CN115172742A - Pre-alkali-metallized sodium vanadium phosphate, preparation method thereof and sodium-ion battery - Google Patents
Pre-alkali-metallized sodium vanadium phosphate, preparation method thereof and sodium-ion battery Download PDFInfo
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Abstract
The invention discloses a pre-alkali-metallized vanadium sodium phosphate with a general formula of Na 3 M x V 2 N x (PO 4 ) 3 Wherein, M is an alkali metal element selected from at least one of Li and K; n is doped metal element selected from at least one of Ni, fe, ca, ti, cr, zn, ag, mo, mg and Mn; x is more than or equal to 0.01 and less than or equal to 1. The invention also discloses a preparation method of the pre-alkali-metalized vanadium sodium phosphate, and a sodium ion battery positive plateAnd a sodium ion battery. The pre-alkali-metalized vanadium sodium phosphate provided by the invention not only solves the problem of low conductivity of the vanadium sodium phosphate material, realizes electrochemical properties such as super-high-rate charge and discharge, but also can supplement the first coulombic efficiency of hard carbon loss of the negative electrode of a full-cell system.
Description
Technical Field
The invention relates to the technical field of sodium-ion batteries, in particular to pre-alkali-metalized vanadium sodium phosphate, a preparation method thereof and a sodium-ion battery.
Background
With the large-scale development of the economy in the world, the energy problem becomes the primary problem restricting the economic development, and under the background, the novel rechargeable battery element represented by the lithium ion battery is gradually paid attention to and applied. But the reserves of lithium resources and minerals are limited and the price is increasing, resulting in shortage of the related lithium resources. In contrast, sodium batteries, which are abundant in resources on earth, will be the focus of future development. The crust of sodium element has abundant reserves and low cost. And because the sodium ion battery has a similar working mechanism with the lithium ion battery, the sodium ion battery will become an excellent substitute of the lithium ion battery in the future.
In sodium ion battery systems, the positive electrode material is a key factor affecting battery performance and cost. Among the currently studied positive electrode materials, the novel NASICON-type vanadium sodium phosphate material has excellent stability and relatively high specific capacity. However, the electrochemical properties, especially the conductivity and the large-rate long-cycle performance, of the vanadium sodium phosphate cathode material directly synthesized by chemical synthesis are limited. Researchers have begun thinking as to how modifications can be made. Wherein, li Xieau et al, the institute of Chinese academy of sciences, adopts an electrochemical pre-precipitation method to successfully prepare a novel sodium-rich vanadium sodium phosphate electrode material (S. Mirza, Z. Song, et al, A simple pre-conditioning strain to advanced performance and energy density of sodium ion batteries with Na 4 V 2 (PO 4 ) 3 as cathode material, journal of Materials Chemistry A, 2020), compensates for the loss of irreversible capacity of the base material sodium vanadium phosphate during the circulation process by pre-alkali metallization, and the reversible specific capacity can reach 103.76 mA.h/g under the current density of 1C (1C = 117mA.h/g). After 100 cycles, the capacity retention rate can reach 78%. However, the method has improved performance of the base material, but has a longer distance from practical application,and the mass production and preparation of the material are not easy to realize. Li (Li, H., et al., underlying chemical machinery Induced by Gradient Mg) cathode material prepared by Li (Li, H., et al., beijing university of industry) by sol-gel method 2+ Distribution of Na-Rich Na 3+x V 2–x Mg x (PO 4 ) 3 The conductivity of the Sodium vanadium phosphate is improved (the specific capacity can reach 95.5mA.h/g under the current density of 15C), but the method does not well solve the defects of the performance of the material and still has a great improvement space.
Therefore, how to simply, effectively, highly and controllably prepare the NASICON type vanadium sodium phosphate cathode material with stable performance becomes one of the key problems in the related technology of the sodium ion battery.
Disclosure of Invention
The invention aims to solve the technical problem of providing a pre-alkali-metallization sodium-supplement vanadium sodium phosphate which is used as a positive electrode material of a sodium ion battery, can improve the problem of low conductivity of the vanadium sodium phosphate material, realizes electrochemical properties such as super-high-rate charge and discharge and the like, and can supplement the first coulombic efficiency of hard carbon loss of a negative electrode of a full battery system.
In order to solve the technical problems, the invention provides the following technical scheme:
the invention provides a pre-alkali-metallized vanadium sodium phosphate with a general formula of Na 3 M x V 2 N x (PO 4 ) 3 Wherein, M is an alkali metal element selected from at least one of Li and K; n is doped metal element selected from at least one of Ni, fe, ca, ti, cr, zn, ag, mo, mg and Mn; x is more than or equal to 0.01 and less than or equal to 1.
Further, the pre-alkali-metallized vanadium sodium phosphate is also subjected to carbon coating, and the obtained material is Na 3 M x V 2 N x (PO 4 ) 3 /C。
Further, M, N and x are selected from (1) or (2):
(1) M is Li, N is Ti, x =0.1;
(2) M is K, N is Ni, x = 0.5.
The second aspect of the invention provides a preparation method of the pre-alkali-metalized vanadium sodium phosphate, which comprises the following steps:
mixing a vanadium source, a sodium source, an M source, an N source and a phosphorus source to form a colloidal mixture with the addition of a solvent;
and (3) placing the colloid mixture in reducing gas, and carrying out heating treatment under ultrahigh vacuum to obtain the pre-alkali-metalized vanadium sodium phosphate.
Further, the sodium source comprises one or more of sodium carbonate, sodium hydroxide, sodium oxide, sodium peroxide, sodium phosphate, sodium sulfate, sodium dihydrogen phosphate, sodium dihydrogen sulfate and sodium phenolate; the vanadium source comprises one or more of vanadium pentoxide, vanadium trioxide, ammonium metavanadate, vanadium phosphate monohydrate, vanadium sulfate and vanadyl sulfate monohydrate; the phosphorus source comprises one or more of ammonium dihydrogen phosphate, sodium dihydrogen phosphate, diammonium hydrogen phosphate, disodium hydrogen phosphate, phosphoric acid and phosphorus pentoxide; the M source comprises one or more of lithium carbonate, lithium oxalate, lithium hydroxide, potassium carbonate, potassium hydroxide, potassium chloride, potassium sulfate and potassium dihydrogen phosphate.
Further, the molar ratio of the vanadium source, the sodium source, the M source, the N source and the phosphorus source is (0.01-2): (0.01-3): (0.01-1): (0.01-3).
Further, when mixing a vanadium source, a sodium source, an M source, an N source and a phosphorus source, the method also comprises the step of performing low-temperature magnetic stirring and/or heating on the obtained mixture; wherein the low temperature is-5 to 15 ℃, and the heating temperature is 20 to 80 ℃.
Further, an additive is added in the process of low-temperature magnetic stirring and/or heating, wherein the additive comprises at least one of citric acid, glucose, sucrose and CTAB.
Further, the additive consists of sucrose and citric acid, and the mass ratio of the sucrose to the citric acid is 1.
Further, the reducing gas includes at least one of hydrogen, nitrogen, and an inert gas.
Further, the vacuum degree of the ultrahigh vacuum is 1 x 10 -9 ~1*10 -4 And MPa, wherein the heating temperature is 320-980 ℃, and the heating time is 0.25-24 h.
The invention provides a sodium ion battery positive plate, which comprises a positive current collector and a positive electrode layer formed on the surface of the positive current collector, wherein the active material in the positive electrode layer is the pre-alkali-metalized vanadium sodium phosphate.
The invention provides a sodium ion battery, which comprises a positive plate, a negative plate, a diaphragm and electrolyte, wherein the diaphragm is arranged to isolate the positive plate from the negative plate, and the positive plate is the sodium ion battery positive plate.
Compared with the prior art, the invention has the beneficial effects that:
1. according to the pre-alkali-metallization vanadium sodium phosphate provided by the invention, the alkali metal elements are introduced while low-valence metal elements are doped, and the obtained vanadium sodium phosphate material is in a pre-alkali-metallization state, so that the problem of low conductivity of the vanadium sodium phosphate material is solved, the electrochemical properties such as super-high-rate charge and discharge are realized, and the first coulombic efficiency of the negative hard carbon loss of a full battery system can be supplemented.
2. The pre-alkali-metalized vanadium sodium phosphate of the invention introduces the alkali metal elements and has a combined action while introducing the doping elements, the combination has strong adaptability to the current electrolyte and hard carbon system, and the performance of the electric core system is greatly improved.
3. The button cell assembled by using the pre-alkali metalized vanadium sodium phosphate as the active material of the positive electrode and the hard carbon electrode as the negative electrode has the discharge capacity of 101.8mA.h/g for the first circle, the specific charge capacity of 123.8 mA.h/g, the first coulombic efficiency of 82.2 percent and the capacity of 127.9/120.32/117.45 mA.h/g under the multiplying power of 0.5/2/5C.
Drawings
FIG. 1 shows Na prepared in example 1 of the present invention 3 Li 0.1 V 2 Ti 0.1 (PO 4 ) 3 The first circle of charge-discharge characteristic curve of the positive electrode material in the sodium ion battery;
FIG. 2 shows Na prepared in example 2 of the present invention 3 K 0.5 V 2 Ni 0.5 (PO 4 ) 3 The performance data of the/C positive electrode material in the sodium ion battery are cycled for 100 times;
FIG. 3 shows Na prepared in example 2 of the present invention 3 K 0.5 V 2 Ni 0.5 (PO 4 ) 3 A first circle of charge-discharge characteristic curve of the/C positive electrode material in the sodium ion battery;
FIG. 4 shows Na prepared in example 2 of the present invention 3 K 0.5 V 2 Ni 0.5 (PO 4 ) 3 A scanning electron microscope image of the/C cathode material.
Detailed Description
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 in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
As described in the background art, sodium vanadium phosphate has excellent stability and relatively high specific capacity, and is a very potential positive electrode material for sodium ion batteries. However, the low conductivity of sodium vanadium phosphate is one of the intrinsic characteristics, and the performance of the material can only be improved by means of single carbon coating or element doping and the like, but cannot be greatly improved. At present, some methods for modifying sodium vanadium phosphate appear in the prior art, and the modification methods can improve the basic performance of the sodium vanadium phosphate material to a certain extent, but have a long distance from application, and are not easy to realize large-scale production and preparation of the material.
In addition, the first turn of hard carbon anodes used in sodium ion batteries is generally associated with a low coulombic efficiency problem because the carbon anodes consume limited sodium in the positive electrode material during battery cycling to form a Solid Electrolyte Interface (SEI) film. The irreversible consumption of sodium in the positive electrode material greatly reduces the energy density and the cycle stability of the sodium-ion battery, and the problem becomes one of the bottlenecks for restricting the development of the sodium-ion battery. The problem of sodium vanadium phosphate as a positive electrode material of a sodium ion battery also exists, which also results in poor adaptability of the sodium vanadium phosphate positive electrode to a hard carbon negative electrode.
Found that Na 3 V 2 (PO 4 ) 3 The material structurally shows that sodium sites are not full, and actually, one more Na atom can be inserted, so that the problem of irreversible sodium consumption in a sodium-ion battery can be effectively solved through positive electrode sodium compensation. However, the introduction of excess sodium in sodium vanadium phosphate is difficult to achieve by conventional methods. The Chinese academy reported a method for electrochemically inserting sodium (S. Mirza, Z. Song, et al., A simple pre-conditioning to advanced performance and engineering sensitivity of sodium ions with Na. As shown in FIGS 4 V 2 (PO 4 ) 3 as cathode material, journal of Materials Chemistry A, 2020): with Na 3 V 2 (PO 4 ) 3 As the positive electrode, the metal sodium is used as the negative electrode, the button cell is assembled, and the sodium atoms are supplemented after one circle of circulation; after the cycle, the positive electrode material changed to Na 4 V 2 (PO 4 ) 3 And then the battery is disassembled, and the positive pole piece is taken out to form the button battery with the negative hard carbon. However, this method is difficult to be industrially applied.
In the invention, through research, the inventor discovers that a low-valence metal element N is doped into sodium vanadium phosphate by a specific method, a structural channel of a crystal is opened by utilizing the N element, redundant Na elements can be conveniently introduced, sodium enrichment of the sodium vanadium phosphate is realized, the technical problem of how to compensate the first coulomb efficiency of the loss of hard carbon of a cathode in a full battery is solved, and meanwhile, the conductivity, the structural stability and the rate capability of a sodium vanadium phosphate cathode material can be improved. Meanwhile, other alkali metal elements Li and K can be introduced by the method, so that the pre-alkali metallization of the vanadium sodium phosphate is realized. In addition, the method is easy to implement in engineering production.
Li and Na belong to the same main group element, but the metal activity of the Li element is strongest, the reducibility is strongest, and the energy released in the electrochemical reaction is also strongest, so that the performance of the Li element added in the same system material is better than that of the Na element and the K element added in the same system material. Secondly, the radius of Li atoms is much smaller than that of Na atoms and K atoms, which makes sodium and potassium ions weaker than lithium ions in moving rate and deintercalation effect on battery electrodes during electrochemical reaction in a battery. Sodium has a relatively low redox potential, resulting in a low output voltage and a final energy density that is lower than that of lithium. K is stronger in reducing property than Na, is larger in atomic radius than Na, is easier to lose electrons, and is stronger in reducing property, so that the performance of K is slightly better than that of Na. Therefore, in addition to the introduction of Na, the energy density, the quick charge capacity and the rate capability of the sodium-ion battery can also be improved by introducing alkali metal elements Li and K to compensate sodium ions.
Specifically, the general formula of the pre-alkali-metallized vanadium sodium phosphate electrode material provided by the invention is Na 3 M x V 2 N x (PO 4 ) 3 Wherein, M is an alkali metal element selected from at least one of lithium (Li) and potassium (K); n is a doped metal element selected from at least one of nickel (Ni), iron (Fe), calcium (Ca), titanium (Ti), chromium (Cr), zinc (Zn), silver (Ag), molybdenum (Mo), magnesium (Mg) and manganese (Mn), and x is more than or equal to 0.01 and less than or equal to 1.
Different from the modified sodium vanadium phosphate electrode material provided by the prior art, the pre-alkali-metalized sodium vanadium phosphate electrode material Na provided by the invention 3 M x V 2 N x (PO 4 ) 3 The introduced doping element N does not occupy the position of the V element in the crystal lattice, but is inserted into the position of the crystal lattice gap, and meanwhile, the alkali metal element is introduced into the crystal lattice, so that the vanadium sodium phosphate is in a pre-alkali metallization state, the irreversible capacity loss of the basic material vanadium sodium phosphate in the circulation process can be compensated, and the reversible specific capacity of the battery is improved.
In some preferred embodiments, when the alkali metal M isWhen the doped metal N is Ti and is Li, x can be 0.1, and the molecular formula of the obtained pre-alkali-metalized sodium vanadium phosphate electrode material is Na 3 Li 0.1 V 2 Ti 0.1 (PO 4 ) 3 。
In some preferred embodiments, when the alkali metal M is K element and the doping metal N is Ni element, x may be 0.5, and the formula of the obtained pre-alkali-metalized sodium vanadium phosphate electrode material is Na 3 K 0.5 V 2 Ni 0.5 (PO 4 ) 3 。
In the invention, the pre-alkali-metalized vanadium sodium phosphate electrode material can be subjected to carbon coating, and the obtained anode material can be expressed as Na 3 M x V 2 N x (PO 4 ) 3 and/C. By carbon coating, on one hand, the conductivity of the material can be improved, and on the other hand, a stable chemical and electrochemical reaction interface can be provided, which is beneficial to the electrochemical performance of the battery.
The invention also discloses a preparation method of the pre-alkali-metalized vanadium sodium phosphate electrode material, which specifically comprises the following steps:
(1) Mixing a vanadium source, a sodium source, an M source, an N source, and a phosphorus source with the addition of a solvent to form a colloidal mixture;
(2) And (3) placing the colloid mixture in reducing gas, and carrying out heating treatment under ultrahigh vacuum to obtain the pre-alkali-metalized vanadium sodium phosphate.
In the step (1), the sodium source includes one or more sodium salts, including but not limited to sodium carbonate, sodium hydroxide, sodium oxide, sodium peroxide, sodium phosphate, sodium sulfate, sodium dihydrogen phosphate, sodium dihydrogen sulfate, sodium phenolate, and the like. The vanadium source may include one or more of vanadium salts, vanadium oxides, metavanadate compounds including, but not limited to, vanadium pentoxide, vanadium trioxide, ammonium metavanadate, vanadium phosphate monohydrate, vanadium sulfate, vanadyl sulfate monohydrate, and the like. The phosphorus source includes one or more of phosphoric acid/phosphates, phosphorus oxides, including but not limited to monoammonium phosphate, monosodium phosphate, diammonium phosphate, disodium phosphate, phosphoric acid, phosphorus pentoxide, and the like. The M source includes one or more metal salts, metal oxides or other alkali metal element-containing precursor compounds, such as lithium carbonate, lithium oxalate, lithium hydroxide, potassium carbonate, potassium hydroxide, potassium chloride, potassium sulfate, potassium dihydrogen phosphate, and the like. The N source includes one or more metal salts, metal oxides, or other N element precursor compounds containing the element N, such as ferrous oxalate, ferroferric oxide, manganese chloride, nickel oxide, nickel sulfate, and the like.
The vanadium source, sodium source, M source, N source and phosphorus source are mixed according to Na 3 M x V 2 N x (PO 4 ) 3 (x is more than or equal to 0.01 and less than or equal to 1) in the stoichiometric ratio. In a preferred embodiment, the vanadium, sodium, M, N and phosphorus sources may be as follows (0.01 to 2): (0.01 to 3): (0.01 to 1): (0.01 to 1): (0.01-3) in a molar ratio. For example in the preparation of the compound Na 3 Li 0.1 V 2 Ti 0.1 (PO 4 ) 3 When in use, ammonium metavanadate is taken as a vanadium source, sodium dihydrogen phosphate is taken as a sodium source and a phosphorus source, lithium carbonate is taken as an M source, and titanium dioxide is taken as an N source. When the molar ratio of ammonium metavanadate, sodium dihydrogen phosphate, lithium carbonate and ferrous oxalate is expressed as x: y: m: n, x is about 2, y is about 3, m is about 0.05 and y is about 0.1.
In the step (1), when the vanadium source, the sodium source, the M source, the N source, and the phosphorus source are mixed, a solvent is added to form a colloidal substance in the mixture. The solvent can be common organic solvent such as ethanol, acetone, etc.
In a preferred embodiment, the vanadium, sodium, M, N and phosphorus sources are contacted and then subjected to low temperature magnetic stirring to uniformly mix the precursor compounds and assist in crosslinking and curing to form a colloidal mixture. The low-temperature magnetic stirring can increase the contact area of the material, and is beneficial to the reaction rate among particle molecules in the subsequent sintering process. The magnetic stirring is preferably high energy magnetic stirring. Preferably, the temperature of the low-temperature magnetic stirring is-5 ℃ to 15 ℃.
Alternatively, after magnetic stirring, a heating treatment may be performed to dry the colloidal mixture to obtain a precursor powder. The heating temperature is preferably 20 ℃ to 80 ℃.
In a preferred embodiment, in order to improve the conductivity of the electrode material, a certain amount of additives can be added during stirring and/or heating of the raw materials, so that a good conductive coating (such as a carbon coating) can be introduced on the surface of the particles, and the conductivity of the material can be improved. The additive is preferably a carbon source, including but not limited to one or more of citric acid, glucose, sucrose, CTAB, and the like. The addition amount of the additive can be determined according to the following molar ratio: the molar ratio of the vanadium source, the sodium source, the M source, the N source, the phosphorus source and the additive is (0.01 to 2): (0.01 to 3): (0.01 to 1): (0.01 to 1): (0.01 to 3): (0.01 to 2.3).
Preferably, the additive consists of sucrose and citric acid, and the mass ratio of sucrose to citric acid is 1.
In the step (2), the colloid mixture is placed in the reducing gas for the purpose of keeping the valence state of the V element unchanged in the subsequent heat treatment process, so that the original structural framework of the vanadium sodium phosphate is stabilized and unchanged, and the V element is ensured not to be replaced by the doping element in the whole preparation process. Wherein the reducing gas comprises at least one of hydrogen, nitrogen and inert gas (helium, neon and argon). In a preferred embodiment, the reducing gas is argon. In other embodiments, the reducing gas is a mixed gas consisting of hydrogen and an inert gas. Preferably, the volume percentage content of the hydrogen in the mixed gas is greater than 0% and less than or equal to 10%, and may be, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%; accordingly, the inert gas may be present in an amount of 90% by volume or more and less than 100% by volume, for example 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%.
In the step (2), the purpose of the ultra-high vacuum is to accelerate the rate of small molecule reaction. Under the reaction condition of ultra-high vacuum, the molecular reaction rate is fast, so that doping elements M and N can not substitute V sites and Na sites, and the elements can be doped to preset positions, thereby ensuring the inventionThe desired effect of (2) is achieved. In the invention, the vacuum degree of the ultrahigh vacuum is 1 x 10 -9 ~1*10 -4 MPa, e.g. 11 x 10 -4 MPa、1*10 -5 MPa、1*10 -6 MPa、1*10 -7 MPa、1*10 -8 MPa、1*10 -9 MPa。
In the step (2), the mixture is heated under the protection of ultrahigh vacuum and reducing gas, so as to obtain the pre-alkali-metalized sodium vanadium phosphate material. Wherein the heating temperature is 320-980 deg.C, such as 320 deg.C, 420 deg.C, 520 deg.C, 620 deg.C, 670 deg.C, 720 deg.C, 820 deg.C, 930 deg.C, 980 deg.C, etc. The heating time is 0.25 to 24 hours, and may be, for example, 0.25 hour, 0.5 hour, 1 hour, 1.5 hour, 2 hours, 3 hours, 4 hours, 6 hours, 8 hours, 12 hours, 16 hours, 24 hours, or the like.
The pre-alkali-metalized vanadium sodium phosphate prepared by the method can be further prepared into a positive plate of a sodium ion battery. The preparation method comprises the following steps: preparing electrode slurry from the pre-alkali-metallized sodium vanadium phosphate, the binder and the conductive agent according to a certain proportion, then coating the electrode slurry on a positive current collector, and drying and tabletting to obtain the positive plate of the sodium-ion battery.
The binder can be selected from binders commonly used in sodium ion batteries, including but not limited to one or more of polyacrylonitrile, polyvinylidene fluoride, polyvinyl alcohol, sodium carboxymethylcellulose, polymethacrylic acid, polyacrylic acid, lithium polyacrylate, polyacrylamide, polyamide, polyimide, polyacrylate, styrene butadiene rubber, sodium alginate, chitosan, polyethylene glycol, guar gum and the like.
The conductive agent can be selected from conductive agents commonly used in sodium ion batteries, and includes but is not limited to one or more of conductive carbon black, carbon nanotubes, graphene and the like.
The invention also provides a sodium ion battery, which comprises a positive plate, a negative plate, a diaphragm and electrolyte, wherein the diaphragm is arranged to isolate the positive plate from the negative plate, and the positive plate is prepared from the pre-alkali-metallized sodium vanadium phosphate.
The separator can be selected from one or more of common separator materials of sodium ion batteries, including but not limited to polypropylene separators, polyethylene separators, polyimide separators and cellulose non-woven fabric separators. The negative electrode sheet may be a negative electrode sheet commonly used for sodium ion batteries, and preferably a carbon-based negative electrode, such as a hard carbon negative electrode.
The present invention is further described below in conjunction with the drawings and the embodiments so that those skilled in the art can better understand the present invention and can carry out the present invention, but the embodiments are not to be construed as limiting the present invention.
The experimental procedures used in the following examples are conventional ones unless otherwise specified, and the materials, reagents and the like used therein are commercially available.
Example 1
The precursors ammonium metavanadate, sodium dihydrogen phosphate, lithium carbonate and titanium dioxide were placed in a closed-sealed glass vessel in a molar ratio of 40. And magnetically stirring the mixture for 0.5 hour by using an ethanol organic solvent at the rotating speed of 230 rpm, mixing at low temperature, heating and drying to prepare a precursor material. After the reaction is finished, the mixture is quickly transferred into an ultrahigh vacuum heating furnace and pressurized to 1.98 x 10 -6 MPa, in a furnace, under the protection of high-purity argon, raising the temperature at the rate of 5 ℃/min, and heating at 670 ℃ for 4.75 hours to obtain Na 3 Li 0.1 V 2 Ti 0.1 (PO 4 ) 3 And (3) a positive electrode material.
Example 2
Preparing ammonium metavanadate, sodium dihydrogen phosphate dihydrate, potassium hydroxide, sucrose, citric acid and a doping material nickel nitrate according to a molar ratio of 4: the ratio of 6.2. After the reaction is finished, the mixture is quickly transferred into an ultrahigh vacuum heating furnace and pressurized to 1.98 x 10 -6 MPa, under the protection of high-purity argon in a furnace, raising the temperature at the rate of 5 ℃/min, and heating at 620 ℃ for 2.3 hours to obtain Na 3 K 0.5 V 2 Ni 0.5 (PO 4 ) 3 And C, a positive electrode material.
Example 3
Example 3 differs from example 1 in that: the doping ratio of Li and Ti is 0.01, and the final product is Na 3 Li 0.01 V 2 Ti 0.01 (PO 4 ) 3 And (3) a positive electrode material.
Example 4
Example 4 differs from example 1 in that: the alkali metal M is K, the doped metal N is Ni, the doping proportion is 0.25, and finally Na is obtained 3 K 0.25 V 2 Ni 0.25 (PO 4 ) 3 And (3) a positive electrode material.
Example 5
Example 5 differs from example 1 in that: the doping ratio of Li is 0.82, the doping metal N is Cr, the doping ratio is 0.82, and finally Na is obtained 3 Li 0.82 V 2 Cr 0.82 (PO 4 ) 3 And (3) a positive electrode material.
Example 6
Example 6 differs from example 1 in that: the doping ratio of Li is 0.93, the doping metal N is Mo, the doping ratio is 0.93, and finally Na is obtained 3 Li 0.93 V 2 Mo 0.93 (PO 4 ) 3 And (3) a positive electrode material.
Example 7
Example 7 differs from example 2 in that: the doping ratio of K is 0.55, the doping metal N is Zn, the doping ratio is 0.55, and finally Na is obtained 3 K 0.55 V 2 Zn 0.55 (PO 4 ) 3 a/C positive electrode material.
Comparative example 1
Comparative example 1 differs from example 1 in that: does not add alkali metal M and doping metal M, and the final product is Na 3 V 2 (PO 4 ) 3 And (3) a positive electrode material.
Comparative example 2
The precursor ammonium metavanadate, sodium dihydrogen phosphate dihydrate, potassium hydroxide, sucrose, citric acid and the doping material nickel nitrate were placed in a closed-seal glass container in a stoichiometric ratio, mixed at 350 rpm for 1.4 hours, and heated to prepare the precursor material. After the reaction is finished, the mixture is quickly transferred into a tube furnace, and is heated at the temperature of 620 ℃ in the furnace under the protection of high-purity argon2.3 h to obtain Na 3.0 K 0.5 V 1.5 Ni 0.5 (PO 4 ) 3 And C, a positive electrode material.
Test example
1. ICP test
Inductively Coupled Plasma-Atomic Emission spectroscopy (ICP) was used to determine the molecular formula of the material. The sample was processed as follows:
(1) About 0.1g of sample is accurately weighed into a 50ml polytetrafluoroethylene digestion tube, and the mass of the sample is recorded.
(2) An appropriate amount of mineral acid (5 ml of concentrated nitric acid/1 ml of hydrofluoric acid) was added to the polytetrafluoroethylene digestion tube. Covering the reaction kettle with a cover, putting the reaction kettle into a stainless steel reaction kettle, putting the reaction kettle into an oven, controlling the temperature to be 190 ℃, heating for about 10 hours, stopping heating, and cooling.
(3) The cooled solution was transferred to a 25ml plastic volumetric flask and made up to volume with deionized water.
(4) A standard test solution was prepared, with the curve concentration points being: 0. 0.5, 1.0, 2.0, 5.0mg/L;
(5) And (3) firstly making a standard solution calibration curve through an ICP-OES instrument, inputting the mass and the volume of the sample, then sequentially testing the digested solution, and testing after the solution is diluted beyond the curve range.
(6) And determining the final content of the element to be tested in each sample through a spectrogram to obtain a test result.
ICP measurement results of the cathode materials prepared in example 2 and comparative example 2 are shown in tables 1 to 2, respectively.
Table 1 ICP measurement result of positive electrode material prepared in example 2
As can be seen from the results in table 1, in the positive electrode material prepared in example 2 of the present invention, the doping element Ni does not occupy the position of the V element, but enters between the lattice gaps; while doping Ni element, potassium element is introduced into the crystal lattice of vanadium sodium phosphate. Tong (Chinese character of 'tong')Its molecular formula is Na measured by ICP 2.97 K 0.52 V 2 Ni 0.48 P 3 O 12 And Na 3 K 0.5 V 2 Ni 0.5 (PO 4 ) 3 And (4) conforming to the standard.
Table 2 ICP measurement results of positive electrode material prepared in comparative example 2
As can be seen from the results of table 2, the positive electrode material prepared in comparative example 2, although potassium element was also introduced into the crystal lattice of sodium vanadium phosphate, the doping element Ni occupied the position of V element. Its molecular formula is Na measured by ICP 2.78 K 0.52 V 1.5 Ni 0.48 P 3 O 12 With Na 3.0 K 0.5 V 1.5 Ni 0.5 (PO 4 ) 3 And (4) conforming to the standard.
2. Battery assembly and testing
The vanadium sodium phosphate materials prepared in the examples and the comparative examples are respectively adopted as positive electrode materials to be assembled into a battery, and the battery performance test is carried out, wherein the specific method comprises the following steps:
according to the positive electrode material: conductive carbon: and PVDF (polyvinylidene fluoride) is weighed as a raw material of the positive electrode, dissolved in a certain amount of NMP (N-methyl pyrrolidone), stirred, coated, dried and cut into pieces according to a mass ratio of 90. According to the hard carbon material of the negative electrode: conductive carbon: and (3) weighing the negative electrode raw material with the mass ratio of CMC of 85. The cut pole pieces were assembled in a glove box (oxygen and water content below 0.01 ppm) according to the battery assembly standard, wherein the electrolyte used was 1M sodium perchlorate, the solvent was a mixed solvent of EC and DMC (volume ratio 1), and the weight of the positive electrode in each single cell was about 1mg to 1.5mg. And (3) standing the assembled battery on a blue electricity standard testing machine for 8 hours, then starting the testing process, adopting 1C multiplying power to charge and discharge, and reading a corresponding capacity value (the theoretical specific capacity is 117.8/370 mAh/g).
FIG. 1 shows Na prepared in example 1 3 Li 0.1 V 2 Ti 0.1 (PO 4 ) 3 Initial capacity plot of the battery as a positive electrode material tested at a current density of 1C. As shown in the figure, in the voltage interval of 2-4V, the battery realizes the initial specific capacity of about 90.74 mA.h/g, has the capacity of 105.4/85.6/77.45 mA.h/g at the multiplying power of 0.5/2/5C, and has very excellent conductive performance.
FIG. 2 shows Na prepared in example 2 3.0 K 0.5 V 1.5 Ni 0.5 (PO 4 ) 3 Cycling performance plots of the cells tested as positive electrode materials at a current density of 1C. As shown in the figure, the capacity retention rate of the battery is still as high as 79.81% after 100 cycles, and the cycling performance is excellent. Fig. 3 is a first circle charge-discharge performance curve of the material. As shown in the figure, the discharge capacity of the first circle of the positive electrode material matched with the battery core is up to 101.8mA.h/g, the charging specific capacity is up to 123.8 mA.h/g, and the first coulombic efficiency is up to 82.2%. Under the multiplying power of 0.5/2/5C, the positive electrode material has the capacity of 127.9/120.32/117.45 mA.h/g respectively, which shows that the positive electrode material really supplements the performance of hard carbon on electrode loss and well exerts the performance of a battery cell. Fig. 4 is an SEM characterization of the material, showing that the particle size distribution is uniform and the surface of the material is tightly coated with carbon, which greatly improves its electrical conductivity.
TABLE 3 main parameters and sodium ion battery performance of examples 3-7 and comparative examples 1-2
As can be seen from the results in Table 3, the vanadium sodium phosphate of comparative example 1, which is not doped, has a specific discharge capacity of only 68.10 mA.h/g and a rate capability at 0.5/2/5C of only 70.21/60.35/54.5 mA.h/g. The vanadium sodium phosphate of the comparative example 2 is not doped, but is coated with carbon, the discharge specific capacity and the rate capability of the vanadium sodium phosphate are improved, the discharge specific capacity is 69.48 mA.h/g, and the rate capability under the condition of 0.5/2/5C is 81.5/70.2/60.5 mA.h/g.
The sodium vanadium phosphate of examples 3 to 7 was modified with elements such as Ti, ni, cr, mo and ZnThe doping of the element also introduces elements such as Li, K and the like during doping, and the discharge specific capacity and the rate capability of the element are obviously improved. Wherein Na was obtained in example 6 3 Li 0.93 V 2 Mo 0.93 (PO 4 ) 3 The specific discharge capacity of the cathode material reaches 85.24 mA.h/g, and the rate capability under 0.5/2/5C reaches 88.6/80.21/74.52 mA.h/g.
Comparative example 2 adopts a common sintering method, and in the obtained cathode material, the doping element Ni occupies the position of the V element, and the molecular formula is Na 3.0 K 0.5 V 1.5 Ni 0.5 (PO 4 ) 3 and/C. The discharge specific capacity of the modified sodium vanadium phosphate is only 80.75 mA.h/g, which is far lower than 101.8mA.h/g of the modified sodium vanadium phosphate in the embodiment 2; the rate performance at 0.5/2/5C is only 85.4/75.68/63.95 mA.h/g, and is also significantly lower than 127.9/120.32/117.45 mA.h/g of example 2. This indicates that the position of the doping element has a significant effect on the performance of the electrode material.
In conclusion, the pre-alkali-metalized sodium vanadium phosphate anode material Na of the invention 3 M x V 2 N x (PO 4 ) 3 The lattice structure of the material can be widened, and the doped metal element and the alkali metal element can be introduced to generate interaction, so that the good specific capacity can be greatly improved and optimized, the hard carbon loss can be compensated, and the performance of the material can be greatly improved.
The above-mentioned embodiments are merely preferred embodiments for fully illustrating the present invention, and the scope of the present invention is not limited thereto. The equivalent substitution or change made by the technical personnel in the technical field on the basis of the invention is all within the protection scope of the invention. The protection scope of the invention is subject to the claims.
Claims (13)
1. The pre-alkali-metalized vanadium sodium phosphate is characterized in that the general formula is Na 3 M x V 2 N x (PO 4 ) 3 Wherein, M is an alkali metal element selected from at least one of Li and K; n is a doped metal element selected from Ni, fe, ca, ti, cr, zn, ag, mo, mg, mnAt least one of; x is more than or equal to 0.01 and less than or equal to 1.
2. The pre-alkali-metalized vanadium sodium phosphate according to claim 1, characterized in that the pre-alkali-metalized vanadium sodium phosphate is further carbon-coated to obtain a material of Na 3 M x V 2 N x (PO 4 ) 3 /C。
3. The pre-alkali-metalized sodium vanadium phosphate according to claim 1, characterized in that M, N and x are selected from (1) or (2):
(1) M is Li, N is Ti, x =0.1;
(2) M is K, N is Ni, x = 0.5.
4. A preparation method of pre-alkali-metalized vanadium sodium phosphate is characterized by comprising the following steps:
mixing a vanadium source, a sodium source, an M source, an N source and a phosphorus source to form a colloidal mixture with the addition of a solvent;
and (3) placing the colloid mixture in reducing gas, and carrying out heating treatment under ultrahigh vacuum to obtain the pre-alkali-metalized vanadium sodium phosphate.
5. The method for preparing pre-alkali-metalized vanadium phosphate sodium according to claim 4, wherein the sodium source comprises one or more of sodium carbonate, sodium hydroxide, sodium oxide, sodium peroxide, sodium phosphate, sodium sulfate, sodium dihydrogen phosphate, sodium dihydrogen sulfate and sodium phenolate; the vanadium source comprises one or more of vanadium pentoxide, vanadium trioxide, ammonium metavanadate, vanadium phosphate monohydrate, vanadium sulfate and vanadyl sulfate monohydrate; the phosphorus source comprises one or more of ammonium dihydrogen phosphate, sodium dihydrogen phosphate, diammonium hydrogen phosphate, disodium hydrogen phosphate, phosphoric acid and phosphorus pentoxide; the M source comprises one or more of lithium carbonate, lithium oxalate, lithium hydroxide, potassium carbonate, potassium hydroxide, potassium chloride, potassium sulfate and potassium dihydrogen phosphate.
6. The method of claim 4, wherein the molar ratio of the vanadium source, the sodium source, the M source, the N source, and the phosphorus source is (0.01-2): (0.01-3): (0.01-1): (0.01-3).
7. The method for preparing pre-alkali-metallized sodium vanadium phosphate according to claim 4, characterized in that when mixing a vanadium source, a sodium source, an M source, an N source and a phosphorus source, it further comprises the step of subjecting the resulting mixture to low-temperature magnetic stirring and/or heating; wherein the low temperature is-5 to 15 ℃, and the heating temperature is 20 to 80 ℃.
8. The method for preparing pre-alkali-metalized vanadium sodium phosphate according to claim 7, wherein an additive is added during the low-temperature magnetic stirring and/or heating, and the additive comprises at least one of citric acid, glucose, sucrose and CTAB.
9. The method for preparing the pre-alkali-metalized sodium vanadium phosphate according to claim 8, wherein the additive consists of sucrose and citric acid, and the mass ratio of the sucrose to the citric acid is 1.
10. The method of preparing pre-alkali-metalized sodium vanadium phosphate according to claim 4, wherein the reducing gas comprises at least one of hydrogen, nitrogen and an inert gas.
11. The method of claim 4, wherein the ultra-high vacuum is applied at a vacuum of 1 x 10 -9 ~1*10 -4 MPa; the heating temperature is 320-980 ℃, and the heating time is 0.25-24 h.
12. A positive plate of a sodium-ion battery, which comprises a positive current collector and a positive layer formed on the surface of the positive current collector, and is characterized in that an active material in the positive layer is the pre-alkali-metalized vanadium sodium phosphate as defined in any one of claims 1 to 3.
13. A sodium ion battery comprising a positive plate, a negative plate, a separator and an electrolyte, wherein the separator is configured to isolate the positive plate from the negative plate, and wherein the positive plate is the positive plate of the sodium ion battery of claim 12.
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| CN114156453A (en) * | 2021-12-01 | 2022-03-08 | 北京理工大学重庆创新中心 | Double-site doped modified sodium vanadium phosphate cathode material and preparation method and application thereof |
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| CN107871865A (en) * | 2017-11-02 | 2018-04-03 | 华中科技大学 | A kind of preparation method of the sodium-ion battery positive material of doping vario-property vanadium phosphate sodium |
| US20210242451A1 (en) * | 2020-02-04 | 2021-08-05 | Korea Advanced Institute Of Science And Technology | Metal-Doped Sodium Vanadium Fluorophosphate/Sodium Vanadium Phosphate (Na3V2(PO4)2F3/Na3V2(PO4)3) Composite for Sodium-Ion Storage Material |
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| CN115642250B (en) * | 2022-11-03 | 2024-04-09 | 江苏正力新能电池技术有限公司 | NASICON type fluorophosphate, positive electrode material and battery |
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