Novel NASICON-type high-voltage sodium vanadium phosphate materials for Na-ion batteries

Abstract

The present invention relates to a material of formula (I): A x V (2-y-z) M y M' z (PO4)3(I) [wherein A is Na or Li, or a mixture of Na and Li, 1 < x < 3, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, M is an electroactive transition element or a mixture of at least two electroactive transition elements, and M' is a non-electroactive element or a mixture of at least two non-electroactive elements], which exhibits a V / Z ratio varying from 212 Å 3 to 246 Å 3 and relates to a material.

Description

[Technical field]

[0001] The present invention relates to a novel Na-based positive electrode active material for Na-ion batteries. The present invention also relates to a method for preparing said material and its use as an electrode material. The present invention also relates to an electrode material comprising said Na-based material and a battery comprising said electrode. [Background technology]

[0002] Lithium-ion batteries are widely used in electric vehicles and portable devices due to their satisfactory energy and power density. However, lithium resources are expensive and unevenly distributed around the world, making it difficult to meet the urgent demand for large-scale energy storage systems.

[0003] In terms of chemical element abundance and cost, the most attractive alternative to Li-ion batteries is sodium due to its abundant and evenly distributed resources and relatively low material costs compared to lithium-ion batteries.

[0004] The performance of Na-ion batteries is partly related to the capacity of the cathode material. Potential cathode materials for sodium-ion batteries include sodium layered transition metal oxides, Prussian blue analogues, and polyanion compounds. Polyanion compounds with NASICON structure are promising choices for the cathode material due to their structural stability, rate capability, and long cycle life. Among them, Na3V2(PO4)3 has been widely studied and has the potential to be used as a cathode material. 4+ / V 3+ The redox couple provides a theoretical capacity of 117.6 mAh / g. During the electrochemical charging and discharging process, the + The two Na3V2(PO4)3 and Na1V2(PO4)3 have a voltage-composition plateau at 1000V / Na. + Ions can be reversibly exchanged. Na3V2(PO4)3 undergoes a moderate volume change of about 8.2% during the electrochemical reaction.

[0005] However, the third Na + Extraction of (Na1V2(PO4)3 to V2(PO4)3) is the final Na + Due to the large transfer energy of Na3V2(PO4)3, it does not undergo electrochemical reactions, which contributes to the mass penalty and capacity limitation. More importantly, the operating voltage of Na3V2(PO4)3 is 3.4 V vs. Na + / Na, which is relatively low.

[0006] Thus, there remains a need for new positive electrode materials that exhibit improved performance compared to prior art positive electrode materials. Summary of the Invention [Problem to be solved by the invention]

[0007] One of the objectives of the present invention is to provide an electrode material, preferably a positive electrode material, that exhibits better performance than prior art electrode materials, particularly conventional Na3V2(PO4)3 or Li3V2(PO4)3 materials.

[0008] In particular, one object of the present invention is to provide a method for the preparation of a soluble ... + / Na or Li + The object of the present invention is to provide an electrode material, preferably a positive electrode material, which exhibits a high operating voltage vs. .gamma. / Li.

[0009] Another specific object of the present invention is to provide an electrode material, preferably a positive electrode material, that exhibits higher energy density than conventional Na3V2(PO4)3 or Li3V2(PO4)3 materials.

[0010] Another specific object of the present invention is to provide an electrode material, preferably a positive electrode material, which exhibits less volume expansion / contraction during electrochemical operation than conventional Na3V2(PO4)3 or Li3V2(PO4)3 materials.

[0011] Another object of the present invention is to provide an electrode material that exhibits a single-phase reaction mechanism during the charge and discharge process. [Means for solving the problem]

[0012] The present invention relates to a compound of formula (I): A x V (2-y-z) M y M' z (PO4)3(I) [In the formula, A is Na or Li, or a mixture of Na and Li; 1 <x<3、 0≦y<1, 0≦z<1, M is an electroactive transition element or a mixture of at least two electroactive transition elements; M' is a non-electroactive element or a mixture of at least two non-electroactive elements. A material comprising: 212Å 3 ~246Å 3 For materials that exhibit a V / Z ratio (volume of a crystalline unit cell per formula unit) that varies with

[0013] By transition element is meant a transition metal.

[0014] The inventors have discovered that the material of formula (I) according to the present invention has some interesting physical and electrochemical properties compared to existing positive electrode materials Na3V2(PO4)3 or Li3V2(PO4)3. For example, when A=Na, the material of formula (I) has a 2.5-4.3 V vs. Na + Approximately 2 reversible Na exchanges within the voltage window of / Na + ions, and the corresponding theoretical capacity is higher than that of Na3V2(PO4)3. Furthermore, the average operating voltage of the material according to the present invention is about 3.75 V vs. Na + / Na (from about 3.4 V for conventional Na3V2(PO4)3). The electrochemical reaction mechanism for the extraction of sodium from this material / insertion of sodium into this material is as follows: Na +The continuous increase in operating voltage occurs via a solid solution (single-phase) mechanism as Na is electrochemically extracted, which differs from the two-phase mechanism seen with "classical" Na3V2(PO4)3. This is highly appreciated as it allows for more cost-effective state-of-charge monitoring than systems with a flat voltage profile. Finally, instead of the "classical" constant voltage 3.4V process of Na3V2(PO4)3, the operating voltage of the material of the present invention ranges from 3.0V to 4.3V vs. Na+ / Na in a graded manner. With the subsequent increase in operating voltage, the theoretical gravimetric energy density of the material of the present invention is therefore subsequently increased by about 15% to 464Wh / kg when compared to conventional Na3V2(PO4)3.

[0015] Preferably, the electroactive transition element M is selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb and Mo, more preferably from the group consisting of Ti, V, Cr, Mn, Fe and Nb.

[0016] Preferably, the non-electroactive element M' is selected from the group consisting of Mg, Al, Sc, Y, Zr, Er, and Ta, more preferably from the group consisting of Mg, Al, and Zr.

[0017] The non-electroactive element M' used for slight doping is especially +2 (Mg 2+ ) or +3(Al 3+ ), a composition containing less than 2 vanadium will have 2 Na + When the high voltage V 4+ / V 5+ It is possible to utilize redox couples, which therefore makes it possible to increase both the energy density exerted and the sustainability of the material.

[0018] When M is a mixture of at least two electroactive transition elements, y represents the sum of the mole fractions of each transition element contained in M.

[0019] When M' is a mixture of at least two non-electroactive elements, z represents the sum of the mole fractions of each non-electroactive element contained in M'.

[0020] Preferably, 0≦y≦0.8, more preferably, 0≦y≦0.5, and even more preferably, 0≦y≦0.2.

[0021] Preferably, 0≦z≦0.5, and more preferably, 0≦z≦0.2.

[0022] According to one embodiment, y=0 and / or z=0.

[0023] Preferably, x varies from 1.1 to 2.9, preferably from 1.2 to 2.8, preferably from 1.3 to 2.7, preferably from 1.4 to 2.6, preferably from 1.5 to 2.5, preferably from 1.6 to 2.4, preferably from 1.7 to 2.3, preferably from 1.8 to 2.2, preferably from 1.9 to 2.1, and / or any other suitable combination of ranges.

[0024] Typically, x, y, and z are selected to ensure electroneutrality of the material of formula (I).

[0025] According to the present invention, the V / Z ratio of a material of formula (I) is expressed as the unit cell volume per formula unit (in Å 3 ). This characteristic is well known to those skilled in the art. The V / Z ratio is determined, for example, from an X-ray or neutron diffraction pattern of a powder of the material of formula (I) according to the invention by fitting the powder diffraction profile using the so-called Le Bail method. The X-ray or neutron diffraction pattern is generally obtained at 25° C. (298 K) (unless otherwise stated). The V / Z ratio is independent of the space group used to represent the crystal structure of the material of formula (I).

[0026] Advantageously, the material of formula (I) is a single-phase material.

[0027] A single-phase material is a solid material composed of a distinct solid phase described by a crystal structure which gives the position of each atom in the formula within a so-called unit cell described by an appropriate space group.

[0028] According to one embodiment, A=Li.

[0029] In this embodiment, the material of formula (I) preferably has a viscosity of 212 Å or less. 3 ~225Å 3 The V / Z ratio changes with time.

[0030] According to another embodiment, A is a mixture of Li and Na. According to this embodiment, x represents the sum of the mole fraction x' of element Li and the mole fraction (1-x') of element Na.

[0031] Preferably, 0≦x′≦1.

[0032] In this embodiment, the material of formula (I) preferably has a viscosity of 212 Å or less. 3 ~235Å 3 The V / Z ratio changes with time.

[0033] According to another embodiment, A=Na.

[0034] In this embodiment, the material of formula (I) preferably has a viscosity of 219 Å or less. 3 ~246Å 3 , preferably 220.2 Å 3 ~239.5Å 3 The V / Z ratio changes with time.

[0035] Preferably, the V / Z ratio is 225 Å. 3 ~239Å 3 , preferably 230 Å 3 ~239Å 3 , preferably 232 Å 3 ~239Å 3 , preferably 234 Å 3 ~239Å 3 , preferably 235 Å 3 ~238Å 3 , preferably 236 Å 3 ~237.5Å 3 , and / or any other suitable combination range.

[0036] Preferably, when 1.8≦x≦2.3, the V / Z ratio is 232 Å. 3 ~239Å 3 , preferably 235 Å 3 ~238Å 3 It changes.

[0037] More preferably, when x=2, the V / Z ratio is 232 Å. 3 ~239Å 3 , advantageously 235 Å 3 ~238Å 3 This means that for x=2, the V / Z ratio is 232Å. 3 ~239Å 3 , advantageously 235 Å 3 ~238Å 3 This means that the V / Z ratio is preferably further defined, with the proviso that it varies with

[0038] The materials of formula (I) according to the invention can be structurally described using a hexagonal unit cell, or alternatively using a monoclinic or triclinic unit cell, depending on the overall Na content and possible Na ion ordering within the framework which creates slight distortions. Preferably, the materials of formula (I) are described using a hexagonal unit cell, which is more symmetrical than the monoclinic or triclinic descriptions.

[0039] Preferably, the material of formula (I) has a lattice with an overall symmetry described by the R32, R-3, R-3c, C2 / c, P-1, or P-3 space group.

[0040] More preferably, the material of formula (I) is structurally described using a hexagonal unit cell and the R-3c space group.

[0041] Preferably, when written using a hexagonal unit cell, the material of formula (I) where A=Na has the following lattice parameters: a 六方晶 is 8.60 to 8.72 Å, preferably 8.64 to 8.68 Å, and more preferably substantially equal to 8.654 Å; c 六方晶is 21.80 to 21.94 Å, preferably 21.88 to 21.94 Å, and more preferably substantially equal to 21.896 Å.

[0042] Preferably, the c / a ratio varies between 2.500 and 2.550, more preferably between 2.505 and 2.545, more preferably between 2.510 and 2.545, more preferably between 2.515 and 2.540, more preferably between 2.520 and 2.538, more preferably between 2.525 and 2.536, more preferably between 2.530 and 2.535, more preferably between 2.531 and 2.535, and / or any other suitable combination of ranges.

[0043] Preferably, in the material of formula (I) where A=Na, when 1.8≦x≦2.3, the c / a ratio varies from 2.520 to 2.545 when written using a hexagonal unit cell. Preferably, in the material of formula (I) where x=2, the c / a ratio varies from 2.520 to 2.540 when written using a hexagonal unit cell.

[0044] Materials of formula (I) where A=Na can be described using a rhombohedral (R-3c) structure in which the sodium ions are located at two sodium sites, Na(1) and Na(2). The Na(1) site is six-coordinated and c 六方晶 The Na(2) site is eight-coordinated and occupies the interstitial space formed by the M2(PO4)3 units.

[0045] Preferably, the material of formula (I) is described by a rhombohedral (R-3c) crystal structure with two types of sodium sites, Na(1) and Na(2), with an average packing factor of Na(1) sites between 0 and 1 and an average packing factor of Na(2) sites between 0 and 1. Packing factor refers to the occupancy of Na(1) and Na(2) sites in the unit cell. Packing factor refers to the number of occupied sites relative to the number of available sites. It is noted that the multiplicity of Na(2) sites is equal to three times the multiplicity of Na(1) sites, therefore the maximum sodium per formula (I) is equal to 1 at Na(1) sites and 3 at Na(2) sites.

[0046] Preferably, the average filling rate of the Na(1) site varies from 0.2 to 0.95, preferably from 0.3 to 0.9, more preferably from 0.5 to 0.8, even more preferably from 0.6 to 0.7, and advantageously is substantially equal to 0.66.

[0047] Preferably, the average filling rate of the Na(2) site varies from 0 to 0.9, preferably from 0.4 to 0.9, more preferably from 0.45 to 0.7, even more preferably from 0.5 to 0.6, and advantageously is substantially equal to 0.54.

[0048] The present invention also relates to a method for preparing a material of formula (I), comprising the following steps: a) A3V (2-α) Z α (PO4)3 and A1V (2-β) Z' β (PO4)3 are preferably mixed in an inert atmosphere to obtain an initial mixture, where A is Li or Na, or a mixture of Na and Li, Z and Z' are elements independently selected from electroactive transition elements, non-electroactive elements, and mixtures thereof, with 0 ≦ α < 1 and 0 ≦ β < 1, b) heating the initial mixture at a temperature of 300°C to 700°C, preferably in an inert atmosphere or under vacuum, and relates to a method.

[0049] Preferably, in the initial mixture, the molar fraction of Na3V (2-w) M' w (PO4)3 is p, and the molar fraction of Na1V (2-z) M'' z (PO4)3 is (1 - p), where 0 < p < 1. More preferably, p varies in the range of 0.05 to 0.95, preferably 0.1 to 0.9, preferably 0.15 to 0.85, preferably 0.2 to 0.8, preferably 0.25 to 0.75, preferably 0.3 to 0.7, preferably 0.35 to 0.65, preferably 0.4 to 0.6, preferably 0.45 to 0.55, and / or any other suitable combination range.

[0050] This process is a solid solution process. A3V in the initial mixture (2-α) Z α (PO4)3 and A1V (2-β) Z' β The mole fraction of (PO4)3 is x V (2-y-z) M y M' z Determine the value of x in (PO4)3, where x=1+2p.

[0051] Preferably, the electroactive transition element is Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, or Mo, more preferably Ti, V, Cr, Mn, Fe, or Nb.

[0052] Preferably, the non-electroactive element is Mg, Al, Sc, Y, Zr, Er, or Ta, more preferably Mg, Al, or Zr.

[0053] Preferably, the method comprises, between steps a) and b), a step a') of pelletizing the initial mixture of step a), preferably under an inert atmosphere, to obtain pellets.

[0054] By using pellets, A3V (2-α) Z α (PO4)3 and A1V (2-β) Z' β Better contact between the particles of (PO4)3 is obtained and thus beneficial to the efficiency of step b).

[0055] Preferably, during step b), the initial mixture (or the pellets) is heated to a temperature between 400°C and 600°C, more preferably between 500°C and 550°C.

[0056] Preferably, the method further comprises, before step a), (2-α) Z α Chemical oxidation of (PO4)3 results in A1V (2-β) Z' β It further comprises the initial step of preparing (PO4)3.

[0057] Preferably, the method further comprises a step c) of cooling the heated initial mixture (or pellets) obtained at the end of step b) to a temperature comprised between 20 and 40°C.

[0058] According to the present invention, the inert atmosphere may be an atmosphere containing N2 and / or Ar and less than 2 ppm O2 and / or less than 2 ppm H2O.

[0059] According to another embodiment, Z and Z' are identical.

[0060] According to another preferred embodiment, Z is an electroactive transition element or a mixture of at least two electroactive transition elements, and Z' is a non-electroactive element or a mixture of at least two non-electroactive elements, or Z is a non-electroactive element or a mixture of at least two non-electroactive elements and Z' is an electroactive transition element or a mixture of at least two electroactive transition elements. In other words, Z corresponds to M and Z' corresponds to M', or Z corresponds to M' and Z' corresponds to M, in the material of formula (I).

[0061] Preferably, α=0 and / or β=0.

[0062] The present invention also relates to a method for preparing a material of formula (I), comprising the steps of: A3V (2-y-z) M y M' z Dispersing (PO4)3 in a solvent, preferably an organic solvent, A is Na or Li, or a mixture of Na and Li; 0≦y<1, 0≦z<1, M is an electroactive transition element or a mixture of at least two electroactive transition elements; M' is a non-electroactive element or a mixture of at least two non-electroactive elements; 2) A3V (2-y-z) M y M' zThe step of adding an oxidizing agent to the dispersion of (PO4)3, 3) The step of stirring the obtained mixture, 4) A where 1 < x < 3 x V (2-y-z) M y M' z The step of obtaining A which includes,

[0063] M, M', y, and z are as defined above for the material of formula (I) according to the present invention.

[0064] Preferably, y = 0 and / or z = 0.

[0065] The molar ratio of the amount of the oxidizing agent to A3V (2-y-z) M y M' z (PO4)3 is n. Preferably, 0 < n < 2. More preferably, n varies in the range of 0.1 to 1.9, preferably 0.2 to 1.8, preferably 0.3 to 1.7, preferably 0.4 to 1.6, preferably 0.5 to 1.5, preferably 0.6 to 1.4, preferably 0.7 to 1.3, preferably 0.8 to 1.2, preferably 0.9 to 1.1, and / or any other suitable combination range.

[0066] A3V (2-y-z) M y M' z The amount of the oxidizing agent added to the dispersion of A x V (2-y-z) M y M' z (PO4)3 determines the value of x of the product A

[0067] Preferably, the oxidizing agent is (2-y-z) M y M' z added dropwise to the dispersion of A

[0068] Preferably, the oxidizing agent is selected from the group consisting of NO2BF4, Na2S2O8, I2, and CHCl3. Advantageously, the oxidizing agent is NO2BF4.

[0069] The present invention also relates to the use of the material of formula (I) according to the invention as an electrode active material for a battery, preferably as a positive electrode active material for a Li-ion or Na-ion battery, more preferably for a Na-ion battery.

[0070] The materials of formula (I) may be used together with one or more additional compounds conventionally used, such as binders and / or conductive additives.

[0071] The electronically conductive additive may be selected from carbon fibers, carbon black, carbon nanotubes, graphite, and the like.

[0072] The binder may advantageously be chosen from fluorinated binders, in particular polytetrafluoroethylene and polyvinylidene fluoride, polymers derived from carboxymethylcellulose, polysaccharides, and latices, in particular latexes of the styrene-butadiene rubber type.

[0073] The present invention also relates to an electrode for a battery, preferably for a Li-ion or Na-ion battery, more preferably for a Na-ion battery, which comprises at least one material of formula (I) according to the present invention.

[0074] The electrode according to the invention may be the positive electrode of a lithium generator or a sodium generator.

[0075] Advantageously, the electrode according to the invention is a positive electrode for a sodium or sodium-ion secondary battery.

[0076] The electrodes may be deposited on an electronically conductive current collector, which may be aluminium.

[0077] Preferably, the material of formula (I) represents between 10% and 95% by weight of the total weight of the electrode, in particular more than 40% by weight and more particularly between 80% and 95% by weight relative to the total weight of said electrode.

[0078] The present invention also relates to a battery, preferably a Li-ion or Na-ion battery, more preferably a Na-ion battery, comprising as electrode active material, preferably as positive electrode active material, at least one material of formula (I) according to the present invention.

[0079] A sodium secondary battery according to the invention may more particularly comprise a positive electrode according to the invention and a negative electrode, for example made of disordered carbon, which, in contrast to lithium secondary batteries, may be deposited on an aluminum current collector, taking into account the fact that sodium ions, unlike lithium ions, do not react with aluminum to form an alloy.

[0080] The negative electrode material, more specifically, has a low specific surface area (<10 m 2 1 / g) and a particle size of about 1 micrometer to about 10 micrometers. This can be selected from hard carbon (non-graphitizable carbon) or soft carbon (graphitizable carbon).

[0081] In this text, the expressions "of" and "in the range of" and "varying from" are equivalent and are intended to mean that the limit is included, unless specifically stated otherwise. [Brief description of the drawings]

[0082] [Figure 1] Figure 1 shows in situ synchrotron X-ray powder diffraction patterns recorded every 3°C as a Na3V2(PO4)3 / Na1V2(PO4)3 mixture (1:1 molar ratio) was heated to 500°C and then cooled to 35°C. [Diagram 2] A series of XRD patterns of several mixtures of Na3V2(PO4)3 and Na1V2(PO4)3 before heat treatment measured at 25 °C (left), and a series of XRD patterns of single phase NaxV2(PO4)3 measured at 25 °C after heat treatment up to 500-550 °C (right). [Diagram 3]Graph showing the evolution of the V / Z ratio (right) and c / a ratio (left) as a function of x for conventional Na3V2(PO4)3 and Na1V2(PO4)3, and the electrochemically observed NaxV2(PO4)3 phase of Na2V2(PO4)3, improved by full pattern matching. [Figure 4] FIG. 1 shows XRD patterns of the material of formula (I) according to the present invention with x=2 (top) and electrochemically observed Na2V2(PO4)3 (bottom) collected in an in situ cell during cycling. [Diagram 5] Schematic diagram of the material of formula (I) with x=2 according to the present invention (left) and the crystal structure of Na2V2(PO4)3 observed electrochemically (right). [Figure 6] Graph of voltage (V vs Na+ / Na) as a function of specific capacity (mAh / g) for the first two cycles of a NaxV2(PO4)3 (according to the invention) / Na metal half-cell with x=2 (left) and specific discharge capacity as a function of cycle number (right). [Figure 7] Operando XRD patterns of Na2V2(PO4)3 according to the present invention as a cathode material in a half-cell against Na metal during charge and discharge at a C-rate of 0.1C (~1 Na+ in 10 h) in the voltage window of (a) 2.5-4.4 V and (b) 1.3-3.0 V vs. Na+ / Na. [Figure 8] Graphs depicting the evolution of (a) unit cell volume per formula unit (V / Z), (b) c / a ratio, (c) total number of Na+ per formula unit, and (d) Na occupancy of Na1 and Na2 sites as a function of scan number. [Figure 9] Figure 13 shows the results of operando XRD measurements during charge and discharge at a C rate of 0.1C (~1 Na+ in 10 h) in the voltage window of (a) 2.5-4.3 V vs. Na+ / Na using conventional Na3V2(PO4)3 as the cathode material in a half-cell against Na metal. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0083] The present invention will be described in more detail in the following examples, but the present invention is not limited to said examples.

[0084] Example 1 Preparation of materials of formula (I) 1.1. Materials of formula (I) can be prepared from mixtures of Na3V2(PO4)3 and Na1V2(PO4)3.

[0085] Synthesis of Na3V2(PO4)3 The synthesis of Na3V2(PO4)3 can be carried out in two steps. First, carbon-coated VPO4 was synthesized by mixing stoichiometric amounts of V2O5 (Alfa Aesar, 99.6%), H3PO4 (Alfa Aesar, 85% in water), and agar (Fisher BioReagents) in deionized water. The solution was stirred overnight at 80 °C in an oil bath and then dried overnight in an oven at 250 °C. The resulting dried powder was ground and placed in a furnace at 890 °C for 2 h under Ar atmosphere with a heating ramp of 5 °C / min. Next, Na3PO4 (Acros organics, 96%) was mixed with the resulting VPO4 in a molar ratio of 1:2 and then heated to 800 °C for 2 h under Ar atmosphere with a heating ramp of 5 °C / min.

[0086] Synthesis of Na1V2(PO4)3 To prepare Na1V2(PO4)3, chemical oxidation of Na3V2(PO4)3 was carried out. Na3V2(PO4)3 was dispersed in acetonitrile (Sigma-Aldrich, 99.8%) using a magnetic stirrer, and the oxidant, nitronium tetrafluoroborate (NO2BF4, Sigma-Aldrich, 95%) in 0.1 M solution in acetonitrile, was added dropwise to the dispersed Na3V2(PO4)3 to carry out the following reaction: Na3V2(PO4)3+2NO2BF4→Na1V2(PO4)3+2NaBF4+2NO2↑

[0087] The resulting solution was stirred overnight and then filtered and washed with acetonitrile.

[0088] Nax Synthesis of V2(PO4)3 Na x V2(PO4)3 can be obtained according to the following chemical reaction: pNa3V2(PO4)3+(1-p)Na1V2(PO4)3→Na 1+2p V2(PO4)3

[0089] The desired molar ratio of Na3V2(PO4)3 and Na1V2(PO4)3 powders were thoroughly mixed in an Ar-filled glove box and preferably pelletized. The resulting powder was then sealed in a gold tube and then heat-treated at 500°C for 12 hours.

[0090] 1.2. The material of formula (I) according to the present invention can also be prepared by controlling the oxidizing agent during the chemical oxidation process of Na3V2(PO4)3 instead of mixing the two materials (Na1V2(PO4)3 and Na3V2(PO4)3) in different ratios.

[0091] Na3V2(PO4)3 was dispersed in acetonitrile (Sigma-Aldrich, 99.8%) using a magnetic stirrer, and the desired amount of a 0.1 M solution of nitronium tetrafluoroborate (NO2BF4, Sigma-Aldrich, 95%) in acetonitrile was introduced dropwise to the dispersed Na3V2(PO4)3 for the following reaction: Na3V2(PO4)3+xNO2BF4(0 <x<2)→Na 3-x V2(PO4)3+xNaBF4+xNO2↑

[0092] The resulting solution was stirred overnight and then filtered and washed with acetonitrile.

[0093] The same considerations apply to the two-phase process of Na, at operating voltages that depend on the nature of the redox couples involved in the reduction or oxidation of V and / or M. + The general formula A x V 2-y-z M y M' zThis also applies to materials with the formula Na1Ti2(PO4)3 (references 1-6). For example, Na1Ti2(PO4)3 and Na3Ti2(PO4)3 are known to exist (y=2), and can be converted by chemically oxidizing or reducing one of the two to the other, or electrochemically by + The same applies to Na3AlV(PO4)3 and Na1AlV(PO4)3 (y=0, z=1), NbTi(PO4)3 and Na2NbTi(PO4)3 (y=2), Na3FeV(PO4)3 and Na1FeV(PO4)3 (y=1). These final members can be isolated, mixed and heated to produce new Na x V 2-y-z M y M' z It is possible to produce a (PO4)3 single-phase material. (References) (1) Masquelier, C.; Croguennec, L. Polyanionic (phosphates, silicates, sulphates,..) frameworks as electrode materials for rechargeable Li (or Na) batteries, Chem. Rev., 113(8), 6552-6591 (2013) (2) F. Lalere, V. Seznec, M. Courty, JN Chotard & C. Masquelier, Improving the energy density of Na3V2(PO4)3- type positive electrodes through V / Al substitution, J. Mater. Chem. A, 3, pp. 16198-16205 (2015) (3) Aragon, M. J.; Lavela, P.; Alcantara, R.; Tirado, J. L. Effect of Aluminum Doping on Carbon Loaded Na3V2(PO4)3as Cathode Material for Sodium-Ion Batteries. Electrochim. Acta 2015, 180, 824-830. https: / / doi.org / 10.1016 / j.electacta.2015.09.044 (4) Liang, L.; Li, X.; Zhao, F.; Zhang, J.; Liu, Y.; Hou, L.; Yuan, C. Construction and Operating Mechanism of High-Rate Mo-Doped Na3V2(PO4)3@C Nanowires toward Practicable Wide-Temperature-Tolerance Na-Ion and Hybrid Li / Na-Ion Batteries. Adv. Energy Mater. 2021, 11 (21), 1-17. https: / / doi.org / 10.1002 / aenm.202100287 (5) Liu, X.; Feng, G.; Wang, E.; Chen, H.; Wu, Z.; Xiang, W.; Zhong, Y.; Chen, Y.; Guo, X.; Zhong, B. Insight into Preparation of Fe-Doped Na3V2(PO4)3@ C from Aspects of Particle Morphology Design , Crystal Structure Modulation , and Carbon Graphitization Regulation. ACS Appl. Mater. Interfaces 2019, 11, 12421-12430. https: / / doi.org / 10.1021 / acsami.8b21257. (6) Zakharkin, MV; Drozhzhin, OA; Ryazantsev, SV; Chernyshov, D.; Kirsanova, MA; Mikheev, IV; Pazhetnov, EM; Antipov, EV; Stevenson, KJ; Antipov, V.; Stevenson, KJ Electrochemical Properties and Evolution of the Phase Transformation Behavior in the NASICON-Type Na 3+x Mn x V 2-x (PO4)3(0≦x≦1) Cathodes for Na-Ion Batteries. J. Power Sources 2020, 470 (February), 228231. https: / / doi.org / 10.1016 / j.jpowsour.2020.228231.

[0094] Example 2 In-situ monitoring of the formation of materials of formula (I) As shown in Figure 1, the reaction of Na3V2(PO4)3 and Na1V2(PO4)3 in Example 1.1 was monitored by in situ temperature-controlled synchrotron XRD patterns. The data was collected in Debye-Scherrer geometry at a wavelength of 0.9529 Å using a 0.5 mm diameter capillary. A mixture of Na3V2(PO4)3 and Na1N2(PQ4)3 in a 1:1 molar ratio was heated to 500°C and then cooled to 35°C while collecting XRD patterns every 3°C. During heating, the entire XRD reflection peaks of the two phases of Na3V2(PO4)3 and Na1V2(PO4)3 shifted to lower angles mainly due to thermal expansion. When the temperature exceeded about 300°C, the two phases began to disappear and a new single phase was formed at the same time, and reaction 1 was completely completed at 500°C. During cooling, the XRD reflection peaks of the new single-phase material were maintained without phase separation down to 35° C., with a slight peak shift to higher angles due to thermal shrinkage.

[0095] Example 3 Structural characterization of materials of formula (I) Using the method described in Example 1.1, several materials of formula (I) with different compositions were prepared and compared with the two final members Na3V2(PO4)3 and Na1V2(PO4)3, as shown in Figure 2. Laboratory X-ray diffraction was performed on a PANalytical X'Pert Pro diffractometer using Co Kα1,2 Radiation was used in reflection geometry. Before heat treatment, two mixed phases with different ratios of Na3V2(PO4)3 and Na1V2(PO4)3 appeared in the XRD patterns. The XRD reflection peaks from various compositions do not shift, but the intensity changes for different molar ratios as shown in Figure 2a. However, after heat treatment, the two mixed phases become a single phase. Also, Na x In V2(PO4)3, as x increases from 1 to 3, the reflection peak shifts to lower angles.

[0096] This is further confirmed by structural analysis using full pattern matching, shown in Figure 3. x In V2(PO4)3, Na + As the number of increases from 1 to 3, the unit cell volume per formula unit (V / Z) gradually increases and the c / a ratio tends to decrease. For comparison purposes, the V / Z and c / a ratios of conventional Na3V2(PO4)3, Na2V2(PO4)3, and NaV2(PO4)3 are also shown.

[0097] Example 4 Comparison of the structure of the material of formula (I) according to the present invention with that of the electrochemically observed material Na2V2(PO4)3 To observe the electrochemistry of the material Na2V2(PO4)3, operando synchrotron XRD measurements were performed in Debye-Scherrer geometry (λ = 0.8266 Å) using an in situ coin cell with a glass window. Each synchrotron XRD pattern was collected every 30 min with a 2θ angle range of 2-40°, a 2θ step size of 0.006°, and an acquisition time of 3.5 min using a MYTHEN detector. The working electrode consisted of Na3V2(PO4)3 powder and carbon black (mass ratio 80 / 20), and Na metal was used as the counter / reference electrode. The assembled coin cell was measured at 0.77 C with a voltage window of 2.0-4.3 V vs. Na + / Na (1C = 58.2 mA / g, i.e. 1Na + / 1e - replacement takes approximately 9 hours).

[0098] Figure 4 shows a comparison of the XRD patterns of the material of formula (I) according to the present invention with x = 2 (collected in a capillary) and electrochemically observed Na2V2(PO4)3 collected in an in situ cell during cycling according to the procedure described above. -1 The difference in the Bragg peaks at clearly indicates that the two structures are different.

[0099] 5 shows the crystal structure of the material of formula (I) according to the invention with x=2 (left) and a schematic diagram of the electrochemically observed Na2V2(PO4)3 (right). A clear difference between the two structures is that the Na sites (sites where Na can be inserted and deinserted) are not in the same position and do not have the same occupancy.

[0100] The following table summarizes the main parameters defined by the structure analysis using the Rietveld method for the material of formula (I) according to the invention with x=2 and for Na2V2(PO4)3 observed electrochemically.

[0101] [Table 1]

[0102] Example 5 Electrochemical evaluation of materials of formula (I) The electrochemical performance of the material of formula (I) where x=2 was tested in a half-cell configuration in a CR2032 type coin cell. The positive electrode consisted of the active material of formula (I) where x=2, carbon black, and poly(vinylidene difluoride) in a mass ratio of 73 / 18 / 9. The electrodes were dried at 80 °C under vacuum for at least 12 hours before cell assembly. The cell assembly used a sheet of Whatman glass fiber (GF / D) as the separator, and the electrolyte consisted of 1 M NaPF6 in ethylene carbonate (EC) / dimethyl carbonate (DMC) (1:1, w / w) containing 2 wt% fluoroethylene carbonate (FEC). The assembled coin cell was tested at 0.1 C with a voltage window of 2.5-4.3 V vs. Na + / Na cycled.

[0103] As shown in FIG 6, the initial charge and discharge capacities were 109.3 and 104.4 mAh / g, respectively, and the irreversibility was 4.5%. The voltage profile of the next cycle was very similar to that of the first cycle, and the Na2V2(PO4)3 of the present invention + This indicates that the extraction / insertion of is highly reversible.

[0104] Example 6 Na + Evolution of the structure of the material of formula (I) during extraction / insertion of An in situ cell with beryllium windows was used, and Cu Kα1,2 Operando X-ray diffraction measurements were performed on a PANalytical Empyrean diffractometer equipped with a 1000 Hz radiation source. Each XRD pattern was collected hourly over a 2θ angle range of 12-40° with a 2θ step size of 0.0167°. The working electrode consisted of Na2V2(PO4)3 powder of the material of formula (I) and carbon black (80 / 20 by weight), with Na metal used as the counter / reference electrode. The same separator and electrolyte as in the coin cell test were used for the operando experiments in Example 5. 2.5-4.4 V and 1.3-3.0 V vs. Na + Two different voltage regions of / Na were investigated, and the electrochemical reaction rate was 0.1 C (1Na + / 1e- The analysis of the XRD data was carried out using the Rietveld method with the Fullprof Suite.

[0105] As shown in Figure 7, the XRD reflection peaks are 2.5 V to 4.4 V and 1.3 V to 3.0 V vs. Na + The voltage windows for both Na / Na shift continuously during cycling, confirming the solid solution mechanism. The evolution of the peak shift during charge and discharge is symmetrical, whereas the voltage windows for Na / Na shift continuously during cycling, confirming the solid solution mechanism. + This indicates that the extraction / insertion mechanism of Na2V2(PO4)3 remains unchanged. Also, the XRD pattern of Na2V2(PO4)3 obtained after the first cycle looks similar to the initial one, implying that the overall electrochemical reaction is highly reversible.

[0106] 2.5~4.4V vs Na + Rietveld refinement from operando XRD measurements when cycled with ZnO / Na further confirms that the electrochemical reactions during charge and discharge are symmetric and reversible, as shown in Figure 8. The unit cell volume of the initial material of formula (I) and the unit cell volume at the end of charge are 236.35(2) Å, respectively. 3 and 222.92(2)Å 3 The volume change is about 5.7%. This is because the volume change is about 5.7% for a similar number of Na + This is lower than the volume change (about 8.2%) of conventional Na3V2(PO4)3 when it participates in the electrochemical reaction. The ratio of parameters c and a increases until near the middle of charging (~12 scans) and then decreases until the end of charging.

[0107] Na + The occupancy rate of Na in the structure + The total number of Na gradually decreases during charging and increases during discharging. + The main contribution to the decrease in the number of Na(2) sites is the decrease in the occupancy of the Na(1) sites. After that, the occupancy of the Na(1) sites decreases rapidly until the end of charging, resulting in a decrease in the total Na(2) sites. + is further decreased (see FIG. 5 for the localization of Na1 and Na2 sites in the crystal structure of the material according to the invention).

[0108] (Example 7 (Comparison)) Electrochemical and structural characterization of conventional Na3V2(PO4)3 A conventional Na3V2(PO4)3 electrode was used, and Mo Kα1,2 Using radiation, 2.5 to 4.3 V vs. Na + / Na, and the same C rate of 0.1C (= 1 Na in 10 hours) + Operando X-ray diffraction measurements for comparison, where the material of formula (I) according to the invention is compared to the conventional Na3V2(PO4)3 Na + The insertion / extraction mechanism is different and shows the typical characteristics of a two-phase reaction between Na3V2(PO4)3 and Na1V2(PO4)3, where during charging the Na3V2(PO4)3 phase decreases while Na1V2(PO4)3 appears, and during discharging the phases appear / disappear. This phenomenon can be seen in Figure 9, where the diffraction peaks corresponding to the (104), (110), and (113) reflections from the two final members Na1V2(PO4)3 and Na3V2(PO4)3 clearly indicate a two-phase mechanism, unlike the material of formula (I) of the present invention.

[0109] The lattice volumes of Na3V2(PO4)3 and Na1V2(PO4)3 are 239.903(17) Å, respectively. 3 and 220.105(8)Å 3 and the volume change is approximately 8.2%, as outlined in the table below.

[0110] [Table 2]

Claims

1. Formula (I): A x V (2-y-z) M y M' z (PO 4 ) 3 (I) [In the formula, A is Na or Li, or a mixture of Na and Li; 1<x<3、 0≦y≦1、 0≦z≦1, M is an electroactive transition element or a mixture of at least two electroactive transition elements; M' is a non-electroactive element or a mixture of at least two non-electroactive elements. The material is 212Å 3 ~246Å 3 The V / Z ratio changes with However, when x=2, the V / Z ratio is 232Å. 3 ~239Å 3 The materials change with time.

2. A=Li, V / Z ratio is 212 Å 3 ~225Å 3 The material of claim 1, wherein

3. A=Na, V / Z ratio is 219 Å 3 ~246Å 3 The material of claim 1, wherein

4. 4. The material of claim 3, wherein when x=2, the V / Z ratio is 235 Å. 3 ~238Å 3 The materials change with time.

5. 5. The material according to claim 3 or 4, wherein x varies from 1.5 to 2.

5.

6. V / Z ratio is 234Å 3 ~239Å 3 The material according to any one of claims 3 to 5, wherein

7. 7. The material according to any one of claims 3 to 6, described by a hexagonal unit cell and exhibiting lattice parameters a and c, the c / a ratio varying from 2.510 to 2.

545.

8. 8. The material according to any one of claims 3 to 7, described using a rhombohedral (R-3c) crystal structure having two types of sodium sites, Na(1) and Na(2), the average packing fraction of the Na(1) sites being between 0.2 and 0.95 in the unit cell and the average packing fraction of the Na(2) sites being between 0 and 0.9 in the unit cell.

9. 9. The material according to any one of claims 1 to 8, which is a single-phase material.

10. A method for preparing a material of formula (I) according to any one of claims 1 to 9, comprising the steps of: a) A 3 V (2-α) Z α (PO 4 ) 3 and A 1 V (2-β) Z' β (PO 4 ) 3 and, preferably under an inert atmosphere, to obtain an initial mixture; A=Li or Na or a mixture of Na and Li; Z and Z' are metallic elements independently selected from electroactive transition elements, non-electroactive elements, and mixtures thereof; 0≦α<1 and 0≦β<1; b) heating the initial mixture at a temperature between 300° C. and 700° C., preferably under an inert atmosphere or under vacuum; A method comprising:

11. In the initial mixture, Na 3 V (2-w) M' w (PO 4 ) 3 has a molar fraction of p, and Na 1 V (2-z) M'' z (PO 4 ) 3 has a molar fraction of (1 - p), where 0 < p < 1. The method according to claim 10.

12. A method for preparing a material of formula (I) according to any one of claims 1 to 9, comprising the steps of: 1) A 3 V (2-y-z) M y M' z (PO 4 ) 3 in a solvent, preferably an organic solvent, A is Na or Li, or a mixture of Na and Li; 0≦y<1、 0≦z<1, M is an electroactive transition element or a mixture of at least two electroactive transition elements; M' is a non-electroactive element or a mixture of at least two non-electroactive elements; 2) A 3 V (2-y-z) M y M' z (PO 4 ) 3 adding an oxidizing agent to the dispersion; 3) stirring the resulting mixture; 4)1 <x<3であるA x V (2-y-z) M y M' z (PO 4 ) 3 and A method comprising:

13. 10. Use of a material of formula (I) according to any one of claims 1 to 9 as an electrode active material for a battery, preferably as a positive electrode active material for a Li-ion or Na-ion battery, more preferably for a Na-ion battery.

14. 10. An electrode for a battery, preferably for a Li-ion or Na-ion battery, more preferably for a Na-ion battery, comprising at least one material of formula (I) according to any one of claims 1 to 9.

15. 10. A battery, preferably a Li-ion or Na-ion battery, more preferably a Na-ion battery, comprising as electrode active material, preferably as positive electrode active material, at least one material of formula (I) according to any one of claims 1 to 9.

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