CN114678509A - Sodium ion battery layered positive electrode material coated with oxyfluoride in situ and preparation method thereof - Google Patents
Sodium ion battery layered positive electrode material coated with oxyfluoride in situ and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a sodium ion battery layered positive electrode material coated with oxyfluoride in situ, which is of a rock salt/layered heterostructure, and the chemical formula of the layered positive electrode material is expressed as NaxTMO2@MaNb(O/F)c，MaNb(O/F)cIs fluorine/oxide, and is formed by uniformly coating a layered metal oxide NaTMO with a rock salt phase2Wherein TM is at least one of transition metals Ni, Co, Mn, Cu, Fe, Ti, M is at least one of Li, Na, N is at least one of transition metals Ni, Co, Mn, Cu, Ti, Zn, Al, Zr, Sn, Sb, W, Ta; x is 2/3-1, a is more than or equal to 0.01 and less than or equal to 0.05, b is more than or equal to 0.01 and less than or equal to 0.05, and c satisfies MaNb(O/F)cThe coating layer has a thickness of 10-15 nm. According to the preparation method of the cathode material, firstly, the layered cathode material is obtained through one-time high-temperature sintering, and then the obtained cathode and the coating material are fully molded and coated through a high-temperature fusion coating machine, so that the high-voltage stable cathode coating material is obtained.
Description
Technical Field
The invention belongs to the field of chemical power sources, and particularly relates to a sodium-ion battery layered positive electrode material coated with oxyfluoride in situ and a preparation method thereof.
Background
With the rapid development of the large-scale energy storage field in the last decade, the problems of insufficient lithium resources and global maldistribution seriously restrict the wide application of the lithium ion battery in the large-scale energy storage field. On the contrary, the sodium ion battery has low cost due to the rich sodium resource, and is considered to have good application prospect in the field of large-scale energy storage.
Among many sodium ion cathode materials, the layered cathode material has the characteristics of high capacity, low pollution and wide raw material range, and is considered to be an ideal cathode material suitable for large-scale energy storage application. However, the chemical potential of the sodium ion couple is lower than that of the lithium ion couple by 0.3V, which causes that the sodium ion battery is inferior to the lithium ion battery in energy density, so that the improvement of the output voltage of the sodium ion battery is the key to make up for the short plate of the sodium ion battery in the energy storage field. However, in the high-voltage layered positive electrode material, due to the desorption of sodium ions, transition metal elution, segregation and the like are likely to occur on the surface of the material, so that the surface structure is collapsed, the layered structure is destroyed, and an amorphous rock salt phase is likely to be formed on the surface; in addition, the activity of transition metal ions and oxygen is enhanced under high voltage, on one hand, unstable CEI is accompanied with decomposition of electrolyte, and on the other hand, oxygen on the surface of the material is precipitated due to oxygen oxidation and reduction, so that the structure of the material is deteriorated, and potential safety hazards are brought. The coating of the positive electrode material of the sodium-ion battery by adopting the coating is a commonly adopted means in the prior art. The coating layer can relieve the corrosion of electrolyte to the material, reduce the dissolution of surface ions and improve the cycling stability of the anode material.
CN112456567A discloses a method for coating a layered anode with an oxide by using a wet method, which, although achieving a good coating effect, brings a series of problems such as drying, crushing, waste liquid treatment, etc., and is not suitable for mass production. Therefore, the development of the uniform coating technology in one step has important significance for simplifying the process flow and reducing the production cost.
In addition, the interface stability of the positive electrode can be improved to a certain degree by the conventional oxide coating, but the phenomenon of oxygen escape of surface crystal lattices under high pressure still exists, so that in order to improve the high-pressure stability of the material, a fluoride is introduced to modify the surface, the surface oxygen activity is reduced, and the coating layer is more resistant to the corrosion of the fluorine-containing electrolyte.
CN112968165A discloses a fluorine modified sodium ion cathode material, and CN113764669A discloses a method for improving material stability by fluorine doping, but because the charges and ionic radii of fluorine and oxygen are different, doping an inlet phase inevitably causes local structural defects and oxygen vacancies in a bulk phase structure, and still cannot meet the requirement of long cycle.
There are also prior art techniques that use ammonium fluoride, or solutions of fluoride-containing salts, as a source of fluorine for coating the fluoride surface, such as CN 114204004A. Alternatively, the fluorine source and the metal oxide are coated with the oxide and the fluoride by a solid phase method, such as the method described in CN 112151798A. The introduced fluorine source comprises other ion sources, and in consideration of the thermal volatilization effect at high temperature, the amount of F in the coating layer is generally smaller than the charge ratio, and the distribution of the F element is not uniform, thereby influencing the structure and the performance of the material. The positive electrode material is coated by a ball milling method, a hydrothermal method, a sol-gel method and an electrodeposition method, but the methods cannot effectively realize the lossless and uniform coating of the surface of the positive electrode material by fluoride without exception.
Disclosure of Invention
In order to solve the problem that the electrochemical performance of the positive electrode material of the sodium-ion battery in the prior art cannot meet the actual requirement, particularly the stability under high pressure, the problem is solved by coating the layered positive electrode material with the oxyfluoride coating, the oxyfluoride coating can be uniformly melted at a lower temperature by utilizing the eutectic effect of the surface residual sodium source and the fluoride and the reaction of the surface residual sodium source and the metal oxide, and further the oxyfluoride can be coated on the positive electrode interface in situ by one-time calcination.
In order to achieve the above object, the present invention provides the following technical solutions:
the layered positive electrode material of the sodium ion battery coated with the oxyfluoride in situ is of a rock salt/layered heterostructure, and the chemical formula is expressed as NaxTMO2@MaNb(O/F)c，MaNb(O/F)cIs fluorine/oxide, and is formed by uniformly coating a layered metal oxide NaTMO with a rock salt phase2Wherein TM is at least one of transition metals Ni, Co, Mn, Cu, Fe, Ti, M is at least one of Li, Na, N is at least one of transition metals Ni, Co, Mn, Cu, Ti, Zn, Al, Zr, Sn, Sb, W, Ta; x is 2/3-1, a is more than or equal to 0.01 and less than or equal to 0.05, b is more than or equal to 0.01 and less than or equal to 0.05, and c satisfies MaNb(O/F)cCharge balancing.
When x is 2/3, the layered positive electrode material is in a P2 phase structure; when x is 1, the layered cathode material is shown to be in an O3 phase structure.
Furthermore, x is 2/3, a is more than or equal to 0.01 and less than or equal to 0.02, and b is more than or equal to 0.01 and less than or equal to 0.02.
Further, the sodium electrical layered cathode material coated by the oxyfluoride coating is characterized in that the thickness of the coating layer is 5-30nm, preferably 10-15 nm.
Furthermore, in an XPS (X-ray diffraction) etching analysis spectrum of the layered positive electrode material of the sodium-ion battery coated with the oxyfluoride in situ, a characteristic peak signal of the transition metal TM from an appearance phase to a bulk phase is gradually enhanced, and a signal of the fluorine/oxide is gradually weakened.
The surface of the layered metal oxide positive electrode material of the conventional sodium ion battery is not protected, and the layered phase on the surface can be degraded after circulation to form a rock salt phase without electrochemical activity.
The second purpose of the invention is to provide a preparation method of the layered positive electrode material of the sodium-ion battery coated with the oxyfluoride in situ, which comprises the following steps:
(S1) source material mixing: feeding a sodium source and a transition metal TM source according to a stoichiometric ratio, feeding the sodium source according to 110-120% of the stoichiometric ratio, and performing ball milling and uniform mixing to form a mixture;
further, a sodium source material required for the positive electrode, which is selected from at least one of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium oxide, and sodium peroxide; a TM source material required for the positive electrode of the present invention, which is selected from at least one of TM oxides, sulfates, nitrates, carbonates, acetates, oxalates, and hydrated compounds thereof; feeding the sodium source removing material according to the stoichiometric ratio determined by the structural general formula, and feeding the sodium source material according to the stoichiometric ratio of 110-120%, and performing ball milling and mixing uniformly to form a mixture, wherein the ball milling and mixing time is 1-50 hours, and the rotating speed of the ball mill is 200-1000 rpm.
The sodium source is in excess of 10-20 at% relative to the TM source, where at represents the number of atoms. The excess sodium source forms residual alkali on the surface of the obtained layered oxide positive electrode material. This residual alkali is generally eliminated. The inventor unexpectedly finds that the sodium source is excessive by more than 10% (the sodium source is excessive by about 3-5% in the prior art), more residual alkali can be formed on the surface, and when the residual alkali is coated subsequently, eutectic effect exists between the residual alkali and the added fluorine source, so that the phenomenon of dissipation and volatilization caused by high temperature during fusion coating is reduced, and the content of fluorine in the coating is close to the charge ratio of the fluorine source; on the other hand, the residual alkali can react with the metal oxide. After the factors are combined, the synergistic coordination effect is achieved, the oxyfluoride can be melted at a lower temperature to form a uniform and compact coating layer, and the circulation stability of the sodium ion cathode material is facilitated.
(S2) sintering of the positive electrode material: calcining the mixture obtained in the step (S1), heating to 600-1000 ℃, preserving the heat for 12-48h, and cooling to room temperature to obtain the layered metal oxide NaxTMO2(x-2/3 or 1);
further, the calcining atmosphere is at least one of oxygen and air, the heating rate is 1-10 ℃/min, and the cooling rate during cooling is 1-10 ℃/min.
(S3) coating of positive electrode material: mixing the material obtained in step (S2) with MaNb(O/F)cAnd fully shaping and coating the source material in a fusion coating machine.
Further, said MaNb(O/F)cThe source material is a fluoride of metal M and/or N, and an oxide of metal N.
Still further, the fluoride of the metal M and/or N is selected from NaF, LiF, NiF2、CoF2、MnF2、CuF2、TiF4At least one of; the oxide of the metal N is selected from ZnO and Al2O3、SnO2、ZrO2、Sb2O5、WO3、Ta2O5At least one of (1).
Further, the metal N oxide is a doped metal oxide or, for example, a zinc-doped aluminum oxide, expressed as (Zn) Al2O3Wherein the Zn doping proportion is 5-10 wt%. The inventor unexpectedly finds that the zinc-doped aluminum oxide is used as the metal oxide raw material of the oxyfluoride coating layer, so that the reversible specific capacity and the cycling stability of the positive electrode material of the sodium-ion battery can be simultaneously improved.
Further, the working conditions of the high-temperature fusion covering machine are as follows: the temperature is 400-1800 plus, the rotating speed of the cladding machine is 500-1800rpm, and the cladding time in the cladding machine is 300-600 min. Preferably, the working conditions of the fusion cladding machine are: coating the mixture for 100-600 min at the rotation speed of 400-600 ℃, 500-800rpm and coating the mixture for 200-600min at the rotation speed of 600-900 ℃, 1200-1500 rpm. The inventors found that, when the fusion coating is performed, the coating is performed for a short time at a low temperature and a low rotation speed (500-.
The invention also provides a sodium ion battery, and the preparation raw material of the anode comprises the layered anode material coated with the oxyfluoride in situ.
Furthermore, the preparation raw materials of the positive electrode also comprise a conductive agent and a binder; the mass ratio of the positive electrode material to the conductive agent to the binder is 6-9: 0.5-2: 0.5-2, preferably 8-9: 0.5-1:0.5-1.
The invention has the beneficial effects that:
the preparation method of the positive electrode disclosed by the invention is solid-phase coating, the coating process is simplified, the synthesis process is simple, the production efficiency is high, and the provided positive electrode material is good in uniformity. In addition, all the raw materials are easy to obtain, nontoxic and low in cost, special protection is not needed in the production process, the compatibility with the existing production equipment is good, and the method is suitable for large-scale production.
Secondly, the surface of the material prepared by the method has a rock salt/layered heterostructure, and the structure of the interface-coated oxyfluoride rock salt is similar to the main inorganic component of the anode interface film after the battery is circulated. By artificial coating, the film forming uniformity and compactness of the CEI are effectively improved, and the dissolution of transition metal, the decomposition of electrolyte, gas generation and the like are effectively inhibited.
Based on the eutectic effect of the residual alkali and the fluoride on the surface of the anode and the high-temperature chemical combination reaction of the sodium source of the residual alkali and the metal oxide, the added fluoride and the residual alkali on the surface have a certain eutectic effect at a proper melting temperature to provide conditions for the subsequent uniform coating of the composite coating layer, and on the other hand, the metal N oxide effectively consumes the residual alkali on the surface through the melting chemical combination reaction to convert harmful residual alkali on the surface into a uniform coating layer with high ionic conductivity, so that the coating effect is uniform and compact, the interface resistance and the interface side reaction are effectively reduced, and the circulation stability of the material is improved.
The in-situ coating strategy on the surface of the anode introduced by the invention effectively reduces the surface residual alkali without influencing the capacity of the anode, so that the redundant surface residual alkali of the original anode is changed into a rock salt phase composite coating layer with electrochemical activity through a melting combination reaction, and the influence of a coating material on the capacity of the anode is further avoided.
The layered positive electrode material of the sodium ion battery coated with the oxyfluoride in situ prepared by the invention has good cycle stability, particularly shows surprisingly excellent stability under high-pressure conditions, and provides a new research direction for industrialization of the sodium ion battery.
Drawings
Fig. 1 is an XRD spectrum of the cathode prepared in example 1;
fig. 2 is an SEM spectrum of the cathode prepared in example 1;
fig. 3 is a TEM spectrum of the positive electrode prepared in example 1;
FIG. 4 is an XPS etch map of example 1.
Detailed Description
The fluoride-coated sodium ion-containing layered positive electrode material of the present invention will be further described with reference to the following specific examples and drawings, but it should be understood that the scope of the present invention is not limited to the following examples.
Unless otherwise defined, 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 is for the purpose of describing particular embodiments only and is not intended to limit the scope of the present invention.
EXAMPLE 1 preparation of P2-Na2/3Ni1/3Mn1/3Ti1/3O2@NaF-Zn(5％)·Al2O3A layered positive electrode material, a positive electrode material,
(S1) weighing 0.0105mmolNa2CO3、0.01mmol NiO、0.01mmol MnO2、0.01mmol TiO2And ethanol with the mass one time of that of the materials are mixed and then placed in a ball milling tank, and the ball-material ratio is controlled to be 20: 1, setting the rotation speed of a ball mill at 500rpm, performing positive and negative rotation modes, performing ball milling for 10 hours, drying and grinding in an oven, and transferring to a vacuum oven for storage.
(S2) pressing the baked precursor into small round pieces with the diameter of 10mm, then placing the small round pieces into a muffle furnace for calcination, raising the temperature to 1000 ℃ at the speed of 5 ℃/min, preserving the heat for 15 hours, and cooling to room temperature to obtain P2-Na2/3Ni1/3Mn1/3Ti1/3O2A layered positive electrode material.
(S3) weighing a proper amount of the P2-Na2/3Ni1/3Mn1/3Ti1/3O2The layered positive electrode material is added with 2 wt% of NaF and 2 wt% of Zn (5%). Al2O3Coating in a high-temperature fusion coating machine, wherein the coating program is set to firstly coat at 800rpm for 2 hours at 400 ℃, then coat at 1500rpm for 6 hours at 750 ℃, and cooling to room temperature to obtain P2-Na2/3Ni1/3Mn1/3Ti1/3O2@NaF-Zn(5％)·Al2O3And transferring the layered positive electrode material to a hand box for standby.
The obtained P2-Na2/3Ni1/3Mn1/3Ti1/3O2@NaF-Zn(5％)·Al2O3The preparation method comprises the following steps of mixing 80 parts, 10 parts and 10 parts by weight of a layered positive electrode material, a conductive additive SP and a binder PVDF, dissolving the mixture in a solvent NMP, stirring to obtain uniform slurry, uniformly coating the slurry on a carbon-coated aluminum foil by using a 200 mu m scraper, drying and slicing to obtain a positive electrode pole piece.
Fig. 4 is an XPS etching spectrum of the positive electrode material of the sodium-ion battery prepared in example 1, wherein peaks of 642eV and 654eV correspond to two characteristic peaks of Mn2p 3/2 and Mn2p 1/2, respectively, and a peak of 686eV corresponds to a characteristic peak of NaF. It can be seen from the figure that Mn is used as a main signal of the positive electrode, and the signal of Mn is gradually increased from the surface to the bulk phase, which means that the surface of the positive electrode is provided with a coating layer, and correspondingly, the signal of NaF is gradually weakened from the surface to the bulk phase, and the surface coating layer is determined to be NaF. In addition, the thickness of the coating layer is determined according to the etching duration, and the surface coating layer is about 10nm as can be seen by combining the electron microscope photos shown in fig. 2 and 3.
Example 2
The procedure is the same as in example 1, except that the coating material is changed to 1 wt% NaF and 1 wt% Zn (5%). Al2O3。
Example 3
The procedure was as in example 1, except that the coating material was changed to 4 wt% NaF and 4 wt% Zn (5%). Al2O3。
Example 4
The procedure was the same as in example 1, except that the coating material was changed to 2 wt% NaF and 2 wt% Al2O3。
Example 5
The procedure was the same as in example 1, except that the coating material was changed to 2 wt% NaF and 2 wt% Sb2O5The coating temperature was changed to 650 degrees for 6 hours.
Example 6
The procedure was as in example 1, except that the coating material was changed to 2 wt% NaF and 2 wt% Ta2O5The coating temperature was changed to 700 ℃ for 6 hours.
Example 7
The procedure was as in example 1, except that the coating material was changed to 2 wt% NaF and 2 wt% WO3The coating temperature was changed to 900 ℃ for 6 hours.
Example 8
The procedure was the same as in example 1, except that the coating material was changed to 2 wt% NaF and 2 wt% Sn (5%). Al2O3。
Example 9
The procedure was the same as in example 1, except that the coating material was changed to 2 wt% NaF and 2 wt% Zr (5%). Al2O3。
Example 10
The procedure was the same as in example 1, except that the coating material was changed to 2 wt% NaF and 2 wt% Cu (5%). Al2O3。
Example 11
The procedure was as in example 1, except that the coating material was changed to 0.7 wt% NaF and 3.3 wt% Zn (5%). Al2O3。
Example 12
The procedure was as in example 1, except that the coating material was changed to 3.2 wt% NaF and 0.8 wt% Zn (5%). Al2O3。
Example 13
The procedure was as in example 1, except that the coating material was changed to 2 wt% NaF and 2 wt% Zn (10%). Al2O3。
Example 14
The procedure was as in example 1, except that the coating material was changed to 2 wt% NaF and 2 wt% Zn (3%). Al2O3。
Example 15
The procedure was as in example 1, except that the coating material was changed to 2 wt% NaF and 2 wt% Zn (15%). Al2O3。
Example 16
The procedure was the same as in example 1, except that in the step (S3), the coating was carried out at 800 ℃ and 1200rpm for 8 hours.
Example 17
The procedure was the same as in example 1, except that in the step (S3), the coating was carried out at 1500rpm at 750 ℃ for 4 hours and at 800rpm at 400 ℃ for 4 hours.
Comparative example 1
The procedure was the same as in example 1, except that the coating material was changed to 4 wt% NaF and the temperature of the integer coating was changed to 400 ℃ for 2 hours and then 900 ℃ for 6 hours.
Comparative example 2
The procedure was the same as in example 1, except that the coating material was changed to 4 wt% TiF4The shaping and coating temperature is changed to 500 ℃ for 2 hours first and then 800 ℃ for 6 hours later.
Comparative example 3
The procedure was as in example 1, except that the coating material was changed to 4 wt% WO3The shaping and coating temperature is changed to 500 ℃ for 2 hours first and then 850 ℃ for 6 hours later.
Comparative example 4
The procedure was as in example 1, except that the coating material was changed to 4 wt% Ta2O5The shaping and coating temperature is changed to 500 ℃ for 2 hours first and then 850 ℃ for 6 hours later.
Comparative example 5
The procedure is as in example 1, except that the coating material is changed to 4 wt% Zn (5%). Al2O3The shaping and coating temperature is changed to 500 ℃ for 2 hours first and then750 degrees 6 hours.
Comparative example 6
Preparation of P2-Na2/3Ni1/3Mn1/3Ti1/3O2Weighing 0.0105mmol sodium carbonate, 0.01mmol nickel oxide, 0.01mmol manganese dioxide, 0.01mmol titanium dioxide, 0.005mmol NaF and a small amount of ethanol, mixing, placing in a ball milling tank, and controlling the ball-to-material ratio to be 20: 1, setting the rotation speed of a ball mill at 500rpm, performing positive and negative rotation modes, performing ball milling for 10 hours, drying and grinding in an oven, and transferring to a vacuum oven for storage.
Pressing the dried precursor into a small round piece with the diameter of 10mm, then placing the small round piece into a muffle furnace for calcination, heating to 950 ℃ at the heating rate of 5 ℃/min, preserving the heat for 15 hours, cooling to room temperature, and transferring to a hand box for later use. And mixing the obtained positive electrode material, a conductive additive SP and a binder PVDF according to parts by weight of 80 parts, 10 parts and 10 parts, dissolving the mixture in a solvent NMP, stirring to obtain uniform slurry, uniformly coating the slurry on a carbon-coated aluminum foil by using a 200-micrometer scraper, drying and slicing to obtain the positive electrode pole piece.
Application exampleTesting of electrochemical Performance
And (3) electrochemical performance testing: the pole pieces obtained in examples 1-4 and comparative example 1 were used as positive electrodes, metal sodium pieces as negative electrodes, glass fibers as separators, and 1mol/L of NaClO4And (PC + 5% FEC) is used as an electrolyte to assemble the button cell. The anode is activated for 3 circles at a current density of 15mA/g within a voltage range of 2.5-4.5V, and then is charged and discharged at a current density of 150mA/g for circulation. The pH of the materials of the examples of the invention and the comparative examples and the electrochemical performance of the corresponding button cells were tested and the results are shown in table 1:
TABLE 1 Positive electrode
The first-turn discharge capacity is the 4 th-turn capacity, and the capacity retention rate of 200 turns is actually that after 204 turns, the capacity is compared with that of the 4 th turn, and the first three turns belong to the formation process.
As can be seen from FIG. 1, the layered structure of the P2 positive electrode is not changed by the artificially designed coating of oxyfluoride, and still can be classified as P63/mmc space group. As seen from the SEM image of fig. 2, the coated and sintered positive electrode is in a stacked sheet shape, has a uniform particle size, and has a smooth surface without obvious particles such as alkali residues.
As can be seen from the test results for each of the example half cells in table 1: after the layered positive electrode material is coated with the oxyfluoride, the discharge specific capacity of the first circle of the sodium battery is slightly reduced, but the capacity retention rate is remarkably improved after 200 circles. For example, in example 1, the reversible discharge specific capacity after 200 circles is still 114.6mAh/g, while in comparative example 6 without coating, the reversible discharge specific capacity is only 68.6 mAh/g. It is worth noting that the thickness of the coating layer needs to be appropriate, as can be seen from a transmission electron microscope image in fig. 3, the inner layer of the material is of a layered structure, and the disordered diffraction stripe of the outer layer is consistent with the stripe of a rock salt phase, which represents that the outer layer coating layer is of a rock salt-like structure, is generated by conversion of residual alkali on the surface of the positive electrode and is a sodium-containing compound, and on one hand, the sodium ion diffusion of the positive electrode material is not influenced, and on the other hand, the influence of the coating on the capacity of the material is reduced. The coating thickness is preferably 10-15 nm. When the coating thickness is too large, the first-circle discharge specific capacity of the battery can be greatly reduced; when the thickness of the coating layer is too thin, the improvement on the long cycle is not great. In addition, compared with the comparison examples 1-5, the coated oxyfluoride has more obvious improvement effect on the long-cycle performance of the layered positive electrode material compared with the simple oxide or fluoride coating.
The inventors have also unexpectedly found that the electrochemical performance of the positive electrode material can be significantly improved by using zinc-doped alumina as the metal oxide and fluoride together as the raw material of the coating layer. The doping proportion of zinc and the proportion of fluoride and metal oxide are required to be in a proper range, so that the optimal electrochemical performance of the cathode material can be achieved.
The invention provides an application of an oxyfluoride coated layered anode in a sodium battery, which contributes to the prior art that the layered anode can be uniformly coated by one-time sintering by utilizing the eutectic effect among residual alkali on the surface of the anode, fluoride and oxide, the coating process is simple, the coating effect is excellent, and the electrochemical performance of the sodium battery under high pressure can be greatly improved. It is to be understood that in the various embodiments of the present invention, although the present invention has been described in detail in connection with specific electrolytes, separators, current collectors, active materials, binders, conductive additives, etc., the above is merely for the purpose of satisfying legal requirements and illustrating the composition of a sodium ion battery, and the present invention is not limited to the given embodiments. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the invention by using the description of the invention or directly or indirectly applied to other related technical fields are included in the protection scope of the invention.
Claims (10)
1. The layered positive electrode material of the sodium ion battery coated with the oxyfluoride in situ is characterized by being of a rock salt/layered heterostructure, and the chemical formula of the layered positive electrode material is expressed as NaxTMO2@MaNb(O/F)c，MaNb(O/F)cIs fluorine/oxide, and the layered metal oxide NaTMO is uniformly coated with rock salt phase2Wherein TM is at least one of transition metals Ni, Co, Mn, Cu, Fe, Ti, M is at least one of Li, Na, N is at least one of transition metals Ni, Co, Mn, Cu, Ti, Zn, Al, Zr, Sn, Sb, W, Ta; x is 2/3-1, a is more than or equal to 0.01 and less than or equal to 0.05, b is more than or equal to 0.01 and less than or equal to 0.05, and c satisfies MaNb(O/F)cCharge balancing.
2. The positive electrode material according to claim 1, wherein x is 2/3, and 0.01. ltoreq. a.ltoreq.0.02, 0.01. ltoreq. b.ltoreq.0.02; the thickness of the coating layer is 5-30nm, preferably 10-15 nm.
3. The cathode material of claim 1, wherein in an XPS (X-ray diffraction) etching analysis spectrum of the layered cathode material for the sodium-ion battery coated with the oxyfluoride in situ, a characteristic peak signal of a transition metal TM from an appearance phase to a bulk phase is gradually increased, and a signal of the fluorine/oxide is gradually reduced.
4. A method for producing a positive electrode material according to any one of claims 1 to 3, characterized by comprising the steps of:
(S1) source material mixing: feeding a sodium source and a transition metal TM source according to a stoichiometric ratio, feeding the sodium source according to 110-120% of the stoichiometric ratio, and performing ball milling and uniform mixing to form a mixture;
(S2) sintering of the positive electrode material: calcining the mixture obtained in the step (S1), heating to 600-1000 ℃, preserving the heat for 12-48h, and cooling to room temperature to obtain the layered metal oxide NaxTMO2X is 2/3 or 1;
(S3) coating of positive electrode material: mixing the material obtained in step (S2) with MaNb(O/F)cAnd fully shaping and coating the source material in a fusion coating machine.
5. The method of claim 4, wherein the sodium source in the step (S1) is at least one selected from the group consisting of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium oxide, and sodium peroxide; a transition metal TM source selected from at least one of TM oxides, sulfates, nitrates, carbonates, acetates, oxalates, and hydrated compounds thereof; feeding the sodium-removing source material according to a stoichiometric ratio determined by a structural general formula, wherein the feeding ratio of the sodium source material is 110-120% of the stoichiometric ratio;
in step (S3), the MaNb(O/F)cThe source material is a fluoride of metal M and/or N, and an oxide of metal N.
6. The method according to claim 4, wherein in the step (S2), the calcination atmosphere is at least one of oxygen and air, the temperature increase rate is 1-10 ℃/min, and the temperature decrease rate during cooling is 1-10 ℃/min.
7. The method of claim 4The preparation method is characterized in that the fluoride of the metal M and/or N is selected from NaF, LiF and NiF2、CoF2、MnF2、CuF2、TiF4At least one of; the oxide of the metal N is selected from ZnO and Al2O3、SnO2、ZrO2、Sb2O5、WO3、Ta2O5At least one of (1).
8. The production method according to claim 7, wherein the oxide of metal N is a doped metal oxide; preferably zinc-doped alumina, expressed as (Zn) Al2O3Wherein the Zn doping proportion is 5-10 wt%.
9. The method according to claim 4, characterized in that, further, the fusion coater is operated under the following conditions: the temperature is 400-1800 plus materials, the rotating speed of the cladding machine is 500-1800rpm, and the cladding time in the cladding machine is 300-600 min;
preferably, the working conditions of the fusion cladding machine are: coating is carried out for 100-200min at the rotation speed of 400-600 ℃, 500-800rpm and then for 200-600min at the rotation speed of 600-900 ℃, 1200-1500 rpm.
10. A sodium ion battery, wherein a preparation raw material of a positive electrode comprises the positive electrode material of any one of claims 1 to 3 or the positive electrode material prepared by the preparation method of any one of claims 4 to 9.
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