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(fluoro sulfonyl)imide and to the use of such composition in an electrolyte for batteries.

Claims

1. A composition [composition (COMP)] comprising: at least one alkali metal salt of bis(fluoro sulfonyl)imide [FSI-salt]; at least one compound of formula (I) or an alkali metal salt thereof as represented in the following formulae, in an amount up to 100 ppm, as measured by ionic chromatography: ##STR00007##

2. The composition (COMP) according to claim 1, wherein said compound of formula (I) or the alkali metal salt thereof is in an amount below 100 ppm.

3. The composition (COMP) according to claim 1, wherein the composition (COMP) comprises at least one alkali metal salt of FSO.sub.3.sup..

4. The composition (COMP) according to claim 3, wherein said alkali metal salt of FSO.sub.3.sup. is in an amount of from 0.1 ppm up to 100 ppm, as measured by ionic chromatography.

5. The composition (COMP) according to claim 1, wherein the composition (COMP) comprises at least one compound of formula (II) or an alkali metal salt thereof as represented in the following formulae: ##STR00008##

6. The composition (COMP) according to claim 5, wherein said compound of formula (II) or the alkali metal salt thereof is in an amount of from 0.5 ppm up to 100 ppm, as measured by ionic chromatography.

7. The composition (COMP) according to claim 1, wherein said alkali metal in each of the FSI-salt, in the alkali metal salt of compound of formula (I) and in the alkali metal salt of compound of formula (II) is selected from lithium, sodium or potassium.

8. The composition (COMP) according to any one of claim 1, wherein said composition (COMP) is a liquid composition.

9. The composition (COMP) according to claim 8, wherein said composition (COMP) further comprises at least one solvent [solvent (S1)].

10. The composition (COMP) according to claim 9, 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, and mixtures thereof.

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

12. 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.

13. 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).

14. A battery composition comprising the composition (COMP) according to claim 1; and a non-aqueous electrolyte solution.

15. The composition (COMP) according to claim 1, wherein said compound of formula (I) or the alkali metal salt thereof is in an amount below 75 ppm.

16. The composition (COMP) according to claim 1, wherein said compound of formula (I) or the alkali metal salt thereof is in an amount below 50 ppm.

17. The composition (COMP) according to claim 1, wherein said compound of formula (I) or the alkali metal salt thereof is in an amount of at least 0.1 ppm,

18. The composition (COMP) according to claim 1, wherein said compound of formula (I) or the alkali metal salt thereof is in an amount of at least 0.5 ppm.

19. The composition (COMP) according to claim 1, said composition (COMP) comprising from 5 to 50 wt. % of said FSI-salt based on the total weight of said liquid composition.

20. The composition (COMP) according to claim 1, said composition (COMP) comprising from 15 to 40 wt. % of said FSI-salt based on the total weight of said liquid composition.

Description

DISCLOSURE OF THE INVENTION

[0020] In the present application: [0021] all the numerical ranges should be understood as including the limits, unless otherwise specified; [0022] any description, even though described in relation to a specific embodiment, is applicable to and interchangeable with other embodiments of the present invention; [0023] where an element or component is said to be included in and/or selected from a list of recited elements or components, it should be understood that in related embodiments explicitly contemplated here, the element or component can also be any one of the individual recited elements or components, or can also be selected from a group consisting of any two or more of the explicitly listed elements or components; any element or component recited in a list of elements or components may be omitted from such list.

[0024] In a first aspect, the the present invention relates to a composition [composition (COMP)] comprising: [0025] at least one alkali metal salt of bis(fluoro sulfonyl)imide [FSI-salt]; [0026] at least one compound of formula (I) as represented below or an alkali metal salt thereof

##STR00003##

in an amount up to 100 ppm, as measured by ionic chromatography.

[0027] Preferably, composition (COMP) comprises said compound of formula (I) or the alkali metal salt thereof in an amount below 100 ppm, more preferably below 75 ppm, even more preferably below 50 ppm and still more preferably below 25 or below 15 ppm.

[0028] Preferably, composition (COMP) comprises said compound of formula (I) or the alkali metal salt thereof in an amount of at least 0.1 ppm, more preferably of at least 0.5 ppm, even more preferably of at least 1.0 ppm.

[0029] Optionally, composition (COMP) can comprise further compounds and/or ingredients.

[0030] For example, composition (COMP) can comprise at least one alkali metal salt of FSO.sub.3.sup. in an amount up to 100 ppm, as measured by ionic chromatography.

[0031] Preferably, said composition (COMP) comprises said at least one alkali metal salt of FSO.sub.3.sup. in an amount from 0.1 ppm to 100 ppm, preferably from 0.5 ppm to 50 ppm, more preferable from 0.5 ppm to 20 ppm and even more preferably from 0.5 ppm to 5 ppm.

[0032] In alternative or at the same time, composition (COMP) can comprise at least one compound of formula (II) or an alkali metal salt thereof:

##STR00004##

[0033] Preferably, said compound of formula (II) is in an amount up to 100 ppm as measured by ionic chromatography.

[0034] Preferably, composition (COMP) comprises said compound (II) in an amount of from 0.5 ppm, more preferably from 0.5 ppm to 100 ppm, even more preferably from 0.5 ppm to 50 ppm, still more preferable from 0.5 ppm to 20 ppm and more more preferably from 0.5 ppm to 5 ppm. As will be further explained in the experimental section, the amounts given for compound (II) are measured by ionic chromatography and calculated based on SO.sub.4.sup.2 response factor.

[0035] For sake of clarity, it should be understood that compounds (I) and (II) exist as represented above or in their deprotonated forms.

[0036] For example, compound (I) exists as follows:

##STR00005##

[0037] Similarly, compound (II) exists as follows:

##STR00006##

[0038] Preferably, said alkali metal in each of the FSI-salt, in the alkali metal salt of compound of formula (I) and in the alkali metal salt of compound of formula (II) is selected from lithium, sodium and potassium.

[0039] Preferably, said composition (COMP) is a liquid composition.

[0040] According to this embodiment, composition (COMP) further comprises at least one solvent [solvent (S1)].

[0041] Preferably, said at least one solvent (S1) is selected in the group comprising, more preferably 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.

[0042] Even more preferably, said solvent (S1) is selected from ethylene carbonate, propylene carbonate, butylene carbonate, tetrahydrofuran, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl acetate, isopropyl acetate and n-butyl acetate, even more preferred solvents include dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl acetate, isopropyl acetate and n-butyl acetate. Advantageously, said solvent (S1) is selected from ethyl methyl carbonate and n-butyl acetate.

[0043] More preferably, said composition (COMP) comprises from 1 to 70 wt. %, even more preferably from 5 to 50 wt. % and still more preferably from 15 to 40 wt. % of said at least one alkali metal salt of bis(fluoro sulfonyl)imide based on the total weight of said liquid composition.

[0044] Advantageously, composition (COMP) according to the present invention is further characterized by a low moisture content.

[0045] Preferably, composition (COMP) has a moisture content equal to or less than 15 ppm, as measured by Karl-Fisher titration.

[0046] Advantageously, composition (COMP) according to the present invention is further characterized by a low content of alcohol.

[0047] Preferably, composition (COMP) has a total alcohol content equal to or less than 20 ppm, as measured by head-space gas chromatography (HS-GC-FID).

[0048] Preferably and advantageously, all raw materials used in the method according to the invention, including reactants, may preferably show very high purity.

[0049] Preferably, their content of metal components such as Na, K, Ca, Mg, Fe, Cu, Cr, Ni, Zn, is below 10 ppm, more preferably below 5 ppm, or below 2 ppm.

[0050] The process for manufacturing the composition (C) according to the present invention is not limited.

[0051] For example, according to an embodiment, composition (COMP) may be manufactured via a method comprising the following steps: [0052] (a) reacting bis(chloro sulfonyl)imide (HCSI) or a salt thereof and ammonium fluoride in a solvent, so as to provide ammonium bis(fluorosulfonyl)imide (NH.sub.4FSI) in the form of suspension; [0053] (b) filtering the suspension obtained in step (a); [0054] (c) adding an anti-solvent, so as to precipitate the NH.sub.4FSI in the form of a solid; [0055] (d) reacting the NH.sub.4FSI obtained in step (c) with at least one salification agent comprising at least one alkali metal salt in a solvent, so as to obtain composition (COMP).

[0056] The steps (a) to (d) can be carried out in a batch, semi-batch or continuous mode.

[0057] Preferably, the HCSI is in the form of a solid or in its molten state. More preferably, when the HCSI is provided in its molten state, before step (a), a step of pre-heating the HCSI at a temperature of at least 40 C. is performed. Advantageously, said preheating step is performed at a temperature higher than 40 C. More preferably, said preheating step is performed at a temperature lower than 150 C.

[0058] As used above and within the present invention, the expression ammonium fluoride includes NH.sub.4F and HF adducts of ammonium fluoride, for example NH.sub.4F(HF).sub.n, wherein n is 1 to 10, preferably 1 to 4, more preferably NH.sub.4F.Math.HF or NH.sub.4F(HF).sub.2. The fluorinating agent may be commercially available, or produced by a known method.

[0059] Preferably, the ammonium fluoride is in the form of a solid.

[0060] According to a preferred embodiment, ammonium fluoride is anhydrous. More preferably, the moisture content is 500 ppm or less.

[0061] The amount of ammonium fluoride used is preferably between 2 and 5 equivalents, per 1 mol of the bis(chlorosulfonyl)imide or the salt thereof.

[0062] Preferably, the solvent of step (a) is selected from aprotic organic solvents. More preferably, said solvent is selected in the group comprising: [0063] cyclic and acyclic carbonates, for instance ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, [0064] cyclic and acyclic esters, for instance gamma-butyrolactone, gamma-valerolactone, methyl formate, methyl acetate, methyl propionate, ethyl acetate, ethyl propionate, isopropyl acetate, propyl propionate, butyl acetate, [0065] cyclic and acyclic ethers, for instance diethyl ether, diisopropyl ether, methyl-t-butyl ether, dimethoxymethane, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxane, 4-methyl-1,3-dioxane, 1,4-dioxane, [0066] amide compounds, for instance N,N-dimethylformamide, N-methyl oxazolidinone, [0067] sulfoxide and sulfone compounds, for instance sulfolane, 3-methyl sulfolane, dimethylsulfoxide, [0068] cyano-, nitro-, chloro-or alkyl-substituted alkane or aromatic hydrocarbon, for instance acetonitrile, valeronitrile, adiponitrile, benzonitrile, nitromethane, nitrobenzene.

[0069] According to a preferred embodiment, the organic solvent for step (a) is selected from the group consisting of ethyl acetate, isopropyl acetate, butyl acetate, ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, valeronitrile and acetonitrile.

[0070] According to a preferred embodiment, the organic solvent is anhydrous.

[0071] Step (a) is preferably carried out at a temperature of between 0 C. and 200 C., preferably between 30 C. and 150 C. and more preferably between 50 C. and 100 C.

[0072] Preferably, step (a) is carried out at atmospheric pressure. However, the reaction can be performed below or above atmospheric pressure.

[0073] The order in which the reactants are added is not limited. According to a preferred embodiment, the ammonium fluoride is first added to the organic solvent. Then, the bis(chlorosulfonyl)imide or a salt thereof may be added to the reaction medium.

[0074] The method for manufacturing the starting HCSI or a salt thereof is not limited.

[0075] For example, HCSI can be prepared by reacting chlorosulfonyl isocyanate and chlorosulfonic acid.

[0076] Preferably, HCSI is prepared under heating, more preferably at a temperature in the range from 80 C. to 180 C.

[0077] HCSI thus obtained can be directly used in the method according to the present invention. Alternatively, HCSI thus obtained can be purified before being used in the method according to the present invention. For example, such purification can be performed by distillation.

[0078] Preferably, the anti-solvent used in step (c) is selected in the group comprising, more preferably consisting of: dichloromethane, 1,2-dichloro-ethane, chloroform, carbon tetrachloride, 1,1,2,2-tetrachloroethane, chloro-benzene, dichlorobenzene, trichlorobenzene, diethyl ether, diisopropyl ether, methyl t-butyl ether, pentane, hexane, heptane. Dichloromethane is particularly preferred.

[0079] Preferably, said at least one alkali metal salt in the salification agent used in step (d) is selected from lithium, sodium and potassium.

[0080] When the salification agent comprises lithium as the alkali metal salt, then the agent is preferably selected from the group consisting of lithium chloride (LiCl), lithium fluoride (LiF), lithium carbonate (Li.sub.2CO.sub.3), lithium sulfate (Li.sub.2SO.sub.4), lithium carboxylate (Li.sub.n(RCO.sub.2).sub.n), Li.sub.2SiO.sub.3, Li.sub.2B.sub.4O.sub.7 and mixtures thereof.

[0081] Preferably, the solvent of step (d) is selected from aprotic organic solvents. More preferably, said solvent is selected in the group comprising the solvents detailed above for step (a).

[0082] According to a preferred embodiment, the organic solvent for step (d) is selected from the group consisting of ethyl acetate, isopropyl acetate, butyl acetate, ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, valeronitrile and acetonitrile.

[0083] Step (d) is preferably carried out at a temperature of between 50 C. and 100 C., preferably between 25 C. and 50 C. and more preferably between 5 C. and 10 C.

[0084] Preferably, step (d) is carried out at atmospheric pressure. However, the reaction can be performed below or above atmospheric pressure.

[0085] In a further object, the present invention relates to the use of said composition (C) as a non-aqueous electrolyte solution in a battery.

[0086] Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

[0087] The present invention will be now described in more detail with reference to the following examples, whose purpose is merely illustrative and not intended to limit the scope of the disclosure.

EXAMPLES

Methods

[0088] Ionic chromatography (IC). The anionic impurities were determined by IC using a Dionex ICS-3000 system with conductivity detection, with the following components: [0089] column: AS20 4*250 mm Analytical and AG20 4*50 mm Guard [0090] suppressor: ASRS 300-4 mm, external water additional type.

[0091] 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.31 ) or commercial samples of KFSO.sub.3.

[0092] The amounts of compounds (I-NFSI) and (II-OFSI) were calculated based on SO.sub.4.sup.2-response factor.

[0093] The alcohol content was determined by GC (Agilent 6890N network GC system) equipped with FID detector and Headspace injector, with Split/splitless injection system.

[0094] 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

[0095] 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

[0096] 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).

[0097] 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.

[0098] 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.

[0099] 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

[0100] 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).

[0101] 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.

[0102] 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.

[0103] 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 Formulations A Formulations B(*) LiPF6 1M 1M Ethyl carbonate (EC) 30% v/v 30% v/v Ethyl methyl carbonate (EMC) 70% v/v 70% v/v LiFSI grade A 5 wt. % LiFSI grade B 5 wt. % (*)comparison

[0104] A commercial solution of LiFSI 5 wt. % in EMC (considered a benchmark in this technical field) was used as a further comparison.

[0105] 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).

[0106] The cells were tested for discharge capacity and thickness change. The results are summarized in the following tables.

TABLE-US-00004 TABLE 2 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 3 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

[0107] As shown in Table 2, 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 3, 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).

[0108] 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.