Electric energy storage device comprising an in-SITU polymerized solid-state electrolyte

Abstract

An electrical energy storage device comprising a first electrode, a second electrode and a solid state electrolyte in contact with such first and second electrodes, and having such electrolyte a composition comprising a polymeric matrix having a structure made by polymerizing an acrylic monomer and at least one thiol-based crosslinker, a lithium ion-containing salt, a plasticizer, a lithium-containing ceramic additive.

Description

[0001] “ELECTRIC ENERGY STORAGE DEVICE COMPRISING AN IN-SITU POLYMERIZED SOLID-STATE ELECTROLYTE”

[0002] DESCRIPTION

[0003] FIELD OF THE INVENTION

[0004] The present invention relates to the field of electrical energy accumulators, e.g. batteries and supercapacitors, in particular an electrical energy accumulator comprising an in situ polymerized solid-state electrolyte.

[0005] STATE OF THE ART

[0006] The electrical energy accumulators currently available on the market, e.g. batteries and supercapacitors, generally comprise two electrodes, one positive and one negative, a porous separator placed between these electrodes and a liquid electrolyte that is used as an ion conductor between the electrodes. The separator, generally made of plastic or glass material, has the function of distancing the electrodes, preventing short circuits but at the same time allowing ionic conduction. However, the presence of a liquid electrolyte inside the electrical energy accumulators causes numerous disadvantages, both in terms of energy density and in terms of safety. For example, the liquid electrolytes available on the market may be flammable and contain substances, e.g. organic solvents or acidic or basic solutions, which are dangerous for the environment or for the user in the event of any leaks or spills from the accumulator. For this reason, solutions have been developed that include a solid- state electrolyte, thanks to which it is possible to guarantee high energy densities and, at the same time, better safety conditions during use. The manufacturing methods of electrical energy accumulators comprising a solid-state electrolyte generally involve the creation of thin polymeric membranes, prepared starting from: a polymer with a structural function, also known as ‘binder’, ‘host’ or ‘ligand’; one or more salts, e.g., in the case of lithium batteries, lithium salts, which provide the ionic species necessary for the operation of the accumulator. Once created, these polymeric membranes are interposed between the two electrodes. However, the mere mechanical contact between the solid-state electrolyte and the electrodes generates a high interface resistance to ionic transport between the various layers that make up the accumulation device, with a consequent deterioration of performance during use. Therefore, to reduce the resistance between the layers of the electrical energy storage device, especially in high-power systems, it is necessary to maximize the contact area between electrodes and electrolyte.

[0007] Therefore, it is always a felt need to create solutions comprising a solid-state electrolyte having a construction configuration that maximizes the contact area between electrodes and electrolyte as much as possible to improve the performance of the accumulator, and in which the solid-state electrolyte can be installed easily and quickly inside the accumulator in order to increase the production capacity of the manufacturing company and at the same time reduce production costs.

[0008] SCOPE AND SUMMARY OF THE INVENTION

[0009] The present invention has the purpose of satisfying at least in part the needs indicated above. This purpose is achieved by means of a mixture of components capable of being injected inside a battery or supercapacitor and reacting in situ, in order to obtain an electrical energy accumulator comprising a solid-state electrolyte having a composition according to claim 1. According to a preferred embodiment of the present invention, an electrical energy accumulator is presented, e.g. a battery or a supercapacitor, comprising a solid-state electrolyte. This electrolyte is arranged inside the accumulator and has a composition such as to significantly reduce the resistance of the device. In particular, to achieve this result, the electrolyte is presented, at the beginning of the manufacturing process of the accumulator, in the form of a mixture of its components in liquid state. The mixture contains all the reagents necessary for, following a chemical reaction, a solid-state electrolyte to form between the electrodes. The possibility of obtaining a solid-state electrolyte starting from a mixture of substances in liquid phase allows the components of the solid-state electrolyte to diffuse into all the pores of the two electrodes of the battery, and to fully exploit the entire surface of the same, contributing to the objective of maximizing the contact area between the electrodes and the electrolyte. According to an aspect of the present invention, such composition comprises a polymeric matrix based on an acrylic monomer and a thiol-based cross-linker having a structure obtained by polymerizing at least one acrylic monomer preferably in a weight percentage between 18% and 50%, even more preferably between 22% and 45%, and the thiol-based cross-linker preferably between 3.5% and 11%, even more preferably between 5% and 9%. Furthermore, the solid-state electrolyte comprises a salt containing lithium ions in a percentage by weight preferably between 15% and 33%, even more preferably between 17% and 29% and a plasticizer in a percentage by weight preferably between 10% and 38%, even more preferably between 11% and 35% and a ceramic additive in a percentage by weight between 4% and 28%.

[0010] According to another preferred variant of the invention, the composition of the solid-state electrolyte has the following percentage composition ratios by weight: the acrylic monomer between 17% and 21%; the thiol-based crosslinkers between 4% and 6%; the salt containing lithium ions between 6.5% and 8.5%; the plasticizer between 55% and 66%; the ceramic additive in a percentage by weight between 2% and 5%; the initiator or catalyst of the polymerization reaction between 0.7% and 0.8%.

[0011] Following the examples above, it can be argued that the useful ranges are as follows: the thiol-based crosslinker is in weight percentage between 3.5% and 11% and more preferably between 4% and 6%, the acrylic monomer is in weight percentage between 16% and 50% and preferably between 17% and 21%. Furthermore, the lithium ion-containing salt is in weight percentage between 5% and 33%, and preferably between 6.5% and 8.5%, the plasticizer is in weight percentage between 10% and 70% and preferably between 55% and 66% and the lithium-containing ceramic additive is in weight percentage between 2% and 28%, preferably between 2% and 5%.

[0012] Advantageously, the production of a solid-state electrolyte using the above composition, in particular the presence of both the thiol crosslinker and the ceramic additive in the composition, has the surprising effect of increasing the ionic conductivity of the electrolyte compared to solutions in which the composition contains either the thiol crosslinker or the ceramic additive. According to a further aspect of the present invention, the solid-state electrolyte is produced starting from a liquid mixture of the above components, which is injected between the electrodes, separated by the separator, during the production phase of the battery. The mixture is then polymerized by activation of an initiator or a catalyst of a polymerization reaction, contained in the mixture preferably between 0.7% and 0.8% by weight. In this way, the electrolyte mixture can be easily and rapidly injected between the electrodes of the accumulator following the production methods already in use in the energy storage systems industry, finding application in the production of energy accumulators of any shape factor (e.g., cylindrical, bag, prismatic). A list of the abbreviations used in this document is provided at the end.

[0013] The dependent claims describe preferred variants of the invention, forming an integral part of this description.

[0014] DESCRIPTION OF THE DRAWINGS

[0015] The construction and functional characteristics of the electrical energy accumulator comprising a solid-state electrolyte can be better understood from the detailed description that follows, in which reference is made to the attached figures that represent a preferred and non-limiting embodiment, in which:

[0016] • Fig. 1 shows the steps of a first method of producing an electrical energy accumulator comprising a porous separator interposed between the electrodes;

[0017] • Fig. 2 shows a schematic view of the composition of the solid-state electrolyte contained within the porous separator;

[0018] • Figs. 3-4 show the relationship between the impedance modulus and the frequency in a first EIS experiment for two different compositions of solid-state electrolyte;

[0019] • Fig. 5 shows the steps of a method of producing an electrical energy accumulator comprising a porous separator interposed between the electrodes in the form of a coin cell;

[0020] • Fig.6 shows the relationship between the impedance modulus and the frequency in a second EIS experiment for two different solid-state electrolyte compositions;

[0021] • Figs.7-8 show a plot relating the normalized imaginary and real impedance components in an EIS experiment for the two different solid-state electrolyte compositions in Fig.6;

[0022] • Fig.9 shows the relationship between the impedance modulus and the frequency in a third EIS experiment for different solid-state electrolyte formulations;

[0023] • Fig.10 shows a plot relating the imaginary and real impedance components in an EIS experiment for the different solid-state electrolyte formulations in Fig.9;

[0024] • Fig.l l shows a plot calculating the different ionic conductivity values for different solid-state electrolyte formulations resulting from the polymerization of the different mixtures in Fig.9.

[0025] • Fig. 12 shows the current-potential diagram (vs. Li / Li+) of the first cycle of a cyclic voltammetry experiment on a SS | | solid state electrolyte | | Li cell, with the derivative plot of the same, in the potential window 2.5-4.2 V vs. Li / Li+. • Fig. 13 shows the current-potential diagram (vs. Li / Li+) of the second cycle of a cyclic voltammetry experiment on a SS | | solid state electrolyte | | Li cell, with its derivative, in the window 2.5-4.2 V vs. Li / Li+.

[0026] • Fig. 14 shows the Bode plot of the EIS experiment for the measurement of the ionic conductivity of the electrolyte between blocking electrodes, on a SS | | solid state electrolyte | | SS cell, with the phase and the impedance modulus as a function of frequency.

[0027] • Fig. 15 shows the Nyquist diagram of the EIS experiment for the measurement of the ionic conductivity of the electrolyte between blocking electrodes, on a SS | | solid state electrolyte | | SS cell, where the imaginary and real components of the impedance are related.

[0028] • Fig. 16 shows the two Nyquist diagrams of the EIS experiments for the measurement of the lithium transfer number, on a Li | | solid state electrolyte | | Li cell, before and after the polarization of the cell with a 10 mV pulse for 30 minutes, where the imaginary and real components of the impedance are related.

[0029] • Fig.17 shows the current versus time curve during the 30 minutes in which the cell is polarized with the 10 mV pulse, for the measurement of the lithium transfer number, on a Li | | solid state electrolyte | | Li cell.

[0030] Fig. 18 shows the results of the fourth constant current discharge cycle of a semisolid-state cell, in LFP | | solid state electrolyte | | Li configuration with the addition of 1 mol / L LiPF6 liquid electrolyte in EC-DMC 1:1 v / v, at discharge currents of 0.02C and 0.05C, in the potential window 3.8-2.5 V vs Li / Li+.

[0031] DETAILED DESCRIPTION OF THE INVENTION

[0032] According to a first preferred embodiment of the present invention, Fig.1-2 shows a schematic view of an electrical energy accumulator, e.g. a battery or a supercapacitor, comprising a solid-state electrolyte polymerized in situ, and a related manufacturing method. In particular, such electrical energy accumulator comprises a casing, a first positive electrode, a second negative electrode and a porous separator interposed between such electrodes so as to keep them spaced apart, thus preventing a short circuit from occurring in use. Preferably, the porous separator can be selected from those already available on the market or made for the specific application. For example, the separator can be made of PP, PE and PET, in paper or glass material. According to a first aspect of the invention, such electrical energy accumulator comprises a solid-state electrolyte in contact with the first and second electrodes. Before being inserted into the battery, the electrolyte appears as a liquid compound comprising a mixture of an acrylic monomer, at least one thiol-based cross-linker, a lithium salt and lithium-containing ceramic additives, polymerizable under the application of a predetermined stimulus. Stimuli that can be used to trigger the polymerization reaction include a temperature change or light radiation. Following polymerization, the electrolyte appears as a polymeric matrix. In particular, when the electrolyte is in a liquid state, it appears as a mixture comprising an acrylic monomer and at least one thiol-based cross-linker, a lithium salt, a lithium-containing ceramic additive, a combination of organic solvents comprising cyclic or linear carbonates as a plasticizer. Furthermore, this mixture comprises at least one initiator of a radical polymerization or a catalyst of a step polymerization reaction between the acrylic monomers and the thiol-based cross -linkers. In particular, the main monomer is, in the preferred embodiment of the invention, acrylate-based; however, other monomers of various nature can be used; the same molecules with methacrylate terminal units are included, whose reactivity is very similar to acrylates, and vinyl. Among the acrylic monomers, substances equipped with one or more polymerizable acrylate groups can be included, by way of example and not limitation, such as: PEGDA, poly (ethylene glycol) methyl ether acrylate tetra(ethylene glycol) diacrylate, ethylene glycol diacrylate, di(ethylene glycol) diacrylate; branched forms including trimethylolpropane triacrylate, pentaerythritol tetraacrylate, dipentaerythritol penta- / hexa-acrylate, trimethylolpropane ethoxylate triacrylate; linear forms such as 1,6-hexanediol diacrylate.

[0033] Furthermore, the crosslinker is at least one and is thiol-based (functional group -SH), and has the function of binding the various chains of acrylic monomers. In particular, the -SH group is used for its ability to react under radical or base-catalyzed Michael addition conditions with acrylates, methacrylates and vinyls. Among the thiol-based monomers, the following can be included, by way of example but not limitation: a first crosslinker chosen from: pentaerythritol tetrakis(3-mercaptopropionate), trimethylolpropane tris(3- mercaptopropionate), 2 -hydroxymethyl-2 -methyl-l,3-propanediol tris-(3- mercaptopropionate); a second crosslinker chosen from: EDDT, 1,2-ethanedi thiol, 1,6- hexanedithiol, 2,2'-thiodiethanethiol, ethylene glycol bis-mercaptoacetate, hexa(ethylene glycol) dithiol.

[0034] Furthermore, the salts used are lithium-based, e.g. LiTFSI, LiOTf, LiFSI, LiPF6, LiClO4, L1NO3, L1BF4.

[0035] Ceramic additives have the function of improving the mechanical properties of the lattice and of helping the conduction of lithium ions, in addition to inhibiting the growth of lithium dendrites. Among the additives containing lithium, the LiSICON type ceramics such as LAGP, LATP, LLZTO, LLZO can be considered as purely exemplary but not limited to. Plasticizers may be a combination of organic solvents comprising cyclic or linear carbonates, preferably a mixture of equal parts by volume of ethylene carbonate and dimethyl carbonate. The radical initiator may be a photoinitiator such as (2-Benzyl-2-(dimethylamino)-l-[4- (morpholinyl) phenyl)] -1-butanone), 2 -hydroxy-4'- (2 -hydroxy ethoxy) -2- methylpropiophenone, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide. Alternatively, the polymerization may be carried out thermally using a thermoinitiator such as 2,2-azobis(2- methylpropionitrile), AIBN, ACVA, benzoyl peroxide. If, however, the reaction proceeds, in one of its synthetic steps or in its entirety, through a reaction path not mediated by radicals, other molecules are able to catalyze the polymerization reaction, such as amines, organic and inorganic catalysts, etc. Therefore, according to a further aspect of the present invention, this liquid monomer mixture is deposited on the first electrode, on which the porous separator is applied in contact. A portion of the liquid mixture is in turn deposited on the porous separator by arranging the second electrode in contact with this separator in a position opposite to the first electrode with respect to the separator. Advantageously, since the electrolyte is in a liquid state when injected between the electrodes, it is possible to create energy accumulators of various geometries and sizes, such as those for pouch cells, button cells, prismatic / cylindrical cells, or other shapes, without therefore having to provide for particular assembly arrangements. For example, the electrodes and the separator coated by the liquid electrolyte may be arranged inside a casing before its closure, e.g. as conventional electrical energy storage devices comprising a liquid electrolyte are generally constructed. Therefore, once the electrodes and the liquid electrolyte have been arranged in the casing, the polymerization of the liquid mixture may be carried out so as to generate a solid state electrolyte comprising a polymerized polymer matrix. In the preferred embodiment of the invention, a first electrode, a second electrode and a porous separator interposed between the two electrodes, opposite each other, are provided; said first electrode, second electrode and porous separator are inserted into a casing for energy storage devices; the mixture is injected inside the casing so as to wet the first electrode, the second electrode and the separator and the casing is subsequently sealed; the radical initiator is a thermoinitiator, and the envelope containing the liquid electrolyte mixture is heated to a predefined temperature to initiate polymerization between the monomers, e.g. by placing the envelope in an oven. For example, the polymerization temperature of the mixture is between 40°C and 120°C, for a time between 1 hour and 12 hours. In the case where the radical initiator is photosensitive, the mixture is spread on a support and exposed to light radiation, e.g. ultraviolet light, to initiate polymerization between the monomers.

[0036] In both cases, the polymerization reaction preferably proceeds by a radical reaction between the thiol and the acrylate in a single step. The synthesis conditions are simple, and the reaction occurs as soon as the stimulus that starts the radical polymerization reaction is provided. Alternatively, a synthetic route may be chosen that proceeds, in one of its synthetic steps, through the addition reaction between the acrylate and the thiol under basic conditions, also known as Michael addition. Therefore, once the mixture has completed polymerization, a solid-state electrolyte is obtained inside the battery casing, which in turn can be sealed, thus becoming ready for use. Advantageously, the realization of a solid-state electrolyte using the above composition, in particular the presence of both the thiol-based cross-linker and the ceramic additive in the composition, has the surprising effect of increasing the ionic conductivity of the electrolyte compared to solutions in which the thiol cross-linker or the ceramic additive is inside the composition. The resulting material from the electrolyte preparation process, in any of its embodiments, is an organic-inorganic hybrid. In addition, solid-state electrolyte mixtures are obtained by direct mixing of the components. For example, mixing can occur, but is not limited to, ball milling, use of planetary mixers, use of magnetic stirrers, other types of mechanical or ultrasonic stirring..

[0037] REALIZATION EXAMPLES

[0038] The realization examples aim to demonstrate the synergistic action between the various components of the mixture and the procedure used to optimize the performance of the solid- state electrolyte resulting from the polymerization of the liquid mixture.

[0039] Realization example 1 The first realization example shows the preparation and characterization procedure of various membranes obtained via photopolymerization of mixtures of an acrylic monomer, a thiol cross-linker, a lithium salt, a ceramic additive and a plasticizer. These membranes are characterized in order to optimize the composition ratio between the components of the mixture to improve the electrochemical characteristics of the solid-state electrolyte.

[0040] PEGDA was chosen as the acrylic monomer for its excellent ability to conduct lithium ions. Its molecular structure is formed by PEO oligomers with polymerizable acrylate ends. PEGDA with different chain lengths are commercially available, from Mn = 250 g / mol (number average molecular mass) up to Mn = 6000 g / mol. LiTFSI is the lithium salt chosen for the electrolyte, given its ability to be a plasticizer of PEO. The latter represents the reference for the other lithium salts, but the formation of the ion-conducting lattice is not linked to the choice of the particular TFSI- anion. A radical initiator for photopolymerization is added to the mixture of oligomer and lithium salt, briefly described in figures INI, (2- Benzyl-2-(dimethylamino)-l-[4-(morpholinyl) phenyl)] -1-butanone), which reacts under the action of ultraviolet light. The choice of photopolymerization is advantageous in terms of spatiotemporal accuracy of the reaction stimulus and the speed of sample fabrication. To improve the properties of the system, PEGDA reacts with a thiol-based species, EDDT, exploiting the thiol-acrylate reaction under radical conditions. The addition of this crosslinker is advantageous in terms of mechanical properties of the solid-state electrolyte and lowering of the polymer glass transition temperature (Tg) compared to a system whose formulation includes only PEGDA, with the latter condition being necessary to ensure ionic conductivity at a good level. The characterization experiments aim at comparing ionic conductivity and mechanical stability between the various mixtures. In all experiments, the ionic resistance is calculated by means of an EIS experiment on the membranes prepared, cut and used as an electrolyte separator in a button cell with steel electrodes. The presence of steel electrodes, which are defined as blocking electrodes, allows to isolate the contribution given by lithium ions alone to the ionic conductivity. The mechanical characteristics are observed qualitatively based on the possibility of transferring the membrane from the support on which the polymerization occurs and cutting them to proceed with the electrochemical characterization. The first mixture contains: PEGDA at 54% by weight, EDDT at 9%, LiTFSI at 36%, (2-Benzyl-2-(dimethylamino)-l-[4-(morpholinyl) phenyl)] -1-butanone) at 1%. The solid-state electrolyte reaches an ionic conductivity of 6.84- 10z-3 mS / cm. Subsequently, the synergy between the components of the patented mixture is demonstrated in a subsequent experiment. Liquid plasticizers, such as ethylene carbonate, are useful for modulating the glass transition temperature, known to those skilled in the art as Tg, of the polymer and improving its conduction capabilities also by virtue of the high dielectric constant. The use of active ceramic particles, such as LAGP, LATP, LLZTO, has the effect of offering additional conductive paths to lithium ions and stopping the growth of lithium dendrites. The addition of EC to the formulation described above helps to obtain a more flexible system than the previous one, with further facilitated lithium ion conduction. The effect of the plasticizer is reflected in an improvement of the conductivity of the system, bringing the conductivity to 2.22- 10z-2 mS / cm, with an evident improvement of the properties of the electrolytic system. The second mixture has the following composition: PEGDA at 47% by weight, EDDT at 8%, LiTFSI at 32%, (2 -Benzyl -2-(dimethylamino)-l- [4-(morpholinyl) phenyl)] -1-butanone) at 1%, EC at 12%. The comparison between the impedance spectra of the two samples is shown in Fig.3-4, with particular attention to the area of the Nyquist plot where the values obtained for high oscillation frequencies of the alternating current electrical signal applied to the samples are concentrated (in red). All the results have been normalized to take into account the geometric characteristics of the samples, setting g(w)=t / [Z(w)-A], with Q(CD) the resistivity in Q-m, t the thickness of the solid- state electrolyte, Z(w) the impedance modulus and A the area of the sample. It can be seen that the addition of the plasticizer has the effect of reducing the electrical resistance of the membrane, with a 2.2-fold improvement in ionic conductivity. The ionic conductivity, o, is calculated as o=t / (R-A), where t is the membrane thickness in m, R is the real impedance measured via EIS where the Nyquist plot trace crosses the real axis of the impedance, and where therefore the phase angle between the impedance components is minimal, and A is the area of the sample in the button cell (2.5440 / v-4 m2). As can be seen, the addition of the plasticizer to the mixture with thiol-acrylate formulation contributes to the improvement of the conductivity, confirming the synergistic action of all the components of the mixture in improving the performance of the solid-state electrolyte resulting from the polymerization of the monomeric mixture for solid-state electrolytes. These experiments form the basis for subsequent optimizations of the mixture formulation, with the addition of LATP particles, a ceramic capable of improving the conductivity and mechanical properties of the system, up to 28% by weight with respect to the total mass of the mixture.

[0041] Realization example 2

[0042] The second realization example concerns the preparation and characterization of mixtures for solid-state electrolytes obtained via polymerization mediated by a thermal stimulus.

[0043] The results presented in this section aim to confirm the synergistic action of the various components of the mixture for solid-state electrolyte with in situ polymerization, starting from what was obtained in the first characterization phase discussed in the previous section. Different mixtures for solid-state electrolyte were prepared, which demonstrate the interaction of the various components of the mixture towards the lowering of the ionic resistance of the system and the consequent improvement of the ionic conduction properties of the electrolytic system.

[0044] The first two solid-state electrolytes prepared represent the reference for the subsequent experiments. The first blend contains 46 wt.% PEGDA, 10 wt.% EDDT, 31 wt.% LiTFSI, a 1 mol / L blend of LiPF6 in 12 wt.% EC-DMC, 1 wt.% ACVA, without any LATP ceramic particles. The 1 mol / L blend of LiPF6 in 1:1 v / v EC-DMC is known to those skilled in the art as LP30. The second blend contains 46 wt.% PEGDA, 30 wt.% LiTFSI, a 1 mol / L blend of LiPF6 in 11 wt.% EC-DMC, 11 wt.% LATP, 1 wt.% ACVA, without any thiol crosslinker in its composition. The ionic strength of the two systems is evaluated by building a button cell with blocking electrodes. The cell is assembled, as shown in Fig. 5, by depositing 100 uL of the electrolyte mixture on a steel coin cell spacer. A battery separator is then put in contact with the mixture, and another 100 uL of the electrolyte. Another steel spacer is placed opposite the previous one. The cell is closed by means of a hydraulic press dedicated to coin cells, and the mixture is polymerized inside the separator and between the two steel electrodes for 2 hours at 100°C.

[0045] The presence of blocking electrodes is necessary to isolate the contribution of the Li+ ion conduction alone in the structure, in an EIS experiment. The Bode plot for the solid state electrolytes discussed is shown in Fig. 6. The Nyquist plot for the same systems is shown in Fig. 7, and an enlargement of the high frequency region of the latter graph is shown in Fig. 8. It is noted that the mixture containing the acrylate monomer, the salt, the plasticizer and the ceramic has a much higher ionic strength than the mixture containing the acrylic monomer, the thiol crosslinker, the salt and the plasticizer.

[0046] The synergistic action of all components is evident when mixtures containing acrylic monomer, thiol crosslinker, salt, plasticizer and ceramic are prepared. The first surprising effect lies in the possibility of processing the second monomer mixture much more easily, with the thiol crosslinker helping in the dispersion of the ceramic particles in the liquid mixture. The most surprising effect, however, is in the electrochemical properties of the solid state electrolytes containing all the components mentioned. In the range of composition ratios mentioned in the patent text, in fact, a decrease in ionic resistance is noted with the co-presence of ceramic and thiol in variable proportions in the lattice, in a surprising manner compared to the preliminary results. Fig. 9 shows the Bode plot of 3 different solid state electrolyte mixtures containing both thiol and ceramic at the same time, with different composition ratios. The mixtures without one of the two components, prepared as a reference and discussed previously, are shown for comparison. All mixtures with ceramic and thiol have lower ionic resistance than the reference mixtures: it is possible to note from the Bode plot, in fact, that all the -co curves of the mixtures for solid-state electrolyte with various percentages of ceramic and thiol are below the curves relating to the reference mixtures, which have only thiol or only ceramic in them (in addition to the acrylic monomer, the plasticizer and the salt). This effect can also be found in the Nyquist plot of the same systems, reported in Fig. 10. It is noted how the semicircle at high frequencies relating to all the systems containing both ceramic and thiol has an intersection with the real axis of the resistances at lower values than those of the reference mixtures, containing only one between thiol and ceramic. Finally, Fig. 11 shows a bar graph demonstrating the synergistic action of the components and the surprising effect of the decrease in ionic resistance, with consequent increase in ionic conductivity, of the solid-state electrolyte mixtures when they include both ceramic and thiol in their composition. The ionic conductivity, o, is calculated as o=t / (R-A), where t is the membrane thickness in m, R is the real impedance measured via EIS where the Nyquist plot trace crosses the real impedance axis, and where therefore the phase angle between the impedance components is minimal, and A is the area of the sample in the button cell (2.5440 / v-4 m2). The three bars from the right in Fig. 11 are related to compositions including both ceramic and thiol inside them, while the two bars from the left are related to the mixture without ceramic or without thiol, respectively. In the best embodiment, the solid- state electrolyte has an ionic conductivity of 4.84CE-2 mS / cm. The procedure described in embodiment 2 can be readily and easily modified to obtain a functioning electric accumulator, as shown in embodiment 3 and in the subsequent embodiment 4. Compared to the present one, the procedure of embodiment 1 aims to obtain control samples for optimization procedures of the composition ratios between the various components of the mixture and accumulators with which to carry out preliminary experiments and not devices intended for trade.

[0047] Realization Example 3

[0048] The third realization example of a solid-state electrolyte polymerizable in situ in a single synthetic step concerns the fabrication of a Lithium-Ion Battery. The mixture contains PEGDA, for its ability to conduct lithium ions. PEGDA with Mn = 250 g / mol is chosen, in order to obtain a rigid polymer network with many crosslinking points between the chains. PEGDA is copolymerized with two thiol-based crosslinkers, EDDT and PETMP. The reaction occurs under radical conditions between thiol groups and double bonds. The acrylate -thiol ratio is 60:40 mol / mol, with 15% of the thiol groups belonging to PETMP and 85% of the thiol groups belonging to EDDT. The radical thiol-acrylate chemistry is chosen for its versatility and the ease of the reaction conditions. The lithium salt chosen is LiTFSI, with an EO:Li ratio of 8:1. LATP is added to the resin in powder form, at 20% by weight with respect to the total mass of the mixture. The addition of PETMP and LATP goes in the direction of obtaining a rigid elastomeric network capable of preventing the growth of lithium dendrites. LATP is a lithium-containing ceramic. A radical initiator, ACVA, at 1% by weight with respect to the mass of PEGDA is added to the mixture of the components mentioned so far. A coin cell is assembled comprising a standard positive electrode based on LMO with PVDF binder and carbon black as a conductive additive (LMO-PVDF-CB 85:5:10 w / w on aluminum foil as collector). The negative electrode chosen for the battery is a cylinder (chip) of lithium metal. The separator is a commercial PE sheet for lithium batteries. The coin cell is assembled by placing the positive electrode on the cathode of the cell, and 100 uL of polymerizable mixture are deposited on the electrode. Next, the PE separator is placed, which soaks in the solid state electrolyte mixture. An additional 100 uL of the mixture is deposited on the separator. At this point, the lithium metal electrode is contacted with the polymerizable solid state electrolyte mixture. The coin cell is sealed using a hydraulic press. All operations involving the solid state electrolyte mixture are performed in a glove box under an argon atmosphere, with water and oxygen levels below 1 ppm. The cell thus created is placed in an oven at 100°C for 2 hours, realizing the in situ polymerization of the solid state electrolyte mixture, through the radical polymerization reaction between the acrylate and thiol units.

[0049] Realization example 4

[0050] The fourth realization example of an in situ polymerizable solid state electrolyte in a single synthetic step concerns the fabrication of a supercapacitor. Also in this case, the mixture contains PEGDA, for its ability to conduct lithium ions. Elowever, PEGDA with Mn = 6000 g / mol is chosen, in order to obtain a less rigid polymer network than that obtained in the previous example. PEGDA is copolymerized with a thiol-based crosslinker, EDDT. The reaction occurs under radical conditions between thiol groups and double bonds. The acrylate -thiol ratio is 60:40 mol / mol. The thiol-acrylate chemistry is chosen for its versatility and the ease of the reaction conditions. The lithium salt chosen is LiFSI, with an EO:Li ratio of 8:1. LATP in powder form is added to the resin, at 10% by weight with respect to the total mass of the mixture. LATP is a lithium-containing ceramic. To the mixture of the components mentioned so far, a radical initiator, ACVA, is added at 1% by weight with respect to the mass of PEGDA

[0051] A symmetrical button cell is assembled comprising two AC-based electrodes with PVDF binder and carbon black as a conductive additive (AC-PVDF-CB 85:5:10 w / w on aluminum foil as collector). The separator is a commercial cellulose foil for supercapacitors. The button cell is assembled by depositing 100 uL of the polymerizable mixture on the positive electrode. Then, the cellulose separator is placed, which soaks in the solid-state electrolyte mixture. An additional 100 uL of the mixture is deposited on the separator. At this point, the negative electrode is brought into contact with the polymerizable solid-state electrolyte mixture. The button cell is sealed with a hydraulic press. All operations involving the use of the solid state electrolyte mixture are carried out in a glove box under an argon atmosphere, with water and oxygen levels lower than 1 ppm. The cell thus created is placed in an oven at 100°C for 2 hours, carrying out the in situ polymerization of the solid state electrolyte mixture, through the radical polymerization reaction between the acrylate and thiol units.

[0052] Realization example 5

[0053] The fifth example of a solid-state electrolyte polymerizable in situ in a single synthetic step concerns the fabrication of a lithium-ion battery, according to claim 3. The polymerizable mixture contains PEGDA as an acrylic monomer at 20.8% by weight, EDDT as a thiol crosslinker at 4.6%, LiPF6 as a lithium salt at 8.1%, a mixture of EC and DMC 1:1 v / v at 63.4% as a plasticizer, 2.4% by weight of LAGP as a ceramic additive, 0.7% of 2-Benzyl-2- (dimethylamino)-l-[4-(morpholinyl) phenyl)] -1-butanone as a reaction initiator. The resin is polymerizable by a light stimulus, and is made by mixing all the components with a laboratory magnetic stirrer. The resulting mixture is spread by blade coating on a Teflon substrate, with an initial height of 400 pm. After 20 minutes under the illumination of an ultraviolet light lamp, the polymerization is complete. The resulting polymer film has a thickness between 100 and 300 pm. Membranes with a diameter of 18 mm are cut from the polymer film, which function as solid-state electrolyte, in order to assemble CR2032 button cells. The characterization of the electrolyte is conducted through experiments on electrochemical cells in various configurations. The electrochemical stability of the system is characterized by creating an electrochemical cell having: a first steel electrode (stainless steel, in English, abbreviated as SS), called the blocking electrode; the solid-state electrolyte interposed between the two electrodes; a lithium metal cylinder (known as a chip), as the second electrode. 12. Fig. 13. Fig.12 shows the current-potential diagram of the first cycle of the cyclic voltammetry experiment, with the graph of its derivative, in the potential window 2.5- 4.2 V vs. Li / Li+, typical potentials of a LFP and lithium metal based battery. It can be seen how in the first cycle the solid state electrolyte undergoes a reaction around 3.3 V vs. Li / Li+. This process can be ascribed to the formation of some decomposition products of the electrolyte on the lithium metal anode, typical of the solid electrolyte interphase (SEI) formation processes. Fig.13 shows the current-potential diagram of the second cycle of the cyclic voltammetry experiment, with its derivative, in the window 2.5-4.2 V vs. Li / Li+. It can be seen here how the electrolyte undergoes redox processes around 3.8 V during the cathodic scan of the potential. This value is taken as the electrochemical stability value of the solid-state electrolyte. Subsequent experiments confirm that the solid-state electrolyte is stable up to a potential value of (3.8+0.2) V vs. Li / Li+. This value allows working with LFP- based cathodes in cells against lithium metal, which typically guarantee a nominal cell voltage around 3.3 V vs. Li / Li+. Therefore, these experiments demonstrate that a battery with LFP cathode, solid-state electrolyte according to claim 2 and lithium-based anode, in the LFP | | solid-state electrolyte | | Li configuration, does not undergo decomposition processes or parasitic reactions during its operation. The ability of the solid-state electrolyte to conduct lithium ions is then characterized with two experiments in two different configurations:

[0054] - SS | | solid-state electrolyte | | SS, to measure the ionic conductivity of the electrolyte between blocking electrodes;

[0055] Li | | solid state electrolyte | | Li, for measuring the lithium transference number, tLi+. In the first experiment, a cell containing a pair of blocking electrodes is constructed to perform an EIS experiment, the results of which are shown in Fig. 14 and Fig. 15. The first shows the Bode plot of the EIS experiment, with the phase and magnitude of the impedance as a function of frequency; the second shows the Nyquist plot of the same experiment, where the imaginary and real components of the impedance are related. The EIS spectrum can be analyzed by fitting the experimental values to an equivalent circuit consisting of a resistor R and a constant phase element Q connected in series. To those skilled in the art, this procedure is known as equivalent circuit modeling (ECM) of a circuit with a resistor in series with a constant phase element (CPE). The model fits the data well in the medium-high frequency region of the Bode and Nyquist digraphs, between 1 MHz and 1 Hz. The ionic conductivity is calculated according to the equation o=t / (R’A), similar to example 1. For this solid-state electrolyte, o=0.37 mS / cm. The lithium transfer number is calculated according to an experimental procedure known as the Bruce-Vincent method by the person skilled in the art, and reported in S. Zugmann etal., Electrochimica Acta, 2011, 56 (11), 3731-4424. A cell is constructed in a symmetric configuration with two lithium metal electrodes: Li | | solid-state electrolyte | | Li. The characterization procedure includes the following steps: measurement of the cell resistance with an EIS experiment; polarization of the cell for 30 min with a low-amplitude pulse; measurement of the cell resistance after polarization. The results are reported in Fig.16 and Fig.17. The first one shows the Nyquist diagrams of the EIS experiments before and after the cell was polarized with a 10 mV pulse for 30 minutes. The second one shows the current versus time curve during the 30 minutes in which the cell was polarized with the 10 mV pulse. Applying the lithium transfer number formula according to the Bruce-Vincent method, it is found that tLi+= 0.12+0.3. The same experiment is repeated bringing the cell to 60°C, to verify the influence of the temperature on the lithium transport properties in the electrolyte. At 60°C we obtain tLi+= 0.19+0.3. The solid-state electrolyte is used to realize a semi-solid-state cell in LFP configuration | | solid- state electrolyte | | Li. The cell contains a lithium metal anode, the solid-state electrolyte, a glass fiber separator soaked in a solution of LiPF6 in EC-DMC 1:1 v / v with a concentration of 1 mol / L, a LFP-based cathode with a normalized specific capacity per unit area of 1 mAh / cm2. This configuration allows evaluating the performance of the solid-state electrolyte in an energy storage system, without any of the other components of the cell influencing the lithium transport kinetics between cathode and anode. The results of the fourth discharge cycle of the semi-solid-state cell, in the potential window 3.8-2.5 V vs Li / Li+, are reported in Fig.18 for two different discharge currents. The battery is able to deliver a specific capacity, normalized to the content of active material in the cathode, of (130.6+2.8) mAh / g at a discharge current of 0.02C; discharged at 0.05C, the battery delivers (83.4+28.7) mAh / g. Limiting the battery potential window, from 4.2-2.5 V vs Li / Li+ to 3.8-2.5 V vs Li / Li+, allows the device to work in conditions that do not stimulate parasitic reactions during its operation. In addition to the implementation examples described, numerous tests have also been performed with other monomers (e.g. PEGDMA), cross-linkers (e.g. PETMP), plasticizers (e.g. propylene carbonate), salts (e.g. LiTFSI) and additives (e.g. LLZO) with good results. In this description, the examples that returned the best results have been reported, however, it is highly presumable that other compounds mentioned and not tested present comparable results having similar behaviors according to what is present in the literature.

[0056] LIST OF ABBREVIATIONS

[0057] • ACVA: 4,4'-Azobis(4-cyanovaleric acid)

[0058] • AC: activated carbon, carbone attivo.

[0059] • AIBN: 2-2’-Azobis(isobutyrronitrile), 2-2’-azobis(isobutirronitrile)

[0060] • CB: carbon black, nerofumo.

[0061] • DMC: dimethyl carbonate, dimetile carbonato.

[0062] • EC: ethylene carbonate, etilene carbonato.

[0063] • EDDT: 2-2’-ethylenedioxy diethanethiol, 2-2’-etilendiossi dietantiolo

[0064] • EIS: electrochemical impedance spectroscopy, spettroscopia di impedenza elettrochimica

[0065] • EO: ethylene oxide, ossido di etilene

[0066] • FSI: fluorosulfonylimide, fluorosolfonilimmide

[0067] • LAGP: lithium aluminium germanium phosphate, fosfato di litio, alluminio e germanio.

[0068] • LATP: lithium aluminium titanium phosphate, fosfato di litio, alluminio e titanio.

[0069] • LFP: lithium iron phosphate, fosfato di ferro e litio.

[0070] • Li: lithium, litio.

[0071] • LiSICON: lithium Super Ionic CONductor, super conduttore ionico di (ioni) litio

[0072] • LLZO: Lithium lanthanum zirconium oxide, ossido misto di litio, lantanio, zirconio

[0073] • LLZTO: Lithium lanthanum zirconium tantalum oxide, ossido misto di litio, lantanio, zirconio, tantalio (tantalum-doped garnet)

[0074] • LMO: lithium manganese oxide, ossido di manganese litiato

[0075] • OTf: trifluoromethanesulfonate, trifluorometansolfonato.

[0076] • PE: polyethylene, polietilene. • PEGDA: polyethylene glycol) diacrylate, polietilenglicole diacrilato.

[0077] • PF6: hexafluorophosphate, esafluorofosfato.

[0078] • PEO: polyethylene oxide, polietilene ossido.

[0079] • PET: polyethylene terephtalate, polietilene tereftalato. • PETMP: pentaerythritol tetrakis -mercaptopropionate, pentaeritrirolo tetrakis- mercaptopropionato

[0080] • PP: polypropylene, polipropilene.

[0081] • PVDF: polyvinylidene fluoride, poli-vinilidene fluoruro.

[0082] • TFSI: bis (trifluoromethanesulfonyl) imide, bis-(trifluorometansulfunil)immide.

Claims

CLAIMS1. An electrical energy accumulator (E) comprising a first electrode (1), a second electrode (2) and a solid-state electrolyte (3) in contact with such first and second electrodes, and having such electrolyte a composition comprising a polymer matrix resulting from the polymerization of- an acrylic monomer and- at least one thiol-based crosslinker,- a salt containing lithium ions,- a plasticizer,- a lithium-based ceramic additive.

2. Electric energy accumulator (E) according to claim 1, wherein the composition of the solid-state electrolyte consists of a polymer matrix based on an acrylic monomer in a percentage by weight of between 18% and 50% and at least one thiol-based cross-linker in a percentage by weight of between 3.5% and 11%, a salt containing lithium ions in a percentage by weight of between 15% and 33%, a plasticizer in a percentage by weight of between 10% and 38%, a ceramic additive in a percentage by weight of between 4% and 28%.

3. Electric energy accumulator (E) according to claim 1, wherein the composition of the solid-state electrolyte has the following percentage composition ratios by weight: the acrylic monomer between 17% and 21%; the thiol-based cross-linkers between 4% and 6%; the salt containing lithium ions between 6.5% and 8.5%; the plasticizer between 55% and 66%; the ceramic additive in a percentage by weight between 2 and 5%;the initiator or catalyst of the polymerization reaction between 0.7% and 0.8%.

4. Electric energy storage device (E) according to claim 2 or 3, wherein the acrylic monomer equipped with one or more polymerizable acrylate groups, consisting of one of PEGDA (polyethylene glycol) diacrylate, CAS 26570-48-9), polyethylene glycol) methyl ether acrylate, tetra(ethylene glycol) diacrylate, ethylene glycol diacrylate, di(ethylene glycol) diacrylate; branched forms including trimethylolpropane triacrylate, pentaerythritol tetraacrylate, dipentaerythritol penta- / hexa-acrylate, trimethylolpropane ethoxylate triacrylate; linear forms such as 1,6-hexanediol diacrylate; vinyl-based species such as tri (ethylene glycol) divinyl ether.

5. Electric energy accumulator (E) according to any of claims 1 - 4, wherein the thiol-based crosslinker comprises- a first crosslinker selected from pentaerythritol tetrakis(3-mercaptopropionate), trimethylolpropane tris(3-mercaptopropionate), 2-hydroxymethyl-2-methyl-l,3-propanediol tris-(3-mercaptopropionate), and- a second crosslinker selected from linear forms such as 2,2'- (ethylenedioxy) diethanethiol, 1,2-ethanedi thiol, 1,6-hexanedithiol, 2,2' -thiodiethanethiol, ethylene glycol bis- mercaptoacetate, hexa(ethylene glycol) dithiol.

6. A battery according to claim 5, wherein said crosslinker comprises a combination of pentaerythritol tetrakis(3-mercaptopropionate) (CAS 7575-23-7) and 2,2'- (ethylenedioxy) diethanethiol (CAS 14970-87-7).

7. An electric energy battery (E) according to any of claims 1 - 6, wherein the salt is lithium- based, e.g. LiTFSI, LiOTf, LiFSI, L1PF6, L1C1O4, L1NO3, L1BF4.

8. A battery according to claim 7, wherein said salt consists of lithium hexafluorophosphate, L1PF6 (CAS 21324-40-3).

9. Electric energy accumulator (E) according to any of claims 1 - 8, wherein the plasticizer isa combination of organic solvents comprising cyclic or linear carbonates.

10. Electric energy accumulator (E) according to claim 9, wherein the plasticizer is a mixture in equal parts by volume of ethylene carbonate (CAS 96-49-1) and dimethyl carbonate (CAS 616-38-6)”.

11. An electric energy accumulator (E) according to any of claims 1 - 10, wherein the ceramic additive is selected from lithium-containing ceramics, such as lithium aluminum titanium phosphate (LATE), lithium lanthanum zirconium oxide (LLZO), lithium aluminum germanium phosphate (LAGE), lithium lanthanum zirconium oxide doped with tantalum (LLZTO).

12. An accumulator according to claim 11, wherein the ceramic additive consists of lithium aluminum germanium phosphate (LAGE).

13. An accumulator according to any preceding claim, further comprising a radical initiator or a polymerization reaction catalyst.

14. A manufacturing method (Ml) of an electrical energy storage device (E) comprising a solid state electrolyte (3) having a composition according to claim 1, wherein such method comprises the steps of:Eroviding a first and a second electrode (1, 2),Eroviding a liquid mixture (4) comprising an acrylic monomer, at least one thiol- based crosslinker, a lithium ion-containing salt, a plasticizer, a lithium-containing ceramic additive and a radical initiator or a polymerization reaction catalyst, Arranging a porous separator (5) positioned between the first and second electrodes, Depositing a portion of the liquid mixture on the first electrode and positioning the porous separator in contact with the first electrode,Depositing a further portion of the liquid mixture on the porous separator and positioning the second electrode in contact with the separator in a manner oppositeto the first electrode with respect to the separator,Sealing the first and second electrodes and activating the radical initiator to polymerize the acrylic monomer and the thiol-based crosslinker to obtain the solid-state electrolyte (3).

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