Sodium layered oxide, its uses and method of manufacture

Abstract

The present invention relates to a sodium layered oxide of formula I: Na x M1 a+ 1-y-z-n M2 b+ y M3 c+ z M4 d+ n O2,(I), where: M1 a+ , M2 b+ , M3 c+ , M4 d+ are different transition metal ions or mixtures thereof, x is a number ranging from 0.5 to less than 1; y, z, and n are numbers ranging from 0.01 to 0.85; y+z+n is less than 1; a, b, c, and d are the oxidation numbers of the transition metal ions M1, M2, M3, and M4, respectively; and The cumulative oxidation state of a transition metal ion, a*(1-yzn)+(b*y)+(c*z)+(d*n), is equal to 4-x; The sodium layered oxide represented by formula I is P2-Na 2 / 3 Ni 1 / 4 Mn 1 / 2 Ti 1 / 6 Zn 1 / 12 O2, P2-Na 2 / 3 Ni 1 / 4 Mn 1 / 2 Ti 1 / 6 Mg 1 / 12 Not O2 or P2-Na 2 / 3 Ni 1 / 4 Mn 1 / 2 Ti 1 / 6 Mg 1 / 12 Not O2.

Description

[Technical Field]

[0001] The present invention relates to novel sodium layered oxide compounds, devices incorporating said compounds such as electrodes comprising said sodium layered oxide compounds, or electrochemical energy storage cells or devices such as Na-ion batteries. The invention further relates to methods of making and / or using such compounds and devices incorporating them. [Background technology]

[0002] Sodium-ion batteries have seen significant growth in recent years as they offer a cost-effective alternative to lithium-ion batteries. Furthermore, the observed safety of sodium-ion cells during external short / zero V discharge makes them more attractive for large-scale applications. Currently, a variety of sodium-ion cell chemistries are available, primarily those using hard carbon anodes and electrolytes based on sodium salts dissolved in organic carbonates (e.g., NaPF6 / NaClO4). 1 On the other hand, the positive electrode is made of polyanionic materials (such as Na3V2(PO4)2F3), sodium-containing layered transition metal oxides (Na x MO2, x ≦ 1, M is a transition metal ion) or Prussian blue analogue (PBA) 2 Among them, the polyanion Na3V2(PO4)2F3 (NVPF) exhibits long-term structural stability and high power capability upon cycling. 3Each cathode family has its own advantages and disadvantages. However, sodium layered oxides have always held greater appeal and promise due to their low molecular weight, high density, and the possibility of tailoring their electrochemical performance by carefully selecting the transition metal ion (M). 4、5 . DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0003] Sodium layered oxides can crystallize in the O3, P2, or P3 structure, where the letters O and P represent the octahedral / columnar coordination of the sodium ions and the number represents the number of MO2 layers in the unit cell. 6 The O3 structure is Na x In MO2, stoichiometric compounds with x close to 1 are preferred. The P2 / P3 structure is x It is suitable for non-stoichiometric compounds where x ≤ 0.8 in MO2. Among the O3, P2, and P3 phases, the O3 phase has been studied more due to its higher sodium content and therefore higher capacity than comparable P2 or P3 phases. However, the P2 and P3 phases have been reported for their power rate capabilities compared to the O3 phase. Finally, a common issue for all O3, P2, and P3 phases is the continuous phase transition from the P-type phase to the O-type phase during cycling (sodium removal and reinsertion).

[0004] Another major problem to be solved with sodium layered oxides is their sensitivity to moist air. 0.67 Ni 0.33 Mn 0.67O2 and O3 NaNi 0.5 Mn 0.5 Both O2 and H2 are very sensitive to moist air. When exposed to moist air, sodium from the alkaline layer is converted into H2. + / H2O / H3O + The surface is substituted / ion-exchanged with Na2CO3 and NaOH to form a second phase. + / H2O / H3O + The intercalation of cations leads to a decrease in electrochemical performance and also causes problems during processing of the electrode coating: due to the presence of carbonate and hydroxide impurities, the material reacts with water to form agglomerates, resulting in gelation and poor compatibility with the Al foil used for electrode processing.

[0005] In the previous patent application WO2020 / 260294, NaNi 0.5 Mn 0.5 O2 material is co-doped with Zn and Ti to form O3-type Na x Ni 0.5-y Zn y Mn 0.5-z Ti z The formation of O2(x~1) was reported. The phase transition of this material is similar to that of the parent phase O3 NaNi 0.5 Mn 0.5 This co-substitution methodology allows the maximum capacity of the material to be reached. Therefore, the potential difference between 2.2 and 4.5 V (vs. Na) + / Na 0 During cycling over a voltage window of 0.1 V, a capacity of 180-200 mAh / g was obtained. x Ni 0.5-y Zn y Mn 0.5-z Ti z O2(x~1) when exposed to moist air, forms the parent phase NaNi, which releases Na to form Na2CO3 and NaOH after short exposure to air. 0.5 Mn 0.5It shows better stability than O2. The improvement in moisture stability is due to the 2+ and Ti 4+ The exact role of these ions is less clear.

[0006] Na in this O3 phase x Ni 0.5-y Zn y Mn 0.5-z Ti z O2(x~1) materials exhibit greater stability when exposed to moist air, but present few (if any) problems when used to prepare electrode slurries. All chemical components, such as solvents and binders, must be completely dry (i.e., free of water), otherwise the slurry will clump and, therefore, result in poor coating, as shown in Figures 1A and 1B. In such cases, similar compositions with lower sodium content are attempted in the hope of improving stability to moisture. However, reducing the sodium content always results in the formation of a second phase, cubic metal oxide (Ni a Zn b )O) with an increase in the amount of Na x Ni 0.5-y Zn y Mn 0.5-z Ti z The synthesis of O2 leads to the formation of a P2-O3 mixture (Figure 2). The presence of such metal oxide impurities is known to increase parasitic reactions with the electrolyte during cycling, adversely affecting cell performance.

[0007] EP3121879A1 describes a compound containing nickel and having the formula M x Ni a-y M 1 b M 2 c M 3 yThe present invention discloses an alkali layered oxide material of the P2 phase, represented by M 1 Mn, M 2 Ti, M 3 When is Zn, ZnO impurities are observed (see paragraph

[0098] ). EP3121879A1 does not say anything about water, but discloses the following compound: Na 2 / 3 Ni 1 / 4 Mn 1 / 2 Ti 1 / 6 Zn 1 / 12 O2, Na 2 / 3 Ni 1 / 4 Mn 1 / 2 Ti 1 / 6 Mg 1 / 12 O2, and Na 2 / 3 Ni 1 / 4 Mn 1 / 2 Ti 1 / 6 Mg 1 / 12 O2.

[0008] The growth of sodium layered oxides is hindered by their reactivity to moist air, which leads to structural degradation, and therefore requires a moisture-free environment for storage and electrode processing. Furthermore, bulk syntheses of sodium layered oxides are often accompanied by impurities of sodium-rich Na3MnO4 and cubic metal oxides.

[0009] To overcome these difficulties, it has surprisingly been found that certain types of sodium layered oxides offer adequate resistance to moisture (water) while providing satisfactory electrochemical properties, such as cycling performance, capacity retention (including full capacity utilization), and / or cell voltage. [Means for solving the problem]

[0010] The sodium layered oxide of the present invention is any of the compounds of formula I: Na x M1 a+ 1-y-z-n M2 b+ yM3 c+ z M4 d+ n O2, (I), where: M1 a+ , M2 b+ , M3 c+ , M4 d+ are different transition metal ions or mixtures thereof, x is a number ranging from 0.5 to exactly one (0.5≦x<1); y, z, and n are numbers ranging from 0.01 to 0.85 (0.01≦y≦0.85, 0.01≦z≦0.85, 0.01≦n≦0.85); y+z+n is less than 1 (y+z+n<1); a, b, c, and d are the oxidation numbers of the transition metal ions M1, M2, M3, and M4, respectively; and The cumulative oxidation state of a transition metal ion, a*(1-yzn)+(b*y)+(c*z)+(d*n), is equal to 4-x; The sodium layered oxide represented by formula I is P2-Na 2 / 3 Ni 1 / 4 Mn 1 / 2 Ti 1 / 6 Zn 1 / 12 O2, P2-Na 2 / 3 Ni 1 / 4 Mn 1 / 2 Ti 1 / 6 Mg 1 / 12 Not O2 or P2-Na 2 / 3 Ni 1 / 4 Mn 1 / 2 Ti 1 / 6 Mg 1 / 12 Not O2.

[0011] Therefore, the sodium layered oxide of formula I according to the present invention has a crystal structure that can be selected from the group consisting of O3 when x is 0.8 to less than 1, P2-O3 mixtures when x is 0.7 to 0.8, preferably 0.701 to 0.799, P3-O3 mixtures when x is 0.7 to 0.85, and P2 or P3 when x is 0.7 or less. Particularly preferably, the crystal structure is a P2-O3 or P3-O3 structure.

[0012] If the accumulated oxidation state exceeds 4-x, the excess sodium used in the synthesis may exist as a second phase of Na2CO3, which can be used as a sacrificial salt, as reported in Reference 7. Alternatively, transition metals may be stabilized in oxidation states lower than their most stable state (e.g., Mn 4+ Instead of Mn 3+ stabilization by

[0013] Alternatively and advantageously, another object of the invention is a sodium layered oxide of formula I': Na x M1 a+ 1-y-z-n M2 b+ y M3 c+ z M4 d+ n O2, (I'), where: M1 a+ , M2 b+ , M3 c+ , M4 d+ are different transition metal ions or mixtures thereof, x is a number ranging from 0.68 to exactly 1 (0.5≦x<1); y, z, and n are numbers ranging from 0.01 to 0.85; y+z+n is less than 1; a, b, c, d are the oxidation numbers of the metal ions M1, M2, M3, M4, respectively; and preferably, the cumulative oxidation state of the transition metal ions a*(1-yzn)+(b*y)+(c*z)+(d*n) is equal to 4-x. In other words, one object of the present invention is a sodium layered oxide of formula I, which exhibits a layered structure consisting of a P2-O3 or O3 phase, preferably a P2-O3 phase.

[0014] As shown in the examples, the layered structure types P2, O3, or mixed P2-O3 or P3-O3 types can be distinguished by X-ray diffraction. XRD patterns can be collected using a Bruker d8 Advance Diffractometer. The following parameters were set to collect the X-ray pattern data: -Detector slit = 9.5 mm -Beam slit = 0.6 mm - Range: 2θ=10°~70° -X-ray wavelength = 1.5406 Å (Angstroms) (CuKα) -Speed: 0.36 seconds / step -Increment: 0.018°

[0015] The data thus obtained was analyzed using Fullprof software, a crystallography tool developed by the Laue-Langevin Institute for Rietveld profiling matching. XRD patterns were compared with the software's integrated database and refined as necessary. Phases are defined by a numerical value x, optionally using X-ray diffraction, including but not limited to the devices described above. Advantageously, the compounds of the present invention are layered metal oxides with a P2, O3, P2-O3, or P3-O3 phase structure, meaning that the compounds are composed of at least 95%, preferably 99%, of the P2, O3, P2-O3, or P3-O3 phase.

[0016] Without being bound by this explanation, it is believed that the stability of the sodium layered oxides of the present invention to reaction with moisture is related to their redox potential. Materials that exhibit a low potential redox reaction may oxidize when in contact with atmospheric H2O and O2. O3 sodium layered oxides are often found to exhibit low redox potential reactions (Na + / Na 0 The improvement in stability to moisture is primarily due to the addition of Ti in the structure. 4+ By introducing Ni, the ionic character of the M-O bond is enhanced. 2+ The redox potential of O3 increases (below 2.5 V, no redox reaction is observed). However, for example, O3 NaNi 0.5-y Zn y Mn 0.5-z Ti z O2 material reacts with moist air as O3 NaNi 0.5 Mn 0.5 During the transition between the P2 and P2-O3 phases reported in this application, Ni 2+ / Ni (2+n)+ Redox: ~3V(Na + / Na 0 A redox potential at the onset of 0.05% (relative to 0.05%) is observed. Such a high redox potential helps improve the stability of the material in moist air.

[0017] In addition to the high redox potential, the P2-O3 material also exhibits differences in the particle surface, with surface enrichment of transition metal ions observed under high-resolution transmission electron microscopy (HAADF-STEM).

[0018] According to the present invention, M1 a+ , M2 b+ , M3 c+ and / or M4 d+Advantageously, the fourth-period transition metals are selected from the group consisting of scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), and zinc (Zn). The fifth-period transition metals, namely yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), technetium (Tc), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), and cadmium (Cd), can also be considered, but are more expensive. The sixth- and seventh-period transition metals, in particular tungsten (W), iridium (Ir), platinum (Pt), and gold (Au), are also considered to be included in the definition of the claimed invention.

[0019] Advantageously, the transition metal ions (M1, M2, M3, M4) are selected to have their most stable oxidation states at room temperature. This proves particularly useful for synthesizing the final material with slow / furnace cooling, without the need for rapid cooling. It also helps to avoid impurities, particularly in cubic metal oxides.

[0020] In formula I or I', M1 is preferably Ni. Furthermore, in formula I or I', M2, M3 and M4 are preferably selected from the group consisting of Mg, Zn, Cu, Fe, V, Cr, Mn, Ge, Sn, Ti, Zr and Co and mixtures thereof, preferably selected from the group consisting of Zn, Mn, Ti, Cu, Fe, Mg and mixtures thereof, and more preferably selected from the group consisting of Zn, Mn and Ti.

[0021] Furthermore, in formula I or I', x is preferably selected in the range of 0.6 to 0.9.

[0022] Advantageously, in the sodium layered oxide of formula I or I', M1 is Ni 2+ and M2 and M4 are Mn 4+ or Ti 4+and y is less than 0.07, preferably less than 0.06 and advantageously less than 0.05.

[0023] In particular, the compounds of the invention described above have the formula Na x Ni 1-y-z-n M2 2+ y Mn z Ti n O2(II), where M2 is selected from the group consisting of Mg, Zn, Cu, Fe, V, Cr, Ge, Sn, Zr, Co and mixtures thereof, preferably selected from the group consisting of Mg, Zn, Cu, Fe and mixtures thereof. M2 is preferably Zn.

[0024] Advantageously, the sodium layered oxide of formula II has a y value of less than 0.07, preferably less than 0.06, advantageously less than 0.05.

[0025] Compounds of formula II are those in which M1, M2, M3, and M4 are Ni, Zn, Mn, and Ti, respectively, and therefore have the formula Na x Ni 1-y-z-n Zn y Mn z Ti n O2(III) corresponds to the sodium layered oxide, which is particularly advantageous. 2+ , Zn 2+ , Mn 4+ , and Ti 4+ Particularly preferred are compounds of formula (III) containing the ion Ni 2+ The use of cheaper elements such as Mn, Ti, and Zn, which minimize ions, can reduce the overall cost of the material. The layered metal oxide exhibits a capacity of 120 mAh / g at an average voltage of 3.7 V (a significantly higher average voltage compared to reported P2 phases) and exhibits long-term cycling stability.

[0026] The specific compounds of the present invention are 0.67 Ni 0.3 Zn 0.03 Mn 0.52 Ti 0.15 It is O2.

[0027] Another specific compound of the present invention is Na 0.76 Ni 0.35 Zn 0.03 Mn 0.52 Ti 0.1 It is O2.

[0028] Another specific compound of the present invention is Na 0.85 Ni 0.38 Zn 0.04 Mn 0.48 Ti 0.1 It is O2.

[0029] In a particularly advantageous embodiment of the present invention, the sodium layered oxide of formula (III) is P2-Na 0.67 Ni 0.3 Zn 0.03 Mn 0.52 Ti 0.15 O2, P2-O3-Na 0.76 Ni 0.35 Zn0.03Mn 0.52 Ti 0.1 O2 and P3-O3-Na 0.85 Ni 0.38 Zn 0.04 Mn 0.48 Ti 0.1 O2.

[0030] Alternatively, Fe 2+ , Cu 2+ , or Mg 2+ Ions such as Zn 2+ may be advantageously used as a total or partial replacement for

[0031] Therefore, particularly preferred compounds or materials of formula II are of the formula NaxNi 1-y-z-n Fe y Mn z Ti n It is one of the O2(IV).

[0032] The preferred compound of the present invention is Na 0.7 Ni 0.2 Fe 0.3 Mn 0.35Ti 0.15 It is O2.

[0033] The preferred compound of the present invention is Na 0.7 Ni 0.25 Fe 0.2 Mn 0.40 Ti 0.15 It is O2.

[0034] Yet another compound or material according to formula II that is also particularly preferred is of formula Na x Ni 1-y-z-n Cu y Mn z Ti n O2(V) or Na x Ni 1-y-z-n Mg y Mn z Ti n It consists of O2(VI).

[0035] Particularly preferred compounds of the present invention are Na 0.67 Ni 0.3 Cu 0.03 Mn 0.52 Ti 0.15 It is O2.

[0036] Particularly preferred compounds of the present invention are Na 0.67 Ni 0.3 Mg 0.03 Mn 0.52 Ti 0.15 It is O2.

[0037] Another embodiment of the present invention relates to a method for producing the sodium layered oxide defined above, namely a method for producing a sodium layered oxide of formula I: Na x M1 a+ 1-y-z-n M2 b+ y M3 c+ z M4 d+ n O2, (I), where: M1 a+ , M2 b+, M3 c+ , M4 d+ are different transition metal ions or mixtures thereof, x is a number ranging from 0.5 to exactly less than 1; y, z, and n are numbers ranging from 0.01 to 0.85; y+z+n is less than 1; a, b, c, and d are the oxidation numbers of the metal ions M1, M2, M3, and M4, respectively; and The cumulative oxidation state of a transition metal ion, a*(1-yzn)+(b*y)+(c*z)+(d*n), is equal to 4-x.

[0038] According to the present invention, the process comprises the following steps: (a) mixing a powder of a sodium precursor and a powder of a transition metal precursor of the sodium layered oxide in stoichiometric amounts to obtain a solid powdered mixture; (b) heating the solid powder mixture, preferably in an air atmosphere, at a temperature in the range of 500°C to 900°C to obtain a calcinated powder; (c) cooling the calcined powder at a rate of 1.5°C / min (preferably 1°C / min) or less; (d) milling the calcined powder to obtain a milled calcined powder; (e) heating the solid powder mixture, preferably in an air atmosphere, at a temperature in the range of 700°C to 1100°C to obtain a ground and re-fired powder; (f) cooling the ground, recalcined powder, advantageously at a rate of 1.5°C / min (preferably 1°C / min) or less;

[0039] The precursor can be selected from suitable compounds containing salts and oxides of sodium or selected metals. Preferred precursors include, but are not limited to, Na2CO3, NiO, ZnO, CuO, MgO, Fe2O3, Mn2O3, and TiO2. It has been found desirable to avoid using excessive amounts of Na2CO3, especially when using Mn, in order to reduce impurities such as Na2CO3 / Na3MnO4. Therefore, when selecting the amount of precursor used, it is preferable to strictly respect the stoichiometry of the resulting compound.

[0040] By "strict respect for stoichiometry" it is meant that it is advantageous to select the amounts of precursors to be within ±5%, preferably ±1%, and even more preferably ±0.5% of the stoichiometric amount.

[0041] The precursor is preferably ground or pulverized, for example by ball milling. In this case, the ball-to-powder ratio may range from 1:10 to 1:30, preferably about 1:20. The mixture is then heated, advantageously to a temperature of 800°C or less, for example 750°C to 799°C. This is the first annealing, or calcination, step. This first calcination step can be carried out for a period of 1 to 24 hours, preferably 4 to 7.5 hours, more preferably 5 to 6 hours, for example 6 hours. This step can be carried out at atmospheric pressure.

[0042] The intermediate grinding step d) can be carried out by ball milling under the same conditions as above. This grinding step can be carried out for a period ranging from 10 minutes to 2 hours, with a grinding step of 1 hour being found to be effective.

[0043] Advantageously, the second or calcination step (e) is carried out at a temperature which may be selected from 900°C to 1000°C, but may alternatively be in the range of 900°C to 999°C or 900°C to 949°C.

[0044] Such a process has been found to produce homogeneous materials having the required single or combined P2, O3, P2-O3, or P3-O3 phases. This second calcination step can be carried out for a period of 1 to 24 hours, preferably 4 to 7.5 hours, more preferably 5 to 6 hours, e.g., 6 hours. This step can be carried out at atmospheric pressure.

[0045] Both the first and second baking steps can be carried out at a heating rate of 1 to 10° C. / min, with a heating rate of 3° C. / min being preferred.

[0046] Also, when performing either or both of the cooling steps c) and f), it is advantageous to perform the cooling at a rate of 1° C. / min or less, which may be important for obtaining the best results, especially the formation of the P3-O3 phase (see Example 8).

[0047] Alternatively, the materials of the present invention can be synthesized using solution synthesis, such as co-precipitation assisted solid state synthesis, sol-gel synthesis, hydrothermal synthesis, or combustion synthesis. In solution synthesis, the precursors typically used are salts, such as metal nitrates, sulfates, carbonates, etc. The same precursors (i.e., oxides) described above can be used, but they must be dissolved (e.g., in nitric acid).

[0048] A further object of the present invention is the compound (i.e. sodium layered oxide) obtained or obtainable according to the process of the present invention.

[0049] Another object of the present invention is an electrode material comprising: - the sodium layered oxide according to the invention as described above; -electronically conductive additives, such as carbon black; and -Optionally a polymer binder.

[0050] The polymer binder may be, for example, PVDF (polyvinylidene fluoride), CMC (sodium carboxymethyl cellulose), and derivatives thereof, with PVDF being preferred.

[0051] The relative proportions of the chemical components may be selected within the ranges shown below: 4 to 20% by weight, preferably 4 to 15% by weight, of a conductive additive such as conductive carbon (carbon black, Super P Carbon manufactured by TIMCAL), 3 to 6% by weight of a polymer binder such as PVDF; and - 20 to 40% by weight of a solvent (or dispersant) such as N-methylpyrrolidone (NMP).

[0052] A further object of the present invention is a method for producing the above electrode material, which method also includes mixing the sodium layered oxide of the present invention with an electronically conductive additive and finally mixing with a polymer binder. The electronically conductive additive is added in a suitable ratio, such as 5 to 20% by weight, relative to the weight of the sodium layered oxide.

[0053] If a binder is used, the mixture is dispersed in a solvent (ie, dispersant) to obtain a slurry, particularly a homogeneous slurry.

[0054] Another object of the present invention is a positive electrode comprising the electrode material according to the present invention in working contact with a current collector. The current collector preferably comprises a carbon material or a metal such as aluminum. It is further preferred that a layer of the sodium layered oxide or electrode material of the present invention is cast onto the current collector, which may be in the form of a sheet, such as aluminum foil.

[0055] A method for producing the above-described positive electrode is a further object of the present invention. The method includes associating or attaching the compound or electrode material of the present invention to a current collector. Simple pressure may also be used. If a binder / dispersant is used, the resulting slurry may be cast onto a current collector such as aluminum foil. The dispersant is then removed, for example, by heating (e.g., to 120°C).

[0056] Advantageously, a compression or pressure step, which may be carried out by a roller machine, may be applied to create or improve the bond between the compound according to the invention or the electrode material.

[0057] A further object of the present invention is an electrochemical cell comprising: -electrolyte; a negative electrode configured to reversibly accept sodium ions from the electrolyte and reversibly release sodium ions to the electrolyte, the negative electrode having at least one current collector; a positive electrode comprising a compound (i.e., a sodium layered oxide) or electrode material as described above, configured to reversibly accept sodium ions from an electrolyte solution and reversibly release sodium ions to the electrolyte solution, the positive electrode having at least one current collector; and -A separator that contacts both the negative and positive electrodes and is mixed with an electrolyte solution containing sodium ions.

[0058] The separator is usually selected from the group consisting of glass fiber, polyolefin separator, cellulose-based film, in particular, the film can be a polypropylene (PP) film, a polyethylene (PE) film, or advantageously a multilayer film of PP+PE+PP.

[0059] The negative electrode advantageously comprises a negative or positive electrode (anode) material consisting of sodium metal, a carbonaceous compound, hard carbon, antimony, tin, phosphorus, or a mixture thereof, such as a mixture of Sn and hard carbon. The positive electrode (anode) material typically comprises an electronically conductive additive, such as carbon black, and optionally a polymer binder. The additive and binder, and their relative proportions, may be as described for the positive electrode material. The negative electrode may also have the same structure and a similar current collector as the positive electrode. Furthermore, the manufacturing method may be the same as described above.

[0060] The electrolyte of the electrochemical cell (battery) of the present invention may comprise: sodium salts, such as sodium hexafluorophosphate (NaPF6), sodium perchlorate (NaClO4), sodium bis(fluorosulfonyl)imide (NaFSI), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), sodium bis(pentafluoroethanesulfonyl)imide (NaBETI), sodium tetrafluoroborate (NaBF4), Na[B(hfip)4]·DME (hfip = hexafluoroisopropyloxy, OiPrF), and Na[B(pp)2] (pp = perfluorinated pinacolate, O2C2(CF3)4), or mixtures thereof; - solvents (or dispersants), such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), propylene carbonate (PC), ethylene carbonate (EC); esters, such as methyl acetate (MA), ethyl acetate (EA), ethyl propionate (EP) or methyl propionate (MP), or mixtures thereof, such as EC / EP mixtures; and - optionally additives, such as vinylene carbonate (VC), 1,3-propane sultone (PS), succinonitrile (SN), sodium difluoro(oxalato)borate (NaODFB), or mixtures thereof, such as VC and SN.

[0061] The sodium salt NaPF6 is preferred.

[0062] The concentration of the sodium salt in respect to the total amount of the solvent may be in the range of 0.1 mol / L to 3 mol / L, preferably 0.5 mol / L to 2 mol / L.

[0063] The concentration of the electrolyte additive may generally vary from 0.05 to 10% by weight, relative to the total weight of the electrolyte composition. Advantageously, the following specific additive concentrations are used: vinylene carbonate (VC) 0.1 to 10% by mass, preferably 0.5 to 5.0% by mass, succinonitrile (SN) 0.1 to 5% by mass, preferably 0.5 to 2.0% by mass, - Sodium difluoro(oxalato)borate (NaODFB) 0.05 to 10% by mass, preferably 0.2 to 1.0% by mass.

[0064] When a mixture of solvents (e.g., a mixture of EC / PC / DMC in a volume ratio of 1:1:2) is used, the electrolyte solution can be prepared by mixing the solvents; then adding a sodium salt (e.g., NaPF6 at a concentration of 1 mol / L); and adding an additive (e.g., 5.0% by weight of VC, 1.0% by weight of SN) to the solution. Preferably, these steps are carried out with stirring, and the order of the addition steps can be changed, for example, by first adding the additive to the solvent and then adding the salt. Advantageously, the entire process is carried out in an inert atmosphere (e.g., under Ar or N2).

[0065] A further object of the present invention is a battery consisting of a series of electrochemical cells (batteries) of the present invention. The positive electrodes, separators, and negative electrodes are stacked layer by layer (one layer of separator for each layer of electrode) and finally folded and / or wound into a cell core. The cell core is placed into a cell shell and dried. Drying can be performed at 85°C under vacuum (e.g., less than -1.0 bar) for 24 hours. An electrolyte is then injected and the Na-ion battery of the present invention is sealed. A method for manufacturing the battery of the present invention is a further object of the present invention.

[0066] Electrochemical cells or batteries according to the present invention may take on a variety of suitable configurations, such as coin cells, pouch cells, cylindrical cells (18650, 21700, 36500, etc.), or prismatic cells.

[0067] Yet a further object of the present invention is the use of the compounds or materials of the present invention as electroactive compounds or materials in cells or batteries, preferably as positive electrode materials.

[0068] Uses of the batteries of the present invention include, for example, incorporation into microgrids for stabilizing power grids, electrochemical storage devices for intermittent renewable energy sources (e.g., solar and wind energy), mobile storage devices for electric vehicles (end-of-life rechargeable buses, rental car fleets), home energy storage devices, and emergency power or energy storage devices for hospitals, schools, factories, computer clusters, servers, businesses, and other public and / or private buildings or infrastructure. The compounds of the present invention or devices incorporating the compounds can be used in, for example, the automotive, computer, banking, video game, leisure, creative, cultural, cosmetics, life science, aviation, pharmaceutical, metal and steel, railway, military, nuclear, naval, space, food, agriculture, construction, glass, cement, textile, packaging, electronics, petrochemical, and chemical industries.

[0069] The foregoing and other objects, aspects, features and advantages of the present invention will become more apparent from the following examples and claims. [Brief explanation of the drawings]

[0070] The invention will now be described with reference to the following drawings:

[0071] [Figure 1] FIG. 1A shows the comparative example slurry, and FIG. 1B shows the slurry applied as a coating on aluminum foil.

[0072] [Figure 2] Figure 2 shows the X-ray diffraction (XRD) patterns of NaxNi0.45Zn0.05Mn0.4Ti0.1O2 with sodium contents varying from 1 to 0.7.

[0073] [Figure 3]FIG. 3 shows the X-ray diffraction patterns of three different sodium layered oxides produced in accordance with the present invention and described in Example 2, compared with the O3 phase NaNi0.45Zn0.05Mn0.4Ti0.1O2, a prior art compound.

[0074] [Figure 4] Figure 4 shows the X-ray diffraction patterns of the compound in Figure 3 immediately after preparation (Figure 4A) and after exposure to 55% relative humidity (Figure 4B).

[0075] [Figure 5] FIG. 5 shows a slurry of the P2-O3 phase Na0.76Ni0.35Zn0.03Mn0.52Ti0.1O2 according to the present invention applied as a coating on an aluminum foil.

[0076] [Figure 6] Figure 6 shows the cycling performance of sodium-ion half-cells with sodium metal anodes: P2 NaO.67NiO.3ZnO.03MnO.52TiO.15O2 (P2 NaO.67MO2), P2-O3 NaO.76NiO.35ZnO.03MnO.52TiO.1O2 (PO-NaO.76MO2), O3 NaO.9NiO.4ZnO.05MnO.4TiO.15O2 (O3 NaO.9MO2), and prior art O3 NaNiO.45ZnO.05MnO.4TiO.1O2 (O3 NaMO2).

[0077] [Figure 7] FIG. 7 shows the cycling performance of the same compounds as in FIG. 6 after exposure to 55% relative humidity.

[0078] [Figure 8]Figure 8 shows the electrochemical performance of the same compounds as in Figure 6 in a Na-ion full cell with hard carbon as the anode. Figure 8A shows the capacity vs. composition profile, Figure 8B shows the capacity retention, and Figure 8C shows a histogram showing the resulting energy and dots (right axis) representing the average voltage of the cells for these materials.

[0079] [Figure 9A] FIG. 9A shows the X-ray diffraction pattern of P2 Na0.7Ni0.2Fe0.3Mn0.35Ti0.15O2.

[0080] [Figure 9B] FIG. 9B shows the cycling performance of a Na-ion half-cell with sodium metal as the negative electrode for P2 Na0.7Ni0.2Fe0.3Mn0.35Ti0.15O2.

[0081] [Figure 10A] FIG. 10A shows the X-ray diffraction pattern of P2 Na0.7Ni0.25Fe0.2Mn0.35Ti0.15O2.

[0082] [Figure 10B] FIG. 10B shows the cycling performance of a Na-ion half-cell with sodium metal as the negative electrode for P2 Na0.7Ni0.25Fe0.2Mn0.35Ti0.15O2.

[0083] [Figure 11] FIG. 11 shows the cycling performance of Na-ion half-cells with sodium metal as the anode using the following compounds (from top to bottom): P2 NaO.67NiO.3CuO.03MnO.52TiO.15O2, NaO.67NiO.3MgO.03MnO.52TiO.15O2, P2 NaO.67NiO.3ZnO.03MnO.52TiO.15O2.

[0084] [Figure 12]12 shows the XRD pattern of P2-O3-Na0.76Ni0.35Zn0.03Mn0.52Ti0.1O2 synthesized with excess Na2CO3 in Example 6. The XRD pattern shows Na2CO3 as a second phase (marked with an asterisk in the figure).

[0085] [Figure 13] FIG. 13 shows the formation of O3-Na0.76Ni0.35Zn0.03Mn0.52Ti0.1O2 by repeated reheating of the mixture obtained in FIG.

[0086] [Figure 14] FIG. 14 shows a derivative plot of the first charge of (a) O3-NaNi0.5Mn0.5O2 corresponding to WO2020 / 260294, (b) Ti-substituted O3-NaNi0.45Zn0.05Mn0.4Ti0.1O2 corresponding to Comparative Example 1, and (c) P2-Na0.67Ni0.3Zn0.03Mn0.52Ti0.15O2 obtained in Example 2 according to the present invention.

[0087] [Figure 15] 15(a) and 15(b) show high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images of P2-O3-Na0.76Ni0.35Zn0.03Mn0.52Ti0.1O2 according to the present invention, and FIG. 15(c) shows the HAADF signal profile from the marked area in FIG. 15(b).

[0088] [Figure 16] FIG. 16 shows the XRD pattern of Na0.85Ni0.38Zn0.04Mn0.48Ti0.1O2 of Example 7.

[0089] [Figure 17] FIG. 17 shows a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) image of P3-O3-Na0.85Ni0.38Zn0.04Mn0.48Ti0.1O2 of Example 7.

[0090] [Figure 18] FIG. 18 shows the XRD patterns of the compound of Example 7 immediately after preparation (FIG. 18(a)) and after exposure to 55% relative humidity for 48 hours (FIG. 18(b)).

[0091] [Figure 19] FIG. 19 shows the high temperature XRD analysis of O3-Na0.85Ni0.38Zn0.04Mn0.48Ti0.1O2.

[0092] [Figure 20] FIG. 20 shows the XRD pattern of Na0.85Ni0.38Zn0.04Mn0.48Ti0.1O2 of Example 8 (FIG. 20(a)) compared with the XRD pattern of Na0.85Ni0.38Zn0.04Mn0.48Ti0.1O2 of Example 7 (FIG. 20(b)). DETAILED DESCRIPTION OF THE INVENTION

[0093] Comparative Example 1 O3 phase NaNi 0.45 Zn 0.05 Mn 0.4 Ti 0.1 O2 was obtained by solid state synthesis as described in Example 1b of WO2020 / 260294. A slurry of this material was obtained by mixing: -Conductive carbon (carbon black, TIMCAL Super P Carbon) 15% by mass - PVDF 5% by mass as binder 30% by weight of N-methylpyrrolidine (NMP) as solvent, the amount of which (i.e. dispersant) can be chosen to obtain the required viscosity of the slurry, since it is subsequently removed during drying.

[0094] Next, the transition metal composition was kept constant and the sodium stoichiometry was varied: O3 phase NaNi 0.45 Zn 0.05 Mn 0.4 Ti 0.1Using the same method as O2, Na 0.9 Ni 0.45 Zn 0.05 Mn 0.4 Ti 0.1 O2, Na 0.8 Ni 0.45 Zn 0.05 Mn 0.4 Ti 0.1 O2 and Na 0.7 Ni 0.45 Zn 0.05 Mn 0.4 Ti 0.1 O2 powder was obtained.

[0095] Figure 1A shows the O3 NaNi 0.45 Zn 0.05 Mn 0.4 Ti 0.1 This shows the formation of agglomerates in an O2 slurry. The slurry was applied to aluminum foil to form an electrode (see Figure 1B). The agglomerates in the slurry caused an uneven coating. The reason for the formation of these agglomerates was found to be that the PVDF-NMP mixture was not dried, containing a few ppm (~10 ppm) of water.

[0096] Na with sodium content x of 1, 0.9, 0.8, and 0.7 x Ni0.45Zn 0.05 Mn 0.4 Ti 0.1 The X-ray diffraction patterns of the O2 chemical composition are shown in Figure 2. By reducing the sodium content to 0.7, the P2 phase begins to appear. However, in all these materials, cubic metal oxide impurities (*Cubic MO) are observed, and their content increases with decreasing sodium content. This demonstrates the importance of fine-tuning the transition metal stoichiometry to match that of sodium.

[0097] <Example 2> The following sodium layered oxides were prepared: P2 phase Na 0.67 Ni 0.3 Zn 0.03 Mn 0.52 Ti0.15 O2 P2-O3 phase Na 0.76 Ni 0.35 Zn 0.03 Mn 0.52 Ti 0.1 O2 O3 phase Na 0.9 Ni 0.4 Zn 0.05 Mn 0.4 Ti 0.15 O2

[0098] The materials were synthesized in a 100 g batch. Stoichiometric amounts of sodium and transition metal precursors (Na2CO3, NiO, ZnO, CuO, MgO, Fe2O3, Mn2O3, TiO2) were mixed by hand grinding and then dry ball milled for 1 h. The ball milling process was carried out in a SPEX8000M™ mixer mill using ball milling balls and a hardened steel container. The ball to powder ratio was approximately 1:20. The mixture was transferred to an alumina crucible and sintered in air at 3 °C for 3 min. -1 The powder was heated at 800°C for 6 hours, followed by slow cooling (1°C / min) to room temperature, followed by a 1-hour intermediate ball milling treatment to ensure uniformity. The powder was then reheated at 900 / 1000°C for 6 hours under the same conditions as above. Excess Na2CO3 was strictly avoided to remove Na2CO3 / Na3MnO4 impurities. The calcined powder was slowly cooled (1°C / min) and quickly transferred to an argon-filled glove box to avoid any reaction with moisture or air. Alternatively, the material can be synthesized using solution synthesis, such as co-precipitation-assisted solid-state synthesis, sol-gel synthesis, hydrothermal synthesis, or combustion synthesis. As shown in Figure 3, the material with the lowest sodium content (x = 0.67) crystallizes in the P2 phase, while a slightly higher sodium content results in a P2-O3 mixture (x = 0.76). Pure O3 phase is obtained at x = 1 and 0.9. However, the x=1 material (prior art) shows a peak of cubic metal oxide impurities, which decreases in the x=0.9 phase.

[0099] Pure P2 phase is formed only when the sodium content is less than or equal to 0.67 (x≦0.67). Similarly, O3 phase is formed when the sodium content is between 0.8 and 1, more specifically when x=1. A P2-O3 mixture can be considered as 75% P2 phase (x=0.67) and 25% O3 phase (x=1).

[0100] Compound P2 Phase Na of the present invention 0.67 Ni 0.3 Zn 0.03 Mn 0.52 Ti 0.15 O2, P2-O3 phase Na 0.76 Ni 0.35 Zn 0.03 Mn 0.52 Ti 0.1 O2 and O3 phase Na 0.9 Ni 0.4 Zn 0.05 Mn 0.4 Ti 0.15 O2 and the prior art compound O3 phase NaNi 0.45 Zn 0.05 Mn 0.4 Ti 0.1 O2 were tested for their moisture-sensitive properties by storing them under a controlled relative humidity (RH) of 55%. The relative humidity was controlled using a saturated solution of Mg(NO3)2.6H2O (Sigma-Aldrich) in water. The saturated magnesium nitrate solution and samples to be analyzed were stored in a sealed desiccator to ensure the required relative humidity.

[0101] As shown in Figure 4, no or very little degradation was observed in the P2 and P2-O3 compositions, whereas the O3 phase Na 0.9 Ni 0.4 Zn 0.05 Mn 0.4 Ti 0.15 Slight deterioration was observed in O2, and O3 phase NaNi 0.45 Zn 0.05 Mn 0.4 Ti 0.1More degradation is observed with O2. This phenomenon was reconfirmed while cycling the "as-prepared" and "air-exposed" materials in Na metal half-cells (Figure 7).

[0102] As disclosed in Comparative Example 1, Na in the P2-O3 phase 0.76 Ni 0.35 Zn 0.03 Mn 0.52 Ti 0.1 A slurry of O2 was prepared. The slurry for electrode coating was prepared in a humid air atmosphere outside the drying chamber, and as shown in Figure 5, no gelling or aggregation was observed.

[0103] Example 3: Cycle Performance and Other Properties The prepared sodium layered oxides were used to investigate their electrochemical performance and tested in half-cell and full-cell configurations. Electrodes according to the present invention were fabricated using one or more of the layered oxide compounds obtained in Example 2.

[0104] The layered oxide active material (positive or working electrode) in all cell configurations was used in powder form. Layered oxide materials for electrochemical analysis were mixed with 15 wt% carbon black (Super P Carbon, 25 TIMCAL) and ball-milled for 30 min using a SPEX8000M mixer mill. A hardened steel ball-milling vessel containing hardened steel balls was used to grind 3 g of oxide at a compound-to-ball weight ratio of 1:35. The cycling performance of the materials was tested in Swagelok-type half cells using sodium metal as the counter electrode and in coin-type sodium-ion full cells using a hard carbon anode.

[0105] The active material for electrochemical analysis, sodium layered oxide, is mixed with 15% carbon to improve electronic conductivity, and the powder electrode is used as is for all electrochemical analyses.

[0106] The hard carbon counter electrode used in the full-cell (all-electric) assembly was prepared in the ambient atmosphere outside the glove box. The hard carbon anode powder was provided by Aekyung Petrochemical Co., Ltd., Korea. The average particle size and BET surface area of ​​this hard carbon were 9 μm and 3.29 m, respectively. 2 g -1 The hard carbon powder thus obtained was mixed with 4 w / w% conductive carbon (Super P carbon manufactured by TIMCAL) and a binder. The binder used here was either PVDF in N-methylpyrrolidine (NMP) or carboxymethylcellulose 25 sodium and / or its derivatives in a water solvent. The negative electrode slurry was prepared by mixing the active material, conductive carbon, and binder in NMP in a ratio of 92:4:4, respectively. The resulting slurry was mixed at a mass loading of 5–6 mg cm. -2 The hard carbon film was coated onto Al foil with a 0.01% SiO2 content. The coated hard carbon film was calendared to reduce the electrode porosity by approximately 50%. The electrodes were cut into circular disks with diameters of 8–13 mm, dried at 80 °C, and stored in an argon-filled glove box before use in full-cell assemblies.

[0107] The active cathode and / or anode materials were balanced according to practically achievable capacity. For example, the hard carbon electrodes used in all cell assemblies were designed for 300 mAh g -1 This shows the discharge capacity of the first cycle, which consists of approximately 170 mAh g-1 Therefore, to balance the positive electrode capacity, a weight ratio of approximately 1.7:1 between the positive and negative electrode materials (O3 NaMO2) / (hard carbon) was used. However, the negative hard carbon electrode was used in excess of approximately 4 w / w% to avoid sodium coating. In other words, an additional amount of negative active material in mg was used to obtain 4% additional capacity relative to the actual amount of negative hard carbon needed to balance the positive electrode. In other words, the electrode capacity was known when the capacity ratio of each electrode was expressed as follows, and the amount of active material in each electrode was adjusted accordingly: Capacity ratio = positive electrode cell capacity / negative electrode cell capacity = pc / ne

[0108] The total mass of active compound in each electrode was then adjusted so that the negative electrode mass of active compound was: Negative electrode mass = positive electrode mass x (pc / ne), where pc is less than ne.

[0109] The full cell was a 2032 (20 mm diameter, 3.2 mm height) coin cell. The hard carbon coated aluminum foil electrode was used as the negative electrode, and 0.8-1 ml of 1 M NaPF6 in propylene carbonate (PC) was used as the electrolyte. Two layers of glass fiber separator 7' (Whatmann, model GF / D (pore size: 2.7 IJm, diameter: 5.5 cm, thickness: 675 IJm)) were used. The separator 7' was cut into a circular disk with a diameter of approximately 18 mm.

[0110] Thus, the P2 material Na formed in our test 0.67 Ni 0.3 Zn 0.03 Mn 0.52 Ti 0.15 O2 (Figure 3) exhibits high stability when exposed to humid air (Figure 4), but has the lowest capacity of the compositions studied, at ~125 mAh / g (Figure 5).

[0111] As shown in Figure 6, by increasing the sodium content above 0.7, the material crystallizes into a major P2 phase with a small amount of O3 phase. This increases the practical capacity to ~140 mAh / g, and the material is found to be very stable when exposed to humid air (Figures 4 and 7). This stability when exposed to humid air is due to the high content of P2 phase and the Zn 2+ and Ti 4+ This is due to the excellent stability of the ion-containing O3 phase. Therefore, the material can be coated into a smooth, homogeneous electrode film by slurrying in normal air / atmosphere (Figure 5). As the sodium content increases further, the material crystallizes into the pure O3 phase, but with improved stability in humid air (e.g., x=0.9).

[0112] Figure 7 shows that the P2 phase exhibits identical electrochemical performance before and after exposure to humid air (Figure 7), demonstrating its stability in humid air. However, phases containing the O3 component exhibit relatively poor electrochemical performance after exposure to humid air. The overall stability in humid air follows the order 0.67Na>>0.76Na>0.9Na>1Na.

[0113] Figure 8 compares the electrochemical performance of four different compositions in a Na-ion full cell. The cycling profiles in Figure 8A show that the maximum capacity achieved is lowest for the P2 phase and highest for the O3 phase. The capacities above 3 V are very similar for all compositions, suggesting that for applications requiring only cycling above 3 V, all four investigated phases have similar capacities, regardless of total capacity. However, the P2-O3 intergrowth exhibits lower redox potentials compared to the pure P2-type material, resulting in superior zero-volt stability of the cell during an external short circuit. Figure 8B compares the capacity retention, showing similar capacity retention for all four samples. Figure 8C compares the specific energy and average voltage of the cells, with the P2 phase exhibiting the highest average voltage of all.

[0114] Next, the P2 and O3 phase materials were analyzed for potential transition metal dissolution during cycling. To obtain desodium-depleted electrodes, the sodium layered oxides were charged to 4.5 V (100% SOC) and washed with dimethyl carbonate (DMC). The recovered electrodes were treated with 1 M NaPF6 in organic carbonate and stored at 55 °C for 1 to 3 weeks. The electrolyte recovered from the solids by filtration was analyzed by inductively coupled plasma (ICP) analysis to determine the dissolved Ni content. Dissolved transition metal ions not only degrade the electrochemical performance of the positive electrode but can also contaminate the negative electrode (HC in Na-ion cells). The P2-rich phase exhibits less Ni dissolution in the electrolyte compared to the O3 phase (0.202% Ni for P2 vs. 2% Ni for O3).

[0115] As already disclosed above, the stability of sodium layered oxides against reactions with moisture appears to be related to their redox potential. O3 sodium layered oxides are often found to be highly susceptible to low potential redox reactions (Na as shown in Figure 14(a)). + / Na 0The improvement in stability against moisture is achieved by first incorporating Ti into the structure. 4+ This is established by introducing Ni 2+ The redox potential of the resulting O3-NaNi increases (no redox reaction is observed below 2.5 V in Figure 14(b)). 0.45 Zn 0.05 Mn 0.4 Ti 0.1 The O2 material reacts with moist air as O3-NaNi 0.5 Mn 0.5 It shows better stability than O2. P2 phase (here, P2-Na 0.67 Ni 0.3 Zn 0.03 Mn 0.52 Ti 0.15 O2), as shown in Figure 14(c), 2+ / Ni (2+n)+ For oxidation-reduction, Na + / Na 0 A starting redox potential of 2.85 V is observed for 1000 ppm. Such a high redox potential helps to improve the stability of the material towards humid air.

[0116] In addition to the high redox potential, the P2-O3-Na 0.76 Ni 0.35 Zn 0.03 M n0.52 Ti 0.1 O2(P2-O3-Na 0.76 MO2) also exhibits differences in the particle surface, with surface enrichment by transition metal ions observed by high-resolution transmission electron microscopy.

[0117] P2-O3-Na 0.76 The structure of MO2 is shown in Figure 15(a) and Figure 15(b), where the P2 phase is observed in the center and the O3 phase is observed on the surface, both indicated by arrows.

[0118] Figure 15(c) shows HAADF signal profiles from the marked areas in Figure 15(b): across the cation layer of the P2 phase (1), across the cation layer of the O3 phase (2), and along the cation layer of the P2 phase (3). The arrows indicate significant HAADF signals in the interlayer space of the O3 phase. The asterisk indicates the tripled period of the HAADF signal along the cation layer of the P2 phase.

[0119] The HAADF signal profile in Figure 15c(2) reveals that the surface O3 phase exhibits cation mixing with the sodium layer. Such transition metal enrichment on the particle surface is expected to improve the moisture stability of the material by reducing surface reactivity.

[0120] Example 4 The following compounds of the invention were prepared using the same method as disclosed in Example 2: P2 phase Na 0.7 Ni 0.2 Fe 0.3 Mn 0.35 Ti 0.15 O2, and P2 phase Na 0.7 Ni 0.25 Fe 0.2 Mn 0.40 Ti 0.15 O2

[0121] The X-ray diffraction patterns in Figures 9A and 10A show that they are both P2 phases. Their contents (see Figures 9B and 10B) indicate that they are P2 Na 0.67 Ni 0.3 Zn 0.03 Mn 0.52 Ti 0.15 Similar to that of O2, but with less nickel and the terrestrially abundant Fe 3+ Figure 10B shows that metallic sodium is used in P2 Na 0.7 Ni 0.25 Fe0.2 Mn 0.35 Ti 0.15 The cycle performance of a Na-ion half-cell with an O2 anode is shown.

[0122] <Example 5> Zn 2+ Cu ions 2+ and Mg 2+ Other M such as 2+ To demonstrate the ease of substitution with ions, the following compounds of the invention were prepared using the same method as disclosed in Example 2: P2-Na 0.67 Ni 0.3 Cu 0.03 Mn 0.52 Ti 0.15 O2; and P2-Na 0.67 Ni 0.3 Mg 0.03 Mn 0.52 Ti 0.15 O2

[0123] Figure 11 shows the Na 0.67 Ni 0.3 Cu 0.03 Mn 0.52 Ti 0.15 O2 and Na 0.67 Ni 0.3 Mg 0.03 Mn 0.52 Ti 0.15 The electrochemical cycle curves of ZnO are shown. 2+ is Cu 2+ or Mg 2+ The parent phase Na is replaced by either 0.67 Ni 0.3 Zn 0.03 Mn 0.52 Ti 0.15 It is identical to O2.

[0124] Example 6 To demonstrate the importance of balancing the stoichiometry properly for end phase control, the synthesis was performed using Na 0.76 Ni 0.35 Zn 0.03 Mn 0.52 Ti0.1 The XRD analysis in Figure 12 shows that the P2-O3 Na 0.76 Ni 0.35 Zn 0.03 Mn 0.52 Ti 0.1 The formation of the O2 phase is shown, but the excess sodium (i.e., 1.1 instead of 0.76) stabilizes it as a secondary phase of Na2CO3. By repeating the grinding and reheating process, the O3 Na1Ni phase is formed, as shown in Figure 13. 0.35 Zn 0.03 Mn 0.52 Ti 0.1 The O2 phase was obtained, but the manganese in this material was Mn 3+ The material is sensitive to moist air and is not stable as an O3 phase. The compound in Figure 12 was ground again and reheated at 1000°C for 6 hours (6 hours at 1000°C, cooling, grinding, and reheating twice at each step). The resulting O3 phase, shown in Figure 13, was exposed to air for only 3 hours, leading to a reaction with moisture to reach a new phase (P3). The already formed pure phase P2-O3 Na 0.76 Ni 0.35 Zn 0.03 Mn 0.52 Ti 0.1 The same effect was obtained by heating O2 with Na2CO3.

[0125] Example 7 To demonstrate the importance of slow cooling, as in Example 6, Na2CO3 was used in excess to 0.85 Ni 0.38 Zn 0.04 Mn 0.48 Ti 0.1 O2 was synthesized by carrying out step (c) at a temperature of 900°C for 6 hours, followed by step (e) at a temperature of 1000°C with intermediate grinding (step (d)). After step (e), the mixture was slowly cooled to a temperature of 200°C at a rate of 1°C / min (step (f)).

[0126] The resulting Na 0.85 Ni 0.38 Zn 0.04 Mn 0.48 Ti0.1 The XRD pattern of O2 is shown in Fig. 16 and indicates that a mixture of P3-O3 phases was obtained.

[0127] Figure 17 shows P3-O3-Na 0.85 Ni 0.38 Zn 0.04 Mn 0.48 Ti 0.1 HAADF-STEM image of O2 shows the presence of several small particles resembling Na2CO3 that do not contain transition metal ions within their structure, along with the enrichment of transition metals at the surface (white arrows).

[0128] Referring to FIG. 18, it was observed that the XRD pattern did not change after exposure to humid air, thereby confirming that P3-O3-Na 0.85 Ni 0.38 Zn 0.04 Mn 0.48 Ti 0.1 O2 has been shown to be stable in moist air.

[0129] O3-Na 0.85 Ni 0.38 Zn 0.04 Mn 0.48 Ti 0.1 19, which shows the high-temperature XRD analysis of O2, it is observed that the initial O3 phase maintains its O3 structure during heating at high temperatures and begins to form the P3 phase as sodium is lost from the structure during the cooling step. In other words, the formation of the P3 phase occurs primarily during the slow cooling step of the synthesis, thus indicating the importance of the slow cooling step in forming the thermodynamically most stable structure for a given stoichiometry.

[0130] Example 8 Na 0.85 Ni 0.38 Zn 0.04 Mn 0.48 Ti 0.1In Example 8, O2 was synthesized using excess NaCO3, i.e., step (c) was carried out at a temperature of 900 °C for 6 hours, followed by step (e) at a temperature of 1000 °C, together with intermediate grinding (step (d)). Contrary to Example 8, in Example 9, step (e) was not followed by a slow cooling step (f), but by a cooling step (f) consisting of directly quenching the sample from 1000 °C to room temperature.

[0131] As shown in Figure 20(a), such synthesis yielded a pure O3 phase, i.e., O3-Na 0.85 Ni 0.38 Zn 0.04 Mn 0.48 Ti 0.1 O2 is reached, while P3-O3-Na is reached by slow cooling. 0.85 Ni 0.38 Zn 0.04 Mn 0.48 Ti 0.1 O2 is obtained (Figure 20(b)).

[0132] <Conclusion> All synthesized materials exhibited better moisture stability than the monosodium O3 materials, with the pure P2 phase materials showing the best stability. 2+ , Zn 2+ , Mn 4+ , and Ti 4+ Among various compositions designed to achieve x = 0.67, 0.76, 0.9, and 1 (for comparison), the best results in terms of humidity stability were achieved with the P2 type Na 0.67 Ni 0.3 Zn 0.03 Mn 0.52 Ti 0.15 Obtained with O2.

[0133] In general, optimizing the stoichiometry and synthesis conditions of the materials is crucial to obtain sodium layered oxides with favorable electrochemical performance. In the formation of P2-O3 and P3-O3 structures, the slow cooling process plays a key role in stabilizing the P-type structure and forming a surface enriched with transition metal layers.

[0134] When achieving the final desired composition, it is necessary to take into account the loss of sodium during the calcination process, so when moving to bulk-scale synthesis, it is necessary to modify (adjust) synthesis conditions such as calcination time and temperature.

[0135] <References> 1.Ivana Hasa, Sathiya Mariyappan, Damien Saurel, Philipp Adelhelm, Alexey Y.Koposov, Christian Masquelier, Laurence Croguennec, Montse Casas-Cabanas. Challenges of today for Na-based batteries of the future: From materials to cell metrics., Journal of Power Sources, 482, p. 228872 (2020). DOI: 10.1016 / j.jpowsour.2020.228872 2.J.-M. Tarascon, Na-ion versus Li-ion batteries: Complementary rather than competitive ness. Joule. 4(8), p.161- 1620 (2020). 3.Y. Subramanian, W. Oh, W. Choi, H. Lee, M. Jeong, R. Thanavel, WS. Yoon, Optimizing high voltage Na3V2(PO4)2F3 cathode for achieving high rate sodium ion batteries with long cycle life. Chemical Engineering Journal. 403, p. 126291 (2021). 4.K. Kubota, S. Kumakura, Y. Yoda, K. Kuroki, and S. Komaba, Electrochemistry and Solid-State Chemistry of NaMeO2(Me = 3d Transition Metals). Adv. Energy Mater., 8, 1703415 (2018). 5.K. Smith, J. Treacher, D. Ledwoch, P. Adamson, and E. Kendrick, Novel High Energy Density Sodium Layered Oxide Cathode Materials: From Material to Cells. ECS Trans., 75, 13-24 (2017). 6.C. Delmas, C. Fouassier, and P. Hagenmuller, Structural Classification and Properties of the Layered Oxides. Phys. BC, 99, 81-85 (1980). 7.M Sathiya, J Thomas, D Batuk, V Pimenta, R Gopalan, JM Tarascon, Dual Stabilization and Sacrificial Effect of Na2CO3for Increasing Capacities of Na-Ion Cells Based on P2-Na x MO2Electrodes. Chemistry of Materials, 29 (14), 5948-5956 (2017).

Claims

1. The sodium layered oxide is of formula I: Na ｘ M1 ａ＋ １－ｙ－ｚ－ｎ M2 ｂ＋ ｙ M3 ｃ＋ ｚ M4 ｄ＋ ｎ O ２ , (-) Where: M1 ａ＋ , M2 ｂ＋ , M3 ｃ＋ , M4 ｄ＋ are different transition metal ions or mixtures thereof, x is a number ranging from 0.5 to less than 1; y, z, n are numbers ranging from 0.01 to 0.85; y+z+n is less than 1; a, b, c, and d are the oxidation numbers of the transition metal ions M1, M2, M3, and M4, respectively; and The cumulative oxidation state of the transition metal ion, a*(1-y-z-n)+(b*y)+(c*z)+(d*n), is equal to 4-x; The sodium layered oxide represented by formula I is P2-Na ２／３ Ni １／４ Mn １／２ Ti １／６ Zn １／１２ O ２ , or P2-Na ２／３ Ni １／４ Mn １／２ Ti １／６ Mg １／１２ O ２ ,isn't it. A sodium layered oxide characterized by:

2. The sodium layered oxide according to claim 1, characterized in that it has a crystal structure that can be selected from the group consisting of O3 when x is 0.8 to less than 1, a P2-O3 mixture when x is 0.7 to 0.8, a P3-O3 mixture when x is 0.7 to 0.85, and P2 when x is 0.7 or less; particularly preferably, the crystal structure is a P2-O3 or P3-O3 structure.

3. 3. The sodium layered oxide according to claim 1, wherein M1 is Ni.

4. 4. The sodium layered oxide according to claim 1, wherein M2, M3 and M4 are selected from the group consisting of Mg, Zn, Cu, Fe, V, Cr, Mn, Ge, Sn, Ti, Zr, Co and mixtures thereof, preferably selected from the group consisting of Zn, Mn, Ti, Cu, Fe, Mg and mixtures thereof, and more preferably selected from the group consisting of Zn, Mn and Ti.

5. 5. The sodium layered oxide of claim 4, wherein M1, M2, M3, and M4 are Ni, Zn, Mn, and Ti, respectively.

6. 4. Sodium layered oxide according to any one of claims 1 to 3, characterized in that M1 is Ni, M2 and M4 are either Mn or Ti, and y is less than 0.07, advantageously less than 0.06, preferably less than 0.

05.

7. Na ０．６７ Ni ０．３ Zn ０．０３ Mn ０．５２ Ti ０．１５ O ２ , Na0.76Ni ０．３５ Zn ０．０３ Mn ０．５２ Ti ０．１ O ２ , Na ０．８５ Ni ０．３８ Zn ０．０４ Mn ０．４８ Ti ０．１ O ２ , Na ０．９ Ni ０．４５ Zn ０．０５ Mn ０．４ Ti ０．１ O ２ , Na ０．７ Ni ０．２ Fe ０．３ Mn ０．３５ Ti ０．１５ O ２ , Na ０．７ Ni ０．２５ Fe ０．２ Mn ０．４０ Ti ０．１５ O ２ , Na ０．６７ Ni ０．３ Cu ０．０３ Mn ０．５２ Ti ０．１５ O ２ , or Na ０．６７ Ni ０．３ Mg ０．０３ Mn ０．５２ Ti ０．１５ O ２ 5. The sodium layered oxide according to claim 1, wherein the sodium layered oxide is represented by the formula:

8. Na ０．６７ Ni ０．３ Zn ０．０３ Mn ０．５２ Ti ０．１５ O ２ , Na ０．７６ Ni ０．３５ Zn ０．０３ Mn ０．５２ Ti ０．１ O ２ , or Na ０．８５ Ni ０．３８ Zn ０．０４ Mn ０．４８ Ti ０．１ O ２ , advantageously P2-Na ０．６７ Ni ０．３ Zn ０．０３ Mn ０．５２ Ti ０．１５ O ２ , P2-O3-Na ０．７６ Ni ０．３５ Zn ０．０３ Mn ０．５２ Ti ０．１ O ２ , or P3-O3-Na ０．８５ Ni ０．３８ Zn ０．０４ Mn ０．４８ Ti ０．１ O ２ 8. The sodium layered oxide of claim 7, characterized in that it has the formula:

9. A method for producing a sodium layered oxide of formula I according to any one of claims 1 to 8, The method comprises the steps of: (a) mixing a powder of a sodium precursor and a powder of a transition metal precursor of the sodium layered oxide in stoichiometric amounts to obtain a solid powder mixture; (b) heating the solid powder mixture in an air atmosphere at a temperature in the range of 500°C to 900°C to obtain a fired powder; (c) cooling the calcined powder at a rate of 1.5°C / min or less; (d) pulverizing the sintered powder to obtain a pulverized sintered powder; (e) heating the solid powder mixture in an air atmosphere at a temperature ranging from 700°C to 1100°C to obtain a ground and re-fired powder; and (f) Cooling the re-fired powder, advantageously at a rate of 1.5°C / min or less. A method for producing a sodium layered oxide, characterized by

10. The electrode material consists of: - sodium layered oxide according to any one of claims 1 to 8; - electronically conductive additives such as carbon black; and - optionally a polymer binder, An electrode material characterized by:

11. An electrochemical cell (battery) comprising: - Electrolyte; a negative electrode configured to reversibly accept sodium ions from the electrolyte and reversibly release sodium ions to the electrolyte, the negative electrode having at least one current collector; a positive electrode comprising the sodium layered oxide of any one of claims 1 to 8 or the electrode material of claim 10, configured to reversibly accept sodium ions from an electrolyte and reversibly release sodium ions to the electrolyte, the positive electrode having at least one current collector; and - A separator in contact with both the negative and positive electrodes and mixed with an electrolyte containing sodium ions. Electrochemical cell (battery) characterized by:

12. 12. The electrochemical cell (battery) of claim 11, wherein the separator is selected from the group consisting of glass fiber, polyolefin separators, and cellulosic films.

13. 13. The electrochemical cell (battery) of claim 11 or claim 12, wherein the negative electrode comprises sodium metal, a carbonaceous compound, hard carbon, antimony, tin, phosphorus, or a mixture thereof.

14. 14. The electrochemical cell of any one of claims 11 to 13, wherein the cell is a coin cell, a pouch cell, a cylindrical cell (18650, 21700, 36500, etc.), or a prismatic cell.

15. 15. The electrochemical cell (battery) of any one of claims 11 to 14, wherein the electrolyte comprises: - sodium salts, for example NaPF ６ , NaClO ４ , NaFSI, NaTFSI, NaBETI, NaBF ４ , Na[B(hexafluoroisopropyloxy, OiPrF)4], Na[B(perfluorinated pinacolate, O ２ C ２ (CF ３ ) ４ ) 2], or mixtures thereof; solvents, such as dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, propylene carbonate, ethylene carbonate; esters, such as methyl acetate, ethyl acetate, ethyl propionate or methyl propionate, or mixtures thereof; and - optionally additives such as vinylene carbonate, 1,3-propane sultone, succinonitrile, sodium difluoro(oxalato)borate, or mixtures thereof. Electrochemical cell (battery) characterized by:

16. A battery comprising a series of electrochemical cells (batteries) according to any one of claims 11 to 15.

17. 9. Use of the sodium layered oxide according to any one of claims 1 to 8 as an electroactive compound in a cell or battery, preferably as a positive electrode material.

Images