Polyanionic precursor, sodium ion battery positive material and preparation method therefor, sodium ion battery, and electric device

Abstract

The present application relates to the field of sodium ion batteries, and provides a polyanionic precursor, a sodium ion battery positive material, and a preparation method therefor, a sodium ion battery, and an electric device. The polyanionic precursor contains a substance having a general chemical formula NaqMm+nM'wPxOy·zH2O. The preparation method for the polyanionic precursor comprises: mixing a metal salt containing M2+ and a first phosphorus source containing pyrophosphate to obtain a mixed solution, and carrying out a reaction to obtain a mixed solution of pyrophosphate containing a divalent metal M; adding an oxidizing agent and a second phosphorus source for reaction, performing solid-liquid separation, and then drying the separated solid, to obtain the polyanionic precursor. The polyanionic precursor of the present application has high tap density, and the prepared sodium ion battery positive material has high purity and excellent electrochemical performance. The polyanionic precursor provided by the present application contains a small amount of insoluble Na, so that a sodium source during the preparation for the positive electrode can be saved.

Description

Polyanion precursor, sodium ion battery cathode material and preparation method thereof, sodium ion battery and electrical equipment

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application with application number 202311200184.1 filed with the Patent Office of China on September 15, 2023, entitled “Polyanion precursor, sodium ion battery positive electrode material and preparation method thereof, sodium ion battery and electrical-related equipment”, the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present application relates to the field of sodium ion batteries, and in particular to a polyanion precursor, a sodium ion battery positive electrode material and a preparation method thereof, a sodium ion battery and electrical equipment. Background Art

[0004] Polyanion positive electrode materials are a very important type of existing sodium ion battery positive electrode materials and have received widespread attention in the field of energy storage.

[0005] Currently, the solid-phase method is the predominant preparation method for polyanionic cathode materials. However, due to inherent uneven mixing, the metal-to-P ratio of the resulting material is difficult to control and the purity is low. The one-step solid-phase synthesis method also suffers from high sintering gas production, resulting in low energy density, compacted density, and tap density of the cathode material, hindering its commercial application.

[0006] Application Contents

[0007] The purpose of this application is to provide a polyanion precursor, a sodium ion battery positive electrode material and a preparation method thereof, a sodium ion battery and electrical equipment to solve the above problems.

[0008] To achieve the above objectives, this application adopts the following technical solutions:

[0009] The present application provides a polyanionic precursor, the general chemical formula of which is Na q M m+n M' w P x O y zH2O;

[0010] Wherein, M is one or more of Fe, Ni, Co, and Mn; M' is one or more of transition metal elements other than M, Mg, Ca, Sr, and Al; m represents M 2+ The content of M 3+The content of q, m, n, w, x, and y is selected according to the valence state of M' to maintain charge balance in the chemical formula.

[0011] Optionally, the polyanionic precursor satisfies one or more of the following conditions:

[0012] (1) M is Fe and Mn;

[0013] (2) The transition metal elements other than M include Ti, V, Cr, Zr, Nb, W, Cr, Cu, Zn, Mo, Sc, and Y;

[0014] (3)0.40≤q / (m+n+w)≤0.65;

[0015] (4)0.26≤q / x≤0.60;

[0016] (5) 0 ≤ m / (m+n) ≤ 0.33; or, 0 ≤ m / (m+n) ≤ 0.30; or, 0 ≤ m / (m+n) ≤ 0.26;

[0017] (6)0≤w / (m+n)≤0.05;

[0018] (7)0.71≤(m+n+w) / x≤0.77;

[0019] (8) The valence of M' is +α, q+2m+3n+αw+5x=2y;

[0020] (9) The valence of M' is +α, 1≤α≤5; or, 2≤α≤4;

[0021] (10) 0≤z / (m+n+w)≤6; or, 0≤z / (m+n+w)≤3;

[0022] (11) The polyanionic precursor contains phosphate and / or pyrophosphate;

[0023] (12) The polyanionic precursor contains pyrophosphate, and the P content in the pyrophosphate accounts for more than 10 wt% of the total P content in the polyanionic precursor;

[0024] (13) The content of Na in the polyanionic precursor is 4 wt%-10 wt%;

[0025] (14) In the polyanionic precursor, the content of P is 15 wt%-25 wt%;

[0026] (15) In the polyanionic precursor, the total content of M and M' is 20 wt%-32 wt%;

[0027] (16) In the polyanionic precursor, the content of S is less than 0.5 wt%;

[0028] (17) In the polyanionic precursor, the total content of S and N is less than 0.8 wt%;

[0029] (18) In the polyanionic precursor, the total content of S, N and C is less than 1.0 wt%;

[0030] (19) The content of heteroelements in the polyanionic precursor is less than 3.0 wt %; or, the content of heteroelements is less than 1.5 wt %;

[0031] (20) In the polyanionic precursor, n(S):n(M+M')≤0.1, or n(S):n(M+M')≤0.06;

[0032] (21) In the polyanionic precursor, n(S+N):n(M+M')≤0.1, or n(S+N):n(M+M')≤0.06;

[0033] (22) In the polyanionic precursor, n(S+N+C):n(P)≤0.1, or n(S+N+C):n(P)≤0.06;

[0034] (23) The polyanionic precursor is in an amorphous state;

[0035] (24) The tap density TD of the polyanionic precursor is 0.9-1.4 g / cm 3 ;

[0036] (25) The BET of the polyanionic precursor is 5-25m 2 / g;

[0037] (26) The average particle size of the primary particles of the polyanionic precursor is 50-200 nm;

[0038] (27) The average particle size D50 of the secondary particles of the polyanionic precursor satisfies the following: 1 μm ≤ D50 ≤ 10 μm;

[0039] (28) The particle size distribution of the polyanionic precursor satisfies the following requirements: D10≤1 μm, 1 μm≤D50≤10 μm, D90≤50 μm;

[0040] (29) The primary particles of the polyanionic precursor are spherical or quasi-spherical;

[0041] (30) In the XRD pattern of the polyanionic precursor, within the test range of 20°≤2θ≤70°, the peak position of the highest peak is between 26° and 32°;

[0042] (31) The polyanionic precursor is poorly soluble in water;

[0043] (32) The polyanionic precursor conforms to the chemical formula Na q M m+n M' w P x O y ·zH2O.

[0044] As the same inventive concept, the present application also provides a polyanionic precursor containing a chemical formula of Na q M m+n M' w (PO4) e (P2O7) f · Substances containing zH2O;

[0045] Wherein, M is one or more of Fe, Ni, Co, and Mn; M' is one or more of transition metal elements other than M, Mg, Ca, Sr, and Al; m represents M 2+ The content of M 3+ The content of q, m, n, w, e, and f is selected according to the valence state of M' to maintain charge balance in the chemical formula.

[0046] The above general formula Na q M m+n M' w P x O y P in zH2O x O y Including phosphate and pyrophosphate, that is, the general formula can also be written as Na q M m+n M' w (PO4) e (P2O7) f ·zH2O, that is, x=e+2f, y=4e+7f.

[0047] Optionally, the polyanionic precursor satisfies one or more of the following conditions:

[0048] (1) M is Fe and Mn;

[0049] (2) The transition metal elements other than M include Ti, V, Cr, Zr, Nb, W, Cr, Cu, Zn, Mo, Sc, and Y;

[0050] (3)0.40≤q / (m+n+w)≤0.65;

[0051] (4)0.26≤q / (e+2f)≤0.60;

[0052] (5) 0 ≤ m / (m+n) ≤ 0.33; or, 0 ≤ m / (m+n) ≤ 0.30; or, 0 ≤ m / (m+n) ≤ 0.26;

[0053] (6)0≤w / (m+n)≤0.05;

[0054] (7)0.71≤(m+n+w) / (e+2f)≤0.77;

[0055] (8) The valence of M' is +α, q+2m+3n+αw+5(e+2f)=2(4e+7f);

[0056] (9) The valence of M' is +α, 1≤α≤5; or, 2≤α≤4;

[0057] (10) 0≤z / (m+n+w)≤6; or, 0≤z / (m+n+w)≤3;

[0058] (11) The polyanionic precursor contains phosphate and / or pyrophosphate;

[0059] (12) The polyanionic precursor contains pyrophosphate, and the P content in the pyrophosphate accounts for more than 10 wt% of the total P content in the polyanionic precursor;

[0060] (13) The content of Na in the polyanionic precursor is 4 wt%-10 wt%;

[0061] (14) In the polyanionic precursor, the content of P is 15 wt%-25 wt%;

[0062] (15) In the polyanionic precursor, the total content of M and M' is 20 wt%-32 wt%;

[0063] (16) In the polyanionic precursor, the content of S is less than 0.5 wt%;

[0064] (17) In the polyanionic precursor, the total content of S and N is less than 0.8 wt%;

[0065] (18) In the polyanionic precursor, the total content of S, N and C is less than 1.0 wt%;

[0066] (19) The content of heteroelements in the polyanionic precursor is less than 3.0 wt %; or, the content of heteroelements is less than 1.5 wt %;

[0067] (20) In the polyanionic precursor, n(S):n(M+M')≤0.1, or n(S):n(M+M')≤0.06;

[0068] (21) In the polyanionic precursor, n(S+N):n(M+M')≤0.1, or n(S+N):n(M+M')≤0.06;

[0069] (22) In the polyanionic precursor, n(S+N+C):n(P)≤0.1, or n(S+N+C):n(P)≤0.06;

[0070] (23) The polyanionic precursor is in an amorphous state;

[0071] (24) The tap density TD of the polyanionic precursor is 0.9-1.4 g / cm 3 ;

[0072] (25) The BET of the polyanionic precursor is 5-25m 2 / g;

[0073] (26) The average particle size of the primary particles of the polyanionic precursor is 50-200 nm;

[0074] (27) The average particle size D50 of the secondary particles of the polyanionic precursor satisfies the following: 1 μm ≤ D50 ≤ 10 μm;

[0075] (28) The particle size distribution of the polyanionic precursor satisfies the following requirements: D10≤1 μm, 1 μm≤D50≤10 μm, D90≤50 μm;

[0076] (29) The primary particles of the polyanionic precursor are spherical or quasi-spherical;

[0077] (30) In the XRD pattern of the polyanionic precursor, within the test range of 20°≤2θ≤70°, the peak position of the highest peak is between 26° and 32°;

[0078] (31) The polyanionic precursor is poorly soluble in water;

[0079] (32) The polyanionic precursor conforms to the chemical formula Na qM m+n M' w (PO4) e (P2O7) f ·zH2O.

[0080] The present application also provides a method for preparing a polyanionic precursor, comprising the following steps:

[0081] Step A: Add M 2+ A metal salt and a first phosphorus source containing pyrophosphate are mixed to obtain a mixed solution, and a first reaction is performed to obtain a mixed solution containing a pyrophosphate salt of a divalent metal M;

[0082] Step B: adding an oxidant and a second phosphorus source to a mixed solution of pyrophosphate containing a divalent metal M to carry out a second reaction, separating the solid and the liquid after the second reaction, and drying the separated solid to obtain the polyanionic precursor; wherein the first phosphorus source and / or the second phosphorus source contain sodium ions.

[0083] Optionally, the preparation method of the polyanionic precursor meets one or more of the following conditions:

[0084] (1) The M-containing 2+ The metal salt includes one or more of a soluble divalent iron salt, a soluble divalent manganese salt, a soluble divalent nickel salt, and a soluble divalent cobalt salt; 2+ The metal salt is one or more of a soluble divalent iron salt, a soluble divalent manganese salt, a soluble divalent nickel salt, and a soluble divalent cobalt salt;

[0085] (2) The M-containing 2+ The metal salt includes one or more of sulfate, nitrate and chloride;

[0086] (3) The M-containing 2+ The metal salt also contains a soluble salt of metal M';

[0087] (4) the first phosphorus source and / or the second phosphorus source include pyrophosphate and / or sodium pyrophosphate;

[0088] (5) The temperature of the first reaction is 50-80° C., and the time of the first reaction is 1-10 hours;

[0089] (6) The oxidant is hydrogen peroxide;

[0090] (7) the molar amount of phosphorus in the pyrophosphate ion accounts for not less than 70% of the total molar amount of phosphorus in the first phosphorus source and the second phosphorus source;

[0091] (8) introducing an oxygen-containing gas during the second reaction;

[0092] (9) The temperature of the second reaction is 55-85°C, and the time of the second reaction is 1-6 hours;

[0093] (10) After the second reaction, aging is performed for 5-20 hours;

[0094] (11) The drying temperature is 80-120°C;

[0095] (12) the molar ratio of phosphorus in the first phosphorus source to that in the second phosphorus source is 2.5-3.6:1;

[0096] (13) The raw materials of the polyanionic precursor do not contain a carbon source.

[0097] As the same inventive concept, the present application also provides a polyanion sodium ion battery positive electrode material, the raw materials of which include a polyanion precursor, a sodium source and a carbon source.

[0098] As the same inventive concept, the polyanionic precursor is the polyanionic precursor defined by the above chemical formula, or the polyanionic precursor obtained by the above method for preparing the polyanionic precursor.

[0099] As the same inventive concept, the present application also provides a polyanion type sodium ion battery positive electrode material, wherein the component of the polyanion type sodium ion battery positive electrode material is a composite of sodium phosphate pyrophosphate metal salt and carbon;

[0100] In the sodium phosphate pyrophosphate metal salt, the metal other than sodium includes M and the optional M'; wherein M is one or more of Fe, Ni, Co, and Mn; and M' is selected from one or more of transition metal elements other than M, Mg, Ca, Sr, and Al.

[0101] Optionally, the polyanion sodium ion battery cathode material meets one or more of the following conditions:

[0102] (1) The compaction density of the polyanion sodium ion battery positive electrode material is 1.8-2.4 g / cm 3 ;

[0103] (2) The specific surface area of ​​the polyanion sodium ion battery positive electrode material is 5-25m 2 / g;

[0104] (3) The average particle size of the primary particles of the polyanion sodium ion battery positive electrode material is 100-400 nm;

[0105] (4) The average particle size D50 of the secondary particles of the polyanion sodium ion battery positive electrode material is 1-5 μm;

[0106] (5) The crystal structure of the sodium metal phosphopyrophosphate belongs to the Pn21a space group;

[0107] (6) The composition of sodium phosphate pyrophosphate is Na4M j M' k (PO4)2P2O7; where 0≤k / j≤0.1, 2.8≤j+k≤3.2;

[0108] (7) The S content of the polyanion sodium ion battery positive electrode material is ≤0.08 wt%; or, the S content is ≤0.05 wt%;

[0109] (8) The N content of the polyanion sodium ion battery positive electrode material is ≤0.08 wt%; or, the N content is ≤0.05 wt%.

[0110] As the same inventive concept, the present application also provides a method for preparing the polyanion sodium ion battery positive electrode material, comprising:

[0111] Mixing raw materials including the polyanion precursor, a carbon source, and a sodium source, crushing, drying, and then sintering to obtain the polyanion sodium ion battery positive electrode material;

[0112] Optionally, the preparation method of the polyanion sodium ion battery positive electrode material meets one or more of the following conditions:

[0113] (1) The carbon source is one or more of sucrose, glucose, crystal sugar, cellulose, phenolic resin, polyethylene glycol, polyvinyl pyrrolidone, starch, polyvinyl alcohol, ionic cellulose gum carbon source, and inorganic carbon source;

[0114] (2) the sodium source comprises one or more of sodium carbonate, sodium bicarbonate, sodium acetate, and sodium oxalate;

[0115] (3) The pulverization is grinding or sand milling;

[0116] (4) The sintering temperature is 500-600°C, and the sintering time is 6-30h.

[0117] As the same inventive concept, the present application also provides a sodium ion battery, comprising the polyanion sodium ion battery positive electrode material.

[0118] As the same inventive concept, the present application also provides an electrical device, including the sodium ion battery.

[0119] Compared with the prior art, the advantages of this application include:

[0120] The polyanionic precursor provided in this application has a uniform distribution of elements and a low content of impurities. The polyanionic precursor contains a certain amount of sodium, which can reduce the amount of sodium source added during the preparation of positive electrode materials, thereby saving costs. The uniform distribution of elements in this precursor makes it very easy to use it as a raw material to obtain high-purity positive electrode materials, with a purity of ≥95%.

[0121] The polyanionic precursor provided in the present application is obtained through a two-step reaction. The morphology of the precursor is easy to control, and a relatively ideal morphology is easy to obtain, and the tap density is relatively high. The ratio of metal M+M' to P is highly close to the ratio required for the positive electrode material (such as 3:4), and there is no need to additionally supplement metal M and M' to P. The process is simple, and no harmful gases containing N and S are generated during sintering, which is environmentally friendly.

[0122] The sodium ion battery positive electrode material provided in the present application uses the above-mentioned polyanion precursor as a raw material. The obtained positive electrode material can fully react with the electrolyte, reduce the sodium ion transmission distance, and thus effectively improve the conductivity and stability of the positive electrode material.

[0123] The positive electrode material prepared by the polyanionic precursor in the present application has few pores and the characteristics of high compaction, and the positive electrode material has the characteristics of high purity, high capacity and stable structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0124] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope of the present application.

[0125] FIG1 is a SEM image of the precursor prepared in Example 2;

[0126] FIG2a is an XRD pattern of the precursor prepared in Example 2;

[0127] FIG2 b is an XRD pattern of the precursor prepared in Example 2 after calcination at 500° C. and 600° C. for 12 h, respectively;

[0128] FIG3 is an XRD pattern of the precursor prepared in Example 21;

[0129] FIG4 is an XRD pattern of the positive electrode material obtained in Comparative Example 2;

[0130] FIG5 is an XRD pattern of the positive electrode material obtained in Example 3;

[0131] FIG6 is a SEM image of the positive electrode material prepared in Example 3;

[0132] FIG7 is an infrared test spectrum of the precursor obtained in Example 5;

[0133] FIG8 is a charge-discharge curve of the positive electrode material obtained in Example 5 in the first cycle. DETAILED DESCRIPTION

[0134] As used herein:

[0135] As used herein, the terms "comprises," "including," "having," "containing" or any other variations thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises a listed element is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0136] The conjunction "consisting of" excludes any unspecified elements, steps, or components. If used in a claim, this phrase renders the claim closed, excluding materials other than those recited, except for conventional impurities associated therewith. Throughout this application, open-ended expressions (e.g., comprising, containing, including) include closed-ended expressions.

[0137] In this application, open-ended expressions (such as include, contain, and comprise) include the meaning of closed-ended expressions.

[0138] In the present application, a plurality of refers to two or more, and a plurality refers to two or more.

[0139] When a quantity, concentration, or other value or parameter is expressed as a range, an optional range, or a range defined by a series of upper and lower optional values, this should be understood to specifically disclose all ranges formed by any pairing of any range upper limit or optional value with any range lower limit or optional value, regardless of whether the range is disclosed alone. For example, when a range of "1 to 5" is disclosed, the described range should be interpreted as including the range of "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5", etc. When a numerical range is described herein, unless otherwise stated, the range is intended to include its end values ​​and all integers and fractions within the range.

[0140] In this application, wt% indicates mass percentage, mol% indicates molar percentage, and vol% indicates volume percentage. When the percentage is not specified, it refers to mass percentage. When calculating the mass percentage of an element / substance in a precursor, the total mass of the precursor should include the mass of crystalline water but exclude the mass of free water.

[0141] In this application, n(A) represents the number of moles of element / substance A, and n(A+B) represents the sum of the number of moles of elements / substances A and B. n(A):n(B) represents the molar ratio of elements / substances A to B.

[0142] The polyanion precursor in this application is an intermediate product for preparing polyanion positive electrode materials. x O y (such as PO4 3- 、P2O7 4- ), this application refers to this intermediate product as a polyanionic precursor. Unless otherwise specified, the "polyanionic precursor" in this application is often referred to as a "precursor".

[0143] "And / or" is used to indicate that one or both of the stated situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0144] In order to solve the problems of large gas production, low compaction and easy generation of impurities in the preparation of polyanionic positive electrode materials in the existing technology, this application adopts the idea of ​​first preparing a polyanionic precursor and then preparing the positive electrode material, which makes it easy to obtain a positive electrode material with high purity and high compaction, while at the same time, the emission of harmful gases is extremely small, achieving a relatively ideal comprehensive effect.

[0145] The present application provides a polyanionic precursor comprising a general chemical formula of Na q M m+n M' w P x O y zH2O; optionally, the polyanionic precursor complies with the above chemical formula;

[0146] Wherein, M is one or more of Fe, Ni, Co, and Mn; M' is one or more of transition metal elements other than M, Mg, Ca, Sr, Al, and; m represents M 2+ The content of M 3+ The content of q, m, n, w, x, and y is selected according to the valence state of M' to maintain charge balance in the chemical formula.

[0147] In certain optional embodiments, the target product of the above-mentioned polyanionic precursor provided in the present application is a phosphate pyrophosphate type positive electrode material, such as the common sodium iron phosphate pyrophosphate, also known as: sodium iron pyrophosphate, whose chemical formula is: Na4Fe3(PO4)2(P2O7); similarly, when iron is replaced by nickel, cobalt or manganese, it can also be sodium nickel phosphate pyrophosphate, sodium cobalt phosphate pyrophosphate, and sodium manganese phosphate pyrophosphate. This type of positive electrode material usually also contains carbon materials to improve its conductivity. The four elements of iron, nickel, cobalt, and manganese are adjacent in position in the periodic table, have similar chemical properties, and have valence states of +2 and +3 at the same time. They can all be used in phosphate pyrophosphate type positive electrode materials. Therefore, the polyanionic precursor materials of the present application use iron, nickel, cobalt, and manganese as the main metal elements to obtain the corresponding target positive electrode materials.

[0148] In the above general formula, compared with the main metal element M, the content of M' is very low. M' can be understood as a doping element. In some embodiments, the introduction of doping elements is a commonly used technical means in the field of positive electrode materials, and doping will improve the performance of certain aspects of the positive electrode material. Since the content of the doping element M' is very low, it will not have a major impact on the structure of the target positive electrode material, and the target positive electrode material can still be formed through the precursor. Therefore, the term "sodium phosphate pyrophosphate" is used in this application to represent a compound containing phosphate, pyrophosphate, sodium and other non-sodium metals, wherein the non-sodium metal is the main metal element M and the optional doping element M'.

[0149] To simplify the description, the polyanionic precursor of the present application is represented by the above chemical formula. It is understood that in some embodiments, hydrogen may be present in the phosphate and pyrophosphate groups, and therefore, in some embodiments, the above formula still contains hydrogen in addition to the water of crystallization.

[0150] In certain embodiments, P x O y Mainly represents phosphate and pyrophosphate. In some embodiments, phosphate and pyrophosphate include hydrogen-containing situations, that is, phosphate or pyrophosphate may contain one or more hydrogens, including monohydrogen phosphate, dihydrogen phosphate, monohydrogen pyrophosphate, dihydrogen pyrophosphate, trihydrogen pyrophosphate, etc.

[0151] The above general formula is defined by the relative ratios of the elements within it. In certain embodiments, the molar number of a particular element may be expressed as an integer for ease of presentation, such as m + n = 1 for the molar number of element M. Alternatively, the sum of the molar numbers of multiple elements may be expressed as an integer, such as m + n + w = ​​1 for the sum of the molar numbers of elements M and M'.

[0152] This application uses infrared to qualitatively test the content of phosphate and pyrophosphate and finds that 750cm -1The signal of a characteristic peak (POP) of pyrophosphate at the position around is weak and difficult to characterize quantitatively. The method for quantitative testing of pyrophosphate in this application, because the precursor is insoluble in water, needs to be dissolved with acid before testing, and pyrophosphate will be partially converted into phosphate under acidic conditions. Therefore, the pyrophosphate obtained by this method can represent the lower limit of the pyrophosphate content in the polyanionic precursor.

[0153] In the above general formula, the content of crystalline water can be measured by thermogravimetric analysis. In certain embodiments, the temperature at which the crystalline water of the precursor is completely dehydrated is about 400°C.

[0154] In the above general formula, the oxygen content, excluding crystal water, is calculated by valence balancing.

[0155] The elements in the above general formula include Na, M, M', P, H, and O, and the remaining elements can be considered as miscellaneous elements. Most of the miscellaneous elements are harmful elements. For example, due to the limitations of the preparation process, there are some impurities such as S and N (usually due to the use of raw materials containing sulfates, nitrates, and ammonium salts). These impurities will cause harmful gases to be generated when the precursor is sintered into the positive electrode material. Therefore, the lower the content of these elements, the better. Non-harmful elements, such as carbon, can also be present among the miscellaneous elements.

[0156] In the above general formula, q represents the Na content. After the precursor obtained in the experiment was washed with water many times, the Na content was still relatively high. It can be seen that this part of Na is insoluble. The presence of this part of Na can reduce the amount of sodium source added when the precursor is sintered into a positive electrode material.

[0157] M 2+ Represents a divalent element M, M 3+ represents a trivalent element M;

[0158] M 2+ The proportion is small. Optionally, m / (m+n) can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 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 or any value between 0 and 0.35; when m / (m+n)=0, that is, m=0, it means that M is not included 2+ ;

[0159] The proportion of M' is small. Optionally, w / (m+n) can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, or any value between 0 and 0.1. When w / (m+n)=0, that is, w=0, it means that the chemical formula does not contain the element M'.

[0160] The total molar amount of M and M' and the total molar amount of phosphorus need to be maintained at about 3:4 to obtain the target positive electrode material product. Without considering doping, in some embodiments, the target positive electrode material can be Na4M3(PO4)2P2O7. Generally, the closer the molar ratio of the precursor material metal M to P is to 3:4, the higher the purity of the positive electrode material Na4M3(PO4)2P2O7 will be.

[0161] Optionally, q / (m+n+w) can be 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, 0.50, 0.51, 0.52, 0.53, 0.54, 0.55, 0.56, 0.57, 0.58, 0.59, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70 or any value between 0.32 and 0.70;

[0162] Optionally, (m+n+w) / x can be 0.68, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80 or any value between 0.68 and 0.80; z / (m+n+w) can be 0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10 or any value between 0 and 10; z represents the amount of crystalline water, and z=0 indicates that no crystalline water is present;

[0163] In the prior art, a sodium source, a carbon source, an iron source, and a phosphorus source are typically blended in liquid or solid phases and then sintered. The resulting mixture is considered a precursor. The polyanionic precursor of the present application primarily provides a phosphorus source and a non-sodium metal source for the target cathode material, meaning that a sodium source and a carbon source still need to be added during the sintering of the cathode material. However, since the precursor of the present application already contains some Na, the amount of sodium source required during the sintering of the cathode material is reduced.

[0164] In an optional embodiment, the polyanionic precursor satisfies one or more of the following conditions:

[0165] (1) M is Fe and Mn;

[0166] (2) The transition metal elements other than M include Ti, V, Cr, Zr, Nb, W, Cr, Cu, Zn, Mo, Sc, and Y;

[0167] (3)0.40≤q / (m+n+w)≤0.65;

[0168] Optionally, q / (m+n+w) can be 0.40, 0.41, 0.42, 0.43, 0.44, 0.45, 0.46, 0.47, 0.48, 0.49, 0.50, 0.51, 0.52, 0.53, 0.54, 0.55, 0.56, 0.57, 0.58, 0.59, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65 or any value between 0.40 and 0.65;

[0169] (4)0.26≤q / x≤0.60;

[0170] Optionally, q / x can be 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, 0.50, 0.51, 0.52, 0.53, 0.54, 0.55, 0.56, 0.57, 0.58, 0.59, 0.60 or any value between 0.26 and 0.60;

[0171] (5) 0 ≤ m / (m+n) ≤ 0.33; or, 0 ≤ m / (m+n) ≤ 0.30; or, 0 ≤ m / (m+n) ≤ 0.26;

[0172] Optionally, m / (m+n) can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 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 or any value between 0 and 0.33;

[0173] (6)0≤w / (m+n)≤0.05;

[0174] Optionally, w / (m+n) can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, or any value between 0 and 0.05;

[0175] (7)0.71≤(m+n+w) / x≤0.77;

[0176] Optionally, (m+n+w) / x may be 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, or any value between 0.73 and 0.77;

[0177] (8) According to the charge balance, when the valence of M' is +α, without considering the influence of other elements, q+2m+3n+αw+5x=2y;

[0178] The valence state of the doping element M' is +α. Among common doping metal elements, 1≤α≤5;

[0179] Optionally, α may be 1, 2, 3, 4 or 5; optionally, 2≤α≤4;

[0180] (9) 0≤z / (m+n+w)≤6; optionally, 0≤z / (m+n+w)≤3;

[0181] Optionally, z / (m+n+w) can be 0, 1, 2, 3, 4, 5, 6, or any value between 0 and 6;

[0182] (10) The polyanionic precursor contains phosphate and / or pyrophosphate; optionally, the P content in the pyrophosphate accounts for more than 10% of the total P content in the polyanionic precursor;

[0183] It should be noted that if acid is added during the reaction, at least part of the pyrophosphate will be converted into phosphate, so the precursor will contain both phosphate and pyrophosphate.

[0184] (11) In the polyanionic precursor, the content of Na is 4 wt%-10 wt%;

[0185] Optionally, in the polyanionic precursor, the content of Na may be 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt% or any value between 4wt% and 10wt%;

[0186] (12) In the polyanionic precursor, the content of P is 15 wt%-25 wt%;

[0187] Optionally, in the polyanionic precursor, the content of P may be 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, 20wt%, 21wt%, 22wt%, 23wt%, 24wt%, 25wt% or any value between 15wt% and 25wt%;

[0188] (13) In the polyanionic precursor, the total content of M and M' is 20 wt%-32 wt%;

[0189] Optionally, in the polyanionic precursor, the total content of M and M' can be 20wt%, 21wt%, 22wt%, 23wt%, 24wt%, 25wt%, 26wt%, 27wt%, 28wt%, 29wt%, 30wt%, 31wt%, 32wt% or any value between 20wt% and 32wt%;

[0190] (14) The content of S in the polyanionic precursor is less than 0.5 wt%;

[0191] Optionally, in the polyanionic precursor, the content of S may be 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.49 wt% or any value less than 0.5 wt%;

[0192] (15) The total content of S and N in the polyanionic precursor is less than 0.8 wt%;

[0193] The S and N impurities in the polyanionic precursor are often due to the presence of sulfate and nitrate in the raw materials. The polyanionic precursor in the present application is insoluble in water, while sulfate and nitrate are soluble in water. Therefore, the S and N impurities can be easily removed by solid-liquid separation to achieve a lower content.

[0194] Optionally, in the polyanionic precursor, the total content of S and N can be 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt% or any value less than 0.8 wt%;

[0195] (16) In the polyanionic precursor, the total content of S, N and C is less than 1.0 wt%;

[0196] Optionally, in the polyanionic precursor, the total content of S, N and C can be 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt% or any value less than 1.0 wt%;

[0197] (17) The content of heteroelements in the polyanionic precursor is less than 3.0 wt %; alternatively, the content of heteroelements is less than 1.5 wt %;

[0198] Optionally, the total content of heteroelements in the polyanionic precursor may be 1.0 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt% or any value less than 3.0 wt%;

[0199] (18) In the polyanionic precursor, n(S):n(M+M')≤0.1, and optionally n(S):n(M+M')≤0.06;

[0200] Optionally, in the polyanionic precursor, n(S):n(M+M') may be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or any value less than or equal to 0.1;

[0201] (19) In the polyanionic precursor, n(S+N):n(M+M')≤0.1, and optionally n(S+N):n(M+M')≤0.06;

[0202] Optionally, in the polyanionic precursor, n(S+N):n(M+M') may be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or any value less than or equal to 0.1;

[0203] (20) In the polyanionic precursor, n(S+N+C):n(P)≤0.1, and optionally n(S+N+C):n(P)≤0.06;

[0204] Optionally, in the polyanionic precursor, n(S+N+C):n(P) may be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or any value less than or equal to 0.1;

[0205] (21) The polyanionic precursor is in an amorphous state, and XRD testing shows that the polyanionic precursor has poor crystallinity.

[0206] In an optional embodiment, the polyanionic precursor satisfies one or more of the following conditions:

[0207] (22) The tap density TD of the polyanionic precursor is 0.9-1.4 g / cm 3 ;

[0208] Optionally, the tap density TD of the polyanionic precursor may be 0.9 g / cm 3 , 1.0g / cm 3 , 1.1g / cm 3 , 1.2g / cm 3 , 1.3g / cm 3 , 1.4g / cm 3 or 0.9-1.4g / cm 3 Any value between

[0209] (23) The BET of the polyanionic precursor is 5-25m 2 / g;

[0210] Optionally, the BET of the polyanionic precursor can be 5m 2 / g、10m 2 / g、15m 2 / g, 20m 2 / g, 25m 2 / g or 5-25m 2 Any value between / g;

[0211] (24) The average particle size of the primary particles of the polyanionic precursor is 50-200 nm;

[0212] Optionally, the average particle size of the primary particles of the polyanionic precursor may be 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm or any value between 50 and 200 nm;

[0213] (25) The average particle size D50 of the secondary particles of the polyanionic precursor satisfies the following: 1 μm ≤ D50 ≤ 10 μm;

[0214] Optionally, the average particle size D50 of the secondary particles of the polyanionic precursor may be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm or any value between 1 and 10 μm;

[0215] (26) The particle size distribution of the polyanionic precursor satisfies the following requirements: D10≤1 μm, 1 μm≤D50≤10 μm, D90≤50 μm;

[0216] Optionally, the polyanionic precursor D10 can be 0.1μm, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm or any value less than or equal to 1μm, and D90 can be 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm or any value less than or equal to 50μm.

[0217] (27) The primary particles of the polyanionic precursor are spherical or quasi-spherical;

[0218] (28) In the XRD pattern of the polyanionic precursor, within the test range of 20°≤2θ≤70°, the peak position of the highest peak is between 26° and 32°;

[0219] Optionally, in the XRD pattern of the polyanionic precursor, within the test range of 20°≤2θ≤70°, the peak position of the highest peak may be 26°, 27°, 28°, 29°, 30°, 31°, 32°, or any position between 26° and 32°;

[0220] (29) The polyanionic precursor is poorly soluble in water.

[0221] As the same inventive concept, the present application also provides a polyanionic precursor containing a chemical formula of Na q M m+n M' w (PO4) e (P2O7) f · Substances containing zH2O;

[0222] Wherein, M is one or more of Fe, Ni, Co, and Mn; M' is one or more of transition metal elements other than M, Mg, Ca, Sr, and Al; m represents M 2+ The content of M 3+ The content of q, m, n, w, e, and f is selected according to the valence state of M' to maintain charge balance in the chemical formula.

[0223] Optionally, m / (m+n) can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 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 or any value between 0 and 0.35; when m / (m+n)=0, that is, m=0, it means that M is not contained 2+; w / (m+n) can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10 or any value between 0 and 0.1; when w / (m+n)=0, that is, w=0, it means that the chemical formula does not contain element M'; q / (m+n+w) can be 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, 0.50, 0.51, 0.52, 0.53, 0.54, 0.55, 0.56, 0.57, 0 0.58, 0.59, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70 or any value between 0.32 and 0.70; (m+n+w) / (e+2f) can be 0.68, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80 or any value between 0.68 and 0.80; e / (e+2f) can be 0, 0.01, 0.02, 0.03, 0.4, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12 2. 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, 0.3 7, 0.38, 0.39, 0.40, 0.41, 0.42, 0.43, 0.44, 0.45, 0.46, 0.47, 0.48, 0.49, 0.50, 0.51, 0.52, 0.53, 0.54, 0.55, 0.56, 0.57, 0.58, 0.59, 0.60, 0.61, 0.6 2, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 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 or any value between 0 and 0.90, when e / (e+2f)=0, that is, e=0, it means that there is no phosphate group; 2f / (e+2f) can be 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, 0.50, 0.51, 0.52, 0.53, 0.54, 0.55, 0.56, 0.57, 0.58, 0.59, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 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, 0.97, 0.98, 0.99, 1 or any value between 0.1-1; z / (m+n+w) can be 0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10 or any value between 0-10; z represents the amount of crystalline water, and when z=0, it means that there is no crystalline water.

[0224] Optionally, the polyanionic precursor satisfies one or more of the following conditions:

[0225] (1) M is Fe and Mn;

[0226] (2) The transition metal elements other than M include Ti, V, Cr, Zr, Nb, W, Cr, Cu, Zn, Mo, Sc, and Y;

[0227] (3)0.40≤q / (m+n+w)≤0.65;

[0228] Optionally, q / (m+n+w) can be 0.40, 0.41, 0.42, 0.43, 0.44, 0.45, 0.46, 0.47, 0.48, 0.49, 0.50, 0.51, 0.52, 0.53, 0.54, 0.55, 0.56, 0.57, 0.58, 0.59, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65 or any value between 0.40 and 0.65;

[0229] (4)0.26≤q / (e+2f)≤0.60;

[0230] Optionally, q / (e+2f) can be 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, 0.50, 0.51, 0.52, 0.53, 0.54, 0.55, 0.56, 0.57, 0.58, 0.59, 0.60 or any value between 0.26 and 0.60;

[0231] (5) 0 ≤ m / (m+n) ≤ 0.33; or, 0 ≤ m / (m+n) ≤ 0.30; or, 0 ≤ m / (m+n) ≤ 0.26;

[0232] Optionally, m / (m+n) can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 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 or any value between 0 and 0.33;

[0233] (6)0≤w / (m+n)≤0.05;

[0234] Optionally, w / (m+n) can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, or any value between 0 and 0.05;

[0235] (7)0.71≤(m+n+w) / (e+2f)≤0.77;

[0236] Optionally, (m+n+w) / (e+2f) may be 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, or any value between 0.73 and 0.77;

[0237] (8) The valence of M' is +α, q+2m+3n+αw+5(e+2f)=2(4e+7f);

[0238] (9) The valence of M' is +α, 1≤α≤5; or, 2≤α≤4;

[0239] Optionally, α can be 1, 2, 3, 4, or 5;

[0240] (10) 0≤z / (m+n+w)≤6; or, 0≤z / (m+n+w)≤3;

[0241] Optionally, z / (m+n+w) can be 0, 1, 2, 3, 4, 5, 6, or any value between 0 and 6;

[0242] (11) The polyanionic precursor contains phosphate and / or pyrophosphate;

[0243] (12) The polyanionic precursor contains pyrophosphate, and the P content in the pyrophosphate accounts for more than 10 wt% of the total P content in the polyanionic precursor;

[0244] (13) The content of Na in the polyanionic precursor is 4 wt%-10 wt%;

[0245] Optionally, in the polyanionic precursor, the content of Na may be 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt% or any value between 4wt% and 10wt%;

[0246] (14) In the polyanionic precursor, the content of P is 15 wt%-25 wt%;

[0247] Optionally, in the polyanionic precursor, the content of P may be 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, 20wt%, 21wt%, 22wt%, 23wt%, 24wt%, 25wt% or any value between 15wt% and 25wt%;

[0248] (15) In the polyanionic precursor, the total content of M and M' is 20 wt%-32 wt%;

[0249] Optionally, in the polyanionic precursor, the total content of M and M' can be 20wt%, 21wt%, 22wt%, 23wt%, 24wt%, 25wt%, 26wt%, 27wt%, 28wt%, 29wt%, 30wt%, 31wt%, 32wt% or any value between 20wt% and 32wt%;

[0250] (16) In the polyanionic precursor, the content of S is less than 0.5 wt%;

[0251] Optionally, in the polyanionic precursor, the content of S may be 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.49 wt% or any value less than 0.5 wt%;

[0252] (17) In the polyanionic precursor, the total content of S and N is less than 0.8 wt%;

[0253] Optionally, in the polyanionic precursor, the total content of S and N can be 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt% or any value less than 0.8 wt%;

[0254] (18) In the polyanionic precursor, the total content of S, N and C is less than 1.0 wt%;

[0255] Optionally, in the polyanionic precursor, the total content of S, N and C can be 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt% or any value less than 1.0 wt%;

[0256] (19) The content of heteroelements in the polyanionic precursor is less than 3.0 wt %; or, the content of heteroelements is less than 1.5 wt %;

[0257] Optionally, the total content of heteroelements in the polyanionic precursor may be 1.0 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt% or any value less than 3.0 wt%;

[0258] (20) In the polyanionic precursor, n(S):n(M+M')≤0.1, or n(S):n(M+M')≤0.06;

[0259] Optionally, in the polyanionic precursor, n(S):n(M+M') may be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or any value less than or equal to 0.1;

[0260] (21) In the polyanionic precursor, n(S+N):n(M+M')≤0.1, or n(S+N):n(M+M')≤0.06;

[0261] Optionally, in the polyanionic precursor, n(S+N):n(M+M') may be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or any value less than or equal to 0.1;

[0262] (22) In the polyanionic precursor, n(S+N+C):n(P)≤0.1, or n(S+N+C):n(P)≤0.06;

[0263] Optionally, in the polyanionic precursor, n(S+N+C):n(P) may be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or any value less than or equal to 0.1;

[0264] (23) The polyanionic precursor is in an amorphous state;

[0265] (24) The tap density TD of the polyanionic precursor is 0.9-1.4 g / cm 3 ;

[0266] Optionally, the tap density TD of the polyanionic precursor may be 0.9 g / cm 3 , 1.0g / cm 3 , 1.1g / cm 3 , 1.2g / cm 3 , 1.3g / cm 3 , 1.4g / cm 3 or 0.9-1.4g / cm 3 Any value between

[0267] (25) The BET of the polyanionic precursor is 5-25m 2 / g;

[0268] Optionally, the BET of the polyanionic precursor can be 5m 2 / g、10m 2 / g、15m 2 / g, 20m 2 / g, 25m 2 / g or 5-25m 2 Any value between / g;

[0269] (26) The average particle size of the primary particles of the polyanionic precursor is 50-200 nm;

[0270] Optionally, the average particle size of the primary particles of the polyanionic precursor may be 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm or any value between 50 and 200 nm;

[0271] (27) The average particle size D50 of the secondary particles of the polyanionic precursor satisfies the following: 1 μm ≤ D50 ≤ 10 μm;

[0272] Optionally, the average particle size D50 of the secondary particles of the polyanionic precursor may be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm or any value between 1 and 10 μm;

[0273] (28) The particle size distribution of the polyanionic precursor satisfies the following requirements: D10≤1 μm, 1 μm≤D50≤10 μm, D90≤50 μm;

[0274] Optionally, the polyanionic precursor D10 can be 0.1μm, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm or any value less than or equal to 1μm, and D90 can be 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm or any value less than or equal to 50μm.

[0275] (29) The primary particles of the polyanionic precursor are spherical or quasi-spherical;

[0276] (30) In the XRD pattern of the polyanionic precursor, within the test range of 20°≤2θ≤70°, the peak position of the highest peak is between 26° and 32°;

[0277] Optionally, in the XRD pattern of the polyanionic precursor, within the test range of 20°≤2θ≤70°, the peak position of the highest peak may be 26°, 27°, 28°, 29°, 30°, 31°, 32° or any position between 26° and 32°;

[0278] (31) The polyanionic precursor is poorly soluble in water;

[0279] (32) The polyanionic precursor conforms to the chemical formula Na q M m+n M' w (PO4) e (P2O7) f ·zH2O.

[0280] The present application also provides a method for preparing a polyanionic precursor, comprising the following steps:

[0281] Step A: Add M 2+ A metal salt and a first phosphorus source containing pyrophosphate are mixed to obtain a mixed solution, and a first reaction is performed to obtain a mixed solution containing a pyrophosphate salt of a divalent metal M;

[0282] Step B: adding an oxidant and a second phosphorus source to a mixed solution of pyrophosphate containing a divalent metal M to carry out a second reaction, separating the solid and the liquid after the second reaction, and drying the separated solid to obtain the polyanionic precursor; wherein the first phosphorus source and / or the second phosphorus source contain sodium ions.

[0283] In an optional embodiment, the preparation method of the polyanionic precursor satisfies one or more of the following conditions:

[0284] (1) The M-containing 2+ The metal salt includes one or more of a soluble divalent iron salt, a soluble divalent manganese salt, a soluble divalent nickel salt, and a soluble divalent cobalt salt; 2+ The metal salt is one or more of a soluble divalent iron salt, a soluble divalent manganese salt, a soluble divalent nickel salt, and a soluble divalent cobalt salt;

[0285] (2) The M-containing 2+ The metal salt includes one or more of sulfate, nitrate and chloride;

[0286] (3) The M-containing 2+ The metal salt also contains a soluble salt of metal M';

[0287] (4) the first phosphorus source and / or the second phosphorus source comprises sodium pyrophosphate;

[0288] (5) The temperature of the first reaction is 50-80° C., and the time of the first reaction is 1-10 hours;

[0289] Optionally, the temperature of the first reaction may be 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C or any value between 50-80°C, and the time of the first reaction may be 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h or any value between 1-10h;

[0290] (6) The oxidant is hydrogen peroxide;

[0291] (7) the molar amount of phosphorus in the pyrophosphate ion accounts for not less than 70% of the total molar amount of phosphorus in the first phosphorus source and the second phosphorus source;

[0292] Optionally, the ratio of the molar amount of phosphorus in the pyrophosphate to the total molar amount of phosphorus in the first phosphorus source and the second phosphorus source can be 70 mol%, 75 mol%, 80 mol%, 85 mol%, 90 mol%, 95 mol% or any value not less than 70%;

[0293] (8) introducing an oxygen-containing gas during the second reaction;

[0294] (9) The temperature of the second reaction is 55-85°C, and the time of the second reaction is 1-6 hours; optionally, the temperature of the second reaction can be 55, 60, 65°C, 70°C, 75°C, 80°C, 85°C, or any value between 55-85°C, and the time of the second reaction can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, or any value between 1-6 hours;

[0295] (10) After the second reaction, aging is performed for 5-20 hours;

[0296] Optionally, the aging time can be 5 h, 10 h, 15 h, 20 h, or any value between 5 and 20 h;

[0297] (11) The drying temperature is 80-120°C;

[0298] Optionally, the drying temperature may be 80°C, 90°C, 100°C, 110°C, 120°C or any value between 80-120°C.

[0299] (12) The molar ratio of phosphorus in the first phosphorus source to that in the second phosphorus source is 2.5-3.6:1.

[0300] Optionally, the molar ratio of phosphorus in the first phosphorus source and the second phosphorus source can be 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1, 3.0:1, 3.1:1, 3.2:1, 3.3:1, 3.4:1, 3.5:1, 3.6:1 or any value between 2.5 and 3.6:1.

[0301] (13) The raw material does not contain a carbon source.

[0302] The target product of this preparation method is the polyanionic precursor, which does not contain carbon, so no carbon source is required in the selection of raw materials. Therefore, even if a carbon-containing substance (such as carbonate) is added to the raw materials, the carbon-containing substance cannot be considered a carbon source.

[0303] As the same inventive concept, the present application also provides a polyanion sodium ion battery positive electrode material, the raw materials of which include a polyanion precursor, a sodium source and a carbon source.

[0304] In certain embodiments, the polyanionic precursor is the polyanionic precursor defined by the above chemical formula, or the polyanionic precursor obtained by the above method for preparing the polyanionic precursor.

[0305] In some embodiments, the polyanion sodium ion battery positive electrode material obtained has a composition of Na4M j M' kA complex of (PO4)2P2O7 and carbon;

[0306] Wherein, M is one or more of Fe, Ni, Co, and Mn; M' is one or more of transition metal elements other than M, Mg, Ca, Sr, and Al; 0≤k / j≤0.1, 2.8≤j+k≤3.2;

[0307] It is understandable that the general formula is Na4M j M' k The molar ratios of Na, phosphate, and pyrophosphate in (PO4)2P2O7 may fluctuate to some extent, such as the molar ratio of Na to P may deviate from 1:1. Therefore, this general formula can be more accurately understood as sodium metal phosphate pyrophosphate.

[0308] Optionally, k / j can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1 or any value between 0 and 0.1, and j+k can be 2.8, 2.9, 3.0, 3.1, 3.2 or any value between 2.8 and 3.2.

[0309] The polyanion sodium ion battery positive electrode material meets one or more of the following conditions:

[0310] (1) The compaction density of the polyanion sodium ion battery positive electrode material is 1.8-2.4 g / cm 3 ;

[0311] Optionally, the compaction density of the polyanion sodium ion battery positive electrode material can be 1.8 g / cm 3 , 1.9g / cm 3 , 2.0g / cm 3 , 2.1g / cm 3 , 2.2g / cm 3 , 2.3g / cm 3 , 2.4g / cm 3 or 1.8-2.4g / cm 3 Any value between

[0312] (2) The specific surface area of ​​the polyanion sodium ion battery positive electrode material is 5-25m 2 / g;

[0313] Optionally, the specific surface area of ​​the polyanion sodium ion battery positive electrode material can be 5m 2 / g、10m 2 / g、15m 2 / g, 20m 2 / g, 25m 2 / g or 5-25m 2 Any value between / g;

[0314] (3) The average particle size of the primary particles of the polyanion sodium ion battery positive electrode material is 100-400 nm;

[0315] Optionally, the average particle size of the primary particles of the polyanion sodium ion battery positive electrode material may be 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm or any value between 100 and 400 nm;

[0316] (4) The average particle size D50 of the secondary particles of the polyanion sodium ion battery positive electrode material is 1-5 μm.

[0317] Optionally, the average particle size D50 of the secondary particles of the sodium ion battery positive electrode material can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm or any value between 1-5 μm.

[0318] As the same inventive concept, the present application also provides a polyanionic sodium ion battery positive electrode material, wherein the component of the polyanionic sodium ion battery positive electrode material is a complex of sodium phosphate pyrophosphate metal salt and carbon; in the sodium phosphate pyrophosphate metal salt, the metal other than sodium includes M and M' which is not necessarily present; wherein M is one or more of Fe, Ni, Co, and Mn; and M' is selected from one or more of transition metal elements other than M, Mg, Ca, Sr, and Al; the polyanionic sodium ion battery positive electrode material satisfies one or more of the following conditions:

[0319] (1) The S content of the polyanionic sodium ion battery positive electrode material is ≤0.08wt%; optionally, the S content is ≤0.07wt%, 0.06wt%, 0.05wt%, 0.04wt%, 0.03wt%, 0.02wt%, 0.01wt% or 0.005wt%; in particular, when the raw material of the polyanionic sodium ion battery positive electrode material includes a S-containing compound, the S content of the positive electrode material can still be maintained within the above range;

[0320] (2) The N content of the polyanionic sodium ion battery positive electrode material is ≤0.08wt%; optionally, the N content is ≤0.07wt%, 0.06wt%, 0.05wt%, 0.04wt%, 0.03wt%, 0.02wt%, 0.01wt% or 0.005wt%; in particular, when the raw material of the polyanionic sodium ion battery positive electrode material includes a N-containing compound, the N content of the positive electrode material can still be maintained within the above range.

[0321] In certain embodiments, the present application further provides a method for preparing the polyanion sodium ion battery positive electrode material, comprising:

[0322] Mixing raw materials including the polyanion precursor, a carbon source, and a sodium source, crushing, drying, and then sintering to obtain the polyanion sodium ion battery positive electrode material;

[0323] Typically, sintering is performed under a protective atmosphere, such as a nitrogen atmosphere.

[0324] In an optional embodiment, the preparation method of the polyanion sodium ion battery positive electrode material meets one or more of the following conditions:

[0325] (1) The carbon source is one or more of sucrose, glucose, crystal sugar, cellulose, phenolic resin, polyethylene glycol, polyvinyl pyrrolidone, starch, polyvinyl alcohol, ionic cellulose gum carbon source, and inorganic carbon source;

[0326] (2) the sodium source comprises one or more of sodium carbonate, sodium bicarbonate, sodium acetate, and sodium oxalate;

[0327] (3) The pulverization is grinding or sand milling;

[0328] (4) The sintering temperature is 500-600°C, and the sintering time is 6-30h.

[0329] Optionally, the sintering temperature can be 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, 560℃, 570℃, 580℃, 590℃, 600℃ or any value between 500-600℃, and the sintering time can be 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, 24h, 26h, 28h, 30h or any value between 6-30h.

[0330] The present application also provides a sodium ion battery, comprising the polyanion sodium ion battery positive electrode material.

[0331] The present application also provides an electrical device, including the sodium ion battery.

[0332] The embodiments of the present application will be described in detail below in conjunction with specific examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present application and should not be considered as limiting the scope of the present application. In the examples, if specific conditions are not specified, the conditions are carried out according to conventional conditions or manufacturer recommendations. The reagents or instruments used are not specified by the manufacturer and are conventional products that can be purchased commercially.

[0333] The amount of carbon source (such as glucose) is calculated based on the total mass of the precursor and the sodium source (such as sodium carbonate). For example, 10% glucose in Example 1 means that the added mass of glucose is 10% of the total mass of the precursor and sodium carbonate.

[0334] Example 1

[0335] This embodiment provides a polyanionic precursor, and the preparation method thereof is as follows:

[0336] 3 mol of ferrous sulfate and 1.5 mol of sodium pyrophosphate were mixed evenly in a 5L reactor, the reaction temperature was controlled at 70°C, and the reaction was carried out for 4 hours. Then, 450 ml of hydrogen peroxide and 0.5 mol of sodium pyrophosphate were added to the reactor, the temperature was maintained at 70°C for 2 hours, and the mixture was aged for 12 hours. The precipitate was filtered and washed three times. The collected filter cake was dried at 100°C for 16 hours to prepare a precursor with an iron-to-phosphorus ratio of 0.738 (molar ratio).

[0337] This embodiment also provides a sodium ion battery positive electrode material, and its preparation method is as follows:

[0338] 1 mol of the precursor was mixed with 2 mol of sodium carbonate, 10% of glucose [wherein, 10% of glucose means that the amount of glucose added accounts for 10% of the total mass of the raw materials (precursor + sodium carbonate), the same below], and 5 L of acetone, and then ball milled for 12 hours, vacuum dried for 10 hours, and then sintered in an atmosphere furnace at 540°C for 12 hours in a nitrogen atmosphere to obtain the target product, sodium ferric pyrophosphate.

[0339] Example 2

[0340] This embodiment provides a polyanionic precursor, and the preparation method thereof is as follows:

[0341] 3 mol of ferrous sulfate and 1.5 mol of sodium pyrophosphate were mixed evenly in a 5L reactor, the reaction temperature was controlled at 75°C, and the reaction was carried out for 6 hours. Then, 300 ml of hydrogen peroxide and 0.5 mol of sodium pyrophosphate were added to the reactor, the temperature was maintained at 75°C for 3 hours, and the mixture was aged for 12 hours. The precipitate was filtered and washed three times. The collected filter cake was dried at 100°C for 16 hours to prepare a precursor with an iron-to-phosphorus ratio of 0.763 (molar ratio).

[0342] FIG1 is a SEM image of the precursor prepared in Example 2. As can be seen from FIG1 , the primary particles of the precursor are tightly packed together, thereby having a higher tap density.

[0343] Figure 2a shows the XRD pattern of the precursor prepared in Example 2, which is amorphous. Figure 2b shows the XRD pattern of the precursor prepared in Example 2 after calcination at 500°C (upper curve) and 600°C (lower curve) for 12 hours, respectively. After calcination at 600°C, a sodium-containing phase appears, confirming that the precursor contains sodium. Figure 2b shows that even after calcination at 500°C, the product still has poor crystallinity and is amorphous.

[0344] This embodiment also provides a sodium ion battery positive electrode material, and its preparation method is as follows:

[0345] 1 mol of the precursor was mixed evenly with 2 mol of sodium carbonate, 12% glucose, and 5 L of ethanol, ball-milled for 12 h, vacuum-dried for 10 h, and then sintered in an atmosphere furnace at 550° C. for 12 h in a nitrogen atmosphere to obtain the target product, sodium ferric pyrophosphate.

[0346] Example 3

[0347] This embodiment provides a polyanionic precursor, and the preparation method thereof is as follows:

[0348] 3 mol of ferrous sulfate and 1.5 mol of sodium pyrophosphate were mixed evenly in a 5L reactor, the reaction temperature was controlled at 80°C, and the reaction was carried out for 8 hours. Then, 400 ml of hydrogen peroxide and 0.5 mol of sodium pyrophosphate were added to the reactor, and the temperature was maintained at 80°C for 3 hours. Air was simultaneously introduced for oxidation and aged for 12 hours. The precipitate was filtered and washed three times. The collected filter cake was dried at 100°C for 16 hours to prepare a precursor with an iron-to-phosphorus ratio of 0.740 (molar ratio).

[0349] This embodiment provides a sodium ion battery positive electrode material, and the preparation method thereof is as follows:

[0350] 1 mol of the precursor was mixed evenly with 2 mol of sodium carbonate, 15% glucose, and 5 L of water, ball-milled for 12 h and sand-milled for 1 h, vacuum-dried for 10 h, and then sintered in an atmosphere furnace at 520° C. for 12 h in a nitrogen atmosphere to obtain the target product, sodium ferric pyrophosphate.

[0351] FIG5 is an XRD pattern of the positive electrode material obtained in Example 3, and XRD shows pure phase Na4Fe3(PO4)2(P2O7).

[0352] Figure 6 is an SEM image of the Na4Fe3(PO4)2(P2O7) cathode material prepared in Example 3. The product inherits the primary particle morphology of the precursor, is spherical and tightly packed together, and is nanometer-sized.

[0353] Example 4

[0354] This embodiment provides a polyanionic precursor, and the preparation method thereof is as follows:

[0355] 3 mol of ferrous sulfate and 1.5 mol of sodium pyrophosphate were mixed evenly in a 5L reactor, the reaction temperature was controlled at 80°C, and the reaction was carried out for 8 hours. Then, 600 ml of hydrogen peroxide and 1 mol of sodium phosphate were added to the reactor, and the temperature was maintained at 80°C for 3 hours. Air was simultaneously introduced for oxidation and aged for 12 hours. The precipitate was filtered and washed three times. The collected filter cake was dried at 100°C for 16 hours to prepare a precursor with an iron-to-phosphorus ratio of 0.746 (molar ratio).

[0356] This embodiment also provides a sodium ion battery positive electrode material, and its preparation method is as follows:

[0357] 1 mol of the precursor was mixed evenly with 2 mol of sodium carbonate, 15% glucose, and 5 L of water, ball-milled for 12 h and sand-milled for 1 h, vacuum-dried for 10 h, and then sintered in an atmosphere furnace at 550° C. for 12 h in a nitrogen atmosphere to obtain the target product, sodium ferric pyrophosphate.

[0358] Example 5

[0359] This embodiment provides a polyanionic precursor, and the preparation method thereof is as follows:

[0360] 3 mol of ferrous sulfate and 1.5 mol of sodium pyrophosphate were mixed evenly in a 5L reactor, the reaction temperature was controlled at 80°C, and the reaction was carried out for 10 hours. Then, 500 ml of hydrogen peroxide and 1 mol of disodium hydrogen phosphate were added to the reactor, and the temperature was maintained at 80°C for 6 hours. Air was simultaneously introduced for oxidation and aged for 12 hours. The precipitate was filtered and washed three times. The collected filter cake was dried at 100°C for 16 hours to prepare a precursor with an iron-to-phosphorus ratio of 0.756 (molar ratio).

[0361] This embodiment also provides a sodium ion battery positive electrode material, and its preparation method is as follows:

[0362] 1 mol of the precursor was mixed evenly with 2 mol of sodium carbonate, 15% glucose, and 5 L of water, sand-milled for 3 h, spray-dried, and then sintered in an atmosphere furnace at 500° C. for 13 h in a nitrogen atmosphere to obtain the target product, sodium ferric pyrophosphate.

[0363] Figure 7 is the infrared test spectrum of the precursor obtained in Example 5. It can be observed that 1050 cm -1 PO2 nearby 2- The characteristic peak of 750cm -1 There is a characteristic peak of POP nearby, 545cm -1 There is a PO nearby 2- The characteristic peaks of

[0364] Example 6

[0365] This embodiment provides a polyanionic precursor, and the preparation method thereof is as follows:

[0366] 3 mol of ferrous nitrate and 1.53 mol of sodium pyrophosphate were mixed evenly in a 5L reactor, the reaction temperature was controlled at 70°C, and the reaction was carried out for 6 hours. Then, 420 ml of hydrogen peroxide and 0.5 mol of sodium pyrophosphate were added to the reactor, and the reaction was carried out at a temperature of 75°C for 3 hours. Air was simultaneously introduced for oxidation and aged for 12 hours. The precipitate was filtered and washed three times. The collected filter cake was dried at 100°C for 16 hours to prepare a precursor with an iron-to-phosphorus ratio of 0.731 (molar ratio).

[0367] This embodiment also provides a sodium ion battery positive electrode material, and its preparation method is as follows:

[0368] 1 mol of the precursor was mixed evenly with 2.0 mol of sodium carbonate, 15% glucose, and 5 L of water, ball-milled for 12 h and sand-milled for 1 h, vacuum-dried for 10 h, and then sintered in an atmosphere furnace at 520° C. for 12 h in a nitrogen atmosphere to obtain the target product, sodium ferric pyrophosphate.

[0369] Example 7

[0370] This embodiment provides a polyanionic precursor, and the preparation method thereof is as follows:

[0371] 3 mol of ferrous nitrate and 1.56 mol of sodium pyrophosphate were mixed evenly in a 5L reactor, the reaction temperature was controlled at 60°C, and the reaction was carried out for 6 hours. Then, 440 ml of hydrogen peroxide and 1 mol of sodium phosphate were added to the reactor, and the reaction was carried out at a temperature of 65°C for 3 hours. Air was simultaneously introduced for oxidation and aged for 12 hours. The precipitate was filtered and washed three times. The collected filter cake was dried at 100°C for 16 hours to prepare a precursor with an iron-to-phosphorus ratio of 0.722 (molar ratio).

[0372] This embodiment also provides a sodium ion battery positive electrode material, and its preparation method is as follows:

[0373] 1 mol of the precursor was mixed evenly with 2.0 mol of sodium carbonate, 15% glucose, and 5 L of water, ball-milled for 12 h and sand-milled for 1 h, vacuum-dried for 10 h, and then sintered in an atmosphere furnace at 520° C. for 12 h in a nitrogen atmosphere to obtain the target product, sodium ferric pyrophosphate.

[0374] Example 8

[0375] This embodiment provides a polyanionic precursor, and the preparation method thereof is as follows:

[0376] 3 mol of ferrous sulfate and 1.50 mol of sodium pyrophosphate were mixed evenly in a 5L reactor, the reaction temperature was controlled at 80°C, and the reaction was carried out for 6 hours. Then, 440 ml of hydrogen peroxide and 0.68 mol of sodium pyrophosphate were added to the reactor, and the reaction was carried out at a temperature of 75°C for 3 hours. Air was simultaneously introduced for oxidation and aged for 12 hours. The precipitate was filtered and washed three times. The collected filter cake was dried at 100°C for 16 hours to prepare a precursor with an iron-phosphorus ratio of 0.694 (molar ratio).

[0377] This embodiment also provides a sodium ion battery positive electrode material, and its preparation method is as follows:

[0378] 1 mol of the precursor was mixed evenly with 2.0 mol of sodium carbonate, 15% glucose, and 5 L of water, ball-milled for 12 h and sand-milled for 1 h, vacuum-dried for 10 h, and then sintered in an atmosphere furnace at 520° C. for 12 h in a nitrogen atmosphere to obtain the target product, sodium ferric pyrophosphate.

[0379] Example 9

[0380] This embodiment provides a polyanionic precursor, and the preparation method thereof is as follows:

[0381] 3 mol of ferrous sulfate and 1.50 mol of sodium pyrophosphate were mixed evenly in a 5L reactor, the reaction temperature was controlled at 80°C, and the reaction was carried out for 6 hours. Then, 440 ml of hydrogen peroxide and 0.40 mol of sodium pyrophosphate were added to the reactor, and the reaction was carried out at a temperature of 75°C for 3 hours. Air was simultaneously introduced for oxidation and aged for 12 hours. The precipitate was filtered and washed three times. The collected filter cake was dried at 100°C for 16 hours to prepare a precursor with an iron-to-phosphorus ratio of 0.790 (molar ratio).

[0382] This embodiment also provides a sodium ion battery positive electrode material, and its preparation method is as follows:

[0383] 1 mol of the precursor was mixed evenly with 2.0 mol of sodium carbonate, 15% glucose, and 5 L of water, ball-milled for 12 h and sand-milled for 1 h, vacuum-dried for 10 h, and then sintered in an atmosphere furnace at 520° C. for 12 h in a nitrogen atmosphere to obtain the target product, sodium ferric pyrophosphate.

[0384] Example 10

[0385] This embodiment provides a polyanionic precursor, and the preparation method thereof is as follows:

[0386] 2.7 mol of ferrous sulfate, 0.3 mol of magnesium sulfate, and 1.53 mol of sodium pyrophosphate were mixed uniformly in a 5L reactor, the reaction temperature was controlled at 80°C, and the reaction was carried out for 6 hours. Then, 400 ml of hydrogen peroxide and 1 mol of sodium phosphate were added to the reactor, and the reaction was carried out at a temperature of 75°C for 3 hours. Air was simultaneously introduced for oxidation, and the mixture was aged for 12 hours. The precipitate was filtered and washed three times. The collected filter cake was dried at 100°C for 16 hours to prepare a precursor with a (M+M') / P ratio of 0.730. Wherein, M=Fe, M'=Mg, and Fe / Mg=91 / 9 (molar ratio).

[0387] This embodiment also provides a sodium ion battery positive electrode material, and its preparation method is as follows:

[0388] 1 mol of the precursor was mixed evenly with 2 mol of sodium carbonate, 15% glucose, and 5 L of water, sand-milled for 3 h, spray-dried, and sintered in an atmosphere furnace at 500° C. for 13 h in a nitrogen atmosphere to obtain the target product, magnesium-doped sodium iron pyrophosphate.

[0389] Example 11

[0390] This embodiment provides a polyanionic precursor, and the preparation method thereof is as follows:

[0391] 2.85 mol of ferrous sulfate, 0.15 mol of copper sulfate, and 1.53 mol of sodium pyrophosphate were mixed uniformly in a 5L reactor, the reaction temperature was controlled at 80°C, and the reaction was carried out for 6 hours. Then, 400 ml of hydrogen peroxide and 0.5 mol of sodium pyrophosphate were added to the reactor and the reaction was carried out at 75°C for 3 hours. Air was introduced for oxidation, and the mixture was aged for 12 hours. The precipitate was filtered and washed three times. The collected filter cake was dried at 100°C for 16 hours to prepare a precursor with a (M+M') / P ratio of 0.733 (molar ratio). wherein M=Fe, M'=Cu, and Fe / Cu=96 / 4 (molar ratio).

[0392] This embodiment also provides a sodium ion battery positive electrode material, and its preparation method is as follows:

[0393] 1 mol of the precursor was mixed evenly with 2 mol of sodium carbonate, 15% glucose, and 5 L of water, sand-milled for 3 h, spray-dried, and sintered in an atmosphere furnace at 500° C. for 13 h in a nitrogen atmosphere to obtain the target product, copper-doped sodium iron pyrophosphate.

[0394] Example 12

[0395] This embodiment provides a polyanionic precursor, and the preparation method thereof is as follows:

[0396] 2.94 mol of ferrous sulfate, 0.06 mol of titanyl sulfate, and 1.53 mol of sodium pyrophosphate were mixed uniformly in a 5L reactor, the reaction temperature was controlled at 80°C, and the reaction was carried out for 6 hours. 400 ml of hydrogen peroxide and 0.5 mol of sodium pyrophosphate were then added to the reactor and the reaction was carried out at 75°C for 3 hours. Air was then introduced for oxidation, and the mixture was aged for 12 hours. The precipitate was filtered and washed three times. The collected filter cake was dried at 100°C for 16 hours to prepare a precursor with a (M+M') / P ratio of 0.735 (molar ratio). M = Fe, M' = Ti, and Fe / Ti = 98 / 2 (molar ratio).

[0397] This embodiment also provides a sodium ion battery positive electrode material, and its preparation method is as follows:

[0398] 1 mol of the precursor was mixed evenly with 2 mol of sodium carbonate, 15% glucose, and 5 L of water, sand-milled for 3 h, spray-dried, and sintered in an atmosphere furnace at 500° C. for 13 h in a nitrogen atmosphere to obtain the target product, titanium-doped sodium iron pyrophosphate.

[0399] Example 13

[0400] This embodiment provides a polyanionic precursor, and the preparation method thereof is as follows:

[0401] 2.7 mol of ferrous sulfate, 0.3 mol of nickel sulfate and 1.53 mol of sodium pyrophosphate were mixed in a 5L reactor, the reaction temperature was controlled at 80°C, and the reaction was carried out for 6 hours. Then, 400 ml of hydrogen peroxide and 1 mol of sodium dihydrogen phosphate were added to the reactor, and the reaction was carried out at a temperature of 75°C for 3 hours. Air was introduced for oxidation, and the mixture was aged for 12 hours. The precipitate was filtered and washed three times. The collected filter cake was dried at 100°C for 16 hours to prepare a precursor with an M / P ratio of 0.740. Fe accounted for 90 mol% of the total M and Ni accounted for 10 mol%.

[0402] Example 14

[0403] This embodiment provides a polyanionic precursor, and the preparation method thereof is as follows:

[0404] 2.7 mol of ferrous sulfate, 0.3 mol of nickel sulfate and 1.52 mol of sodium pyrophosphate were mixed in a 5L reactor, the reaction temperature was controlled at 80°C, and the reaction was carried out for 6 hours. Then, 400 ml of hydrogen peroxide and 0.5 mol of sodium pyrophosphate were added to the reactor and the reaction was carried out at a temperature of 75°C for 3 hours. Air was introduced for oxidation and the reaction was aged for 12 hours. The precipitate was filtered and washed three times. The collected filter cake was dried at 100°C for 16 hours to prepare a precursor with an M / P ratio of 0.747. Fe accounted for 91 mol% of the total M and Ni accounted for 9 mol%.

[0405] Example 15

[0406] This embodiment provides a polyanionic precursor, and the preparation method thereof is as follows:

[0407] 2.7 mol of ferrous sulfate, 0.3 mol of cobalt sulfate, and 1.53 mol of sodium pyrophosphate were mixed uniformly in a 5L reactor, the reaction temperature was controlled at 80°C, and the reaction was carried out for 8 hours. Then, 400 ml of hydrogen peroxide and 1 mol of sodium dihydrogen phosphate were added to the reactor and reacted for 4 hours. Air was introduced for oxidation, and the mixture was aged for 12 hours. The precipitate was filtered and washed three times. The collected filter cake was dried at 100°C for 16 hours to prepare a precursor with an M / P ratio of 0.739. Fe accounted for 92 mol% of the total M and Co accounted for 8 mol%.

[0408] Example 16

[0409] This embodiment provides a polyanionic precursor, and the preparation method thereof is as follows:

[0410] 2.7 mol of ferrous sulfate, 0.3 mol of cobalt sulfate and 1.52 mol of sodium pyrophosphate were mixed in a 5L reactor, the reaction temperature was controlled at 80°C, and the reaction was carried out for 6 hours. Then, 400 ml of hydrogen peroxide and 0.5 mol of sodium pyrophosphate were added to the reactor, and the reaction was carried out at a temperature of 75°C for 3 hours. Air was introduced for oxidation, and the mixture was aged for 12 hours. The precipitate was filtered and washed three times. The collected filter cake was dried at 100°C for 16 hours to prepare a precursor with an M / P ratio of 0.745 (molar ratio). Fe accounted for 92 mol% of the total M and Co accounted for 8 mol%.

[0411] Example 17

[0412] This embodiment provides a polyanionic precursor, and the preparation method thereof is as follows:

[0413] 2.85 mol of ferrous sulfate, 0.15 mol of manganese sulfate and 1.53 mol of sodium pyrophosphate were mixed in a 5L reactor, the reaction temperature was controlled at 80°C, and the reaction was carried out for 6 hours. Then, 400 ml of hydrogen peroxide and 1 mol of sodium phosphate were added to the reactor, and the reaction was carried out at a temperature of 75°C for 3 hours. Air was introduced for oxidation, and the mixture was aged for 12 hours. The precipitate was filtered and washed three times. The collected filter cake was dried at 100°C for 16 hours to prepare a precursor with an M / P ratio of 0.736. Fe accounted for 95 mol% of the total M and Mn accounted for 5 mol%.

[0414] This embodiment also provides a sodium ion battery positive electrode material, and its preparation method is as follows:

[0415] 1 mol of the precursor was mixed evenly with 2 mol of sodium carbonate, 15% glucose, and 5 L of water, sand-milled for 3 h, spray-dried, and then sintered in an atmosphere furnace at 500° C. for 13 h in a nitrogen atmosphere to obtain the target product, sodium ferric pyrophosphate.

[0416] Example 18

[0417] This embodiment provides a polyanionic precursor, and the preparation method thereof is as follows:

[0418] 2.91 mol of ferrous sulfate, 0.09 mol of manganese sulfate, and 1.53 mol of sodium pyrophosphate were mixed in a 5L reactor, the reaction temperature was controlled at 80°C, and the reaction was carried out for 6 hours. 420 ml of hydrogen peroxide and 0.5 mol of sodium pyrophosphate were then added to the reactor and the reaction was carried out at 75°C for 3 hours. Air was then introduced for oxidation, and the mixture was aged for 12 hours. The precipitate was filtered and washed three times. The collected filter cake was dried at 100°C for 16 hours to prepare a precursor with an M / P ratio of 0.734. Fe accounted for 97 mol% of the total M and Mn accounted for 3 mol%.

[0419] This embodiment also provides a sodium ion battery positive electrode material, and its preparation method is as follows:

[0420] 1 mol of the precursor was mixed evenly with 2 mol of sodium carbonate, 15% glucose, and 5 L of water, sand-milled for 3 h, spray-dried, and then sintered in an atmosphere furnace at 500° C. for 13 h in a nitrogen atmosphere to obtain the target product, sodium ferric pyrophosphate.

[0421] Example 19

[0422] This embodiment provides a polyanionic precursor, and the preparation method thereof is as follows:

[0423] 2.7 mol of ferrous sulfate, 0.3 mol of manganese sulfate and 1.50 mol of sodium pyrophosphate were mixed in a 5L reactor, the reaction temperature was controlled at 80°C, and the reaction was carried out for 6 hours. Then, 400 ml of hydrogen peroxide and 0.5 mol of sodium pyrophosphate were added to the reactor and the reaction was carried out at a temperature of 75°C for 3 hours. Air was introduced for oxidation and the reaction was aged for 12 hours. The precipitate was filtered and washed three times. The collected filter cake was dried at 100°C for 16 hours to prepare a precursor with an M / P ratio of 0.743. Fe accounted for 90 mol% of the total M and Mn accounted for 10 mol%.

[0424] Example 20

[0425] This embodiment provides a polyanionic precursor, and the preparation method thereof is as follows:

[0426] 2.7 mol of ferrous sulfate, 0.3 mol of manganese sulfate and 1.50 mol of sodium pyrophosphate were mixed in a 5L reactor, the reaction temperature was controlled at 80°C, and the reaction was carried out for 6 hours. Then, 400 ml of hydrogen peroxide and 1 mol of sodium phosphate were added to the reactor, and the reaction was carried out at a temperature of 75°C for 3 hours. Air was introduced for oxidation, and the mixture was aged for 12 hours. The precipitate was filtered and washed three times. The collected filter cake was dried at 100°C for 16 hours to prepare a precursor with an M / P ratio of 0.741. Fe accounted for 90 mol% of the total M and Mn accounted for 10 mol%.

[0427] Example 21

[0428] This embodiment provides a polyanionic precursor, and the preparation method thereof is as follows:

[0429] 1.5 mol of ferrous sulfate, 1.5 mol of manganese sulfate and 1.50 mol of sodium pyrophosphate were mixed in a 5L reactor, the reaction temperature was controlled at 80°C, and the reaction was carried out for 6 hours. Then, 400 ml of hydrogen peroxide and 0.5 mol of sodium pyrophosphate were added to the reactor and the reaction was carried out at a temperature of 75°C for 3 hours. Air was introduced for oxidation and the reaction was aged for 12 hours. The precipitate was filtered and washed three times. The collected filter cake was dried at 100°C for 16 hours to prepare a precursor with an M / P ratio of 0.751. Fe accounted for 49 mol% of the total M and Mn accounted for 51 mol%.

[0430] Example 22

[0431] This embodiment provides a polyanionic precursor, and the preparation method thereof is as follows:

[0432] 1.5 mol of ferrous sulfate, 1.5 mol of manganese sulfate and 1.52 mol of sodium pyrophosphate were mixed uniformly in a 5L reactor, the reaction temperature was controlled at 80°C, and the reaction was carried out for 6 hours. Then, 400 ml of hydrogen peroxide and 0.5 mol of sodium pyrophosphate were added to the reactor, and the reaction was carried out at a temperature of 75°C for 3 hours. Air was introduced for oxidation, and the mixture was aged for 12 hours. The precipitate was filtered and washed three times. The collected filter cake was dried at 100°C for 16 hours to prepare a precursor with an M / P ratio of 0.746. Fe accounted for 50 mol% of the total M and Mn accounted for 50 mol%.

[0433] Example 23

[0434] This embodiment provides a polyanionic precursor, and the preparation method thereof is as follows:

[0435] 3 mol of manganese sulfate and 1.53 mol of sodium pyrophosphate were uniformly mixed in a 5L reactor, the reaction temperature was controlled at 60°C, and the reaction was carried out for 6 hours. 400 ml of hydrogen peroxide and 1 mol of sodium dihydrogen phosphate were then added to the reactor and the reaction was carried out at 75°C for 3 hours. Air was then introduced for oxidation and the mixture was aged for 12 hours. The precipitate was filtered and washed three times. The collected filter cake was dried at 100°C for 16 hours to prepare a precursor with a Mn / P molar ratio of 0.746. Figure 3 shows the XRD pattern of the precursor prepared in Example 21, which is amorphous.

[0436] Example 24

[0437] This embodiment provides a polyanionic precursor, and the preparation method thereof is as follows:

[0438] 3 mol of manganese sulfate and 1.5 mol of sodium pyrophosphate were mixed evenly in a 5L reactor, the reaction temperature was controlled at 70°C, and the reaction was carried out for 6 hours. Then, 400 ml of hydrogen peroxide and 0.5 mol of sodium pyrophosphate were added to the reactor, and the reaction was carried out at a temperature of 75°C for 3 hours. Air was simultaneously introduced for oxidation and aged for 12 hours. The precipitate was filtered and washed three times. The collected filter cake was dried at 100°C for 16 hours to prepare a precursor with a Mn / P ratio of 0.752 (molar ratio).

[0439] Example 25

[0440] This embodiment provides a polyanionic precursor, and the preparation method thereof is as follows:

[0441] 3 mol of manganese sulfate and 1.53 mol of sodium pyrophosphate were mixed evenly in a 5L reactor, the reaction temperature was controlled at 60°C, and the reaction was carried out for 6 hours. Then, 400 ml of hydrogen peroxide and 1 mol of sodium phosphate were added to the reactor, and the reaction was carried out at a temperature of 75°C for 3 hours. Air was simultaneously introduced for oxidation and aged for 12 hours. The precipitate was filtered and washed three times. The collected filter cake was dried at 100°C for 16 hours to prepare a precursor with a Mn / P ratio of 0.741 (molar ratio).

[0442] Example 26

[0443] This embodiment provides a polyanionic precursor, and the preparation method thereof is as follows:

[0444] 3 mol of manganese sulfate and 1.5 mol of sodium pyrophosphate were mixed evenly in a 5L reactor, the reaction temperature was controlled at 70°C, and the reaction was carried out for 6 hours. Then, 400 ml of hydrogen peroxide and 0.5 mol of sodium pyrophosphate were added to the reactor, and the reaction was carried out at a temperature of 75°C for 3 hours. Air was simultaneously introduced for oxidation and aged for 12 hours. The precipitate was filtered and washed three times. The collected filter cake was dried at 100°C for 16 hours to prepare a precursor with a Mn / P ratio of 0.748 (molar ratio).

[0445] Example 27

[0446] This embodiment provides a polyanionic precursor, and the preparation method thereof is as follows:

[0447] 2.9 mol manganese sulfate, 0.1 mol copper sulfate, and 1.53 mol sodium pyrophosphate were mixed uniformly in a 5L reactor, the reaction temperature was controlled at 60°C, and the reaction was carried out for 6 hours. 400 ml of hydrogen peroxide and 1 mol sodium phosphate were then added to the reactor and the reaction was carried out at 75°C for 3 hours. Air was then introduced for oxidation, and the mixture was aged for 12 hours. The precipitate was filtered and washed three times. The collected filter cake was dried at 100°C for 16 hours to prepare a precursor with a (M+M') / P ratio of 0.745 (molar ratio), wherein M = Mn, M' = Cu, and Mn / Cu = 97 / 3 (molar ratio).

[0448] Example 28

[0449] This embodiment provides a polyanionic precursor, and the preparation method thereof is as follows:

[0450] 2.8 mol manganese sulfate, 0.2 mol aluminum sulfate, and 1.53 mol sodium pyrophosphate were mixed uniformly in a 5L reactor, the reaction temperature was controlled at 70°C, and the reaction was carried out for 6 hours. 400 ml of hydrogen peroxide and 0.5 mol sodium pyrophosphate were then added to the reactor and the reaction was carried out at 75°C for 3 hours. Air was then introduced for oxidation, and the mixture was aged for 12 hours. The precipitate was filtered and washed three times. The collected filter cake was dried at 100°C for 16 hours to prepare a precursor with a (M+M') / P ratio of 0.741 (molar ratio). Here, M = Mn, M' = Al, and Mn / Al = 94 / 6 (molar ratio).

[0451] Example 29

[0452] This embodiment provides a polyanionic precursor, and the preparation method thereof is as follows:

[0453] 3.0 mol of nickel sulfate and 1.53 mol of sodium pyrophosphate were mixed evenly in a 5L reactor, the reaction temperature was controlled at 70°C, and the reaction was carried out for 6 hours. Then, 400 ml of hydrogen peroxide and 0.5 mol of sodium pyrophosphate were added to the reactor, and the reaction was carried out at a temperature of 75°C for 3 hours. Air was simultaneously introduced for oxidation and aged for 12 hours. The precipitate was filtered and washed three times. The collected filter cake was dried at 100°C for 16 hours to prepare a precursor with a Ni / P ratio of 0.768 (molar ratio).

[0454] Example 30

[0455] This embodiment provides a polyanionic precursor, and the preparation method thereof is as follows:

[0456] 3.0 mol of nickel sulfate and 1.53 mol of sodium pyrophosphate were mixed evenly in a 5L reactor, the reaction temperature was controlled at 70°C, and the reaction was carried out for 6 hours. Then, 400 ml of hydrogen peroxide and 1 mol of sodium phosphate were added to the reactor, and the reaction was carried out at a temperature of 75°C for 3 hours. Air was simultaneously introduced for oxidation and aged for 12 hours. The precipitate was filtered and washed three times. The collected filter cake was dried at 100°C for 16 hours to prepare a precursor with a Ni / P ratio of 0.778 (molar ratio).

[0457] Example 31

[0458] This embodiment provides a polyanionic precursor, and the preparation method thereof is as follows:

[0459] 3.0 mol of cobalt sulfate and 1.53 mol of sodium pyrophosphate were mixed evenly in a 5L reactor, the reaction temperature was controlled at 70°C, and the reaction was carried out for 6 hours. Then, 400 ml of hydrogen peroxide and 0.5 mol of sodium pyrophosphate were added to the reactor, and the reaction was carried out at a temperature of 75°C for 3 hours. Air was simultaneously introduced for oxidation and aged for 12 hours. The precipitate was filtered and washed three times. The collected filter cake was dried at 100°C for 16 hours to prepare a precursor with a Co / P ratio of 0.787 (molar ratio).

[0460] Example 32

[0461] This embodiment provides a polyanionic precursor, and the preparation method thereof is as follows:

[0462] 3.0 mol of cobalt sulfate and 1.53 mol of sodium pyrophosphate were mixed evenly in a 5L reactor, the reaction temperature was controlled at 70°C, and the reaction was carried out for 6 hours. Then, 400 ml of hydrogen peroxide and 1 mol of sodium phosphate were added to the reactor, and the reaction was carried out at a temperature of 75°C for 3 hours. Air was simultaneously introduced for oxidation and aged for 12 hours. The precipitate was filtered and washed three times. The collected filter cake was dried at 100°C for 16 hours to prepare a precursor with a Co / P ratio of 0.783 (molar ratio).

[0463] Comparative Example 1

[0464] This comparative example provides a sodium ion battery positive electrode material, and its preparation method is as follows:

[0465] Mix 3 mol of ferrous sulfate, 4 mol of ammonium dihydrogen phosphate, 2 mol of sodium carbonate, 10% glucose [wherein, 10% glucose means that the amount of glucose added accounts for 10% of the total mass of the raw materials] and 5 L of acetone, ball mill for 12 hours, vacuum dry for 10 hours, and then sinter in an atmosphere furnace at 540°C in a nitrogen atmosphere for 12 hours to obtain the target product Na4Fe3(PO4)2(P2O7).

[0466] Comparative Example 2

[0467] This comparative example provides a sodium ion battery positive electrode material, and its preparation method is as follows:

[0468] Mix 3 mol of ferric phosphate, 1 mol of ammonium dihydrogen phosphate, 2 mol of sodium carbonate, 10% glucose [wherein, 10% glucose means that the amount of glucose added accounts for 10% of the total mass of the raw materials] and 5 L of water, sand grind for 2 hours, spray dry and granulate, and then put into an atmosphere furnace in a nitrogen atmosphere at 520°C for 14 hours to obtain the target product Na4Fe3(PO4)2(P2O7).

[0469] It should be noted that the positive electrode material is directly synthesized in Comparative Example 2, and the precursor used to synthesize this positive electrode material is iron phosphate. In this application (such as Table 10 and Table 12), the precursor of Comparative Example 2 refers to iron phosphate.

[0470] FIG4 is an XRD pattern of the positive electrode material obtained in Comparative Example 2, and XRD shows obvious impurity phase NaFePO4.

[0471] The elemental analysis results of the precursors prepared in Examples 1-12 are compared, and the results are shown in Table 1, Table 2, Table 3, and Table 4 below. The main elements of the precursors are Fe / P, and they contain a small amount of Na. Some embodiments contain a small amount of doping elements. The elemental analysis results of the precursors prepared in Examples 13-22 are compared, and the results are shown in Table 5 below. The main elements of the precursors are Fe, (Ni / Co / Mn), and P, and they contain a small amount of Na. The elemental analysis results of the precursors prepared in Examples 23-28 are compared, and the results are shown in Table 6 below. The main elements of the precursors are Mn and P, and they contain a small amount of Na. Some embodiments contain a small amount of doping elements. The elemental analysis results of the precursors prepared in Examples 29-30 are compared, and the results are shown in Table 7 below. The main elements of the precursors are Ni and P, and they contain a small amount of Na. The elemental analysis results of the precursors prepared in Examples 31-32 are compared, and the results are shown in Table 8 below. The main elements of the precursors are Co and P, and they contain a small amount of Na. The particle size analysis results of the precursors and cathode materials prepared in Examples 1-12 and Comparative Examples 1-2 were compared, and the results are shown in Table 10. The S, N, and C elemental analysis results of the cathode materials prepared in Examples 1-12 and Comparative Examples 1-2 were compared, and the results are shown in Table 9.

[0472] The iron content was determined by the potassium dichromate titration method (GB 4102.2-83), the P content was determined by the quinoline phosphomolybdate gravimetric method (YS T 1028.3-2015), and other metal elements and S were tested by ICP.

[0473] Table 1 Elemental analysis results of precursors

[0474] Table 2 Elemental analysis results of precursors

[0475] Table 3 Elemental analysis results of precursors

[0476] Table 4 Elemental analysis results of precursors

[0477] Table 5 Elemental analysis results of precursors

[0478] Table 6 Elemental analysis results of precursors

[0479] Table 7 Elemental analysis results of precursors

[0480] Table 8 Elemental analysis results of precursors

[0481] Table 9 Elemental analysis results of positive electrode materials

[0482] Table 10 Particle size test results

[0483] According to the total Fe, Fe 2+ 、 The test results of P and Na, the theoretical chemical formula of Example 1 calculated after balancing the general formula is Na 0.54 Fe(0.21+0.79)P 1.36 O 5.05 1.53H2O. It is understandable that due to test errors and the possible presence of impurity elements or elements that cannot be measured, the theoretical molecular formula may deviate from the actual one. The theoretical molecular formula is calculated based on the test results of various elements and valence balance, assuming that the molar number of Fe is 1. The theoretical chemical formula of other embodiments is not repeated here.

[0484] The test results of the pyrophosphate content of Examples 1-3 are shown in Table 11. The test steps for pyrophosphate are as follows: accurately weigh 1g of the precursor sample, use an appropriate amount of concentrated hydrochloric acid to fully dissolve it at room temperature, and then use a spectrophotometer to measure the phosphate content in the sample. Then take another 1g of the precursor sample, use an appropriate amount of concentrated hydrochloric acid to fully dissolve it in a heated state, use a spectrophotometer to measure the total phosphorus content, and then subtract the phosphate content from the total phosphorus content to obtain the pyrophosphate test result. Since the use of concentrated hydrochloric acid for room temperature dissolution will cause the pyrophosphate to be partially converted into phosphate, the pyrophosphate value tested by this method will be low.

[0485] The direct test result of the above method is the pyrophosphate content (wt%), i.e., the percentage of the mass of P in the pyrophosphate to the total mass of the precursor, as shown in the second column of Table 11. The third column of Table 11 shows the total P content in the polyanionic precursors obtained by other methods (derived from Table 1); the fourth column of Table 11 is obtained by dividing the second column of data by the third column of data, representing the ratio of P in the pyrophosphate to the total P in the precursor.

[0486] Table 11 Pyrophosphate test results of precursors

[0487] The comprehensive indicators of the positive electrode materials prepared in some examples and comparative examples were compared, and the results are shown in Table 12 below:

[0488] Table 12 Performance indicators

[0489] As shown in Table 12 above, the method provided by the present application can be used to prepare a positive electrode material with high compaction density and high gram capacity. Since the precursor prepared by the liquid phase precipitation method has good crystallinity and a large tap density, it is beneficial to fully contact and react with the sodium source as a matrix during sintering. Therefore, the obtained positive electrode material also has a large compaction density and tap density. In addition, the primary particle size of the positive electrode material after sintering is 100-400nm, which is beneficial for the positive electrode material to fully infiltrate and react with the electrolyte, and can reduce the sodium ion transmission distance, thereby effectively improving the conductivity and stability of sodium iron pyrophosphate, thereby obtaining a positive electrode material with a large gram capacity. Figure 5 is a comparison of the XRD patterns of the positive electrode material products of Example 3. It can be seen that the product diffraction peak intensity is high and the half-peak width is narrow. It is a high-purity positive electrode material. The main phase components are: Na4Fe3(PO4)2(P2O7). The proportion of NaFePO4 impurity phase after fitting calculation is less than 2%, indicating that a positive electrode material with substantially no impurity phase can be obtained by using this precursor.

[0490] The precursor obtained in Example 5 was used to prepare the positive electrode material, which was tested using a carbon-sulfur analyzer. The results showed that the carbon content of the positive electrode material was 3.70 wt %, and the sulfur content was 0.0364 wt %.

[0491] The test methods or standards involved in this application include GB / T 5162-2021 Determination of the tap density of metal powders, GB / T 19587-2017 Determination of the specific surface area of ​​solid substances by gas adsorption BET method, GB / T 19077-2016 Particle size distribution by laser diffraction method, YS / T928.3-2013 Chemical analysis methods of nickel, cobalt and manganese hydroxides Part 3: Determination of nickel, cobalt and manganese content by inductively coupled plasma atomic emission spectrometry, etc.

[0492] The XRD information of this application was measured by X-ray diffractometer, and the X-ray wavelength was

[0493] The performance test method of the positive electrode material in this application is as follows:

[0494] The positive electrode material, conductive carbon black SP, and binder PVDF were mixed into a slurry at a mass ratio of 7:2:1 and coated onto aluminum foil. The film was then dried in a vacuum oven at 110°C for 4 hours. The electrode film was punched into discs with a radius of 0.6 mm using a sheet puncher. Sodium metal was used as the counter electrode, and the electrolyte consisted of 1 mol / L NaClO4 EC+PC (1:1 vol%)+5% FEC (where EC is ethylene carbonate, PC is polycarbonate, and FEC is a fluoroethylene carbonate additive). The separator was glass fiber. CR2016 button cells were assembled in a glove box.

[0495] The button cell was subjected to constant current charge and discharge tests at a current density of 0.1C (1C = 129 mAh / g). Figure 8 shows the charge and discharge curves for the Na4Fe3(PO4)2(P2O7) electrode in Example 5 during the first cycle. Within the voltage range of 1.5-4.2V, the electrode exhibited a reversible specific capacity of 110 mAh / g at an average discharge potential of 3.1V, demonstrating high capacity.

[0496] The compaction density of the positive electrode material in this application is tested using a UTM7305 microcomputer-controlled electronic pressure testing machine under a pressure of 3 tons. The test mold is a cylinder with a diameter of 13 mm.

[0497] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application. Industrial Applicability

[0498] The present application discloses a polyanion precursor, a sodium ion battery cathode material and a preparation method thereof, a sodium ion battery and an electrical device. The polyanion precursor contains a chemical formula of Na q M m+n M' w P x O y ·zH2O. The preparation method of the polyanionic precursor comprises: 2+A metal salt and a first phosphorus source containing pyrophosphate are mixed to obtain a mixed solution, and the mixture is reacted to obtain a mixed solution containing a pyrophosphate salt of a divalent metal M; an oxidant and a second phosphorus source are added to react, and the separated solid is dried after solid-liquid separation to obtain a polyanion precursor. The polyanion precursor of the present application has a high tap density, and the prepared sodium ion battery positive electrode material has high purity and excellent electrochemical performance. The polyanion precursor provided in the present application contains a small amount of insoluble Na, which can save sodium source when preparing positive electrode materials and has industrial applicability.

Claims

1. A polyanionic precursor, characterized in that: Contains the chemical formula Na q M m+n M' w P x O y · Substances containing H2O; Wherein, M is one or more of Fe, Ni, Co, and Mn; M' is one or more of transition metal elements other than M, Mg, Ca, Sr, and Al; m represents M 2+ The content of M 3+ The content of 0≤m / (m+n)≤0.35, 0≤w / (m+n)≤0.1, 0.32≤q / (m+n+w)≤0.70, 0.68≤(m+n+w) / x≤0.80, 0≤z / (m+n+w)≤10, and the values ​​of q, m, n, w, x, and y are selected according to the valence state of M' so that the chemical formula maintains charge balance.

2. The polyanionic precursor according to claim 1, characterized in that One or more of the following conditions are met: (1) M is Fe and Mn; (2) The transition metal elements other than M include Ti, V, Cr, Zr, Nb, W, Cr, Cu, Zn, Mo, Sc, and Y; (3) 0.40≤q / (m+n+w)≤0.65; (4) 0.26≤q / x≤0.60; (5) 0≤m / (m+n)≤0.33; or, 0≤m / (m+n)≤0.30; or, 0≤m / (m+n)≤0.26; (6) 0≤w / (m+n)≤0.05; (7) 0.71≤(m+n+w) / x≤0.77; (8) The valence state of M' is +α, q+2m+3n+αw+5x=2y; (9) The valence state of M' is +α, 1≤α≤5; or, 2≤α≤4; (10) 0≤z / (m+n+w)≤6; or, 0≤z / (m+n+w)≤3; (11) The polyanionic precursor contains phosphate and / or pyrophosphate; (12) The polyanionic precursor contains pyrophosphate, and the P content in the pyrophosphate accounts for more than 10 wt% of the total P content in the polyanionic precursor; (13) In the polyanionic precursor, the content of Na is 4wt%-10wt%; (14) In the polyanionic precursor, the content of P is 15wt%-25wt%; (15) In the polyanionic precursor, the total content of M and M' is 20wt%-32wt%; (16) In the polyanionic precursor, the content of S is less than 0.5 wt %; (17) In the polyanionic precursor, the total content of S and N is less than 0.8 wt %; (18) In the polyanionic precursor, the total content of S, N and C is less than 1.0 wt%; (19) In the polyanionic precursor, the content of the impurity element is less than 3.0 wt %; or, the content of the impurity element is less than 1.5 wt %; (20) In the polyanionic precursor, n(S):n(M+M')≤0.1, or n(S):n(M+M')≤0.06; (21) In the polyanionic precursor, n(S+N):n(M+M')≤0.1, or n(S+N):n(M+M')≤0.06; (22) In the polyanionic precursor, n(S+N+C):n(P)≤0.1, or n(S+N+C):n(P)≤0.06; (23) The polyanionic precursor is in an amorphous state; (24) The tap density TD of the polyanionic precursor is 0.9-1.4 g / cm 3 ; (25) The BET of the polyanionic precursor is 5-25m 2 / g; (26) The average particle size of the primary particles of the polyanionic precursor is 50-200 nm; (27) The average particle size D50 of the secondary particles of the polyanionic precursor satisfies: 1 μm ≤ D50 ≤ 10 μm; (28) The particle size distribution of the polyanionic precursor satisfies: D10≤1 μm, 1 μm≤D50≤10 μm, D90≤50 μm; (29) The primary particles of the polyanionic precursor are spherical or quasi-spherical; (30) In the XRD pattern of the polyanionic precursor, within the test range of 20°≤2θ≤70°, the peak position of the highest peak is between 26° and 32°; (31) The polyanionic precursor is poorly soluble in water; (32) The polyanionic precursor conforms to the chemical formula Na q M m+n M' w P x O y ·zH2O.

3. A polyanionic precursor, characterized in that Contains the chemical formula Na q M m+n M' w (PO4) e (P2O7) f · Substances containing H2O; Wherein, M is one or more of Fe, Ni, Co, and Mn; M' is one or more of transition metal elements other than M, Mg, Ca, Sr, and Al; m represents M 2+ The content of M 3+ content, 0≤m / (m+n)≤0.35, 0≤w / (m+n)≤0.1, 0.32≤q / (m+n+w)≤0.70, 0.68≤(m+n+w) / (e+2f)≤0.80, 0≤e / (e+2f)≤0.90, 0.1≤2f / (e+2f)≤1, 0≤z / (m+n+w)≤10, and the values ​​of q, m, n, w, e, and f are selected according to the valence state of M' so that the chemical formula maintains charge balance.

4. The polyanionic precursor according to claim 3, characterized in that One or more of the following conditions are met: (1) M is Fe and Mn; (2) The transition metal elements other than M include Ti, V, Cr, Zr, Nb, W, Cr, Cu, Zn, Mo, Sc, and Y; (3) 0.40≤q / (m+n+w)≤0.65; (4) 0.26≤q / (e+2f)≤0.60; (5) 0≤m / (m+n)≤0.33; or, 0≤m / (m+n)≤0.30; or, 0≤m / (m+n)≤0.26; (6) 0≤w / (m+n)≤0.05; (7)0.71≤(m+n+w) / (e+2f)≤0.77; (8) The valence state of M' is +α, q+2m+3n+αw+5(e+2f)=2(4e+7f); (9) The valence state of M' is +α, 1≤α≤5; or, 2≤α≤4; (10) 0≤z / (m+n+w)≤6; or, 0≤z / (m+n+w)≤3; (11) The polyanionic precursor contains phosphate and / or pyrophosphate; (12) The polyanionic precursor contains pyrophosphate, and the P content in the pyrophosphate accounts for more than 10 wt% of the total P content in the polyanionic precursor; (13) In the polyanionic precursor, the content of Na is 4wt%-10wt%; (14) In the polyanionic precursor, the content of P is 15wt%-25wt%; (15) In the polyanionic precursor, the total content of M and M' is 20wt%-32wt%; (16) In the polyanionic precursor, the content of S is less than 0.5 wt %; (17) In the polyanionic precursor, the total content of S and N is less than 0.8 wt %; (18) In the polyanionic precursor, the total content of S, N and C is less than 1.0 wt%; (19) In the polyanionic precursor, the content of the impurity element is less than 3.0 wt %; or, the content of the impurity element is less than 1.5 wt %; (20) In the polyanionic precursor, n(S):n(M+M')≤0.1, or n(S):n(M+M')≤0.06; (21) In the polyanionic precursor, n(S+N):n(M+M')≤0.1, or n(S+N):n(M+M')≤0.06; (22) In the polyanionic precursor, n(S+N+C):n(P)≤0.1, or n(S+N+C):n(P)≤0.06; (23) The polyanionic precursor is in an amorphous state; (24) The tap density TD of the polyanionic precursor is 0.9-1.4 g / cm 3 ; (25) The BET of the polyanionic precursor is 5-25m 2 / g; (26) The average particle size of the primary particles of the polyanionic precursor is 50-200 nm; (27) The average particle size D50 of the secondary particles of the polyanionic precursor satisfies: 1 μm ≤ D50 ≤ 10 μm; (28) The particle size distribution of the polyanionic precursor satisfies: D10≤1 μm, 1 μm≤D50≤10 μm, D90≤50 μm; (29) The primary particles of the polyanionic precursor are spherical or quasi-spherical; (30) In the XRD pattern of the polyanionic precursor, within the test range of 20°≤2θ≤70°, the peak position of the highest peak is between 26° and 32°; (31) The polyanionic precursor is poorly soluble in water; (32) The polyanionic precursor conforms to the chemical formula Na q M m+n M' w (PO4) e (P2O7) f ·zH2O.

5. A method for preparing a polyanionic precursor, characterized in that: The following steps are involved: Step A: Add M 2+ A metal salt and a first phosphorus source containing pyrophosphate are mixed to obtain a mixed solution, and a first reaction is performed to obtain a mixed solution containing a pyrophosphate salt of a divalent metal M; Step B: adding an oxidant and a second phosphorus source to a mixed solution of pyrophosphate containing a divalent metal M to carry out a second reaction, separating the solid and the liquid after the second reaction, and drying the separated solid to obtain the polyanionic precursor; wherein the first phosphorus source and / or the second phosphorus source contain sodium ions.

6. The method for preparing a polyanionic precursor according to claim 5, characterized in that: One or more of the following conditions are met: (1) The M-containing 2+ The metal salt includes one or more of a soluble divalent iron salt, a soluble divalent manganese salt, a soluble divalent nickel salt, and a soluble divalent cobalt salt; 2+ The metal salt is one or more of a soluble divalent iron salt, a soluble divalent manganese salt, a soluble divalent nickel salt, and a soluble divalent cobalt salt; (2) The M-containing 2+ The metal salt includes one or more of sulfate, nitrate and chloride; (3) The M-containing 2+ The metal salt also contains a soluble salt of metal M'; (4) the first phosphorus source and / or the second phosphorus source comprises pyrophosphate and / or sodium pyrophosphate; (5) The temperature of the first reaction is 50-80° C., and the time of the first reaction is 1-10 h; (6) The oxidant is hydrogen peroxide; (7) the molar amount of phosphorus in the pyrophosphate ion accounts for no less than 70% of the total molar amount of phosphorus in the first phosphorus source and the second phosphorus source; (8) introducing an oxygen-containing gas during the second reaction; (9) The temperature of the second reaction is 55-85° C., and the time of the second reaction is 1-6 hours; (10) aging after the second reaction, the aging time is 5-20 hours; (11) The drying temperature is 80-120°C; (12) The molar ratio of phosphorus in the first phosphorus source to that in the second phosphorus source is 2.5-3.6:1; (13) The raw materials of the polyanionic precursor do not contain a carbon source.

7. A polyanion sodium ion battery positive electrode material, characterized in that: The raw materials of the sodium ion battery positive electrode material include a polyanion precursor, a sodium source and a carbon source.

8. The polyanion sodium ion battery positive electrode material according to claim 7, characterized in that: The polyanionic precursor is the polyanionic precursor described in claims 1-4, or is a polyanionic precursor obtained by the preparation method of the polyanionic precursor described in claims 5-6.

9. A polyanion sodium ion battery positive electrode material, characterized in that: The component of the positive electrode material of the polyanion type sodium ion battery is a composite of sodium phosphate pyrophosphate metal salt and carbon; In the sodium phosphate pyrophosphate metal salt, the metal other than sodium includes M and M' which is not necessarily present; wherein M is one or more of Fe, Ni, Co, and Mn; and M' is selected from one or more of transition metal elements other than M, Mg, Ca, Sr, and Al; The polyanion sodium ion battery positive electrode material meets one or more of the following conditions: (1) The compaction density of the polyanion sodium ion battery positive electrode material is 1.8-2.4 g / cm 3 ; (2) The specific surface area of ​​the polyanion sodium ion battery positive electrode material is 5-25m 2 / g; (3) The average particle size of the primary particles of the polyanion sodium ion battery positive electrode material is 100-400 nm; (4) The average particle size D50 of the secondary particles of the polyanion sodium ion battery positive electrode material is 1-5 μm; (5) The crystal structure of the sodium phosphophosphate metal salt belongs to the Pn21a space group; (6) The chemical formula of the sodium phosphophosphate metal salt is Na4M j M' k (PO4)2P2O7; wherein k / j≤0.1, 2.8≤j+k≤3.2; (7) The S content of the polyanion sodium ion battery positive electrode material is ≤0.08wt%; or, the S content is ≤0.05wt%; (8) The N content of the polyanion sodium ion battery positive electrode material is ≤0.08wt%; or, the N content is ≤0.05wt%.

10. A method for preparing the polyanion sodium ion battery positive electrode material according to any one of claims 7 to 9, characterized in that: include: The raw materials including the polyanion precursor, the carbon source and the sodium source are mixed, crushed, dried and then sintered to obtain the polyanion sodium ion battery positive electrode material.

11. The preparation method according to claim 10, characterized in that: The preparation method meets one or more of the following conditions: (1) The carbon source is one or more of sucrose, glucose, crystal sugar, cellulose, phenolic resin, polyethylene glycol, polyvinyl pyrrolidone, starch, polyvinyl alcohol, ionic cellulose gum carbon source, and inorganic carbon source; (2) The sodium source includes one or more of sodium carbonate, sodium bicarbonate, sodium acetate, and sodium oxalate; (3) The pulverization is grinding or sand milling; (4) The sintering temperature is 500-600°C, and the sintering time is 6-30h.

12. A sodium ion battery, characterized in that: The invention comprises the polyanionic sodium ion battery positive electrode material according to any one of claims 7 to 9.

13. An electrical equipment, characterized in that: Including the sodium ion battery as described in claim 12.

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