COMPOSITION COMPRISING AN ALKALI METAL SALT OF BIS(FLUORO SULFONYL)IMIDE

Abstract

The present invention relates to a composition comprising an alkali metal salt of bis(fluorosulfonyl)imide and to the use of such composition in an electrolyte for batteries.

Claims

1. A composition comprising: at least one alkali metal salt of bis(fluorosulfonyl)imide; at least one alkali metal salt of FSO.sub.3 in an amount up to 100 ppm, as measured by ionic chromatography; at least one compound of formula (I) or a salt thereof as represented in the following formulae, in an amount up to 100 ppm, as measured by ionic chromatography: ##STR00007## and at least one compound of formula (II) or a salt thereof as represented in the following formulae, in an amount up to 100 ppm as measured by ionic chromatography: ##STR00008##

2. The composition (COMP) according to claim 1, wherein said at least one alkali metal salt of FSO.sub.3.sup. is in an amount from 0.1 ppm to 100 ppm.

3. The composition (COMP) according to claim 1, wherein said compound of formula (I) or the salt thereof is present in an amount from 0.1 ppm to 100 ppm as measured by ionic chromatography.

4. The composition (COMP) according to claim 1, wherein said compound (II) or the salt thereof is present in an amount from 0.5 ppm to 100 ppm as measured by ionic chromatography and calculated based on SO.sub.4.sup.2 response factor.

5. The composition (COMP) according to, wherein said salt in each of the FSI-salt, in FSO.sub.3.sup., in compound of formula (I) and in compound of formula (II) is a salt with: lithium, sodium and potassium.

6. The composition (COMP) according to claim 1, wherein said composition (COMP) is a liquid composition.

7. The composition (COMP) according to claim 6, wherein said composition (COMP) further comprises at least one solvent [solvent (S1)].

8. The composition (COMP) according to claim 7, wherein said at least one solvent (S1) is selected in the group consisting of: ethylene carbonate, propylene carbonate, butylene carbonate, -butyrolactone, -valerolactone, dimethoxymethane, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxane, 4-methyl-1,3-dioxolane, methyl formate, methyl acetate, methyl propionate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, sulfolane, 3-methylsulfolane, dimethylsulfoxide, N,N-dimethylformamide, N-methyl oxazolidinone, acetonitrile, valeronitrile, benzonitrile, ethyl acetate, isopropyl acetate, n-butyl acetate, nitromethane and nitrobenzene.

9. The composition (COMP) according to claim 1, said composition (COMP) comprising from 1 to 70 wt. % of said at least one FSI-salt based on the total weight of said liquid composition.

10. The composition (COMP) according to claim 1, said composition (COMP) having a moisture content equal to or less than 15 ppm, as measured by Karl-Fisher titration.

11. The composition (COMP) according to claim 1, said composition (COMP) having a total alcohol content equal to or less than 20 ppm, as measured by head-space gas chromatography (HS-GC-FID).

12. A method comprising incorporating the composition of claim 1 into a non-aqueous electrolyte solution in a battery.

Description

EXAMPLES

Methods

[0099] Ionic chromatography (IC). The anionic impurities were determined by IC using a Dionex ICS-3000 system with conductivity detection, with the following components: [0100] column: AS20 4*250 mm Analytical and AG20 4*50 mm Guard [0101] suppressor: ASRS 300-4 mm, external water additional type.

[0102] The amounts of F.sup., Cl.sup., FSO.sub.3.sup. (or LiFSO.sub.3) in LiFSI solutions were measured quantitatively after calibration using commercial standard solutions (F.sup., Cl.sup.) or commercial samples of KFSO.sub.3.

[0103] The amounts of compounds (I) and (II) were calculated based on SO.sub.4.sup.2 response factor.

[0104] The alcohol content was determined by GC (Agilent 6890N network GC system) equipped with FID detector and Headspace injector, with Split/splitless injection system.

[0105] The .sup.19F-NMR purity of LiFSI was determined using the Area % method on a Bruker advance NMR 300 MHz equipment.

TABLE-US-00001 Product FSO.sub.2N(Li)SO.sub.2F LiFSO.sub.3 FSO.sub.2NH.sub.2 Chemical shift in ppm 52.8 39.6 58.4

[0106] The moisture content of final LiFSI solutions was determined under an inert atmosphere by means of a KF Titrator, such as Mettler C30S device.

Example 1Preparation of LiFSI Grade a According to the Invention

[0107] Synthesis of HCSI. Into a glass-lined 2 m.sup.3 vessel equipped with baffles, a mechanically stirred shaft, a glass-lined DN300 distillation column and heat exchanger, pressure and temperature sensors and liquid and gas glass-lined inlets and outlets, a PTFE-venting, PTFE-gaskets and receiving glass-lined tanks, the whole system being connected to an alkali scrubber, were reacted chlorosulfonyl isocyanate (983 kg) and chlorosulfonic acid (850 kg) by heating progressively to 100-120 C., then up to 140-145 C. over 22 h until gas evolution stopped. The reaction mixture was distilled in order to isolate a pure HCSI fraction (1100 kg).

[0108] Synthesis of ammonium-FSI. Into a PFA-coated 5 m.sup.3 vessel equipped with PFA-lined baffles, a mechanically stirred PFA-coated shaft, a PTFE-lined connectors and heat exchanger, the whole system being connected to an alkali scrubber, ethyl methyl carbonate (3200 kg) and anhydrous ammonium fluoride (840 kg) were introduced. The suspension was homogenized before the HCSI (1098 kg) obtained as disclosed above was introduced progressively, while maintaining the mixture's temperature below 80 C. After complete addition, the suspension was heated at 80 C. for 22 h and cooled to room temperature (RT). The resulting slurry was filtered and the cake washed with additional ethyl methyl carbonate (800 kg). The resulting filtrate (4639 kg) was transferred to a separate 5 m.sup.3 steel vessel equipped with a mechanically stirred shaft, baffles, liquid and gas inlets and outlets and a distillation equipment. The filtrate was mixed with water (139 kg) and 25% aqueous ammonia (30 kg) and stirred at RT for 1 h. Then, wet ethyl methyl carbonate was distilled off, and the resulting concentrate (1482 kg) was filtered and transferred into a glass-lined 5 m.sup.3 vessel equipped with baffles, a mechanically stirred shaft and a heat exchanger. The filtered concentrate was precipitated by controlled addition of dichloromethane (2400 kg). The resulting slurry was filtered onto a stainless steel 5 m.sup.3 filter, the cake washed with additional dichloromethane (600 kg). Crude ammonium bis(fluoro sulfonyl)imide was isolated as a wet solid and further dried to provide a crude dry product (888 kg). The crude NH.sub.4FSI was partitioned in 3 batches and each batch was separately purified. Each batch was dissolved at 20 wt. % in trifluoroethanol at 60-65 C. into a 5 m.sup.3 steel vessel equipped with baffles, a mechanically stirred shaft, a heat exchanger, pressure and temperature sensors and liquid and gas inlets and outlets, a PTFE-venting, PTFE-gaskets and receiving tanks, the whole system being connected to an organic vapors management system. After complete dissolution, 1,4-Dioxane was added over 3 h. After complete 1,4-Dioxane addition, the suspension was cooled to 25 C. over 3 h and maintained at RT for 12 h. The resulting slurry was filtered, and the white solid thus obtained was washed with TFE/Dioxane (75/25 w/w). This protocol was repeated until the impurity profile reached the intermediate required specifications.

[0109] Synthesis of LiFSI. Lithiation was performed into a glass-lined 5 m.sup.3 vessel equipped with baffles, a mechanically stirred shaft, and a heat exchanger, as follows. A 10 wt % solution (based on NH.sub.4FSI) of NH.sub.4FSI. Dioxane in ethyl methyl carbonate was prepared, filtered, then was subjected to a first lithiation step by adding at 1.1 eq of LiOH.Math.H.sub.2O at atmospheric pressure (Patm) and 0 C. to the solution. This mixture was stirred at P.sub.atm over 22 h at 0 C. A second step of ammonia removal was then performed until the NH.sub.4.sup.+ residual content was <10 ppm, and the residual 1,4-dioxane content was <100 ppm. All the 3 batches were subsequently filtered and the resulting filtrates were submitted to distillation.

[0110] Three batches were obtained, each containing 30 wt. % LiFSI in EMC, which were characterized by NMR, GC Head-space, ionic chromatography, KF, ICP, turbidimetry, colorimetry and pH. The results are reported in Table 1 as average.

Comparative Example 1Preparation of LiFSI Grade B of Comparison

[0111] The LiFSI solution employed in comparative example 1 is prepared according to the method described in Example 1 and Example 3 of patent application published as WO 2021/074142 (in the name of Solvay SA).

[0112] Three batches were obtained, each containing 30 wt. % LiFSI in EMC, which were characterized by NMR, GC Head-space, ionic chromatography, KF, ICP, and pH. The results are reported in Table 1 as average.

TABLE-US-00002 TABLE 1 Example 1 Comp Example 1(*) LiFSI Grade A LiFSI Grade B FSO.sub.3.sup. <1 ppm 121.3 ppm compound (I) <1 ppm 32.3 ppm compound (II) 79.3 ppm 155 ppm Alcohol <20 ppm <34 ppm Moisture 11.3 ppm 34.0 ppm F.sup. <1 ppm 3 ppm ({circumflex over ()}) Cl.sup. <1 ppm 3 ppm ({circumflex over ()}) pH 6.1 5.6 Na.sup.+ <1 ppm <1 ppm K.sup.+ <1 ppm 2 ppm Other metals <1 ppm <1 ppm (*)of comparison ({circumflex over ()}) value obtained on one batch only <1 ppm is intended to indicate a value below the quantification limit of the method used, but above the detection limit of the method.

[0113] Each of the compositions comprising EMC and LiFSI prepared as described above in Example 1 and Comparative Example 1 were used for preparing the formulations suitable to be tested in pouch cells.

[0114] Three batches of Formulation A according to the invention were prepared. Two batches of Formulation B of comparison were prepared. The Formulations A and the Formulations B comprised the ingredients shown below:

TABLE-US-00003 TABLE 2 Formulations A Formulations B(*) LiPF6 1M 1M Ethyl carbonate (EC) 30% v/v 30% v/v Ethyl methyl carbonate 70% v/v 70% v/v (EMC) LiFSI grade A 5 wt. % LiFSI grade B 5 wt. % (*)comparison

[0115] A commercial solution of LiFSI 5 wt. % in EMC (considered a benchmark in this technical field) was used as a further comparison.

[0116] The pouch cells were as follows: NCM622/graphite from UTP (4.2V, 965.3 mAh). Test temperature was 45 C. Charge: 1 C/4.2V (CC-CV). Discharge: 1 C/3.0 C (CC).

[0117] The cells were tested for discharge capacity and thickness change. The results are summarized in the following tables.

TABLE-US-00004 TABLE 3 Initial discharge Retention capacity capacity (mAh) (%) after 500 cycles Commercial Sample(*) 896.7 73.5% Formulation A batch 1 906.7 73.1% Formulation A batch 2 906.2 73.4% Formulation A batch 3 904.6 73.3% Formulation B batch 1(*) 899.0 n/p Formulation B batch 2(*) 898.0 n/p (*)of comparison

TABLE-US-00005 TABLE 4 Thickness change during storage test at 60 C. Commercial Formulation Formulation Formulation Sample(*) A1 A2 A3 Initial 2.90 mm 2.91 mm 2.93 mm 2.92 mm 1 week 12.11 mm 11.81 mm 11.78 mm 11.68 mm 2 weeks 12.59 mm 12.23 mm 12.24 mm 12.17 mm 3 weeks 12.49 mm 12.24 mm 12.30 mm 12.30 mm 4 weeks 12.66 mm 12.30 mm 12.55 mm 12.52 mm delta (initial 436.6% 422.7% 428.3% 428.8% 4 w) (*)of comparison

[0118] As shown in Table 3, the formulations according to the present invention showed a higher initial discharge capacity than the benchmark and after 500 cycles, they maintained a retention capacity comparable to the benchmark. Differently, as shown in Table 4, compared to the benchmark, the formulations according to the present invention had a lower thickness change during storage test at 60 C. (which is due to a diminished gas evolution and degradation within the pouch cell).

[0119] Differently, the formulations B (of comparison) had an initial discharge capacity below 900, which was lower than the initial of formulations A according to the invention.