A Cr-containing vanadium-based phosphate cathode material, its preparation method, battery, and energy storage device

Abstract

The present invention provides a vanadium-based phosphate cathode material containing Cr and a preparation method thereof, a battery, and an energy storage device. The chemical formula of the cathode material is Na 3+x(3‑n) V 1+y Cr δ Fe 1‑δ‑x‑y M n+ x (PO4)3, where 0<δ≤0.5, 0≤x≤0.5, 0≤y<1, 0<δ+x+y≤0.9, n is an integer greater than or equal to 1, M n+ Including Li + , K + Mg 2+ , Ca 2+ 、Sr 2+ 、Zn 2+ 、Co 2+ 、Ni 2+ 、Cu 2+ 、Y 3+ 、La 3+ 、Zr 4+ 、Sn 4+ 、Nb 5+ or W 6+ The phosphate cathode material containing V, Cr and Fe prepared in the present invention has excellent performance and low V dosage, which effectively improves the energy density of the material.

Description

Technical Field

[0001] The present invention relates to the field of sodium ion batteries, and in particular to a vanadium-based phosphate positive electrode material and a preparation method thereof, a battery, and an energy storage device. Background Art

[0002] Since its first commercialization in 1991, lithium-ion batteries have been widely used in fields such as electric vehicles and electronic devices due to their advantages such as high energy density, long cycle life, and wide operating temperature range. However, the content of lithium resources in the earth's crust is only 0.0017wt%, and the distribution of lithium resources in geographical space is also very uneven. In contrast, sodium resources are abundant on Earth, which makes sodium-ion batteries expected to become an important supplement to lithium-ion batteries. In addition, sodium and lithium are elements of the same main group and have similar chemical and physical properties. Sodium-ion batteries and lithium-ion batteries have similar energy storage mechanisms. Therefore, the mature experience of lithium-ion batteries can be used as a reference when developing sodium-ion batteries.

[0003] Sodium superionic conductor (NASICON) is a typical vanadium-based phosphate cathode material. Na3V2(PO4)3 is a typical representative of the NASICON series of compounds. Its crystal structure is a rhombus structure of the R-3c space group. VO6 octahedrons and PO4 tetrahedrons are connected in a shared angle manner to form a three-dimensional [V2P3O 12 ]Network skeleton, for Na + Two different storage sites (Na1 and Na2) are provided. Studies have shown that only the two Na at the Na2 position can be extracted from the structure to achieve 2 mol V 3+ / V 4+ The reversible redox reaction of Na3V2(PO4)3 is performed, and the remaining inert Na molecule located at the Na1 position always remains in the crystal structure of the material. The theoretical capacity is only 117.6mAh / g, and the voltage platform is about 3.3V. Studies have shown that in Na3V2(PO4)3, V 4+ / V 5+ The activation of the redox couple is of great importance because V 4+ / V 5+ The reaction potential of the electrode is high and can provide additional capacity, which can improve the energy density of this positive electrode material. Theoretical calculation results show that in Na3V2(PO4)3, V 4+ / V 5+ The redox platform is 4.78V, which obviously exceeds the stable voltage range for normal operation of the electrolyte. Aragón et al. first studied the Na3V 2-x Cr x (PO4)3 positive electrode material, indicating that after the introduction of Cr, V 4+ / V 5+The redox platform can be reduced to about 4.0V. Rui Liu et al. used the sol-gel method to synthesize Na3VCr(PO4)3 cathode material to further activate V 4+ / V 5+ The redox potential is low, but its reversibility is poor, and the release of effective specific capacity still needs to be improved; at the same time, due to the lack of electronic conductivity and structural stability, the cycle performance and rate performance of this type of positive electrode material also have a lot of room for improvement. Subsequently, Tirado's team confirmed that the cheaper Fe 3+ It is also possible to achieve V 4+ / V 5+ The redox potential is activated, but its overall electrochemical performance is still not ideal. Therefore, in response to the above dilemma, a new element (combination) is designed to replace the V in Na3V2(PO4)3 to activate V to the greatest extent possible. 4+ / V 5+ The redox potential can be increased to improve the effective specific capacity and working potential of the material. At the same time, the inherent characteristics of the doping elements can be used to improve the rate and cycle performance, which is of great significance to the future development of V-based phosphate positive electrodes. Summary of the Invention

[0004] The purpose of the present invention is to provide a V-based phosphate positive electrode material doped with Cr and Fe to promote V 4+ / V 5+ The reversible activation of the Cr and Fe doped NASICON structure increases the effective specific capacity and the average working potential of the material, thereby increasing the energy density of the phosphate cathode material. Furthermore, the excellent solid solubility of the Cr and Fe doped NASICON structure further optimizes the structural stability of the material, making the phosphate cathode material significantly more competitive and cost-effective.

[0005] One of the purposes of the present invention is to provide a vanadium-based phosphate positive electrode material, the chemical formula of which is Na 3+x(3-n) V 1+y Cr δ Fe 1-δ-x-y M n+ x (PO4)3,

[0006] Where, 0<δ≤0.5, 0≤x≤0.5, 0≤y<1, 0<δ+x+y≤0.9, n is an integer greater than or equal to 1, M n+ Including Li + , K + Mg 2+ , Ca 2+ 、Sr 2+ 、Zn 2+ 、Co 2+ 、Ni 2+、Cu 2+ 、Y 3+ 、La 3+ 、Zr 4+ 、Sn 4+ 、Nb 5+ or W 6+ Any one or a combination of at least two of .

[0007] Preferably, the cathode material is loaded in a carbon skeleton to form Na 3+x(3-n) V 1+y Cr δ Fe 1-δ-x-y M n+ x (PO4)3@C positive electrode material.

[0008] Preferably, M n+ The element combination includes: Li + and K + Combination of K + and Mg 2+ Combination of Mg 2+ and Ca 2+ Combination of Ca 2+ and Zn 2+ Combination of Co 2+ and Ni 2+ combination of;

[0009] The value of δ is 0.1, 0.2, 0.3, 0.4 or 0.5; the value of x is 0, 0.1, 0.2, 0.3, 0.4 or 0.5; the value of y is 0, 0.1, 0.2, 0.3, 0.4 or 0.5; and the value of n is 1, 2, 3, 4, 5 or 6.

[0010] The present invention also provides a preparation method for any of the above-mentioned positive electrode materials, the preparation method comprising: synthesizing the positive electrode material by using any one of a solid phase method, a spray drying method and a sol-gel method.

[0011] Preferably, the preparation method comprises: mixing a raw material with a solvent to obtain a precursor, drying the precursor and then sintering the precursor to obtain the positive electrode material;

[0012] Wherein, the raw materials include sodium source, vanadium source, chromium source, iron source, phosphorus source and M metal ion source;

[0013] Preferably, the sodium source comprises any one or a combination of at least two of sodium bicarbonate, sodium carbonate, sodium acetate, sodium nitrate, sodium hydroxide or sodium oxalate;

[0014] Preferably, the sodium source comprises: a combination of sodium bicarbonate and sodium carbonate, a combination of sodium carbonate and sodium acetate, a combination of sodium acetate and sodium nitrate, a combination of sodium nitrate and sodium hydroxide, or a combination of sodium hydroxide and sodium oxalate;

[0015] Preferably, the vanadium source comprises: any one or a combination of at least two of vanadium pentoxide, vanadium tetroxide, vanadium trioxide, vanadium oxide, ammonium metavanadate, ammonium vanadate, vanadium oxyacetylacetonate or vanadium acetylacetonate;

[0016] Preferably, the vanadium source includes: a combination of vanadium pentoxide and vanadium tetroxide, a combination of vanadium tetroxide and vanadium trioxide, a combination of vanadium trioxide and vanadium oxide, a combination of vanadium oxide and ammonium metavanadate, a combination of ammonium metavanadate and ammonium vanadate, a combination of ammonium vanadate and vanadyl acetylacetonate, or a combination of vanadyl acetylacetonate and vanadium acetylacetonate;

[0017] Preferably, the phosphorus source comprises: any one or a combination of at least two of phosphoric acid, sodium diammonium phosphate, ammonium dihydrogen phosphate, disodium hydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate or sodium phosphate;

[0018] Preferably, the phosphorus source comprises: a combination of phosphoric acid and ammonium dihydrogen phosphate, a combination of sodium dihydrogen phosphate and ammonium dihydrogen phosphate, a combination of ammonium dihydrogen phosphate and diammonium hydrogen phosphate, a combination of disodium hydrogen phosphate and diammonium hydrogen phosphate, or a combination of ammonium phosphate and sodium phosphate;

[0019] Preferably, the chromium source comprises: any one of chromium trioxide, chromium trioxide, chromium nitrate, chromium phosphate, chromium sulfide, chromium carbide, chromium nitride, ammonium chromate, ammonium dichromate, sodium chromate, chromium acetate, chromous acetate, chromium acetate hydroxide, chromium isopropoxide or chromium acetylacetonate, or a combination of at least two thereof;

[0020] Preferably, the chromium source comprises: a combination of chromium trioxide and chromium trioxide, a combination of chromium nitrate and chromium phosphate, a combination of chromium sulfide and chromium carbide, a combination of chromium nitride and ammonium chromate, a combination of ammonium dichromate and sodium chromate, a combination of chromium acetate and chromous acetate, or a combination of chromium isopropoxide and chromium acetylacetonate;

[0021] Preferably, the iron source comprises: any one or a combination of at least two of ferric nitrate, ferric acetylacetonate, ferric oxide, ferric chloride, ferric bromide, ferric sulfate or ferric hydroxide;

[0022] Preferably, the iron source comprises: a combination of ferric sulfate and ferric oxide, a combination of ferric acetylacetonate and ferric bromide, a combination of ferric nitrate and ferric acetylacetonate, a combination of ferric hydroxide and ferric sulfate, or a combination of ferric chloride and ferric bromide;

[0023] Preferably, the metal ion source comprises Li + , K + Mg2+ , Ca 2+ 、Sr 2+ 、Zn 2+ 、Co 2+ 、Ni 2+ 、Cu 2+ 、Y 3+ 、La 3+ 、Zr 4+ 、Sn 4+ 、Nb 5+ or W 6+ Any one or a combination of at least two of the corresponding acid, base, sodium salt or ammonium salt;

[0024] Preferably, the metal ion source includes: Li + The corresponding base and K + The corresponding acid combination, K + Corresponding acid and Mg 2+ The corresponding combination of alkali, Mg 2+ The corresponding sodium salts and Ca 2+ The corresponding combination of ammonium salts, Ca 2+ The corresponding acid and Zn 2+ The corresponding base combination, Co 2+ The corresponding sodium salt and Ni 2+ The corresponding base combination;

[0025] Preferably, the preparation method further comprises: performing a grinding process after the drying;

[0026] Preferably, the drying temperature is 50-150°C, more preferably 90-120°C;

[0027] Preferably, the drying temperature is 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C or 150°C;

[0028] Preferably, the grinding treatment time is 1 min to 48 h, more preferably 30 min to 2 h;

[0029] Preferably, the grinding treatment time is 1 min, 5 min, 10 min, 20 min, 30 min, 40 min, 50 min, 1 h, 5 h, 10 h, 15 h, 20 h, 25 h, 30 h, 35 h, 40 h, 45 h or 48 h;

[0030] Preferably, the sintering atmosphere includes an inert atmosphere and / or a reducing atmosphere;

[0031] Preferably, the reducing atmosphere comprises carbon monoxide and / or hydrogen; the inert atmosphere comprises argon and / or nitrogen;

[0032] Preferably, the sintering temperature is 500-900°C, more preferably 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C or 900°C;

[0033] Preferably, the sintering time is 2 to 20 hours, more preferably 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours or 20 hours.

[0034] Preferably, the raw material further comprises a reducing agent;

[0035] Preferably, the reducing agent comprises any one or a combination of at least two of oxalic acid, ascorbic acid, sucrose, glucose, hydroxylamine hydrochloride, ethanol, dopamine hydrochloride, citric acid, malic acid or ethylenediaminetetraacetic acid;

[0036] Preferably, the reducing agent comprises: a combination of sucrose and glucose, a combination of oxalic acid and ethanol, a combination of ascorbic acid and hydroxylamine hydrochloride, a combination of citric acid and oxalic acid, a combination of dopamine hydrochloride and glucose, a combination of malic acid and ascorbic acid, a combination of oxalic acid and ethylenediaminetetraacetic acid, or a combination of hydroxylamine hydrochloride and oxalic acid;

[0037] Preferably, the raw material further comprises a carbon source;

[0038] Preferably, the carbon source comprises any one or a combination of at least two of citric acid, oleic acid, polyvinyl pyrrolidone, polyethylene glycol, glucose, ascorbic acid, sucrose, starch, graphene, carbon nanotubes or Ketjen black;

[0039] Preferably, the carbon source comprises: a combination of glucose and citric acid, a combination of sucrose and oleic acid, a combination of polyvinyl pyrrolidone and polyethylene glycol, a combination of polyethylene glycol and glucose, a combination of ascorbic acid and sucrose, a combination of glucose and starch, or a combination of carbon nanotubes and Ketjen black;

[0040] Preferably, the molar ratio of the carbon source to the metal ion source is 0 to 10:1, more preferably 0 to 3:1;

[0041] Preferably, the molar ratio of the carbon source to the metal ion source is 0, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1 or 10:1;

[0042] Preferably, the solvent comprises any one of deionized water, ethanol or acetone, or a combination of at least two thereof;

[0043] Preferably, the solvent includes: a combination of deionized water and ethanol, a combination of deionized water and acetone, or a combination of ethanol and acetone.

[0044] The present invention also provides a sodium ion battery, comprising any one of the above-mentioned positive electrode materials.

[0045] The present invention also provides an energy storage device, which includes the above-mentioned sodium ion battery.

[0046] Preferably, the energy storage device is used as an energy storage device for low-speed electric vehicles, solar power generation, wind power generation, smart grid peak regulation, distributed power stations, backup power supplies or communication base stations.

[0047] The present invention also provides an application of the above-mentioned positive electrode material, wherein the positive electrode material is applied to a sodium ion battery.

[0048] Compared with the prior art, the present invention has the following effects:

[0049] (1) The phosphate cathode material containing V, Cr and Fe prepared in the present invention has an average discharge voltage of about 3.5 V and has the advantage of high energy density.

[0050] (2) The phosphate cathode material of the present invention has good electrochemical properties. The discharge capacity reaches 107 mAh / g at 0.2C and can still obtain a capacity of 85 mAh / g at 5C. The capacity retention rate after 1000 cycles at 5C is above 92%. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 This is the XRD pattern of the V-based phosphate cathode material containing Cr, Fe and Zn prepared in Example 1 of the present invention;

[0052] Figure 2 is a scanning electron microscope image of a V-based phosphate cathode material containing Cr, Fe and Zn prepared in Example 1 of the present invention;

[0053] Figure 3 This is a first cycle charge-discharge curve of the V-based phosphate cathode material containing Cr, Fe and Zn prepared in Example 1 of the present invention at 0.2C;

[0054] Figure 4 This is a rate performance diagram of a V-based phosphate cathode material containing Cr, Fe, and Zn prepared in Example 1 of the present invention;

[0055] Figure 5 1 is a graph showing the cycling performance of the V-based phosphate cathode material containing Cr, Fe and Zn prepared in Example 1 of the present invention at 5C;

[0056] Figure 6 This is a comparison of the first cycle charge and discharge curves of the phosphate positive electrode materials prepared in Example 1 and Comparative Example 1 at 0.2C. DETAILED DESCRIPTION

[0057] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0058] Example 1

[0059] This embodiment provides a method for preparing a V-based phosphate positive electrode material containing Cr, Fe and Zn:

[0060] 3mmol sodium dihydrogen phosphate, 0.1mmol sodium acetate, 1mmol vanadyl sulfate, 0.7mmol chromium acetate, 0.2mmol ferric nitrate, 0.1mmol zinc oxide and a certain amount of oxalic acid and sucrose were added to a ball mill, ethanol was used as a solvent, and the mixture was sealed and centrifuged for 24 hours. After the reaction, the obtained precursor was dried at 100 degrees Celsius and ground into powder. It was placed in a tube furnace with an argon atmosphere and sintered at 600 degrees Celsius for 10 hours to obtain Na 3.1 VCr 0.7 Fe 0.2 Zn 0.1 (PO4)3@C positive electrode material. Figure 1 is the XRD pattern of the positive electrode material of this embodiment, Figure 2 3 is a scanning electron microscope image of the positive electrode material of this embodiment.

[0061] Example 2

[0062] This embodiment provides a method for preparing a V-based phosphate positive electrode material containing Cr, Fe and Mg:

[0063] 3mmol sodium dihydrogen phosphate, 0.1mmol sodium carbonate, 1.4mmol ammonium metavanadate, 0.15mmol chromium trioxide, 0.1mmol ferric nitrate, 0.2mmol magnesium carbonate and a certain amount of hydroxylamine hydrochloride and citric acid were added to a ball mill, acetone was used as a solvent, and the mixture was sealed and centrifuged for 20 hours. After the reaction was completed, the precursor was dried at 100 degrees Celsius and ground into powder. It was placed in a tube furnace with an argon atmosphere and sintered at 700 degrees Celsius for 12 hours to obtain Na 3.2 V 1.4 Cr 0.3 Fe 0.1 Mg 0.2 (PO4)3@C positive electrode material.

[0064] Example 3

[0065] This embodiment provides a method for preparing a V-based phosphate positive electrode material containing Cr, Fe and Mn:

[0066] 3mmol sodium acetate, 0.15mmol sodium carbonate, 0.65mmol vanadium trioxide, 0.05mmol chromium trioxide, 0.3mmol ferric nitrate, 0.3mmol manganese acetate, and 3mmol phosphoric acid were added to an acetone solution containing citric acid, and then the mixed solution was placed in a water bath at 100 degrees Celsius with magnetic stirring until the ethanol was completely evaporated. The obtained precursor was dried at 120 degrees Celsius, ground into a powder state, and sintered at 650 degrees Celsius in an argon atmosphere tube furnace for 18 hours to obtain Na 3.3 V 1.3 Cr 0.1 Fe 0.3 Mn 0.3 (PO4)3@C positive electrode material.

[0067] Example 4

[0068] This embodiment provides a method for preparing a positive electrode material containing Cr, Fe and V-based phosphate:

[0069] 3.0mmol sodium acetate, 0.5mmol ammonium polyvanadate, 0.15mmol chromium trioxide, 0.2mmol ferric chloride, 3mmol phosphoric acid and a certain amount of glucose were added to a ball mill, water was used as a solvent, and the mixture was sealed and centrifuged for 18h. After the reaction, the precursor was dried at 120 degrees Celsius, ground into powder, and sintered at 750 degrees Celsius in an argon atmosphere tube furnace for 10 hours to obtain Na 3.0 V 1.5 Cr 0.3 Fe 0.2 (PO4)3@C positive electrode material.

[0070] Comparative Example 1

[0071] This comparative example provides a method for preparing a phosphate positive electrode material containing only V and Cr:

[0072] 3mmol of sodium acetate, 1mmol of vanadyl sulfate, 0.5mmol of chromium trioxide, and a certain amount of oxalic acid and sucrose were added to a ball mill jar with ethanol as the solvent. The jar was sealed and centrifuged for 24 hours. After the reaction, the resulting precursor was dried at 100 degrees Celsius, ground into a powder, and sintered at 600 degrees Celsius in an argon atmosphere tube furnace for 10 hours to obtain the Na3VCr(PO4)3@C cathode material.

[0073] Comparative Example 2

[0074] This comparative example provides a method for preparing a phosphate positive electrode material containing only V and Fe:

[0075] 3mmol of sodium dihydrogen phosphate, 1mmol of ammonium metavanadate, 1mmol of ferric acetylacetonate, and a certain amount of citric acid were added to a ball mill jar with deionized water as the solvent. The jar was sealed and centrifuged for 12 hours. After the reaction, the resulting precursor was dried at 100°C and ground into a powder. The powder was then sintered at 750°C in an argon atmosphere in a tube furnace for 12 hours to obtain the Na3VFe(PO4)3@C cathode material.

[0076] The electrochemical performance of the positive electrode materials prepared in Examples 1-4 and Comparative Examples 1-2 was analyzed.

[0077] Among them, the electrochemical performance analysis is as follows:

[0078] 1. Battery preparation

[0079] (1) Preparation of battery positive electrode sheets: The prepared phosphate positive electrode material, Ketjen black, and polytetrafluoroethylene binder were ground and mixed uniformly in a mass ratio of 7:2:1, and then rolled thoroughly using a roller mill to form a film of uniform thickness. After drying in a vacuum drying oven at 120°C for 5 hours, the obtained positive electrode film was cut into square pieces with a side length of approximately 6 mm. After accurately weighing the square pieces, the mass of the active material in the positive electrode sheet was calculated based on the formula composition.

[0080] (2) Battery assembly:

[0081] The above-obtained square positive electrode sheet, 16 mm diameter separator, 15 mm diameter sodium sheet, spring sheet and gasket were assembled into a 2032 type testable button battery in a glove box (oxygen content less than 0.01 ppm, water content less than 0.01 ppm).

[0082] 2. Electrochemical performance test method:

[0083] The electrochemical properties of the prepared positive electrode materials were tested on the assembled batteries using the Wuhan Blue Electric high-performance battery testing system. Figure 3-Figure 5 They are the first cycle charge and discharge curve diagram, rate performance diagram and cycle performance diagram of the positive electrode material of Example 1 at 0.2C and 5C, respectively. Figure 6 1 is a comparison of the first cycle charge and discharge curves of the phosphate cathode materials prepared in Example 1 and Comparative Example 1 at 0.2 C. The performance test results of each embodiment and comparative example are shown in Table 1.

[0084] Table 1

[0085]

[0086]

[0087] By comparing the above examples 1-4 and comparative examples 1-2, it can be concluded that the introduction of Cr and Fe elements can effectively activate the V in the V-based phosphate cathode material. 4+ / V 5+ The voltage platform increases the effective specific capacity of the material on the one hand, while further improving the average working voltage potential of the material, making the material have a higher energy density. In addition, the three elements V, Cr and Fe exhibit good solid solubility properties and multi-metal ion synergy, and have excellent kinetic characteristics. The 0.2C first discharge specific capacity of Examples 1-4 is above 107 mAh / g, the 5C discharge specific capacity is above 85 mAh / g, the 2C first discharge specific capacity is above 98 mAh / g, and the 5C cycle retention rate after 1000 cycles is above 86%. As can be seen from Table 1, Example 2 is higher than other examples in all indicators, and the 0.2C initial discharge specific capacity of Example 2 is increased by (113-98) / 98=15% relative to that of Comparative Example 2, the 5C discharge specific capacity of Example 2 is increased by (103-60) / 60=72% relative to that of Comparative Example 2, and the 2C initial discharge specific capacity of Example 2 is increased by (107-73) / 73=47% relative to that of Comparative Example 2. The performance improvement is very obvious, and it is a preferred embodiment of the present invention. The corresponding positive electrode material chemical formula is Na 3.2 V 1.4 Cr 0.3 Fe 0.1 Mg 0.2 (PO4)3@C.

[0088] In addition, due to the unique carbon skeleton structure and reasonable composition design, the prepared materials exhibit good rate performance and cycle performance, and have broad application prospects.

[0089] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A Cr-containing vanadium-based phosphate positive electrode material, characterized in that: The chemical formula of the positive electrode material is Na 3+x(3-n) V 1+ y Cr δ Fe 1-δ-x-y M n+ x (PO4)3, Wherein, the value of δ is 0.1, 0.2, 0.3, 0.4 or 0.5; the value of x is 0.1, 0.2, 0.3, 0.4 or 0.5; the value of y is 0, 0.1, 0.2, 0.3, 0.4 or 0.5; the value of n is 2, 0<δ+x+y≤0.9, M n+ Including Mg 2+ 、Zn 2+ Any one of .

2. The positive electrode material according to claim 1, characterized in that The positive electrode material is loaded in the carbon skeleton to form Na 3+x(3-n) V 1+y Cr δ Fe 1-δ-x-y M n+ x (PO4)3@C positive electrode material.

3. A method for preparing the positive electrode material according to any one of claims 1 to 2, characterized in that: The preparation method comprises: synthesizing the positive electrode material by adopting any one of a solid phase method, a spray drying method and a sol-gel method.

4. The preparation method according to claim 3, characterized in that The preparation method comprises: mixing raw materials with a solvent to obtain a precursor, drying the precursor and then sintering the precursor to obtain the positive electrode material; Wherein, the raw materials include sodium source, vanadium source, chromium source, iron source, phosphorus source and M metal ion source; The sodium source includes any one or a combination of at least two of sodium bicarbonate, sodium carbonate, sodium acetate, sodium nitrate, sodium hydroxide or sodium oxalate; The vanadium source includes any one of vanadium pentoxide, vanadium tetroxide, vanadium trioxide, vanadium oxide, ammonium metavanadate, ammonium vanadate, vanadyl acetylacetonate or vanadium acetylacetonate, or a combination of at least two thereof; The phosphorus source includes any one of phosphoric acid, sodium diammonium phosphate, ammonium dihydrogen phosphate, disodium hydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate or sodium phosphate, or a combination of at least two thereof; The chromium source comprises: any one of chromium trioxide, chromium trioxide, chromium nitrate, chromium phosphate, chromium sulfide, chromium carbide, chromium nitride, ammonium chromate, ammonium dichromate, sodium chromate, chromium acetate, chromous acetate, chromium acetate hydroxide, chromium isopropoxide or chromium acetylacetonate, or a combination of at least two thereof; The iron source includes any one or a combination of at least two of ferric nitrate, ferric acetylacetonate, ferric oxide, ferric chloride, ferric bromide, ferric sulfate or ferric hydroxide; The preparation method further comprises: performing a grinding process after the drying; The drying temperature is 50-150°C; The grinding treatment time is 1 min to 48 h; The sintering atmosphere includes an inert atmosphere and / or a reducing atmosphere; The sintering temperature is 500-900°C; The sintering time is 2 to 20 h.

5. The preparation method according to claim 4, The sodium source comprises: a combination of sodium bicarbonate and sodium carbonate, a combination of sodium carbonate and sodium acetate, a combination of sodium acetate and sodium nitrate, a combination of sodium nitrate and sodium hydroxide, or a combination of sodium hydroxide and sodium oxalate; The vanadium source includes: a combination of vanadium pentoxide and vanadium tetroxide, a combination of vanadium tetroxide and vanadium trioxide, a combination of vanadium trioxide and vanadium oxide, a combination of vanadium oxide and ammonium metavanadate, a combination of ammonium metavanadate and ammonium vanadate, a combination of ammonium vanadate and vanadyl acetylacetonate, or a combination of vanadyl acetylacetonate and vanadium acetylacetonate; The phosphorus source includes: a combination of phosphoric acid and ammonium dihydrogen phosphate, a combination of sodium dihydrogen phosphate and ammonium dihydrogen phosphate, a combination of ammonium dihydrogen phosphate and diammonium hydrogen phosphate, a combination of disodium hydrogen phosphate and diammonium hydrogen phosphate, or a combination of ammonium phosphate and sodium phosphate; The chromium source includes: a combination of chromium trioxide and chromium trioxide, a combination of chromium nitrate and chromium phosphate, a combination of chromium sulfide and chromium carbide, a combination of chromium nitride and ammonium chromate, a combination of ammonium dichromate and sodium chromate, a combination of chromium acetate and chromous acetate, or a combination of chromium isopropylate and chromium acetylacetonate; The iron source includes: a combination of ferric sulfate and ferric oxide, a combination of ferric acetylacetonate and ferric bromide, a combination of ferric nitrate and ferric acetylacetonate, a combination of ferric hydroxide and ferric sulfate, or a combination of ferric chloride and ferric bromide.

6. The preparation method according to claim 4, characterized in that The raw materials also include a reducing agent; The reducing agent includes any one or a combination of at least two of oxalic acid, ascorbic acid, sucrose, glucose, hydroxylamine hydrochloride, ethanol, dopamine hydrochloride, citric acid, malic acid or ethylenediaminetetraacetic acid; The raw materials also include a carbon source; The carbon source comprises any one or a combination of at least two of citric acid, oleic acid, polyvinyl pyrrolidone, polyethylene glycol, glucose, ascorbic acid, sucrose, starch, graphene, carbon nanotubes or Ketjen black; The molar ratio of the carbon source to the metal ion source is 0-10:1; The solvent includes any one of deionized water, ethanol or acetone, or a combination of at least two of them.

7. The preparation method according to claim 6, characterized in that The reducing agent includes: a combination of sucrose and glucose, a combination of oxalic acid and ethanol, a combination of ascorbic acid and hydroxylamine hydrochloride, a combination of citric acid and oxalic acid, a combination of dopamine hydrochloride and glucose, a combination of malic acid and ascorbic acid, a combination of oxalic acid and ethylenediaminetetraacetic acid, or a combination of hydroxylamine hydrochloride and oxalic acid; The carbon source includes: a combination of glucose and citric acid, a combination of sucrose and oleic acid, a combination of polyvinyl pyrrolidone and polyethylene glycol, a combination of polyethylene glycol and glucose, a combination of ascorbic acid and sucrose, a combination of glucose and starch, or a combination of carbon nanotubes and Ketjen black; The solvent includes: a combination of deionized water and ethanol, a combination of deionized water and acetone, or a combination of ethanol and acetone.

8. A sodium ion battery, characterized in that: The battery comprises the positive electrode material according to any one of claims 1 to 2.

9. An energy storage device, characterized in that: The energy storage device comprises the sodium ion battery according to claim 8.

10. The energy storage device according to claim 9, characterized in that: The energy storage device is used for low-speed electric vehicles, solar power generation, wind power generation, smart grid peak regulation, distributed power stations, backup power supplies or communication base stations.

11. Use of the positive electrode material according to any one of claims 1 to 2, characterized in that: The positive electrode material is applied to sodium ion batteries.

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