Silyl ester phosphinates as electrolyte additives

Abstract

A non-aqueous electrolyte composition containing (i) at least one aprotic organic solvent; (ii) a compound of formula (I) (iii) at least one ion containing conducting salt; and (iv) optionally one or more additives. ##STR00001##

Claims

1. A non-aqueous electrolyte composition, comprising: at least one aprotic organic solvent; (ii) a silyl ester phosphinate, wherein the silyl ester phosphinate is selected from the group consisting of compounds of formulae (I.5) to (I.8): ##STR00028## (iii) at least one lithium ion containing conducting salt; and (iv) optionally one or more additives.

2. An electrochemical cell, comprising the electrolyte composition according to claim 1.

3. The electrolyte composition according to claim 1, wherein the electrolyte composition contains 0.001 to 10 wt.-% of the silyl ester phosphinate based on a total weight of the electrolyte composition.

4. The electrolyte composition according to claim 1, wherein the at least one lithium ion conducting salt is selected from the group consisting of (a) a salt of formula Li.sup.+[X].sup.−, where X is Y.sup.1(R.sup.7).sub.4 or Y.sup.2(R.sup.8).sub.6; Y.sup.1 is B or Al; Y.sup.2 is P, Sb or As; each R.sup.7 and R.sup.8 are independently F, R.sup.9 or OR.sup.9; R.sup.9 is C.sub.1-C.sub.6 alkyl, C.sub.2-C.sub.6 alkenyl, C.sub.2-C.sub.6 alkynyl, C.sub.5-C.sub.7 (hetero)aryl, and C.sub.6-C.sub.13 (hetero)aralkyl which is optionally substituted by one or more F; wherein one or two pairs of R.sup.7 or one, two, or three pairs of R.sup.8 are optionally combined and jointly be ##STR00029## forming a cycle with Y.sup.1 or Y.sup.2, respectively: ##STR00030## is a bidentate radical derived from a 1,2-, 1,3- or 1,4-diol, from a 1,2-, 1,3- or 1,4-dicarboxylic acid or from a 1,2-, 1,3- or 1,4-hydroxycarboxylic acid; (b) a salt of formula Li[Z(C.sub.nF.sub.2n+1SO.sub.2).sub.m], where m is 1 when Z is oxygen or sulfur, m is 2 when Z is nitrogen or phosphorus, m is 3 when Z is carbon or silicon, and n is an integer ranging from 1 to 20; and (c) LiClO.sub.4; LiCF.sub.3SO.sub.3; Li.sub.2SiF.sub.6; LiAlCl.sub.4, Li(N(SO.sub.2F).sub.2), and lithium oxalate.

5. The electrolyte composition according to claim 1, wherein the at least one lithium ion containing conducting salt contains at least one F.

6. The electrolyte composition according to claim 1, wherein the at least one lithium ion containing conducting salt is selected from the group consisting of LiPF.sub.6, LiAsF.sub.6, LiCF.sub.3SO.sub.3, LiBF.sub.4, lithium difluoro oxalato borate, lithium bis(oxalato) borate, LiClO.sub.4, LiN(SO.sub.2C.sub.2F.sub.5).sub.2, LiN(SO.sub.2CF.sub.3).sub.2, and LiN(SO.sub.2F).sub.2.

7. The electrolyte composition according to claim 1, wherein the at least one aprotic organic solvent is selected from the group consisting of a fluorinated or non-fluorinated cyclic or acyclic organic carbonate, a fluorinated or non-fluorinated ether or polyether, a fluorinated or non-fluorinated cyclic ether, a fluorinated or non-fluorinated cyclic or acyclic acetale or ketale, a fluorinated or non-fluorinated orthocarboxylic acid ester, a fluorinated or non-fluorinated cyclic or acyclic ester or diester of carboxylic acid, a fluorinated or non-fluorinated cyclic or acyclic sulfone, a fluorinated or non-fluorinated cyclic or acyclic nitrile or dinitrile, a fluorinated or non-fluorinated cyclic or acyclic phosphate, and mixtures thereof.

8. The electrolyte composition according to claim 1, wherein the at least one aprotic organic solvent is selected from the group consisting of fluorinated or non-fluorinated ether or polyether, a fluorinated or non-fluorinated cyclic or acyclic organic carbonate, and mixtures thereof.

Description

(1) The present invention is further illustrated by the following examples that do not, however, restrict the invention.

(2) Experimental Section:

(3) I. Electrolyte Additives:

(4) The additives were synthesized following standard silylation procedures M1 [use of silylchloride and amine base, according to Woronkow, Sgonnik, Zhurnal Obshchei Khimii, engl. Edit., Vol. 27 (1957), pages 1550 to 1553] or M2 [use of bis(trimethylsilyl)ether (HMDSO), according to N. Weferling, R. Schmutzler, Zeitschrift für Naturforschung, B: Chemical Sciences, Vol. 43 (1988), pages 1524 to 1528] from the respective phosphinic acids (RPH(O)OH). Non-commercial phosphonic acids were prepared by hydrolysis of dichlorophospines according to procedure M3 [according to G. M. Kosolapoff, J. S. Powell, Journal of the American Chemical Society, Vol. 72 (1950), pages 4291 to 4292], AlBN-mediated Hydrophosphosphinylation M4 or Michael-addition M5 [both according to M. S. Markoulides, A. C. Regan, Tetrahedron Letters, Vol. 52 (2011), pages 2954 to 2956].

(5) TABLE-US-00001 TABLE 1 Electrolyte additives employed A1 A2 A3 A4 A5
A2 Trimethylsilyl Methylphosphinate (CAS: 99136-11-5)

(6) Following method M1, Me.sub.3SiCl (1.5 eq, 236 mmol, 25.8 g) was added at RT to a solution of methylphosphinic acid (1 eq, 157 mmol, 14.0 g; prepared using M3) and trimethylamine (1.5 eq, 236 mmol, 23.8 g) in 350 mL toluene. The formed suspension was further stirred at 50° C. for 3 h until .sup.31P NMR measurement indicated full conversion. The formed precipitate was filtered off, washed with 200 mL toluene and concentrated in vacuo to obtain a colorless oil, which was further distilled (bp.: 53-54° C., 3.4 mbar) to yield compound A2 (18.4 g, 121 mmol, 77% yield).

(7) .sup.1H NMR (500 MHz, CDCl.sub.3) δ 7.20 (dq, J=546.4, 2.1 Hz, 1H), 1.45 (dd, J=15.1, 2.0 Hz, 3H), 0.26 (s, 9H). .sup.31P NMR (203 MHz, CDCl.sub.3) δ 21.43.

(8) A3 Trimethylsilyl Cyclohexylphosphinate (CAS: 77339-71-0)

(9) Following method M2, to a suspension of cyclohexylphosphinic acid (1.0 eq, 33 mmol, 5.0 g; prepared using M4) in 25 mL toluene was slowly added HMDS (0.6 eq, 20 mmol, 3.3 g) and the formed gel further stirred at 90° C. for 2 h until .sup.31P NMR measurement indicated full conversion. The formed precipitate was filtered off, washed with 200 mL toluene and concentrated in vacuo to obtain a colorless oil, which was further distilled (bp.: 120° C. (0.4 mbar) to yield compound A3 (4.4 g, 19 mmol, 58% yield).

(10) .sup.1H NMR (500 MHz, CDCl.sub.3) δ 6.76 (dd, J=525.9, 1.5 Hz, 1H), 1.90-1.45 (m, 6H), 1.25-1.06 (m, 5H), 0.22 (s, 9H). .sup.31P NMR (203 MHz, CDCl.sub.3) δ 31.79.

(11) A4 Trimethylsilyl Phenylphosphinate (CAS: 27262-80-2)

(12) Following method M1, Me.sub.3SiCl (1.0 eq, 150 mmol, 16.5 g) was added at RT to a solution of phenylphosphinic acid (1.0 eq, 150 mmol, 21.3 g; prepared using M3) and trimethylamine (1.05 eq, 158 mmol, 15.9 g) in 350 mL toluene. The formed suspension was further stirred at 50° C. for 3 h until .sup.31P NMR measurement indicated full conversion. The formed precipitate was filtered off, washed with 200 mL toluene and concentrated in vacuo to obtain a colorless oil, which was further distilled (bp.: 71° C., 0.15 mbar) to yield compound A4 (27.6 g, 129 mmol, 86% yield).

(13) .sup.1H NMR (500 MHz, CDCl.sub.3) δ 7.71 (ddd, J=14.2, 8.2, 1.4 Hz, 2H), 7.60 (d, J=566.6 Hz, 1H), 7.56-7.50 (m, 1H), 7.46 (ddd, J=8.5, 6.8, 3.5 Hz, 2H), 0.27 (s, 9H). .sup.31P NMR (203 MHz, CDCl.sub.3) δ 13.21.

(14) A5 Trimethylsilyl Hexylphosphinate (CAS: 77339-70-9)

(15) Following method M2, to a suspension of hexylphosphinic acid (1.0 eq, 33 mmol, 5.0 g; prepared using M4) in 25 mL toluene was slowly added HMDS (0.6 eq, 20 mmol, 3.2 g) and the formed gel further stirred at 90° C. for 6 h until .sup.31P NMR measurement indicated full conversion. The formed precipitate was filtered off, washed with 200 mL toluene and concentrated in vacuo to obtain a colorless oil, which was further distilled (bp.: 110° C. (0.1 mbar) to yield compound A5 (5.4 g, 24 mmol, 73% yield).

(16) .sup.1H NMR (500 MHz, CDCl.sub.3) δ 7.06 (dt, J=534.2, 1.9 Hz, 1H), 1.66 (dtdd, J=15.2, 7.3, 5.9, 1.9 Hz, 2H), 1.55-1.46 (m, 2H), 1.40-1.30 (m, 2H), 1.25 (pd, J=6.3, 5.4, 3.0 Hz, 4H), 0.84 (t, J=6.9 Hz, 3H), 0.27 (s, 9H). .sup.31P NMR (203 MHz, CDCl.sub.3) δ 27.30.

(17) II. Electrolyte Compositions

(18) The electrolyte compositions containing 1.0 M LiPF.sub.6 in a mixture of ethyl carbonate (EC, BASF), diethyl carbonate (DEC, BASF), monofluoroethylene carbonate (FEC, BASF), and vinylene carbonate (VC) were prepared. Different comparative and inventive additives were added to these compositions as indicated in Table 2. “vol. %” refers to the volume of the solvents in the electrolyte composition, “wt. %” refer to the total weight of the electrolyte composition. All solvents were dry (water content <3 ppm). All electrolyte compositions were prepared and stored in an Ar-filled glovebox having oxygen and water levels below 1.0 ppm.

(19) TABLE-US-00002 TABLE 2 Electrolyte compositions employed Solvents Additives Electrolyte [vol. %] [wt. %] composition EC DEC FEC VC A1 A3 A4 A5 EL 1 (comparative) 30 70 1.5 1 — — — — EL 2 (comparative) 30 70 1.5 1 2 — — — EL 3 (inventive) 30 70 1.5 1 — 2 — — EL 4 (inventive) 30 70 1.5 1 — — 2 — EL 5 (inventive) 30 70 1.5 1 — — — 2
III. Electrochemical Cells
III.1) NCM622/Graphite Pouch Cells

(20) The positive electrodes for the electrochemical cycling experiments in pouch cells were prepared by coating on aluminum foil (thickness=17 μm) using a roll coater a slurry containing cathode active material, carbon black and polyvinylidene fluoride (PVdF) binders suspended in N-methyl-2-pyrrolidinone (NMP). The electrode tapes were dried in a hot air chamber and dried further under vacuum at 130° C. for 8 h and the electrodes were pressed using a roll pressor. The cathode active materials employed were Li(Ni.sub.0.6Co.sub.0.2Mn.sub.0.2)O.sub.2 (NCM622). For the negative electrodes, an aqueous slurry aqueous was prepared by mixing graphite and carbon black with CMC (carboxymethyl cellulose) and SBR (styrene butadiene rubber). The obtained slurry was coated onto copper foil (thickness=9 μm) by using a roll coater and dried under hot air chamber (80° C. to 120° C.). The loading of the resulted electrode was found to be ca. 10 mg/cm.sup.2. The electrodes were pressed by roll pressor to an approximate thickness of 72 μm. Pouch cells (250 mAh) were assembled in Ar-filled glove box, comprising NCM positive electrodes and graphite negative electrodes with a separator superposed between cathode and anode. Thereafter, all cells were filled with electrolyte, as described in Tables 2, in an argon-filled glove box having oxygen and water levels below 1.0 ppm and their electrochemical testing carried out in a Maccor 4000 battery-test system.

(21) IV. Evaluation of the Electrochemical Cells

(22) IV.1) Evaluation of Cycling of Pouch Cell Comprising NCM-622 Cathode and Graphite Anode

(23) IV.1.1) Formation

(24) Pouch full-cells prepared comprising a NCM-622 cathode and graphite anode were charged at a constant current of 0.1 C either to a voltage of 3.7 V or during maximum 2 hours. Then, the cells were stored for 17 hours at 45° C. followed by degassing and initial volume measurements carried out via Archimedes measurements in water at ambient temperature.

(25) IV.1.2) High Temperature Storage of Pouch Full-Cell Comprising NCM622//Graphite and NCM811//Graphite at 60° C.

(26) After completing the formation procedure, the cells were charged up to 4.2 V at ambient temperature and then stored at 60° C. for 14 days. The generated gas amount (mL) during the storage was determined by Archimedes measurements in water at ambient temperature and the results are summarized in Table 6. The final charge (CCCV charge, 0.2 C, 4.2 V, 0.015 C cut-off) and discharge (CC discharge, 0.2 C, 3.0 V cut-off) capacities were measured after storage tests. The capacity retention after cycling is expressed as the ratio between the final and initial discharge capacity. The cell resistance after cycling was determined by charging the cells up to 50% SOC and DC internal resistance (DCIR) measurements by applying a current interrupt. The results are presented in Table 3. The inventive electrochemical cells show clearly lower gas generation than the comparative cells.

(27) TABLE-US-00003 TABLE 3 Results obtained from NCM-622//Graphite cells storage experiments at 60° C. Cell Resistance Cell volume change change after 14 days after 14 days storage at 60° C. storage at 60° C. Electrolyte [Ohm cm.sup.2] [mL] Comparative EL 1 21.3 1.86 Example 1 Comparative EL 2 23.8 1.29 Example 2 Inventive EL 3 70.0 0.31 Example 1 Inventive EL 4 43.6 0.27 Example 2 Inventive EL 5 23.9 0.26 Example 3