Highly compacted precursor for sodium-ion battery cathode material and preparation method thereof

Abstract

The application discloses a precursor for a high-compaction polyanionic sodium-ion battery positive electrode material and a preparation method thereof. x PO y ·mH2O, wherein M is a transition metal element Fe and / or Mn, the value range of x, y and m is in a relationship of 0.4

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of sodium ion batteries, in particular to a precursor for a high-compaction polyanionic sodium ion battery positive electrode material and a preparation method thereof. BACKGROUND

[0002] The polyanionic sodium ion battery positive electrode material includes sodium iron pyrophosphate phosphate, sodium pyrophosphate iron, sodium vanadium phosphate, sodium vanadium fluorophosphate and the like, is a three-dimensional framework structure formed by the mutual intersection arrangement of alkali metal tetrahedrons, transition metal tetrahedrons / octahedrons and anion tetrahedrons / triangular prisms in a common point / surface / line mode, and has excellent structural stability, thermodynamic stability, cycle stability, rate performance and the like, and has been widely favored by the market.

[0003] At present, the commercially available sodium iron pyrophosphate and the like are synthesized by a solid phase method, high-crystallinity anhydrous FePO4 and FeC2O4 are used as transition metal precursor sources, water-soluble sodium sources, phosphorus sources and carbon sources are combined, and the material is prepared through processes such as grinding mixing, spray drying and sintering.

[0004] However, the high-crystallinity FePO4 and FeC2O4 are difficult to completely dissolve in the solid grinding process, and the solid particles with a size of tens to hundreds of nanometers are often suspended in the solution, the solid particles contain tens of thousands of atoms, and from the local point of view, the sodium, transition metal and phosphorus elements in the slurry are difficult to mix uniformly, and the sintering process is prone to cause phase separation, and affect the exertion of the electrochemical performance of the material.

[0005] Meanwhile, the high-crystallinity anhydrous FePO4 and FeC2O4 solid particles are difficult to melt and agglomerate in the sintering process, a large number of pores are left in the product particle, the compactness of the material is affected, and the compaction density is low. Therefore, in order to obtain a polyanionic material with high phase purity, high compaction and low manufacturing process cost, a suitable precursor needs to be developed. SUMMARY

[0006] The application aims to provide a precursor for a high-compaction polyanionic sodium ion battery positive electrode material and a preparation method thereof, which has the characteristics of high compaction density, high phase purity, meeting different system requirements, excellent electrochemical performance and low cost.

[0007] The application can be implemented by the following technical scheme:

[0008] The application discloses a precursor for a high-compaction polyanionic sodium ion battery positive electrode material, the chemical general formula of the precursor is M x PO y·mH2O, wherein M is transition metal element Fe and / or Mn, the value range relation of x, y, m is 0.4 < x < 1, y = 3.5 / 3.75; m >= 0.

[0009] Another aspect of the present application is to protect a preparation method of a high-compaction polyanionic sodium-ion battery cathode material precursor, comprising the following steps:

[0010] S1, preparation of a precursor solution: wet mixing a transition metal source and an organic acid, temperature control reaction, to generate a precursor solution;

[0011] S2, preparation of a pre-oxidized precursor solution: adding an oxidizing agent to the above solution to oxidize the divalent metal ions in the solution to trivalent, to generate a pre-oxidized precursor solution;

[0012] S3, preparation of an ionic mixture: adding a phosphorus source to the above pre-oxidized precursor solution to form a uniform ionic mixture;

[0013] S4, preparation of a precursor powder: drying the above ionic mixture to remove moisture, to obtain a dried precursor powder;

[0014] S5, high-temperature calcination: high-temperature calcination of the above precursor powder to remove volatile components in the powder, and at the same time, to make the phosphate group undergo polycondensation reaction, and after natural cooling, M x PO y ·mH2O material.

[0015] The precursor of the present application has a general chemical formula of M x PO y ·mH2O, which uses a transition metal source to react with an organic acid to form water-soluble transition metal ions, then uses an oxidizing agent to oxidize and mix with a phosphorus source, evaporates to remove the solvent, and then further calcines to deoxidize the phosphate group to pyrophosphate, to finally form the required precursor material. The precursor is a long-range disordered structure formed by the mutual embedding of transition metal ions and phosphate groups / pyrophosphate groups, has a small particle size, and has no crystallinity, is extremely easy to grind and disperse, has good uniformity when mixed with other components, and has high phase purity and compaction density of the prepared material after sintering, and excellent electrochemical performance.

[0016] Further, in step S1, the molar ratio of the transition metal source and the organic acid is 1:5-15; the purpose is to ensure that there are enough hydrogen ions in the solution to dissolve the transition metal source, so that it is completely dissolved in the solution in the form of ions; when the molar ratio of the transition metal source and the organic acid is less than 1:5, the transition metal source cannot be effectively dissolved.

[0017] Further, in step S1, the temperature of the temperature-controlled reaction is 70-120°C. When the temperature is lower than 70°C, the transition metal oxide cannot be effectively dissolved, and when the temperature is higher than 120°C, the reaction speed is too fast, the energy consumption is high, there is a safety risk, and the cost investment is large.

[0018] Further, in step S2, the amount of the added oxidizing agent is 1-2.5 times the molar amount of the transition metal ions in the solution. When the molar amount of the oxidizing agent is less than 1 times the molar amount of the transition metal ions, the excess metal ions in the solution cannot effectively undergo oxidation reaction, and when the molar amount of the oxidizing agent is more than 2.5 times the molar amount of the transition metal ions, the residual oxidizing agent increases the production cost.

[0019] Further, in step S5, the temperature of the high-temperature calcination is 150-400°C. The purpose is to decompose the volatile components such as carbon, oxygen, and hydrogen in the precursor, and at the same time, to make part of the phosphate groups polycondense into pyrophosphate groups under the catalysis of hydrogen ions, so as to finally form MxPOy·mH2O material; when the temperature is lower than 150°C, the volatile components in the precursor powder are difficult to be completely decomposed and removed, and at the same time, the phosphate groups are also difficult to polycondense into pyrophosphate groups; and when the temperature is higher than 400°C, the MxPOy·mH2O material is transitionally melted and crystallized to form dense and hard block-shaped particles, which affects the subsequent synthesis of the material. x PO y ·mH2O material; when the temperature is lower than 150°C, the volatile components in the precursor powder are difficult to be completely decomposed and removed, and at the same time, the phosphate groups are also difficult to polycondense into pyrophosphate groups; and when the temperature is higher than 400°C, the MxPOy·mH2O material is transitionally melted and crystallized to form dense and hard block-shaped particles, which affects the subsequent synthesis of the material.

[0020] Further, in step S2, the oxidizing agent is one or two or more of hydrogen peroxide, peroxyacetic acid, and oxygen, which can oxidize the transition metal ions. The purpose is to oxidize the divalent metal ions in the solution, so that they can undergo reduction reaction in the subsequent preparation of the polyanion material, and form a better framework structure in the high-temperature process.

[0021] Further, in step S1, the transition metal source is iron source and / or manganese source. The iron source is one or two or more of elemental iron, red iron oxide, ferrous oxide, magnetite, iron hydroxide, hydroxyl iron oxide, ferrous hydroxide, ferric citrate, and ferric oxalate, and the manganese source is one or two or more of elemental manganese, manganese monoxide, manganese dioxide, dimanganese trioxide, trimanganese tetraoxide, manganese oxalate, manganese hydroxide, manganous acid anhydride, manganic acid anhydride, and permanganic acid anhydride. The organic acid is one or two or more of formic acid, acetic acid, citric acid, malic acid, ascorbic acid, tartaric acid, and salicylic acid.

[0022] Further, in step S3, the phosphorus source is one or two or more of phosphoric acid, pyrophosphoric acid, metaphosphoric acid, and polyphosphoric acid.

[0023] Further, in step S4, the drying method is one or two or more of flash drying, spray drying, high-temperature pyrolysis, freeze drying, air blowing drying, and natural evaporation.

[0024] The application discloses a precursor for a high-compaction polyanionic sodium ion battery positive electrode material and a preparation method thereof.

[0025] First, the compaction density is high, M x PO y The mH2O precursor and the additional sodium source are uniformly mixed through grinding, mutual bonding between elements is realized, the distance between ions is short, a crystal nucleus can be formed in situ without long-distance diffusion, continuously diffuses and grows along the epitaxy, a dense large-grain single crystal is formed, the distribution of pores between the crystals is less, and the compaction density is greatly improved.

[0026] Second, the phase purity is high: M x PO y The transition metal, phosphate or pyrophosphate in the mH2O precursor is uniformly mixed, when the mH2O precursor is used to prepare the polyanionic material, only a water-soluble sodium source required by the preparation needs to be supplemented, the water-soluble sodium source penetrates into the material through the pores in the precursor, uniform mixing between elements is realized, and a high-phase-purity material is prepared.

[0027] Third, different system requirements are met: M x PO y The element ratio of the mH2O precursor is y=3.5 / 3.75, that is, the mH2O precursor can be used to prepare a pure pyrophosphate precursor or a phosphate / pyrophosphate composite precursor by adjusting the PH and the element content, the mH2O precursor is suitable for the structural design requirements of existing polyanionic systems (including materials such as pyrophosphate iron / manganese sodium, pyrophosphate phosphate iron / manganese sodium and non-metering ratio composite phosphate iron / manganese sodium), and the structure of a high-purity-phase material can be controlled.

[0028] Fourth, the electrochemical performance is excellent: because M x PO y The mH2O precursor can realize uniform mixing between elements, so that the material prepared from the mH2O precursor has the characteristics of high crystallinity and high phase purity, the elements in the structure are regularly and orderly arranged, the sodium ion deintercalation energy barrier is low, the material has high charge and discharge capacity and excellent rate performance.

[0029] Fifth, the cost is low: M x PO y The sintering temperature of the mH2O precursor is low, the crystallinity is weak, and the bonding energy between the transition metal and the phosphate / pyrophosphate in the structure is weak, so that the mH2O precursor can realize uniform mixing without long-time grinding when the mH2O precursor is used to prepare the polyanionic material, the energy consumption of front-end grinding and the equipment investment are greatly reduced, and the production cost is effectively reduced. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 For the application example 1, the.Fe 0.7275 PO3.75 • Preparation of 0.01 H2O precursor and Na4Fe 2.91 (PO4)2P2O7 material SEM.

[0031] Figure 2 is Preparation of Na4Fe 2.91 (PO4)2P2O7 material SEM. DETAILED DESCRIPTION

[0032] In order to make the technical personnel in the technical field better understand the technical solutions of the present application, the product of the present application will be further described in detail below in combination with embodiments.

[0033] The application discloses a high-compaction polyanionic sodium-ion battery positive electrode material precursor, which has a chemical general formula of M x PO y ·mH2O, wherein M is a transition metal element Fe and / or Mn, the value range relationship of x, y and m is 0.4

[0034] Another aspect of the application is to protect a preparation method of a high-compaction polyanionic sodium-ion battery positive electrode material precursor, which comprises the following steps:

[0035] S1, preparation of a precursor solution: wet-mixing a transition metal source and an organic acid, temperature-controlled reaction to generate a precursor solution;

[0036] S2, preparation of a pre-oxidized precursor solution: adding an oxidizing agent to the above solution to oxidize the divalent metal ions in the solution into trivalent, and generating a pre-oxidized precursor solution;

[0037] S3, preparation of an ionic mixture: adding a phosphorus source to the above pre-oxidized precursor solution to form a uniform ionic mixture;

[0038] S4, preparation of a precursor powder: drying the above ionic mixture to remove water, and obtaining a dried precursor powder;

[0039] S5, high-temperature calcination: high-temperature calcining the above precursor powder, and obtaining M x PO y ·mH2O material after natural cooling.

[0040] Further, in step S1, the molar ratio of the transition metal source and the organic acid is 1:5-15.

[0041] Further, in step S1, the temperature-controlled reaction temperature is 70-120°C.

[0042] Further, in step S2, the amount of the oxidizing agent added is 1-2.5 times the molar amount of the transition metal ions in the solution.

[0043] Further, in step S5, the temperature of the high-temperature calcination is 150-400°C.

[0044] Further, in step S2, the oxidizing agent is one or two or more of hydrogen peroxide, peroxyacetic acid, and oxygen.

[0045] Further, in step S1, the transition metal source is an iron source and / or a manganese source, the iron source is one or two or more of elemental iron, red iron oxide, ferrous oxide, magnetite, iron hydroxide, iron oxyhydroxide, ferrous hydroxide, ferric citrate, and ferric oxalate, the manganese source is one or two or more of elemental manganese, manganese monoxide, manganese dioxide, dimanganese trioxide, trimanganese tetraoxide, manganese oxalate, manganese hydroxide, manganous anhydride, manganic anhydride, and permanganic anhydride, and the organic acid is one or two or more of formic acid, acetic acid, citric acid, malic acid, ascorbic acid, and tartaric acid.

[0046] Further, in step S3, the phosphorus source is one or two or more of phosphoric acid, pyrophosphoric acid, metaphosphoric acid, and polyphosphoric acid.

[0047] Further, in step S4, the drying method is one or two or more of flash drying, spray drying, high-temperature pyrolysis, freeze drying, air blowing drying, and natural evaporation.

[0048] Example 1

[0049] This example relates to a precursor for a high-compaction polyanionic sodium-ion battery cathode material, the precursor having a general chemical formula of M x PO y ·mH2O, wherein M is a transition metal element Fe, the value range relationship of x, y, and m is 0.4 < x < 1, y = 3.5 / 3.75, and m ≥ 0.

[0050] The precursor is prepared by the following method:

[0051] S1, preparation of a precursor solution: wet-mixing a transition metal source and an organic acid according to a molar ratio of 1:15, controlling the temperature to 100°C to react, and generating a precursor solution. Specifically, the transition metal source is an iron source, the iron source is iron hydroxide, iron oxyhydroxide, ferrous hydroxide, ferric citrate, and ferric oxalate, and the organic acid is formic acid, acetic acid, citric acid, and malic acid.

[0052] S2, preparation of pre-oxidized precursor solution: an oxidizing agent is added to the above solution to oxidize the divalent metal ions in the solution to trivalent, thereby generating a pre-oxidized precursor solution. Specifically, the amount of the oxidizing agent added is 1.5 times the molar amount of the transition metal ions in the solution; the oxidizing agent is hydrogen peroxide, peroxyacetic acid.

[0053] S3, preparation of ionic mixture: a phosphorus source is added to the above pre-oxidized precursor solution to form a uniform ionic mixture. Specifically, the phosphorus source is phosphoric acid, pyrophosphoric acid, metaphosphoric acid.

[0054] S4, preparation of precursor powder: the above ionic mixture is dried to remove moisture, thereby obtaining a dried precursor powder. Specifically, the drying method is flash drying, spray drying.

[0055] S5, high-temperature calcination: the above precursor powder is subjected to high-temperature calcination, and after natural cooling, a M x PO y ·mH2O material is obtained. Specifically, the temperature of the high-temperature calcination is 150°C.

[0056] Example 2

[0057] This example relates to a high-compaction precursor for a polyanionic sodium-ion battery cathode material, which has a chemical general formula of M x PO y ·mH2O, wherein M is a transition metal element Mn, the value range relationship of x, y, m is 0.4 < x < 1, y = 3.5 / 3.75; m ≥ 0.

[0058] The precursor is prepared by the following method:

[0059] S1, preparation of precursor solution: a transition metal source and an organic acid are mixed wet according to a molar ratio of 1:10, and a precursor solution is generated by controlling the temperature to 120°C. Specifically, the transition metal source is a manganese source, and the manganese source is trimanganese tetraoxide, manganese oxalate, manganese hydroxide, manganous anhydride, manganic anhydride, permanganic anhydride; the organic acid is formic acid, acetic acid, salicylic acid.

[0060] S2, preparation of pre-oxidized precursor solution: an oxidizing agent is added to the above solution to oxidize the divalent metal ions in the solution to trivalent, thereby generating a pre-oxidized precursor solution. Specifically, the amount of the oxidizing agent added is 1.5 times the molar amount of the transition metal ions in the solution; the oxidizing agent is hydrogen peroxide, peroxyacetic acid.

[0061] S3, preparation of ionic mixture: a phosphorus source is added to the above pre-oxidized precursor solution to form a uniform ionic mixture. Specifically, the phosphorus source is phosphoric acid, pyrophosphoric acid, metaphosphoric acid.

[0062] S4, Preparation of precursor powder: dry the above ion state mixture to remove moisture to obtain dry precursor powder. Specifically, the drying method is high temperature pyrolysis, air drying.

[0063] S5, High temperature calcination: high temperature calcination of the above precursor powder, and after natural cooling, M x PO y ·mH2O material. Specifically, the high temperature calcination temperature is 400°C.

[0064] Example 3

[0065] This embodiment relates to a high compaction precursor for polyanionic sodium ion battery cathode material, the chemical formula of the precursor is M x PO y ·mH2O, wherein M is transition metal elements Fe and Mn, the value range relationship of x, y, m is 0.4 < x < 1, y = 3.5 / 3.75; m ≥ 0.

[0066] The precursor is prepared by the following method:

[0067] S1, Preparation of precursor solution: wet mix transition metal source and organic acid according to the molar ratio of 1:5-15, control the temperature at 70°C to react, and generate precursor solution. Specifically, the transition metal source is iron source and manganese source, the iron source is magnetite, iron hydroxide, iron hydroxide, ferrous hydroxide, iron citrate, iron oxalate, and the manganese source is elemental manganese, manganese monoxide, manganese dioxide; the organic acid is citric acid, malic acid, ascorbic acid.

[0068] S2, Preparation of pre-oxidized precursor solution: add oxidizing agent to the above solution to oxidize the divalent metal ions in the solution to trivalent, and generate pre-oxidized precursor solution. Specifically, the addition amount of oxidizing agent is 2.5 times the molar amount of transition metal ions in the solution; the oxidizing agent is hydrogen peroxide.

[0069] S3, Preparation of ion state mixture: add phosphorus source to the above pre-oxidized precursor solution to form a uniform ion state mixture. Specifically, the phosphorus source is metaphosphoric acid, polyphosphoric acid.

[0070] S4, Preparation of precursor powder: dry the above ion state mixture to remove moisture to obtain dry precursor powder. Specifically, the drying method is cold drying, air drying.

[0071] S5, High temperature calcination: high temperature calcination of the above precursor powder, and after natural cooling, M x PO y ·mH2O material. Specifically, the high temperature calcination temperature is 300°C.

[0072] Example 4

[0073] The embodiment relates to a precursor for a high-compaction polyanionic sodium-ion battery positive electrode material, the precursor has a chemical general formula of M x PO y ·mH2O, wherein M is a transition metal element Fe, the value range relationship of x, y and m is 0.4 < x < 1, y = 3.5 / 3.75, and m >= 0.

[0074] The precursor is prepared by the following method.

[0075] S1, preparation of a precursor solution: transition metal sources and organic acids are mixed in a wet method according to a molar ratio of 1:8, temperature control is 100 DEG C, and a precursor solution is generated. Specifically, the transition metal source is an iron source, the iron source is elemental iron, red iron oxide, ferrous oxide, magnetite, iron hydroxide, hydroxyl iron oxide, ferrous hydroxide; the organic acid is formic acid, acetic acid, citric acid, malic acid, ascorbic acid.

[0076] S2, preparation of a pre-oxidized precursor solution: an oxidizing agent is added to the above solution, so that divalent metal ions in the solution are oxidized into trivalent, and a pre-oxidized precursor solution is generated. Specifically, the addition amount of the oxidizing agent is 1-2.5 times the molar amount of the transition metal ions in the solution; the oxidizing agent is peracetic acid, oxygen.

[0077] S3, preparation of an ionic mixture: a phosphorus source is added to the above pre-oxidized precursor solution, and a uniform ionic mixture is formed. Specifically, the phosphorus source is phosphoric acid, pyrophosphoric acid.

[0078] S4, preparation of a precursor powder: the above ionic mixture is dried to remove water, and a dried precursor powder is obtained. Specifically, the drying mode is air drying, natural evaporation.

[0079] S5, high-temperature calcination: the above precursor powder is high-temperature calcined, and the M x PO y ·mH2O material is obtained after natural cooling. Specifically, the high-temperature calcination temperature is 250 DEG C.

[0080] Embodiment 5

[0081] The embodiment relates to a precursor for a high-compaction polyanionic sodium-ion battery positive electrode material, the precursor has a chemical general formula of M x PO y ·mH2O, wherein M is a transition metal element Mn, the value range relationship of x, y and m is 0.4 < x < 1, y = 3.5 / 3.75, and m >= 0.

[0082] The precursor is prepared by the following method.

[0083] S1, Preparation of precursor solution: the transition metal source and organic acid are mixed in a molar ratio of 1:12, and the reaction is controlled at 110°C to generate a precursor solution. Specifically, the transition metal source is a manganese source, and the manganese source is elemental manganese, manganese monoxide, manganese dioxide, or manganese sesquioxide; the organic acid is formic acid, acetic acid, citric acid, or malic acid.

[0084] S2, Preparation of pre-oxidized precursor solution: an oxidizing agent is added to the above solution to oxidize the divalent metal ions in the solution to trivalent, generating a pre-oxidized precursor solution. Specifically, the amount of oxidizing agent added is 2 times the molar amount of transition metal ions in the solution; the oxidizing agent is hydrogen peroxide, peroxyacetic acid, or oxygen.

[0085] S3, Preparation of ionic mixture: a phosphorus source is added to the above pre-oxidized precursor solution to form a uniform ionic mixture. Specifically, the phosphorus source is metaphosphoric acid or polyphosphoric acid.

[0086] S4, Preparation of precursor powder: the above ionic mixture is dried to remove moisture, obtaining a dry precursor powder. Specifically, the drying method is spray drying.

[0087] S5, High-temperature calcination: the above precursor powder is high-temperature calcined, and after natural cooling, a Na4Fe x PO y ·0.01H2O material is obtained. Specifically, the high-temperature calcination temperature is 350°C.

[0088] Application Example 1 Preparation of Fe 0.7275 PO 3.75 ·0.01H2O precursor and synthesis of Na4Fe 2.91 (PO4)2P2O7 material and its electrochemical performance

[0089] Step 1: high-purity iron powder and formic acid are mixed in a molar ratio of 1:10 with water, heated and reacted at 100°C to generate a transparent green solution; Step 2: hydrogen peroxide is slowly added to the above green solution, and the amount of addition is 1.5 times the molar amount of iron ions in the solution, so that the divalent iron ions in the solution are oxidized to trivalent, generating a pre-oxidized precursor solution; Step 3: phosphoric acid is added to the above pre-oxidized precursor solution, and the amount of addition is 5.15 times the molar amount of iron ions in the solution, forming a uniform ionic mixture; Step 4: the above ionic mixture is spray dried, with an inlet air temperature of 300°C and an outlet air temperature of 100°C, to remove moisture and obtain a dry precursor powder; Step 5: the above precursor powder is high-temperature calcined to remove volatile components such as carbon, hydrogen, and oxygen in the powder, and to make the phosphate group deoxidize and polycondense to form pyrophosphate group, and after natural cooling, a Fe 0.7275 PO 3.75 ·0.01H2O material is obtained.

[0090] FePO4·0.01H2O precursor, sodium acetate and citric acid were mixed with water in a ratio of 1:4:0.2 (molar ratio of sodium acetate), and then ground for about 0.1 h. Compared with Comparative Example 1, the grinding time was greatly reduced, and the main reason was that the FePO4·0.01H2O precursor was in a low-temperature sintering phase, the particle crystallinity was low, the ion bonding energy was weak, and the grinding was easy. 0.7275 PO4·0.01H2O precursor, sodium acetate and citric acid were mixed with water in a ratio of 1:4:0.2 (molar ratio of sodium acetate), and then ground for about 0.1 h. Compared with Comparative Example 1, the grinding time was greatly reduced, and the main reason was that the FePO4·0.01H2O precursor was in a low-temperature sintering phase, the particle crystallinity was low, the ion bonding energy was weak, and the grinding was easy. 3.75 PO4·0.01H2O precursor, sodium acetate and citric acid were mixed with water in a ratio of 1:4:0.2 (molar ratio of sodium acetate), and then ground for about 0.1 h. Compared with Comparative Example 1, the grinding time was greatly reduced, and the main reason was that the FePO4·0.01H2O precursor was in a low-temperature sintering phase, the particle crystallinity was low, the ion bonding energy was weak, and the grinding was easy. 0.7275 PO4·0.01H2O precursor, sodium acetate and citric acid were mixed with water in a ratio of 1:4:0.2 (molar ratio of sodium acetate), and then ground for about 0.1 h. Compared with Comparative Example 1, the grinding time was greatly reduced, and the main reason was that the FePO4·0.01H2O precursor was in a low-temperature sintering phase, the particle crystallinity was low, the ion bonding energy was weak, and the grinding was easy. 3.75 PO4·0.01H2O precursor, sodium acetate and citric acid were mixed with water in a ratio of 1:4:0.2 (molar ratio of sodium acetate), and then ground for about 0.1 h. Compared with Comparative Example 1, the grinding time was greatly reduced, and the main reason was that the FePO4·0.01H2O precursor was in a low-temperature sintering phase, the particle crystallinity was low, the ion bonding energy was weak, and the grinding was easy. 2.91 PO4·0.01H2O precursor, sodium acetate and citric acid were mixed with water in a ratio of 1:4:0.2 (molar ratio of sodium acetate), and then ground for about 0.1 h. Compared with Comparative Example 1, the grinding time was greatly reduced, and the main reason was that the FePO4·0.01H2O precursor was in a low-temperature sintering phase, the particle crystallinity was low, the ion bonding energy was weak, and the grinding was easy.

[0091] Figure 1 PO4·0.01H2O precursor, sodium acetate and citric acid were mixed with water in a ratio of 1:4:0.2 (molar ratio of sodium acetate), and then ground for about 0.1 h. Compared with Comparative Example 1, the grinding time was greatly reduced, and the main reason was that the FePO4·0.01H2O precursor was in a low-temperature sintering phase, the particle crystallinity was low, the ion bonding energy was weak, and the grinding was easy. 2.91 PO4·0.01H2O precursor, sodium acetate and citric acid were mixed with water in a ratio of 1:4:0.2 (molar ratio of sodium acetate), and then ground for about 0.1 h. Compared with Comparative Example 1, the grinding time was greatly reduced, and the main reason was that the FePO4·0.01H2O precursor was in a low-temperature sintering phase, the particle crystallinity was low, the ion bonding energy was weak, and the grinding was easy. 3 PO4·0.01H2O precursor, sodium acetate and citric acid were mixed with water in a ratio of 1:4:0.2 (molar ratio of sodium acetate), and then ground for about 0.1 h. Compared with Comparative Example 1, the grinding time was greatly reduced, and the main reason was that the FePO4·0.01H2O precursor was in a low-temperature sintering phase, the particle crystallinity was low, the ion bonding energy was weak, and the grinding was easy. 0.7275 PO4·0.01H2O precursor, sodium acetate and citric acid were mixed with water in a ratio of 1:4:0.2 (molar ratio of sodium acetate), and then ground for about 0.1 h. Compared with Comparative Example 1, the grinding time was greatly reduced, and the main reason was that the FePO4·0.01H2O precursor was in a low-temperature sintering phase, the particle crystallinity was low, the ion bonding energy was weak, and the grinding was easy. 3.75 PO4·0.01H2O precursor, sodium acetate and citric acid were mixed with water in a ratio of 1:4:0.2 (molar ratio of sodium acetate), and then ground for about 0.1 h. Compared with Comparative Example 1, the grinding time was greatly reduced, and the main reason was that the FePO4·0.01H2O precursor was in a low-temperature sintering phase, the particle crystallinity was low, the ion bonding energy was weak, and the grinding was easy.

[0092] The PO4·0.01H2O precursor, sodium acetate and citric acid were mixed with water in a ratio of 1:4:0.2 (molar ratio of sodium acetate), and then ground for about 0.1 h. Compared with Comparative Example 1, the grinding time was greatly reduced, and the main reason was that the FePO4·0.01H2O precursor was in a low-temperature sintering phase, the particle crystallinity was low, the ion bonding energy was weak, and the grinding was easy. 2.91 PO4·0.01H2O precursor, sodium acetate and citric acid were mixed with water in a ratio of 1:4:0.2 (molar ratio of sodium acetate), and then ground for about 0.1 h. Compared with Comparative Example 1, the grinding time was greatly reduced, and the main reason was that the FePO4·0.01H2O precursor was in a low-temperature sintering phase, the particle crystallinity was low, the ion bonding energy was weak, and the grinding was easy. , SurP, PVDF5130 are mixed in a ratio of 9.5:0.2:0.3 by mass NMP, and the above materials are mixed uniformly using a high-speed homogenizer to form a black slurry with uniform color and high fluidity, The PO4·0.01H2O precursor, sodium acetate and citric acid were mixed with water in a ratio of 1:4:0.2 (molar ratio of sodium acetate), and then ground for about 0.1 h. Compared with Comparative Example 1, the grinding time was greatly reduced, and the main reason was that the FePO4·0.01H2O precursor was in a low-temperature sintering phase, the particle crystallinity was low, the ion bonding energy was weak, and the grinding was easy.

[0093] The electrochemical performance test results in Table 1 show that the discharge gram capacity of the Na4Fe 2.91 (PO4)2P2O7 electrode is 125.4 mAh / g at a 0.1C (1C = 129 mAh / g) rate, which is much higher than the discharge gram capacity of 98.2 mAh / g in Comparative Example 1, which is related to the high phase purity of the material, indicating that there are fewer unfavorable factors such as vacancies, defects, dislocations, etc. in the material that restrict the capacity performance, thereby realizing the play of high capacity performance. In addition, as shown in Table 1, the capacity retention rate of the electrode at a 10C rate is as high as 98.2% compared with 0.1C, which is much higher than 78.6% in Comparative Example 1, which is related to the high phase purity of the material. The higher the phase purity of the material, the higher the integrity of the primary grains, the fewer the number of grain boundaries between the grains, and the lower the resistance to the migration process of sodium ions, thereby greatly improving the rate performance. Ultimately, the capacity retention rate of the electrode at a 1C rate after 1000 cycles is 99.1%, with almost no decay. The higher capacity retention rate is related to the lower porosity of the material, which will reduce the side reactions at the interface between the electrolyte and the material to some extent, effectively reducing the dissolution of ions, thereby improving the stability of the structure. At the same time, the high phase purity of the material reduces the content of the grain boundary, and the volume expansion during the repeated deintercalation of sodium ions is more uniform, and the particle degradation is smaller, which helps to improve the cycle stability.

[0094] Application Example 2 Mn 0.5 PO 3.5 Preparation of Mn

[0095] Step 1: Mn2O3, formic acid were mixed with water in a molar ratio of 1:14, and heated to react at 120°C to form a transparent brown solution; Step 2: hydrogen peroxide was slowly added to the above brown solution, and the amount of addition was 1.9 times the molar amount of manganese ions in the solution, so that the manganese ions in the solution were oxidized to form a pre-oxidized precursor solution; Step 3: pyrophosphoric acid was added to the above pre-oxidized precursor solution, and the amount of addition was 0.5 times the molar amount of manganese ions in the solution, forming a uniform ionic mixture; Step 4: the above ionic mixture was flash dried, and the flash heating temperature was 280°C to remove water, obtaining a dry precursor powder; Step 5: the above precursor powder was calcined at high temperature to remove volatile components such as carbon, hydrogen and oxygen in the powder, and at the same time, a small amount of phosphate in the solution was further deoxidized and polycondensed to form pyrophosphate, and after natural cooling, Mn 0.5 PO 3.5 ·0.03H2O material was obtained.

[0096] Mn 0.5 PO 3.5• 0.03H2O precursor, sodium acetate and glucose (added amount is 0.2 times of the molar amount of sodium acetate) are mixed with water in a ratio of 1:2:0.2, and then ground. The grinding time and energy consumption are significantly lower than those of Comparative Example 2, and the process cost is lower. When the solid particle size Dmax in the slurry is ≤ 30 nm, the slurry is spray dried at an inlet temperature of 300°C and an outlet temperature of 100°C to remove water, and a dry precursor powder is obtained. Finally, the precursor powder is calcined at 650°C for 12 h in a nitrogen atmosphere, and after natural cooling, the Na2MnP2O7 material is obtained.

[0097] The results in Table 1 show that the porosity of the Na2MnP2O7 material is 1.1%, which is much lower than that of Comparative Example 2. This is related to the lower particle size distribution of the precursor during the grinding process, which increases the degree of local ion mutual melting bonding during sintering, making the material particles more dense, the particle growth more dense, the porosity lower, and the compacted density higher (2.27 g / cm 3 ). The XRD diffraction curve refinement calculation further proves that the phase purity of the material is as high as 99.8%, which is much higher than that of Comparative Example 2 (79.2%), indicating that the Mn 0.5 PO 3.5 • The uniform distribution of elements in the 0.03H2O precursor can effectively promote the growth of crystals during sintering, shorten the ion diffusion distance during sintering, and make it easier to crystallize and nucleate, forming a material with high crystallinity and high phase purity.

[0098] , SurP, PVDF5130 are mixed in a ratio of 9.5:0.2:0.3 by mass Na2MnP2O7 material NMP, and the above materials are mixed uniformly using a high-speed homogenizer to form a black slurry with uniform color and high fluidity, In Figure 2 The black slurry was then coated on an aluminum foil using a 150-um four-sided coater, and the film was dried in a vacuum drying oven at 100°C for 2 hours. The electrode film was punched into a circular sheet with a radius of 0.6 mm using a sheet puncher, and a CR2016 type button cell was assembled in a glove box using metallic sodium as the counter electrode, 1 mol / L NaClO4 EC+DEC (1:1 vol%) + 5% FEC as the electrolyte, and a PP / PE / PP three-layer separator.

[0099] The electrochemical performance test results in Table 1 show that the electrode has a discharge capacity of 115.1 mAh / g at a rate of 0.1C (1C = 120 mAh / g), and the capacity is high, which is related to the high phase purity of the material. The higher the phase purity, the more the number of redox charges in the structure, which is more conducive to the 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 96.5% compared with 0.1C, which is much higher than 35.4% in Comparative Example 2, indicating that the higher the phase purity of the material, the fewer the number of crystal defects and grain boundaries, the lower the diffusion energy barrier of sodium ions in the structure, and the faster the ion transmission rate, which is more conducive to the improvement of the rate performance. Finally, the capacity retention rate of the electrode at a rate of 1C after 1000 cycles is 95.9%, which shows excellent cycle stability, indicating that the higher the phase purity of the material, the better the crystal completeness, the higher the isotropy of the crystal expansion, the lower the powder rate of the interface structure, and the more excellent the cycle stability. In addition, the smaller specific surface area of the material will also reduce the catalysis of the electrolyte under high pressure, thereby reducing the side reaction of the material interface and improving the cycle stability.

[0100] Comparative Example 1 2.91 Na4Fe

[0101] The anhydrous FePO4, phosphoric acid, sodium acetate, and citric acid (added amount is 0.2 times the molar amount of sodium acetate) were mixed with water in a molar ratio of 2.91:1.0:4.0 and ground for about 10H. The grinding time is longer than that of Application Example 1, the energy consumption is larger, the equipment investment is more, and the cost is higher. When the solid particle size Dmax in the slurry is ≤30 nm, the slurry is spray dried, the inlet temperature is 300°C, and the outlet temperature is 90°C. The water is removed to obtain a dry precursor powder. Finally, the precursor powder is calcined at 600°C for 10h in a nitrogen atmosphere, and the Na4Fe 2.91 (PO4)2P2O7material is obtained after natural cooling.

[0102] The Na4Fe 2.91 (PO4)2P2O7material. The SEM of the material is about 50-100 nm of primary particles stacked together, and there are a large number of pores on the particles, and the particle density is low. The results in Table 1 show that the porosity of the material is 17.9%, which is much higher than that of Application Example 1, which is related to the anhydrous FePO4 precursor. The precursor is a high-temperature sintering phase, the particle hardness is large, and there are many angles after grinding. These particles are stacked together during spraying to form a porous spherical arrangement. The porosity cannot be removed after sintering, resulting in an increase in porosity and a decrease in compacted density (1.96 g / cm 3). The XRD diffraction curve refinement calculation further proves that the phase purity of the material is only 78.4%, which is far lower than that of application example 1, indicating that it is difficult to realize uniform mixing between ions in the FePO4 precursor during the grinding process, which easily causes the generation of impurities during the sintering process, affecting the phase purity of the material.

[0103] , SurP, PVDF5130 are mixed in a ratio of 9.5:0.2:0.3 by mass Na4Fe 2.91 (PO4)2P2O7material NMP, and the above materials are mixed uniformly using a high-speed homogenizer to form a black slurry with uniform color and high fluidity, The , SurP, PVDF5130 are mixed in a ratio of 9.5:0.2:0.3 by mass Then the black slurry was coated on the aluminum foil by using a 150 um four-side coater, and the film was dried in a vacuum drying oven at 100°C for 2 hours. The electrode film was punched into a circular sheet with a radius of 0.6 mm by using a sheet puncher, and a CR2016 type button cell was assembled in a glove box by 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.

[0104] The results in Table 1 show that the discharge gram capacity of the material is only 90.3 mAh / g at a 0.1C (1C=129 mAh / g) rate, which is far lower than that of the material in application example 1, which is consistent with the lower phase purity of the material, indicating that the material prepared by using anhydrous FePO4 as the precursor may contain non-active sodium iron phosphate or low-capacity sodium iron pyrophosphate impurities, which reduces the effective active ingredients, transition metal redox number and sodium ion deintercalation number per unit mass, and reduces the material gram capacity. In addition, as shown in Table 1, the capacity retention rate of the electrode at a 10C rate is only 78.6% compared with that at a 0.1C rate, and the lower rate performance is related to the existence of impurities in the material, and the crystal boundary between the phases will hinder the transmission of sodium ions, thereby causing the rate performance of the material to decrease. Finally, the capacity retention rate of the electrode at a 1C rate after 1000 weeks of cycling is only 88.6%, which decays seriously, and the reasons are that, on the one hand, the volume expansion rates of different phases in the Na4Fe 2.91 (PO4)2P2O7material are different, causing the material to powder at the grain boundary and affecting the structural integrity. On the other hand, the high porosity of the material will cause the reaction of the interface and the electrolyte at high voltage, and the ion dissolution at the material interface will be intensified, affecting the cycle stability of the material. In summary, the Na4Fe 2.91 (PO4)2P2O7material prepared by using anhydrous FePO4 as the precursor will accelerate the deterioration of the electrochemical performance of the material due to the inhomogeneity of the material reaction caused by the lower phase purity and higher porosity.

[0105] Preparation of Na2MnP2O7material by using Mn2O3 precursor and its electrochemical performance

[0106] Mn2O3, pyrophosphoric acid, sodium acetate were mixed with water in a molar ratio of 0.5:1.0:2.0, and glucose (added amount was 0.2 times the molar amount of sodium acetate) was ground for about 18H. The grinding time was longer than that of application example 2, mainly because the crystallinity of Mn2O3 was high, the crystal hardness was large, and it was difficult to grind, resulting in high process energy consumption, low efficiency, and high cost investment. When the solid particle size Dmax in the slurry was ≤30 nm, the slurry was spray dried at an inlet temperature of 300°C and an outlet temperature of 100°C to remove water, and a dry precursor powder was obtained. Finally, the precursor powder was calcined at 650°C for 12h in a nitrogen atmosphere, and after natural cooling, Na2MnP2O7 material was obtained.

[0107] The physicochemical test data in Table 1 showed that the porosity of the material was 15.4%, much higher than that of application example 2, which was related to the Mn2O3 precursor. This type of precursor is a high-temperature sintering phase, and the particle hardness is large, and after grinding, there are many edges and corners, and after spray drying, it is easy to form a porous structure by stacking each other, and after sintering, these pores cannot be removed, resulting in an increase in porosity and specific surface area, and a decrease in compacted density (1.79 g / cm 3 ). Further XRD diffraction curve refinement calculation proved that the phase purity of the material was only 79.2%, much lower than that of application example 2, indicating that the Mn2O3 precursor crystal grain was hard to grind and powder, which was not conducive to the uniform mixing of ions in the grinding process, causing phase separation during sintering, affecting the crystal structure and phase purity of the material.

[0108] NMP, and the above materials are mixed uniformly using a high-speed homogenizer to form a black slurry with uniform color and high fluidity, Na2MnP2O7 material ​ ​ Then a black slurry was coated on an aluminum foil using a 150um four-side coater, and the film was dried in a vacuum drying oven at 100°C for 2 hours. The electrode film was punched into a circular sheet with a radius of 0.6mm using a sheet puncher, and a metal sodium was used as a counter electrode, 1mol / L NaClO4EC+DEC (1:1vol%) +5%FEC was used as an electrolyte, and a PP / PE / PP three-layer separator was used as a separator, and a CR2016 type button cell was assembled in a glove box.

[0109] The results in Table 1 show that the discharge gram capacity of the material is only 69.8 mAh / g at 0.1C (1C = 120 mAh / g), which is much lower than the result in application example 2, which is related to the lower phase purity of the material, indicating that the uneven mixing of elements in the material prepared by taking Mn2O3 as the precursor may produce other impurities, resulting in the decrease of the gram capacity of the material. In addition, the capacity retention rate of the electrode at 10C is only 35.4% compared with 0.1C, and the lower rate performance is related to a large number of crystal boundaries between the phases, which will lead to the decrease of the sodium ion transmission rate, resulting in the decrease of the rate performance of the material. Finally, the capacity retention rate of the electrode at 1C is only 76.3% after 1000 cycles, which is seriously attenuated, which indirectly reflects the instability of the material structure. The reason is related to the higher specific surface area of the material, which will catalyze the reaction of the electrolyte at high voltage, resulting in the problems of interface dissolution, structure rock rockization and the like, which will affect the cycle stability of the material.

[0110] Table 1 Performance test results

[0111]

[0112] The above examples are only specific embodiments of the present application, which are described in detail, but they cannot be understood as the limitation of the scope of the patent of the present application. It should be noted that for ordinary skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, and these obvious alternative forms all belong to the protection scope of the present application.

Claims

1. A precursor for a high-voltage polyanionic sodium-ion battery cathode material, characterized in that: The chemical general formula of the precursor is M x PO y ·mH2O, where M is a transition metal element Fe and / or Mn, and the value range relationship of x, y, and m is 0.4 < x < 1, y = 3.5 or 3.75, m ≥ 0; The preparation method of this precursor includes the following steps: S1. Preparation of precursor solution: The transition metal source and organic acid are wet-mixed and reacted under controlled temperature to generate precursor solution. The molar ratio of transition metal source and organic acid is 1:5-15, and the temperature of the reaction is controlled at 70-120℃. S2. Preparation of pre-oxidation precursor solution: Add an oxidant to the above solution to oxidize the divalent metal ions in the solution to trivalent metal ions, thereby generating a pre-oxidation precursor solution. The amount of oxidant added is 1-2.5 times the molar amount of transition metal ions in the solution. The oxidant is one or more of hydrogen peroxide, peracetic acid, and oxygen. S3. Preparation of ionic mixture: Add phosphorus source to the above pre-oxidized precursor solution to form a homogeneous ionic mixture; S4. Preparation of precursor powder: The above ionic mixture is dried to remove moisture and obtain dried precursor powder. S5. High-temperature calcination: The above precursor powder is calcined at high temperature, and after natural cooling, M is obtained. x PO y The mH2O material is calcined at temperatures ranging from 150 to 400°C.

2. The precursor for high-voltage polyanionic sodium-ion battery cathode material according to claim 1, characterized in that: In step S1, the transition metal source is an iron source and / or a manganese source. The iron source is one or more of elemental iron, iron oxide red, ferrous oxide, iron(II,III) oxide, ferric hydroxide, ferric hydroxide, ferrous citrate, and ferric oxalate. The manganese source is one or more of elemental manganese, manganese monoxide, manganese dioxide, manganese trioxide, manganese tetroxide, manganese oxalate, manganese hydroxide, manganese anhydride, manganese anhydride, and permanganate anhydride. The organic acid is one or more of formic acid, acetic acid, citric acid, malic acid, ascorbic acid, tartaric acid, and salicylic acid.

3. The precursor for high-voltage polyanionic sodium-ion battery cathode material according to claim 1, characterized in that: In step S3, the phosphorus source is one or more of phosphoric acid, pyrophosphoric acid, metaphosphoric acid, and polyphosphoric acid.

4. The precursor for high-voltage polyanionic sodium-ion battery cathode material according to claim 1, characterized in that: In step S4, the drying method is one or more of the following: flash drying, spray drying, high-temperature pyrolysis, freeze drying, forced-air drying, and natural evaporation.

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