Mixed oxide of titanium and niobium comprising a trivalent metal

Abstract

A lithium-free mixed titanium and niobium oxide, including at least one trivalent metal M, and having a molar ratio Nb/Ti greater than 2, said oxide being selected from the group including the material of formula (I) and the material of formula (II):
M.sub.xTi.sub.12xNb.sub.2+xO.sub.7(I) where 0<x0.20; 0.30.3;
M.sub.xTi.sub.22xNb.sub.10+xO.sub.29(II) where 0<x0.40; 0.30.3.

Claims

1. A lithium-free mixed titanium and niobium oxide, comprising at least one trivalent metal M, and having a molar ratio Nb/Ti greater than 2, wherein said oxide is selected from the group consisting of a material of formula (I) and a material of formula (II):
M.sub.xTi.sub.12xNb.sub.2+xO.sub.7(I) where 0<x0.20; 0.30.3;
M.sub.xTi.sub.22xNb.sub.10xO.sub.29(II) where 0<x0.40; 0.30.3.

2. The mixed titanium and niobium oxide of claim 1, wherein the at least one trivalent metal M is selected from the group consisting of iron, gallium, molybdenum, aluminum, boron, and mixtures thereof.

3. The mixed titanium and niobium oxide of claim 1, wherein the at least one trivalent metal M is iron.

4. An electrode comprising the mixed titanium and niobium oxide of claim 1.

5. An Li-ion accumulator comprising the electrode of claim 4.

6. The mixed titanium and niobium oxide of claim 1, wherein the at least one trivalent metal M is gallium.

7. The mixed titanium and niobium oxide of claim 1, having a theoretical specific capacity in a range of 368 mAh/g to 396 mAh/g, inclusive.

8. The mixed titanium and niobium oxide of claim 1, having a chemical formula Ga.sub.0.10Ti.sub.0.80Nb.sub.2.10O.sub.7.

9. The mixed titanium and niobium oxide of claim 1, having a chemical formula Fe.sub.0.10Ti.sub.0.80Nb.sub.2.10O.sub.7.

10. A method of preparing the mixed titanium and niobium oxide of claim 1, comprising the steps of: solvothermally treating a solution containing at least: a titanium precursor, a niobium precursor, and a precursor of the at least one trivalent metal to obtain a mixed titanium and niobium oxide; optionally, mechanically grinding the mixed titanium and niobium oxide obtained at the end of the solvothermal treatment; and, calcining the mixed titanium and niobium oxide.

11. The method of claim 10, comprising performing the calcination step at a temperature in a range from 700 C. to 1,200 C.

12. The method of claim 10, comprising performing the solvothermal treatment step at a temperature in a range from 200 C. to 250 C.

13. The method of claim 10, comprising performing the solvothermal treatment step for a duration in a range from 2 hours to 10 hours.

14. The method of claim 10, wherein the titanium precursor is selected from the group consisting of titanium oxysulfate (TiOSO.sub.4); titanium isopropoxide (Ti(OCH(CH.sub.3).sub.2).sub.4); titanium chloride (TiCl.sub.4); and titanium butoxide (Ti(OC.sub.4H.sub.9).sub.4).

15. The method of claim 10, wherein the niobium precursor is selected from the group consisting of niobium chloride and niobium ethoxide.

16. The method of claim 10, wherein the precursor of the at least one trivalent metal is selected from the group consisting of FeCl.sub.3, Fe(NO.sub.3).sub.3; Fe.sub.2(SO.sub.4).sub.3; GaCl.sub.3; Ga(NO.sub.3).sub.3; Ga.sub.2(SO.sub.4).sub.3; MoCl.sub.3; AlCl.sub.3; Al(NO.sub.3).sub.3; Al.sub.2(SO.sub.4).sub.3; and BCl.sub.3.

17. The method of claim 10, comprising performing the calcination step for a duration in a range from 30 minutes to 2 hours.

18. The method of claim 10, comprising cooling the mixed oxide by 5 C. to 20 C. after the calcination step.

Description

DESCRIPTION OF THE DRAWING

(1) FIG. 1 shows the graph corresponding to the specific capacity at different rates (10C, C, C/10) of mixed oxide materials TiNb.sub.2O.sub.7 (prior art) and Ga.sub.0.10Ti.sub.0.80Nb.sub.2.10O.sub.7 (invention).

EMBODIMENTS OF THE INVENTION

Example 1: Synthesis of Ga0.10Ti0.80Nb2.10O7

(2) 0.125 g of GaCl.sub.3 and 4.025 g of NbCl.sub.5 are dissolved in 10 mL of anhydrous ethanol under an inert atmosphere (argon) and magnetic stirring. The solution is transferred under air.

(3) Are then added to this solution, 6.052 g of titanium oxysulfate (TiOSO.sub.4) at 15% by mass in sulfuric acid, followed by 10 mL of ethanol to dissolve the precursors, all this under a magnetic stirring. The pH of the solution is adjusted to 10 by slow addition of ammonia NH.sub.3 at 28% by mass into water.

(4) The paste is transferred into a Teflon container having a 90-mL capacity, which is then placed in an autoclave. The paste is then heated up to 220 C. for 5 hours with a heating and cooling ramp of 2 and 5 C./min, respectively.

(5) The paste is then washed with distilled water by centrifugation until a pH between 6 and 7 is obtained.

(6) The resulting compound is heated at 60 C. for 12 hours and then mechanically crushed (MC) for 30 min at 500 rpm (revolutions per minute) in hexane.

(7) After evaporation of the solvent, the powder is calcinated at 950 C. for 1 hour with a heating/cooling ramp of 3 C./min to crystallize Ga.sub.0.10Ti.sub.0.80Nb.sub.2.10O.sub.7.

Example 2: Synthesis of Fe0.10Ti0.80Nb2.10O7

(8) 0.116 g of FeCl.sub.3 and 4.025 g of NbCl.sub.5 are dissolved in 10 mL of anhydrous ethanol under an inert atmosphere (argon) and magnetic stirring.

(9) The resulting solution is transferred under air.

(10) Are then added to this solution, 6.052 g of titanium oxysulfate (TiOSO.sub.4) at 15% by mass in sulfuric acid and 10 mL of ethanol to dissolve the precursors, all this under a magnetic stirring. The pH of the solution is adjusted to 10 by slow addition of ammonia NH.sub.3 at 28% by mass into water.

(11) The paste is transferred into a Teflon container having a 90-mL capacity, which is then placed in an autoclave. The paste is then heated up to 220 C. for 5 hours with a heating and cooling ramp of 2 and 5 C./min, respectively.

(12) The paste is then washed with distilled water by centrifugation until a pH between 6 and 7 is obtained. The compound is heated at 60 C. for 12 hours and then mechanically crushed (MC) for 30 min at 500 rpm in hexane.

(13) After evaporation of the solvent, the powder is calcinated at 950 C. for 1 hour with a heating/cooling ramp of 3 C./min to crystallize Fe.sub.0.10Ti.sub.0.80Nb.sub.2.10O.sub.7.

Example 3

(14) A metal lithium accumulator of button cell format is prepared, which comprises the following elements: a negative lithium electrode (16-mm diameter, 130-m thickness) deposited on a nickel disk used as a current collector; a positive electrode formed of a disk having a 14-mm diameter sampled from a composite film having a 25-m thickness comprising the materials of the invention prepared according to examples 1 and 2 (80% by mass), Super P carbon (10% by mass) as an electron conductor, and polyvinylidene fluoride (10% by mass) as a binder, all being deposited on an aluminum current collector (sheet having a 20-micrometer thickness); an electrode separator impregnated with a liquid electrolyte based on the LiPF6 salt (1 mol/L) dissolved in a mixture of ethyl carbonate, propylene carbonate, and dimethyl carbonate.

(15) The electrochemical performance (specific capacity) between 3.0 and 1.0 V at different rates of Ga.sub.0.10Ti.sub.0.80Nb.sub.2.10O.sub.7 (invention) have been measured and compared with those of TiNb.sub.2O.sub.7 (prior art) (FIG. 1).

(16) TABLE-US-00001 TABLE 1 Capacity loss percentages for TiNb.sub.2O.sub.7, Ga.sub.0.10Ti.sub.0.80Nb.sub.2.10O.sub.7, and Fe.sub.0.10Ti.sub.0.80Nb.sub.2.10O.sub.7 calculated at C/10 between the 5.sup.th and 20.sup.th cycles, at C between the 10.sup.th and 100.sup.th cycle, and at 10 C between the 20.sup.th and 200.sup.th cycles. Compounds calcinated TiNb.sub.2O.sub.7 Ga.sub.0.10Ti.sub.0.80Nb.sub.2.10O.sub.7 Fe.sub.0.10Ti.sub.0.80Nb.sub.2.10O.sub.7 at 950 C. (Prior art) (example 1) (example 2) C/10 5 3 7 C 34 16 12 10 C 26 19 11

(17) Generally, the mixed oxides according to the invention have lower capacity losses than the prior art TiNb.sub.2O.sub.7 material.