CN116053470B - Iron-based composite positive electrode active material, and preparation method and application thereof - Google Patents

Iron-based composite positive electrode active material, and preparation method and application thereof Download PDF

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CN116053470B
CN116053470B CN202310339358.6A CN202310339358A CN116053470B CN 116053470 B CN116053470 B CN 116053470B CN 202310339358 A CN202310339358 A CN 202310339358A CN 116053470 B CN116053470 B CN 116053470B
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CN116053470A (en
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纪效波
高金强
侯红帅
邹国强
邓文韬
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Shenzhen Jingong Energy Co ltd
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Central South University
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
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    • H—ELECTRICITY
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Abstract

The invention provides an iron-based composite positive electrode active material, a preparation method and application thereof, wherein the chemical formula of the positive electrode active material is Na 4 Fe x Ni y Co z Mn a Mg b Ti c (PO 4 ) 2 P 2 O 7 Wherein y is more than or equal to 0.05 and less than or equal to 0.15,0.05, z is more than or equal to 0.15,0.05 and less than or equal to a is more than or equal to 0.15,0.05 and less than or equal to 0.15,0.05, c is more than or equal to 0.15, and x+y+z+a+b+c=3; fe is +2 valent, ni is +2 valent, co is +2 valent, mn is +2 valent, mg is +2 valent, ti is +2 valent; according to the invention, the voltage platform, the conductivity and the structural stability of the high-voltage power supply are effectively improved by doping specific metal elements; the preparation method provided by the invention has the advantages of simple process and good repeatability, and is suitable for industrial application.

Description

Iron-based composite positive electrode active material, and preparation method and application thereof
Technical Field
The invention relates to the technical field of positive electrode materials, in particular to an iron-based composite positive electrode active material, and a preparation method and application thereof.
Background
The secondary battery is a novel green energy storage mode, and the lithium ion battery is widely applied to aspects of human society life nowadays. The high cost of the lithium ion battery and the limitation of resource shortage of lithium, cobalt and the like at the present stage are difficult to meet the requirement of future scale energy storage. The sodium ion battery has the advantages of rich resources, high cost performance and the like, and is expected to be widely applied to the fields of electric bicycles, low-speed electric vehicles and fixed energy storage. Sodium ion batteries have potential application prospects especially in large-scale energy storage systems with low energy density requirements.
Among the positive electrode materials, iron-based polyanion compounds have the advantages of high energy density, high power density, good stability and the like, and become one of the research hot spots. Iron-based polyanionic sodium ion battery positive electrode material sodium iron phosphate sodium iron pyrophosphate Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 Is one ofThe emerging sodium ion battery anode material has a super ion conductor (NASICON) frame structure constructed by phosphate radicals and pyrophosphate radicals, has wide sodium ion diffusion channels dispersed in crystals, has higher specific capacity and a charge-discharge platform, and is a sodium ion battery anode material with excellent prospect. However, as with most polyanion-type materials, the intrinsic electronic conductivity of the material is low, the voltage is generally low, the energy density of the battery is reduced, and meanwhile, the actual specific capacity, the multiplying power performance, the stability and the like of the material are limited due to the defects of large bulk electron and ion transfer resistance and the like caused by improper preparation methods and the like, so that the further commercial application of the material is limited.
Disclosure of Invention
Based on the problems of poor electron conductivity, low voltage platform and poor cycle stability of the sodium iron phosphate pyrophosphate material in the prior art, one of the purposes of the invention is to provide a novel iron-based composite positive electrode material which not only has higher conductivity, but also has high voltage platform and energy density and excellent cycle stability.
In order to achieve the above object, the technical scheme of the present invention is as follows:
an iron-based composite positive electrode active material, the chemical formula of which is Na 4 Fe x Ni y Co z Mn a Mg b Ti c (PO 4 ) 2 P 2 O 7 Wherein y is more than or equal to 0.05 and less than or equal to 0.15,0.05, z is more than or equal to 0.15,0.05 and less than or equal to a is more than or equal to 0.15,0.05 and less than or equal to 0.15,0.05, c is more than or equal to 0.15, and x+y+z+a+b+c=3; fe is +2 valent, ni is +2 valent, co is +2 valent, mn is +2 valent, mg is +2 valent, ti is +2 valent.
In some embodiments, the positive electrode active material has the formula: na (Na) 4 Fe 2.5 Ni 0.1 Co 0.1 Mn 0.1 Mg 0.1 Ti 0.1 (PO 4 ) 2 P 2 O 7 。
Another object of the present invention is to provide a method for preparing the positive electrode active material according to any one of the above embodiments, comprising the steps of:
s1, mixing a sodium source, an iron source, a nickel source, a cobalt source, a manganese source, a magnesium source, a titanium source and a phosphorus source, and ball milling to obtain a precursor;
and S2, placing the precursor obtained in the step S1 in an inert gas atmosphere, sintering at 500-650 ℃, and crushing to obtain the iron-based composite anode active material.
In some embodiments, in step S2, the temperature is raised to 300 to 400 ℃ to preheat, and then raised to 500 to 650 ℃ to sinter.
In some embodiments, the temperature is raised to 300-400 ℃ and then preheated for 2-6 hours, and then raised to 500-650 ℃ and sintered for 8-24 hours.
In some embodiments, the molar ratio of sodium, iron, nickel, cobalt, manganese, titanium, phosphorus in the sodium source, iron source, nickel source, cobalt source, manganese source, magnesium source, titanium source, and phosphorus source is 4: x: y: and z: a: b: c:4.
in some embodiments, in step S1, the ball milling rotation speed is 400-800 r/min; and/or ball milling time is 0.5-10 h. Specifically, the ball milling mode is as follows: adding the raw materials into ball milling equipment, adding a small amount of volatile organic solvent (ethanol or isopropanol, etc.) to completely wet the raw materials, performing ball milling, and freeze-drying to obtain the precursor. Preferably, the conditions of freeze-drying are: vacuum freeze drying is carried out at the temperature of minus 50 to minus 30 ℃ for 1 to 10 hours.
In some embodiments, the sodium source comprises at least one of disodium dihydrogen pyrophosphate, sodium carbonate, sodium oxalate, sodium citrate.
In some embodiments, the iron source comprises at least one of ferrous oxalate, ferrous sulfate, ferrous ammonium sulfate.
In some embodiments, the nickel source comprises at least one of nickel oxide, nickel oxalate, nickel carbonate, nickel hydroxide.
In some embodiments, the cobalt source comprises at least one of cobalt oxide, cobalt oxalate, cobalt carbonate, cobalt hydroxide.
In some embodiments, the manganese source comprises at least one of manganese monoxide, manganese dioxide, manganese oxalate.
In some embodiments, the magnesium source comprises at least one of magnesium oxalate, magnesium sulfate, magnesium carbonate, magnesium nitrate.
In some embodiments, the titanium source comprises at least one of titanium monoxide, titanium dioxide, titanium sulfate, titanium oxalate.
In some embodiments, the phosphorus source comprises at least one of monoammonium phosphate, diammonium phosphate, pyrophosphoric acid, sodium pyrophosphate.
In some embodiments, the inert gas is at least one of nitrogen and argon.
It is a third object of the present invention to provide a positive electrode material including the positive electrode active material of any one of the above embodiments.
A fourth object of the present invention is to provide a positive electrode comprising the above positive electrode material.
The fifth object of the present invention is to provide an electrochemical energy storage device, comprising the above positive electrode. In particular, the electrochemical energy storage devices include, but are not limited to, sodium ion primary batteries, sodium ion secondary batteries, sodium ion capacitors, and the like.
Compared with the prior art, the invention has the following beneficial effects:
according to the invention, specific low-valence metal ions are doped in the iron-based polyanion type positive electrode active material, and crystal lattice defects including transition metal vacancies, sodium ion vacancies and the like are generated by doping induction of the specific metal ions, so that the charge transmission energy barrier in the charge-discharge process is reduced, the electronic conductivity of the phosphate material is improved, the advantages of high charge transmission rate, high ion transmission speed and the like are achieved, meanwhile, the thermal stability and chemical stability of the material are enhanced, the positive electrode active material has an excellent voltage platform, high energy density and cycle stability, and meanwhile, the conductivity is good. The doped nickel, cobalt and manganese are used for participating in redox to improve a voltage platform, so that the energy density of the sodium ion battery is effectively improved, a sodium ion diffusion channel is widened as a lattice support, the sodium ion transmission speed is improved, the structural thermal stability and the electrochemical stability are improved, the low-valence titanium and magnesium can reduce the forbidden band width of the material, accelerate the conduction of electrons on the surface and in a bulk phase of particles, and a positive electrode active material with good conductivity can be obtained without coating carbon, so that the problem of poor conductivity of ferric pyrophosphate nano electrons is fundamentally solved.
The positive electrode active material provided by the invention has the advantages of high voltage (reaching 3.2V), long discharge platform, good cycle stability, excellent rate performance, good chemical stability and thermal stability, good conductivity, and excellent electrochemical performance, and is applied to an electrochemical energy storage device.
According to the preparation method of the positive electrode active material, the low-cost iron is used as a main transition metal element, and the ball milling and sintering process is adopted, so that the iron-based composite positive electrode material with high crystallinity, wide temperature range, high conductivity, high specific capacity, high working voltage, excellent cycle stability and excellent multiplying power performance can be prepared, the particle size of the obtained positive electrode active material is 10 nm-5 mu m, the preparation process is simple, the cost is low, the product is stable, the repeatability is good, and the industrialization is convenient.
Drawings
FIG. 1 shows an iron-based composite Na prepared in example 1 of the present invention 4 Fe 2.5 Ni 0.1 Co 0.1 Mn 0.1 Mg 0.1 Ti 0.1 (PO 4 ) 2 P 2 O 7 SEM images of (a);
FIG. 2 shows an iron-based composite Na prepared in example 1 of the present invention 4 Fe 2.5 Ni 0.1 Co 0.1 Mn 0.1 Mg 0.1 Ti 0.1 (PO 4 ) 2 P 2 O 7 An XRD pattern of (b);
FIG. 3 is an iron-based composite Na prepared in example 1 of the present invention 4 Fe 2.5 Ni 0.1 Co 0.1 Mn 0.1 Mg 0.1 Ti 0.1 (PO 4 ) 2 P 2 O 7 And the iron-based composite material Na prepared in comparative example 1 4 Fe 3 (PO 4 ) 2 P 2 O 7 An impedance diagram of the assembled battery;
FIG. 4 shows a process according to example 1 of the present inventionPrepared iron-based composite material Na 4 Fe 2.5 Ni 0.1 Co 0.1 Mn 0.1 Mg 0.1 Ti 0.1 (PO 4 ) 2 P 2 O 7 A charge-discharge curve graph of (2);
FIG. 5 shows an iron-based composite Na prepared in example 1 of the present invention 4 Fe 2.5 Ni 0.1 Co 0.1 Mn 0.1 Mg 0.1 Ti 0.1 (PO 4 ) 2 P 2 O 7 Is a cyclic graph of (a).
Detailed Description
In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. The invention may be embodied in many other forms than described herein and similarly modified by those skilled in the art without departing from the spirit or scope of the invention, which is therefore not limited to the specific embodiments disclosed below.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.
Example 1
Iron-based composite material Na 4 Fe 2.5 Ni 0.1 Co 0.1 Mn 0.1 Mg 0.1 Ti 0.1 (PO 4 ) 2 P 2 O 7 The preparation method of (2) comprises the following steps:
(1) The method comprises the steps of designing and generating 0.03mol of target product, mixing 0.01 mol of sodium pyrophosphate, 0.025 mol of ferrous oxalate, 0.001 mol of nickel oxalate, 0.001 mol of cobalt oxalate, 0.001 mol of manganese oxalate, 0.001 mol of magnesium oxalate, 0.001 mol of titanium oxalate and 0.02 mol of diammonium hydrogen phosphate in a ball milling tank, performing high-speed ball milling at a ball milling rate of 800r/min for 10 hours, and obtaining a precursor;
(2) Placing the precursor obtained in the step (1) in argon atmosphere, heating to 350 ℃ firstly, preheating for 2 hours, heating to 650 ℃ and sintering for 24 hours, and completing sinteringThen, the materials are fully ground by a mortar to obtain the iron-based composite material Na 4 Fe 2. 5 Ni 0.1 Co 0.1 Mn 0.1 Mg 0.1 Ti 0.1 (PO 4 ) 2 P 2 O 7 。
The obtained iron-based composite material Na 4 Fe 2.5 Ni 0.1 Co 0.1 Mn 0.1 Mg 0.1 Ti 0.1 (PO 4 ) 2 P 2 O 7 SEM and XRD analysis were performed, and the analysis results are shown in fig. 1 and 2, respectively.
As can be seen from FIG. 1, the synthesized iron-based composite material Na 4 Fe 2.5 Ni 0.1 Co 0.1 Mn 0.1 Mg 0.1 Ti 0.1 (PO 4 ) 2 P 2 O 7 The particle size distribution is uniform, and the single particle size is about 100 nm-200 nm.
FIG. 2 shows successful synthesis of iron-based composite Na 4 Fe 2.5 Ni 0.1 Co 0.1 Mn 0.1 Mg 0.1 Ti 0.1 (PO 4 ) 2 P 2 O 7 。
The iron-based composite material Na prepared in the embodiment 4 Fe 2.5 Ni 0.1 Co 0.1 Mn 0.1 Mg 0.1 Ti 0.1 (PO 4 ) 2 P 2 O 7 The preparation method of the positive electrode plate as the positive electrode active material specifically comprises the following steps:
the iron-based composite material prepared in the embodiment is weighed as an active substance, 10wt.% of acetylene black is added as a conductive agent, 10wt.% of PVDF is added as a binder, a proper amount of N-methylpyrrolidone (NMP) is added after full grinding and uniformly mixed to obtain slurry, and the slurry is coated on a carbon-coated aluminum foil current collector and dried to obtain the positive electrode plate.
Assembling the obtained positive electrode plate and sodium plate into a button cell, wherein an adopted electrolyte system is as follows: 1M NaClO4/EC DMC: EMC (1:1:1) and then electrochemical performance testing was performed.
The electrochemical performance results are shown in fig. 4 and 5.
As can be seen from fig. 4, the iron-based composite material is as Na 4 Fe 2.5 Ni 0.1 Co 0.1 Mn 0.1 Mg 0.1 Ti 0.1 (PO 4 ) 2 P 2 O 7 The button cell assembled by the positive electrode plate made of the positive electrode active material and the sodium plate has the initial charging specific capacity of 111mAh g under the 1C multiplying power -1 The specific discharge capacity is 111mAh g -1 。
Fig. 5 shows that the iron-based composite material obtained in this example is used as a positive electrode active material, and the button cell assembled with the sodium sheet has a charge-discharge efficiency of about 99% at a 1C rate for 100 cycles, and exhibits good stability.
The results of the conductivity test of the iron-based composite material obtained in this example and the results of the impedance test of the assembled battery are shown in table 1 and fig. 3.
Table 1 resistivity test results of the iron-based composite material obtained in example 1
Figure SMS_1
Example 2
The preparation method of the iron-based composite material of the embodiment comprises the following steps:
(1) The method comprises the steps of designing and generating 0.03mol of target product, mixing 0.01 mol of sodium pyrophosphate, 0.025 mol of ferrous oxalate, 0.001 mol of nickel oxide, 0.001 mol of cobalt oxide, 0.001 mol of manganese oxide, 0.001 mol of magnesium oxide, 0.001 mol of titanium oxide and 0.02 mol of diammonium hydrogen phosphate in a ball milling tank, performing high-speed ball milling at a ball milling rate of 800r/min for 10 hours, and obtaining a precursor;
(2) Placing the precursor obtained in the step (1) in argon atmosphere, preheating for 2 hours at 350 ℃, then sintering at 650 ℃ for 24 hours, fully grinding the material by using a mortar, and obtaining the iron-based composite material Na 4 Fe 2.5 Ni 0.1 Co 0.1 Mn 0.1 Mg 0.1 Ti 0.1 (PO 4 ) 2 P 2 O 7 。
The iron-based composite material Na prepared in the embodiment 4 Fe 2.5 Ni 0.1 Co 0.1 Mn 0.1 Mg 0.1 Ti 0.1 (PO 4 ) 2 P 2 O 7 And preparing a positive electrode plate as a positive electrode active material, and then assembling the positive electrode plate and the sodium plate into a button cell for electrochemical performance test. Through test, the initial charge specific capacity is 108mAh g under 1C multiplying power -1 The specific discharge capacity is 108mAh g -1 The charge-discharge efficiency of 100 cycles at 1C rate was maintained at about 95%.
Example 3
The preparation of the iron-based composite material of this example comprises the following steps:
(1) The method comprises the steps of designing and generating 0.03mol of target product, mixing 0.01 mol of sodium pyrophosphate, 0.025 mol of ferrous oxalate, 0.001 mol of nickel oxalate, 0.001 mol of cobalt oxalate, 0.001 mol of manganese oxalate, 0.001 mol of magnesium oxalate, 0.001 mol of titanium oxalate and 0.02 mol of diammonium hydrogen phosphate in a ball milling tank, performing high-speed ball milling at a ball milling rate of 800r/min for 10 hours, and obtaining a precursor;
(2) Placing the precursor obtained in the step (1) in a nitrogen atmosphere, preheating for 2 hours at the temperature of 350 ℃, then sintering at the temperature of 550 ℃ for 12 hours, fully grinding the material by using a mortar, and obtaining the iron-based composite material Na 4 Fe 2.5 Ni 0.1 Co 0.1 Mn 0.1 Mg 0.1 Ti 0.1 (PO 4 ) 2 P 2 O 7 。
The iron-based composite material Na prepared in the embodiment 4 Fe 2.5 Ni 0.1 Co 0.1 Mn 0.1 Mg 0.1 Ti 0.1 (PO 4 ) 2 P 2 O 7 And preparing a positive electrode plate as a positive electrode active material, and then assembling the positive electrode plate and the sodium plate into a button cell for electrochemical performance test. Through test, the initial charge specific capacity is 105mAh g under 1C multiplying power -1 The specific discharge capacity is 104mAh g -1 The charge-discharge efficiency of 100 cycles at 1C rate was kept around 94%.
Comparative example 1
A method for preparing an iron-based composite material, comprising the steps of:
(1) The method comprises the steps of designing and generating 0.03mol of target product, mixing 0.01 mol of sodium pyrophosphate, 0.03mol of ferrous oxalate and 0.02 mol of diammonium hydrogen phosphate in a ball milling tank, performing high-speed ball milling at a ball milling rate of 800r/min for 10 hours to obtain a precursor;
(2) Placing the precursor obtained in the step (1) in argon atmosphere, preheating for 2 hours at 350 ℃, then sintering at 650 ℃ for 24 hours, fully grinding the material by using a mortar to obtain the iron-based composite material Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 。
The composite material prepared in the comparative example is used as a positive electrode active material to prepare a positive electrode plate, and then the positive electrode plate and a sodium plate are assembled into a button cell for electrochemical performance test. Through test, the initial charge specific capacity is 105mAh g under 1C multiplying power -1 The specific discharge capacity is 102mAh g -1 The charge-discharge efficiency of 100 cycles at 1C rate was maintained at about 73%.
The results of the conductivity test of the iron-based composite material obtained in this comparative example and the results of the impedance test of the assembled battery are shown in table 2 and fig. 3.
Table 2 results of resistivity test of the iron-based composite material obtained in comparative example 1
Figure SMS_2
Comparative example 2
A method for preparing an iron-based composite material, comprising the steps of:
(1) The method comprises the steps of designing and generating 0.03mol of target product, mixing 0.01 mol of sodium pyrophosphate, 0.025 mol of ferrous oxalate, 0.001 mol of nickel oxalate, 0.001 mol of cobalt oxalate, 0.001 mol of manganese oxalate, 0.001 mol of magnesium oxalate, 0.001 mol of titanium oxalate and 0.02 mol of diammonium hydrogen phosphate in a ball milling tank, performing high-speed ball milling at a ball milling rate of 800r/min for 10 hours, and obtaining a precursor;
(2) And (3) placing the precursor obtained in the step (1) in an air atmosphere, preheating for 2 hours at the temperature of 350 ℃, then sintering at the temperature of 650 ℃ for 24 hours, and fully grinding the material by using a mortar to obtain a final product.
And preparing a positive electrode plate by taking the final product prepared in the comparative example as a positive electrode active material, and then assembling the positive electrode plate and a sodium plate into a button cell for electrochemical performance test. Through test, the first charge specific capacity is 51mAh g under 1C multiplying power -1 Specific discharge capacity of 30mAh g -1 The charge-discharge efficiency of 100 cycles at 1C rate was kept around 14%.
As no inert atmosphere protection is carried out, the comparative example is obtained by mixing oxide materials, the materials are mixture of various hetero phases, the specific capacity is low, the circulation stability is poor, and the iron-based composite material Na is illustrated 4 Fe 2.5 Ni 0.1 Co 0.1 Mn 0.1 Mg 0.1 Ti 0.1 (PO 4 ) 2 P 2 O 7 Inert atmosphere protection is a necessary condition in the preparation process.
Comparative example 3
A method for preparing an iron-based composite material, comprising the steps of:
(1) The method comprises the steps of designing and generating 0.03mol of target product, mixing 0.01 mol of sodium pyrophosphate, 0.025 mol of ferrous oxalate, 0.001 mol of nickel oxalate, 0.001 mol of cobalt oxalate, 0.001 mol of manganese oxalate, 0.001 mol of magnesium oxalate, 0.001 mol of titanium oxalate and 0.02 mol of diammonium hydrogen phosphate in a ball milling tank, performing high-speed ball milling at a ball milling rate of 800r/min for 10 hours, and obtaining a precursor;
(2) Placing the precursor obtained in the step (1) in argon atmosphere, preheating for 2 hours at 350 ℃, then sintering at 450 ℃ for 24 hours, fully grinding the material by using a mortar, and obtaining the iron-based high-entropy composite material Na 4 Fe 2.5 Ni 0.1 Co 0.1 Mn 0.1 Mg 0.1 Ti 0.1 (PO 4 ) 2 P 2 O 7 。
Preparing a positive electrode plate by taking the composite material prepared in the comparative example as a positive electrode active material, and then assembling the positive electrode plate and a sodium plate into a button cellAnd (5) performing electrochemical performance test. Through test, the first charge specific capacity is 84mAh g under 1C multiplying power -1 Specific discharge capacity of 71mAh g -1 The charge-discharge efficiency of 100 cycles at 1C rate was kept around 52%.
According to analysis, the composite material obtained in the comparison example has low crystallinity due to the fact that the sintering temperature is too low, and mixed with impurity phases, so that the specific capacity is low, the cycle stability is poor, and further the fact that the proper sintering temperature is an important factor for preparing the anode material of the iron-based sodium ion battery is explained.
Comparative example 4
(1) The control example is designed to generate 0.03mol of target product, and 0.01 mol of sodium pyrophosphate, 0.025 mol of ferrous oxalate, 0.001 mol of nickel oxalate, 0.001 mol of cobalt oxalate, 0.001 mol of manganese oxalate, 0.001 mol of magnesium oxalate, 0.001 mol of titanium dioxide and 0.02 mol of diammonium hydrogen phosphate are placed in a ball milling tank for mixing, ball milling is performed at a high speed, the ball milling rate is 800r/min, and the ball milling time is 10 hours, so that a precursor is obtained;
(2) Placing the precursor obtained in the step (1) in argon atmosphere, preheating for 2 hours at 350 ℃, then sintering at 650 ℃ for 24 hours, fully grinding the material by using a mortar after sintering, and obtaining the Na containing the +4-valent titanium doped iron-based high-entropy composite material 4 Fe 2.5 Ni 0.1 Co 0.1 Mn 0.1 Mg 0.1 Ti 0.1 (PO 4 ) 2 P 2 O 7 。
The composite material prepared in the comparative example is used as a positive electrode active material to prepare a positive electrode plate, and then the positive electrode plate and a sodium plate are assembled into a button cell for electrochemical performance test. Through test, the first charge specific capacity is 102mAh g under 1C multiplying power -1 The specific discharge capacity is 101mAh g -1 The charge-discharge efficiency of 100 cycles at 1C rate was kept around 89%. .
Table 3 resistivity test results of the iron-based composite material obtained in comparative example 4
Figure SMS_3
The technical features of the above-described embodiments may be arbitrarily combined, and all possible combinations of the technical features in the above-described embodiments are not described for brevity of description, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.
The above examples illustrate only a few embodiments of the invention, which are described in detail and are not to be construed as limiting the scope of the invention. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the invention, which are all within the scope of the invention. Accordingly, the scope of protection of the present invention is to be determined by the appended claims.

Claims (10)

1. An iron-based composite positive electrode active material is characterized in that the chemical formula is Na 4 Fe x Ni y Co z Mn a Mg b Ti c (PO 4 ) 2 P 2 O 7 Wherein y is more than or equal to 0.05 and less than or equal to 0.15,0.05, z is more than or equal to 0.15,0.05 and less than or equal to a is more than or equal to 0.15,0.05 and less than or equal to 0.15,0.05, c is more than or equal to 0.15, and x+y+z+a+b+c=3; fe is +2 valent, ni is +2 valent, co is +2 valent, mn is +2 valent, mg is +2 valent, ti is +2 valent.
2. The iron-based composite positive electrode active material according to claim 1, wherein the positive electrode material has a chemical formula: na (Na) 4 Fe 2.5 Ni 0.1 Co 0.1 Mn 0.1 Mg 0.1 Ti 0.1 (PO 4 ) 2 P 2 O 7 。
3. The method for preparing the iron-based composite positive electrode active material according to claim 1 or 2, characterized by comprising the steps of:
s1, mixing a sodium source, an iron source, a nickel source, a cobalt source, a manganese source, a magnesium source, a titanium source and a phosphorus source, and ball milling to obtain a precursor;
and S2, placing the precursor obtained in the step S1 in an inert gas atmosphere, sintering at 500-650 ℃, and crushing to obtain the iron-based composite anode material.
4. The method for preparing an iron-based composite positive electrode active material according to claim 3, wherein in the step S2, the temperature is raised to 300-400 ℃ for preheating, and then raised to 500-650 ℃ for sintering.
5. The method for preparing an iron-based composite positive electrode active material according to claim 3, wherein the molar ratio of sodium, iron, nickel, cobalt, manganese, magnesium, titanium, and phosphorus in the sodium source, the iron source, the nickel source, the cobalt source, the manganese source, the magnesium source, the titanium source, and the phosphorus source is 4: x: y: and z: a: b: c:4.
6. the method for preparing the iron-based composite positive electrode active material according to claim 3, wherein in the step S1, the ball milling speed is 400-800 r/min; and/or ball milling time is 0.5-10 h.
7. The method for preparing an iron-based composite positive electrode active material according to claim 3, wherein the sodium source comprises at least one of disodium dihydrogen pyrophosphate, sodium carbonate, sodium oxalate, sodium citrate;
and/or, the iron source comprises at least one of ferrous oxalate, ferrous sulfate and ferrous ammonium sulfate;
and/or the nickel source comprises at least one of nickel oxide, nickel oxalate, nickel carbonate, nickel hydroxide;
and/or the cobalt source comprises at least one of cobalt oxide, cobalt oxalate, cobalt carbonate and cobalt hydroxide;
and/or the manganese source comprises at least one of manganese monoxide, manganese dioxide and manganese oxalate;
and/or the magnesium source comprises at least one of magnesium oxalate, magnesium sulfate, magnesium carbonate and magnesium nitrate;
and/or the titanium source comprises at least one of titanium monoxide, titanium dioxide, titanium sulfate and titanium oxalate;
and/or the phosphorus source comprises at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, pyrophosphoric acid and sodium pyrophosphate.
8. A positive electrode material comprising the positive electrode active material according to claim 1 or 2.
9. A positive electrode comprising the positive electrode material according to claim 8.
10. An electrochemical energy storage device comprising the positive electrode of claim 9.
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