Lithium phosphate niobium bronzoids and bronzes

Abstract

The present disclosure concerns lithium-phosphate niobium bronzoTds and bronzes having either of the following formula: Li2Nb4P2O16 or LiNb3P2O13 and the process for their manufacture, comprising the following steps: Providing a sodium-phosphate niobium bronzoid or bronze; mixing and grinding the sodium-phosphate niobium bronzoid or bronze with a Li-comprising precursor to obtain a mixture M2; pelletizing the mixture M2 to obtain a pellet P2; annealing the pellet P2; grinding the pellet to obtain a powder W2; washing and drying the powder W2.

Description

DescriptionLITHIUM PHOSPHATE NIOBIUM BRONZOIDS AND BRONZESTECHNICAL FIELD

[0001] The present disclosure relates to sodium-phosphate niobium bronzoid and bronzes and lithium-phosphate niobium bronzoids and bronze, in particular as compounds for electrode materials for batteries. The present disclosure further relates to methods for the preparation of these bronzoids and bronzes. The present disclosure further relates to the use of these phosphate niobium bronzoids and bronzes as anode materials and as materials suitable for supercapacitors and to batteries comprising such bronzoids and bronzes as anode material.BACKGROUND ART

[0002] Lithium-ion batteries (LIBs) are a key player for multiscale-system power sources, ranging from portable electronic devices to transportation electric vehicles. It is, however, well known that the capacity of commercial graphite anode is insufficient for meeting ever increasing human desires for longer mileages per charge. It is not surprising that intensive efforts are still actively attempted to search for new anodic materials of ultrahigh lithium capacity and long-term durability as alternatives to graphite. [Applied Surface Science (2023), 640, 158424]

[0003] LIBs are the most widely used energy storage devices to power portable electronic devices and electric vehicles, owing to their high energy density, long-service life, and environmental friendliness. Graphite with low cost and high capacity is a common anode material used in commercial LIBs, but has the underlying Li dendrite issue, especially under high rates, that severely impedes the enhancement of fast-charging LIBs. Metal oxides with intercalation-type lithium storage mechanism are considered as an alternative anode material for safe and fast-charging LIBs due to the reduced risk of Li dendrite at low voltages [Journal of Power Sources (2023), 564, 232672],

[0004] Some phosphate niobium bronzes and bronzoids as Na4NbsP4O32, Na3CaNb7MP4O32 (M = Ti, Zr, Sn), Na2Ca2Nb7MP4O32 (M = Al, Fe), Na3ANb7TiP4O32 (A = Sr, Ba) and Na3BaNbsP4O32 are known, which confirms the ability of niobium to form bronzes and bronzoids with the MPTBp (monophosphate tungsten bronzes with pentagonal tunnels (MPTBp)) structure. [Mat. Res. Bull., Vol. 26, pp. 1051 -1057, 1991.]

[0005] One niobium phosphate bronze Na3Nb7P4O29 as a representative of the monophosphate niobium bronzes with pentagonal tunnels, with the general formula Nax(NbO3)2m(PO2)4, belonging to the MPTBp’s structural family was disclosed previously. [Journal of Solid-State Chemistry, 101 , 137- 144 (1992)]. A Niobium phosphate bronze with a formula Na2NbeP4O26 was also disclosed [Journal of Solid-State Chemistry 95, 245-252 (1991 )].

[0006] Niobium-based oxides have recently attracted great attention as anode material for LIBs because of high theoretical capacity, high working potential and outstanding rate performance. Nevertheless, the practical capacity of niobium-based oxides still cannot meet the demand for electrical energy storage applications in electric vehicles for low conductivity and poor ion transfer. [Chemical Engineering Journal (Amsterdam, Netherlands) (2020), 384, 123314], Wadsley-Roth phase niobium titanium oxide (TiNb2O?) is widely regarded as a promising anode candidate for fast-charging lithium- ion batteries due to its safe working potential and doubled capacity in comparison to the commercial fast-charging anode material (lithium titanium oxide, Li4TisOi2). Although good fast charge / discharge performance was shown for nanostructured TiNb2O?, the small size would cause low energy density of batteries, as well as parasitic reactions. [Renming Zhan et all. Materials Horizons (2023), 10(11 ), 5246-5255], TiNb2O? (TNO) is regarded as a promising anode candidate for lithium-ion batteries due to its high capacity and suitable lithiation potential to avoid Li plating issue, but it suffers from the poor rate capability.

[0007] There is a need to develop high energy and high-rate anode materials, providing a better fast-charging capability for lithium-ion batteries.

[0008] It is an object of the present disclosure to provide new phosphate niobium bronzoids and bronzes which are safer compared to Si and graphite allowing high power, high-rate anode material.

[0009] It is a further object of the present disclosure to provide a method for preparing said phosphate niobium bronzoids and bronzes.

[0010] It is a further object of the present disclosure to provide a battery comprising new phosphate niobium bronzoids and bronzes as anode materials and / or as materials suitable for supercapacitors and / or hybrid supercapacitors.SUMMARY

[0011] In a first aspect, the present disclosure concerns a sodium-phosphate niobium bronzoid or bronze having a general formula (I) Nax(PO2)2(NbO3)m where 0<x<16; 1<m<6, wherein: a. when x=2 and m=4, the sodium-ion niobium based compound is crystallized in the monoclinic space group P2i / c with lattice constants a = 19.080 (7) A, b = 5.349 (2) A, c = 13.250 (5) A, |3 = 109.957 (17), V = 1271 .2 A3(8) and V / Z = 317.8 A3(8). b. when x= 1 and m= 3, the sodium-ion niobium based compound is crystallized in the orthorhombic space group P2i2i2 with lattice constants a = 19.827 (4) A, b = 14.425 (3) A, c = 5.388 (13) A, V = 1541.2 A3(13) and V / Z = 256.8 A3(13).

[0012] Here within, the lattice constants are reported with standard deviation values. The values inside the bracket correspond to the standard deviation (±) of the last digit after the decimal point to the mentioned parameters.

[0013] To the best knowledge of the inventors, these sodium-phosphate niobium bronzoids or bronzes of this composition and crystal structure had not been reported yet. In particular, a new crystal structure was found for Na2Nb4P20i6 (x=2, m=2).

[0014] Sodium-phosphate niobium bronzoids and bronzes of the present disclosure were found to be useful as anode materials, but were also found to be useful intermediary products in the manufacture of Sodium-phosphate niobium bronzoids or bronzes.

[0015] In a second aspect, the present disclosure concerns a method for the manufacture of sodium-phosphate niobium bronzoids and bronzes having a general formula (I) Nax(PO2)2(NbO3)m where 0<x<16; 1 <m<6, comprising the following steps: a. annealing a mixture of precursors M1 ; b. grinding the annealed mixture M1 ; c. pelletizing the ground mixture M1 to obtain a pellet P1 ; d. annealing the pellet P1 ; wherein M1 comprises a niobium precursor, a phosphate precursor, and a sodium precursor.

[0016] In a third aspect, the present disclosure concerns a lithium-phosphate niobium bronzoid or bronze having a general formula (II) Lix(PO2)2(NbO3)m where 0<x<16; 1<m<6.

[0017] In a lithium-phosphate niobium bronzoid or bronze of the present disclosure, when x=2 and m=4, the lithium-phosphate niobium bronzoid or bronze is crystallized in the orthorhombic space group Pna2i with lattice constants a = 17.423 (9) A, b = 6.710 (4) A, c = 5.194 (3) A, V = 606.4 A3(10) and V / Z = 303.2 A3(10); and

[0018] In a lithium-phosphate niobium bronzoid or bronze of the present disclosure, when x=1 and m=3, the lithium-phosphate niobium bronzoid or bronze is crystalized in the orthorhombic space group P2i2i2 with lattice constants a = 19.511 (8) A, b = 14.252 (6) A, c = 5.330 (4) A, V = 1481 .9 A3(9) and V / Z = 246.9 A3(9).

[0019] In a fourth aspect, the present disclosure concerns a method for the manufacture of lithium-phosphate niobium bronzoids and bronzes having a general formula (II) Lix(PO2)2(NbO3)m where 0<x<16; 1 <m<6, comprising the following steps: a. Providing a sodium-phosphate niobium bronzoid or bronze, in particular obtained by the method above; b. Mixing and grinding the sodium-phosphate niobium bronzoid or bronze with a Li-comprising precursor to obtain a mixture M2; c. Pelletizing the mixture M2 to obtain a pellet P2; d. Annealing the pellet P2; e. Grinding the pellet to obtain a powder P2 f. Washing and drying the powder P2;

[0020] The present disclosure further concerns battery anode materials comprising sodium-phosphate niobium bronzoids or bronzes or lithium-phosphate niobium bronzoids or bronzes of the present disclosure or manufactured according to a method of the present disclosure, as well as batteries, in particular rechargeable batteries, comprising these battery anode materials.

[0021] It was found that the sodium-phosphate niobium bronzoids or bronzes or lithium- phosphate niobium bronzoids or bronzes of the present disclosure can be used in anode materials in batteries, in particular rechargeable batteries. Both Na and Li compounds are safer compared to Si and graphite and provide a high power.

[0022] Lithium-phosphate niobium bronzoids or bronzes were found to have higher reversible capacity and energy density than sodium-phosphate niobium bronzoids or bronzes

[0023] In a further aspect, the present disclosure discloses a method for preparing the new phosphate niobium bronzoids and bronzes.BRIEF DESCRIPTION OF THE FIGURES

[0024] Further features and advantages of the disclosure can be ascertained from the following detailed description that is provided in connection with the Figure described below:

[0025] Figure 1 : X-ray powder diffraction pattern of Na2Nb4P20i6.

[0026] Figure 2: X-ray powder diffraction pattern of Li2Nb4P20i6.

[0027] Figure 3: X-ray powder diffraction pattern of NaNb3P20i3.

[0028] Figure 4: X-ray powder diffraction pattern of LiNb3P20i3. With the experimental data (circles) overlayed with calculated pattern (black line), Bragg positions ( | ) and difference curve (bottom line).

[0029] Figure 5: Cell-1 Voltage vs. Capacity profile of Na2Nb4P20i6 vs. Na.

[0030] Figure 6: Cell-2 Voltage vs. Capacity profile of Na2Nb4P20i6 vs. Li.

[0031] Figure 7: Cell-3 Voltage vs. Capacity profile of Li2Nb4P20ievs. Li.

[0032] Figure 8: Cell-4 Voltage vs. Capacity profile of NaNbsP20i3 vs. Li.

[0033] Figure 9: Cell-5 Voltage vs. Capacity profile of LiNbsP20i3 vs. Li.DETAILED DESCRIPTION

[0034] In the following detailed description, preferred embodiments are described in detail to enable practice of the disclosure. Although the disclosure is described with reference to these specific preferred embodiments, it will be understood that the disclosure is not limited to these preferred embodiments. To the contrary, the disclosure includes numerous alternatives, modifications and equivalents as will become apparent from consideration of the following detailed description and accompanying figures.

[0035] The term “comprising”, as used herein and in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It needs to be interpreted as specifying the presence of the stated features,integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression “a composition comprising components A and B” should not be limited to compositions consisting only of components A and B. It means that with respect to the present disclosure, the only relevant components of the composition are A and B. Accordingly, the terms “comprising” and “including” encompass the more restrictive terms “consisting essentially of” and “consisting of”.

[0036] Due to the similar size of niobium (ionic radii of Nb5+in octahedral coordination ~0.64 A) and tungsten (ionic radii of W6* in octahedral coordination ~0.6 A), for the class of materials named “Monophosphate Tungsten Bronzes (MPTB)”, it makes possible to form isotopic compounds that similarly occupy octahedral coordination. Thus, replacing tungsten (W1) with niobium (Nbv) results in structures that are similar to MPTB with the addition of foreign alkali metal cation(s), yielding the general formula Ax(PO2)2(NbO3)m known as "Bronzoids” or “Bronzes” depending on the mixed-valence (or not) of the niobium.

[0037] 'About" as used herein referring to a measurable value such as a parameter, an amount, a temporal duration, and the like, is meant to encompass variations of + / -20% or less, preferably + / -10% or less, more preferably + / -5% or less, even more preferably + / - 1 % or less, and still more preferably + / -0.1 % or less of and from the specified value, in so far such variations are appropriate to perform in the present disclosure. However, it is to be understood that the value to which the modifier "about" refers is itself also specifically disclosed.

[0038] As used herein, the term “and / or,” when used in a list of two or more items, means that any one of the listed items can be employed by itself, or any combination of two or more of the listed items, can be employed. For example, if a composition is described as containing components A, B, and / or C, the composition can contain A alone; B alone; C alone; A and B in combination; A and C in combination; B and C in combination; or A, B, and C in combination.

[0039] As used herein, a range of values “between X and Y” and “from X to Y” includes the endpoints of X and Y.

[0040] Table 1 illustrates the differences in crystal structure between the sodium-ion bronzoid or bronze Na2Nb4P20i6 reported in prior art and the sodium-ion bronzoid orbronze Na2Nb4P20i6 of the present disclosure, as well as the crystal structure of the lithium-ion bronzoid or bronze Li2Nb4P20i6 of the present disclosure obtained from the sodium-ion bronzoid or bronze Na2Nb4P20i6 of the present disclosure.

[0041] Inventors were able to synthesize the new material LiNbsP20i3 and were able to perform electrochemical testing. The new compound LiNbsP20i3 shows a better electrochemical performance in comparison to its Na analogue NaNb3P20i3.

[0042] Table 1 : Unit Cell parameters, Volume (V), Volume per formula Unit (V / Z), Density (g / cm3) for Na2Nb4P20i6 and Li2Nb4P20i6.The values inside the bracket correspond to the standard deviation (±) of the last digit after the decimal point to the mentioned parameters.

[0043] The crystal structure of the member m=4 of phosphate niobium bronzoid Na2Nb4P20i6, consists of ReC -type slabs which are four octahedra of NbOe, bordered by single PO4 tetrahedral units, forming rows of pentagonal tunnels along the b axis at the junction between octahedral slabs. Two sorts of “cages” exist in the structure: empty ones, built by one tetrahedron and seven octahedra and filled ones, built by four tetrahedra and eight octahedra, formed by corner sharing between PO4 tetrahedra with NbOe octahedral units.

[0044] Table 2: Unit Cell parameters, Volume (V), Volume per formula Unit (V / Z), Density (g / cm3) for NaNb3P20i3 and LiNb3P20i3.

[0045] The structure of the m=3 member of phosphate niobium bronzoid NaNb3P20i3, is composed of isolated PO4 tetrahedra connected to ReOs-type slabs of NbOe octahedra, generating pentagonal tunnels.

[0046] The second aspect of the present disclosure concerns a method for the manufacture of sodium-phosphate niobium bronzoids and bronzes having a general formula (I) Nax(PO2)2(NbO3)m where 0<x<16; 1 <m<6, comprising the following steps: a. Annealing a mixture of precursors M1 ; b. Grinding the annealed mixture of precursors; thereby the mixture is homogenized, in particular regarding particle size; c. Pelletizing the ground mixture M1 to obtain a pellet P1 ; d. Annealing the pellet P1 . wherein M1 comprises a niobium precursor, in particular a niobium oxide, preferably Nb2O5, a phosphate precursor, and a sodium precursor

[0047] In an embodiment of the method for the manufacture of sodium-phosphate niobium bronzoids and bronzes, the phosphate precursor is selected from NaH2PO4 and (NH4)2HPO4 and a mixture of NaH2PO4 and (NH4)2HPO4.

[0048] In an embodiment of the method for the manufacture of sodium-phosphate niobium bronzoids and bronzes, the sodium precursor is selected from NaH2PO4and Na2COs and a mixture of NaH2PO4and Na2CO3.

[0049] It may be noted that a single precursor may serve as Na precursor and phosphate precursor such as in the case of NaH2PO4. This does however not preclude the further addition of additional Na and / or phosphate precursors.

[0050] In an embodiment of the method for the manufacture of sodium-phosphate niobium bronzoids and bronzes, annealing M1 is performed at a temperature between 200 and 500°C for a duration of between 1 and 3h.

[0051] In an embodiment of the method for the manufacture of sodium-phosphate niobium bronzoids and bronzes, annealing M1 is performed in air and at ambient pressure.

[0052] In an embodiment of the method for the manufacture of sodium-phosphate niobium bronzoids and bronzes, annealing M1 is performed by heating the mixture at a rate of 0.6 to 1 °C / min up to a temperature of between 200°C and 500°C, and holding the mixture at that temperature for a duration of between 1 and 3h.

[0053] In an embodiment of the method for the manufacture of sodium-phosphate niobium bronzoids and bronzes, grinding of the annealed M1 is performed for a duration of 20 to 60 minutes. Any suitable grinding method may be used among those known to the person skilled in the art.

[0054] In an embodiment of the method for the manufacture of sodium-phosphate niobium bronzoids and bronzes, pelletizing of the ground mixture is performed a pressure of 5 ton for a duration of 5 to 10 minutes. .

[0055] In an embodiment of the present disclosure, annealing the pellet P1 is performed in air.

[0056] In an embodiment of the method for the manufacture of sodium-phosphate niobium bronzoids and bronzes, the annealing the pellet P1 is performed at a temperature of between 800 and 1200°C. The heat-up rate may range from 2 to 3 °C / min. The holding duration may range from 12 to 24 hours.

[0057] In a further aspect, the present disclosure provides a method for preparing a lithium-phosphate niobium bronzoids and bronzes comprising the steps of: a. Providing a sodium-phosphate niobium bronzoid or bronze; b. Mixing and grinding the sodium-phosphate niobium bronzoid or bronze with a Li-comprising precursor to obtain a mixture M2; c. Pelletizing the mixture M2 to obtain a pellet P2; d. Annealing the pellet P2; e. Grinding the pellet to obtain a powder W2;f. Washing and drying the powder W2.

[0058] In an embodiment of the method for preparing a Lithium-phosphate niobium bronzoids and bronzes, the sodium-phosphate niobium bronzoid or bronze has the general formula (I) Nax(PO2)2(NbO3)m where 0<x<16; 1 <m<6. It may in particular be obtained by the method for preparing sodium-phosphate niobium bronzoids and bronzes in any of its embodiments or combination of embodiments.

[0059] In an embodiment of the method for preparing a Lithium-phosphate niobium bronzoids and bronzes, the lithium comprising precursor is LiNO3

[0060] In an embodiment of the method for preparing a Lithium-phosphate niobium bronzoids and bronzes, the mixing and grinding step have a duration of 20 to 60 min. Mixing and grinding may be performed according to any suitable method known to the person skilled in the art.

[0061] In an embodiment of the method for preparing a Lithium-phosphate niobium bronzoids and bronzes, the pelletizing M2 is performed under a pressure of 5 tons for a duration of 5 to 10 minutes.

[0062] In an embodiment of the method for preparing a Lithium-phosphate niobium bronzoids and bronzes, annealing the pellet P2 is performed in air under ambient pressure and at a temperature ranging from 200 to 500°C at a temperature ramp-up rate of 0.6-1 °C / m in for a duration of 6 to 13 hours.

[0063] In an embodiment of the method for preparing a Lithium-phosphate niobium bronzoids and bronzes, washing W2 is performed using distilled water. The washing step helps to removed soluble salts such as the lithium containing precursor and / or any generated sodium salts.

[0064] In an embodiment of the method for preparing a Lithium-phosphate niobium bronzoids and bronzes, washing W2 is performed by 3 to 5 cycles of washing using distilled water and centrifugation, in particular at about 10,000 rpm for 10 to 15 minutes.

[0065] In an embodiment of the method for preparing a Lithium-phosphate niobium bronzoids and bronzes, drying W2 is performed at a temperature ranging from 60 to 80 °C, typically for 8 to 12 hours, for example overnight.

[0066] The inventors found that lithium-based phosphate niobium bronzoid and bronze compounds may be formed via an ionic exchange in molten-salt medium occurring whenusing the method of the present disclosure. Following this approach, the Na- niobium bronzoid and bronzes with Li-com prising precursor are mixed with a determined stochiometric ratio, formed into a pellet, and then heated, for example inside a muffle furnace, to the desired temperature in air. The partially-melted sample obtained is washed with water to eliminate traces of remaining salts to retrieve the pure product, which is dried and used for further studies.

[0067] In a further aspect, the present disclosure provides a negative electrode material, or anode material, comprising a lithium-phosphate niobium bronzoid or bronze having a general formula (II) Lix(PO2)2(NbO3)m where 0<x<16; 1 <m<6 or a sodium-phosphate niobium bronzoid or bronze having a general formula (I) Nax(PO2)2(NbO3)m where 0<x<16; 1 <m<4. The lithium-phosphate niobium bronzoid or bronze or a sodiumphosphate niobium bronzoid or bronze may be according to any embodiment or combination of embodiments of the present disclosure or obtained by a method for preparing sodium-phosphate niobium bronzoids and bronzes or lithium-phosphate niobium bronzoids and bronzes in any of its embodiments or combination of embodiments.

[0068] The present disclosure further concerns an energy storage device, such as a supercapacitor or a battery, in particular a rechargeable battery, comprising a negative electrode material, or anode material, according to the present disclosure.

[0069] In an embodiment of the present disclosure, the battery is a lithium-ion battery, preferably a lithium-ion rechargeable battery. Preferably the battery comprises a positive electrode comprising a cathode active material, a negative electrode comprising an anode active material according to the present disclosure, an electrolyte, and a separator.

[0070] An additional aspect of the present disclosure concerns the use of a battery according to the present disclosure in either one of a portable computer, a tablet, a mobile phone, an energy storage system (ESS), an electric vehicle (EV) or in a hybrid electric vehicle (HEV), preferably in an electric vehicle or in a hybrid electric vehicle.EXAMPLES and EXPERIMENTAL TESTS

[0071] The disclosure is described below in greater details with reference to examples, but the disclosure is not limited in any way by these examples, as long as it does not exceed the scope and spirit of the present disclosure.Experimental tests used in the examples

[0072] The following analysis methods are used in the Examples:

[0073] Powder X-ray Diffraction - The new compounds were subjected to PXRD investigations using a laboratory D8 Advance Broker diffractometer (CuKa radiation, = 1 .5418 A), at 298 K, in the 29 range of 5-70°, with a scan step width of 0.006° and a scan rate of 3.0 s / step. High quality XRD patterns were used for Rietveld refinement of the structures.

[0074] Synchrotron X-ray Diffraction - SXRPD patterns were recorded at an acquisition time of ~1.0 min in the 26 angular range of 0.5-70°, with a wavelength of 0.8265 A using Debye-Scherrer geometry with a MYTHEN detector at the MSPD beamline of the ALBA synchrotron.

[0075] X-ray energy dispersive spectroscopy - X-MAX 80 OXFORD instruments were used to examine the chemical composition of the new compounds and estimate the potential extent of Li exchange. The amount of Na (wt%) concentration is reduced significantly after the exchange process, from 5.00 (wt%) in Na2Nb4P20i6 to 0.29 (wt%) in Li2Nb4P20i6 respectively. The amount of Na (wt%) concentration is reduced significantly after the consecutive 2 exchange processes from 4.28 (wt%) in NaNbsP20i3 to 0.34 (wt%) in LiNb3P20i3.

[0076] Scanning Electron Microscopy & Scanning Electron Microscopy with Energy Dispersive X-ray Analysis (SEM & SEM-EDX) - Scanning electron microscopy (SEM, FEI Quanta 200F field emission scanning electron microscope) was used to study the shape and size of NaNb2PO8 / Na2Nb4P2Oie / NaNb3P2Oi3 and LiNb2PO8 / Li2Nb4P2Oie / LiNb3P2Oi3 powders.

[0077] The SEM images of Na2Nb4P20i6 and Li2Nb4P20i6 show non-homogenous distribution of particle sizes for both with an average value of ~3 pm. SEM images of NaNb3P20i3 and LiNb3P20i3 show non-homogenous distribution of particle sizes for both with an average value of ~3 pm.

[0078] Density measurement / Pycnometer - Micromeritics AccuPyc 1330 Gas (Helium) Pycnometer was used to determine the pycnometric density using cylindrical sample holders of dimensions 19 mm OD x 39.8 mm long x 0.254 mm wall (0.750 in. OD x 1 .570 in. long ±0.005 in. x 0.010 in. wall) for a standard (10 cm3) holder. At a temperature of 27.8°C, measurements were made for 28 minutes while introducing a pressure of 0.005 psig / min to achieve a pressure of 19.500 psig to record results. A total of 5 cycles with 20purges per cycle were carried out for Na2Nb4P20i6 (2.9 g) and Li2Nb4P20i6 (5.5 g); and for NaNbsP20i3 (1.8 g) and LiNbsP20i3 (4.4 g).

[0079] Table 3: Pycnometric DensityEXAMPLES

[0080] The present disclosure is further illustrated by the following examples. All the processes below were carried out in air (std atmospheric condition).Example 1 : Synthesis of Na2Nb4P2O16

[0081] Na2Nb4P20i6 was synthesized using a solid-state reaction method in air.

[0082] Nb205(1.44g) (Sigma-Aldrich, 99.9%) and NaH2PO4(0.65 g) (Merck, 98%) were taken in 1 :1 ratio, mixed using a mortar and pestle for 30 minutes (powders were used as received).

[0083] This powder sample was then transferred into an alumina crucible and annealed in air at 300 °C for 3 hours using a ramp rate of 0.6°C / min in a muffle furnace (Nabertherm). The resultant powder retrieved was again re-grinded for 30 minutes using a mortar and pestle to homogenize the mixture thoroughly.

[0084] This powder was then turned into a 13 mm-diameter pellet using a pellet maker (Eurolab) under a 5 ton of pressure for 10 minutes.

[0085] Following that, it was put into an alumina crucible to be annealed in air at 1000°C at a ramp rate of 2.3°C / min for 24 hours in a muffle furnace (Nabertherm).

[0086] The resultant pellet obtained after the reaction was ground into powder using a mortar and pestle before being subjected to further material and electrochemical analysis.Example 2: Synthesis of NaNb3P2O13

[0087] NaNb3P20i3 was synthesized using a solid-state reaction method in air.

[0088] Nb205(1.395g) (Sigma-Aldrich, 99.9%), Na2CO3(0.185 g) (Sigma Aldrich, > 99.5%) and (NH4)2HPO4 (0.924 g) (Sigma Aldrich, > 99.0%) were taken in 3:1 :4 ratio,mixed and grinded using a mortar and pestle for 30 minutes (powders were used as received).

[0089] This powder sample was then transferred into a porcelain crucible and annealed in air at 300 °C at a ramp rate of 0.6°C / min for 3 hours in a muffle furnace (Nabertherm). The resultant powder retrieved was again re-grinded for 30 minutes using a mortar and pestle to homogenize the mixture thoroughly.

[0090] This powder was then turned into a 13 mm-diameter pellet using a pellet maker (Eurolab) under 5 tons of pressure for 10 minutes.

[0091] Following that, it was put into an alumina crucible to be annealed in air at 600°C at a ramp rate of 1 ,38°C / min for 7 hours in a muffle furnace (Nabertherm).

[0092] The resultant powder retrieved was again re-grinded for 30 minutes using a mortar and pestle to homogenize the mixture thoroughly.

[0093] This powder was then turned into a 13 mm-diameter pellet using a pellet maker (Eurolab) under 5 tons of pressure for 10 minutes.

[0094] Following that, it was again put into an alumina crucible to be annealed in air at 1000 °C at a ramp rate of 2.04°C / min for 24 hours in a muffle furnace (Nabertherm).

[0095] The resultant pellet obtained after the reaction was ground into powder using a mortar and pestle before being subjected to further material and electrochemical analysis.Example 3: Synthesis of Li2Nb4P2O13

[0096] Na2Nb4P20i6 (1.5 g) synthesized previously and LiNOs (1.406g g) (Alfa Aesar, 99%) excess were taken in 1 :5 ratio, ground and mixed well to properly homogenize the sample using a mortar and pestle for 30 minutes.

[0097] This powder was then turned into a 13 mm diameter pellet using a pellet maker (Eurolab) under 5 tons of pressure for 10 minutes.

[0098] The pellet sample was then transferred into an alumina crucible and annealed in air at 300 °C at a ramp rate of 0.6°C / min for 12 hours in a muffle furnace (Nabertherm). The resultant puffed up mixture retrieved was again ground into fine powder using a mortar and pestle.

[0099] The obtained powder was then subjected to washing via centrifugation method to remove the excess LiNOs and NaNOs present in the powder mixture.

[0100] The powder was put into a 50 ml centrifugation tube, filled with distilled water to a volume of 40 ml, and then centrifuged for 15 minutes at a program speed of 10,000 rpm with 5 washing stages.

[0101] To eliminate any remaining water traces in the sample, the recovered powder was allowed to dry in a normal oven set at 70°C overnight.

[0102] Finally, the powder was then placed within a glass sample vial and placed inside a Buchi apparatus, which applied vacuum and maintained the sample at 150°C for 12 hours in order to more effectively remove moisture from the sample and prepare the powder for further material and electrochemical examination.Example 4: Synthesis of LiNb3P2O13

[0103] NaNb3P20i3 (1 .5 g) synthesized previously and LiNOs (0.904 g) (Alfa Aesar, 99%) excess were taken in 1 :5 ratio, grinded and mixed well to properly homogenise the sample using a mortar and pestle for 30 minutes.

[0104] This powder was then turned into a 13 mm diameter pellet using a pellet maker (Eurolab) under 5 tons of pressure for 10 minutes.

[0105] The pellet sample was then transferred into an alumina crucible and annealed in air at 300 °C for 12 hours at a ramp rate of 7 hours in a muffle furnace (Nabertherm). The resultant puffed up mixture retrieved was again ground into fine powder using a mortar and pestle.

[0106] This obtained powder was then subjected to washing via centrifugation method to remove the excess LiNOs and NaNOs present in the powder mixture.

[0107] The powder was put into a 50 ml centrifugation tube, filled with distilled water to a volume of 40 ml, and then centrifuged for 15 minutes at a programmed speed of 10,000 rpm with 5 washing stages.

[0108] To eliminate any remaining water traces in the sample, the recovered powder was allowed to dry in a normal oven set at 70°C overnight.

[0109] Finally, the powder was then placed within a glass sample vial and placed inside a Buchi apparatus, which applied vacuum and maintained the sample at 150°C for 12 hours in order to more effectively remove moisture from the sample and prepare the powder for further material and electrochemical examination.Example of Electrode Fabrication

[0110] Using an example ratio of 80:15:5 (Active material: C45: PVDF). a. Initially 0.7 g to 2 g of active material was ball-milled (spex) with 0.087 g to 0.37 g of C45 to enhance better contact between the carbon and the active material. b. In order to create a 40% dry mass that is neither too viscous nor too liquid, the slurry is created by adding 1.3125 g or 3.76 g of NMP to the dry mix. The slurry is casted on Copper current collector, dried and calendared. c. Finally, electrodes disc of 13 mm diameter is cut for electrochemical testing.

[0111] The Niobium bronzoids and bronzes materials Na2Nb4P20i6 and Li2Nb4P20i6 are expected to theoretically reversibly exchange 8 Li / Na atoms per formula unit through the redox activities of 2 Nb redox couples per Nb: Nb5+ / Nb4+and Nb4+ / Nb3+, leading to a theoretical capacity of 291 mAh / g and 305 mAh / g respectively. Electrochemical studies have been carried out on Na2Nb4P20i6 and Li2Nb4P20i6 tape casted electrodes, using Na and Li as the counter electrode for the production of half cells (CR2016 type coin-cells) using an LP30 electrolyte (solvionic) at a C rate of C / 10 (C here is considered for 1 electron transfer) in a voltage window of 3.0 to 0.1V.

[0112] The comparison between the insertion and de-insertion of Na vs. Li atoms into the structure of Na2Nb4P20i6 highlights that the performance of Na2Nb4P20i6 vs. Li was better when compared to Na2Nb4P20i6 vs. Na.

[0113] Results highlights that Li2Nb4P20i6 vs. Li has a better capacity and performance on comparison to Na2Nb4P20i6 vs. Li.

[0114] Table 4: Electrochemical Data on Na2Nb4P20i6 vs Na, Na2Nb4P20i6 & Li2Nb4P20i6 vs Li

[0115] The Niobium bronzoid and bronze phase materials, NaNb3P20i3 and LiNb3P20i3 are expected theoretically to reversibly exchange 6 Li atoms through the redox activities of 2 Nb redox couples per Nb: Nb5+ / Nb4+and Nb4+ / Nb3+leading to a theoretical capacity of 281 mAh / g and 289 mAh / g respectively. Electrochemical studies have been carried out on NaNbsP20i3 and LiNbsP20i3 tape casted electrodes, using Li as the counter electrode for the production of coin cells (2016 half-cells) and LP30 electrolyte (solvionic).

[0116] The voltage vs. capacity profile of both NaNbsP20i3 and LiNbsP20i3 vs. Li at C / 10 clearly differentiates the higher capacity performance of LiNbsP20i3 from NaNb3P20i3.

[0117] Table 5: Electrochemical Data on NaNb3P20i3 & LiNbsP20i3 vs Li.

[0118] In the provided figures (5-9); the bottom x axis corresponds to the capacity in mAhg’1, the top x axis corresponds to the number of atoms (Li / Na) inserted into the system and the y axis correlates to the potential (V vs. Li / Li+or Na / Na+).

Claims

Claims

1. A Lithium-phosphate niobium bronzoid or bronze having a general formula (II) Lix(PO2)2(NbO3)m where 0<x<16; 1<m<6.

2. Lithium-phosphate niobium bronzoid or bronze according to claim 1 having a general formula Li2Nb4P20i6, which is crystallized in an orthorhombic space group Pna2- with lattice constants a = 17.423 (9) A, b = 6.710 (4) A, c = 5.194 (3) A, V = 606.4 A3(10) and V / Z = 303.2 A3(10).

3. Lithium-phosphate niobium bronzoid or bronze according to claim 1 having a general formula LiNb3P20i3which is crystallized in an orthorhombic space group P2i2i2 with lattice constants a = 19.511 (8) A, b = 14.252 (6) A, c = 5.330 (4) A, V = 1481.9 A3(9) and V / Z = 246.9 A3(9).

4. Method for preparing a Li-based phosphate niobium bronzoids and bronzes comprising the steps of: a. Providing a sodium-phosphate niobium bronzoid or bronze; b. Mixing and grinding the sodium-phosphate niobium bronzoid or bronze with a Li-comprising precursor to obtain a mixture M2; c. Pelletizing the mixture M2 to obtain a pellet P2; d. Annealing the pellet P2; e. Grinding the pellet to obtain a powder W2; f. Washing and drying the powder W2;

5. Method according to claim 4 wherein the sodium-phosphate niobium bronzoid or bronze has the general formula (I) Nax(PO2)2(NbO3)m where 0<x<16; 1<m<6.

6. Method according to claim 4 or claim 5 wherein the lithium comprising precursor is LiNO3.

7. Method according to any one of claims 4 to 6 wherein mixing and grinding to obtain a mixture M2 has a duration of 20 to 60 min.

8. Method according to any one of claims 4 to 8 wherein pelletizing the mixture M2 is performed under a pressure of 5 tons for a duration of 5 to 10 minutes.

9. Method according to any one of claims 4 to 9 wherein annealing the pellet P2 is performed in air under ambient pressure and at a temperature ranging from 200 to 500°C at a temperature ramp-up rate of 0.6 to 1°C / min for a duration of 6 to 13 hours.

10. Method according to any one of claims 4 to 9 wherein the washing of the powder W2 is performed using distilled water.

11. Method according to any one of claims 4 to 10 wherein drying of P2 is performed at a temperature ranging from 60 to 80 °C.

12. Anode material, comprising a lithium-phosphate niobium bronzoid or bronze having a general formula (I) Lix(PO2)2(NbO3)m where 0<x<16; 1 <m<6.

13. Energy storage device comprising an anode material, according to claim 13.

14. Use of an energy storage device according to claim 13 in either one of a portable computer, a tablet, a mobile phone, an energy storage system , an electric vehicle or in a hybrid electric vehicle..

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