Polyanionic sodium-ion battery cathode material precursor and preparation method thereof

Abstract

The application discloses a kind of polyanionic sodium ion battery positive electrode material precursor and preparation method thereof, and the chemical general formula of the precursor is A x M y OH z PO4 or A x M y H z PO4, wherein A is alkali metal element Na, M is one or two or more of transition metal elements Fe, V, Co or Mn, and the value range of x, y, z is 0 respectively

Description

TECHNICAL FIELD

[0001] The application relates to the secondary technology field, in particular to a polyanionic sodium ion battery positive electrode material precursor and a preparation method thereof. BACKGROUND

[0002] The polyanionic sodium ion battery positive electrode material has high structural stability, thermodynamic stability, excellent cycle stability and rate performance and is favored by the market. At present, the polyanionic material systems researched more on the market include sodium iron pyrophosphate phosphate, sodium vanadium phosphate and sodium vanadium fluorophosphate, which are formed by the mutual intersection of alkali metal tetrahedron, transition metal tetrahedron / octahedron and anion tetrahedron / triangular group in a common point / surface / line manner to form a three-dimensional framework structure. The polyanionic material is prepared by a solid phase method, and the obtained material has low phase purity and poor electrochemical performance.

[0003] At present, the commercially available sodium iron pyrophosphate phosphate and sodium vanadium phosphate material are synthesized by a solid phase method. High crystallinity FePO4, FeC2O4 and V2O5 are used as transition metal precursor sources, combined with water-soluble sodium sources and water-soluble phosphorus sources, and the material is prepared through processes such as grinding mixing, spray drying and sintering. However, the high crystallinity FePO4, FeC2O4 and V2O5 solid is difficult to completely dissolve in the grinding process, and exists in the slurry in the form of nanocrystalline with a size of 200-300 nm, so that the sodium ions, transition metal ions and anions in the slurry cannot be effectively mixed in an ionic state, and the phase separation is easily caused in the sintering process, thereby affecting the electrochemical performance of the material. Meanwhile, the high crystallinity FePO4, FeC2O4 and V2O5 solid has a long grinding time, high energy consumption and large process investment cost. Therefore, in order to obtain a polyanionic sodium ion battery material with high phase purity and low manufacturing process cost, a suitable precursor needs to be developed for the material. The precursor needs to contain the elements required by the prepared material and exist in the form of amorphous bonding. SUMMARY

[0004] The application aims to provide a preparation method of a polyanionic sodium ion battery positive electrode material precursor, which has the characteristics of controllable structure, low cost, simple process, high phase purity and excellent electrochemical performance.

[0005] The application can be implemented by the following technical scheme:

[0006] The application discloses a preparation method of a polyanionic sodium ion battery positive electrode material precursor, and the chemical general formula of the precursor is A x M y OH z PO4 or A x M y Hz PO4, wherein A is an alkali metal element Na, M is one or two or more of transition metal elements Fe, V, Co or Mn, the value ranges of x, y and z are respectively 0 < x < 0.5, 0.4 < y < 1.0, 0 < z < 0.5 and x + 3y - z = 3, and the preparation method of the precursor comprises the following steps:

[0007] S1, preparation of a precursor solution: dissolving and mixing a transition metal source and an inorganic phosphoric acid, adding an acid liquid to control the pH of the solution and heating to promote the dissolution of the transition metal source, to obtain a precursor solution;

[0008] S2, preparation of a pre-oxidized precursor solution: adding hydrogen peroxide to the above precursor solution to oxidize the divalent metal ions in the solution to trivalent, to obtain a pre-oxidized precursor solution;

[0009] S3, preparation of a pre-precipitated precursor slurry: heating and boiling the above pre-oxidized precursor solution to remove volatile acid, to obtain a pre-precipitated precursor slurry;

[0010] S4, preparation of a neutral precursor slurry: neutralizing the pre-precipitated precursor slurry with a sodium alkali source, to obtain a neutral precursor slurry;

[0011] S5, solid-liquid separation: drying the neutral precursor slurry to realize solid-liquid separation, to obtain a polyanionic positive electrode material precursor powder.

[0012] The application provides a polyanionic sodium ion battery positive electrode material precursor preparation process, and the chemical general formula of the precursor is A x M y (OH - or H + ) z PO4. x M y (OH - or H + ) z PO4, which is prepared by heating and dissolving cheap transition metal elements or oxides thereof, inorganic phosphoric acid and volatile acid, adding hydrogen peroxide to oxidize the transition metal ions in the solution, heating and boiling the solution to remove volatile acid, generating a precipitated precursor slurry, neutralizing the slurry with a sodium alkali source, and evaporating and drying to obtain a polyanionic positive electrode material A x M y (OH - or H + ) z PO4 precursor powder.

[0013] Further, in step S1, the pH range is 0-2; the purpose is to achieve rapid dissolution of the transition metal source in an acidic environment to complete the uniform mixing between the transition metal elements and phosphorus elements; when the pH is higher than 2, the hydrogen ion concentration in the solution is reduced, the dissolution rate of the transition metal source is reduced, and the dissolution is incomplete; the heating temperature range is 50-80℃; the purpose is to increase the ion activity in the solution and accelerate the dissolution of the transition metal source; when the temperature is lower than 50℃, the dissolution rate of the transition metal source is low, and when the temperature is higher than 80℃, the solution will boil, and the volatilization of the acid will change the pH of the solution, which is not conducive to the continuous reaction.

[0014] Further, in step S2, the amount of hydrogen peroxide added is 1-3 times the molar amount of the metal elements in the transition metal source; the purpose is to ensure that the divalent metal ions in the solution can be completely oxidized.

[0015] Further, in step S3, the boiling temperature range is 80-100℃; the purpose is to remove the excess volatile acid in the solution, reduce the hydrogen ion concentration in the solution, increase the solution PH, and induce the combination of transition metal ions and phosphate to form H x M y PO4or M y PO4precipitate.

[0016] Further, in step S4, the neutralization condition is that the pH of the slurry reaches 6-8; the purpose is to use the alkalinity of the alkali metal sodium source to consume the hydrogen ions in the solution or H x M y PO4precipitate, achieve the exchange of alkali metal ions and hydrogen ions, and then introduce alkali metal elements into the final precursor.

[0017] Further, in step S5, the drying method of the neutral slurry is one or more of spray drying, high-temperature evaporation, flash drying, and high-temperature cracking; the purpose is to use high temperature to achieve rapid separation between solid and liquid in the slurry, prevent ion segregation caused by slow evaporation, and affect the ion uniformity in the precursor.

[0018] Further, in step S1, the inorganic phosphoric acid is one or more of phosphoric acid, pyrophosphoric acid, and metaphosphoric acid; the acid solution for controlling pH is one or more of formic acid, acetic acid, hydrofluoric acid, nitric acid, and hydrochloric acid.

[0019] Further, in step S1, the transition metal source is one or two or more of an iron source, a vanadium source, a cobalt source, and a manganese source, the iron source is one or two or more of iron single substance, iron oxide, ferrous oxide, magnetite, ferrous hydroxide, and ferric hydroxide, the vanadium source is one or two or more of vanadium single substance, vanadium pentoxide, vanadium monoxide, and vanadium dioxide, the cobalt source is one or two or more of cobalt single substance, cobalt oxide, cobalt tetraoxide, and cobaltic oxide, and the manganese source is one or two or more of manganese single substance, manganese monoxide, manganese dioxide, and manganese sesquioxide.

[0020] Further, in step S4, the alkali metal sodium source is one or two or more of sodium hydroxide, sodium oxide, sodium peroxide, sodium carbonate, and sodium bicarbonate.

[0021] Another aspect of the present application is to protect a polyanionic sodium ion battery cathode material precursor, which is prepared by the above preparation method.

[0022] The polyanionic sodium ion battery cathode material precursor and the preparation method thereof have the following beneficial effects:

[0023] First, controllable preparation of amorphous disordered precursor structure: A x M y (OH - or H + ) z The PO4 precursor is a disordered amorphous structure in which alkali metal ions, transition metal ions, hydroxide ions / hydrogen ions, and phosphate ions are connected by van der Waals forces and weak interionic interaction forces, and the distribution of the ions in the structure is extremely uniform.

[0024] Second, low cost: the preparation process of the present application uses transition metal single substances and oxides as inexpensive transition metal sources, dissolves them with inorganic phosphoric acid and volatile acid to ensure uniform mixing of the ions, then removes and recovers the volatile acid by heating, and finally neutralizes the proton hydrogen in the solution with an alkaline sodium source, and after drying, an amorphous disordered polyanionic sodium ion battery cathode material precursor is obtained. The raw material cost of this preparation process is low, the process route is simple to implement, and it is easy to mass produce.

[0025] Third, simple process: A x M y (OH - or H + ) z PO4 as a polyanionic sodium ion battery cathode material synthesis precursor, which does not need to add transition metal sources and phosphorus sources in the material synthesis process, only needs to supplement a small amount of sodium source and carbon source, and realizes the sodium source and carbon source in A x My (OH - or H + ) z The dispersion of PO4 on the surface utilizes the high diffusion kinetics of sodium ions during high-temperature sintering to achieve diffusion, nucleation, and crystal growth within the precursor. This process avoids the lengthy grinding and mixing process of sodium, transition metal, and phosphorus sources required in the synthesis of traditional polyanionic materials, significantly shortening the material preparation time and reducing energy consumption during the manufacturing process.

[0026] Fourth, high phase purity: The phase purity of the material is directly related to the uniformity of mixing of sodium, transition metal elements, and phosphate ions during the preparation process. x M y (OH - or H + ) z In the PO4 precursor, the elements are bonded to each other in ionic form, and the mixing uniformity is high. During the sintering process, the bonding growth process between the elements can be achieved without long-distance melting diffusion. The resulting phase structure has low defects, high crystallinity, and high phase purity.

[0027] Fifth, excellent electrochemical performance: Electrochemical performance is directly related to the crystal structure of the material, with A... x M y (OH - or H + ) z Materials prepared from PO4 precursors have high phase purity, resulting in smoother sodium ion migration pathways and lower resistance from vacancy defects, antisite defects, and grain boundaries. Consequently, the sodium ion migration rate and insertion / extraction rate are significantly improved, leading to excellent rate performance and high capacity characteristics in the materials. Attached Figure Description

[0028] Figure 1 In this application example 1 and comparative example 1, Na 4.24 Fe 2.88 XRD of (PO4)2P2O7 material (* marks impurity phase diffraction peaks in the figure);

[0029] Figure 2 To apply Na in Example 1 and Comparative Example 1 4.24 Fe 2.88 (PO4)2P2O7 material charge-discharge curves for the first week. Detailed Implementation

[0030] To enable those skilled in the art to better understand the technical solution of the present invention, the product of the present invention will be further described in detail below with reference to embodiments.

[0031] The application discloses a preparation method of a polyanionic sodium ion battery positive electrode material precursor x M y OH z PO4 or A x M y H z PO4, wherein A is an alkali metal element Na, M is one or two or more of transition metal elements Fe, V, Co or Mn, the value ranges of x, y and z are respectively 0 < x < 0.5, 0.4 < y < 1.0 and 0 < z < 0.5, and x + 3y - z = 3, and the preparation method comprises the following steps:

[0032] S1, preparation of a precursor solution: a transition metal source and an inorganic phosphoric acid are dissolved and mixed, acid liquid is added to control the pH of the solution and heating is performed to promote the dissolution of the transition metal source, so that the precursor solution is prepared;

[0033] S2, preparation of a pre-oxidized precursor solution: hydrogen peroxide is added to the precursor solution to oxidize the divalent metal ions in the solution into trivalent, so that the pre-oxidized precursor solution is prepared;

[0034] S3, preparation of a pre-precipitated precursor slurry: the pre-oxidized precursor solution is heated to boil to remove volatile acid, so that the pre-precipitated precursor slurry is prepared;

[0035] S4, preparation of a neutral precursor slurry: the pre-precipitated precursor slurry is neutralized by an alkali metal source, so that the neutral precursor slurry is prepared;

[0036] S5, solid-liquid separation: the neutral precursor slurry is dried to realize solid-liquid separation, so that the polyanionic positive electrode material precursor powder is obtained.

[0037] Further, in step S1, the pH range is 0-2; the purpose is to realize rapid dissolution of the transition metal source in an acidic environment to complete uniform mixing between the transition metal element and the phosphorus element; when the pH is higher than 2, the hydrogen ion concentration in the solution is reduced, the dissolution rate of the transition metal source is reduced, and the dissolution is incomplete; the heating temperature range is 50-80 DEG C; the purpose is to increase the ion activity in the solution and accelerate the dissolution of the transition metal source; when the temperature is lower than 50 DEG C, the dissolution rate of the transition metal source is low, and when the temperature is higher than 80 DEG C, the solution will boil, the volatilization of the acid will change the pH of the solution, and the reaction cannot continue.

[0038] Further, in step S2, the hydrogen peroxide is added in an amount of 1-3 times the molar amount of the metal element in the transition metal source; the purpose is to ensure that the divalent metal ions in the solution can be completely oxidized.

[0039] Further, the heating boiling temperature range in step S3 is 80-100℃, which aims to remove the excess volatile acid in the solution, reduce the hydrogen ion concentration in the solution, increase the solution PH, and induce the transition metal ions to combine with phosphate to generate H x M y PO4 or M y PO4 precipitation.

[0040] Further, in step S4, the neutralization condition is that the slurry pH range reaches 6-8; which aims to consume the solution or H x M y PO4 precipitation with the basicity of the alkali metal sodium source, realize the exchange of alkali metal ions and hydrogen ions, and further introduce the alkali metal element in the final precursor.

[0041] Further, in step S5, the drying method of the neutral slurry is one or more than two of spray drying, high-temperature evaporation, flash drying, and high-temperature cracking; which aims to realize the rapid separation between solid and liquid in the slurry by high temperature, prevent ion segregation caused by slow evaporation, and affect the ion uniformity in the precursor.

[0042] Further, in step S1, the inorganic phosphoric acid is one or more than two of phosphoric acid, pyrophosphoric acid, and metaphosphoric acid; and the acid liquid for controlling pH is one or more than two of formic acid, acetic acid, hydrofluoric acid, nitric acid, and hydrochloric acid.

[0043] Further, in step S1, the transition metal source is one or more than two of iron source, cobalt source, and manganese source, the iron source is one or more than two of iron single substance, iron oxide, ferrous oxide, magnetite, ferrous hydroxide, and ferric hydroxide, the vanadium source is one or more than two of single substance vanadium, di vanadium pentoxide, vanadium monoxide, and di vanadium trioxide, the cobalt source is one or more than two of single substance cobalt, cobalt oxide, and cobalt tetraoxide, and the manganese source is one or more than two of single substance manganese, manganese monoxide, manganese dioxide, and di manganese trioxide.

[0044] Further, in step S4, the alkali metal sodium source is one or more than two of sodium hydroxide, sodium oxide, sodium peroxide, sodium carbonate, and sodium bicarbonate.

[0045] Another aspect of the present application is to protect a kind of polyanionic sodium ion battery positive material precursor, which is prepared by the above method.

[0046] Example 1

[0047] This embodiment relates to a kind of polyanionic sodium ion battery positive material precursor, and the chemical general formula of the precursor is A x M y OH zPO4or A x M y H z PO4, wherein A is an alkali metal element Na, M is a transition metal element Fe, the value ranges of x, y, z are respectively 0 < x < 0.5, 0.4 < y < 1.0, 0 < z < 0.5 and x + 3y - z = 3, and the preparation method of the precursor comprises the following steps:

[0048] S1, preparation of a precursor solution: a transition metal source and an inorganic phosphoric acid are dissolved and mixed, an acid solution is added to control the pH of the solution and heating is promoted to facilitate the dissolution of the transition metal source, thereby obtaining a precursor solution. Specifically, the pH range is 2, and the heating temperature range is 565℃.

[0049] S2, preparation of a pre-oxidized precursor solution: hydrogen peroxide is added to the above-mentioned precursor solution to oxidize the divalent metal ions in the solution to trivalent, thereby generating a pre-oxidized precursor solution. Specifically, the amount of hydrogen peroxide added is 1.1 times the molar amount of metal elements in the transition metal source.

[0050] S3, preparation of a pre-precipitated precursor slurry: the above-mentioned pre-oxidized precursor solution is heated and boiled to remove volatile acid, thereby generating a pre-precipitated precursor slurry. Specifically, the heating and boiling temperature range is 100℃.

[0051] S4, preparation of a neutral precursor slurry: the pre-precipitated precursor slurry is neutralized with a sodium alkali source, thereby generating a neutral precursor slurry. Specifically, the neutralization condition is that the pH range of the slurry reaches 7.

[0052] S5, solid-liquid separation: the neutral precursor slurry is dried to achieve solid-liquid separation, thereby obtaining a polyanionic positive electrode material precursor powder. Specifically, the drying method of the neutral slurry is spray drying.

[0053] In this embodiment, the inorganic phosphoric acid is phosphoric acid and pyrophosphoric acid. The acid solution for pH is formic acid and acetic acid. The transition metal source is an iron source, and the iron source is iron single element and iron oxide. The sodium alkali source is sodium hydroxide, sodium oxide and sodium peroxide.

[0054] Example 2

[0055] This embodiment relates to a polyanionic sodium ion battery positive electrode material precursor, and the chemical general formula of the precursor is A x M y OH z PO4or A x M y H zA M H PO4, wherein A is an alkali metal element Na, M is a transition metal element Fe, the value ranges of x, y, z are respectively 0 < x < 0.5, 0.4 < y < 1.0, 0 < z < 0.5 and x + 3y - z = 3, and the preparation method of the precursor comprises the following steps:

[0056] S1, preparation of a precursor solution: a transition metal source and an inorganic phosphoric acid are dissolved and mixed, an acid solution is added to control the pH of the solution and heating is performed to promote the dissolution of the transition metal source, thereby obtaining a precursor solution. Specifically, the pH range is 1, and the heating temperature range is 50°C.

[0057] S2, preparation of a pre-oxidized precursor solution: hydrogen peroxide is added to the above-mentioned precursor solution to oxidize the divalent metal ions in the solution to trivalent, thereby generating a pre-oxidized precursor solution. Specifically, the amount of hydrogen peroxide added is 3 times the molar amount of metal elements in the transition metal source.

[0058] S3, preparation of a pre-precipitated precursor slurry: the above-mentioned pre-oxidized precursor solution is heated and boiled to remove volatile acid, thereby generating a pre-precipitated precursor slurry. Specifically, the heating and boiling temperature range is 90°C.

[0059] S4, preparation of a neutral precursor slurry: the pre-precipitated precursor slurry is neutralized with a sodium alkali source, thereby generating a neutral precursor slurry. Specifically, the neutralization condition is that the pH range of the slurry reaches 6.

[0060] S5, solid-liquid separation: the neutral precursor slurry is dried to achieve solid-liquid separation, thereby obtaining a precursor powder for a polyanionic positive electrode material. Specifically, the drying method of the neutral slurry is high-temperature evaporation.

[0061] In this embodiment, the inorganic phosphoric acid is metaphosphoric acid; the acid solution for controlling the pH is formic acid or acetic acid. The transition metal source is an iron source, and the iron source is ferrous oxide or magnetite. The sodium alkali source is sodium oxide, sodium peroxide or sodium carbonate.

[0062] Example 3

[0063] This embodiment relates to a polyanionic sodium ion battery positive electrode material precursor, which has a chemical general formula of A x M y OH z PO4 or A x M y H z PO4, wherein A is an alkali metal element Na, M is a transition metal element Fe, the value ranges of x, y, z are respectively 0 < x < 0.5, 0.4 < y < 1.0, 0 < z < 0.5 and x + 3y - z = 3, and the preparation method of the precursor comprises the following steps:

[0064] S1, preparation of precursor solution: dissolve and mix transition metal source and inorganic phosphoric acid, add acid solution to control solution pH and heat to promote dissolution of transition metal source, to obtain precursor solution. Specifically, the pH range is 0.5, and the heating temperature range is 80℃.

[0065] S2, preparation of pre-oxidized precursor solution: add hydrogen peroxide to the above-mentioned precursor solution to oxidize divalent metal ions in the solution to trivalent, to obtain pre-oxidized precursor solution. Specifically, the amount of hydrogen peroxide added is 2 times the molar amount of metal elements in the transition metal source.

[0066] S3, preparation of pre-precipitated precursor slurry: heat and boil the above-mentioned pre-oxidized precursor solution to remove volatile acid, to obtain pre-precipitated precursor slurry. Specifically, the heating and boiling temperature range is 80℃.

[0067] S4, preparation of neutral precursor slurry: neutralize the pre-precipitated precursor slurry with sodium source to obtain neutral precursor slurry. Specifically, the neutralization condition is that the pH range of the slurry reaches 8.

[0068] S5, solid-liquid separation: dry the neutral precursor slurry to achieve solid-liquid separation, to obtain the precursor powder for polyanionic positive electrode material. Specifically, the drying method of the neutral slurry is spray drying or high-temperature evaporation.

[0069] In this embodiment, the inorganic phosphoric acid is phosphoric acid, pyrophosphoric acid, or metaphosphoric acid; the acid solution for pH control is hydrofluoric acid or nitric acid. The transition metal source is iron source, and the iron source is ferrous oxide, magnetite, ferrous hydroxide, or ferric hydroxide. The sodium source is sodium carbonate or sodium bicarbonate.

[0070] Example 4

[0071] This embodiment relates to a polyanionic sodium ion battery positive electrode material precursor, which has a chemical general formula of A x M y OH z PO4 or A x M y H z PO4, wherein A is alkali metal element Na, M is transition metal element V, the value ranges of x, y and z are respectively 0

[0072] S1, preparation of precursor solution: dissolve and mix transition metal source and inorganic phosphoric acid, add acid solution to control solution pH and heat to promote dissolution of transition metal source, to obtain precursor solution. Specifically, the pH range is 1, and the heating temperature range is 60℃.

[0073] S2, preparation of pre-oxidized precursor solution: hydrogen peroxide is added to the above-mentioned precursor solution to oxidize the divalent metal ions in the solution to trivalent, thereby generating a pre-oxidized precursor solution. Specifically, the amount of hydrogen peroxide added is 1.3 times the molar amount of metal elements in the transition metal source.

[0074] S3, preparation of pre-precipitation precursor slurry: the above-mentioned pre-oxidized precursor solution is heated to boiling to remove volatile acids, thereby generating a pre-precipitation precursor slurry. Specifically, the heating boiling temperature range is 95°C.

[0075] S4, preparation of neutral precursor slurry: the pre-precipitation precursor slurry is neutralized with a sodium source to generate a neutral precursor slurry. Specifically, the neutralization condition is that the pH of the slurry reaches 7.

[0076] S5, solid-liquid separation: the neutral precursor slurry is dried to achieve solid-liquid separation, thereby obtaining a precursor powder for a polyanionic positive electrode material. Specifically, the drying method of the neutral slurry is flash drying and high-temperature pyrolysis.

[0077] In this embodiment, the inorganic phosphoric acid is phosphoric acid and metaphosphoric acid; the acid solution for regulating pH is formic acid and hydrochloric acid. The transition metal source is a vanadium source, and the vanadium source is vanadium monoxide, vanadium dioxide, and divanadium trioxide. The alkali metal sodium source is sodium oxide, sodium peroxide, and sodium carbonate.

[0078] Example 5

[0079] This embodiment relates to a polyanionic sodium ion battery positive electrode material precursor, which has a chemical general formula of A x M y OH z PO4 or A x M y H z PO4, wherein A is an alkali metal element Na, M is a transition metal element V, the value ranges of x, y and z are respectively 0

[0080] S1, preparation of precursor solution: a transition metal source and inorganic phosphoric acid are dissolved and mixed, an acid solution is added to regulate the pH of the solution and heating is promoted to promote the dissolution of the transition metal source, thereby preparing a precursor solution. Specifically, the pH range is 1, and the heating temperature range is 70°C.

[0081] S2, preparation of pre-oxidized precursor solution: hydrogen peroxide is added to the above-mentioned precursor solution to oxidize the divalent metal ions in the solution to trivalent, thereby generating a pre-oxidized precursor solution. Specifically, the amount of hydrogen peroxide added is 1.3 times the molar amount of metal elements in the transition metal source.

[0082] S3, preparation of pre-precipitation precursor slurry: the pre-oxidized precursor solution is heated to boiling to remove volatile acid to form a pre-precipitation precursor slurry. Specifically, the heating boiling temperature range is 85°C.

[0083] S4, preparation of neutral precursor slurry: the pre-precipitation precursor slurry is neutralized with a sodium source to form a neutral precursor slurry. Specifically, the neutralization conditions are that the pH of the slurry reaches 7.

[0084] S5, solid-liquid separation: the neutral precursor slurry is dried to achieve solid-liquid separation, and a polyanionic positive electrode material precursor powder is obtained. Specifically, the drying method of the neutral slurry is spray drying and high-temperature pyrolysis.

[0085] In this embodiment, the inorganic phosphoric acid is phosphoric acid, pyrophosphoric acid, and metaphosphoric acid; the acid solution for regulating pH is formic acid, acetic acid, and hydrochloric acid. The transition metal source is vanadium source, and the vanadium source is elemental vanadium and vanadium pentoxide. The alkali metal sodium source is sodium hydroxide and sodium oxide.

[0086] Example 6

[0087] This embodiment relates to a polyanionic sodium ion battery positive electrode material precursor, which has a chemical general formula of A x M y OH z PO4 or A x M y H z PO4, wherein A is an alkali metal element Na, M is a transition metal element V, the value ranges of x, y, and z are 0

[0088] S1, preparation of precursor solution: dissolve and mix the transition metal source and inorganic phosphoric acid, add acid solution to regulate the pH of the solution and heat to promote the dissolution of the transition metal source, and prepare the precursor solution. Specifically, the pH range is 1.5, and the heating temperature range is 75°C.

[0089] S2, preparation of pre-oxidized precursor solution: add hydrogen peroxide to the above-mentioned precursor solution to oxidize the divalent metal ions in the solution to trivalent, and generate a pre-oxidized precursor solution. Specifically, the amount of hydrogen peroxide added is 1.3 times the molar amount of metal elements in the transition metal source.

[0090] S3, preparation of pre-precipitation precursor slurry: the pre-oxidized precursor solution is heated to boiling to remove volatile acid to form a pre-precipitation precursor slurry. Specifically, the heating boiling temperature range is 85°C.

[0091] S4, Preparation of neutral precursor slurry: the pre-precipitation precursor slurry is neutralized by adding a sodium alkali source to generate a neutral precursor slurry. Specifically, the neutralization condition is that the pH range of the slurry reaches 7.5.

[0092] S5, Solid-liquid separation: the neutral precursor slurry is dried to achieve solid-liquid separation, thereby obtaining a polyanionic positive electrode material precursor powder. Specifically, the drying method of the neutral slurry is spray drying.

[0093] In this embodiment, the inorganic phosphoric acid is phosphoric acid, pyrophosphoric acid, and metaphosphoric acid; the acid solution for regulating pH is one or more than two of acetic acid and hydrochloric acid. The transition metal source is a vanadium source, and the vanadium source is vanadic oxide or divanadic oxide. The sodium alkali source is sodium peroxide, sodium carbonate, or sodium bicarbonate.

[0094] Example 7

[0095] This embodiment relates to a polyanionic sodium ion battery positive electrode material precursor, which has a chemical general formula of A x M y OH z PO4 or A x M y H z PO4, wherein A is an alkali metal element Na, M is a transition metal element Co or Mn, the value ranges of x, y, and z are respectively 0

[0096] S1, Preparation of precursor solution: the transition metal source and inorganic phosphoric acid are dissolved and mixed, an acid solution is added to regulate the pH of the solution, and heating is performed to promote the dissolution of the transition metal source, thereby preparing a precursor solution. Specifically, the pH range is 1.7, and the heating temperature range is 70°C.

[0097] S2, Preparation of pre-oxidized precursor solution: hydrogen peroxide is added to the above-mentioned precursor solution to oxidize the divalent metal ions in the solution to trivalent, thereby generating a pre-oxidized precursor solution. Specifically, the amount of hydrogen peroxide added is 1.7 times the molar amount of metal elements in the transition metal source.

[0098] S3, Preparation of pre-precipitation precursor slurry: the above-mentioned pre-oxidized precursor solution is heated and boiled to remove volatile acid, thereby generating a pre-precipitation precursor slurry. Specifically, the heating and boiling temperature range is 96°C.

[0099] S4, Preparation of neutral precursor slurry: the pre-precipitation precursor slurry is neutralized by adding a sodium alkali source to generate a neutral precursor slurry. Specifically, the neutralization condition is that the pH range of the slurry reaches 6.5.

[0100] S5, solid-liquid separation: dry the neutral precursor slurry to achieve solid-liquid separation, thereby obtaining the precursor powder for the polyanionic positive electrode material. Specifically, the drying method of the neutral slurry is spray drying or flash drying.

[0101] In the present embodiment, the inorganic phosphoric acid is phosphoric acid, pyrophosphoric acid, or metaphosphoric acid; the acid solution for regulating pH is formic acid or acetic acid; the transition metal source is a cobalt source or a manganese source, the cobalt source is elemental cobalt, cobalt oxide, or tricobalt tetroxide, and the manganese source is dimanganese trioxide or trimanganese tetroxide; and the alkali metal sodium source is sodium peroxide or sodium carbonate.

[0102] Embodiment 8

[0103] The present embodiment relates to a polyanionic sodium ion battery positive electrode material precursor, which has a chemical general formula A x M y OH z PO4 or A x M y H z PO4, wherein A is an alkali metal element Na, M is a transition metal element Co or Mn, and x, y, and z are in the ranges of 0 < x < 0.5, 0.4 < y < 1.0, and 0 < z < 0.5, respectively, and x + 3y - z = 3, and the preparation method of the precursor comprises the following steps:

[0104] S1, preparation of a precursor solution: dissolve and mix a transition metal source and inorganic phosphoric acid, add an acid solution to regulate the pH of the solution, and heat to promote the dissolution of the transition metal source, thereby preparing a precursor solution. Specifically, the pH range is 1, and the heating temperature range is 60°C.

[0105] S2, preparation of a pre-oxidized precursor solution: add hydrogen peroxide to the above-mentioned precursor solution to oxidize the divalent metal ions in the solution to trivalent, thereby generating a pre-oxidized precursor solution. Specifically, the amount of hydrogen peroxide added is 2.3 times the molar amount of the metal elements in the transition metal source.

[0106] S3, preparation of a pre-precipitated precursor slurry: heat and boil the above-mentioned pre-oxidized precursor solution to remove volatile acids, thereby generating a pre-precipitated precursor slurry. Specifically, the heating and boiling temperature range is 83°C.

[0107] S4, preparation of a neutral precursor slurry: neutralize the pre-precipitated precursor slurry with an alkali metal sodium source, thereby generating a neutral precursor slurry. Specifically, the neutralization condition is that the pH range of the slurry reaches 6.5.

[0108] S5, solid-liquid separation: dry the neutral precursor slurry to achieve solid-liquid separation, thereby obtaining the precursor powder for the polyanionic positive electrode material. Specifically, the drying method of the neutral slurry is spray drying.

[0109] In the present embodiment, the inorganic phosphoric acid is phosphoric acid, pyrophosphoric acid, and metaphosphoric acid; the acid solution for regulating pH is formic acid, acetic acid, and nitrous acid. The transition metal source is a cobalt source and a manganese source. The cobalt source is tricobalt tetroxide and high cobalt oxide. The manganese source is elemental manganese, manganese monoxide, manganese dioxide, and dimanganese trioxide. The alkali metal sodium source is sodium hydroxide, sodium oxide, sodium peroxide, and sodium carbonate.

[0110] Embodiment 9

[0111] The present embodiment relates to a polyanionic sodium-ion battery cathode material precursor, which has a chemical general formula of A x M y OH z PO4or A x M y H z PO4, wherein A is an alkali metal element Na, M is a transition metal element Co and Mn, the value ranges of x, y and z are respectively 0

[0112] S1, preparation of a precursor solution: dissolve and mix a transition metal source and inorganic phosphoric acid, add an acid solution to regulate the pH of the solution and heat to promote the dissolution of the transition metal source, to obtain a precursor solution. Specifically, the pH range is 1, and the heating temperature range is 65°C.

[0113] S2, preparation of a pre-oxidized precursor solution: add hydrogen peroxide to the above-mentioned precursor solution to oxidize the divalent metal ions in the solution to trivalent, to generate a pre-oxidized precursor solution. Specifically, the amount of hydrogen peroxide added is 2 times the molar amount of metal elements in the transition metal source.

[0114] S3, preparation of a pre-precipitated precursor slurry: heat and boil the above-mentioned pre-oxidized precursor solution to remove volatile acid, to generate a pre-precipitated precursor slurry. Specifically, the heating and boiling temperature range is 90°C.

[0115] S4, preparation of a neutral precursor slurry: neutralize the pre-precipitated precursor slurry with an alkali metal sodium source, to generate a neutral precursor slurry. Specifically, the neutralization condition is that the pH range of the slurry reaches 7.

[0116] S5, solid-liquid separation: dry the neutral precursor slurry to achieve solid-liquid separation, to obtain a polyanionic cathode material precursor powder. Specifically, the drying method of the neutral slurry is spray drying.

[0117] In the present embodiment, the inorganic phosphoric acid is phosphoric acid, pyrophosphoric acid, metaphosphoric acid; the acid liquid for regulating pH is formic acid, acetic acid. The transition metal source is cobalt source, manganese source, the cobalt source is elemental cobalt, cobalt oxide, tricobalt tetroxide, cobaltic oxide, the manganese source is elemental manganese, manganese monoxide, manganese dioxide, dimanganese trioxide, trimanganese tetroxide. The alkali metal sodium source is one or two or more of sodium hydroxide, sodium oxide, sodium peroxide, sodium carbonate, sodium bicarbonate.

[0118] Application Example 1 Na 0.64 Fe 0.72 H 0.2 PO4 precursor and Na 4.24 Fe 2.88 Synthesis of (PO4)2P2O7 material and its electrochemical performance

[0119] In the present embodiment, the Na 0.64 Fe 0.72 H 0.2 PO4 precursor is prepared by the following method, which comprises the following steps:

[0120] Step 1: Iron oxide red and phosphoric acid are mixed with water in a molar ratio of 0.36:1, formic acid is used to regulate the solution pH to 1.0, and the solution is heated at 60°C until the iron oxide red is completely dissolved, generating a transparent light green solution;

[0121] Step 2: Hydrogen peroxide is added to the above light green solution to oxidize the divalent iron in the solution to trivalent iron, generating a pre-oxidized brown-red precursor solution;

[0122] Step 3: The above brown-red precursor solution is heated and boiled at 90°C to evaporate excess formic acid, while generating a white pre-precipitate slurry;

[0123] Step 4: 0.64 moles of sodium hydroxide are added to the pre-precipitate slurry to neutralize it, reacting off excess hydrogen ions in the solution while introducing sodium ions into the solution;

[0124] Step 5: The above neutral precursor slurry is spray dried to remove excess water, achieving solid-liquid separation, and the Na 0.64 Fe 0.72 H 0.2 PO4 precursor powder is obtained.

[0125] The Na 0.64 Fe 0.72 H 0.2PO4 precursor, sodium acetate, and sucrose (added amount is 0.3 times the molar amount of sodium acetate) are mixed with water in a ratio of 1:1.66 (molar ratio), and ground for about 1 hour (in Comparative Example 1, a commercial FePO4 precursor is used, and the grinding time needs to be 15 hours, which is low in efficiency and high in energy consumption). When the particle size Dmax of the solid particles in the test slurry is ≤100 nm, the slurry is spray dried at an inlet temperature of 280°C and an outlet temperature of 100°C to achieve solid-liquid separation, and dry precursor powder is obtained. Finally, the precursor powder is calcined at 650°C for 10 hours in a nitrogen atmosphere, and after natural cooling, Na 4.24 Fe 2.88 (PO4)2P2O7 material.

[0126] Figure 1 Na 4.24 Fe 2.88 (PO4)2P2O7 material. The diffraction curve is regular and orderly, and there is almost no obvious impurity phase diffraction peak. Compared with Comparative Example 1, there is no obvious sodium iron phosphate impurity phase diffraction peak at diffraction angles of 20°, 24°, 43°, and 45°, which indicates that the mixing uniformity of Na, Fe, P, and other elements is high during the precursor preparation process, and the ion local diffusion can realize the formation and growth of the crystal nucleus during the sintering process, and finally a high-phase-purity Na 4.24 Fe 2.88 (PO4)2P2O7 material. The results in Table 1 show that the phase purity of the material is as high as 99.2% calculated by refining the XRD diffraction curve, which is much higher than that of Comparative Example 1, proving that the Na 0.64 Fe 0.72 H 0.2 PO4 precursor is excellent in adaptability for synthesizing high-phase-purity materials.

[0127] Na 4.24 Fe 2.88 (PO4)2P2O7 material, SurP, and PVDF5130 are mixed in a ratio of 9.5:0.2:0.3 by mass with NMP, and a high-speed homogenizer is used to mix the above materials uniformly to form a black slurry with uniform color and high fluidity. Then, a 150-μm four-side coater is used to coat the black slurry on an aluminum foil, and the film is dried in a vacuum drying oven at 100°C for 2 hours. A punching machine is used to punch the electrode film into a circular sheet with a radius of 0.6 mm, a metal sodium is used as the counter electrode, a 1 mol / L NaClO4 EC+DEC (1:1 vol%) +5% FEC is used as the electrolyte, and a PP / PE / PP three-layer separator is used as the separator to assemble a CR2016 type button cell in a glove box.

[0128] Figure 2 Na 4.24 Fe2.88 The first cycle charge-discharge curve of the (PO4)2P2O7 electrode, the discharge gram capacity of the material is 126.3 mAh / g at 0.1C (1C=129 mAh / g) rate, which is close to the theoretical specific capacity (129 mAh / g) of the material, and is much higher than the discharge gram capacity of 94.2 mAh / g in Comparative Example 1, indicating that the material has high phase purity, few defects in the crystal structure, high crystal completeness, more complete transition metal redox, and high capacity. In addition, as shown in Table 1, the capacity retention rate of the electrode at 10C rate is as high as 97.9% compared with 0.1C, which is much higher than 87.2% in Comparative Example 1. The possible reason is that the higher the phase purity of the material, the higher the completeness of the primary crystal grains, the fewer the grain boundaries between the crystal grains, the lower the resistance to sodium ion migration, and the rate performance is greatly improved. Finally, the capacity retention rate of the electrode at 1C rate after 1000 cycles is 99.2%, almost no decay, which may be due to the high crystal completeness of the material, the isotropic interaction force in the sodium extraction process of each crystal, and the stress generated by the volume expansion is not concentrated, so the cycle stability is maintained. In summary, the Na 0.64 Fe 0.72 H 0.2 PO4 precursor prepared by the method has excellent electrochemical performance. 4.24 Fe 2.88 The Na

[0129] Application Example 2 Na 0.95 (OH) 0.1 V 0.657 PO4 precursor and synthesis of Na 3.09 V 1.97 (PO4)3 material and its electrochemical performance

[0130] In this example, the Na 0.95 (OH) 0.1 V 0.657 The preparation method of the Na

[0131] Step 1: V2O5 and phosphoric acid are mixed with water according to a molar ratio of 0.3375:1, acetic acid is used to control the pH of the solution to 0.8, and the solution is heated to 70°C until V2O5 is completely dissolved, generating a transparent light red solution;

[0132] Step 2: Add hydrogen peroxide to the above light red solution to prevent reduction of vanadium ions in the solution and form a stable light red precursor solution;

[0133] Step 3: Boil the above brown-red precursor solution at 95°C to evaporate excess acetic acid and generate a brown pre-precipitate slurry.

[0134] Step 4: Neutralization by adding 0.95 moles of sodium hydroxide in the pre-precipitation slurry to react with the excess hydrogen ions in the solution and introduce sodium ions into the solution;

[0135] Step 5: Spray drying the above neutral precursor slurry to remove excess water and achieve solid-liquid separation, thereby obtaining Na 0.95 (OH) 0.1 V 0.657 PO4precursor powder.

[0136] The Na 0.95 (OH) 0.1 V 0.657 PO4precursor, sodium acetate, and glucose (added in an amount of 0.2 times the molar amount of sodium acetate) are mixed and ground with water in a molar ratio of 1:0.241. The grinding time is about 0.5H (in Comparative Example 2, a commercial V2O5precursor is used, and the grinding time needs to be 12H, which is high in energy consumption and time). When the particle size Dmax of the solid particles in the slurry is ≤150 nm, the slurry is spray dried at an inlet temperature of 300°C and an outlet temperature of 90°C to achieve solid-liquid separation, thereby obtaining a dry precursor powder. Finally, the precursor powder is calcined at 750°C for 8h in a nitrogen atmosphere, and after natural cooling, the Na 3.09 V 1.97 (PO4)3material is obtained. The results in Table 1 show that the material has a high phase purity of 98.3%, which is much higher than 82.1% in Comparative Example 2, indicating that the material prepared from the Na 0.95 (OH) 0.1 V 0.657 PO4precursor has a high degree of uniformity among raw materials and is less likely to phase separate during sintering due to local non-uniformity.

[0137] The Na 3.09 V 1.97 (PO4)3material, SurP, and PVDF5130 are mixed in a mass ratio of 9.5:0.2:0.3 with NMP, and the above materials are uniformly mixed using a high-speed homogenizer to form a black slurry with uniform color and high fluidity. The black slurry is then coated on an aluminum foil using a 150um four-side coater, and the film is dried in a vacuum drying oven at 100°C for 2 hours. The electrode film is punched into a circular sheet with a radius of 0.6mm using a sheet puncher, and a CR2016 type button cell is assembled in a glove box using metallic sodium as the counter electrode, 1 mol / L NaClO4EC+DEC (1:1 vol%)+5%FEC as the electrolyte, and a PP / PE / PP three-layer separator.

[0138] The electrochemical performance test results in Table 1 show that the electrode has a discharge gram capacity of 116.8 mAh / g at a rate of 0.1C (1C = 120 mAh / g), which is almost close to the exertion of the theoretical specific capacity (120 mAh / g) thereof, and is much higher than the discharge gram capacity of 100.3 mAh / g in Comparative Example 2, which is related to the higher phase purity of the material. The higher the phase purity of the material, the fewer the vacancies, defects and the like in the crystal structure, and the higher the completeness of the crystal form, which is more conducive to the exertion of high capacity of the material. In addition, as shown in Table 1, the capacity retention rate of the electrode at a rate of 10C is as high as 96.8% compared with 0.1C, which is much higher than 85.2% in Comparative Example 2, indicating that the higher the phase purity of the material, the fewer the crystal defects, and the lower the diffusion energy barrier of sodium ions in the structure, and there is no problem of high diffusion energy barrier caused by defects. In addition, the higher phase purity avoids the problem of grain boundary diffusion caused by impurities, and thus has higher diffusion performance, which is manifested as the improvement of the rate performance. Finally, the capacity retention rate of the electrode at a rate of 1C after 1000 cycles is 98.6%, and there is almost no capacity attenuation, indicating that the higher the phase purity of the material, the better the completeness of the crystal form, and the interaction force in the process of deintercalation of sodium in each crystal tends to be the same, and the stress caused by volume expansion is no longer concentrated, and the cycle stability is improved. In summary, the Na 0.95 (OH) 0.1 V 0.657 PO4 precursor has more excellent electrochemical performance due to the higher phase purity. 3.09 V 1.97 (PO4)3 material.

[0139] Comparative Example 1 Na 4.24 Fe 2.88 (PO4)2P2O7 material and its electrochemical performance

[0140] In this embodiment, the preparation method of the Na 4.24 Fe 2.88 (PO4)2P2O7 material includes the following steps:

[0141] FePO4, phosphoric acid, sodium acetate, sucrose (added amount is 0.15 times the molar amount of sodium acetate) and water are mixed and ground according to a molar ratio of 2.88:1.12:4.24, and the grinding time is about 15H (compared with Application Example 1, the efficiency is reduced, and the energy consumption is greatly increased). When the solid particle size Dmax in the test slurry is ≤100 nm, the slurry is spray dried, the inlet air temperature is 280°C, and the outlet air temperature is 100°C, to realize solid-liquid separation, and obtain dry precursor powder. Finally, the precursor powder is calcined at 650°C for 10h in a nitrogen atmosphere, and the Na 4.24 Fe 2.88 (PO4)2P2O7 material is obtained after natural cooling.

[0142] Figure 1 Na 4.24 Fe 2.88 XRD of the (PO4)2P2O7 material, in which there are many small disordered diffraction peaks in the diffraction curve, indicating that there are obvious impurity microcrystals in the material. By comparison, the diffraction peaks generated at diffraction angles of 20°, 24°, 43° and 45° can be attributed to the sodium iron phosphate impurity phase. The formation reason is related to the uniformity of element mixing in the precursor slurry in the material synthesis. Although FePO4 in the precursor has been ground to below 100 nm, its own high crystallinity is difficult to melt in the high-temperature sintering process, resulting in that it is used as a template in the sintering process, and sodium ions are embedded into its crystal lattice to form a sodium iron phosphate impurity phase. The results in Table 1 show that by refining the XRD diffraction curve, it can be calculated that the phase purity of the material is only 75.4%, which is much lower than that of the application example 1, proving that using FePO4 as a precursor has certain barriers in synthesizing materials, and it is difficult to prepare a material with high phase purity.

[0143] Na 4.24 Fe 2.88 The (PO4)2P2O7 material, SurP and PVDF5130 were mixed in a mass ratio of 9.5:0.2:0.3 with NMP, and a high-speed homogenizer was used to mix the above materials uniformly to form a black slurry with uniform color and high fluidity. Then a 150-μm four-side coater was used to coat the black slurry on an aluminum foil, and the film was dried in a 100°C vacuum drying oven for 2 hours. A punching machine was used to punch the electrode film into a circular sheet with a radius of 0.6 mm. A metal sodium was used as a counter electrode, 1 mol / L NaClO4 EC+DEC (1:1 vol%)+5% FEC was used as an electrolyte, and a PP / PE / PP three-layer separator was used as a separator to assemble a CR2016 type button cell in a glove box.

[0144] Figure 2 Na 4.24 Fe 2.88The first cycle charge-discharge curve of the (PO4)2P2O7 electrode, the material has a discharge capacity of only 94.2 mAh / g at 0.1C (1C = 129 mAh / g) rate, which is much lower than the discharge capacity of the material in application example 1, which is consistent with the lower purity of the material, indicating the presence of non-active sodium iron phosphate impurities, which reduces the effective active ingredients per unit mass of the material, the number of transition metal redox and the number of sodium ions extracted, and the material capacity is reduced. In addition, as shown in Table 1, the capacity retention rate of the electrode at 10C rate is only 87.2% compared with 0.1C, the lower rate performance is related to the presence of sodium iron phosphate impurities in the material, there are more grain boundaries between the impurities and the main phase, the transmission rate of sodium ions at the grain boundary is low, and there is a certain hysteresis, which leads to the decline of the rate performance of the material. Finally, the capacity retention rate of the electrode at 1C rate after 1000 cycles is only 91.3%, which has a certain decay, the reason is that during the charge-discharge process, Na 4.24 Fe 2.88 The continuous expansion and contraction of the (PO4)2P2O7 main phase crystal will cause micro-cracks between the crystal surface and the sodium iron phosphate crystal, and the electrolyte will penetrate into the surface, which will accelerate the dissolution of the interface elements and cause the destruction of the interface structure, thus reducing the cycle stability. In summary, the Na 4.24 Fe 2.88 The non-uniformity of the material reaction caused by the lower phase purity of the Na

[0145] Synthesis of Na 3.09 V 1.97 (PO4)3 material and its electrochemical performance

[0146] The preparation steps of the Na 3.09 V 1.97 (PO4)3 material include:

[0147] V2O5, phosphoric acid, sodium acetate, and glucose (added amount is 0.1 times the molar amount of sodium acetate) are mixed and ground with water in a molar ratio of 0.985:3:3.09, and the grinding time is about 12H (the grinding efficiency is lower than that in application example 2, and the energy consumption increases). When the solid particle size Dmax in the test slurry is ≤150 nm, the slurry is spray dried, the inlet air temperature is 300°C, and the outlet air temperature is 90°C, to achieve solid-liquid separation, and obtain dry precursor powder. Finally, the precursor powder is calcined at 750°C for 8h in a nitrogen atmosphere, and after natural cooling, the Na 3.09 V 1.97(PO4)3material. The results in Table 1 show that the phase purity of the material is only 82.1%, indicating that the material prepared from the V2O5 precursor has poor mixing uniformity among raw materials, i.e., even if the V2O5 is ground to a nano state, its high crystallinity cannot be melted during sintering, resulting in uneven ion distribution in the local area and a large amount of impurities.

[0148] Na 3.09 V 1.97 The Na 3.09 V 1.97 (PO4)3material, SurP, and PVDF5130 were mixed in a mass ratio of 9.5:0.2:0.3 with NMP, and a high-speed homogenizer was used to mix the above materials uniformly to form a black slurry with uniform color and high fluidity. Then, a 150-μm four-side coater was used to coat the black slurry on an aluminum foil, and the film was dried in a vacuum drying oven at 100°C for 2 hours. A puncher was used to punch the electrode film into a circular sheet with a radius of 0.6 mm, and a CR2016 type button cell was assembled in a glove box with a metal sodium as a counter electrode, 1 mol / L NaClO4EC+DEC (1:1 vol%)+5% FEC as an electrolyte, and a PP / PE / PP three-layer separator.

[0149] The results of the electrochemical performance test in Table 1 show that the discharge gram capacity of the material is only 100.3 mAh / g at a rate of 0.1C (1C=120 mAh / g), which is much lower than that of the material in Application Example 2, indicating that the low phase purity of the material and the presence of a large amount of impurities reduce the effective active ingredients per unit mass of the material, resulting in a decrease in the gram capacity of the material. In addition, as shown in Table 1, the capacity retention rate of the electrode at a rate of 10C is only 85.2% compared with that at a rate of 0.1C, and the low rate performance is related to the presence of impurities in the material. The impurities are mostly in the form of nano-microcrystals embedded in the main phase material, resulting in a large number of grain boundaries in the complex phase structure. The ion diffusion energy barrier at the grain boundaries is high, and it is usually difficult to diffuse effectively. The macroscopic reaction is a decrease in the rate performance. Finally, the capacity retention rate of the electrode at a rate of 1C after 1000 cycles is only 89.5%, which decays to a certain extent. The reason is that, during the charging and discharging process, the continuous expansion and contraction of the Na 3.09 V 1.97 The micro-cracks between the main phase crystals of Na 3.09 V 1.97 The anisotropy of the reaction of the Na

[0150] Table 1 Performance test results

[0151]

[0152] The above embodiments are merely specific embodiments of the present application and are described in more detail and in a specific manner, but should not be construed as limiting the scope of the patent rights of the present application. It should be noted that, for those of ordinary skill in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, and these obvious replacement forms all belong to the protection scope of the present application.

Claims

1. A preparation method of a cathode material precursor for a polyanionic sodium ion battery, the chemical general formula of the precursor being A x M y OH z PO4, where A is the alkali metal element Na, M is one or more of the transition metal elements Fe, V, Co or Mn, and the value ranges of x, y, and z are 0 < x < 0.5, 0.4 < y < 1.0, 0 < z < 0.5 and x + 3y - z = 3, respectively. The characteristics are The preparation method of this precursor includes the following steps: S1. Preparation of precursor solution: Dissolve and mix transition metal source and inorganic phosphoric acid, add acid to adjust the pH of the solution and heat to promote the dissolution of transition metal source to obtain precursor solution. Inorganic phosphoric acid is one or more of phosphoric acid, pyrophosphoric acid and metaphosphoric acid, and transition metal source is one or more of iron source, vanadium source, cobalt source and manganese source. S2. Preparation of pre-oxidized precursor solution: Hydrogen peroxide is added to the above precursor solution to generate a pre-oxidized precursor solution; S3. Preparation of preprecipitated precursor slurry: The above preoxidation precursor solution is heated and boiled to generate preprecipitated precursor slurry. S4. Preparation of neutral precursor slurry: Neutralize the preprecipitated precursor slurry with an alkali metal sodium source to generate a neutral precursor slurry. S5. Solid-liquid separation: Dry the neutral precursor slurry to achieve solid-liquid separation, thereby obtaining the precursor powder for polyanionic cathode materials.

2. The method for preparing the precursor of the polyanionic sodium-ion battery cathode material according to claim 1, characterized in that: In step S1, the pH range is 0-2, and the heating temperature range is 50-80℃.

3. The method for preparing the precursor of the polyanionic sodium-ion battery cathode material according to claim 1, characterized in that: In step S2, the amount of hydrogen peroxide added is 1-3 times the molar amount of the metal element in the transition metal source.

4. The method for preparing the precursor of the polyanionic sodium-ion battery cathode material according to claim 1, characterized in that: In step S3, the heating and boiling temperature range is 80-100℃.

5. The method for preparing the precursor of the polyanionic sodium-ion battery cathode material according to claim 1, characterized in that: In step S4, the neutralization condition is that the pH range of the slurry is 6-8.

6. The method for preparing the precursor of the polyanionic sodium-ion battery cathode material according to claim 1, characterized in that: In step S5, the drying method for the neutral slurry is one or a combination of two or more of the following: spray drying, high-temperature evaporation, flash drying, and high-temperature pyrolysis.

7. The method for preparing the precursor of the polyanionic sodium-ion battery cathode material according to claim 1, characterized in that: In step S1, the acid used to adjust the pH is one or more of formic acid, acetic acid, hydrofluoric acid, nitric acid, and hydrochloric acid.

8. The method for preparing the precursor of the polyanionic sodium-ion battery cathode material according to claim 1, characterized in that: In step S1, the iron source is one or more of elemental iron, ferric oxide, ferrous oxide, iron(II) tetroxide, ferrous hydroxide, and ferric hydroxide; the vanadium source is one or more of elemental vanadium, vanadium pentoxide, vanadium monoxide, vanadium dioxide, and vanadium trioxide; the cobalt source is one or more of elemental cobalt, cobalt oxide, cobalt(II) tetroxide, and high cobalt oxide; and the manganese source is one or more of elemental manganese, manganese monoxide, manganese dioxide, manganese(II) tetroxide, and manganese(II) tetroxide.

9. The method for preparing the precursor of the polyanionic sodium-ion battery cathode material according to claim 1, characterized in that: In step S4, the alkali metal sodium source is one or more of sodium hydroxide, sodium oxide, sodium peroxide, sodium carbonate, and sodium bicarbonate.

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