Iron-manganese-based polyanionic compounds, preparation and use in sodium-ion batteries

Abstract

The present application relates to phosphate, pyrophosphate or phosphoric acid pyrophosphate composite polyanion positive electrode material for sodium ion battery, preparation method and application thereof in sodium ion battery; the phosphate, pyrophosphate or phosphoric acid pyrophosphate composite polyanion positive electrode has one or two or more above structures shown in formula I-1 or I-2, formula II-1 or II-2, formula III-1 or III-2, formula IV-1 or IV-2; simple synthesis process, the ion conductivity and electronic conductivity of the material are improved through the cell regulation mechanism, the prepared phosphate, pyrophosphate or phosphoric acid pyrophosphate composite polyanion compound electrode material has high specific capacity and good rate performance and cycle stability.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion batteries, and relates to sodium-ion battery electrode materials, particularly to phosphate, pyrophosphate or phosphate-pyrophosphate composite polyanionic compound electrode materials, their preparation methods and applications in sodium-ion battery electrode materials. Background Technology

[0002] Lithium-ion batteries (LIBs) are widely used in electric vehicles and electronic devices due to their significant advantages such as high energy density, high electrode potential, stable cycle performance, and environmental friendliness. However, in recent years, the limitation of lithium sources has led to the high price of lithium-ion battery cathode materials. Sodium-ion batteries, on the other hand, have attracted increasing attention because they have a similar working principle to lithium-ion batteries and sodium sources are inexpensive and abundant. Therefore, it is particularly important to develop high-performance sodium-ion battery cathode materials.

[0003] Polyanionic sodium-ion battery cathode materials, such as sodium iron (manganese) phosphate, sodium iron (manganese) pyrophosphate, and sodium iron (manganese) pyrophosphate, are preferred cathode materials for alkali metal-ion batteries due to their high raw material abundance, structural stability, high safety, and high redox potential. During the electrochemical redox reaction of manganese ions, the significant difference in ionic radius between high-valence and divalent manganese ions leads to severe cell volume shrinkage at the end of charging, resulting in greater resistance to sodium ion insertion into the cathode structure during discharge and thus poorer reversibility of the battery's charge-discharge behavior. Within the voltage range where ester electrolytes can operate stably (<4.5V vs Na...),... + / Na), manganese ions can undergo Mn 2+ / Mn 3+ (3.6-3.8V vs Na + / Na) and Mn 3+ / Mn 4+ (4.1-4.3V vs Na + The variable valence reaction process of / Na) can achieve >1e- / Mn 2+ Electron transfer processes can improve the specific capacity of materials, but due to differences in chemical environment, some sodium ions in the structure cannot undergo reversible insertion / extraction processes, thus preventing the formation of 1e- / Mn-. 2+ The electrochemical reaction provides available sodium ions, and the presence of inert sodium ions results in a low specific capacity of the material. Summary of the Invention

[0004] This invention provides a novel phosphate, pyrophosphate, or phosphate-pyrophosphate composite polyanionic compound. Firstly, by controlling the appropriate iron-manganese ratio in the high-manganese structure, it helps regulate solid solution and phase transition behavior during charge-discharge processes, improving the reversibility of charge-discharge processes and reducing polarization during high-rate charge-discharge. Simultaneously, optimizing the iron-manganese ratio can create certain defect states in the structure, further improving the material's rate performance. Secondly, by introducing a small amount of metal ions (with ionic radii similar to Mn) into the unit cell structure... 2+ (Similar to) this method, it can effectively alleviate the cell volume change during charge and discharge caused by the radius difference of manganese ions between different valence states, reduce the cycle performance degradation caused by manganese dissolution due to radius differences, and reduce the rate drop caused by cell shrinkage due to high-valence manganese ions, thus improving the structural reversibility during charge and discharge. Finally, partial ion doping at the alkali metal sodium sites can activate the inert sodium ions in the structure and promote Mn 2+ / Mn 3+ / Mn 4+ The occurrence of electrochemical reactions enables materials to achieve higher specific capacity.

[0005] A sodium-ion battery electrode material based on iron-manganese polyanionic compounds, wherein lithium-ion and magnesium-ion sites are doped and directionally exchanged and rearranged via electrochemical ion exchange. The electrode material is a C-supported compound. The polyanionic compound has one or more of the structures shown below, wherein both Fe and Mn are Fe2+. 2+ Mn 2+ :

[0006] Na 3.8 Li 0.1 Fe 1.25 Mn 1.65 Zn 2+ 0.05 Zr 4+ 0.05 (PO4)2P2O7@C,

[0007] Na 3.8 Li 0.1 Fe 1.25 Mn 1.695 Zn 2+ 0.005 Zr 4+ 0.05 (PO4)2P2O7@C,

[0008] Na 3.8 Li 0.1 Fe 1.25 Mn 1.51 Zn 2+ 0.19 Zr4+ 0.05 (PO4)2P2O7@C,

[0009] Na 3.89 Li 0.1 Fe 1.25 Mn 1.695 Zn 2+ 0.05 Zr 4+ 0.005 (PO4)2P2O7@C,

[0010] Na 3.52 Li 0.1 Fe 1.25 Mn 1.51 Zn 2+ 0.05 Zr 4+ 0.19 (PO4)2P2O7@C,

[0011] Na 3.89 Li 0.01 Fe 1.25 Mn 1.65 Zn 2+ 0.05 Zr 4+ 0.05 (PO4)2P2O7@C,

[0012] Na 3.75 Li 0.15 Fe 1.25 Mn 1.65 Zn 2+ 0.05 Zr 4+ 0.05 (PO4)2P2O7@C,

[0013] Na 3.8 Li 0.1 Fe 1.35 Mn 1.55 Zn 2+ 0.05 Zr 4+ 0.05 (PO4)2P2O7@C,

[0014] Na 3.8 Li 0.1 Fe 0.6 Mn 2.3 Zn 2+ 0.05 Zr 4+ 0.05 (PO4)2P2O7@C,

[0015] Na3.8 Mg 0.05 Fe 1.25 Mn 1.65 Zn 2+ 0.05 Zr 4+ 0.05 (PO4)2P2O7@C.

[0016] The mass content of C is 1 wt% - 10 wt%.

[0017] The mass content of C is 3 wt% - 6 wt%.

[0018] The preparation process of the polyanionic compound includes the following steps:

[0019] Step 1), using one or more of solid-phase calcination method, sol-gel method, and solvothermal method, mixing sodium source, phosphorus source, iron source, manganese source, divalent zinc source, tetravalent zirconium source, and carbon source to obtain a solid substance;

[0020] The mixing method is one or more than two of ball milling, pot milling, sand milling, water dissolution, mechanical stirring, and melting method;

[0021] Step 2), performing heat treatment on the solid substance obtained in step 1); the solid substance is in powder state after being treated by crushing, ball milling, or pot milling before heat treatment;

[0022] The heat treatment includes a process of treating at the first temperature T1 and a process of treating at the second temperature T2 in sequence; the temperature T1 is 300 ≤ T1 ≤ 400 °C, and the treatment time is 0.5 - 8 h;

[0023] The temperature T2 is 500 °C < T1 ≤ 800 °C, and the treatment time is 3 - 20 h;

[0024] The heat treatment is carried out in a specific flowing atmosphere, and the specific atmosphere is selected from at least one of inert atmospheres including argon, helium, and nitrogen, or an inert atmosphere gas containing H2 with a volume concentration greater than 0 to less than 50%; Step 3)a, using the heat-treated solid substance obtained in step 2) as the active material of the positive electrode to make a positive electrode plate, forming a half-cell with a sodium metal negative electrode, separating the active material from the sodium metal negative electrode by a separator, and after assembling and encapsulating the battery case, performing charge and discharge cycling 5 - 15 times in the voltage range of 1.5V - 4.5V vsNa + / Na, the electrolyte is (0.7 - 1.5) mol / L NaClO4 / EC ethylene carbonate / DEC diethyl carbonate, V / V = (0.2 - 0.5) / (0.5 - 0.8) / (0.5 - 5) wt% FEC fluoroethylene carbonate, and then charging to 4.5V vs Na +After / Na is cut off, the positive electrode is removed from the battery in the glove box, cleaned with DMC dimethyl carbonate 3-5 times, and then evaporated in the glove box to obtain the evaporated electrode.

[0025] Step 3)b: Reassemble the dried electrode with the lithium metal anode to form a half-cell. The active material and the lithium metal anode are separated by a separator. After assembly, seal the battery casing. The electrolyte is selected as (0.05-0.3) mol / L LiPF6 + (0.35-1.45) mol / L NaClO4 / EC / DEC, V / V = (0.2-0.5) / (0.5-0.8) / (0.5-5) wt% FEC mol / L fluoroethylene carbonate, at 4.3V-4.6V vs Li + Perform 5-15 charge-discharge cycles within the / Li voltage range, then charge to 4.5V-4.6V vs Li. + / Li ends, and charging will continue in the glove box to 4.5V-4.6V vs Li. + The positive electrode plate in the battery that is cut off after / Li is removed from the battery, cleaned with DMC dimethyl carbonate 3-5 times, and then dried in a glove box.

[0026] After disassembly, cleaning, and evaporation, the electrodes are reassembled in a glove box with a sodium metal anode to form a half-cell. The active material and the sodium metal anode are separated by a separator. After assembly and encapsulation, the electrolyte is (0.7–1.5) mol / L NaClO4 / EC ethylene carbonate / DEC diethyl carbonate, V / V = (0.2–0.5) /

[0027] (0.5-0.8) / (0.5~5)wt% FEC fluoroethylene carbonate, with glass fiber membrane as the separator, and charge-discharge cycled 5-10 times within the voltage range of 1.5V-4.5V; after the battery is discharged, remove the positive electrode from the battery in the glove box, clean it with DMC dimethyl carbonate 3-5 times, and then dry it in the glove box;

[0028] The active material in the positive electrode obtained by disassembly is the polyanionic compound;

[0029] Alternatively, the evaporated electrode can be reassembled with a metallic Mg anode to form a half-cell. The electrolyte can be selected as (0.1-0.4) mol / L Mg(TFSI)²⁺ + (0.3-1.4) mol / L NaClO₄ / EC ethylene carbonate / DEC diethyl carbonate, with V / V = (0.2-0.5) / (0.5-0.8) / (0.5-5) wt% FEC fluoroethylene carbonate or (0.15-0.5) mol / L Mg(TFSA)²⁺ + (0.3-0.135) mol / L NaClO₄ / EC ethylene carbonate / DEC diethyl carbonate, with V / V = (0.2-0.5) / (0.5-0.8) / (0.5-5) wt% FEC fluoroethylene carbonate.

[0030] Alternatively, Mg(TFSA)2+(0.3~1.4)mol / L NaClO4 / EC ethylene carbonate / DEC diethyl carbonate, V / V=(0.2~0.5) / (0.3~1.4) / (0.5~5)wt% FEC fluoroethylene carbonate, at 4.0V-4.2V vs Mg 2+ Perform 5-15 charge-discharge cycles within the / Mg voltage range, then charge to 4.1V-4.2V vs Mg. 2+ After / Mg, the charge will stop, and the Mg will be charged to 4.1V-4.2V in the glove box. 2+ The positive electrode sheet of the battery after / Mg cutoff is disassembled from the battery, cleaned with DMC dimethyl carbonate 3-5 times, and then dried in a glove box. The active material in the disassembled positive electrode sheet is the polyanionic compound mentioned above.

[0031] The solid-state calcination method described in step 1) includes the following process: uniformly mixing sodium source, phosphorus source, iron source, manganese source, B source and carbon source to obtain a solid precursor;

[0032] When insoluble raw materials are present in the sodium, phosphorus, iron, manganese, B, and carbon sources, the mixing method is ball milling, jar milling, or sand milling. A solvent is added during mixing to obtain a precursor slurry. The solvent is water, ethanol, or a mixture of water and ethanol. The mass ratio of water to the total mass of the mixed solvent is (30-80) wt%, and the mass ratio of ethanol to the total mass of the mixed solvent is (20-70) wt%. When the particle size range of the precursor slurry is 0.5 μm-1.0 μm, the precursor slurry is pumped into the atomizer of a spray dryer using a peristaltic pump to collect the powder. After drying, the precursor slurry yields a solid precursor with a particle size of 20 μm-30 μm.

[0033] When no insoluble raw materials are present in the sodium, phosphorus, iron, manganese, B, and carbon sources, the mixing method is to add a solvent during dissolution to obtain a precursor solution. The solvent is water. The precursor solution is pumped into the atomizer of a spray dryer using a peristaltic pump to collect the powder. After drying, the precursor slurry yields a solid precursor with a particle size of 20μm-30μm.

[0034] In the two methods described above, the spray drying process controls the feed flow rate to be 20 mL / min to 60 mL / min, the inlet air temperature to be 120℃ to 195℃, the outlet air temperature to be 80℃ to 110℃, and the compressed air pressure to be 0.03 kPa to 0.9 kPa. The precursor slurry is pumped into the atomizer of the spray dryer using a peristaltic pump, and the powder is collected. After drying, the precursor slurry yields precursor powder with a particle size of 20 μm to 30 μm.

[0035] Alternatively, the sol-gel method described in step 1) includes the following process: When no insoluble raw materials are present in the sodium, phosphorus, iron, manganese, B, and carbon sources, and the mixing method is water dissolution, a solvent is added to obtain a precursor solution. The solvent is water. The water in the precursor solution is evaporated by water bath heating until it reaches a gel state, and then transferred to a forced-air drying oven for drying. The water bath heating temperature is 65℃-95℃; the drying temperature is 70℃-120℃; the dried solid is ground or ball-milled into powder to obtain a solid precursor with a particle size of 25μm-35μm. The ball milling speed is 300r / min-800r / min; the ball milling time is 2h-8h.

[0036] Alternatively, the solvothermal method described in step 1) includes the following steps:

[0037] a. The sodium source, phosphorus source, iron source, manganese source, B source, and carbon source are transferred into the polytetrafluoroethylene inner liner of the reaction vessel. During mixing, a solvent is added to obtain the precursor reaction solution. The solvent is water, ethanol, or a mixture of water and ethanol. The mass of water in the mixed solvent accounts for (30-80) wt% of the total mass of the mixed solvent, and the mass of ethanol accounts for (20-70) wt% of the total mass of the mixed solvent.

[0038] b. Transfer the precursor reaction solution to a forced-air drying oven at a temperature of 120℃-200℃ for 8-20 hours. After the above process is completed, remove the reactor, pour out the upper layer of reaction solution, and transfer the solid precipitate at the bottom of the reactor to a centrifuge tube. Wash the precipitate three to five times with deionized water and ethanol, respectively. Collect the precipitate after washing and transfer it to a forced-air drying oven at a temperature of 80℃-120℃. After drying, the solid precursor can be obtained.

[0039] The solid-state calcination method described in step 1) includes the following process: when the sodium source, phosphorus source, iron source, manganese source, B source, and carbon source are mixed in a melting manner, the above raw materials are placed in a graphite crucible and rapidly heated to a temperature at which all the above raw materials exhibit a fluid state, maintained for 0.5 hours, and then rapidly cooled to room temperature in 2-5 minutes to obtain molten raw materials; the above molten raw materials are ball-milled to obtain solid precursors, the particle size of the solid precursors being 25μm-35μm; the ball milling speed is 300r / min-800r / min; and the ball milling time is 2 hours-8 hours.

[0040] The sodium source is selected from at least one of sodium hydroxide, sodium carbonate, sodium bicarbonate, sodium acetate, sodium citrate, sodium oxalate, sodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, sodium pyrophosphate, and sodium hydrogen pyrophosphate.

[0041] The iron source is selected from one or more of the following: iron powder, iron(II,III) oxide, ferric oxide, ferrous oxide, ferric oxalate, ferrous oxalate dihydrate, ferric phosphate, ferric pyrophosphate, ferrous citrate, ferric nitrate, ferrous nitrate, ferric sulfate, ferrous sulfate, ferric chloride, ferrous chloride, ferric acetate, ferrous ammonium sulfate, ferric citrate, ferric ammonium citrate, and sodium ferric citrate succinate.

[0042] The manganese source is selected from one or more of manganese monoxide, manganese dioxide, manganese trioxide, manganese tetroxide, manganese hydroxide, manganese sulfate, manganese chloride, manganese nitrate, manganese phosphate, manganese phosphate, manganese dihydrogen phosphate, and manganese nitrate tetrahydrate.

[0043] The phosphorus source is selected from at least one of the following: ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium phosphate, pyrophosphate, sodium pyrophosphate, and sodium hydrogen pyrophosphate.

[0044] The B source is selected from one or more of the oxides, hydroxides, carbonates, sulfates, chlorides, sulfates, and phosphates corresponding to its metal ions;

[0045] The carbon source is selected from at least one of starch, carboxymethyl starch, sodium carboxymethyl starch, sodium alginate, citric acid, oxalic acid, ammonium citrate, ascorbic acid, formaldehyde, acetaldehyde, lactic acid, malic acid, glucose, sucrose, maltose, and maltodextrin.

[0046] The application of the iron-manganese based polyanionic compound sodium-ion battery electrode material in sodium-ion batteries is characterized by the use of the polyanionic compound as the active material in the electrode material for sodium-ion batteries. The polyanionic compound serves as the positive electrode active material in sodium-ion batteries.

[0047] In the positive electrode material, the content of the polyanionic compound electrode material is (60-98) wt%.

[0048] The positive electrode material also contains a conductive agent and a binder, and the mass ratio of the polyanionic compound, the conductive agent and the binder is (60-98) wt%:(1-39) wt%:(1-39) wt%.

[0049] The conductive agent is at least one of carbon black, conductive graphite, carbon fiber, carbon nanotubes, and graphene.

[0050] The adhesive is polyvinylidene fluoride, and the polyvinylidene fluoride is at least one of PVDF5130, HSV900, and kynar761A.

[0051] Beneficial effects

[0052] The invention of the aforementioned novel phosphate, pyrophosphate, or phosphate-pyrophosphate complex polyanionic compounds offers several advantages. First, by controlling the iron-manganese ratio in the high-manganese structure, the rate performance of the material can be improved, and polarization during charge and discharge can be reduced. Second, it can effectively mitigate the cell volume changes in manganese-based phosphate polyanionic materials during charge and discharge, and improve the reversibility of the electrochemical redox behavior of manganese ions, thereby enhancing the rate performance and cycle stability of the material. Finally, the simultaneous incorporation of a small amount of metal ions at the sodium sites can alter the chemical environment of inert sodium ions in the structure, stimulating the release of inert sodium ions and promoting the release of Mn. 2+ / Mn 3+ / Mn 4+ The occurrence of electrochemical reactions increases the specific capacity of the material, thereby improving the energy density of sodium phosphate-based batteries;

[0053] The synthesis process is simple. By improving the ionic and electronic conductivity of the material through the unit cell regulation mechanism, the prepared phosphate, pyrophosphate, or phosphate-pyrophosphate composite polyanionic compound electrode materials have high specific capacity and good rate performance and cycle stability. Detailed Implementation

[0054] Example 1-Na 3.8 Li 0.1 Fe 1.25 Mn 1.65 Zn 2+ 0.05 Zr 4+ 0.05 (PO4)2P2O7@C

[0055] 1) Add 350 mL of deionized water to a beaker, then add 0.2125 mol of citric acid monohydrate (C6H2O) sequentially. 10O8, 3.7g starch, 0.125mol ferric nitrate nonahydrate Fe(NO3)3·9H2O, 0.165mol manganese nitrate Mn(NO3)2 aqueous solution (50wt%), 0.005mol zinc acetate dihydrate Zn(Ac)2·2H2O, 0.005mol zirconium nitrate Zr(NO3) 4， The above ingredients are stirred until fully dissolved;

[0056] 2) Then add 0.39 mol sodium dihydrogen phosphate dihydrate NaH2PO4·2H2O (sodium source / phosphorus source) and 0.01 mol ammonium dihydrogen phosphate NH4H2PO4 (phosphorus source) to the above aqueous solution, and continue stirring until the raw materials are completely dissolved to form a precursor solution;

[0057] 3) The precursor solution is passed into a spray drying device for spray drying (inlet temperature 160℃, outlet temperature 90℃, feed flow rate 50ml / min, compressed gas pressure 0.8KPa) to obtain precursor powder;

[0058] 4) Subsequently, the precursor powder was transferred to a high-temperature tube furnace under argon atmosphere for heat treatment. The first stage heat treatment temperature was 300℃ for 6 hours, and the second stage heat treatment temperature was 650℃ for 12 hours. The heat-treated product was subjected to Refined XRD and ICP (mainly detecting elements: Na / Fe / Mn / Zn / Zr / P) tests. Refined XRD showed that the heat-treated product was consistent with the crystal structure of Na4Fe3(PO4)2P2O7, belonging to the R3c space group. ICP test showed that the elemental ratio between Na:Fe:Mn:Zn:Zr:P was 3.901:1.2497:1.6498:0.0498:0.0501:3.995, which is Na 3.9 Fe 1.25 Mn 1.65 Zn 0.05 Zr 0.05 The (PO4)2P2O7@C material, consistent with the XRD refined structure, is designated as sample 1#. XPS analysis was performed on the iron and manganese content in sample 1#. The peak results showed that iron and manganese in sample 1# were Fe2+, Fe3+, ... 2+ and Mn 2+ Meanwhile, the carbon content of sample 1# was found to be 5 wt%.

[0059] 5) Sample 1# was used as the active material and mixed evenly with conductive agent acetylene black and binder polyvinylidene fluoride at a mass ratio of 8:1:1. An appropriate amount of solvent N-methylpyrrolidone was added and mixed thoroughly to form a paste. This paste was then applied to the aluminum current collector, dried, and cut into 14mm diameter discs. The areal density of the active material was 1.1–3.2 mg / cm³.2 (Here it is 2.1 mg / cm) 2 This was used as the positive electrode of the battery, with metallic sodium as the negative electrode. The electrolyte was 1M NaClO4 / EC / DEC / 5wt% FEC (EC / DEC V / V = 1:1; the EC / DEC ratio used in the examples below is the same as here). A glass fiber membrane was used as the separator. The assembled battery was subjected to charge-discharge tests, undergoing 10 charge-discharge cycles at 0.2C / 0.2C within the voltage range of 1.5V-4.5V. The discharge specific capacity data of the stable cycles were recorded in Table 1. After charging to 4.5V, the charging was stopped. The positive electrode was removed from the battery in a glove box. After disassembly and cleaning five times with DMC, the electrodes were dried in a glove box. A portion of the electrodes was then subjected to ICP (primarily detecting Na / Fe / Mn / Zn / Zr / P) testing. The ICP results showed that the elemental ratio of Na:Fe:Mn:Zn:Zr:P was 0.899:1.247:1.649:0.049:0.0505:3.998, indicating that when charged to 4.5V, three reversible sodium ions underwent insertion and extraction. Simultaneously, XPS analysis was performed on the iron and manganese in the electrodes. The peak results showed that the iron and manganese in the electrodes were Fe... 3+ and Mn 3+ That is, only Fe occurred. 2+ / 3+ and Mn 2+ / 3+ Redox reactions between them;

[0060] 6) Reassemble the dried electrode from step 5) into a half-cell with a lithium metal anode in a glove box. The electrolyte is 0.2 mol / L LiPF6 + 0.8 mol / L NaClO4 / EC / DEC / 5 wt% FEC (EC / DEC V / V = 1:1; the solvent EC / DEC ratio used in the examples below is the same as here). A glass fiber membrane is used as the separator. The electrolyte is 4.3V-4.6V vs Li + Within the / Li voltage range, 10 charge-discharge cycles were performed at 0.2C / 0.2C. The charge specific capacity of the first cycle and the discharge specific capacity of the last cycle were recorded in Table 1. Then, the battery was charged to 4.6V vs Li. + After the Li cutoff, the positive electrode was removed from the battery in a glove box, cleaned 5 times with DMC, and then dried in the glove box. The electrode from step 6) was then subjected to ICP testing. The results showed that the elemental ratio between Na:Li:Fe:Mn:Zn:Zr:P was 0.789:0.095:1.246:1.648:0.0495:0.0493:3.992. XPS analysis of iron and manganese in the electrode revealed peak values ​​of Fe, Mn, Zn, Zr, and P, respectively. 3+ and Mn 3+That is, Fe occurred 2+ / 3+ and Mn 2+ / 3+ / 4+ Redox reactions between them;

[0061] 7) After disassembling and cleaning the dried electrode from step 6), reassemble it in a glove box with a sodium metal negative electrode to form a half-cell. The electrolyte is 1.0 mol / L NaClO4 / EC / DEC / 5 wt% FEC (EC / DEC V / V = 1:1; the EC / DEC ratio used in the examples below is the same as here). A glass fiber membrane is used as the separator. Charge-discharge cycles are performed within the 1.5V-4.5V voltage range. Then, 10 charge-discharge cycles are performed at 0.2C / 0.2C within the 1.5V-4.5V voltage range, followed by 10 charge-discharge cycles at 1.0C / 1.0C. After stabilizing at 0.2C / 0.2C and 1.0C / 1.0C, the cells are released... The specific capacity data is recorded in Table 1. After the battery is discharged in step 7), the positive electrode is removed from the battery in a glove box. After cleaning with DMC 3-5 times, it is dried in the glove box. The ICP test results show that the elemental ratio between Na:Li:Fe:Mn:Zn:Zr:P is 3.79:0.09:1.247:1.649:0.049:0.0489:4.01. XPS test is performed simultaneously. The peak results show that iron and manganese in the above electrode are Fe 2+ and Mn 2+ The electrodes from a battery charged to 4.5V were cleaned five times with DMC, dried in a glove box, and then subjected to XPS and ICP tests. XPS results showed that the prepared electrode material contained Fe. 3+ and Mn 4+ ICP test results show that the elemental ratio between Na:Li:Fe:Mn:Zn:Zr:P is 0.65:0.095:1.25:1.651:0.0503:0.05:4, which means that reversible insertion / extraction of more than 3 sodium ions can be achieved.

[0062] 8) At the same time, record the capacity retention rate of the battery after the above 200 cycles in Table 1. After disassembling the battery in the glove box, remove the separator, clean it with DMC 3-5 times, evaporate it in the glove box, and detect the percentage of the mass of manganese dissolved on the separator to the mass of manganese in the positive electrode structure by ICP technology, and record it in Table 1.

[0063] Example 2-Na 3.8 Li 0.1 Fe 1.25 Mn 1.695 Zn 2+ 0.005 Zr 4+ 0.05 (PO4)2P2O7@C

[0064] The process and conditions are the same as in Example 1, except that:

[0065] 1) Add 350 mL of deionized water to a beaker, then add 0.2125 mol of citric acid monohydrate (C6H2O) sequentially. 10 O8, 3.7g starch, 0.125mol ferric nitrate nonahydrate Fe(NO3)3·9H2O, 0.1695mol manganese nitrate Mn(NO3)2 aqueous solution (50wt%), 0.0005mol zinc acetate dihydrate Zn(Ac)2·2H2O, 0.005mol zirconium nitrate Zr(NO3)4, the above raw materials are stirred until fully dissolved;

[0066] 4) Refined-XRD and ICP tests were performed on the heat-treated product, and the elemental ratio between Na:Fe:Mn:Zn:Zr:P was 3.901:1.248:1.649:0.00499:0.0498:3.998, indicating that Na... 3.9 Fe 1.25 Mn 1.65 Zn 0.005 Zr 0.05 The (PO4)2P2O7@C material, consistent with the XRD refined structure, is designated as sample 2#. XPS analysis was performed on the iron and manganese content in sample 2#. The peak results showed that iron and manganese in sample 2# were Fe2+, Fe3+, Fe2 ... 2+ and Mn 2+ Meanwhile, the carbon content of sample 2# was tested to be 4.7 wt%.

[0067] 5) Using sample 2# as the active material, the positive electrode was removed from the battery in a glove box, cleaned three times with DMC, and then dried in the glove box. A portion of the electrode was then subjected to ICP (mainly detecting elements: Na / Fe / Mn / Zn / Zr / P) testing. The ICP test results showed that the elemental ratio between Na:Fe:Mn:Zn:Zr:P was 0.895:1.25:1.65:0.00497:0.0499:3.998.

[0068] 6) After cleaning the electrode sheet disassembled in step 6), perform ICP testing. The test results show that the elemental ratio between Na:Li:Fe:Mn:Zn:Zr:P is 0.8:0.0998:1.2498:1.65:0.00498:0.05:4.

[0069] 7) After the battery has finished discharging, remove the positive electrode from the battery in a glove box. Clean it 5 times with DMC, then dry it in the glove box. The ICP test results show that the elemental ratio between Na:Li:Fe:Mn:Zn:Zr:P is 3.797:0.1:1.2498:1.65:0.00495:0.05:3.995. After cleaning the electrodes of a battery charged to 4.5V with DMC 3-5 times, the ICP test results show that the elemental ratio between Na:Li:Fe:Mn:Zn:Zr:P is 0.68:0.1:1.25:1.65:0.005:0.05:4.

[0070] Example 3-Na 3.8 Li 0.1 Fe 1.25 Mn 1.51 Zn 2+ 0.19 Zr 4+ 0.05 (PO4)2P2O7@C

[0071] The process and conditions are the same as in Example 1, except that:

[0072] 1) Add 350 mL of deionized water to a beaker, then add 0.2125 mol of citric acid monohydrate (C6H2O) sequentially. 10 O8, 3.7g starch, 0.125mol ferric nitrate nonahydrate Fe(NO3)3·9H2O, 0.151mol manganese nitrate Mn(NO3)2 aqueous solution (50wt%), 0.019mol zinc acetate dihydrate Zn(Ac)2·2H2O, 0.005mol zirconium nitrate Zr(NO3)4, the above raw materials are stirred until fully dissolved;

[0073] 4) Refined-XRD and ICP tests were performed on the heat-treated product, and the elemental ratio between Na:Fe:Mn:Zn:Zr:P was 3.901:1.248:1.509:0.19:0.0498:3.998, indicating that Na... 3.9 Fe 1.25 Mn 1.51 Zn 0.19 Zr 0.05 The (PO4)2P2O7@C material, consistent with the XRD refined structure, is designated as sample 3#. XPS analysis was performed on the iron and manganese content in sample 3#. The peak results showed that iron and manganese in sample 3# were Fe3+, Fe2+, ... 2+ and Mn 2+ Meanwhile, the carbon content of sample 1# was tested to be 5.7 wt%.

[0074] 5) Using sample 3# as the active material, the positive electrode was removed from the battery in a glove box, cleaned 4 times with DMC, and then dried in the glove box. A portion of the electrode was then subjected to ICP (mainly detecting elements: Na / Fe / Mn / Zn / Zr / P) testing. The ICP test results showed that the elemental ratio between Na:Fe:Mn:Zn:Zr:P was 0.895:1.25:1.51:0.19:0.0499:3.998.

[0075] 6) After cleaning the electrode sheet disassembled in step 6), perform ICP testing. The test results show that the elemental ratio between Na:Li:Fe:Mn:Zn:Zr:P is 0.799:0.0998:1.2498:1.508:0.1902:0.05:3.998.

[0076] 7) After the battery has finished discharging, remove the positive electrode from the battery in a glove box. Clean it with DMC 3-5 times, then dry it in the glove box. The ICP test results show that the elemental ratio between Na:Li:Fe:Mn:Zn:Zr:P is 3.795:0.1:1.2498:1.5101:0.19:0.0499:3.995. After cleaning the electrodes of a battery charged to 4.5V with DMC 3-5 times, the ICP test results show that the elemental ratio between Na:Li:Fe:Mn:Zn:Zr:P is 0.7:0.1:1.2498:1.5101:0.19:0.0499:3.99.

[0077] Example 4-Na 3.89 Li 0.1 Fe 1.25 Mn 1.695 Zn 2+ 0.05 Zr 4+ 0.005 (PO4)2P2O7@C

[0078] The process and conditions are the same as in Example 1, except that:

[0079] 1) Add 350 mL of deionized water to a beaker, then add 0.2125 mol of citric acid monohydrate (C6H2O) sequentially. 10 O8, 3.7g starch, 0.125mol ferric nitrate nonahydrate Fe(NO3)3·9H2O, 0.1695mol manganese nitrate Mn(NO3)2 aqueous solution (50wt%), 0.005mol zinc acetate dihydrate Zn(Ac)2·2H2O, 0.0005mol zirconium nitrate Zr(NO3)4, the above raw materials are stirred until fully dissolved;

[0080] 2) Then add 0.399 mol sodium dihydrogen phosphate dihydrate NaH2PO4·2H2O (sodium source / phosphorus source) and 0.001 mol ammonium dihydrogen phosphate NH4H2PO4 (phosphorus source) to the above aqueous solution, and continue stirring until the raw materials are completely dissolved to form a precursor solution;

[0081] 4) Refined-XRD and ICP tests were performed on the heat-treated product, and the elemental ratio between Na:Fe:Mn:Zn:Zr:P was 3.987:1.248:1.6948:0.0498:0.00498:3.998, indicating that Na... 3.99 Fe 1.25 Mn 1.695 Zn 0.05 Zr 0.005 The (PO4)2P2O7@C material, consistent with the XRD refined structure, is designated as sample 4#. XPS analysis was performed on the iron and manganese content in sample 4#. The peak results showed that iron and manganese in sample 4# were Fe3+, Fe2+, ... 2+ and Mn 2+ Meanwhile, the carbon content of sample 4# was tested to be 4.8 wt%.

[0082] 5) Using sample 4# as the active material, the positive electrode was removed from the battery in a glove box, cleaned three times with DMC, and then dried in the glove box. A portion of the electrode was then subjected to ICP (mainly detecting elements: Na / Fe / Mn / Zn / Zr / P) testing. The ICP test results showed that the elemental ratio between Na:Fe:Mn:Zn:Zr:P was 0.99:1.2495:1.6949:0.05:0.00499:3.998.

[0083] 6) After cleaning the electrode sheet disassembled in step 6), perform ICP testing. The test results show that the elemental ratio between Na:Li:Fe:Mn:Zn:Zr:P is 0.89:0.0998:1.2498:1.6949:0.0495:0.005:3.998.

[0084] 7) After the battery has finished discharging, remove the positive electrode from the battery in a glove box. Clean it 5 times with DMC, then dry it in the glove box. The ICP test results show that the elemental ratio between Na:Li:Fe:Mn:Zn:Zr:P is 3.8905:0.0998:1.2498:1.69448:0.05:0.00499:3.995. After cleaning the electrodes of a battery charged to 4.5V 3-5 times with DMC, the ICP test results show that the elemental ratio between Na:Li:Fe:Mn:Zn:Zr:P is 0.689:0.1:1.25:1.695:0.05:0.00499:3.99.

[0085] Example 5-Na 3.52 Li 0.1 Fe 1.25 Mn 1.51 Zn 2+ 0.05 Zr 4+ 0.19 (PO4)2P2O7@C

[0086] The process and conditions are the same as in Example 1, except that:

[0087] 1) Add 350 mL of deionized water to a beaker, then add 0.2125 mol of citric acid monohydrate (C6H2O) sequentially. 10 O8, 3.7g starch, 0.125mol ferric nitrate nonahydrate Fe(NO3)3·9H2O, 0.15mol manganese nitrate Mn(NO3)2 aqueous solution (50wt%), 0.005mol zinc acetate dihydrate Zn(Ac)2·2H2O, 0.019mol zirconium nitrate Zr(NO3)4, the above raw materials are stirred until fully dissolved;

[0088] 2) Then add 0.362 mol sodium dihydrogen phosphate dihydrate NaH2PO4·2H2O (sodium source / phosphorus source) and 0.038 mol ammonium dihydrogen phosphate NH4H2PO4 (phosphorus source) to the above aqueous solution, and continue stirring until the raw materials are completely dissolved to form a precursor solution;

[0089] 4) Refined-XRD and ICP tests were performed on the heat-treated product, and the elemental ratio between Na:Fe:Mn:Zn:Zr:P was 3.6198:1.249:1.5101:0.0498:0.1901:3.998, indicating that Na... 3.62 Fe 1.25 Mn 1.51 Zn 0.05 Zr 0.19The (PO4)2P2O7@C material, consistent with the XRD refined structure, is designated as sample 5#. XPS analysis was performed on the iron and manganese content in sample 5#. The peak results showed that iron and manganese in sample 5# were Fe3+, Fe2+, ... 2+ and Mn 2+ Meanwhile, the carbon content of sample 1# was tested to be 4.2 wt%.

[0090] 5) Using sample 5# as the active material, the positive electrode was removed from the battery in a glove box, cleaned 5 times with DMC, and then dried in the glove box. A portion of the electrode was then subjected to ICP (mainly detecting elements: Na / Fe / Mn / Zn / Zr / P) testing. The ICP test results showed that the elemental ratio between Na:Fe:Mn:Zn:Zr:P was 0.62:1.2495:1.51:0.05:0.19:3.998.

[0091] 6) After cleaning the electrode sheet disassembled in step 6), perform ICP testing. The test results show that the elemental ratio between Na:Li:Fe:Mn:Zn:Zr:P is 0.52:0.0998:1.2498:1.5102:0.0495:0.005:3.998.

[0092] 7) After the battery has finished discharging, remove the positive electrode from the battery in a glove box. Clean it 5 times with DMC, then dry it in the glove box. The ICP test results show that the elemental ratio between Na:Li:Fe:Mn:Zn:Zr:P is 3.52:0.0998:1.2498:1.5101:0.05:0.19:3.995. After cleaning the electrodes of a battery charged to 4.5V 3-5 times with DMC, the ICP test results show that the elemental ratio between Na:Li:Fe:Mn:Zn:Zr:P is 0.38:0.1:1.25:1.51:0.05:0.19:3.99.

[0093] Example 6-Na 3.89 Li 0.01 Fe 1.25 Mn 1.65 Zn 2+ 0.05 Zr 4+ 0.05 (PO4)2P2O7@C

[0094] The process and conditions are the same as in Example 1, except that:

[0095] 2) Then add 0.399 mol sodium dihydrogen phosphate dihydrate NaH2PO4·2H2O (sodium source / phosphorus source) and 0.001 mol ammonium dihydrogen phosphate NH4H2PO4 (phosphorus source) to the above aqueous solution, and continue stirring until the raw materials are completely dissolved to form a precursor solution;

[0096] 4) The heat-treated product was subjected to Refined XRD and ICP (mainly detecting elements: Na / Fe / Mn / Zn / Zr / P). The ICP test showed that the elemental ratio between Na:Fe:Mn:Zn:Zr:P was 3.991:1.2497:1.6498:0.0498:0.0501:3.995, which is Na. 3.89 Fe 1.25 Mn 1.65 Zn 0.05 Zr 0.05 The (PO4)2P2O7@C material, consistent with the XRD refined structure, is designated as sample 6#. XPS analysis was performed on the iron and manganese content in sample 6#. The peak results showed that iron and manganese in sample 6# were Fe3+, Fe2+, ... 2+ and Mn 2 + Meanwhile, the carbon content of sample 6# was tested to be 4.65 wt%.

[0097] 5) Sample 6# was used as the active substance.

[0098] 6) Reassemble the dried electrode from step 5) into a half-cell with a lithium metal anode in a glove box. The electrolyte is 0.05 mol / L LiPF6 + 0.8 mol / L NaClO4 / EC / DEC / 5 wt% FEC. Take the disassembled and cleaned electrode from step 6) for ICP testing. The test results show that the elemental ratio between Na:Li:Fe:Mn:Zn:Zr:P is 0.889:0.0099:1.2478:1.648:0.0495:0.0496:3.997.

[0099] 7) After the battery in step 7) has finished discharging, remove the positive electrode from the battery in a glove box, clean it 5 times with DMC, and then dry it in the glove box. The ICP test results show that the elemental ratio between Na:Li:Fe:Mn:Zn:Zr:P is 3.89:0.01:1.249:1.649:0.049:0.0489:4.01. After the electrode in the battery charged to 4.5V is cleaned 3-5 times with DMC, and then dried in the glove box, XPS and ICP tests are performed. The ICP test results show that the elemental ratio between Na:Li:Fe:Mn:Zn:Zr:P is 0.72:0.01:1.25:1.651:0.0501:0.05:4.

[0100] Example 7-Na 3.75 Li 0.15 Fe 1.25 Mn 1.65 Zn 2+ 0.05 Zr 4+ 0.05 (PO4)2P2O7@C

[0101] The process and conditions are the same as in Example 1, except that:

[0102] 2) Then add 0.385 mol sodium dihydrogen phosphate dihydrate NaH2PO4·2H2O (sodium source / phosphorus source) and 0.015 mol ammonium dihydrogen phosphate NH4H2PO4 (phosphorus source) to the above aqueous solution, and continue stirring until the raw materials are completely dissolved to form a precursor solution;

[0103] 4) The heat-treated product was subjected to Refined XRD and ICP (mainly detecting elements: Na / Fe / Mn / Zn / Zr / P). The ICP test showed that the elemental ratio between Na:Fe:Mn:Zn:Zr:P was 3.851:1.2497:1.6498:0.0498:0.0501:3.995, which is Na. 3.85 Fe 1.25 Mn 1.65 Zn 0.05 Zr 0.05 The (PO4)2P2O7@C material, consistent with the XRD refined structure, is designated as sample 7#. XPS analysis was performed on the iron and manganese content in sample 7#. The peak results showed that iron and manganese in sample 7# were Fe2+, Fe3+, ... 2+ and Mn 2 + Meanwhile, the carbon content of sample 6# was tested to be 4.58 wt%.

[0104] 5) Sample 7# was used as the active substance;

[0105] 6) Reassemble the dried electrode from step 5) into a half-cell with a lithium metal anode in a glove box. The electrolyte is 0.3 mol / L LiPF6 + 0.8 mol / L NaClO4 / EC / DEC / 5% FEC. Take the disassembled and cleaned electrode from step 6) for ICP testing. The test results show that the elemental ratio between Na:Li:Fe:Mn:Zn:Zr:P is 0.75:0.15:1.248:1.648:0.0497:0.0498:3.996.

[0106] 7) After the battery in step 7) has finished discharging, remove the positive electrode from the battery in a glove box, clean it 5 times with DMC, and then dry it in the glove box. The ICP test results show that the elemental ratio between Na:Li:Fe:Mn:Zn:Zr:P is 3.75:0.15:1.2489:1.649:0.049:0.0489:4.01. After the electrode in the battery charged to 4.5V is cleaned 3-5 times with DMC, and then dried in the glove box, XPS and ICP tests are performed. The ICP test results show that the elemental ratio between Na:Li:Fe:Mn:Zn:Zr:P is 0.665:0.101:1.25:1.651:0.0501:0.05:4.

[0107] Example 8-Na 3.8 Li 0.1 Fe 1.35 Mn 1.55 Zn 2+ 0.05 Zr 4+ 0.05 (PO4)2P2O7@C

[0108] The process and conditions are the same as in Example 1, except that:

[0109] 1) Add 350 mL of deionized water to a beaker, then add 0.2125 mol of citric acid monohydrate (C6H2O) sequentially. 10 O8, 3.7g starch, 0.135mol ferric nitrate nonahydrate Fe(NO3)3·9H2O, 0.155mol manganese nitrate Mn(NO3)2 aqueous solution (50wt%), 0.005mol zinc acetate dihydrate Zn(Ac)2·2H2O, 0.005mol zirconium nitrate Zr(NO3)4, the above raw materials are stirred until fully dissolved;

[0110] 4) The heat-treated product was subjected to Refined XRD and ICP (mainly detecting elements: Na / Fe / Mn / Zn / Zr / P). The ICP test showed that the elemental ratio between Na:Fe:Mn:Zn:Zr:P was 3.9:1.2497:1.6498:0.0498:0.0501:3.995, which is Na. 3.9 Fe 1.25 Mn 1.65 Zn 0.05 Zr 0.05 The (PO4)2P2O7@C material, consistent with the XRD refined structure, is designated as sample 8#. XPS analysis was performed on the iron and manganese content in sample 8#. The peak results showed that iron and manganese in sample 8# were Fe2+, Fe3+, ... 2+ and Mn 2+Meanwhile, the carbon content of sample 8# was found to be 5 wt%.

[0111] 5) Sample #8 was used as the active material; after charging to 4.5V and then stopping, the positive electrode was removed from the battery in a glove box, cleaned three times with DMC, and then dried in the glove box. A portion of the electrode was taken for ICP (mainly detecting elements: Na / Fe / Mn / Zn / Zr / P) testing. The ICP test results showed that the elemental ratio between Na:Fe:Mn:Zn:Zr:P was 0.899:1.347:1.549:0.049:0.0505:3.998, meaning that when charged to 4.5V, there were three reversible sodium ion insertion / extraction processes in the structure. Simultaneously, XPS testing was performed on the iron and manganese elements in the above electrode. The peak results showed that the iron and manganese in the above electrode were Fe... 3+ and Mn 3+ That is, only Fe occurred. 2+ / 3+ and Mn 2+ / 3+ Redox reactions between them;

[0112] 6) ICP testing was performed on the electrode sheet after disassembly and cleaning in step 6). The test results showed that the elemental ratio between Na:Li:Fe:Mn:Zn:Zr:P was 0.798:0.095:1.346:1.548:0.0495:0.0493:3.992. XPS analysis was also performed on the iron and manganese elements in the electrode sheet. The peak separation results showed that the iron and manganese in the electrode sheet were Fe... 3+ and Mn 3+ That is, Fe occurred 2+ / 3+ and Mn 2+ / 3+ / 4+ Redox reactions between them;

[0113] 7) After the battery has finished discharging in step 7), remove the positive electrode from the battery in a glove box. Clean it 5 times with DMC, then dry it in the glove box. ICP testing shows the elemental ratio of Na:Li:Fe:Mn:Zn:Zr:P to be 3.79:0.099:1.347:1.549:0.0499:0.0499:4.01. XPS testing was also performed, and the peak results showed that iron and manganese in the electrode were Fe... 2+ and Mn 2+ The electrodes from a battery charged to 4.5V were cleaned 3-5 times with DMC, then dried in a glove box before XPS and ICP testing. XPS results showed that the prepared electrode material contained Fe. 3+ and Mn 4+ ICP test results show that the elemental ratio among Na:Li:Fe:Mn:Zn:Zr:P is 0.73:0.099:1.35:1.551:0.0501:0.05:4.

[0114] Example 9-Na 3.8 Li 0.1 Fe 0.6 Mn 2.3 Zn 2+ 0.05 Zr 4+ 0.05 (PO4)2P2O7@C

[0115] The process and conditions are the same as in Example 1, except that:

[0116] 1) Add 350 mL of deionized water to a beaker, then add 0.2125 mol of citric acid monohydrate (C6H2O) sequentially. 10 O8, 3.7g starch, 0.06mol ferric nitrate nonahydrate Fe(NO3)3·9H2O, 0.23mol manganese nitrate Mn(NO3)2 aqueous solution (50wt%), 0.005mol zinc acetate dihydrate Zn(Ac)2·2H2O, 0.005mol zirconium nitrate Zr(NO3)4, the above raw materials are stirred until fully dissolved;

[0117] 4) The heat-treated product was subjected to Refined-XRD and ICP (mainly detecting elements: Na / Fe / Mn / Zn / Zr / P). The ICP test showed that the elemental ratio between Na:Fe:Mn:Zn:Zr:P was 3.901:0.597:2.298:0.0498:0.0501:3.99, which is Na. 3.9 Fe 0.6 Mn 2.3 Zn 0.05 Zr 0.05 The (PO4)2P2O7@C material, consistent with the XRD refined structure, is designated as sample 9#. XPS analysis was performed on the iron and manganese content in sample 9#. The peak results showed that iron and manganese in sample 9# were Fe2+, Fe3+, ... 2+ and Mn 2+ Meanwhile, the carbon content of sample 8# was found to be 5 wt%.

[0118] 5) Sample 9# was used as the active material; after charging to 4.5V and then stopping, the positive electrode was removed from the battery in a glove box, cleaned three times with DMC, and then dried in the glove box. A portion of the electrode was taken for ICP (mainly detecting elements: Na / Fe / Mn / Zn / Zr / P) testing. The ICP test results showed that the elemental ratio between Na:Fe:Mn:Zn:Zr:P was 0.901:0.597:2.298:0.0498:0.0501:3.99, meaning that when charged to 4.5V, there were three reversible sodium ion insertion / extraction processes in the structure. Simultaneously, XPS testing was performed on the iron and manganese elements in the above electrode. The peak results showed that the iron and manganese in the above electrode were Fe... 3+ and Mn 3+ That is, only Fe occurred. 2+ / 3+ and Mn 2+ / 3+ Redox reactions between them;

[0119] 6) ICP testing was performed on the electrode sheet after disassembly and cleaning in step 6). The test results showed that the elemental ratio between Na:Li:Fe:Mn:Zn:Zr:P was 3.801:0.1:0.597:2.298:0.0498:0.0501:3.99. XPS analysis was also performed on the iron and manganese elements in the electrode sheet. The peak separation results showed that the iron and manganese in the electrode sheet were Fe... 3+ and Mn 3+ That is, Fe occurred 2+ / 3+ and Mn 2+ / 3+ / 4+ Redox reactions between them;

[0120] 7) After the battery has finished discharging in step 7), remove the positive electrode from the battery in a glove box. Clean it 5 times with DMC, then dry it in the glove box. ICP testing shows the elemental ratio between Na:Li:Fe:Mn:Zn:Zr:P is 3.81:0.1:0.597:2.298:0.0498:0.0501:3.99. XPS testing was also performed, and the peak results showed that iron and manganese in the electrode were Fe... 2+ and Mn 2+ The electrodes from a battery charged to 4.5V were cleaned 3-5 times with DMC, then dried in a glove box before XPS and ICP testing. XPS results showed that the prepared electrode material contained Fe. 3+ and Mn 4+ ICP test results show that the elemental ratio between Na:Li:Fe:Mn:Zn:Zr:P is 0.68:0.1:0.597:2.298:0.0498:0.0501:3.99.

[0121] Example 10-Na 3.8 Mg0.05 Fe 1.25 Mn 1.65 Zn 2+ 0.05 Zr 4+ 0.05 (PO4)2P2O7@C

[0122] The process and conditions are the same as in Example 1, except that:

[0123] 4) Designated as sample 10#, the iron and manganese ions in sample 10# were analyzed by XPS. The peak results showed that the iron and manganese ions in sample 10# were Fe2+, Fe2+, Fe3+, Fe2+, Fe3+, Fe4 ... 2+ and Mn 2+ Meanwhile, the carbon content of sample 10# was tested to be 4.25 wt%.

[0124] 5) Sample 10# was used as the active substance.

[0125] 6) Reassemble the dried electrode from step 5) into a half-cell with a lithium metal anode in a glove box. The electrolyte is 0.2 mol / L Mg(TFSI)2 + 0.8 mol / L NaClO4 / EC / DEC / 5% FEC. A glass fiber membrane is used as the separator. The electrolyte concentration is 4.0V-4.2V vs Mg. 2+ Within the / Mg voltage range, 10 charge-discharge cycles were performed at 0.2C / 0.2C. The charge specific capacity of the first cycle and the discharge specific capacity of the last cycle were recorded in Table 1. Then, the capacitor was charged to 4.2V. 2+ After the / Mg cutoff, the positive electrode is removed from the battery in a glove box. It is then cleaned with DMC 3-5 times and dried in a glove box. The electrode after disassembly and cleaning in step 6) is then subjected to ICP testing. The test results show that the elemental ratio between Na:Mg:Fe:Mn:Zn:Zr:P is 0.799:0.0495:1.246:1.648:0.0498:0.0497:3.997.

[0126] 7) After the battery has finished discharging in step 7), remove the positive electrode from the battery in a glove box. Clean it three times with DMC, then dry it in the glove box. ICP testing shows the elemental ratio of Na:Mg:Fe:Mn:Zn:Zr:P to be 3.79:0.049:1.247:1.649:0.049:0.0489:4.01. XPS testing was also performed, and the peak results showed that iron and manganese in the electrode were Fe... 2+ and Mn 2+The electrodes from a battery charged to 4.5V were cleaned five times with DMC, dried in a glove box, and then subjected to XPS and ICP tests. XPS results showed that the prepared electrode material contained Fe. 3+ and Mn 4+ ICP test results show that the elemental ratio among Na:Mg:Fe:Mn:Zn:Zr:P is 0.68:0.0495:1.25:1.6501:0.0501:0.05:4.

[0127] Comparative Example 1-Na 3.8 Li 0.1 Fe 1.25 Mn 1.699 Zn 2+ 0.001 Zr 4+ 0.05 (PO4)2P2O7@C

[0128] 1) Add 350 mL of deionized water to a beaker, then add 0.2125 mol of citric acid monohydrate (C6H2O) sequentially. 10 O8, 3.7g starch, 0.125mol ferric nitrate nonahydrate Fe(NO3)3·9H2O, 0.1699mol manganese nitrate Mn(NO3)2 aqueous solution (50wt%), 0.0001mol zinc acetate dihydrate Zn(Ac)2·2H2O, 0.005mol zirconium nitrate Zr(NO3)4, the above raw materials are stirred until fully dissolved;

[0129] 2) Then add 0.39 mol sodium dihydrogen phosphate dihydrate NaH2PO4·2H2O (sodium source / phosphorus source) and 0.01 mol ammonium dihydrogen phosphate NH4H2PO4 (phosphorus source) to the above aqueous solution, and continue stirring until the raw materials are completely dissolved to form a precursor solution;

[0130] 3) The precursor solution is passed into a spray drying device for spray drying (inlet temperature 160℃, outlet temperature 90℃, feed flow rate 50ml / min, compressed gas pressure 0.8KPa) to obtain precursor powder;

[0131] 4) Subsequently, the precursor powder was transferred to a high-temperature tube furnace under argon atmosphere protection for heat treatment. The first stage heat treatment temperature was 300℃ for 6 hours, and the second stage heat treatment temperature was 650℃ for 12 hours. The heat-treated product was subjected to Refined XRD and ICP (mainly detecting elements: Na / Fe / Mn / Zn / Zr / P) tests. Refined XRD showed that the heat-treated product was consistent with the crystal structure of Na4Fe3(PO4)2P2O7, belonging to the R3c space group. ICP test showed that the elemental ratio between Na:Fe:Mn:Zn:Zr:P was 3.90:1.2497:1.699:0.001:0.0501:3.995, which is Na 3.9 Fe 1.25 Mn 1.699 Zn 0.001 Zr 0.05 The (PO4)2P2O7@C material, consistent with the XRD refined structure, is denoted as sample A#. XPS analysis was performed on the iron and manganese content in sample A#. The peak results showed that iron and manganese in sample A# were Fe2+, Fe3+, ... 2+ and Mn 2+ Meanwhile, the carbon content of sample A# was found to be 5 wt%.

[0132] 5) Sample A# was used as the active material and mixed evenly with conductive agent acetylene black and binder polyvinylidene fluoride at a mass ratio of 8:1:1. An appropriate amount of solvent N-methylpyrrolidone was added and mixed thoroughly to form a paste. This paste was then applied to the aluminum current collector, dried, and cut into 14mm diameter discs. The areal density of the active material was 1.1–3.2 mg / cm³. 2 (Here it is 2.1 mg / cm) 2This was used as the positive electrode of the battery, with metallic sodium as the negative electrode. The electrolyte was 1M NaClO4 / EC / DEC / 5wt% FEC (EC / DEC V / V = 1:1), and a glass fiber membrane was used as the separator. The assembled battery was subjected to charge-discharge tests, undergoing 10 charge-discharge cycles at 0.2C / 0.2C within a voltage range of 1.5V-4.5V. The discharge specific capacity data after stable cycles were recorded in Table 1. After charging to 4.5V, the positive electrode was removed from the battery in a glove box and cleaned using DMC. After 3-5 cycles, the electrodes were dried in a glove box. A portion of the electrode was then subjected to ICP (primarily detecting Na / Fe / Mn / Zn / Zr / P) testing. The ICP results showed that the elemental ratio of Na:Fe:Mn:Zn:Zr:P was 0.899:1.247:1.699:0.001:0.0502:3.998, indicating that when charged to 4.5V, three reversible sodium ions underwent insertion and extraction. Simultaneously, XPS analysis was performed on the iron and manganese in the electrode. The peak separation results showed that the iron and manganese in the electrode were Fe... 3+ and Mn 3+ That is, only Fe occurred. 2+ / 3+ and Mn 2+ / 3+ Redox reactions between them;

[0133] 6) Reassemble the dried electrode from step 5) into a half-cell with a lithium metal anode in a glove box. The electrolyte is 0.2 mol / L LiPF6 + 0.8 mol / L NaClO4 / EC / DEC / 5 wt% FEC. A glass fiber membrane is used as the separator. The electrolyte is 4.3V-4.6V vs Li + Within the / Li voltage range, 10 charge-discharge cycles were performed at 0.2C / 0.2C. The charge specific capacity of the first cycle and the discharge specific capacity of the last cycle were recorded in Table 1. Then, the battery was charged to 4.6V vs Li. + After the Li cutoff, the positive electrode was removed from the battery in a glove box. It was cleaned 3-5 times with DMC and then dried in the glove box. The cleaned electrode from step 6) was subjected to ICP testing. The results showed that the elemental ratio between Na:Li:Fe:Mn:Zn:Zr:P was 0.799:0.01:1.246:1.699:0.001:0.0493:3.992. XPS testing was also performed on the iron and manganese in the electrode. The peak separation results showed that the iron and manganese in the electrode were Fe... 3+ and Mn 3+ That is, Fe occurred 2+ / 3+ and Mn 2+ / 3+ / 4+ Redox reactions between them;

[0134] 7) After disassembling and cleaning the dried electrode from step 6), reassemble it in a glove box with a sodium metal anode to form a half-cell. The electrolyte is 1.0 mol / L NaClO4 / EC / DEC / 5% FEC, and the separator is a glass fiber membrane. Perform charge-discharge cycles within the 1.5V-4.5V voltage range, including 10 cycles at 0.2C / 0.2C and 10 cycles at 1.0C / 1.0C within the 1.5V-4.5V voltage range. Record the discharge specific capacity data after stabilization at 0.2C / 0.2C and 1.0C / 1.0C in Table 1; take the discharge from step 7). After the battery was decommissioned, the positive electrode was removed from the battery in a glove box. It was then cleaned 3-5 times with DMC, dried in the glove box, and subjected to ICP testing. The elemental ratio of Na:Li:Fe:Mn:Zn:Zr:P was 3.8:0.1:1.247:1.699:0.001:0.0499:4.01. XPS testing was also performed, and the peak separation results showed that iron and manganese in the electrode were Fe... 2+ and Mn 2+ The electrodes from a battery charged to 4.5V were cleaned 3-5 times with DMC, then dried in a glove box before XPS and ICP testing. XPS results showed that the prepared electrode material contained Fe. 3+ and Mn 4 + ICP test results show that the elemental ratio between Na:Li:Fe:Mn:Zn:Zr:P is 0.75:0.1:1.25:1.699:0.001:0.05:4.

[0135] 8) At the same time, record the capacity retention rate of the battery after the above 200 cycles in Table 1. After disassembling the battery in the glove box, remove the separator, clean it with DMC 3-5 times, evaporate it in the glove box, and detect the percentage of the mass of manganese dissolved on the separator to the mass of manganese in the positive electrode structure by ICP technology, and record it in Table 1.

[0136] Comparative Example 2-Na 3.8 Li 0.1 Fe 1.075 Mn 1.42 Zn 2+ 0.5 Zr 4+ 0.05 (PO4)2P2O7@C

[0137] The process and conditions are the same as in Comparative Example 1, except that:

[0138] 1) Add 350 mL of deionized water to a beaker, then add 0.2125 mol of citric acid monohydrate (C6H2O) sequentially. 10O8, 3.7g starch, 0.01075mol ferric nitrate nonahydrate Fe(NO3)3·9H2O, 0.142mol manganese nitrate Mn(NO3)2 aqueous solution (50wt%), 0.05mol zinc acetate dihydrate Zn(Ac)2·2H2O, 0.005mol zirconium nitrate Zr(NO3)4, the above raw materials are stirred until fully dissolved;

[0139] 4) The heat-treated product was subjected to Refined XRD and ICP (mainly detecting elements: Na / Fe / Mn / Zn / Zr / P). The ICP test showed that the elemental ratio between Na:Fe:Mn:Zn:Zr:P was 3.90:1.075:1.42:0.5:0.05:3.997, which is Na. 3.9 Fe 1.075 Mn 1.42 Zn 0.5 Zr 0.05 The (PO4)2P2O7@C material, consistent with the XRD refined structure, is denoted as sample A#. XPS analysis was performed on the iron and manganese content in sample A#. The peak results showed that iron and manganese in sample A# were Fe2+, Fe3+, ... 2+ and Mn 2+ Meanwhile, the carbon content of sample A# was found to be 5 wt%.

[0140] 5) Using sample A# as the active material, charge to 4.5V and then stop. Remove the positive electrode from the battery in a glove box, clean it 3-5 times with DMC, and then dry it in the glove box. Take a portion of the electrode for ICP (mainly detecting elements: Na / Fe / Mn / Zn / Zr / P) testing. The ICP test results show that the elemental ratio between Na:Fe:Mn:Zn:Zr:P is 0.899:1.075:1.42:0.5:0.05:3.998, meaning that when charged to 4.5V, there are three reversible sodium ion insertion / extraction processes in the structure. Simultaneously, XPS testing was performed on the iron and manganese elements in the above electrode. The peak results show that the iron and manganese in the above electrode are Fe... 3+ and Mn 3 + That is, only Fe occurred. 2+ / 3+ and Mn 2+ / 3+ Redox reactions between them;

[0141] 6) The electrode sheet after disassembly and cleaning in step 6) was subjected to ICP testing. The test results showed that the elemental ratio between Na:Li:Fe:Mn:Zn:Zr:P was 0.799:0.1:1.075:1.42:0.5:0.05:3.992. Simultaneously, XPS analysis was performed on the iron and manganese elements in the electrode sheet. The peak separation results showed that iron and manganese in the electrode sheet were Fe... 3+ and Mn3+ That is, Fe occurred 2+ / 3+ and Mn 2+ / 3+ / 4+ Redox reactions between them;

[0142] 7) After the battery has finished discharging in step 7), remove the positive electrode from the battery in a glove box. Clean it 3-5 times with DMC, then dry it in the glove box. ICP testing shows the elemental ratio of Na:Li:Fe:Mn:Zn:Zr:P to be 3.8:0.1:1.075:1.42:0.5:0.05:4.01. XPS testing is also performed, and the peak results show that iron and manganese in the electrode are Fe... 2+ and Mn 2+ The electrodes from a battery charged to 4.5V were cleaned 3-5 times with DMC, then dried in a glove box before XPS and ICP testing. XPS results showed that the prepared electrode material contained Fe. 3+ and Mn 4+ ICP test results show that the elemental ratio among Na:Li:Fe:Mn:Zn:Zr:P is 0.72:0.1:1.075:1.42:0.5:0.05:4.

[0143] Comparative Example 3-Na 3.794 Li 0.1 Fe 1.25 Mn 1.697 Zn 2+ 0.05 Zr 4+ 0.003 (PO4)2P2O7@C

[0144] The process and conditions are the same as in Comparative Example 1, except that:

[0145] 1) Add 350 mL of deionized water to a beaker, then add 0.2125 mol of citric acid monohydrate (C6H2O) sequentially. 10 O8, 3.7g starch, 0.125mol ferric nitrate nonahydrate Fe(NO3)3·9H2O, 0.1697mol manganese nitrate Mn(NO3)2 aqueous solution (50wt%), 0.005mol zinc acetate dihydrate Zn(Ac)2·2H2O, 0.0003mol zirconium nitrate Zr(NO3)4, the above raw materials are stirred until fully dissolved;

[0146] 2) Then add 0.3894 mol sodium dihydrogen phosphate dihydrate NaH2PO4·2H2O (sodium source / phosphorus source) and 0.0106 mol ammonium dihydrogen phosphate NH4H2PO4 (phosphorus source) to the above aqueous solution, and continue stirring until the raw materials are completely dissolved to form a precursor solution;

[0147] 4) The heat-treated product was subjected to Refined-XRD and ICP (mainly detecting elements: Na / Fe / Mn / Zn / Zr / P). The ICP test showed that the elemental ratio between Na:Fe:Mn:Zn:Zr:P was 3.894:1.2497:1.697:0.0499:0.00299:3.99, which is Na. 3.894 Fe 1.25 Mn 1.697 Zn 0.05 Zr 0.003 The (PO4)2P2O7@C material, consistent with the XRD refined structure, is denoted as sample C#. XPS analysis was performed on the iron and manganese content in sample C#. The peak results show that iron and manganese in sample C# are Fe3+, Fe2+, and Fe3+, respectively. 2+ and Mn 2 + Meanwhile, the carbon content of the material in sample C# was tested to be 4.8 wt%.

[0148] 5) Using sample C# as the active material; after charging to 4.5V and then stopping, the positive electrode was removed from the battery in a glove box, cleaned 3-5 times with DMC, and then dried in a glove box. A portion of the electrode was taken for ICP (mainly detecting elements: Na / Fe / Mn / Zn / Zr / P) testing. The ICP test results showed that the elemental ratio between Na:Fe:Mn:Zn:Zr:P was 0.894:1.2497:1.697:0.0498:0.00299:3.998.

[0149] 6) The electrode sheet after disassembly and cleaning in step 6) was subjected to ICP testing. The test results showed that the elemental ratio between Na:Li:Fe:Mn:Zn:Zr:P was 0.794:0.1:1.2496:1.697:0.04995:0.00299:3.997. Simultaneously, XPS testing was performed on the iron and manganese elements in the electrode sheet. The peak separation results showed that the iron and manganese elements in the electrode sheet were Fe... 3+ and Mn 3+ That is, Fe occurred 2+ / 3+ and Mn 2+ / 3+ / 4+ Redox reactions between them;

[0150] 7) The elemental ratios of Na:Li:Fe:Mn:Zn:Zr:P in the ICP test results were 3.794:0.1:1.2497:1.697:0.04998:0.00299:4.01. Simultaneously, XPS analysis was performed, and the peak separation results showed that iron and manganese in the above electrode were Fe... 2+ and Mn 2+The electrodes from a battery charged to 4.5V were cleaned 3-5 times with DMC, then dried in a glove box before XPS and ICP testing. XPS results showed that the prepared electrode material contained Fe. 3+ and Mn 4+ ICP test results show that the elemental ratio among Na:Li:Fe:Mn:Zn:Zr:P is 0.71:0.1:1.2497:1.697:0.04998:0.00299:4.01.

[0151] Comparative Example 4-Na 3.2 Li 0.1 Fe 1.17 Mn 1.48 Zn 2+ 0.05 Zr 4+ 0.3 (PO4)2P2O7@C

[0152] The process and conditions are the same as in Comparative Example 1, except that:

[0153] 1) Add 350 mL of deionized water to a beaker, then add 0.2125 mol of citric acid monohydrate (C6H2O) sequentially. 10 O8, 3.7g starch, 0.117mol ferric nitrate nonahydrate Fe(NO3)3·9H2O, 0.148mol manganese nitrate Mn(NO3)2 aqueous solution (50wt%), 0.005mol zinc acetate dihydrate Zn(Ac)2·2H2O, 0.03mol zirconium nitrate Zr(NO3)4, the above raw materials are stirred until fully dissolved;

[0154] 2) Then add 0.32 mol sodium dihydrogen phosphate dihydrate NaH2PO4·2H2O (sodium source / phosphorus source) and 0.08 mol ammonium dihydrogen phosphate NH4H2PO4 (phosphorus source) to the above aqueous solution, and continue stirring until the raw materials are completely dissolved to form a precursor solution;

[0155] 4) The heat-treated product was subjected to Refined-XRD and ICP (mainly detecting elements: Na / Fe / Mn / Zn / Zr / P). The ICP test showed that the elemental ratio between Na:Fe:Mn:Zn:Zr:P was 3.3:1.17:1.48:0.05:0.3:3.99, which is Na. 3.3 Fe 1.17 Mn 1.48 Zn 0.05 Zr 0.3 The (PO4)2P2O7@C material, consistent with the XRD-refined structure, is denoted as sample D#. XPS analysis was performed on the iron and manganese content in sample D#. The peak results showed that iron and manganese in sample D# were Fe3+, Fe2+, ...2+ and Mn 2+ Meanwhile, the carbon content of the material in sample D# was tested to be 4.6 wt%.

[0156] 5) Using sample D# as the active material; after charging to 4.5V and then stopping, the positive electrode was removed from the battery in a glove box, cleaned 3-5 times with DMC, and then dried in a glove box. A portion of the electrode was taken for ICP (mainly detecting elements: Na / Fe / Mn / Zn / Zr / P) testing. The ICP test results showed that the elemental ratio between Na:Fe:Mn:Zn:Zr:P was 0.3:1.17:1.48:0.05:0.3:3.998.

[0157] 6) The electrode sheet after disassembly and cleaning in step 6) was subjected to ICP testing. The test results showed that the elemental ratio between Na:Li:Fe:Mn:Zn:Zr:P was 0.2:0.1:1.17:1.48:0.05:0.3:3.997. Simultaneously, XPS analysis was performed on the iron and manganese elements in the electrode sheet. The peak separation results showed that iron and manganese in the electrode sheet were Fe... 3+ and Mn 3+ That is, Fe occurred 2+ / 3+ and Mn 2 + / 3+ / 4+ Redox reactions between them;

[0158] 7) The elemental ratios of Na:Li:Fe:Mn:Zn:Zr:P in the ICP test results were 3.2:0.1:1.17:1.48:0.05:0.3:4.01. Simultaneously, XPS analysis was performed, and the peak separation results showed that iron and manganese in the above electrode were Fe... 2+ and Mn 2 + The electrodes from a battery charged to 4.5V were cleaned 3-5 times with DMC, then dried in a glove box before XPS and ICP testing. XPS results showed that the prepared electrode material contained Fe. 3+ and Mn 4+ ICP test results show that the elemental ratio between Na:Li:Fe:Mn:Zn:Zr:P is 0.2:0.1:1.17:1.48:0.05:0.4:4.01.

[0159] Comparative Example 5-Na 3.795 Li 0.005 Fe 1.25 Mn 1.65 Zn 2+ 0.05 Zr 4+ 0.05 (PO4)2P2O7@C

[0160] The process and conditions are the same as in Comparative Example 1, except that:

[0161] 1) Add 350 mL of deionized water to a beaker, then add 0.2125 mol of citric acid monohydrate (C6H2O) sequentially. 10 O8, 3.7g starch, 0.125mol ferric nitrate nonahydrate Fe(NO3)3·9H2O, 0.165mol manganese nitrate Mn(NO3)2 aqueous solution (50wt%), 0.005mol zinc acetate dihydrate Zn(Ac)2·2H2O, 0.005mol zirconium nitrate Zr(NO3)4, the above raw materials are stirred until fully dissolved;

[0162] 2) Then add 0.3895 mol sodium dihydrogen phosphate dihydrate NaH2PO4·2H2O (sodium source / phosphorus source) and 0.0105 mol ammonium dihydrogen phosphate NH4H2PO4 (phosphorus source) to the above aqueous solution, and continue stirring until the raw materials are completely dissolved to form a precursor solution;

[0163] 4) The heat-treated product was subjected to Refined XRD and ICP (mainly detecting elements: Na / Fe / Mn / Zn / Zr / P). The ICP test showed that the elemental ratio between Na:Fe:Mn:Zn:Zr:P was 3.895:1.2497:1.648:0.05:0.0501:3.999, which is Na. 3.895 Fe 1.25 Mn 1.65 Zn 0.05 Zr 0.05 The (PO4)2P2O7@C material, consistent with the XRD refined structure, is denoted as sample E#. XPS analysis was performed on the iron and manganese content in sample E#. The peak results show that the iron and manganese content in sample E# are Fe2+, Fe3+, ... 2+ and Mn 2 + Meanwhile, the carbon content of the material in sample E# was tested to be 5 wt%.

[0164] 5) Sample E# was used as the active material; after charging to 4.5V and then stopping, the positive electrode was removed from the battery in a glove box. It was cleaned 3-5 times with DMC, then dried in the glove box. A portion of the electrode was taken for ICP (mainly detecting elements: Na / Fe / Mn / Zn / Zr / P) testing. The ICP test results showed that the elemental ratio between Na:Fe:Mn:Zn:Zr:P was 0.895:1.2497:1.649:0.0498:0.0501:3.998, meaning that when charged to 4.5V, there were 3 reversible sodium ion insertion / extraction processes in the structure. Simultaneously, XPS testing was performed on the iron and manganese elements in the electrode. The peak results showed that the iron and manganese in the electrode were Fe...3+ and Mn 3+ That is, only Fe occurred. 2+ / 3+ and Mn 2+ / 3+ Redox reactions between them;

[0165] 6) Reassemble the dried electrode from step 5) into a half-cell with a lithium metal anode in a glove box. The electrolyte is 0.01 mol / L LiPF6 + 0.8 mol / L NaClO4 / EC / DEC / 5% FEC. Then charge to 4.6V vs Li + After the / Li cutoff, the positive electrode was removed from the battery in a glove box. It was cleaned 3-5 times with DMC and then dried in the glove box. The electrode from step 6) was then subjected to ICP testing. The results showed that the elemental ratio between Na:Li:Fe:Mn:Zn:Zr:P was 0.795:0.005:1.248:1.6498:0.04995:0.0498:3.992. XPS testing was also performed on the iron and manganese in the electrode. The peak results showed that the iron and manganese in the electrode were Fe... 3+ and Mn 3+ That is, Fe occurred 2+ / 3+ and Mn 2 + / 3+ / 4+ Redox reactions between them;

[0166] 7) After the battery has finished discharging in step 7), remove the positive electrode from the battery in a glove box. Clean it 3-5 times with DMC, then dry it in the glove box. ICP testing shows the elemental ratio of Na:Li:Fe:Mn:Zn:Zr:P to be 3.895:0.005:1.249:1.6499:0.04996:0.0499:4.01. XPS testing is also performed, and the peak results show that iron and manganese in the electrode are Fe... 2+ and Mn 2+ The electrodes from a battery charged to 4.5V were cleaned 3-5 times with DMC, then dried in a glove box before XPS and ICP testing. XPS results showed that the prepared electrode material contained Fe. 3+ and Mn 4+ ICP test results show that the elemental ratio between Na:Li:Fe:Mn:Zn:Zr:P is 0.83:0.005:1.25:1.64995:0.0495:0.05:4;

[0167] Comparative Example 6-Na 3.7 Li 0.2 Fe 1.25 Mn 1.65 Zn 2+0.05 Zr 4+ 0.05 (PO4)2P2O7@C

[0168] The process and conditions are the same as in Comparative Example 1, except that:

[0169] 1) Add 350 mL of deionized water to a beaker, then add 0.2125 mol of citric acid monohydrate (C6H2O) sequentially. 10 O8, 3.7g starch, 0.125mol ferric nitrate nonahydrate Fe(NO3)3·9H2O, 0.165mol manganese nitrate Mn(NO3)2 aqueous solution (50wt%), 0.005mol zinc acetate dihydrate Zn(Ac)2·2H2O, 0.005mol zirconium nitrate Zr(NO3)4, the above raw materials are stirred until fully dissolved;

[0170] 2) Then add 0.39 mol sodium dihydrogen phosphate dihydrate NaH2PO4·2H2O (sodium source / phosphorus source) and 0.01 mol ammonium dihydrogen phosphate NH4H2PO4 (phosphorus source) to the above aqueous solution, and continue stirring until the raw materials are completely dissolved to form a precursor solution;

[0171] 4) The heat-treated product was subjected to Refined XRD and ICP (mainly detecting elements: Na / Fe / Mn / Zn / Zr / P). The ICP test showed that the elemental ratio between Na:Fe:Mn:Zn:Zr:P was 3.8:1.2497:1.648:0.05:0.0501:3.999, which is Na. 3.8 Fe 1.25 Mn 1.65 Zn 0.05 Zr 0.05 The (PO4)2P2O7@C material, consistent with the XRD refined structure, is denoted as sample F#. XPS analysis was performed on the iron and manganese content in sample F#. The peak results showed that iron and manganese in sample E# were Fe2+ and Fe2+, respectively. 2+ and Mn 2+ Meanwhile, the carbon content of the material in sample E# was tested to be 5 wt%.

[0172] 5) Sample F# was used as the active material; after charging to 4.5V and then stopping, the positive electrode was removed from the battery in a glove box. It was cleaned 3-5 times with DMC, then dried in the glove box. A portion of the electrode was taken for ICP (mainly detecting elements: Na / Fe / Mn / Zn / Zr / P) testing. The ICP test results showed that the elemental ratio between Na:Fe:Mn:Zn:Zr:P was 0.8:1.247:1.649:0.0498:0.0501:3.998, indicating that at 4.5V, there were three reversible sodium ion insertion / extraction processes in the structure. Simultaneously, XPS testing was performed on the iron and manganese elements in the electrode. The peak results showed that the iron and manganese in the electrode were Fe... 3+ and Mn 3+ That is, only Fe occurred. 2+ / 3+ and Mn 2+ / 3+ Redox reactions between them;

[0173] 6) Reassemble the dried electrode from step 5) into a half-cell with a lithium metal anode in a glove box. The electrolyte is 0.5 mol / L LiPF6 + 0.8 mol / L NaClO4 / EC / DEC / 5% FEC. Then charge to 4.6V vs Li + After the Li cutoff, the positive electrode was removed from the battery in a glove box. It was cleaned 3-5 times with DMC and then dried in the glove box. The cleaned electrode from step 6) was subjected to ICP testing. The results showed that the elemental ratio between Na:Li:Fe:Mn:Zn:Zr:P was 0.7:0.2:1.248:1.6498:0.04995:0.0498:3.992. XPS analysis of iron and manganese in the electrode revealed peak values ​​of Fe, Mn, Zn, Zr, and P, respectively. 3+ and Mn 3+ That is, Fe occurred 2+ / 3+ and Mn 2+ / 3+ / 4+ Redox reactions between them;

[0174] 7) After the battery has finished discharging in step 7), remove the positive electrode from the battery in a glove box. Clean it 3-5 times with DMC, then dry it in the glove box. ICP testing shows the elemental ratio of Na:Li:Fe:Mn:Zn:Zr:P to be 3.7:0.2:1.249:1.6499:0.04996:0.0499:4.01. XPS testing is also performed, and the peak results show that iron and manganese in the electrode are Fe... 2+ and Mn 2+ The electrodes from a battery charged to 4.5V were cleaned 3-5 times with DMC, then dried in a glove box before XPS and ICP testing. XPS results showed that the prepared electrode material contained Fe.3+ and Mn 4+ ICP test results show that the elemental ratio between Na:Li:Fe:Mn:Zn:Zr:P is 0.7:0.2:1.25:1.64995:0.0495:0.05:4.

[0175] Comparative Example 7-Na 3.8 Li 0.1 Fe 1.45 Mn 1.45 Zn 2+ 0.05 Zr 4+ 0.05 (PO4)2P2O7@C

[0176] The process and conditions are the same as in Comparative Example 1, except that:

[0177] 1) Add 350 mL of deionized water to a beaker, then add 0.2125 mol of citric acid monohydrate (C6H2O) sequentially. 10 O8, 3.7g starch, 0.145mol ferric nitrate nonahydrate Fe(NO3)3·9H2O, 0.145mol manganese nitrate Mn(NO3)2 aqueous solution (50wt%), 0.005mol zinc acetate dihydrate Zn(Ac)2·2H2O, 0.005mol zirconium nitrate Zr(NO3)4, the above raw materials are stirred until fully dissolved;

[0178] 4) The heat-treated product was subjected to Refined XRD and ICP (mainly detecting elements: Na / Fe / Mn / Zn / Zr / P). The ICP test showed that the elemental ratio between Na:Fe:Mn:Zn:Zr:P was 3.9:1.2497:1.648:0.05:0.0501:3.999, which is Na. 3.9 Fe 1.45 Mn 1.45 Zn 2+ 0.05 Zr 4+ 0.05 The (PO4)2P2O7@C material, consistent with the XRD refined structure, is denoted as sample G#. XPS analysis was performed on the iron and manganese content in sample G#. The peak results showed that iron and manganese in sample G# were Fe2+, Fe3+, ... 2+ and Mn 2+ Meanwhile, the carbon content of the material in sample G# was tested to be 4.2 wt%.

[0179] 5) Sample G# was used as the active material; after charging to 4.5V and then stopping, the positive electrode was removed from the battery in a glove box. It was cleaned 3-5 times with DMC, then dried in the glove box. A portion of the electrode was taken for ICP (mainly detecting elements: Na / Fe / Mn / Zn / Zr / P) testing. The ICP test results showed that the elemental ratio between Na:Fe:Mn:Zn:Zr:P was 0.9:1.45:1.45:0.0498:0.0501:3.998, indicating that at 4.5V, there were three reversible sodium ion insertion / extraction processes in the structure. Simultaneously, XPS testing was performed on the iron and manganese elements in the electrode. The peak results showed that the iron and manganese in the electrode were Fe... 3+ and Mn 3+ That is, only Fe occurred. 2+ / 3+ and Mn 2+ / 3+ Redox reactions between them;

[0180] 6) ICP testing was performed on the electrode sheet after disassembly and cleaning in step 6). The test results showed that the elemental ratio between Na:Li:Fe:Mn:Zn:Zr:P was 0.7:0.1:1.45:1.45:0.0498:0.0499:3.992. XPS analysis was also performed on the iron and manganese elements in the electrode sheet. The peak separation results showed that the iron and manganese in the electrode sheet were Fe... 3+ and Mn 3+ That is, Fe occurred 2+ / 3+ and Mn 2+ / 3+ / 4+ Redox reactions between them;

[0181] 7) After the battery has finished discharging in step 7), remove the positive electrode from the battery in a glove box. Clean it 3-5 times with DMC, then dry it in the glove box. ICP testing shows the elemental ratio of Na:Li:Fe:Mn:Zn:Zr:P to be 3.7:0.2:1.45:1.45:0.0499:0.0499:4.01. XPS testing is also performed, and the peak results show that iron and manganese in the electrode are Fe... 2+ and Mn 2+ The electrodes from a battery charged to 4.5V were cleaned 3-5 times with DMC, then dried in a glove box before XPS and ICP testing. XPS results showed that the prepared electrode material contained Fe. 3+ and Mn 4+ ICP test results show that the elemental ratio between Na:Li:Fe:Mn:Zn:Zr:P is 0.68:0.2:1.45:1.45:0.05:0.05:4.

[0182] Comparative Example 8-Na 3.8 Li 0.1Fe2Mn 0.9 Zn 2+ 0.05 Zr 4+ 0.05 (PO4)2P2O7@C

[0183] The process and conditions are the same as in Comparative Example 1, except that:

[0184] 1) Add 350 mL of deionized water to a beaker, then add 0.2125 mol of citric acid monohydrate (C6H2O) sequentially. 10 O8, 3.7g starch, 0.2mol ferric nitrate nonahydrate Fe(NO3)3·9H2O, 0.09mol manganese nitrate Mn(NO3)2 aqueous solution (50wt%), 0.005mol zinc acetate dihydrate Zn(Ac)2·2H2O, 0.005mol zirconium nitrate Zr(NO3)4, the above raw materials are stirred until fully dissolved;

[0185] 4) The heat-treated product was subjected to Refined XRD and ICP (mainly detecting elements: Na / Fe / Mn / Zn / Zr / P). The ICP test showed that the elemental ratio between Na:Fe:Mn:Zn:Zr:P was 3.9:2:0.9:0.05:0.05:3.99, which is Na. 3.9 Fe2Mn 0.9 Zn 2+ 0.05 Zr 4+ 0.05 The (PO4)2P2O7@C material, consistent with the XRD refined structure, is denoted as sample H#. XPS analysis was performed on the iron and manganese content in sample H#. The peak results showed that iron and manganese in sample H# were Fe2+, Fe3+, ... 2+ and Mn 2+ Meanwhile, the carbon content of the material in sample H# was tested to be 5 wt%.

[0186] 5) Using sample H# as the active material; after charging to 4.5V and then stopping, the positive electrode was removed from the battery in a glove box, cleaned 3-5 times with DMC, and then dried in the glove box. A portion of the electrode was taken for ICP (mainly detecting elements: Na / Fe / Mn / Zn / Zr / P) testing. The ICP test results showed that the elemental ratio between Na:Fe:Mn:Zn:Zr:P was 0.9:2:0.9:0.0498:0.0501:3.998, meaning that when charged to 4.5V, there were 3 reversible sodium ion insertion / extraction processes in the structure. Simultaneously, XPS testing was performed on the iron and manganese elements in the above electrode. The peak results showed that the iron and manganese in the above electrode were Fe... 3+ and Mn 3+ That is, only Fe occurred. 2+ / 3+ and Mn2+ / 3+ Redox reactions between them;

[0187] 6) The electrode sheet after disassembly and cleaning in step 6) was subjected to ICP testing. The test results showed that the elemental ratio between Na:Li:Fe:Mn:Zn:Zr:P was 0.8:0.1:2:0.9:0.0499:0.05:3.997. Simultaneously, XPS analysis was performed on the iron and manganese elements in the electrode sheet. The peak separation results showed that the iron and manganese in the electrode sheet were Fe... 3+ and Mn 3+ That is, Fe occurred 2+ / 3+ and Mn 2 + / 3+ / 4+ Redox reactions between them;

[0188] 7) After the battery has finished discharging in step 7), remove the positive electrode from the battery in a glove box. Clean it 3-5 times with DMC, then dry it in the glove box. ICP testing shows the elemental ratio of Na:Li:Fe:Mn:Zn:Zr:P to be 3.8:0.1:2:0.9:0.05:0.05:4.01. XPS testing is also performed, and the peak results show that iron and manganese in the electrode are respectively Fe... 2+ and Mn 2+ The electrodes from a battery charged to 4.5V were cleaned 3-5 times with DMC, then dried in a glove box before XPS and ICP testing. XPS results showed that the prepared electrode material contained Fe. 3+ and Mn 4+ ICP test results show that the elemental ratio between Na:Li:Fe:Mn:Zn:Zr:P is 0.72:0.1:2:0.9:0.05:0.05:4.

[0189] Table 1:

[0190]

[0191]

[0192]

[0193] in conclusion

[0194] This invention patent provides a novel phosphate, pyrophosphate, or phosphate-pyrophosphate complex polyanionic compound and its preparation method. By precisely controlling the cell structure and the composite ratio between iron and manganese, the ionic and electronic conductivity of the compound are improved, effectively controlling the phase transition behavior during charge and discharge, enhancing the reversibility of electrochemical behavior, and improving reaction kinetics. This results in improved specific capacity, rate performance, and cycle stability of the material. The prepared Na... 3.8Li 0.1 Fe 1.25 Mn 1.65 Zn 2+ 0.05 Zr 4+ 0.05 (PO4)2P2O7@C, discharge capacity up to 135mAh / g at 0.2C, median voltage up to 3.69V, discharge capacity up to 115mAh / g at 1.0C, and capacity retention up to 93% after 200 cycles under 1C / 1C charge-discharge conditions.

[0195] The iron-manganese composite ratio affects the electrochemical behavior (e.g., solid solution, phase transition) of the material during charge and discharge. When iron and manganese coexist, the material follows a reaction mechanism of both solid solution and phase transition during charge and discharge. When iron undergoes electrochemical redox behavior, the material exhibits a solid solution reaction mechanism; when manganese undergoes electrochemical redox behavior, the material exhibits a phase transition reaction mechanism. Different iron-manganese composite ratios affect the reversibility of the electrochemical behavior of the above two reaction mechanisms, thereby affecting the rate performance and capacity retention under cycling conditions of the material. Through the embodiments and comparative examples in this invention, it was found that when Na... 3.8 Li 0.1 Fe 1.25 Mn 1.65 Zn 2+ 0.05 Zr 4+ 0.05 When the y-value in the (PO4)2P2O7@C structure satisfies 3>y1>1.5, the prepared material exhibits excellent rate performance and capacity retention. At 0.2C, the discharge capacity reaches 125-135 mAh / g, with a median voltage as high as 3.3V-3.69V. At 1.0C, the discharge capacity reaches 93-115 mAh / g, and under 1C / 1C charge-discharge conditions, the capacity retention rate after 200 cycles is as high as 88%-94%. (e.g., Examples 1, 8-9, Comparative Examples 7-8)

[0196] To alleviate the problem of cell volume shrinkage caused by the difference in ionic radii between high-valent and divalent manganese ions, a small amount of B-source ions is introduced into the cell structure (when the compound is as described in Formula I-1 or I-2, or Formula II-1 or II-2, the range of z is 0.005 ≤ z < 0.2, preferably 0.05 ≤ z ≤ 0.1; when the compound is as described in Formula III-1 or III-2, or Formula IV-1 or IV-2, the range of z is 0.005 ≤ z ≤ 0.05, preferably 0.01 ≤ z ≤ 0.02);). The B-source ions interact with Mn... 2+Metal ions with similar ionic radii can effectively mitigate the aforementioned volume changes, improve the reversibility of the material during charge and discharge, reduce polarization during charge and discharge, and enhance the rate performance of the material. The appropriate amount of B source ions added also affects these effects. When the amount added is too low, the improvement effect is not significant, while when the amount added is too high, it will affect the number of active transition metal redox sites in the unit cell structure, thus affecting the specific capacity of the material; for example, Zn in Examples 1-3. 2+ With the introduction of ions, when 0.005 ≤ z < 0.2, the discharge specific capacity at 0.2C can reach 120-135 mAh / g, and the median voltage is as high as 3.65V-3.69V. At 1.0C, the discharge specific capacity can reach 105-115 mAh / g, and the capacity retention rate after 200 cycles under 1C / 1C charge-discharge conditions is as high as 91.5%-93%. Example 1 is further preferred. However, when the above conditions are not met, both the specific capacity and the discharge voltage decrease to some extent (e.g., Comparative Examples 1-2). The JT effect of manganese in the cell structure can cause instability in the manganese cycling process, which in turn affects the cycle life. Adding an appropriate amount of boron source ions to the structure can also stabilize the manganese sites and further improve the cycling stability. For example, in Examples 1 and 3-4, the retention rate after 200 cycles at 1.0C / 1.0C can be as high as 87%-93%. However, in Comparative Examples 3-4, the performance decreased due to inappropriate addition amount, insignificant manganese stabilization effect, or excessive addition affecting the number of active sites.

[0197] Manganese ions contain Mn 2+ / Mn 3+ (3.6-3.8V vs Na+ / Na) and Mn 3+ / Mn 4+ The variable oxidation state reaction process (4.1-4.3V vs Na+ / Na) can achieve >1e- / Mn. 2+ Electron transfer processes can improve the specific capacity of materials, but due to differences in chemical environment, some sodium ions in the structure cannot undergo reversible insertion / extraction processes, thus preventing the formation of 1e- / Mn-. 2+ The electrochemical reaction provides available sodium ions, but the presence of inert sodium ions leads to a low specific capacity of the material. At the same time, the doping of a small amount of lithium ions and magnesium ions at the sodium sites activates the electrochemical activity of inert sodium ions, thereby increasing the specific capacity of the material. Under the above dual effect, the development of high specific energy iron-manganese polyanionic cathode materials has been achieved.

[0198] The lithium-ion and magnesium-ion sites were doped using an electrochemical ion exchange method for directional exchange and rearrangement. The electrode material prepared above was then charged in a battery to 4.5V vs Na. + / Na cutoff, XPS test results show that only Fe occurred at this point. 2+ / 3+and Mn 2+ / 3+ The redox reaction between the electrodes was investigated, and the disassembled electrode sheets were assembled into a half-cell with metallic lithium in an electrolyte containing lithium salt, and the cells were tested within a specific voltage range (4.3V-4.6V vs Li). + The process involves charging and discharging Li, during which there is essentially no initial charge capacity, meaning the inert sodium ions in the structure cannot be inserted or removed. However, there is discharge capacity, indicating that a certain amount of lithium ions are inserted into the structure, and within this voltage range, Li... + It continuously embeds and rearranges within the structure to reach a stable state, charged to (4.6V vs Li) + The electrode sheets disassembled after the Li+ (Li) reaction, after ICP testing, showed that the lithium-ion intercalation rate in the structure was approximately 0.1%. After reassembling the battery with metallic sodium, the discharge capacity was significantly improved. When the battery was recharged to (4.5V vs Na)... + ICP testing results show that Li does not participate in redox reactions during subsequent charge and discharge processes, remaining essentially unchanged at 0.1V, and the number of remaining sodium ions in the unit cell structure is reduced compared to the initial state, indicating a reversible intercalation / deintercalation activity with an increase in sodium ions. XPS analysis shows that when recharged to (4.5V vs Na), + / Na), Fe occurred 2+ / 3+ and Mn 2+ / 3+ / 4+ The redox reaction between the electrodes significantly improved the specific capacity. The ion concentration in the electrolyte during the electrochemical ion exchange reaction also significantly affected the effect of the process (e.g., Examples 6-7). When the lithium salt concentration in the electrolyte was 0.05 mol / L to 0.3 mol / L, 0.1 mol of Li could be effectively intercalated into the cathode material. When the concentration was too low, the lithium ion mobility was too low to achieve the above intercalation effect. When the concentration was too high, excessive intercalation would cause disorder in the cell structure, leading to performance degradation (e.g., Comparative Examples 5-6). When Mg was used… 0.05 The above effects can also be achieved (e.g., Example 10);

[0199] Similarly, the above principles also apply to other electrode materials with different structures involved in this invention patent, such as Na. 2.9-x Li a Fe 2-y-z Mn y B z (PO4)P2O7@C, Na 2.9-x Mg b Fe 2-y-z Mn y B z (PO4)P2O7@C, Na 1-x Li a Fe 1-y-z Mny B z PO4@C, Na 1-x Mg b Fe 1-y-z Mn y B z PO4@C, Na 2-x Li a Fe 1-y-z Mn y B z P2O7@C, Na 2-x Mg b Fe 1-y-z Mn y B z Both P2O7@C and P2O7@C can be used to prepare materials with excellent rate performance and cycle performance.

Claims

1. Iron-manganese-based polyanionic compound sodium-ion battery electrode material, characterized in that, The site doping of lithium ion and magnesium ion is directionally exchanged and rearranged by electrochemical ion exchange method, and the electrode material is a C-loaded compound; The polyanionic compound has one or two or more of the structures shown below, in which Fe, Mn are each Fe 2+ , Mn 2+ : Na 3.8 Li 0.1 Fe 1.25 Mn 1.65 Zn 2+ 0.05 Zr 4+ 0.05 (PO4)2P2O7@C, Na 3.8 Li 0.1 Fe 1.25 Mn 1.695 Zn 2+ 0.005 Zr 4+ 0.05 (PO4)2P2O7@C, Na 3.8 Li 0.1 Fe 1.25 Mn 1.51 Zn 2+ 0.19 Zr 4+ 0.05 (PO4)2P2O7@C, Na 3.89 Li 0.1 Fe 1.25 Mn 1.695 Zn 2+ 0.05 Zr 4+ 0.005 (PO4)2P2O7@C, Na 3.52 Li 0.1 Fe 1.25 Mn 1.51 Zn 2+ 0.05 Zr 4+ 0.19 (PO4)2P2O7@C, Na 3.89 Li 0.01 Fe 1.25 Mn 1.65 Zn 2+ 0.05 Zr 4+ 0.05 (PO4)2P2O7@C, Na 3.75 Li 0.15 Fe 1.25 Mn 1.65 Zn 2+ 0.05 Zr 4+ 0.05 (PO4)2P2O7@C, Na 3.8 Li 0.1 Fe 1.35 Mn 1.55 Zn 2+ 0.05 Zr 4+ 0.05 (PO4)2P2O7@C, Na 3.8 Li 0.1 Fe 0.6 Mn 2.3 Zn 2+ 0.05 Zr 4 + 0.05 (PO4)2P2O7@C, Na 3.8 Mg 0.05 Fe 1.25 Mn 1.65 Zn 2+ 0.05 Zr 4+ 0.05 (PO4)2P2O7@C.

2. The electrode material of claim 1, wherein, the mass content of C is 1wt%-10wt%.

3. The electrode material of claim 1, wherein, the mass content of C is 3wt%-6wt%.

4. A preparation method of the electrode material of claim 1 or 2, wherein, the preparation process of the polyanionic compound comprises the following steps: Step 1), one or more of solid phase calcination method, sol-gel method, and solvothermal method is used to mix sodium source, phosphorus source, iron source, manganese source, B source, and carbon source to obtain a solid substance; the B source is zinc source and zirconium source, the mixing method is one or more of ball milling, jar milling, sand milling, water dissolution, mechanical stirring, and melting method; Step 2), the solid substance obtained in Step 1) is subjected to heat treatment; the solid substance is in a powder state after being treated by crushing, ball milling, and jar milling before the heat treatment; the heat treatment comprises a process of treatment at a first temperature T1 and a process of treatment at a second temperature T2; the temperature T1 is 300≤T1≤400℃, and the treatment time is 0.5-8h; the temperature T2 is 500℃<T1≤800℃, and the treatment time is 3-20h; the heat treatment is performed in a specific flow atmosphere, and the specific atmosphere is selected from at least one of inert atmospheres including argon, helium, and nitrogen, or an inert atmosphere gas containing H2 with a volume concentration of greater than 0 to less than 50%; Step 3) a, the heat-treated solid matter obtained in step 2) is made into a positive electrode sheet as an active material of a positive electrode, and a half-cell is formed with a metal sodium negative electrode, the active material and the metal sodium negative electrode are separated by a separator, after the assembly is completed, the battery is packaged in a battery shell, and then charged and discharged in a voltage range of 1.5V-4.5V vs Na + / Na for 5-15 times, the electrolyte is (0.7-1.5) mol / L NaClO4 / EC ethylene carbonate / DEC diethyl carbonate, V / V=(0.2-0.5) / (0.5-0.8) / (0.5-5) wt% FEC fluoroethylene carbonate, and then charged to 4.5V vs Na + / Na, the positive electrode sheet is disassembled from the battery in a glove box, washed 3-5 times with DMC dimethyl carbonate, and then evaporated in a glove box to obtain an evaporated electrode; Step 3) b, re-assemble the half-cell with the dried electrode and metal lithium negative electrode, the active material and metal lithium negative electrode are separated by a separator, after the assembly is completed, the battery is packaged in a battery case, and the electrolyte is selected as (0.05-0.3) mol / L LiPF6+ (0.35-1.45) mol / L NaClO4 / EC / DEC, V / V=(0.2-0.5) / (0.5-0.8) / (0.5-5) wt% FEC fluorinated ethylene carbonate, and the battery is charged and discharged in a voltage range of 4.3V-4.6V vs Li + / Li for 5-15 times, and then charged to 4.5V-4.6V vs Li + / Li, the positive electrode sheet in the battery charged to 4.5V-4.6V vs Li + / Li is disassembled from the battery, washed 3-5 times with DMC dimethyl carbonate, and then dried in a glove box; the disassembled and cleaned electrode is evaporated in a glove box, and is combined with a metal sodium negative electrode to form a half battery; the active material and the metal sodium negative electrode are separated by a diaphragm; after the assembly is completed, the battery shell is packaged, the electrolyte is (0.7-1.5)mol / L NaClO4 / EC ethylene carbonate / DEC diethyl carbonate, V / V=(0.2-0.5) / (0.5-0.8) / (0.5-5)wt% FEC fluorinated ethylene carbonate, the diaphragm is selected from a glass fiber membrane, and the charging and discharging cycle is performed 5-10 times in a voltage range of 1.5V-4.5V; the battery after the discharging is completed is disassembled in the glove box, the positive electrode sheet is disassembled from the battery, cleaned 3-5 times with DMC dimethyl carbonate, and evaporated in the glove box; the active material in the positive electrode sheet obtained by disassembly is the polyanionic compound; or, the electrode is reassembled with the metal Mg negative electrode to form a half battery, and the electrolyte is selected from (0.1-0.4) mol / L Mg(TFSI)2+ (0.3~1.4) mol / L NaClO4 / EC ethylene carbonate / DEC diethyl carbonate, V / V= (0.2~0.5) / (0.5-0.8) ) / (0.5~5) wt% FEC fluorinated ethylene carbonate or (0.15-0.5) mol / L Mg(TFSA)2+ (0.3~1.4) mol / L NaClO4 / EC ethylene carbonate / DEC diethyl carbonate, V / V= (0.2~0.5) / (0.3~1.4) / (0.5~5) wt% FEC fluorinated ethylene carbonate, and the battery is subjected to charge-discharge cycles in the voltage range of 4.0V-4.2V vs Mg 2+ / Mg for 5-15 times, and then charged to 4.1V-4.2V vs Mg 2+ / Mg, and then charged to 4.1V-4.2V vs Mg 2+ / Mg, and then charged to 4.1V-4.2V vs Mg / Mg, and then charged to 4.1V-4.2V vs Mg 5. The preparation method according to claim 4, characterized in that, the solid phase calcination method in Step 1) comprises the following process: sodium source, phosphorus source, iron source, manganese source, B source, and carbon source are uniformly mixed to obtain a solid precursor. When the insoluble raw materials exist in the sodium source, the phosphorus source, the iron source, the manganese source, the B source and the carbon source, the mixing method is ball milling, tank milling or sand milling, a solvent is added during mixing to obtain a precursor slurry, the solvent is water, ethanol or a mixed solvent of water and ethanol, the mass of water in the mixed solvent accounts for (30-80) wt% of the total mass of the mixed solvent, and the mass of ethanol accounts for (20-70) wt% of the total mass of the mixed solvent, when the particle size of the precursor slurry ranges from 0.5 μm to 1.0 μm, the precursor slurry is pumped into a atomizer of a spray dryer through a peristaltic pump, and powder is collected; the precursor slurry is dried to obtain a solid precursor with a particle size of 20 μm-30 μm; When the insoluble raw materials do not exist in the sodium source, the phosphorus source, the iron source, the manganese source, the B source and the carbon source, the mixing method is dissolution, a solvent is added during mixing to obtain a precursor solution, the solvent is water, the precursor solution is pumped into a atomizer of a spray dryer through a peristaltic pump, and powder is collected; the precursor solution is dried to obtain a solid precursor with a particle size of 20 μm-30 μm; In the two methods, the spray drying is controlled as follows: the feeding flow rate is 20 mL / min-60 mL / min, the air inlet temperature is 120℃-195℃, the air outlet temperature is 80℃-110℃, and the compressed air pressure is 0.03 KPa-0.9 KPa, the precursor slurry or the precursor solution is pumped into a atomizer of a spray dryer through a peristaltic pump, and powder is collected; the precursor slurry or the precursor solution is dried to obtain a precursor powder with a particle size of 20 μm-30 μm, Alternatively, the sol-gel method in step 1) includes the following process: when the insoluble raw materials do not exist in the sodium source, the phosphorus source, the iron source, the manganese source, the B source and the carbon source, the mixing method is selected as water dissolution, a solvent is added during mixing to obtain a precursor solution, the solvent is water, the water in the precursor solution is evaporated to a gel state through water bath heating, and then the precursor solution is transferred to an air drying oven for drying; the water bath heating temperature is 65℃-95℃; the drying temperature is 70℃-120℃; the obtained solid is ground or ball milled into a powder state to obtain a solid precursor with a particle size of 25 μm-35 μm; the ball milling speed is 300 r / min-800 r / min; and the ball milling time is 2 h-8 h; Alternatively, the solvothermal method in step 1) includes the following steps: a, the sodium source, the phosphorus source, the iron source, the manganese source, the B source and the carbon source are transferred into a inner container made of polytetrafluoroethylene in a reaction kettle, a solvent is added during mixing to obtain a precursor reaction solution, the solvent is water, ethanol or a mixed solvent of water and ethanol, the mass of water in the mixed solvent accounts for (30-80) wt% of the total mass of the mixed solvent, and the mass of ethanol accounts for (20-70) wt% of the total mass of the mixed solvent; b, the precursor reaction solution is transferred to a blast drying oven, the temperature is 120-200℃; the time is set to 8-20h; after the above process is completed, the reactor is taken out, the upper reaction solution is poured out, the solid precipitate at the bottom of the reactor is transferred to a centrifuge tube, washed with deionized water and ethanol for three to five times, respectively, the precipitate after washing is collected, transferred to a blast drying oven, the temperature is 80-120℃, and the solid precursor is obtained after drying.

6. The preparation method of claim 4, wherein: The solid phase calcination method in step 1) includes the following process: when the mixing method of the sodium source, the phosphorus source, the iron source, the manganese source, the B source and the carbon source is melting, the above raw materials are placed in a graphite crucible, rapidly heated to a temperature at which the above raw materials are in a flowable state, and maintained for 0.5h, and then rapidly cooled to room temperature in 2-5min to obtain a molten raw material; the molten raw material is obtained by ball milling to obtain a solid precursor, the particle size of the solid precursor is 25-35μm; the ball milling speed is 300-800r / min; the ball milling time is 2-8h.

7. The preparation method of claim 4, wherein: the sodium source is at least one of sodium hydroxide, sodium carbonate, sodium bicarbonate, sodium acetate, sodium citrate, sodium oxalate, sodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, sodium pyrophosphate, sodium hydrogen pyrophosphate; the iron source is one or more of iron powder, magnetite, magnetite, ferrous oxide, iron oxalate, ferrous oxalate dihydrate, iron phosphate, iron pyrophosphate, ferrous citrate, iron nitrate, ferrous nitrate, iron sulfate, ferrous sulfate, iron chloride, ferrous chloride, iron acetate, ammonium ferrous sulfate, iron citrate, ammonium iron citrate, sodium succinate citrate iron; the manganese source is one or more of manganese monoxide, manganese dioxide, manganese dioxide, manganese trioxide, manganese hydroxide, manganese sulfate, manganese chloride, manganese nitrate, manganese phosphate, manganese phosphate, manganese dihydrogen phosphate, manganese nitrate tetrahydrate; the phosphorus source is at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium phosphate, pyrophosphoric acid, sodium pyrophosphate, sodium hydrogen pyrophosphate; the B source is one or more of oxides, hydroxides, carbonates, sulfates, chlorides, sulfates, phosphates of the metal ions thereof; the carbon source is at least one of starch, carboxymethyl starch, sodium carboxymethyl starch, sodium alginate, citric acid, oxalic acid, ammonium citrate, ascorbic acid, formaldehyde, acetaldehyde, lactic acid, malic acid, glucose, sucrose, maltose, maltodextrin.

8. Use of the ferromanganese-based polyanionic compound electrode material of claim 1 or 2 in a sodium-ion battery, characterized in that, The polyanionic compound is used as an active material of an electrode material for a sodium ion battery.

9. Use according to claim 8, characterized in that, The polyanionic compound is used as a positive active material of a sodium ion battery.

10. Use according to claim 9, characterized in that, In the positive electrode material, the content of the polyanionic compound electrode material is (60-98)wt%. The positive electrode material further contains a conductive agent and a binder, and the mass ratio of the polyanionic compound, the conductive agent and the binder is (60-98)wt%:(1-39)wt%:(1-39)wt%. The conductive agent is at least one of carbon black, conductive graphite, carbon fiber, carbon nanotube and graphene. The binder is polyvinylidene fluoride, and the polyvinylidene fluoride is at least one of PVDF5130, HSV900 and kynar761A.

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