Hybrid electrolyte

Abstract

A nanoparticulate organic hybrid material comprising inorganic nanoparticles covalently grafted with at least one anion of an organic sodium or lithium salt is provided. In addition, a process for preparing the nanoparticulate organic hybrid material and its use in the preparation of electrolytes suitable for lithium and sodium secondary batteries are provided.

Claims

1. A nanoparticulate organic hybrid material comprising inorganic nanoparticles covalently grafted with at least one anion of an organic sodium or lithium salt through a linker group, said nanoparticulate hybrid material having the following formula (I): ##STR00017## wherein: Np represents the inorganic nanoparticle; L is the linker group selected from C.sub.1-C.sub.6 alkylene and phenyl-C.sub.1-C.sub.4-alkylene group, ##STR00018## is the anion of the organic sodium or lithium salt, and X+ is a sodium or lithium cation.

2. The nanoparticulate organic hybrid material according to claim 1, wherein the inorganic nanoparticles are composed of SiO.sub.2.

3. The nanoparticulate organic hybrid material according to claim 1, wherein L is selected from (CH.sub.2).sub.3 and -phenylene-CH.sub.2CH.sub.2.

4. The nanoparticulate organic hybrid material according to claim 1, wherein the inorganic nanoparticles are further grafted with at least an organic polymeric segment.

5. The nanoparticulate organic hybrid material according to claim 4, wherein the organic polymeric segment is a polyethylene glycol segment.

6. The nanoparticulate organic hybrid material according to claim 1, further comprising a binder selected from the group consisting of polyethylene oxide, polyethylene glycol dimethylether and mixtures thereof.

7. A process for the preparation of a nanoparticulate organic hybrid material as defined in claim 1, said process comprising reacting a compound of formula (III): ##STR00019## wherein: RG is a reacting group; L is a C.sub.1-C.sub.6 alkylene or phenylene-C.sub.1-C.sub.4-alkylene group; and X(+) is a cation of a base, with an inorganic nanoparticle, in the presence of an inorganic sodium or lithium salt.

8. The process according to claim 7, wherein compound of formula (III) is prepared by reacting a compound of formula (IV): ##STR00020## wherein: L is a C.sub.1-C.sub.6 alkylene or phenylene-C.sub.1-C.sub.4-alkylene group, and RG is a reacting group, with the compound: ##STR00021## in the presence of a base.

9. The process according to claim 7, wherein the reactive group is an alkoxysiloxane group.

10. The process according to claim 7, wherein the inorganic nanoparticle is composed of SiO.sub.2.

11. The process according to claim 7, wherein the inorganic nanoparticles are further grafted with at least an organic polymeric segment, said process further comprises attaching the organic polymeric segment to the inorganic nanoparticle through a covalent bond.

12. The process according to claim 11, which further comprises the addition of a binder selected from the group consisting of polyethylene oxide, polyethylene glycol dimethylether and mixtures thereof to the grafted nanoparticles.

13. The process according to claim 7, which further comprises the addition of a binder selected from the group consisting of polyethylene oxide, polyethylene glycol dimethylether and mixtures thereof to the grafted nanoparticles.

14. An electrolyte suitable for its use in a sodium or lithium battery, said electrolyte comprising a nanoparticulate organic hybrid material as defined in claim 1.

15. A sodium or lithium battery which comprises an electrolyte as defined in claim 14.

16. A nanoparticulate organic hybrid material having a formula (II): ##STR00022## wherein; represents an inorganic nanoparticle, L is a C.sub.1-C.sub.6 alkylene or phenylene-C.sub.1-C.sub.4-alkylene group; X+ is a sodium or lithium cation; n is an integer ranging from 3 to 100; q is an integer ranging from 1 to 100; p is an integer ranging from 0 to 100.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows the characterization of SiO.sub.2 nanoparticles grafted with the anion of the sodium salt (SiO.sub.2-anion) by Transmission Electron Microscopy (TEM).

(2) FIG. 2 shows the structure of SiO.sub.2 nanoparticles grafted with PEG9 and the anion of the sodium salt (SiO.sub.2-anion-PEG9) where L is phenyl ethyl and the Mw of the PEG is 600.

(3) FIG. 3 shows the characterization of SiO.sub.2 nanoparticles functionalized with the anion of the sodium salt and with a) PEG9 or b) PEG44 (SiO.sub.2-anion-PEG9 and SiO.sub.2-anion-PEG44) by Transmission Electron Microscopy (TEM).

(4) FIG. 4 shows the characterization of the SiO.sub.2 nanoparticles grafted with PEG-9 and the anion of the sodium salt (SiO.sub.2-anion-PEG9) by NMR (a) .sup.13C; (b) .sup.19F and (c) .sup.29Si.

(5) FIG. 5 shows the characterization of SiO.sub.2 nanoparticles grafted with PEG9 and the anion of the sodium salt (SiO.sub.2-anion-PEG9) by thermogravimetric analysis (TGA).

(6) FIG. 6 shows histograms of TEM measurements of (i) commercial SiO.sub.2 nanoparticles; (ii) SiO.sub.2-anion nanoparticles; (iii) SiO.sub.2-anion-PEG9 nanoparticles; (iv) SiO.sub.2-anion-PEG44 nanoparticles and (v) DLS measurements of commercial SiO.sub.2 nanoparticles, SiO.sub.2-anion nanoparticles and SiO.sub.2-anion-PEG9 nanoparticles.

(7) FIG. 7 shows the ionic conductivity of the polymer electrolytes prepared by: a) SiO.sub.2-anion and b) SiO.sub.2PEG9-anion nanoparticles.

(8) FIG. 8 shows the ionic conductivities of SiO.sub.2-anion and SiO.sub.2-anion-PEG9 electrolytes at room temperature.

(9) FIG. 9 shows the ionic conductivity of the polymer electrolytes prepared by: a) SiO.sub.2-anion-PEG9 and b) SiO.sub.2-anion-PEG44 nanoparticles in the presence of different amounts of PEGDME.

DETAILED DESCRIPTION OF THE INVENTION

(10) The present invention relates to a nanoparticulate organic hybrid material (NOHM) comprising an inorganic nanoparticle core to which an organic sodium or lithium salt is covalently attached.

(11) The sodium or lithium salt derives from a highly delocalized anion which is attached to the nanoparticle through an organic hydrocarbon linker (L group).

(12) The inorganic nanoparticle is therefore covalently grafted with at least one anion of the sodium or lithium salt remaining said anion anchored to the nanoparticle, with only sodium or lithium cations being mobile.

(13) The structure of the nanoparticulate organic hybrid material of the invention is shown below:

(14) ##STR00004## wherein: Np represents the inorganic nanoparticle; L is a linker group selected from C.sub.1-C.sub.6 alkylene and phenyl-C.sub.1-C.sub.4-alkylene group,

(15) ##STR00005##
is the anion of the organic sodium or lithium salt, and X.sup.+ is a sodium or lithium cation.

(16) By the term inorganic nanoparticle it is understood an inorganic physical entity, which is independent and observable, whose effective size in at least one dimension is less than 1 m, i.e. a size between 1 and 999 nm, preferably between 1 and 500 nm, more preferably between 1 and 100 nm, even more preferably between 1 and 50 nm, and much more preferably between 1 and 10 nm. Nanoparticles have a very high surface area to volume ratio which allows attaching numerous organic fragments on the surface of the nanoparticles. Extensive libraries of nanoparticles, composed of an assortment of different sizes, shapes, and materials, and with various chemical and surface properties, have been constructed. In this regard, a variety of nanoparticles can be used as cores, including multi-lobed nanoparticles, conductive nanoparticles, metal nanoparticles, hollow nanoparticles, quantum dots, nanocrystals, magnetic nanoparticles, metal nanoparticles, metal oxide nanoparticles and nanorods.

(17) In a particular embodiment, the inorganic nanoparticle is composed of a material selected from the group consisting of a metal oxide, a metal and a metal salt. Examples of metal oxides include SiO.sub.2, SnO.sub.2, Fe.sub.2O.sub.3, Fe.sub.3O.sub.4, Co.sub.3O.sub.4, MgO, SrO, BaO, CaO, TiO.sub.2, ZrO.sub.2, FeO, V.sub.2O.sub.3, V.sub.2O.sub.5, Mn.sub.2O.sub.3, NiO, CuO, Al.sub.2O.sub.3, ZnO, Ag.sub.2O. Metal oxides include both oxides, metal hydroxides, metal hydrated oxides, metal oxohydroxides or metal oxoperoxohydroxides. Examples of metals include Y, Zr, La, Ce, Mg, Sr, Ba, Ca, Ti, Fe, V, Mn, Ni, Cu, Al, Si, Zn, Ag, Au or Co.

(18) In a preferred embodiment, nanoparticles are composed of a metal oxide, more preferably is SiO.sub.2.

(19) The inorganic nanoparticles may be grafted with a single anion of the organic lithium or sodium salt or with multiple anions of the lithium or sodium salt. Preferably, the nanoparticles are grafted with 1 to 100 anions of the lithium or sodium salt, more preferably with 1 to 20 anions of the lithium or sodium salt.

(20) The anion of the organic sodium or lithium salt is covalently bonded to the inorganic nanoparticle through a linker group. In a particular embodiment, said linker group (L) is a C.sub.1-C.sub.6 alkylene group. The term alkylene refers to a straight or branched divalent hydrocarbon residue, containing no insaturation, having one to six carbon atoms, and which is attached to the nanoparticle by a single bond and to the sulfonyl group by the other single bond, e.g., methylene, ethylene, n-propylene, n-butylene, pentylene, hexylene, and isomers. In a preferred embodiment, L is a propylene group (CH.sub.2).sub.3.

(21) Other L may be found with a phenylene group intercalated between the alkylene and the SO.sub.2 group. In fact, in a preferred embodiment, L is a phenylene-C.sub.1-C.sub.4-alkylene group, more preferably is phenylene ethylene (C.sub.6H.sub.4)CH.sub.2CH.sub.2.

(22) In a preferred embodiment, the linker L is selected from (CH.sub.2).sub.3 and phenyl-CH.sub.2CH.sub.2

(23) In another preferred embodiment, cation X.sup.+ is sodium.

(24) In a particular embodiment, the nanoparticulate hybrid material which is grafted with the anion of the sodium or lithium salt has an organic content of less than 50%, more preferably the organic content ranges from 10 to 25%.

(25) In another preferred embodiment, nanoparticles are further grafted with at least a single organic polymeric segment of a polymer material selected from polyethers, polyesters, polyamides, polysiloxanes, polysulfides, polysulfonates, polysulfonamides, poly(thio ester)s, polyamines and block-copolymers.

(26) Preferred organic polymeric materials are polyethylene glycol (PEG), polyethylene oxide (PEO) and polyoxyethylene (POE). In a preferred embodiment, the organic polymer material is polyethylene glycol, even more preferably is polyethylene glycol monomethyl ether with M.sub.w comprised between 100 and 5000, preferably between 300 and 3500, even more preferably between 1000 and 2500. In a more preferred embodiment, the organic polymer material is PEG9 or PEG44. By the terms PEG9 and PEG44 is understood a polymer containing a polyethyleneoxy chain with 9 and 44 units of ethylene oxide, respectively.

(27) The inorganic nanoparticles may be grafted with a single organic polymeric segment or with multiple organic polymeric segments. Preferably, the nanoparticles are grafted with 1 to 100 organic polymeric segments, more preferably with 1 to 20 organic segments.

(28) In a particular embodiment, the nanoparticulate hybrid material which is grafted with the anion of the organic sodium or lithium salt and the organic polymer material has an organic content ranging from 15 to 50%, more preferably the organic content ranges from 20 to 40%.

(29) The nanoparticulate organic hybrid material (NOHM) grafted with the anion of the organic salt and the organic polymeric segments exhibit liquid-like properties so that the NOHM moves freely and flows in the absence of a suspending solvent. Thus, NOHM are in the form of a self-suspended suspension, wherein the nanoparticles are loose.

(30) In a particular embodiment, the nanoparticulate organic hybrid material has a formula (II):

(31) ##STR00006## wherein: represents an inorganic nanoparticle; L is a C.sub.1-C.sub.6 alkylene or phenylene-C.sub.1-C.sub.4-alkylene group; X+ is a sodium or lithium cation; n is an integer ranging from 3 to 100; q is an integer ranging from 1 to 100; p is an integer ranging from 0 to 100.

(32) In a preferred embodiment, L is selected from (CH.sub.2).sub.3 and phenylene-CH.sub.2CH.sub.2.

(33) In another preferred embodiment, n ranges from 3 to 100, more preferably from 3 to 50, more preferably from 5 to 50.

(34) In another preferred embodiment, q ranges from 1 to 20, more preferably from 1 to 10.

(35) In another preferred embodiment, p ranges from 1 to 20, more preferably from 1 to 10.

(36) In another preferred embodiment, the material constitutive of the inorganic nanoparticle is a metal oxide, more preferably is SiO.sub.2.

(37) In another particular embodiment of the invention, the nanoparticulate organic hybrid material is dispersed in a binder or plasticizer selected from PEG, polyethylene glycol dimethyl ether (PEGDME) and mixtures thereof in order to improve the ionic conductivity. Preferably, said binder is added to the hybrid material in amounts ranging from 1 to 50 wt % with respect to the weight of the hybrid material.

(38) Alternatively, the nanoparticulate organic hybrid material is dispersed in a binder based on a polymer comprising a high fraction (60%) of CH.sub.2CH.sub.2O units, optionally plasticized with PEGDME, organic cyclic carbonates, -butyrolactone or tetralkyl sulfamides.

(39) A second aspect of the present invention relates to a process for the preparation of the nanoparticulate organic hybrid material of the invention. Said process comprises attaching at least an anion of an organic sodium or lithium salt to an inorganic nanoparticle via a covalent bond through an organic linker.

(40) In a particular embodiment, the process for obtaining the nanoparticulate organic hybrid material includes the reaction of a pre-synthesized organic salt bearing the linker L and reacting groups at one end, with complementary functional groups naturally present on or introduced onto the nanoparticles.

(41) Thus, the process of the invention comprises reacting a compound of formula (III):

(42) ##STR00007## wherein: RG is a reacting group; L is a C.sub.1-C.sub.6 alkylene or phenylene-C.sub.1-C.sub.4-alkylene group; and X.sup.(+) is a cation of a base,
with an inorganic nanoparticle,
in the presence of an inorganic sodium or lithium salt.

(43) For example, the nanoparticulate organic hybrid materials are produced by dispersing the pre-synthesized organic salt of formula (III) and an inorganic nanoparticle within the same solution. Preferably, a pre-synthesized organic salt containing terminal reactive functional groups (e.g. alkoxysiloxane groups) is dissolved in water to form a dilute solution. The precursor core nanoparticles, stored in the form of an aqueous suspension, is diluted with an aqueous solution. Temporary hydrogen bonds are created between the organic salt and hydroxyl groups that have formed at the surface of the inorganic nanoparticles. The temporary bonds can then be cured between the inorganic nanoparticle core and the organic salt, resulting in permanent covalent bonds.

(44) The reaction of the pre-synthesized organic salt with the functional groups of the nanoparticle is performed in the presence of an inorganic sodium o lithium salt, such as a lithium or sodium carbonate, in order to provide with the lithium or sodium cations.

(45) In a preferred embodiment, the reacting groups present at one end of the pre-synthesized organic salt of formula (III) are alkoxysiloxane groups, such as (CH.sub.3O).sub.3Si or (C.sub.2H.sub.5O).sub.3Si.

(46) In another preferred embodiment, the material constitutive of the inorganic nanoparticle is SiO.sub.2.

(47) The pre-synthesized organic salt can be formed by reacting a compound of formula (IV):

(48) ##STR00008## wherein: L is a C.sub.1-C.sub.6 alkylene or phenylene-C.sub.1-C.sub.4-alkylene group, and RG is a reacting group,
with the compound:

(49) ##STR00009##
in the presence of a base.

(50) The base can be for example triethylamine, so as the countercation of the compound of formula (III) would be EtNH.sub.3.sup.(+).

(51) Therefore, in a further preferred embodiment, the process of the invention comprises: a) reacting a compound of formula (IVa):

(52) ##STR00010## wherein L is a C.sub.1-C.sub.6 alkylene or phenylene-C.sub.1-C.sub.4-alkylen group, with the compound:

(53) ##STR00011## in the presence of a base, to obtain a compound of formula (IIIa):

(54) ##STR00012## b) reacting a nanoparticle of silicon dioxide with the compound of formula (IIIa) in the presence of a sodium or lithium carbonate.

(55) In a particular embodiment, when the nanoparticulate organic hybrid material of the invention is also grafted with at least a single organic polymeric segment, the process for the preparation of said hybrid material also comprises attaching the organic polymeric segment to the inorganic nanoparticle. The organic polymer is also attached to the inorganic nanoparticle via a covalent bond.

(56) The organic polymeric segments used in accordance to this embodiment can be produced by a variety of techniques known to those skilled in the art, including bulk, solution, dispersion, emulsion, condensation, anionic, free-radical and living radical polymerization.

(57) The same methodology as described for the attachment of the organic salt to the nanoparticle can be used to attach the organic polymeric segment.

(58) Therefore, one approach to produce said nanoparticle organic hybrid material is the graft-to methodology, which involves the reaction of a pre-synthesized polymer bearing reactive groups at one end of the chain with complementary functional groups naturally present on or introduced onto the nanoparticle.

(59) For example, the nanoparticle organic hybrid material is produced by dispersing the reactive polymer, the pre-synthesized organic salt and the inorganic nanoparticle in the same solution. In particular, the pre-synthesized organic salt and the polymer, both containing terminal reactive functional groups (e.g. alkoxysiloxane) are dissolved in water to form a dilute solution. The precursor core nanoparticles, stored in the form of an aqueous suspension, is diluted with an aqueous solution. Temporary hydrogen bonds are created between the organic salt and hydroxyl groups that have formed at the surface of the inorganic nanoparticles and between the organic polymer and hydroxyl groups that have formed at the surface of the inorganic nanoparticles. The temporary bonds can then be cured between the inorganic nanoparticle core and the organic salt and between the inorganic core and the organic polymer, resulting in permanent covalent bonds.

(60) In a preferred embodiment, both the organic salt and the organic polymer have alkoxysiloxanes as terminal reacting groups. In a further preferred embodiment, the organic polymer containing terminal reactive functional group is alkoxysiloxane-PEG-OH or alkoxysiloxane-PEG-epoxide.

(61) In another preferred embodiment, the nanoparticles are composed of SiO.sub.2.

(62) In a further preferred embodiment, the process of the invention comprises: a) reacting a compound of formula (IVa):

(63) ##STR00013## wherein L is a C.sub.1-C.sub.6 alkylene or phenylene-C.sub.1-C.sub.4-alkylene group, with the compound:

(64) ##STR00014## in the presence of a base, to obtain a compound of formula (IIIa):

(65) ##STR00015## b) reacting a nanoparticle of silicon dioxide with the compound of formula (IIIa) and with the compound of formula (V):

(66) ##STR00016## wherein n ranges from 3 to 100, in the presence of a sodium or lithium carbonate.

(67) In a preferred embodiment, n ranges from 5 to 50.

(68) In all the embodiments, L is preferably selected from (CH.sub.2).sub.3 and -phenyl-CH.sub.2CH.sub.2.

(69) In a particular embodiment, the process for the preparation of the nanoparticulate organic hybrid material further comprises subjecting the obtained nanoparticulate organic hybrid material to a dialysis process. This technique is widely known by a skilled person. It includes the separation of the suspended nanoparticulate hybrid material from dissolved ions or small molecules though the pores of a semipermeable membrane.

(70) In a preferred embodiment, the process of the invention further comprises the addition of a binder selected from polyethylene oxide and polyethylene glycol dimethylether to the grafted nanoparticles.

(71) The nanoparticulate organic hybrid material of the invention is useful for a wide range of application but, in particular, for the preparation of electrolytes for rechargeable batteries.

(72) Thus, a further aspect of the present invention refers to an electrolyte suitable for its use in a sodium or lithium battery, said electrolyte comprising a nanoparticulate hybrid material as defined above.

(73) Finally, another aspect of the invention relates to a lithium or sodium rechargeable battery comprising: (i) an electrolyte as describe above, (ii) a lithium or sodium anode, and (iii) a cathode.

EXAMPLES

Example 1: Synthesis of Triethylammonium 2-[(Trifluoromethanesulfonylimido)-N-4-sulfonylphenyl]ethyl trimethoxysilane

(74) This synthesis is carried out according to the process described in J. Am. Chem. Soc. 2009, 131, 2882. 2-(4-Chlorosulfonylphenyl) ethyltrimethoxysilane (2 g) was added under argon to a solution of trifluoromethanesulfonamide (1 g) and triethylamine (3.38 g) into 30 mL of methylene dichloride. The reaction mixture was stirred and heated at 40 C. overnight. An orange-brown-colored wax was obtained after distillation of the solvent.

Example 2: Synthesis of SiO2 Nanoparticles Functionalized with the Anion of a Na Salt

(75) An alkaline stabilized dispersion of silica nanoparticles was diluted to 4 wt % particle fraction by addition of aqueous sodium hydroxide solution, pH11 following the procedure described in J. Mater. Chem. 2011, 21, 10094. Triethylammonium 2-[(Trifluoromethanesulfonylimido)-N-4-sulfonylphenyl]ethyl-trimethoxysilane at a ratio of 1.5 g per 1.0 g SiO.sub.2 nanoparticles was added dropwise at 100 C. Following, the reaction solution was heated for 12 hours at 100 C. After 24 hours, an excess of Na.sub.2CO.sub.3 in hot water was added to grafted SiO.sub.2 nanoparticles to remove the triethylamine. After removing the water, the product was dialyzed with a cellulose acetate (supplier, Aldrich) for several days in water to remove any remaining free organosilane. Finally, MP-TsOH (macroporous polystyrene sulfonic acid) columns were used to remove any remaining triethylamine of dialyzed SiO.sub.2 nanoparticles. SiO.sub.2 nanoparticles functionalized with the anion of the sodium salt (i.e., trifluoromethanesulfonylimido-N-4-sulfonylphenyl) were obtained after distillation of the solvent.

(76) FIG. 1 shows the characterization of such nanoparticles by TEM.

Example 3: Synthesis of SiO2 Nanoparticles Functionalized with PEG and the Anion of a Na Salt

(77) An alkaline stabilized dispersion of silica nanoparticles was diluted to 4 wt % particle fraction by addition of aqueous sodium hydroxide solution, pH11. [Methoxy(polyethyleneoxy)propyl]trimethoxysilane [0.75 g, M.sub.w600 (wherein the polyethyleneoxy chain has 9 units of ethylene oxide) or Mw2130 (wherein the polyethyleneoxy chain has 44 units of ethylene oxide)] and triethylammonium 2-[(Trifluoromethanesulfonylimido)-N-4-sulfonylphenyl]ethyl-trimethoxysilane (0.75 g) were added to 1.0 g SiO.sub.2 nanoparticles dropwise at 100 C. Following, the reaction solution was heated for 12 hours at 100 C. The next day, an excess of Na.sub.2CO.sub.3 in hot water was added to SiO.sub.2 nanoparticles functionalized to remove the tryethylamine. After removing the water, the product was dialyzed for several days in water to remove any remaining free organosilane. Finally, SiO.sub.2 nanoparticles functionalized with PEG-9 or PEG-44 and anion were obtained after distillation of the solvent.

(78) The chemical structure of the obtained SiO.sub.2 nanoparticle grafted with the sodium salt and PEG-9 is depicted in FIG. 2.

(79) FIG. 3 shows the characterization of SiO.sub.2 nanoparticles functionalized with PEG-9 or PEG-44 and the anion of the sodium salt by TEM.

(80) The hybrid nanoparticles obtained according to the procedure described in examples 2 and 3 were characterized by NMR confirming the organic functionalization of the inorganic nanoparticle. FIG. 4 shows the characterization of the SiO.sub.2 nanoparticles grafted with PEG-9 and the anion of the sodium salt by .sup.13C, .sup.19F and .sup.29Si NMR.

(81) The organic content of each functionalized nanoparticle was obtained by measurements of thermogravimetric analysis (TGA). In this way, the organic content of SiO.sub.2-anion-PEG44 (36%) is higher than SiO.sub.2-anion-PEG9 (28%), which could be due to the fact that the chain of the polymer used to prepare SiO.sub.2-anion-PEG44 nanoparticles is longer than the chain used to prepare SiO.sub.2-anion-PEG44 nanoparticles. FIG. 5 shows the characterization of SiO.sub.2-anion-PEG9 nanoparticles by TGA. The maximum weight loss rate temperature (T.sub.max) is approximately 310 C. for both hybrid nanoparticles.

(82) Therefore, these hybrid nanoparticles show a good thermal stability to be used as polymer electrolytes.

(83) The organic content of SiO.sub.2-anion nanoparticles (18%) is lower than SiO.sub.2-anion-PEG nanoparticles which could be due to the double functionalization (PEG and the anion of the sodium salt) in SiO.sub.2-anion-PEG nanoparticles.

(84) The size of all nanoparticles was measured by transmission electron microscopy (TEM) and dynamic light scattering measurements (DLS). As shown in FIG. 6 (i-iv), SiO.sub.2 nanocores show sizes of approximately 10 nm all of them. DLS measurements (FIG. 6(v)) indicate that hybrid nanoparticles, SiO.sub.2-anion, SiO.sub.2-anion-PEG9 and SiO.sub.2-anion-PEG44, present sizes of approximately 14, 18 and 25, respectively. Therefore, these nanoparticles are comprised of approximately 4, 8 and 15 nm organic shells to each SiO.sub.2 nanocores. Furthermore, the size of un-functionalized SiO.sub.2 nanoparticles was confirmed by DLS measurements, which was satisfyingly very similar to the value deduced from TEM (approximately 10 nm).

Example 4: Preparation of Polymer/SiO2 Nanohybrid Electrolytes and Measurements of Na+ Conductivity

(85) A dispersion of SiO.sub.2 nanoparticles functionalized with the anion of the Na salt and obtained according to the procedure described in example 2 was prepared in methanol and water. The dispersion of grafted SiO.sub.2 nanoparticles (0.013 g is equivalent to 1 mol of Na) was added to a mixture of polyethylene glycol dimethyl ether (PEGDME, 0.050 g, M.sub.w=250) and polyethylene oxide (PEO, 0.050 g, M.sub.w=510.sup.6) at ratio 1:1 in weight. After mixing, samples were dried in the convection oven at 80 C. overnight and for at least 24 hours under vacuum.

(86) In the same way, a dispersion of SiO.sub.2 nanoparticles functionalized with polyethylene glycol (PEG9) (Mw470) and the sodium salt and obtained according to the procedure described in example 3, was immersed into a matrix of polyethylene oxide (PEO, Mw5.10.sup.6) and polyethylenglycol dimethylether (PEGDME, Mw250) at ratio 1:1 in weight. After mixing, samples were dried in the convection oven at 80 C. overnight and for at least 24 hours under vacuum.

(87) A study of the relationship between the sodium ion concentration and the ionic conductivity was performed. For this, several polymer electrolytes (Table I) were prepared with 20 units of ethylene oxide of the polymers with respect to different amount of sodium (in moles) (EO/NA40 or 20 or 10 or 6.5).

(88) TABLE-US-00001 TABLE I Nomenclature of the polymer electrolytes Polymer electrolytes PEO:PEGDME EO/Na SiO.sub.2-anion (EO/Na~40) 1 g:1 g 40 SiO.sub.2-anion (EO/Na~20) 20 SiO.sub.2-anion (EO/Na~10) 10 SiO.sub.2-anion (EO/Na~6.5) 6.5 SiO.sub.2-PEG9-anion (EO/Na~40) 1 g:1 g 40 SiO.sub.2-PEG9-anion (EO/Na~20) 20 SiO.sub.2-PEG9-anion (EO/Na~10) 10 SiO.sub.2-PEG9-anion (EO/Na~6.5) 6.5

(89) The hybrid polymer electrolytes obtained were characterized electrochemically with complex impedance measurements.

(90) The ionic conductivity measurement of the polymer electrolytes were carried out by AC impedance spectroscopic technique using a Solartron 1260 over the frequency range from 1 Hz to 1 MHz with a signal level of 10 mV. The conductivity measurements of polymer electrolytes were carried out by sandwiching the samples between two stainless-steel (SS) electrodes. The temperature dependence of the ionic conductivity was performed in a temperature range from 25 to 80 C.

(91) FIG. 7 shows the ionic conductivity of the polymer electrolytes prepared by: a) SiO.sub.2-anion and b) SiO.sub.2PEG9-anion nanoparticles.

(92) As can be seen in FIG. 7, the ionic conductivity increases with temperature in both hybrid polymer electrolytes (SiO.sub.2-anion and SiO.sub.2-anion-PEG). The polymer electrolytes prepared by SiO.sub.2-anion nanoparticles present the highest ionic conductivity with 2 moles of sodium ions (0.026 g of SiO.sub.2-anion per 0.100 g of PEO-PEGDME), while beyond this concentration, the conductivity decreases for these electrolytes. This behavior could be due to an excess of nanoparticles, which generates a hindrance in the mobility of the sodium ions into the polymer matrix. The polymer electrolytes prepared by SiO.sub.2PEG-anion nanoparticles present the highest ionic conductivity with 1 mol of sodium ions (0.020 g of SiO.sub.2PEG-anion).

(93) On the other hand, the ionic conductivities of both hybrid electrolytes (SiO.sub.2-anion and SiO.sub.2PEG-anion) are compared at room temperature in FIG. 8, showing that SiO.sub.2 PEG-anion electrolytes with a ratio EO/Na20 have an ionic conductivity very similar to SiO.sub.2-anion electrolytes with a ratio EO/Na10. Hence, SiO.sub.2PEG-anion electrolytes require fewer sodium ions to obtain ionic conductivities of 10.sup.5 S/cm.

(94) Finally, the electrochemical windows of SiO.sub.2-anion (EO/Na10) and SiO.sub.2PEG-anion (EO/Na20) electrolytes (that have the highest ionic conductivities), were evaluated by cyclic voltammetry measurements showing a very similar electrochemical window, 4.4V and 3.8V, respectively.

Example 5: Preparation of Polymer/SiO2 Nanohybrid Electrolytes with Different Amounts of PEGDME and Measurements of Ionic Conductivity

(95) A dispersion of SiO.sub.2 nanoparticles functionalized with PEG9 or PEG44 and the anion of the socium salt, obtained following the procedure described in example 3, was prepared in water. Polymer electrolytes were synthesized by immersion of SiO.sub.2 nanoparticles (grafted with PEG and Na salt) in different amounts (50 wt %, 30 wt %, 10 wt % and 0 wt %) of the plasticizer PEGDME 5 (M.sub.w=250). After mixing, samples were dried in the convection oven at 80 C. overnight and for at least 24 hours under vacuum.

(96) Once the polymer electrolytes were prepared, their effect on the ionic conductivity was studied. FIG. 9 shows the ionic conductivity of the polymer electrolytes prepared by: a) SiO.sub.2-anion-PEG9 and b) SiO.sub.2-anion-PEG44 nanoparticles. As can be seen, the ionic conductivity increases with the temperature and with the addition of PEGDME for both hybrid polymer electrolytes (SiO.sub.2-anion-PEG9 and SiO.sub.2-anion-PEG44). Furthermore the ionic conductivity is very similar for both hybrid electrolytes, regardless of the amount of plasticizer added.

(97) A maximum conductivity of 10.sup.5 S/cm is observed both for the hybrid polymer electrolyte prepared by SiO.sub.2-anion-PEG9 or SiO.sub.2-anion-PEG44 nanoparticles and 50 wt % PEGDME at room temperature. Hence, these values of ionic conductivities so similar seem to indicate that the grafting of the nanoparticle with polymer of molecular weight 470 or 2010 has not influence on the ionic conductivity of hybrid nanoparticles. However, the mechanical properties of SiO.sub.2-anion-PEG44-50 wt % PEGDME electrolyte are better than that for SiO.sub.2-anion-PEG9-50 wt % PEGDME electrolyte. Such fact could be attributed to the higher molecular weight of the PEG44.

(98) Finally, the electrochemical window of SiO.sub.2-anion-PEG44-50% wt PEGDME electrolyte (the one with highest ionic conductivity with good mechanical properties) was evaluated by cyclic voltammetry measurements using stainless-steel electrodes. The resulting potential window was 5.0V, which is an acceptable working voltage range for device applications, particularly as a polymer electrolyte in sodium rechargeable batteries.