Method for producing a positive electrode material comprising at least one Na-based solid crystalline phase by ball milling using Na3P

Abstract

The present invention relates to a method for producing a positive electrode material comprising at least one Na-based solid crystalline phase selected in the group consisting of Na-based crystalline P2-phases, Na-based solid crystalline phases of formula Na.sub.(3+x)V.sub.2(PO.sub.4).sub.3 with 0<x3 and Na-based solid crystalline phases of formula Na.sub.(3+y)V.sub.2(PO.sub.4).sub.2F.sub.3 with 0<y3, for a battery using sodium ions as electrochemical vector, said method using a ball milling process involving Na.sub.3P as starting material.

Claims

1. A method for producing a positive electrode material comprising at least one Na-based solid crystalline phase selected in the group consisting of Na-based crystalline P2-phases, Na-based solid crystalline phases of formula Na.sub.(3+x)V.sub.2(PO.sub.4).sub.3 with 0<x3 and Na-based solid crystalline phases of formula Na.sub.(3+y)V.sub.2(PO.sub.4).sub.2F.sub.3 with 0<y3, for a battery using sodium ions as electrochemical vector, said method comprising at least one step of ball milling a powder of Na.sub.3P with a powder of at least one positive-electrode active material capable of inserting sodium ions reversibly and selected in the group consisting of solid Na-based crystalline P2-phases, Na.sub.3V.sub.2(PO.sub.4).sub.3 and Na.sub.3V.sub.2(PO.sub.4).sub.2F.sub.3, said step of ball milling being carried out in a dry atmosphere and without heating.

2. The method of claim 1, wherein the Na-based solid crystalline P2-phases are selected from the group consisting of Na.sub.0.67Fe.sub.0.5Mn.sub.0.5O.sub.2, Na.sub.0.67MnO.sub.2, Na.sub.0.74CoO.sub.2, Na.sub.0.67Co.sub.0.67Mn.sub.0.33O.sub.2, Na.sub.0.67Ni.sub.0.25Mn.sub.0.75O.sub.2 and Na.sub.0.67Ni.sub.1/3Mn.sub.2/3O.sub.2.

3. The method according to claim 1, wherein the positive-electrode active material capable of inserting sodium ions reversibly is selected from the group consisting of Na.sub.3V.sub.2(PO.sub.4).sub.3, Na.sub.3V.sub.2(PO.sub.4).sub.2F.sub.3, Na.sub.0.67Fe.sub.0.5Mn.sub.0.5O.sub.2, Na.sub.0.67MnO.sub.2, Na.sub.0.74CoO.sub.2, Na.sub.0.67Co.sub.0.67Mn.sub.0.33O.sub.2, Na.sub.0.67Ni.sub.0.25Mn.sub.0.75O.sub.2 and Na.sub.0.67Ni.sub.1/3Mn.sub.2/3O.sub.2.

4. The method according to claim 1, wherein the amount of Na.sub.3P varies from 2 w % to 40 w % with regard to the weight of positive-electrode active material.

5. The method according to claim 1, wherein the ball milling step can be performed in the presence of an electronically conducting agent in powder form.

6. The method according to claim 1, wherein the molar ratio of Na.sub.3P/positive-electrode active material varies from 0.05 to 2.

7. The method according to claim 1, wherein the step of ball-milling is carried out with an inert gas.

8. The method according to claim 1, wherein the step of ball-milling is performed at a temperature ranging from 25 to 80 C.

9. The method according to claim 1, wherein the ball-milling step is carried out in a hard steel ball-miller jar containing a weight of milling-balls (W.sub.mb) such as the weight ratio W.sub.mb/W.sub.s, with W.sub.s being the total weight of powder materials contained in the jar, ranges from 10 to 60.

10. The method according to claim 1, wherein the ball milling step is carried out in a ball-miller operating by centrifuging movements of the balls at a rotation speed set at a value ranging from 200 and 1000 rotations per minute.

11. The method according to claim 1, wherein the effective duration of the ball-milling step varies from 0.1 to 50 hours.

12. The method according to claim 1, wherein the process is used to prepare NaFe.sub.0.5Mn.sub.0.5O.sub.2 and the ball milling step is carried out with Na.sub.3P and Na.sub.0.67Fe.sub.0.5Mn.sub.0.5O.sub.2 for 0.5 h to 5 h and with a molar ratio of Na.sub.3P/Na.sub.0.67Fe.sub.0.5Mn.sub.0.5O.sub.2 varying from 0.11 to 0.30.

13. The method according to claim 1, wherein the process is used to prepare Na.sub.4V.sub.2(PO.sub.4).sub.3 and the ball milling step is carried out with Na.sub.3P and Na.sub.3V.sub.2(PO.sub.4).sub.3 for 1 h to 5 h and with a molar ratio of Na.sub.3P/Na.sub.3V.sub.2(PO.sub.4).sub.3 varying from 0.33 to 1.0.

14. The method according to claim 1, wherein the process is used to prepare Na.sub.4V.sub.2(PO.sub.4).sub.2F.sub.3 and the ball milling step is carried out with Na.sub.3P and Na.sub.3V.sub.2(PO.sub.4).sub.2F.sub.3 for 1 h to 5 h and with a molar ratio of Na.sub.3P/Na.sub.3V.sub.2(PO.sub.4).sub.3 varying from 0.33 to 1.0.

15. The method according to claim 1, wherein the process further comprises a step of mixing Na.sub.3P with the positive electrode material comprising at least one Na-based solid crystalline phase selected in the group consisting of Na-based crystalline P2-phases, Na-based solid crystalline phases of formula Na.sub.(3+x)V.sub.2(PO.sub.4).sub.3 with 0<x3 and Na-based solid crystalline phases of formula Na.sub.(3+y)V.sub.2(PO.sub.4).sub.2F.sub.3 with 0<y3, so as to form a positive electrode composite material.

Description

EXAMPLE 1

Preparation of Na.SUB.4.V.SUB.2.(PO.SUB.4.).SUB.2.F.SUB.3 .by Ball Milling with Na.SUB.3.P

[0056] 1) Preparation of Na.sub.3V.sub.2(PO.sub.4).sub.2F.sub.3

[0057] Na.sub.3V.sub.2(PO.sub.4).sub.2F.sub.3 was first prepared by traditional solid state reactions according to the method disclosed by L. Croguennec et al. (Chemistry of Materials, 2014, 26, 4238-4247).

[0058] 2) Preparation of Na.sub.3P by Ball-Milling

[0059] Stoichiometric amounts of metallic sodium as bulk (1.38 g, Sigma) and red phosphorus (0.62 g, Alfa, 325 mesh) were filled into a hard steel ball-milled jar of a Spex 8000M ball-miller (30 cm.sup.3) in an Ar-filled glove box and equipped with seven hard steel balls, each having a weight of 7 g and a diameter of 12 mm. These solid materials were ball milled for 2-10 h to obtain Na.sub.3P particles.

[0060] 3) Preparation of Na.sub.4V.sub.2(PO.sub.4).sub.2F.sub.3

[0061] Na.sub.3V.sub.2(PO.sub.4).sub.2F.sub.3 were ball milled with excess amount of Na.sub.3P (1 Na.sub.3P per Na.sub.3V.sub.2(PO.sub.4).sub.2F.sub.3) to make Na.sub.4V.sub.2(PO.sub.4).sub.2F.sub.3. 1.0 g of Na.sub.3V.sub.2(PO.sub.4).sub.2F.sub.3 and 0.24 g of Na.sub.3P were filled into a hard steel ball-milled jar (30 cm.sup.3) (Spex 8000M) in an Ar-filled glove box and equipped with four hard steel balls, each having a weight of 7 g and a diameter of 12 mm Na.sub.4V.sub.2(PO.sub.4).sub.2F.sub.3 was obtained after 3 h of ball milling.

[0062] The XRD patterns of Na.sub.4V.sub.2(PO.sub.4).sub.2F.sub.3 thus obtained and of initial Na.sub.3V.sub.2(PO.sub.4).sub.2F.sub.3 are given in FIG. 1 annexed [intensity (in arbitrary units) as a function of angle 2 (in degrees)].

EXAMPLE 2

Preparation of Na.SUB.4.V.SUB.2.(PO.SUB.4.).SUB.2.F.SUB.3 .(in Mixture with Na.SUB.3.V.SUB.2.(PO.SUB.4.).SUB.2.F.SUB.3.) by Ball Milling with Na.SUB.3.P

[0063] Na.sub.3V.sub.2(PO.sub.4).sub.2F.sub.3 and Na.sub.3P were prepared according to example 1.

[0064] Na.sub.3V.sub.2(PO.sub.4).sub.2F.sub.3 was ball milled with stoichiometric amount of Na.sub.3P prepared according to the method given in step 2) of example 1 (0.167 Na.sub.3P per Na.sub.3V.sub.2(PO.sub.4).sub.2F.sub.3) to make Na.sub.4V.sub.2(PO.sub.4).sub.2F.sub.3 in mixture with Na.sub.3V.sub.2(PO.sub.4).sub.2F.sub.3. 1.0 g of Na.sub.3V.sub.2(PO.sub.4).sub.2F.sub.3 and 0.04 g of Na.sub.3P were filled into a hard steel ball-milled jar (30 cm.sup.3) (Spex 8000M) in an Ar-filled glove box and equipped with four hard steel balls, each having a weight of 7 g and a diameter of 12 mm. An intimate mixture of 0.5 mole of Na.sub.3V.sub.2(PO.sub.4).sub.2F.sub.3 (starting material) and 0.5 mole Na.sub.4V.sub.2(PO.sub.4).sub.2F.sub.3 was obtained after 3 h of ball milling. This intimate mixture which represents a composite material can be used as an active material.

[0065] The XRD patterns of the composite material thus obtained and of initial Na.sub.3V.sub.2(PO.sub.4).sub.2F.sub.3 are given in FIG. 2 annexed [intensity (in arbitrary units) as a function of angle 2 (in degrees)].

EXAMPLE 3

Preparation of Na.SUB.1.Fe.SUB.0.5.Mn.SUB.0.5.O.SUB.2 .by Ball-Milling with Na.SUB.3.P

[0066] 1) Preparation of Na.sub.0.67Fe.sub.0.5Mn.sub.0.5O.sub.2

[0067] Firstly, Na.sub.0.67Fe.sub.0.5Mn.sub.0.5O.sub.2 (denoted Na.sub.0.67FMO) was prepared by solid state reaction according to the method reported by S Komaba et al. (Nature Materials, 2012, 11, 512).

[0068] 2) Preparation of Na.sub.1Fe.sub.0.5Mn.sub.0.5O.sub.2

[0069] Na.sub.0.67Fe.sub.0.5Mn.sub.0.5O.sub.2 was ball milled with excess amount of Na.sub.3P prepared according to the method given in step 2) of example 1 (0.22 Na.sub.3P per Na.sub.0.67Fe.sub.0.5Mn.sub.0.5O.sub.2) to make Na.sub.1Fe.sub.0.5Mn.sub.0.5O.sub.2. 1 g of Na.sub.0.67FMO and 0.21 g of Na.sub.3P were filled into a hard steel ball-milled jar (30 cm.sup.3) (Spex 8000M) in an Ar-filled glove box and equipped with four hard steel balls, each having a weight of 7 g and a diameter of 12 mm Na.sub.1Fe.sub.0.5Mn.sub.0.5O.sub.2 was obtained after ball milling for 2 h.

[0070] The XRD patterns of Na.sub.1Fe.sub.0.5Mn.sub.0.5O.sub.2 thus obtained and of initial Na.sub.0.67Fe.sub.0.5Mn.sub.0.5O.sub.2 are given in FIG. 3 annexed [intensity (in arbitrary units) as a function of angle 2 (in degrees)].

EXAMPLE 4

Preparation of Na.SUB.1.Fe.SUB.0.5.Mn.SUB.0.5.O.SUB.2./Na.SUB.3.P Positive-Electrode Composite Material by Ball-Milling with Na.SUB.3.P and Further Addition of Na.SUB.3.P

[0071] Na.sub.1Fe.sub.0.5Mn.sub.0.5O.sub.2 was prepared according to example 3.

[0072] Na.sub.1Fe.sub.0.5Mn.sub.0.5O.sub.2 was mixed by short time ball milling (i.e. during 10 min approximately) with 10% by weight of Na.sub.3P, so as to form a positive-electrode composite material which has improved electrochemical performances compared to Na.sub.1Fe.sub.0.5Mn.sub.0.5O.sub.2 as such or Na.sub.0.67Fe.sub.0.5Mn.sub.0.5O.sub.2.