Polyanionic precursor and preparation method thereof, sodium ion battery positive electrode material and sodium ion battery

Abstract

The invention provides a polyanionic precursor and a preparation method thereof, a sodium ion battery positive electrode material and a sodium ion battery. The polyanionic precursor comprises a sodium element, an iron element and a phosphorus element; wherein the total amount of substance of the iron element is NFe, the total amount of substance of the phosphorus element is NP, and the ratio of the total amount of substance of the iron element NFe to the total amount of substance of the phosphorus element NP is larger than or equal to 0.8 and smaller than or equal to 0.9. The polyanionic precursor disclosed by the invention has a relatively high iron-phosphorus ratio, is beneficial to exerting the battery capacity, and meanwhile, improves the rate capability of the battery, so that the battery can still keep stable electrochemical performance in a high-rate charge-discharge scene.

Description

Technical Field

[0001] This application belongs to the field of battery technology, specifically relating to a polyanionic precursor and its preparation method, a sodium-ion battery cathode material, and a sodium-ion battery. Background Technology

[0002] Sodium-ion batteries possess advantages such as abundant resources, low cost, low-temperature resistance, safety, and convenience, making them an important complement to lithium-ion batteries. They are expected to see rapid development in various fields, including low-speed electric vehicles, electric boats, home / industrial energy storage, 5G communication base stations, data centers, large-scale renewable energy integration, and smart grids. Developing sodium-ion batteries can reduce or eliminate the use of expensive elements such as lithium, cobalt, and nickel, thereby lowering energy storage costs. Therefore, sodium-ion batteries are highly competitive in the grid energy storage field, representing an excellent alternative to lithium-ion batteries and potentially becoming a rising star in rechargeable battery technology.

[0003] The superior performance of sodium-ion batteries, including cycle stability, capacity, and voltage, largely depends on the preparation of the cathode material. Oxide cathode materials theoretically have high specific capacity, making them suitable for developing high-energy-density rechargeable batteries, while polyanion cathode materials have a more stable structure, making them suitable for developing long-life rechargeable batteries. Developing high-performance cathode material precursors with high specific capacity and high cycle performance has become a research hotspot and key direction in the field of sodium-ion batteries. Summary of the Invention

[0004] This application provides a polyanionic precursor and its preparation method, a sodium-ion battery cathode material, and a sodium-ion battery, aiming to solve at least one of the aforementioned technical problems in the prior art.

[0005] In a first aspect, embodiments of this application provide a polyanionic precursor, which includes sodium, iron, and phosphorus elements; wherein the total amount of iron is N. Fe The total amount of phosphorus is N. P The total amount of iron, N Fe Total amount of substance of phosphorus N P The ratio satisfies 0.8 ≤ N Fe / N P ≤0.9.

[0006] According to an embodiment of the first aspect of this application, the iron element includes ferrous iron (Fe2+), and the amount of ferrous iron (Fe2+) is m. Fe The total amount of substance N of iron Fe The ratio satisfies 0.1 ≤ m Fe / N Fe ≤0.5, can be selected as 0.3≤m Fe / N Fe ≤0.5.

[0007] According to an embodiment of the first aspect of this application, the polyanionic precursor satisfies one or more of the following conditions: ① The polyanionic precursor further includes an element M, wherein M is selected from one or more of transition metal elements other than Fe, Mg, Ca, Sr, and Al; optionally, the transition metal elements other than Fe include one or more of Ni, Co, Mn, Ti, V, Cr, Zr, Nb, W, Cr, Cu, Zn, Mo, Sc, and Y; ② The polyanionic precursor further includes an element M, wherein the amount of substance w of element M is equal to the total amount of substance N of iron. Fe The ratio satisfies 0 ≤ w / N Fe ≤0.1; ③ The polyanionic precursor also includes element M, the amount of sodium q and the total amount of iron N. Fe The ratio of the sum of the amounts of substance w of element M and element M satisfies 0.2 ≤ q / (N) Fe +w)≤0.45; ④The amount of sodium q and the total amount of phosphorus N P The ratio satisfies 0 P ≤0.4.

[0008] According to an embodiment of the first aspect of this application, the polyanionic precursor includes a chemical formula of Na. q Fe m+n M w (H x P y O z The substance is a ·bH₂O; wherein M is selected from one or more transition metal elements other than Fe, Mg, Ca, Sr, and Al; m is Fe 2+ The content of, n is Fe 3+ The content of

[0009] According to an embodiment of the first aspect of this application, one or more of the following conditions are met: A. The tap density of the polyanionic precursor is 0.6 g / cm³. 3 -1.4g / cm 3 B. The Dv50 of the polyanionic precursor is 2μm-5μm; C. The specific surface area of ​​the polyanionic precursor is 15m². 2 / g-35m 2 / g, optional 19m 2 / g-28m 2 ​​ / g; D, The polyanionic precursor includes secondary particles composed of primary particles; optionally, the primary particles include flake and / or block-shaped primary particles.

[0010] Secondly, embodiments of this application provide a method for preparing a polyanionic precursor, comprising: in an inert gas atmosphere, passing an iron ion solution and a solution including sodium ions and pyrophosphate ions into a reaction vessel for co-precipitation reaction to obtain a polyanionic precursor, wherein the molar ratio of iron to phosphorus in the reaction system is controlled to be (0.8-0.9):1.

[0011] According to an embodiment of the second aspect of this application, the method further includes simultaneously introducing an iron ion solution and a solution including sodium ions and pyrophosphate ions into a reaction vessel, and simultaneously introducing a solution containing element M into the reaction vessel to mix and perform a co-precipitation reaction to obtain a polyanionic precursor; optionally, element M is selected from one or more of transition metal elements other than Fe, Mg, Ca, Sr and Al; optionally, transition metal elements other than Fe include one or more of Ni, Co, Mn, Ti, V, Cr, Zr, Nb, W, Cr, Cu, Zn, Mo, Sc and Y.

[0012] And / or, after the coprecipitation reaction is completed, an aging treatment is also included; optionally, the aging treatment time is 0.5h to 10h; optionally, the pH value of the aging treatment is 3.0-5.0.

[0013] According to an embodiment of the second aspect of this application, the preparation method satisfies at least one of the following conditions: a. The solution comprising sodium ions and pyrophosphate ions comprises sodium pyrophosphate solution; b. The iron-containing solution is selected from one or more of ferrous sulfate solution, ferrous chloride solution, and ferrous oxalate solution; c. The flow rate of the iron-containing solution into the reaction vessel is 16-19% / h of the reaction vessel volume; d. The flow rate of the solution comprising sodium ions and pyrophosphate ions into the reaction vessel is 30-35% / h of the reaction vessel volume; e. The iron ion concentration in the iron-containing solution is 86-93 g / L; f. The pH value of the coprecipitation reaction is 3-5; g. The temperature of the coprecipitation reaction is 45°C. o C~65 o C; h. The stirring frequency of the coprecipitation reaction is 23Hz~28Hz; i. The preparation method also includes post-treatment of the precipitate; optionally, the post-treatment includes solid-liquid separation, washing and drying.

[0014] Thirdly, embodiments of this application provide a sodium-ion battery cathode material. The raw materials for the sodium-ion battery cathode material include the polyanionic precursor in the embodiments of the first aspect of this application or the polyanionic precursor prepared by the polyanionic precursor preparation method in the embodiments of the second aspect of this application.

[0015] Fourthly, embodiments of this application provide a sodium-ion battery, including the sodium-ion battery cathode material described in the embodiments of the third aspect of this application.

[0016] Fifthly, this application provides an electrical device, including the sodium-ion battery described in the fourth aspect of this application.

[0017] In this embodiment, the iron-to-phosphorus ratio of the polyanionic precursor is within a suitable range, making it easier to obtain fine particles with high surface energy during the reaction. These fine particles are prone to non-directional aggregation, forming porous aggregates, thus yielding a polyanionic precursor with a loose porous structure and high specific surface area. The loose porous structure and high specific surface area can increase the contact area between the precursor and the sodium salt in the subsequent reaction, which is beneficial for the rapid and uniform penetration of the sodium salt, resulting in higher reactivity and a more complete reaction. This facilitates the preparation of cathode materials with uniform elemental distribution and high purity, thereby solving the problem of unbalanced elemental distribution and low purity caused by uneven mixing in existing solid-phase cathode material preparation methods.

[0018] In addition, the loose structure and large specific surface area can increase the contact interface between the cathode material and the electrolyte, which is conducive to the full contact of the electrolyte and reduces the electrolyte wetting resistance. At the same time, the porous structure can provide abundant channels for ion transport, accelerate the migration rate of sodium ions and electrons, improve the transport rate, and facilitate the utilization of capacity. It also improves the rate performance of the battery, enabling the battery to maintain stable electrochemical performance under high-rate charge and discharge scenarios. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0020] Figure 1 The SEM image of the polyanionic precursor of Example 3 of this application is shown; Figure 2 The elemental distribution diagram of the polyanionic precursor EDS of Embodiment 3 of this application is shown; Figure 3 The EDS elemental distribution diagram of the cathode material of Embodiment 3 of this application is shown. Detailed Implementation

[0021] The following detailed description, with appropriate reference to the accompanying drawings, discloses the polyanionic precursor and its preparation method, as well as the sodium-ion battery cathode material and embodiments of the sodium-ion battery. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0022] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for a specific parameter, it is understood that ranges of 60~110 and 80~120 are also expected. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this application, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, characterized in that a and b are both real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0023] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0024] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0025] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0026] In this application, "multiple" refers to two or more (including two). In this application, "multiple times" refers to two or more (including two).

[0027] In view of the need to improve the performance of batteries in the prior art, this application provides a polyanionic precursor and its preparation method, a sodium-ion battery cathode material, and a sodium-ion battery.

[0028] In a first aspect, embodiments of this application provide a polyanionic precursor, which includes sodium, iron, and phosphorus elements; wherein the total amount of iron is N. Fe The total amount of phosphorus is N. P The total amount of iron, N Fe Total amount of substance of phosphorus N P The ratio satisfies 0.8 ≤ N Fe / N P ≤0.9.

[0029] In this embodiment, the iron-to-phosphorus ratio of the polyanionic precursor is within a suitable range, making it easier to obtain fine particles with high surface energy during the reaction. These fine particles are prone to non-directional aggregation, forming porous aggregates, thus yielding a polyanionic precursor with a loose porous structure and high specific surface area. The loose porous structure and high specific surface area can increase the contact area between the precursor and the sodium salt in the subsequent reaction, which is beneficial for the rapid and uniform penetration of the sodium salt, resulting in higher reactivity and a more complete reaction. This facilitates the preparation of cathode materials with uniform elemental distribution and high purity, thereby solving the problem of unbalanced elemental distribution and low purity caused by uneven mixing in existing solid-phase cathode material preparation methods.

[0030] In addition, the loose structure and large specific surface area can increase the contact interface between the cathode material and the electrolyte, which is conducive to the full contact of the electrolyte and reduces the electrolyte wetting resistance. At the same time, the porous structure can provide abundant channels for ion transport, accelerate the migration rate of sodium ions and electrons, improve the transport rate, and facilitate the utilization of capacity. It also improves the rate performance of the battery, enabling the battery to maintain stable electrochemical performance under high-rate charge and discharge scenarios.

[0031] For example, N Fe / N P The value can be any value among 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, and 0.90, or a range between any two.

[0032] In some embodiments, the iron element includes ferrous iron (Fe2+), and the amount of ferrous iron (m) is... Fe The total amount of substance N of iron Fe The ratio satisfies 0.1 ≤ m Fe / N Fe ≤0.5; preferably, the amount of substance m of ferrous iron. Fe The total amount of substance N of iron Fe The ratio satisfies 0.3 ≤ m Fe / N Fe ≤0.5.

[0033] For example, m Fe / N Fe The value can be any value among 0.1, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45 and 0.5 or any value between two of them.

[0034] This application embodiment achieves a high iron-to-phosphorus ratio by controlling the proportion of divalent iron in the total iron element, resulting in a polyanionic precursor with a loose porous structure and high specific surface area, which is beneficial for improving the electrochemical performance of subsequent cathode materials. When m Fe / N Fe Below 0.1, the ferrous iron content is too low, the iron-to-phosphorus ratio is low, the precursor structure is dense, and the reactivity is low; when m Fe / N Fe When the content is higher than 0.5, the content of ferrous iron is too high, the iron-to-phosphorus ratio is too high, which affects the structural stability of the precursor.

[0035] Furthermore, by controlling the proportion of ferrous iron in the total iron content to maintain a high level, the consumption of reducing agent can be reduced during the subsequent synthesis of cathode materials, further lowering raw material costs. Moreover, the reaction process is easier to control, which is conducive to industrial-scale production.

[0036] In some embodiments, the polyanionic precursor further includes an element M, where M is selected from one or more transition metal elements other than Fe, Mg, Ca, Sr, and Al; optionally, the transition metal elements other than Fe include one or more of Ni, Co, Mn, Ti, V, Cr, Zr, Nb, W, Cr, Cu, Zn, Mo, Sc, and Y.

[0037] In some embodiments, the polyanionic precursor further includes an element M, wherein the amount of element M w is equal to the total amount of iron N. Fe The ratio satisfies 0 ≤ w / N Fe ≤0.1; The element M can be understood as a dopant, which improves some aspects of the performance of the cathode material. Since the content of the dopant element M is low, it will not have a significant impact on the structure of the target cathode material. The type and amount of M can be flexibly selected according to the performance requirements of the target cathode material.

[0038] For example, w / N Fe The value can be any value among 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, and 0.1, or a range between any two.

[0039] In some embodiments, the polyanionic precursor further includes element M, and the amount of sodium q and the total amount of iron N are also included. Fe The ratio of the sum of the amounts of substance w of element M and element M satisfies 0.2 ≤ q / (N) Fe +w)≤0.45; For example, q / (N Fe The value of +w) can be any value from 0.2, 0.24, 0.26, 0.28, 0.30, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, 0.40, 0.41, 0.42, 0.43, 0.44, 0.45 or any value between two of these.

[0040] In some embodiments, the amount of sodium q and the total amount of phosphorus N are... P The ratio satisfies 0 P ≤0.4.

[0041] For example, q / N P The value can be any value among 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35 and 0.4 or any value between two of them.

[0042] In some embodiments, the polyanionic precursor includes the chemical formula Na. q Fe m+n M w (H x P y O z The substance is a ·bH₂O; wherein M is selected from one or more transition metal elements other than Fe, Mg, Ca, Sr, and Al; m is Fe 2+ The content of, n is Fe​3+ The content of

[0043] The polyanionic precursors in the embodiments of this application can be represented by the above-described general chemical formula. It is understood that in some embodiments, the anionic groups include, for example, phosphate, monohydrogen phosphate, dihydrogen phosphate, pyrophosphate, monohydrogen pyrophosphate, dihydrogen pyrophosphate, trihydrogen pyrophosphate, etc.

[0044] For example, q can take any value from 0.26, 0.28, 0.30, 0.31, 0.32, 0.33, 0.34, and 0.35, or a range between any two.

[0045] Fe 2+ This represents the divalent element Fe. 3+ This represents the trivalent element Fe, where m is Fe. 2+ The content of, n is Fe 3+ The content. m represents 1 mol of polyanionic precursor (Na₂O₃). q Fe m+n M w (H x P y O z )·bH2O) Fe in 2+ The molar amount, n represents 1 mol of polyanionic precursor (Na₂O₃). q Fe m+n M w (H x P y O z )·bH2O) Fe in 3+ The molar amount.

[0046] For example, m+n can take any value from 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90 or any value between two of them.

[0047] ​For example, m / (m+n) can take any value from 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.30, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, 0.40, 0.41, 0.42, 0.43, 0.44, 0.45, 0.46, 0.47, 0.48, 0.49, and 0.50, or a range between any two.

[0048] M is a dopant element, and M accounts for a small percentage. w is the content of M.

[0049] For example, m+n+w can take any value from 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92 and 0.93 or a range between any two.

[0050] For example, w / (m+n) can take any value from 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, and 0.1, or any value between any two. When w / (m+n) = 0, that is, w = 0, it means that the chemical formula does not contain element M.

[0051] For example, q / (m+n+w) can take any value from 0.20, 0.24, 0.26, 0.28, 0.30, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, 0.40, 0.41, 0.42, 0.43, and 0.44, or a range between any two.

[0052] For example, x can take any value from 0, 1, 2, or any range between two of them.

[0053] For example, y can take any value from 0.93, 0.94, 0.95, 0.96, 0.97, 0.99, 0.99, 1.00, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, and 1.1, or a range between any two.

[0054] For example, q / y can take any value from 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.30, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, and 0.40, or a range between any two.

[0055] For example, (m+n+w) / y can take any value from 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, and 0.97, or a range between any two.

[0056] b represents 1 mol of polyanionic precursor (Na) q Fe m+n M w (H x P y O z The molar amount of water in (bH2O).

[0057] The value of b / (m+n+w) can be any value from 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, and 10, or any value between any two. When b / (m+n+w) = 0, that is, b = 0, it means that the chemical formula does not contain water.

[0058] In some embodiments, the polyanionic precursor satisfies one or more of the following conditions: In some embodiments, the tap density of the polyanionic precursor is 0.6 g / cm³. 3 -1.4g / cm 3 .

[0059] Tap density reflects the compactness of material packing under certain vibration conditions; a higher tap density means that more active material can be accommodated per unit volume. Polyanionic precursors have tap densities within the aforementioned range, enabling better compaction of the positive electrode active material during electrode fabrication and improving volumetric energy density.

[0060] For example, the tap density of the polyanionic precursor is 0.6 g / cm³. 3 0.7g / cm 3 0.75g / cm 30.80g / cm 3 0.85g / cm 3 0.90g / cm 3 0.95g / cm 3 1.00g / cm 3 1.05g / cm 3 1.10 g / cm 3 1.15g / cm 3 1.20g / cm 3 1.25g / cm 3 1.30g / cm 3 1.35g / cm 3 and 1.4g / cm 3 Any value in the range or any value between the two.

[0061] In some embodiments, the Dv50 of the polyanionic precursor is 2 μm-5 μm.

[0062] For example, the Dv50 of the polyanionic precursor is any value among 2 μm, 2.5 μm, 3.0 μm, 3.5 μm, 4 μm, 4.5 μm and 5 μm or a range between any two.

[0063] In some embodiments, the specific surface area of ​​the polyanionic precursor is 15 m². 2 / g-35m 2 / g.

[0064] The specific surface area of ​​the polyanionic precursor in this embodiment is within the above range, which means that the precursor particles have more surface active sites, ensuring the contact area between the cathode material and the electrolyte and improving the rate performance.

[0065] For example, the specific surface area of ​​the polyanionic precursor is 15 m². 2 / g, 16m 2 / g、17m 2 / g、18m 2 / g、19m 2 / g、20m 2 / g、21m 2 / g、22m 2 / g、23m 2 / g、24m 2 / g、25m 2 / g、26m 2 / g、27m 2 / g、28m 2 / g、29m 2 / g、30m 3 / g、31m 3 / g、32m 3 / g、33m 3 / g、34m 3 / g and 35m 3 Any value in / g or a range between both. Optionally, the specific surface area is 19m². 2 / g-28m 2 / g.

[0066] In some embodiments, the polyanionic precursor includes secondary particles composed of primary particles.

[0067] In some embodiments, the primary particles of the polyanionic precursor include sheet-like and / or block-like primary particles.

[0068] In this embodiment, the primary particles can be flake-shaped primary particles, block-shaped primary particles, or both flake-shaped and block-shaped primary particles.

[0069] Currently, the solid-state method is the main preparation method for polyanionic cathode materials. However, due to the inherent defect of uneven mixing in the solid-state method, the ratio of metal to phosphorus in the obtained material is difficult to control and the distribution uniformity is poor.

[0070] The inventors of this application also noted that the one-step solid-state synthesis method has the problem of large sintering gas production, which leads to low energy density, compaction density, and tap density of the cathode material, affecting its commercial application.

[0071] In view of the above problems, in a second aspect, embodiments of this application provide a method for preparing a polyanionic precursor, which uses a liquid phase method to achieve the control and preparation of the precursor elemental composition.

[0072] The method for preparing the polyanionic precursor provided in this application includes: under an inert gas atmosphere, a solution containing iron ions and a solution containing sodium ions and pyrophosphate ions are introduced into a reaction vessel and mixed to carry out a coprecipitation reaction to obtain the polyanionic precursor, wherein the molar ratio of iron to phosphorus in the reaction system is controlled to be (0.8-0.9):1.

[0073] In this embodiment, a polyanionic precursor is prepared by co-precipitation. Liquid-phase mixing can achieve uniform contact of each ion. Compared with physical mixing by solid-phase method, it can significantly improve the mixing uniformity of raw materials, ensure that the proportion of elements such as iron and phosphorus in the precursor matches the target value, reduce the deviation of element proportion, and improve the purity of material.

[0074] The method for preparing polyanionic precursors provided in this application does not require the addition of oxidants, thus retaining a certain amount of ferrous ions in the precursor, which can reduce the preparation cost of the precursor and reduce the amount of reducing agent added during the preparation of cathode materials, which is beneficial for further cost savings.

[0075] The introduction of an inert gas atmosphere can isolate oxygen, prevent the oxidation of ferrous ions, ensure that the content of ferrous ions in the precursor is stable within the target range, guarantee the establishment of the valence equilibrium system, so that the reaction does not require the addition of a reducing agent, simplifying the process and reducing the introduction of impurities.

[0076] In some embodiments, the inert gas atmosphere is selected from one or more of nitrogen and argon.

[0077] By controlling the molar ratio of iron to phosphorus in the reaction system to (0.8-0.9):1, the crystal growth direction of the precursor can be directionally controlled, promoting the formation of the target phase while inhibiting the formation of impurity phases, thereby further enhancing the structural stability and reactivity of the precursor.

[0078] For example, the concentration ratio of iron ions to pyrophosphate ions is any value or a range between 0.80:1, 0.81:1, 0.82:1, 0.83:1, 0.84:1, 0.85:1, 0.86:1, 0.87:1, 0.88:1, 0.89:1, 0.90:1, and (0.8-0.9):1.

[0079] In some embodiments, the preparation method provided in this application further includes simultaneously introducing an iron ion solution and a solution including sodium ions and pyrophosphate ions into a reaction vessel, and simultaneously introducing a solution containing element M into the reaction vessel to mix and carry out a co-precipitation reaction to obtain a polyanionic precursor.

[0080] In this embodiment, by introducing element M in the coprecipitation reaction, a polyanionic precursor containing element M is finally obtained.

[0081] In some embodiments, element M is selected from one or more transition metal elements other than Fe, Mg, Ca, Sr, and Al.

[0082] In some embodiments, transition metal elements other than Fe include one or more of Ni, Co, Mn, Ti, V, Cr, Zr, Nb, W, Cr, Cu, Zn, Mo, Sc, and Y.

[0083] In some embodiments, the solution comprising sodium ions and pyrophosphate ions comprises a sodium pyrophosphate solution.

[0084] Sodium pyrophosphate, as a single solute, avoids the introduction of other cations, reducing the difficulty and cost of subsequent washing and impurity removal. It also allows for control of the sodium ion to pyrophosphate ion ratio, ensuring a stable ionic composition in the solution. Compared to mixed systems of pyrophosphate and other sodium salts, sodium pyrophosphate solutions have a more stable pH, reducing the impact of pH fluctuations on the product phase during the reaction.

[0085] In some embodiments, the iron-containing solution is selected from one or more of ferrous sulfate solution, ferrous chloride solution, and ferrous oxalate solution.

[0086] In some embodiments, the flow rate of the iron ion solution into the reaction vessel is 16-19% / h of the reaction vessel volume.

[0087] In some embodiments, the flow rate of the solution comprising sodium ions and pyrophosphate ions into the reaction vessel is 30-35% / h of the reaction vessel volume.

[0088] For example, the flow rate of the iron ion-containing solution is any value among 16% / h, 17% / h, 18% / h, and 19% / h of the reaction vessel volume, or a range between any two.

[0089] For example, the flow rate of the solution comprising sodium ions and pyrophosphate ions is any value or a range between 30.0% / h, 30.5% / h, 31.0% / h, 32.0% / h, 32.5% / h, 33.0% / h, 33.5% / h, 34.0% / h, 34.5% / h, and 35.0% / h of the reaction vessel volume.

[0090] In this embodiment, by adjusting the flow rate of the iron ion solution and the solution including sodium ions and pyrophosphate ions, the ion concentration of the reaction system can be stabilized during the dropwise addition process, thereby achieving uniform growth of the product particles.

[0091] In some embodiments, the iron ion concentration in the iron-containing solution is 86-93 g / L.

[0092] For example, the iron ion concentration in the iron-containing solution is any value or a range between any two of 86 g / L, 86.5 g / L, 87 g / L, 87.5 g / L, 88 g / L, 88.5 g / L, 89 g / L, 89.5 g / L, 90 g / L, 90.5 g / L, 91 g / L, 91.5 g / L, 92 g / L, 92.5 g / L, and 93 g / L.

[0093] Within the above concentration range, the reaction efficiency per unit volume of solution can be improved, the volume of solution required for the reaction can be reduced, and the cost of the reaction vessel can be lowered.

[0094] In some embodiments, the pH value of the coprecipitation reaction is 3 to 5. Optionally, the pH value of the coprecipitation reaction is 3.5 to 4.5.

[0095] For example, the pH value of the coprecipitation reaction is any value or a range between any two of 3, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5 and 5.

[0096] In some embodiments, the temperature of the coprecipitation reaction is 45°C. o C~65 o C.

[0097] For example, the temperature of the coprecipitation reaction is any value or a range between any two of 45°C, 46°C, 47°C, 48°C, 49°C, 50°C, 51°C, 52°C, 53°C, 54°C, 55°C, 56°C, 57°C, 58°C, 59°C, 60°C, 61°C, 62°C, 63°C, 64°C, and 65°C.

[0098] In some embodiments, the stirring frequency of the coprecipitation reaction is 23 Hz to 28 Hz.

[0099] For example, the stirring frequency of the coprecipitation reaction is any value of 23Hz, 24Hz, 25Hz, 26Hz, 27Hz and 28Hz or a range between any two.

[0100] In some embodiments, the coprecipitation reaction is further further included by an aging treatment; optionally, the aging treatment time is 0.5h to 10h; optionally, the pH value of the aging treatment is 3.0-5.0.

[0101] Aging treatment can further crystallize and improve the stability of the crystal structure of the coprecipitated products, while promoting the dissolution of small particles and the growth of large particles, thus optimizing the particle size distribution.

[0102] For example, the aging time is any value or a range between 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9.0h, 9.5h, and 10h.

[0103] Maintaining the aging pH value between 3.0 and 5.0 can prevent hydrolysis or oxidation of the product during the aging process, ensuring the stability of the product composition and structure.

[0104] For example, the aging pH value is any value among 3, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9 and 5.0 or a range between any two.

[0105] In some embodiments, the preparation method further includes post-treatment of the precipitate; optionally, the post-treatment includes solid-liquid separation, washing, and drying.

[0106] The precipitate is post-treated to remove impurity ions attached to the surface, resulting in a purified product.

[0107] For example, the washing process involves alternating between deionized water and ethanol 3-5 times to ensure that the precipitate is thoroughly cleaned. The precipitate is then dried at 80-120°C for 12-24 hours to remove moisture, yielding the polyanionic precursor.

[0108] Thirdly, embodiments of this application provide a sodium-ion battery cathode material. The raw materials for the sodium-ion battery cathode material include the polyanionic precursor in the embodiments of the first aspect of this application or the polyanionic precursor prepared by the polyanionic precursor preparation method in the embodiments of the second aspect of this application.

[0109] For example, a method for preparing a sodium-ion battery cathode material includes: mixing raw materials including a polyanionic precursor, a carbon source, and a sodium source, pulverizing, drying, and then sintering to obtain the sodium-ion battery cathode material.

[0110] Sintering is typically carried out under a protective atmosphere, such as a nitrogen atmosphere.

[0111] In some embodiments, the preparation method of the polyanionic sodium-ion battery cathode material satisfies one or more of the following conditions: (1) The carbon source is one or more of the following: sucrose, glucose, rock sugar, cellulose, phenolic resin, polyethylene glycol, polyvinylpyrrolidone, starch, polyvinyl alcohol, ionic cellulose gum carbon source, and inorganic carbon source; (2) Sodium sources include one or more of sodium carbonate, sodium bicarbonate, sodium acetate, and sodium oxalate; (3) Crushing into grinding or sand milling; (4) The sintering temperature is 500-600℃ and the sintering time is 6-30h.

[0112] Optionally, the sintering temperature can be any value between 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, 560℃, 570℃, 580℃, 590℃, 600℃, or 500℃ and 600℃, and the sintering time can be any value between 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, 24h, 26h, 28h, 30h, or 6h and 30h.

[0113] Fourthly, embodiments of this application provide a sodium-ion battery, including the sodium-ion battery cathode material described in the embodiments of the third aspect of this application.

[0114] The sodium-ion battery provided in this application embodiment includes the above-mentioned sodium-ion battery cathode material, which enables the battery to have high capacity, good cycle and rate performance.

[0115] Fifthly, this application provides an electrical device, including the sodium-ion battery described in the fourth aspect of this application.

[0116] Example 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 weight, 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.

[0117] Example 1: A polyanionic precursor is prepared by the following method: Prepare a ferrous sulfate solution with a Fe concentration of 89 g / L and a sodium pyrophosphate solution with a P concentration of 32 g / L; The reaction temperature was set at 50℃, the stirring frequency at 25Hz, and nitrogen was introduced as a protective gas. The prepared ferrous sulfate solution and sodium pyrophosphate solution were pumped into the reactor at a flow rate ratio of 1:1.93. The flow rate of the ferrous sulfate solution was 17.8% / h of the reactor volume, and the flow rate of the sodium pyrophosphate solution was 34.3% / h of the reactor volume. The molar ratio of iron to phosphorus in the reaction was controlled at 0.8:1, and the pH value was 4.0±0.5. After co-precipitation, a reaction slurry was obtained. The reaction temperature was maintained at 50℃, the stirring frequency at 25Hz, and the pH value at 4.0±0.5. After aging for 1 hour, the slurry was discharged. After filtering and washing twice, the slurry underwent drying, crushing, and packaging to obtain the precursor. The precursor was then treated with Na... q Fe m+n Mw (H x P y O z When )·bH2O is expressed as a general formula, q=0.35, y=1, and b / (m+n+w)=0.25 are measured.

[0118] This embodiment also provides a sodium-ion battery cathode material, the preparation method of which is as follows: The amount of precursor is based on the amount of Fe. 1 mol of precursor is mixed with 2 mol of sodium carbonate, 5% glucose [wherein 5% glucose means that the amount of glucose added accounts for 5% of the total mass of raw materials (precursor + sodium carbonate), the same below], and water. After being mixed evenly, the mixture is sand-milled for 3 hours, spray-dried, and then sintered in an atmosphere furnace at 540°C for 12 hours under a nitrogen atmosphere to obtain sodium-ion battery cathode material.

[0119] Example 2: A polyanionic precursor was prepared in Example 2 using a method similar to that in Example 1, except that: The prepared ferrous sulfate solution and sodium pyrophosphate solution were pumped into the reactor at a flow ratio of 1:1.88. The flow rate of the ferrous sulfate solution was 17.8% / h of the reactor volume, and the flow rate of the sodium pyrophosphate solution was 33.5% / h of the reactor volume. The molar ratio of iron to phosphorus in the reaction was controlled at 0.82:1. The precursor was then... q Fe m+n M w (H x P y O z When )·bH2O is expressed as a general formula, q=0.33, y=1, and b / (m+n+w)=0.25 are measured.

[0120] This embodiment also provides a sodium-ion battery cathode material, which is prepared using a method similar to that in Example 1, except that: The precursor prepared in this embodiment is used as the raw material.

[0121] Example 3: A polyanionic precursor was prepared in Example 3 using a method similar to that in Example 1, except that: The prepared ferrous sulfate solution and sodium pyrophosphate solution were pumped into the reactor at a flow ratio of 1:1.81. The flow rate of the ferrous sulfate solution was 17.8% / h of the reactor volume, and the flow rate of the sodium pyrophosphate solution was 32.3% / h of the reactor volume. The molar ratio of iron to phosphorus in the reaction was controlled at 0.85:1. The precursor was prepared using Na... q Fe m+n M w(H x P y O z When )·bH2O is expressed as a general formula, q=0.31, y=1, and b / (m+n+w)=0.25 are measured.

[0122] This embodiment also provides a sodium-ion battery cathode material, which is prepared using a method similar to that in Example 1, except that: The precursor prepared in this embodiment is used as the raw material.

[0123] Figure 1 This is a SEM image of the polyanionic precursor prepared in Example 3. Figure 2 The figure shows the EDS elemental distribution of the polyanionic precursor. As can be seen from the figure, the elements in the polyanionic precursor are evenly distributed.

[0124] Figure 3 The figure shows the EDS elemental distribution of the cross-section of the sodium-ion battery cathode material prepared from the precursor in this embodiment. As can be seen from the figure, the elements in the sodium-ion battery cathode material prepared from the precursor are evenly distributed.

[0125] Example 4: A polyanionic precursor was prepared in Example 4 using a method similar to that in Example 2, except that: The reaction temperature is 45℃. The precursor is reacted with Na... q Fe m+n M w (H x P y O z When )·bH2O is expressed as a general formula, q=0.33, y=1, and b / (m+n+w)=0.25 are measured.

[0126] This embodiment also provides a sodium-ion battery cathode material, which is prepared using a method similar to that in Example 1, except that: The precursor prepared in this embodiment is used as the raw material.

[0127] Example 5: A polyanionic precursor was prepared in Example 5 using a method similar to that in Example 2, except that: The reaction temperature is 55℃. The precursor is reacted with Na... q Fe m+n M w (H x P y O z When )·bH2O is expressed as a general formula, q=0.33, y=1, and b / (m+n+w)=0.25 are measured.

[0128] This embodiment also provides a sodium-ion battery cathode material, which is prepared using a method similar to that in Example 1, except that: The precursor prepared in this embodiment is used as the raw material.

[0129] Example 6: A polyanionic precursor was prepared in Example 6 using a method similar to that in Example 2, except that: The prepared ferrous sulfate solution and sodium pyrophosphate solution were pumped into the reactor at a flow ratio of 1:1.71. The flow rate of the ferrous sulfate solution was 17.8% / h of the reactor volume, and the flow rate of the sodium pyrophosphate solution was 30.5% / h of the reactor volume. The molar ratio of iron to phosphorus in the reaction was controlled at 0.9:1. The precursor was prepared using Na... q Fe m+ n M w (H x P y O z When )·bH2O is expressed as a general formula, q=0.26, y=1, and b / (m+n+w)=0.25 are measured.

[0130] This embodiment also provides a sodium-ion battery cathode material, which is prepared using a method similar to that in Example 1, except that: The precursor prepared in this embodiment is used as the raw material.

[0131] Example 7: A polyanionic precursor was prepared in Example 8 using a method similar to that in Example 1, except that: Prepare a ferrous sulfate solution with a Fe concentration of 89 g / L, a sodium pyrophosphate solution with a P concentration of 32 g / L, and a manganese sulfate solution with a Mn concentration of 0.001 g / L. The prepared manganese sulfate solution was added to the reaction vessel at 20% of its volume. Ferrous sulfate solution and sodium pyrophosphate solution were pumped into the reaction vessel at a flow rate ratio of 1:1.88, with the ferrous sulfate solution flowing at 17.8% / h of the reaction vessel volume and the sodium pyrophosphate solution flowing at 33.5% / h. The molar ratio of iron to phosphorus was controlled at 0.82:1, and the manganese doping amount was 0.5% of the theoretical precursor mass. The precursor was then treated with Na... q Fe m+ n M w (H x P y O zWhen )·bH2O is expressed as a general formula, the measured values ​​are q=0.33, y=1, w / (m+n)=0.025, q / (m+n+w)=0.4, (m+n+w) / y=0.84, and b / (m+n+w)=0.24.

[0132] This embodiment also provides a sodium-ion battery cathode material, which is prepared using a method similar to that in Example 1, except that: The precursor prepared in this embodiment is used as the raw material.

[0133] Comparative Example 1: A polyanionic precursor is prepared by the following method: Prepare a ferrous sulfate solution with a Fe concentration of 89 g / L, a sodium pyrophosphate solution with a P concentration of 32 g / L, a hydrogen peroxide solution of 27 wt%, and a dilute sulfuric acid solution of 133 g / L. The reaction temperature was set at 50℃, the stirring frequency at 25Hz, and nitrogen gas was introduced as a protective gas. The prepared ferrous sulfate solution and sodium pyrophosphate solution were pumped into the reactor at a flow rate ratio of 1:1.18. The flow rate of the ferrous sulfate solution was 17.8% / h of the reaction vessel volume, and the flow rate of the sodium pyrophosphate solution was 21% / h of the reaction vessel volume. The pH value of the reaction was controlled at 4.0±0.5. After 2 hours of co-precipitation reaction, a preliminary precipitate was formed.

[0134] The prepared sodium pyrophosphate solution, hydrogen peroxide solution, and dilute sulfuric acid solution were pumped into the reactor. The flow rate of the pyrophosphate solution was 8.3% / h of the total reactor volume, and the flow rate of the hydrogen peroxide solution was 1% / h of the total reactor volume. Dilute sulfuric acid was introduced to adjust the pH value of the liquid to 4.6±0.5 to obtain a reaction slurry. The reaction temperature was maintained at 50℃ and the reaction stirring frequency was 25Hz. After aging for 1 hour, the material was discharged. The slurry was filtered and washed twice, and then dried, crushed, and packaged to obtain the precursor.

[0135] This comparative example also provides a sodium-ion battery cathode material, which is prepared using a method similar to that in Example 1, except that: (1) The precursor prepared in this comparative example was used as the raw material; (2) Add glucose at 10% of the total mass of raw materials (precursor + sodium carbonate).

[0136] Comparative Example 2: A polyanionic precursor is prepared by the following method: Prepare a ferrous sulfate solution with a Fe concentration of 89 g / L, a sodium pyrophosphate solution with a P concentration of 32 g / L, a hydrogen peroxide solution with a 27 wt% concentration, and a dilute sulfuric acid solution with a 133 g / L concentration. The reaction temperature was set at 50℃, the stirring frequency at 25Hz, and nitrogen gas was introduced as a protective gas. The prepared ferrous sulfate solution and sodium pyrophosphate solution were pumped into the reactor through a pipeline reactor at a flow rate of 1:1.18. The flow rate of the ferrous sulfate solution was 17.8% / h of the reactor volume, and the flow rate of the sodium pyrophosphate solution was 21% / h of the reactor volume. The pH of the reaction was controlled at 4.0±0.5. After 2 hours of co-precipitation, a preliminary precipitate was formed.

[0137] The prepared sodium pyrophosphate solution, hydrogen peroxide solution, and dilute sulfuric acid solution were pumped into the reactor. The flow rate of the pyrophosphate solution was 2.32% / h of the total reactor volume, and the flow rate of the hydrogen peroxide solution was 1% / h of the total reactor volume. Dilute sulfuric acid was introduced to adjust the pH value of the liquid to 4.6±0.5 to obtain a reaction slurry. The reaction temperature was maintained at 50℃ and the reaction stirring frequency was 25Hz. After aging for 1 hour, the material was discharged. The slurry was filtered and washed twice, and then dried, crushed, and packaged to obtain the precursor.

[0138] This comparative example also provides a sodium-ion battery cathode material, which is prepared using a method similar to that in Example 1, except that: (1) The precursor prepared in this comparative example was used as the raw material; (2) Add glucose at 10% of the total mass of raw materials (precursor + sodium carbonate).

[0139] Test section The polyanionic precursors prepared in the examples and comparative examples were subjected to index parameter testing and electrochemical performance testing.

[0140] The particle size D50 of the secondary particles was determined by a laser particle size analyzer (instrument model: Mastersizer3000) in accordance with the national standard GB / T 19077-2016 Particle size analysis by laser diffraction. Tap density test method: The tap density was determined by a powder tap density tester (model: Dandong Baite BT-302) in accordance with the national standard GB / T 5162-2021 Determination of tap density of metal powders. Specific surface area test method: The specific surface area was determined by a fully automated nitrogen adsorption specific surface area analyzer (instrument model: BELPREP-VACII / BELSORP-MINI-X) in accordance with the national standard GB / T 19587-2017 "Determination of specific surface area of ​​solid substances by gas adsorption BET method". Elemental distribution uniformity test: EDS uses an X-ray energy dispersive spectroscopy scanner to determine the elemental composition of the material particles; Element content test: 1. Detection method for ferrous iron: (1) Dissolve the sample, adjust the volume, and then aliquot the test solution; (2) In a sulfur-phosphorus mixed acid medium, sodium diphenylamine sulfonate was used as an indicator and potassium dichromate standard solution was used for titration until the purple endpoint.

[0141] 2. Methods for detecting total iron: (1) Dissolve the sample, adjust the volume, and then aliquot the test solution; (2) Reduce iron in hydrochloric acid medium; (3) First, titrate the excess reducing agent with potassium dichromate solution until it is colorless, then add sulfuric acid and sodium diphenylamine sulfonate indicator, and continue to titrate with potassium dichromate standard solution until the purple endpoint is reached; 3. The determination of phosphorus content refers to the gravimetric method of quinoline phosphomolybdate (YS T 1028.3-2015). 4. Other metallic elements were tested using ICP.

[0142] The physicochemical test results of the polyanionic precursors in the examples and comparative examples are shown in Table 1.

[0143] Table 1

[0144] Electrochemical performance testing The sodium-ion battery cathode materials prepared in the above embodiments and comparative examples were tested, and the results are shown in Table 1. Simultaneously, cathode materials were prepared using these materials and assembled into batteries. The battery performance was then tested, specifically including the following steps: The positive electrode material was mixed with polyvinylidene fluoride and acetylene black in a mass ratio of 9:0.5:0.5, with N-methyl-pyrrolidone added as a solvent. This mixture was then uniformly coated onto aluminum foil as the positive electrode. The positive electrode sheet was rolled to the required compaction density and then punched into a circular sheet for later use. After drying, in a glove box, a sodium metal sheet was used as the negative electrode, a 1 mol / L NaClO4 solution as the electrolyte, and glass fiber as the separator to assemble a CR2032 coin cell. First, it was activated by charge-discharge for 3 weeks at a current density of 0.1C (1C=129mAh / g), and finally by charge-discharge for 50 weeks at a current density of 1C. The charging cutoff voltage was 4.2V, and the discharging cutoff voltage was 2.0V.

[0145] The test results of the button batteries prepared in Examples 1-7 and Comparative Examples 1-2 are shown in Table 2.

[0146] Table 2

[0147] As shown in Tables 1 and 2, when the polyanionic precursor has a high phosphorus-to-iron ratio, the cathode material prepared from it exhibits excellent rate and cycle performance while maintaining high capacity performance. Furthermore, compared to Comparative Examples 1-2, the polyanionic precursors prepared in Examples 1-7 require less reducing agent in the subsequent preparation of the cathode material, further reducing raw material costs and facilitating industrial-scale production.

[0148] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A polyanionic precursor, characterized in that, The polyanionic precursor comprises sodium, iron, and phosphorus; wherein the total amount of iron is N. Fe The total amount of phosphorus is N. P The total amount of iron, N Fe The total amount of phosphorus N P The ratio satisfies 0.8 ≤ N Fe / N P ≤0.

9.

2. The polyanionic precursor according to claim 1, characterized in that, The iron element includes ferrous iron (Fe2+), and the amount of ferrous iron (Fe2+) is m. Fe The total amount of substance N of the iron element Fe The ratio satisfies 0.1 ≤ m Fe / N Fe ≤0.5, can be selected as 0.3≤m Fe / N Fe ≤0.

5.

3. The polyanionic precursor according to claim 1, characterized in that, The polyanionic precursor satisfies one or more of the following conditions: ① The polyanionic precursor also includes element M, which is selected from one or more of transition metal elements other than Fe, Mg, Ca, Sr and Al; optionally, the transition metal elements other than Fe include one or more of Ni, Co, Mn, Ti, V, Cr, Zr, Nb, W, Cr, Cu, Zn, Mo, Sc and Y. ② The polyanionic precursor also includes element M, wherein the amount of substance w of element M is equal to the total amount of substance N of iron element. Fe The ratio satisfies 0 ≤ w / N Fe ≤0.1; ③ The polyanionic precursor also includes element M, wherein the amount of sodium q and the total amount of iron N are... Fe The ratio of the sum of the amounts of substance w of element M and the substance M satisfies 0.2 ≤ q / (N) Fe +w)≤0.45; ④ The amount of sodium q and the total amount of phosphorus N P The ratio satisfies 0 P ≤0.4.​ 4. The polyanionic precursor according to claim 1, characterized in that, The polyanionic precursor includes Na... q Fe m+n M w (H x P y O z Substances containing bH2O; Where M is selected from one or more transition metal elements other than Fe, Mg, Ca, Sr, and Al; m is Fe 2+ The content of, n is Fe 3+ The content of <q / y≤0.4,0≤b / (m+n+w)≤10。 5. The polyanionic precursor according to any one of claims 1-4, characterized in that, One or more of the following conditions must be met: A. The tap density of the polyanionic precursor is 0.6 g / cm³. 3 -1.4g / cm 3 ; B. The Dv50 of the polyanionic precursor is 2μm-5μm; C. The specific surface area of ​​the polyanionic precursor is 15 m². 2 / g-35 m 2 / g, optional 19m 2 / g-28m 2 / g; D. The polyanionic precursor includes secondary particles composed of primary particles; optionally, the primary particles include plate-like and / or block-like primary particles.

6. A method for preparing a polyanionic precursor, characterized in that, include: Under an inert gas atmosphere, a solution containing iron ions and a solution containing sodium ions and pyrophosphate ions are introduced into a reaction vessel and mixed to carry out a co-precipitation reaction to obtain the polyanionic precursor. The molar ratio of iron to phosphorus in the reaction system is controlled to be (0.8-0.9):

1.

7. The method for preparing the polyanionic precursor according to claim 6, characterized in that, The method further includes simultaneously introducing a solution containing iron ions and a solution containing sodium ions and pyrophosphate ions into a reaction vessel, and simultaneously introducing a solution containing element M into the reaction vessel to perform a co-precipitation reaction to obtain the polyanionic precursor; optionally, element M is selected from one or more of transition metal elements other than Fe, Mg, Ca, Sr and Al; optionally, transition metal elements other than Fe include one or more of Ni, Co, Mn, Ti, V, Cr, Zr, Nb, W, Cr, Cu, Zn, Mo, Sc and Y; And / or, the coprecipitation reaction is further subjected to an aging treatment after completion; optionally, the aging treatment time is 0.5h to 10h; optionally, the pH value of the aging treatment is 3.0-5.

0.

8. The method for preparing the polyanionic precursor according to claim 6 or 7, characterized in that, The preparation method satisfies at least one of the following conditions: a. The solution comprising sodium ions and pyrophosphate ions includes a sodium pyrophosphate solution; b. The iron-containing solution is selected from one or more of ferrous sulfate solution, ferrous chloride solution, and ferrous oxalate solution; c. The flow rate of the iron-containing solution into the reaction vessel is 16-19% / h of the reaction vessel volume; d. The flow rate of the solution containing sodium ions and pyrophosphate ions into the reaction vessel is 30-35% / h of the reaction vessel volume; e. The iron ion concentration in the iron-containing solution is 86-93 g / L; f. The pH value of the coprecipitation reaction is 3-5; g. The temperature of the coprecipitation reaction is 45°C. o C ~65 o C; h. The stirring frequency for the coprecipitation reaction is 23Hz~28Hz; i. The preparation method further includes post-treatment of the precipitate; optionally, the post-treatment includes solid-liquid separation, washing and drying.

9. A sodium-ion battery cathode material, characterized in that, The raw materials for the sodium-ion battery cathode material include the polyanionic precursor as described in any one of claims 1-5 or the polyanionic precursor prepared by the polyanionic precursor preparation method described in any one of claims 6-8.

10. A sodium-ion battery, characterized in that, Includes the sodium-ion battery cathode material as described in claim 9.

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