Electrolyte composition including a specific combination of additives, its use as non-aqueous liquid electrolyte in a Na-ion battery and Na-ion battery including such an electrolyte composition

Abstract

Some embodiments include an electrolyte composition for a battery using sodium ions as electrochemical vector, to the use of such an electrolyte composition as non-aqueous liquid electrolyte in a sodium-ion battery and to a sodium-ion battery comprising such a non-aqueous liquid electrolyte. In some embodiments, the amount of (oxalato)borate ranges from 0.05 to 10 wt. %, relative to the total weight of the electrolyte composition.

Claims

1. An electrolyte composition comprising at least a sodium salt dissolved in at least one solvent and a combination of additives, wherein: said solvent is selected from the group consisting of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, propylene carbonate, ethyl acetate, ethyl propionate, methyl propionate and mixtures thereof; the combination of additives includes at least: sodium difluoro(oxalato)borate (NaODFB), as a first additive, at least a nitrile of formula (I):
N≡C—(CH.sub.2).sub.n,—C≡N  (I) with n being an integer equal to 2, 3 or 4, as a second additive; and 1,3-propane sultone or ethylene sulfate, as a third additive, wherein the amount of (oxalato)borate ranges from 0.05 to 10 wt. %, relative to the total weight of the electrolyte composition.

2. The electrolyte composition according to claim 1, wherein nitrile of formula (I) is succinonitrile.

3. The electrolyte composition according to claim 2, wherein the amount of succinonitrile ranges from 0.1 to 5.0 wt. %, relative to the total weight of the electrolyte composition.

4. The electrolyte composition according to claim 1, wherein the amount of nitrile of formula (I) ranges from 0.1 to 10 wt. %, relative to the total weight of the electrolyte composition.

5. The electrolyte composition according to claim 1, wherein the amount of said third additive ranges from 0.1 to 5.0 wt. %, relative to the total weight of the electrolyte composition.

6. The electrolyte composition according to claim 1, wherein said third additive is 1,3-propane sultone.

7. The electrolyte composition according to claim 1, wherein the solvent is a mixture of at least two solvents comprising ethylene carbonate as a first solvent and a second solvent selected from the group consisting of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, propylene carbonate, ethyl acetate, ethyl propionate and methyl propionate.

8. The electrolyte composition according to claim 1, wherein the mixture of at least two solvents comprises a mixture of ethylene carbonate and propylene carbonate in a volume ratio of 1:1.

9. The electrolyte composition according to claim 1, wherein said combination of additives further comprises a forth additive selected from the group consisting of vinylene carbonate and vinylethylene carbonate.

10. The electrolyte composition according to claim 9, wherein the amount of said forth additive ranges from 0.1 to 10.0 wt. %, relative to the total weight of the electrolyte composition.

11. The electrolyte composition according to claim 1, wherein said electrolyte composition includes sodium difluoro(oxalato)borate, succinonitrile, 1,3-propane sultone and vinylene carbonate.

12. The electrolyte composition according to claim 1, wherein said electrolyte composition includes sodium difluoro(oxalato)borate, succinonitrile, 1,3-propane sultone and vinylene carbonate in a mixture of ethylene carbonate and propylene carbonate in a volume ratio of 1:1.

13. A non-aqueous liquid electrolyte for use in a Na-ion battery comprising an electrolyte composition according to claim 1.

14. The electrolyte according to claim 13, wherein said Na-ion battery comprises a hard carbon negative electrode including a binder.

15. A non-aqueous liquid electrolyte to reduce self-discharge and enhance retention capacity in a Na-ion battery comprising an electrolyte composition according to claim 1.

16. A Na-ion battery comprising: at least one positive electrode comprising at least one positive electrode active material and a current collector, at least one negative electrode comprising a negative electrode active material, and at least one separator impregnated with a non-aqueous liquid electrolyte, said separator being disposed between said positive electrode and said negative electrode, wherein said non-aqueous liquid electrolyte is an electrolyte composition of claim 1.

17. The Na-ion battery according to claim 16, wherein the negative electrode active material of the negative electrode is a carbon material and said negative electrode further comprises a polymer binder.

18. The Na-ion battery according to claim 17, wherein said polymer binder is carboxymethylcellulose.

Description

(1) The electrochemical performances, in terms of self-discharge and capacity retention, of each of cells Na—B1 to Na—B11 are reported on annexed FIG. 1 to:

(2) FIG. 1 gives the evolution of the voltage (V) as a function of capacity (in mAh g.sup.−1 based on the positive electrode active material mass) for battery Na—B1 according to the invention,

(3) FIG. 2 gives the evolution of the capacity (in mAh g.sup.−1 based on the positive electrode active material mass) as a function of the number of cycles for battery Na—B1 according to the invention,

(4) FIG. 3 gives the evolution of the voltage (V) as a function of capacity (in mAh g.sup.−1 based on the positive electrode active material mass) for battery Na—B2 according to the invention,

(5) FIG. 4 gives the evolution of the capacity (in mAh g.sup.−1 based on the positive electrode active material mass) as a function of the number of cycles for battery Na—B2 according to the invention,

(6) FIG. 5 gives the evolution of the voltage (V) as a function of capacity (in mAh g.sup.−1 based on the positive electrode active material mass) for battery Na—B3 not forming part of the invention,

(7) FIG. 6 gives the evolution of the capacity (in mAh g.sup.−1 based on the positive electrode active material mass) as a function of the number of cycles for battery Na—B3 not forming part of the invention,

(8) FIG. 7 gives the evolution of the voltage (V) as a function of capacity (in mAh g.sup.−1 based on the positive electrode active material mass) for battery Na—B4 not forming part of the invention,

(9) FIG. 8 gives the evolution of the capacity (in mAh g.sup.−1 based on the positive electrode active material mass) as a function of the number of cycles for battery Na—B4 not forming part of the invention,

(10) FIG. 9 gives the evolution of the voltage (V) as a function of capacity (in mAh g.sup.−1 based on the positive electrode active material mass) for battery Na—B5 not forming part of the invention,

(11) FIG. 10 gives the evolution of the capacity (in mAh g.sup.−1 based on the positive electrode active material mass) as a function of the number of cycles for battery Na—B5 not forming part of the invention,

(12) FIG. 11 gives the evolution of the voltage (V) as a function capacity (in mAh g.sup.−1 based on the positive electrode active material mass) for battery Na—B6 not forming part of the invention,

(13) FIG. 12 gives the evolution of the capacity (in mAh g.sup.−1 based on the positive electrode active material mass) as a function of the number of cycles for battery Na—B6 not forming part of the invention,

(14) FIG. 13 gives the evolution of the voltage (V) as a function of capacity (in mAh g.sup.−1 based on the positive electrode active material mass) for battery Na—B7 not forming part of the invention,

(15) FIG. 14 gives the evolution of the capacity (in mAh g.sup.−1 based on the positive electrode active material masse) as a function of the number of cycles for battery Na—B7 not forming part of the invention,

(16) FIG. 15 gives the evolution of the voltage (V) as a function of capacity (in mAh g.sup.−1 based on the positive electrode active material mass) for battery Na—B8 not forming part of the invention,

(17) FIG. 16 gives the evolution of the capacity (in mAh g.sup.−1 based on the positive electrode active material mass) as a function of the number of cycles for battery Na—B8 not forming part of the invention,

(18) FIG. 17 gives the evolution of the voltage (V) as a function of capacity (in mAh g.sup.−1 based on the positive electrode active material mass) for battery Na—B9 not forming part of the invention,

(19) FIG. 18 gives the evolution of the capacity (in mAh g.sup.−1 based on the positive electrode active material mass) as a function of the number of cycles for battery Na—B9 not forming part of the invention,

(20) FIG. 19 gives the evolution of the voltage (V) as a function of capacity (in mAh g.sup.−1 based on the positive electrode active material mass) for battery Na—B10 not forming part of the invention,

(21) FIG. 20 gives the evolution of the capacity (in mAh g.sup.−1 based on the positive electrode active material mass) as a function of the number of cycles for battery Na—B10 not forming part of the invention,

(22) FIG. 21 gives the evolution of the voltage (V) as a function of capacity (in mAh g.sup.−1 based on the positive electrode active material mass) for battery Na—B11 according to the invention,

(23) FIG. 22 gives the evolution of the capacity (in mAh g.sup.−1 based on the positive electrode active material mass) as a function of the number of cycles for battery Na—B11 according to the invention.

(24) As disclosed in the comparative examples (like EC3˜EC10), single, binary and wrong ternary combination of additives cannot achieve the purpose of decreased self-discharge and enhanced capacity retention ability at 55° C. In contrast, with the properly chosen combination of additives according to the present invention (like EC1), the side reactions occurring at both positive and negative electrodes can be suppressed, hence enabling to achieve good cycling performances. However, for even better results, i.e. for a full optimization leading to higher capacity retention capability, the addition of vinylene carbonate is preferred. Moreover, we experienced that the good flexibility and wettability of CMC, as opposed to PVdF, is beneficial to the formation of a passivating layer from the additives which shows high efficacy for limiting side reactions.