Patent Application
20250174654
The present disclosure claims priority to Chinese Patent Application No. 202210957755.5 filed on Aug. 10, 2022 and entitled “POSITIVE ELECTRODE ACTIVE MATERIAL, AND PREPARATION METHOD THEREFOR AND USE THEREOF” which is incorporated herein by reference in its entirety.
The present disclosure relates to the technical field of batteries, and specifically to positive electrode active materials, and preparation methods therefor and uses thereof.
A positive electrode material for a battery is a key component in the battery, and has a great influence on the battery performance. For example, among numerous positive electrode materials for sodium ion batteries, sodium superionic conductor positive electrode materials are a polyanion-type material, which have become the research focus in recent years because of their potential advantages such as stable crystal structure, adjustable working voltage and high theoretical specific capacity. However, such materials have some shortcomings, such as poor electronic conductivity, difficult diffusion of active ions, and low charging and discharging voltage plateau, which seriously restrict the large-scale application of such materials in sodium batteries.
It is believed in the industry that doping modification of the above materials can solve the existing problems. However, the existing doping schemes have no obvious effect on the improvement of the charging and discharging voltage and the diffusion of active ions.
In view of this, the present disclosure provides positive electrode active materials. By doping the phosphorus site of an alkali metal vanadium phosphate with at least one of As, Sb, and Bi, etc., the charging and discharging voltage and ionic conductivity of the material can be effectively improved.
Specifically, in a first aspect of the present disclosure, positive electrode active materials are provided. The general formula of the positive electrode active material includes A3V2-xMx(P1-yEyO4)3, where A represents an alkali metal element; M represents a doping element that substitutes for V; M includes one or more of a transition metal element and a rare earth element; E represents a doping element that substitutes for P; E includes one or more of As, Sb, and Bi; and 0≤x≤1, and 0<y≤1/3.
Appropriate substitution of element P in the lattice of A3V2(PO4)3 by doping an element of the same group having an ionic radius larger than P can cause cell expansion, expand the transport channel of A+ ions, reduce the energy barrier of A+ ion migration, improve the electronic conductivity of the material, and thus promote the improvement of the rate performance of the material. Moreover, the doping of element E at the phosphorus site can also improve the working voltage of the doped A3V2(PO4)3 material, which is conducive to the improvement of the energy density.
In an embodiment, M includes one or more of Cr, Mn, Fe, Co, Ni, Cu, Zn, Ti, Mo, Nb, Zr, La, and Ce.
In an embodiment, M includes one or more of Cr, Mn, Fe, and Ti.
In an embodiment, E is one or more of As and Bi.
In an embodiment, M is Fe, and E is As.
In an embodiment, A includes one or more of Li, Na, and K.
In an embodiment, x is in the range of 0.001≤x≤1.
In an embodiment, x is in the range of 0.01≤x≤1.
In an embodiment, x is in the range of 0.3≤x≤0.5.
In an embodiment, y is in the range of 1/18≤y≤1/3.
In an embodiment, y is 1/6, 1/3, or 1/18.
In an embodiment, y is in the range of 1/18≤y≤1/6.
In an embodiment, y is in the range of 1/6≤y≤1/3. In a second aspect of the present disclosure, methods for preparing a positive electrode active material are provided, which include the following steps.
Element sources of various elements for the positive electrode active material to be prepared, with the general formula of A3V2-xMx(P1-yEyO4)3, are mixed to obtain a precursor material, where A represents an alkali metal element; M represents a doping element that substitutes for V; M includes one or more of a transition metal element and a rare earth element; E represents a doping element that substitutes for P; E includes one or more of As, Sb, and Bi; and 0≤x≤1, and 0<y≤1/3.
The precursor material is sintered, to obtain the positive electrode active material.
The methods for preparing a positive electrode active material have a simple preparation process and are easy to operate, thus being suitable for use in large-scale production.
In an embodiment, the precursor material is prepared by a sol-gel method as follows. An A source, a vanadium source, a phosphorus source, an M source and an E source are mixed in a solvent, and the obtained mixed solution is heated and stirred until the solvent is evaporated to dryness, to obtain the precursor material.
In an embodiment, the precursor material is prepared by solid-phase ball milling as follows. An A source, a vanadium source, a phosphorus source, an M source and an E element-containing doping anion source are ball milled in the absence of a solvent, to obtain the precursor material.
In an embodiment, the sintering is carried out under an inert gas atmosphere, the sintering temperature is 400-900° C., and the sintering time is 10-30 h.
In an embodiment, the inert gas includes one or more of nitrogen, argon, and helium.
In a third aspect of the present disclosure, positive electrodes are provided. The positive electrode includes a positive electrode active material provided in the first aspect of the present disclosure. The positive electrode can be used to provide a battery with good rate performance and high energy density.
In a fourth aspect of the present disclosure, secondary batteries are provided. The secondary battery includes a positive electrode provided in the third aspect of the present disclosure.
In a fifth aspect of the present disclosure, electric devices are provided. The electric device includes a secondary battery provided in the fourth aspect of the present disclosure.
Sodium vanadium phosphate (Na3V2(PO4)3, NVP) is a common sodium superionic conductor (NASICON) positive electrode material, having stable crystal structure, strong safety performance, and high theoretical specific capacity, but poor ionic conductivity and electronic conductivity, and thus poor rate performance and low charging and discharging voltage plateau, which are not conducive to the improvement of the energy density of the sodium battery.
In view of the problems associated with NVP, an embodiment of the present disclosure provides a positive electrode active material. The general formula of the positive electrode active material includes A3V2-xMx(P1-yEyO4)3, where A represents an alkali metal element; M represents a doping element that substitutes for V; M includes one or more of a transition metal element and a rare earth element; E represents a doping element that substitutes for P; E includes one or more of As, Sb, and Bi; and x represents the molar ratio at which element Vis replaced by element M, y represents the molar ratio at which element P is replaced by element E, 0≤x≤1, and 0<y≤1/3.
Element E is an element of the same group having an ionic radius larger than P. E can be easily doped into the lattice of A3V2(PO4)3, to replace P at some positions, and cause cell expansion. This expands the transport channel of A+ ions, reduces the energy barrier of migration, and reduces the repulsive effect of surrounding atoms, thus improving the migration rate of A+ ions and improving the rate performance. Furthermore, the crystal structure of the A3V2(PO4)3 material includes a PO4 tetrahedron and a VO6 octahedron, and they are connected by common oxygen (O) atoms at the vertices. The doping of element E at the phosphorus site will change the charge value of O atoms around it, which in turn forces the charge environment around V atoms to change, and induces element V to undergo a redox reaction at a high potential, thus improving the working voltage of the doped A3V2(PO4)3 material, and facilitating the improvement of the energy density of the material. Moreover, the doping of element E at the phosphorus site can also reduce the band gap of the M doped A3V2(PO4)3 material, to cause more electrons to gather near the Fermi surface and improve the electronic conductivity of the material. Additionally, the doping amount of element E is controlled not to be too high, to ensure that the material has not only good structural stability, but also good electronic conductivity, good ionic conductivity, and high charging and discharging voltage plateau, Therefore, the battery can be promoted to have good safety, good rate performance, and high energy density, etc.
Further, when an appropriate amount of element E is used for doping at P site and an appropriate amount of metal element M for doping at vanadium (V) site in A3V2(PO4)3, with the synergistic effect of doping of element M at V site and doping of element E at P site, the voltage plateau of the dually doped material can be further improved compared with the A3V2(P1-yEyO4)3 material doped with E alone and the A3V2-xMx(PO4)3 material doped with element M alone. The charging and discharging voltage plateau of the dually doped material is obviously improved, and the energy barrier of A+ ion migration is obvious reduced.
In an embodiment of the present disclosure, M may include one or more of chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), titanium (Ti), molybdenum (Mo), niobium (Nb), zirconium (Zr), La (lanthanum), and cerium (Ce). However, the present disclosure is not limited thereto.
In some embodiments of the present disclosure, M includes one or more of Cr, Mn, Fe, Co, Ni, Cu, Zn, Ti, Mo, Nb, and Zr. The cost of these elements is lower than that of lanthanide elements La and Ce. The ionic radii of Ti, Mo, Nb and Zr are larger than that of V ions. The introduction of these doping elements will also cause the lattice expansion of A3V2(PO4)3, thus facilitating the migration of A+ ions. However, the ionic radii of Cr, Mn, Fe, Co, Ni, Cu, and Zn are slightly smaller than that of V ions. If these elements are simply doped into A3V2(PO4)3, the cell volume will be reduced; but after the introduction of the above-mentioned element E, the cell volume will be increased, which promotes the improvement of the diffusion performance of the material. In some other embodiments of the present disclosure, to better balance the cost of element M and its influence on the ionic conductivity and working voltage of the material, element M can be one or more selected from Ti, Cr, Mn and Fe. These elements are also helpful to improve the working voltage of the doped materials, and can easily replace vanadium. Among them, Fe has the lowest cost.
In an embodiment of the present disclosure, E includes at least one of As, Sb and Bi. The ionic radii of As, Sb and Bi are all larger than that of P. By doping them at P site (that is, replacing the position of P atoms in the crystal structure of A3V2(PO4)3 with E atoms), the cell volume of A3V2-xMx(P1-yEyO4)3 can be appropriately expanded, to reduce the energy barrier of A ion migration. The ionic radii of As, Sb and Bi are not unduly larger than that of P, which can ensure that the material has not only higher stability of crystal structure, but also higher ionic conductivity. In some embodiments, element E is As and/or Bi. As and P are nonmetallic elements having similar properties, and As is easier to replace P.
In some embodiments, element M is Fe, and element E is As. In this case, the preparation cost of A3V2-xMx(P1-yEyO4)3 is low, and P is replaced by As, whereby the migration rate of A ions is improved to enhance the rate performance of the material, and the working voltage is improved to enhance the energy density of the material.
In an embodiment of the present disclosure, element A may specifically include one or more of Li, Na, and K, etc. Element A can be selected according to the specific type of the secondary battery. For example, when the battery active material A3V2-xMx(P1-yEyO4)3 is used in a sodium secondary battery, element A is Na.
In some embodiments of the present disclosure, x is in the range of 0.001≤x≤1, and further in the range of 0.01≤x≤1. By controlling the doping amount of M within the above range, the loss of electrochemical activity of A3V2-xMx(P1-yEyO4)3 caused by a too high doping amount of element M can be avoided, and the failure to improve the electronic conductivity due to a too low doping amount of element M is also avoided. In some embodiments, x is in the range of 0.001-0.5, preferably in the range of 0.01-0.5, further preferably in the range of 0.1-0.5, and more preferably in the range of 0.3-0.5.
In some embodiments of the present disclosure, y is in the range of 1/18≤y≤1/3. By controlling the doping amount of element E in the above range, the cell volume of A3V2-xMx(P1-yEyO4)3 is increased and the ionic conductivity is improved, without increasing the risk of structural disintegration due to excessive changes in its crystal structure. Therefore, the material is ensured to have good cycle performance, the working voltage of the material is improved, and the band gap of the material is extremely narrow, thus improving the conductivity.
In some embodiments of the present disclosure, y is 1/6. In this case, the energy barrier for migration of A ions in the A3V2-xMx(P1-yEyO4)3 material is extremely low, the rate performance of the material is excellent, and the cycle performance is also excellent. In some other embodiments, y is 1/3. In this case, the A3V2-xMx(P1-yEyO4)3 material has the highest working voltage and the most excellent electronic conductivity. In some other embodiments, y is 1/18. In this case, the A3V2-xMx(P1-yEyO4)3 material has a very high degree of crystallinity, and a very good structural stability. In some embodiments, y is in the range of 1/18≤y≤1/6. In some other embodiments, y is in the range of 1/6≤y≤1/3.
Correspondingly, as shown in
Step 10: Element sources of various elements in the positive electrode active material A3V2-xMx(P1-yEyO4)3 to be prepared are mixed, to obtain a precursor material, where A represents an alkali metal element; M represents a doping element that substitutes for V; M includes one or more of a transition metal element and a rare earth element; E represents a doping element that substitutes for P; E includes one or more of As, Sb, and Bi; and 0≤x≤1, and 0<y≤1/3.
Step 20: The precursor material is sintered, to obtain the positive electrode active material.
The methods for preparing the positive electrode active material have a simple preparation process and are easy to operate, thus being suitable for use in large-scale production.
In Step 10, the various element sources used to prepare the positive electrode active material include an A source, a vanadium source, a phosphorus source, an M source containing a doping metal element M, and an E source containing a doping element E. The A source, vanadium source, M source, phosphorus source, and E source can be weighed according to the weight ratio of elements A, V, M, P, and E of 3:(2-x):x:(1-y):y. Additionally, considering that the alkali metal element is prone to element loss in the subsequent sintering process, the A source may be in 10% excess or less.
The A source may include one or more of a sodium source, a lithium source, and a potassium source, specifically one or more of a nitrate, an oxalate, an acetate, an acetylacetonate, a carbonate, a sulfate, a phosphate, a hydroxide and the like of an alkali metal element. The vanadium source may be one or more of a trivalent vanadium source, a tetravalent vanadium source, and a pentavalent vanadium source, etc. It can be specifically an oxide (such as vanadium pentoxide, vanadium tetraoxide, vanadium trioxide, etc.), a hydroxide, a metavanadate (such as ammonium metavanadate, and sodium metavanadate, etc.), a nitrate, a sulfate, a phosphate, an oxalate, and an acetate of vanadium, vanadium acetylacetonate, and vanadyl acetylacetonate. The M source containing a doping metal element M may be similar to the vanadium source mentioned above, and may be one or more selected from an oxide, a hydroxide, a nitrate, a sulfate, a phosphate, an oxalate, an acetate, and an acetylacetonate of element M. The phosphorus source may be a polyanion group source of P, for example, an oxyacid group source of P. In some embodiments, the phosphorus source may include one or more of H3PO4, Na3PO4, and a dihydrogen phosphate, a hydrogen phosphate, and an orthophosphate of Li+, Na+, K+, and NH4+. The E source may be one or more of oxides, acids, salts and others corresponding to As, Sb and Bi. In some embodiments, the E source can be a doping anion source containing element E, such as one or more of oxyacids and oxysalts corresponding to As, Sb and Bi. Among the above element sources, the phosphorus source may be the same substance as the alkali metal source, vanadium source or M source, for example, sodium phosphate can serve as the phosphorus source and the sodium source.
In the present disclosure, the mixing method can be a liquid-phase method or a solid-phase method. The solid-phase method may be one or more of mechanical stirring, ball milling, and mechanical fusion, etc. The liquid-phase method may be sol-gel method, hydrothermal/solvothermal method, and liquid-phase high-energy ball milling method, etc. The solvent used in the liquid-phase method may be one or more of water, ethanol, and acetone, etc.
In some embodiments, the precursor material is prepared by solid-phase ball milling. The process is specifically as follows. The alkali metal source, vanadium source, phosphorus source, M source and doping anion source containing element E are ball-milled in the absence of a solvent, to obtain the precursor material.
In some other embodiments, the precursor material is prepared by sol-gel method. The process is specifically as follows. The alkali metal element source, vanadium source, and phosphorus source are mixed with the M source and doping anion source containing element E in a solvent, and the obtained mixed solution is heated and stirred until the solvent is evaporated to dryness, to obtain the precursor material. The various element sources will react in the process of heating and stirring, to obtain the precursor material. The precursor material can be transformed into the required positive electrode active material after sintering. In an embodiment of the present disclosure, the temperature of the heating and stirring can be 30-200° C., for example, 40-100° C., depending on the boiling point of the solvent used. The stirring speed during the heating and stirring can be 300-900 rpm, and the time can be 1-6 h.
In an embodiment of the present disclosure, the sintering is carried out under an inert gas atmosphere, the sintering temperature is 400-900° C., and the sintering time is 10-30 h. The inert gas may be one or more of nitrogen, argon and helium, and argon and helium are preferred.
An embodiment of the present disclosure further provides a positive electrode. The positive electrode includes the positive electrode active material. The positive electrode can be used to prepare secondary batteries with excellent performance such as good rate performance and high energy density.
In an embodiment of the present disclosure, the positive electrode generally includes a positive electrode current collector and a positive electrode active material layer arranged on at least one side surface of the positive electrode current collector, where the positive electrode active material layer includes the positive electrode active material. Additionally, the positive electrode active material layer may also contain a binder and an optional conductive agent. The binder and the conductive agent can be conventional choices in the field of batteries.
The positive electrode current collector may be various materials suitable for use as the positive electrode current collector, including, but not limited to, a metallic foil, an alloy foil, a metallized polymer film, or the aforementioned materials coated with carbon. The metallic foil may be an aluminum foil, the alloy foil may be an aluminum alloy foil, and the metal plated on the surface of the polymer film may be an aluminum layer or an aluminum alloy layer.
An embodiment of the present disclosure further provides a secondary battery, where the secondary battery includes the positive electrode. The secondary battery may be specifically a lithium secondary battery, a sodium secondary battery or a potassium secondary battery.
Given the use of doped A3V2(PO4)3 as a positive electrode active material, the secondary battery has high energy density, good rate performance and good cycle performance.
An embodiment of the present disclosure also provides an electric device. The electric device includes the secondary battery. The electric device may be a vehicle, ship, 3 C product (including computers, communications, consumer electronics, etc.), or energy storage system.
As the doped A3V2(PO4)3 is used as a positive electrode active material in the secondary battery, the secondary battery has high energy density, good rate performance and good cycle performance. When used in an electric device, it can improve the performance and market competitiveness of the electric device.
The secondary battery may be a liquid battery using a liquid electrolyte solution, or a semi-solid or solid battery using a semi-solid electrolyte or a solid electrolyte. In some embodiments, the secondary battery may include a positive electrode sheet, a negative electrode sheet, and a separator and an electrolyte solution arranged between the positive electrode sheet and the negative electrode sheet. In some other embodiments, the secondary battery may include a positive electrode sheet, a negative electrode sheet, and a semi-solid electrolyte or a solid electrolyte arranged between the positive electrode sheet and the negative electrode sheet. Additionally, when a semi-solid electrolyte or a solid electrolyte is used, the positive electrode sheet and the negative electrode sheet may also contain a semi-solid electrolyte material or a solid electrolyte material.
The technical solution of the present disclosure will be further described in detail by way of examples.
A positive electrode active material has a general formula of Na3V1.5Fe0.5(P17/18As1/18O4)3 (As1-Fe—NVP).
The As1-Fe—NVP was prepared as follows.
(1) According to a molar ratio of Na element:V element:Fe element:P element:As element=3:1.5:0.5:17/18:1/18, a sodium source (specifically sodium nitrate), a vanadium source (specifically vanadium pentoxide), a Fe source (specifically ferrous oxide), a phosphorus source (specifically phosphoric acid), and an As source (specifically ammonium arsenate) were weighed, mixed in the solvent ethanol, and heated at 80° C. with stirring, until the solvent was evaporated to dryness, to obtain a precursor material.
(2) The precursor material was sintered for 12 h under a nitrogen atmosphere at a sintering temperature of 800° C., to obtain Na3V1.5Fe0.5(P17/18As1/18O4)3.
A positive electrode active material has a general formula of Na3V1.5Fe0.5(P5/6As1/6O4)3 (As3-Fe—NVP).
The preparation method of As3-Fe—NVP was the same as that in Example 1, except that: the amounts of the P source and the As source were changed, such that the molar ratio of the Fe element:P element:As element was 0.5:5/6:1/6.
A positive electrode active material has a general formula of Na3V1.5Fe0.5(P2/3As1/3O4)3 (As6-Fe—NVP).
The preparation method of As6-Fe—NVP was the same as that in Example 1, except that: the amounts of the P source and the As source were changed, such that the molar ratio of the Fe element:P element:As element was 0.5:2/3:1/3.
A positive electrode active material has a general formula of Na3V2(PO4)3 (NVP).
The preparation method of NVP was the same as that in Example 1, except that: no As source and Fe source were introduced.
A positive electrode active material has a general formula of Na3V1.5Fe0.5(PO4)3 (Fe—NVP).
The preparation method of Fe—NVP was the same as that in Example 1, except that: no As source was introduced.
In
In
In
According to the molecular configurations of the compounds shown in
The cell volume change rate of the uncharged vs fully charged state is described with As1-Fe—NVP as an example. The cell volume change rate of the uncharged vs fully charged state is obtained by dividing the absolute difference between the cell volume of the fully charged NaV1.5Fe0.5(P17/18As1/18O4)3 and the cell volume of the uncharged Na3V1.5Fe0.5(P17/18As1/18O4)3 (As1-Fe—NVP) by the cell volume of the uncharged state. For the open-circuit voltage of the uncharged compound A3V2-xMx(P1-yEyO4)3, the lattice constants and the total energy of the cell structures of the uncharged and fully charged compounds can be obtained from their respective molecular configurations, with which the open-circuit voltage of A3V2-xMx(P1-yEyO4)3 is calculated. The band gap can be calculated from a distribution curve of density of state of the material. The energy barrier for Na ion migration can be calculated by Nudged Elastic Band (NEB) method or the improved NEB method.
As can be seen from Table 1, for the cell volume of each compound, when NVP is doped with Fe alone, the cell volume is reduced because the atomic radius of Fe is smaller than that of V. When As is further doped into NVP doped with Fe, the cell volume becomes larger with the increase of the doping concentration of As, which indicates that the introduction of As promotes the cell expansion.
The doping of Fe alone and the co-doping of Fe and As result in different cell volume changes of the uncharged vs charged states of the material. As can be seen from Table 1, As3-Fe—NVP has the smallest cell volume change of the uncharged vs fully charged states and the highest stability of crystal structure. Additionally, although the cell volume change rates of Fe—NVP, As1-Fe—NVP, and As3-Fe—NVP of the uncharged vs fully charged states is larger than that of NVP, their crystal structures are stable, which ensures that the structure will not disintegrate due to excessive deformation during the charging and discharging process.
For the open-circuit voltage of each compound, as can be seen from Table 1, the open-circuit voltage of the material co-doped with Fe and As (Examples 1-3) is improved compared with undoped NVP and Fe—NVP doped with iron alone. When the material is used in a sodium battery, the energy density of the battery is enhanced. Additionally, with the increase of the doping concentration of As, the open-circuit voltage of NVP co-doped with Fe and As increases constantly, thus increasing the energy density of the battery. Because the open-circuit voltage of a material is generally higher than its working voltage, when the open circuit voltage of material A is higher than that of material B, the working voltage of material A is generally higher than that of material B. Therefore, the energy density of the prepared battery can be estimated by comparing the open-circuit voltages of different materials.
For the band gap of each compound, as can be seen from Table 1, the band gap of undoped NVP is wider, indicating a larger resistance. The band gap of Fe—NVP doped with iron alone can be reduced to 0.82 eV; and co-doping of Fe and As can further reduce the band gap. As3-Fe—NVP and As6-Fe—NVP have almost no band gap, indicating that they have high conductivity.
For the energy barrier for migration of each compound, as can be seen from Table 1, the energy barrier for migration of Na in NVP is relatively high and about 0.612 eV. The energy barrier for Na ion migration is increased after the introduction of Fe doped alone. This is mainly because the ionic radius of Fe is small, and the doping of iron alone causes the cell volume of NVP to decrease. In contrast, the energy barrier for migration of Na ions in As1-Fe—NVP, As3-Fe—NVP, and As6-Fe—NVP co-doped with Fe and As is obviously reduced, and the ionic conductivity is improved, thus improving the charging and discharging rate of the material.
Additionally,
A positive electrode active material has a general formula of Na3V1.5Fe0.5(P5/6Sb1/6O4)3.
The preparation method of Na3V1.5Fe0.5(P5/6Sb1/6O4)3 was the same as that for Na3V1.5Fe0.5(P5/6As1/6O4)3 in Example 2, except that: the As source was replaced by a Sb source (specifically sodium antimonate).
A positive electrode active material has a general formula of Na3V1.5Fe0.5(P5/6Bi1/6O4)3.
The preparation method of Na3V1.5Fe0.5(P5/6Bi1/6O4)3 was the same as that for Na3V1.5Fe0.5(P5/6As1/6O4)3 in Example 2, except that: the As source was replaced by a Bi source (specifically ammonium bismuth citrate).
A positive electrode active material has a general formula of Na3V1.8Fe0.2 (P5/6As1/6O4)3.
The preparation method of Na3V1.8Fe0.2 (P5/6As1/6O4)3 was the same as that for Na3V1.5Fe0.5(P5/6As1/6O4)3 in Example 2, except that: the amounts of the Fe source and the V source were changed, such that the molar ratio of V:Fe element was 1.8:0.2.
A positive electrode active material has a general formula of Na3V1.99Fe0.01 (P5/6As1/6O4)3.
The preparation method of Na3V1.99Fe0.01 (P5/6As1/6O4)3 was the same as that for Na3V1.5Fe0.5(P5/6As1/6O4)3 in Example 2, except that: the amounts of the Fe source and the V source were changed, such that the molar ratio of V:Fe element was 1.99:0.01.
A positive electrode active material has a general formula of Na3V1.5Ti0.5(P5/6As1/6O4)3.
The preparation method of Na3V1.5Ti0.5(P5/6As1/6O4)3 was the same as that for Na3V1.5Fe0.5(P5/6As1/6O4)3 in Example 2, except that: the Fe source was replaced by a Ti source (specifically titania).
A positive electrode active material has a general formula of Na3V1.5Cr0.5(P5/6As1/6O4)3.
The preparation method of Na3V1.5Cr0.5(P5/6As1/6O4)3 was the same as that for Na3V1.5Fe0.5(P5/6As1/6O4)3 in Example 2, except that: the Fe source was replaced by a Cr source (specifically chromium oxide).
A positive electrode active material has a general formula of Na3V1.5Nb0.5(P5/6As1/6O4)3.
The preparation method of Na3V1.5Nb0.5(P5/6As1/6O4)3 was the same as that for Na3V1.5Fe0.5(P5/6As1/6O4)3 in Example 2, except that: the Fe source was replaced by a Nb source (specifically sodium niobate).
A positive electrode active material has a general formula of Na3V2(P17/18As1/18O4)3.
The preparation method of Na3V2(P17/18As1/18O4)3 was the same as that in Example 1, except that no doping source-Fe source was used.
A positive electrode active material has a general formula of Na3V2(P5/6As1/6O4)3.
The preparation method of Na3V2(P5/6As1/6O4)3 was the same as that in Example 2, except that no doping source-Fe source was used.
A positive electrode active material has a general formula of Na3V2(P2/3As1/3O4)3.
The preparation method of Na3V2(P2/3As1/3O4)3 was the same as that in Example 3, except that: no doping source-Fe source was used.
A positive electrode active material has a general formula of Na3 VFe(P5/6As1/6O4)3.
The preparation method of Na3VFe(P5/6As1/6O4)3 was the same as that for Na3V1.5Fe0.5(P5/6As1/6O4)3 in Example 2, except that: the amounts of the Fe source and the V source were changed, such that the molar ratio of V:Fe element was 1:1.
A positive electrode active material has a general formula of Na3V1.5Fe0.5(P35/36As1/36O4)3. The preparation method was the same as that for Na3V1.5Fe0.5(P5/6As1/6O4)3 in Example 2, except that the amounts of the P source and the As source were changed, such that the molar ratio of the Fe element:P element:As element was 0.5:35/36:1/36.
A positive electrode active material has a general formula of Na3V1.5Mn0.5(P5/6As1/6O4)3.
A positive electrode active material has a general formula of Na3V1.5Mn0.5(P5/6Bi1/6O4)3.
A positive electrode active material has a general formula of Na3V1Mn1(P5/6Bi1/6O4)3.
A positive electrode active material has a general formula of Na3V1.5Mn0.5(P5/6Sb1/6O4)3.
A positive electrode active material has a general formula of Na3V1.5Ti0.5(P5/6Bi1/6O4)3.
Table 2 below summarizes relevant electrochemical performances of positive electrode active materials in Examples 4-20.
As can be seen from Table 2, compared with the undoped Na3V2(PO4)3 in Example 1, the dually doped sodium vanadium phosphate material provided in Examples 4-10 and 14-20 of the present disclosure can not only maintain good structural stability, but also have high open-circuit voltage, narrow band gap, and low energy barrier for Na ion migration, thus resulting in high energy density and good rate performance. Additionally, by comparing Examples 11-13 with Examples 1-3 in Table 1, it can be seen that when Na3V2(PO4)3 is only doped with the same content of As without iron, the cell volume of the obtained material is larger, the cell volume change rate of the fully charged state vs uncharged state is smaller, and the energy barrier for migration of sodium ions is reduced. As a result, the rate performance of the battery is improved, but the open-circuit voltage and conductivity of the material are reduced slightly. Additionally, when Na3V2(PO4)3 is doped with the same amount of As, Sb or Bi, the open-circuit voltage of the material can be further improved after Mn is doped at V site.
To further support the beneficial effects of the embodiments of the present disclosure, the materials of the above examples and comparative examples were made into batteries and their electrochemical performances were tested. Relevant results are shown in Table 3.
The manufacturing process of the battery was as follows: {circle around (1)} Preparation of positive electrode sheet: The positive active material of each example or comparative example, the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVEF) were added into the solvent NMP (N-methylpyrrolidone) according to a weight ratio of 88:6:6, and uniformly stirred to obtain a positive electrode slurry. The positive electrode slurry was coated on a positive electrode current collector that was an aluminum foil, and then dried, rolled and cut, to obtain a positive electrode sheet. {circle around (2)} Preparation of negative electrode sheet: The negative electrode active material (specifically hard carbon) and the binder (specifically styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC-Na) at a weight ratio of 2:3) were mixed in ionic water according to a weight ratio of 95:5, and stirred until uniform, to obtain a negative electrode slurry. The negative electrode slurry was coated on a negative electrode current collector that was a copper foil, and then dried, rolled and cut, to obtain a negative electrode sheet. {circle around (3)} Assembly of battery: The positive electrode sheet, a separator, and the negative electrode sheet were stacked sequentially to obtain a dry battery cell. The dry battery cell was wound and placed in an aluminum-plastic film that was an outer packaging foil, and an electrolyte solution was injected. After vacuum packaging, standing, formation, shaping and other procedures, the preparation of the sodium full battery was completed.
The battery of each example and comparative example were tested for the following electrochemical performances.
1) Cycle performance: Each battery was subjected to a charging and discharging cycle test at a rate of 0.5 C at 25° C. The voltage range was 2.5-4.3V. When charged, the battery was charged at a constant current of 0.5 C until the cut-off voltage was 4.3V, and then charged at a constant voltage until the cut-off current is 0.05 C. When discharged, the battery was discharged at a constant current of 0.5 C to 2.5V. The first-cycle discharging capacity per gram and the capacity retention rate of each battery after 50 cycles were recorded. The first-cycle discharging capacity per gram is equal to the ratio of the first-cycle discharging capacity of each sodium full battery to the weight of the positive electrode active material in the battery. The capacity retention rate after 50 cycles is equal to the ratio of the discharging capacity after 50 cycles to the first-cycle discharging capacity.
Additionally, the discharging curve in the charging-discharging curve obtained by constant-current charging and discharging of each battery at 0.5 C was integrated and divided by the discharging capacity, to obtain the average voltage of each battery. The relevant results are summarized in Table 3 below, and the cycle curves of some examples and comparative examples are summarized in
2) Rate performance: The change of the discharging capacity per gram of each battery at 0.5 C, 1 C, 5 C, and 10 C vs cycles was tested at 25° C. The voltage range was 2.5-4.3V. The rate performance curves of some examples and comparative examples are shown in
As can be seen from Table 3, compared with the sodium battery prepared with the material of Comparative Example 1, the sodium batteries prepared with the materials provided in Examples 1-20 of the present disclosure have a higher voltage plateau and a higher first-cycle discharging capacity ratio at 10 C/0.5 C, indicating a higher rate performance of the battery. Moreover, the cycle performance of the battery is not obviously reduced. Additionally, the batteries of Examples 1-7 and 14-15 have a higher voltage plateau and better rate performance than the battery of Comparative Example 2.
Exemplary embodiments of the present disclosure have been described above. It should be noted that several improvements and modifications can be made by those of ordinary skill in the art without departing from the principle of the present disclosure, which shall fall within the protection scope of the present disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202210957755.5 | Aug 2022 | CN | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/CN2023/111284 | Aug 2023 | WO |
| Child | 19036400 | US |
