2 (1), the molar ratio of pyrophosphate and ascorbic acid in the ferrous phosphate, pyrophosphate solution is 1:1.02:0.1.

[0176] [Example 5]

[0177] The manufacturing process is similar to Example 1, the main difference being that in step 2 (1), the molar ratio of pyrophosphate and ascorbic acid in the ferrous phosphate, pyrophosphate solution is 1:1.05:0.05.

[0178] [Example 6]

[0179] The manufacturing process is similar to Example 1, the main difference being that in step 2 (1), the molar ratio of pyrophosphate and ascorbic acid in the ferrous phosphate, pyrophosphate solution is 1:1:0.15.

[0180] [Example 7]

[0181] The manufacturing process is similar to Example 1, the main difference being that in step 2 (1), the molar ratio of pyrophosphate and ascorbic acid in the ferrous phosphate, pyrophosphate solution is 1:1.1:0.02.

[0182] [Example 8]

[0183] The manufacturing process is similar to Example 1, the main difference being that the molar ratio of sodium ions to ferrous ions in step 2 (1) is 1:1.

[0184] [Example 9]

[0185] The manufacturing process is similar to Example 1, the main difference being that the molar ratio of sodium ions to ferrous ions in step 2 (1) is 1.08:1.

[0186] [Example 10]

[0187] The manufacturing process is similar to Example 1, the main difference being that an equal molar amount of sodium citrate is used instead of sodium acetate in step 2 (1).

[0188] [Example 11]

[0189] The manufacturing process is similar to Example 1, the main difference being that sodium dihydrogen phosphate and citric acid are used instead of sodium citrate and sodium acetate in step 2 (1), where the total molar amount of citric acid is equal to the total molar amount of sodium citrate and sodium acetate, and the molar ratio of sodium ions to ferrous ions in the mixed solution is maintained at 1.03:1.

[0190] [Comparative Example 1]

[0191] The manufacturing process is similar to Example 1, the main difference being that Step 1 is omitted and (1) of Step 2 is replaced by the next step: iron phosphate (iron-phosphorus ratio 0.97:1, BET specific surface area 8.7 m² 2 (g), sodium carbonate, trisodium phosphate, and citric acid are mixed, water is added to form a slurry, and then ground until the particle size of the slurry is 320 nm, and the molar ratio of sodium, iron, and phosphorus in the slurry is 4.03:3:4.04. In step 2 (3), the calcination temperature is 550°C.

[0192] [Comparative Example 2]

[0193] The manufacturing process is similar to Comparative Example 1, the main difference being that the calcination temperature in step 2 (3) is 650℃.

[0194] II. Test Method

[0195] 1. The compaction density of the anode material was measured using a compaction density meter, with a test pressure of 3 tons (T) and a compression time of 30 seconds.

[0196] 2. The thickness of the carbon-containing coating layer can be measured by the following method. The thickness of the carbon-containing coating layer is observed using a transmission electron microscope (e.g., HITACHI HT7800).

[0197] 3. The coverage rate of the carbon-containing coating layer is measured using a transmission electron microscope (TEM) and an X-ray energy spectrometer (EDX).

[0198] 4. The average particle size of the anode material can be tested by the following method. It is measured using a laser particle size analyzer. The measuring equipment may be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Co., Ltd., UK.

[0199] 5. The mass ratio of Na4Fe3(PO4)2P2O7 and NaFePO4 in the anode material can be tested using the following method. The XRD spectrum of the anode material is measured, and the ratio of the heights of the strongest peak and the next strongest peak in the XRD is tested, i.e., the mass ratio of Na4Fe3(PO4)2P2O7 and NaFePO4.

[0200] 6. The specific surface area of ​​the anode material can be tested using the following method. It is measured using the nitrogen adsorption specific surface area analysis test method in accordance with GB / T 19587-2017 and calculated using the BET (Brunauer Emmett Teller) method.

[0201] 7. The powder resistivity of the anode material can be tested by the following method. It can be measured using a resistivity meter (e.g., the ST2722 powder resistivity meter from Suzhou Jingge Electronic Co., LTD).

[0202] 8. The ratio of each element and the Ti content in the anode material are tested using inductively coupled plasma atomic emission spectroscopy (ICP-OES).

[0203] 9. The pH value of the anode material can be tested by the following method. A certain amount of anode material is added to an appropriate amount of deionized water according to a constant solid-liquid ratio (e.g., mass-volume ratio 1:10), and the anode material is completely dispersed in the water using a magnetic mixer to form a uniform suspension; a pH electrode is immersed in the suspension using a pH meter test method and the potential difference is measured, and the pH value of the suspension is calculated based on the relationship between the potential difference and the pH value to obtain the pH value of the anode material.

[0204] 10. Iron leaching amount of anode material: 1 g of the test sample is added to 100 mL of a hydrogen fluoride-ethanol solution with a concentration of 0.1 mol / L and stirred to dissolve at 45°C for 30 minutes, then filtered, and the iron element content, i.e., the iron leaching amount, of the obtained filtrate is measured by inductively coupled plasma atomic emission spectroscopy (ICP-OES).

[0205] 11. The free sodium content of the anode material is measured by potentiometric titration.

[0206] 12. Characteristics Test of Sodium Ion Batteries

[0207] (1) Preparation of a positive electrode plate: The positive electrode material prepared in the above examples and comparative examples, conductive carbon black, and polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 85:8:7, and a suitable amount of N-methylpyrrolidone (NMP) is added to form a uniform electrode slurry, then the electrode slurry is evenly coated onto an aluminum foil and vacuum dried, then cut into a circular electrode sheet with a diameter of 15 mm, and then immediately transferred to a glove box for later use.

[0208] (2) Assembly of the battery: metallic sodium is used as the counter electrode, glass fiber is used as the separator, the solute of the electrolyte is sodium perchlorate, the solvent of the electrolyte is propylene carbonate, ethylene carbonate and fluoroethylene carbonate (volume ratio 1:1:0.05), the concentration of sodium perchlorate in the electrolyte is 1 mol / L, and it is assembled into a CR2032 button type battery, and the entire assembly process is carried out in a glove box filled with argon gas.

[0209] (3) Charging capacity, discharging capacity, cycle performance test

[0210] Using a constant current charge / discharge mode at 25°C, charge / discharge tests are performed at current densities of 0.2C and 1C, the charge cutoff voltage is 4.0V and the discharge cutoff voltage is 2.0V, and the first charge specific capacity, first discharge specific capacity, and capacity retention rate after 500 cycles of each battery are obtained.

[0211] The performance tests of the cathode materials and sodium ion batteries according to each of the above-described examples and comparative examples are as shown in Tables 1 to 3 below.

[0212] [Table 1]

[0213]

[0214] [Table 2]

[0215]

[0216] [Table 3]

[0217]

[0218] III. Analysis of Test Results for Each Example and Comparative Example

[0219] Through Figures 2 and 3, it can be seen that the anode materials prepared in Example 1 and Example 2 have a more uniform particle shape.

[0220] Combining Tables 1 and 2, the anode materials prepared in each example have a mass fraction of sodium element of 14% to 16%, a mass fraction of iron element of 25% to 26%, a mass fraction of phosphorus element of 17% to 21%, and a mass fraction of carbon element of 1.2% to 4.5%, all of which are within the qualifying range; the leaching of free sodium and iron is also relatively low. Comparative Example 1 was prepared by adopting a conventional solid-state method and has a relatively low calcination temperature. The anode materials prepared by the liquid-state method in each example can achieve a uniform mixture of pyrophosphate groups, phosphate groups, ferrous ions, sodium ions, etc., and do not require conversion to pyrophosphate. Since the solid diffusion path is shorter, calcination is possible at a higher temperature, the residual amount of sodium iron phosphate impurity phase is smaller, the structure is more stable, the compaction density is higher, and the amount of free sodium and iron leaching is much smaller compared to the anode material obtained in Comparative Example 1. In addition, Comparative Example 2 adopted a conventional solid-state method to manufacture the anode material, and the calcination temperature was higher than that of Comparative Example 1. In each example, the anode material manufactured by the liquid-state method can achieve a uniform mixture of pyrophosphate groups, phosphate groups, ferrous ions, sodium ions, etc. compared to Comparative Example 2, and since conversion to pyrophosphate is not required, at a calcination temperature equivalent to or higher than that of Comparative Example 2, the residual amount of sodium iron phosphate impurity phase in the anode material of the example is much less than the residual amount of sodium iron phosphate impurity phase in the anode material obtained in Comparative Example 2.

[0221] In addition, as can be seen in Table 2, in each example, the mass ratio of NaFePO4 in the cathode material is less than 0.15%, and the specific surface area is 10 m² 2 / g~15.5m 2 / g, compaction density is 2.25g / mL~2.45g / mL, powder resistivity is 14Ω·cm~45Ω·c, and carbon-containing coating layer thickness is greater than 3nm and coverage rate is greater than 98%.

[0222] In addition, as can be seen in Table 3, the first charge capacity at 0.2C of each example is higher than 120mAh / g, the first discharge capacity at 0.2C is higher than 112mAh / g, the first discharge capacity at 1C is higher than 101mAh / g, and the 500-week capacity retention rate is greater than 97.5%.

[0223] When combining the data in Tables 2 and 3, each example adopts a cathode material prepared according to the method for preparing a cathode material provided in this application, thereby reducing the formation of the sodium iron phosphate impurity phase; thus, the mass ratio of the sodium iron phosphate impurity phase in each example is relatively low; however, since Comparative Examples 1 and 2 prepared sodium iron phosphate pyrophosphate using a solid-state method, the residue of the impurity phase increases, and thus the mass ratio of the sodium iron phosphate impurity phase in Comparative Examples 1 and 2 is relatively high. When the correspondingly obtained cathode material is applied to a battery, the battery of each example was tested to have a significantly higher charge capacity, discharge capacity, and capacity retention rate than Comparative Examples 1 and 2.

[0224] Furthermore, as can be seen from the data of Examples 1, 4 to 7, the molar ratio of ferrous phosphate, pyrophosphate group source (pyrophosphate), and first reducing agent (ascorbic acid) affects the mass ratio of the sodium iron phosphate impurity phase, and thus affects the charge capacity, discharge capacity, and capacity retention rate of the battery; when the molar ratio is between 1:1.02:0.1 and 1:1.1:0.02, the mass ratio of the sodium iron phosphate impurity phase is lower, and the battery capacity and cycle performance are higher. As can be seen from the data of Examples 1, 8 to 9, when the molar ratio of sodium ions and ferrous ions changes, it has a constant effect on the mass ratio of the sodium iron phosphate impurity phase. As can be seen from the data of Examples 1 and 10, the combined use of sodium citrate and sodium acetate is advantageous for improving the compaction density of the cathode material and the coverage rate of the carbon-containing coating layer of the cathode material, and accordingly, the capacity and cycle performance of the cathode material are improved. As can be seen from the data of Example 1 and Example 11, compared to Example 11, which used sodium dihydrogen phosphate and citric acid as the sodium source and carbon source, respectively—that is, introduced the sodium source and carbon source separately—Example 1 adopts a method of simultaneously introducing the sodium source and carbon source using sodium citrate and sodium acetate, and the capacity and cycle performance of the manufactured cathode material are relatively high.

[0225] In summary, by controlling the mass ratio of the sodium iron phosphate impurity phase in the cathode material to a range of 0% to 0.15%, the cathode material and the battery can be superior in terms of capacity and cycle performance.

[0226] It should be noted that the present application is not limited to the embodiments described above. The embodiments described above are merely examples, and any embodiment having substantially the same configuration as the technical concept and achieving the same functional effect within the scope of the technical solution of the present application is included within the technical scope of the present application. Furthermore, any various modifications that a person skilled in the art may make to the embodiments without departing from the gist of the present application, or any other forms formed by combining some components of the embodiments, are all included within the scope of the present application.

Claims

Claim 1 A positive electrode material comprising a core, wherein the core contains sodium iron phosphate pyrophosphate or contains sodium iron phosphate pyrophosphate and sodium iron phosphate, and the mass ratio of sodium iron phosphate to sodium iron phosphate in the positive electrode material is (0~0.15):(99.85~100). Claim 2 The anode material according to claim 1, wherein the anode material further comprises a carbon-containing coating layer covering at least a portion of the surface of the core; wherein the thickness of the carbon-containing coating layer is 2 nm to 5 nm; and wherein the carbon-containing coating layer covers the surface of the core with a coverage rate of 97% to 100%. Claim 3 In claim 1, (1) a condition in which the compaction density of the anode material is 2.25 g / mL to 2.45 g / mL; (2) a specific surface area of ​​the anode material is 10 m 2 / g~15.5m 2 A positive electrode material characterized by satisfying one or more of the following conditions: (3) a condition in which the resistivity of the positive electrode material is 14Ω·cm to 45Ω·cm. Claim 4 A method for manufacturing an anode material comprising: a step of obtaining a first mixed solution by mixing a phosphate source, a ferrous source, a pyrophosphate source, a sodium source, a first reducing agent, and a solvent; a step of obtaining a precursor by drying the first mixed solution; and a step of obtaining an anode material by calcining the precursor; wherein the anode material comprises a core, and the core contains sodium iron phosphate pyrophosphate or contains sodium iron phosphate pyrophosphate and sodium iron phosphate, and the mass ratio of the sodium iron phosphate to the sodium iron phosphate in the anode material is (0~0.15):(99.85~100). Claim 5 In claim 4, (1) the sodium source comprises an organic sodium salt, wherein the organic sodium salt comprises one or more of sodium citrate, sodium acetate, sodium malate, and sodium lactate, and when the organic sodium salt comprises sodium citrate and sodium acetate, the molar ratio of sodium citrate to sodium acetate is (0.1–0.6):(0.4–0.9); (2) the first reducing agent comprises one or more of titanium trichloride, ammonium sulfite, and ascorbic acid; (3) the ferrous source comprises one or more of ferrous acetate and ferrous phosphate; (4) the phosphate source comprises one or more of ferrous phosphate and phosphoric acid; (5) the pyrophosphate source comprises pyrophosphate and / or pyrophosphate, wherein the pyrophosphate comprises sodium pyrophosphate and / or ammonium pyrophosphate; (6) the iron element, phosphorus element, and the first in the first mixed solution A method for manufacturing an anode material, characterized by satisfying one or more of the following conditions: (7) a condition in which the molar ratio of the reducing agent is 3:(4.04~4.1):(0.05~0.1) and the molar ratio of the phosphorus element in the pyrophosphate source and the phosphorus element in the first mixed solution is (2.04~2.1):(4.04~4.1); (1~1.08):1; (8) a condition in which the solvent includes one or more of purified water, deionized water, and distilled water; (9) a condition in which the average particle size of the precursor is 5μm~20μm. Claim 6 In claim 4, the ferrous source is selected from ferrous phosphate, and the manufacturing method further comprises the steps of: adding a first pH adjuster to a second mixed solution containing ferrous salt and a second reducing agent to adjust the pH value of the second mixed solution to 7.2 to 7.5 to obtain a sol containing ferrous hydroxide; and adding a second pH adjuster to the sol to adjust the pH value of the sol to 3.5 to 4.5 to obtain ferrous phosphate; wherein the first pH adjuster comprises ammonia water and / or sodium hydroxide, and when the first pH adjuster comprises ammonia water, the concentration of the first pH adjuster is 5 mol / L to 10 mol / L; the second reducing agent comprises one or more of sodium borohydride, phosphoric acid, and hydrazine hydrate; the second pH adjuster comprises phosphoric acid; and the molar ratio of the iron element in the ferrous salt and the second reducing agent in the second mixed solution is A method for manufacturing an anode material characterized by being 1:(0.01~0.1). Claim 7 A method for manufacturing an anode material according to claim 6, characterized by further including, after the step of adjusting the pH value of the sol to 3.5 to 4.5, the step of raising the temperature of the sol to 80℃ to 95℃ and stirring for 30 to 60 minutes. Claim 8 A method for manufacturing an anode material according to claim 4, wherein the calcination treatment comprises raising the temperature of the precursor to a preset temperature and holding it at the preset temperature; wherein the preset temperature is 600°C to 700°C; wherein the holding time is 4h to 8h; wherein the calcination treatment is performed under a protective atmosphere; and wherein the protective atmosphere comprises a nitrogen atmosphere and / or an argon atmosphere. Claim 9 A positive electrode plate characterized by comprising a positive electrode material according to any one of claims 1 to 3, or a positive electrode material manufactured by a method for manufacturing a positive electrode material according to any one of claims 4 to 8. Claim 10 A sodium ion battery characterized by including a positive electrode plate according to claim 9.

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