DE102018006111A1 - Solid state electrolytes and their production - Google Patents

Abstract

The invention discloses a particularly rapid process for preparing a solid polymer electrolyte (SPE) by a cationic ring opening and polymerization reaction of a precursor solution comprising at least one lithium salt and at least one liquid heterocyclic monomer or oligomer, the ring opening and polymerization reaction being carried out in the absence of a solvent The polymer solid electrolyte produced in this way regularly has a low glass transition temperature of less than - 50 ° C. Solid electrolytes investigated to date have an ionic conductivity between 5 · 10S cm and 1.2 · 10S cm at 30 ° C, as well as a broad electrochemical stability window of more than 5 V against Li / Liauf (SPE) is an important candidate for the development of a fully-fledged lithium metal battery.

Description

The invention relates to the field of polymeric solid polymer electrolytes (SPE) for lithium-ion batteries, and in particular to their manufacture.

State of the art

Due to the possibility of producing a complete solid-state energy storage system, polymer electrolytes are proposed as a safe alternative to existing and widespread liquid electrolytes based on organic carbonates ^[1] .

In the field of lithium-ion batteries (LiB), more safety, architectural lightness, high temperature resistance and good economy are expected through the use of solid materials.

However, there are also some restrictions with a complete solid-state energy storage system, such as. B. a relatively low ionic conductivity, low cation transport properties and strict processing conditions (use of expensive and / or toxic organic solvents), which have hitherto prevented commercial implementation.

Researchers have already proposed several approaches ^[2] , including the most promising in-situ preparation ^[3,4] of UV-induced and / or the thermally induced production of polymer electrolytes using an established solvent-free process such as radical polymerization ^[5] .

The radical polymerization induced by heat or UV radiation requires an initiator that generates free radicals. However, the problem with radical initiators is that they produce by-products such as O ₂ or N ₂ when polymerized with classic initiators such as alkyl peroxides or azobisisobutyronitrile.

Other types of radical initiators require very high temperatures or a suitable solvent for the effective polymerization. In the case of UV-induced polymerization, although the process is well established and fast, if the electrolyte has to be deposited over the electrode, disadvantageous no complete conversion from monomer to polymer is achieved, since the reaction does not take place in the unexposed (dark) area ,

It is therefore desirable to think about alternatives to classic methods and the use of monomers.

Another method for the production of polymer electrolytes is provided by ring opening reactions.

A ring-opening polymerization is a chain polymerization in which a cyclic monomer is converted into a mostly linear polymer by breaking the bond and then forming a (mostly) similar bond to a further unit. However, there are also examples in which a highly branched product is obtained by using nonlinear monomers.

In ring-opening polymerizations (ROP), a distinction is made between radical, anionic ring-opening polymerizations (AROP) and cationic ring-opening polymerizations (CROP).

CROP processes ^[6] for the production of polymers are well established industrially. They usually use Bronsted acids (e.g. HCl, H ₂ SO ₄ , HClO ₄ and HOSO ₂ CF ₃ ) and / or Lewis acids (BF ₃ ) as starting materials. The reaction is usually carried out by heat or UV radiation.

Cationic ring opening polymerization (CROP) can be an alternative technique that can produce target-specific polymers for the development of solid state electrolytes for lithium-ion batteries. However, CROP processes are not yet widely used in the field of lithium-ion batteries.

Dreyfuss et al. Already in 1976 ^[7] showed that alkali salts can be an initiator for the cationic polymerization of heterocyclic molecules. Miwa et al. ^[8.9] that the Ring opening polymerization of oxetanes using lithium salts such as lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ) and bis (trifluoromethane) sulfonimide lithium salt (LiN (CF ₃ SO ₂ ) ₂ ) can take place in the presence of suitable solvents. Later they also showed that the solvent plays a crucial role in the polymerization kinetics. This first work laid the foundation for the alkali salt-induced ring opening polymerization of heterocyclic monomers.
Recently, Cui et al. ^[10] investigated the idea of polymerizing epoxy oligomers with lithium salt and demonstrated the performance of solid-state electrolytes in LiFePO ₄ -based lithium metal cells. They reported the preparation of a solid polymer electrolyte using LiDFOB in a catalytic amount (1.5% by weight) to initiate the ring opening polymerization reaction, which they carried out at 80 ° C for 4 hours. They produced a solid electrolyte membrane that has an ionic conductivity of 0.089 mS cm ^-1 under ambient conditions. They also showed that these membranes have an electrochemical stability window of 4.5 V compared to Li / Li ⁺ and that the corresponding cells cycled under ambient conditions for 100 cycles ^[10].

However, the process is time-consuming and the LiDFOB used rearranges itself and leads to CO ₂ as a gas.

Previous CROP processes generally use Brcensted acids (for example HCl, H ₂ SO ₄ , HClO ₄ and HOSO ₂ CF ₃ ) and I or Lewis acids (BF3) as catalysts as a disadvantage.

Task and solution

The object of the invention is to provide an alternative, fast and effective process for the production of the aforementioned polymeric solid electrolytes (ESP) for use in lithium batteries and corresponding polymeric solid electrolytes.

The objects of the invention are achieved by a method for producing a polymer solid electrolyte (SPE) with the features of the skin claim and by a polymer electrolyte (SPE) with the features according to the auxiliary claim.

Advantageous refinements of the method and of the polymer electrolyte result from the claims which refer back to them.

Subject of the invention

The present invention describes the production of a polymer solid electrolyte (SPE) for lithium batteries. In particular, a novel preparative method for producing a completely cross-linked, three-dimensional (3D) network-based solid polymer electrolyte via a cationic ring opening polymerization (CROP) is proposed.

The crosslinked solid-state electrolytes are produced by a rapid process in which heterocyclic monomers or also oligomers based on epoxy are opened in the presence of at least one suitable lithium salt. The at least one lithium salt is able to generate a Lewis acid or an initiating species for the polymerization.

Monomers are low molecular weight, reactive molecules that can combine to form unbranched or branched polymers. Monomers can be individual substances, but also mixtures of different compounds. An oligomer is understood to mean a molecule which is composed of several structurally identical or similar units. A larger number of units is called a polymer.

A Lewis acid is an electrophilic electron pair acceptor, so it can attach electron pairs. Accordingly, a Lewis base is an electron pair donor that can donate electron pairs. With the Lewis acid term, it is possible to explain the acidic properties of substances that are not Bronsted proton donors.

In general, the lithium salts used according to the invention, such as lithium tetrafluoroborate (LiBF ₄ ), lithium difluoro (oxalato) borate (LiDFOB), lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ) and lithium bis (fluorosulfonyl) imide (LiFSI), are based on the anion of Super acids. For example Tetrafluoroborate ion (BF ₄ -) as a precursor for sulfur hexafluoride (SF ₃ ), a Lewis acid. Lithium tetrafluoroborate (LiBF ₄ ) has proven to be particularly suitable and effective as an initiating species.

All of the above-mentioned suitable lithium salts lead to polymerization in combination with the monomers or oligomers, although the polymerization time and the temperature depend on the type and concentration of the lithium salt added. A general scheme for a polymer formation reaction via a cationic ring opening polymerization (CROP) is in 1 shown.

Within the scope of the invention it has also been found that mixtures of suitable lithium salts can bring about additional positive effects. For example, it has been shown that the addition of LiDFOB hardly influences the polymerization time and the polymerization temperature due to the decomposition of the salt. On the other hand, it was also found that the addition of LiDFOB has a positive effect on the conversion of monomers into polymers. However, higher concentrations of LIDFOB lead to gas formation in the polymer membrane. Nevertheless, the combination of LiBF ₄ and LiDFOB, for example, has proven to be very effective for the polymerization. In addition, an addition LiDFOB was advantageous in further improving the overall electrochemical performance.

Other lithium salts, such as lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) or lithium bis (oxalato) borate (LiBOB), can be added to at least one of the aforementioned lithium salts, but they do not participate in the polymerization and are therefore not included in the Condition that the appropriate lithium salt must be able to generate a Lewis acid or an initiating species for the polymerization. However, LiTFSI can be added, for example, to improve ion conductivity and cycle performance. However, it does not take part in a polymerization reaction.

In this respect, in the method for producing a polymeric solid electrolyte by a cationic ring opening and polymerization reaction of a precursor solution which comprises at least one liquid heterocyclic monomer or at least one liquid oligomer, this precursor solution is one or more lithium salts from the group lithium tetrafluoroborate (LiBF ₄ ), lithium difluoro (oxalato) borate (LiDFOB), lithium perchlorate (LiC-IO ₄ ), lithium hexafluorophosphate (LiPF ₆ ) and lithium bis (fluorosulfonyl) imide (LiFSI) with or without additional lithium salts from the group LiTFSI or LiBOB added.

Monomers or oligomers which carry at least one glycidyl ether residue or also more than one glycidyl ether residue (bifunctional, trifunctional, tetrafunctional or multifunctional) can be used in particular in the process according to the invention.

The formula for a glycidyl ether residue is shown below.

1. a) Verbindungen umfassend Monoglycidylether, wie in 9A aufgeführt,
2. b) Verbindungen umfassend Diglycidylether, wie in 9B aufgeführt.
3. c) Verbindungen umfassend Tri- oder Tertraglycidylether, wie in 9C aufgeführt.
4. d) Verbindungen umfassend substituiertes PSS-(3-Glycidyl)propoxy-Heptaisobutyl oder Cyclosiloxane, wie in 9D aufgeführt.
5. e) Verbindungen umfassend Polyglycidylether, wie in 9E aufgeführt.

Furthermore, a list of compounds is made available which are suitable as liquid monomers or as liquid oligomers for the production of the polymeric solid electrolyte according to the invention, the list being exemplary and not exhaustive.

1. a) Compounds comprising monoglycidyl ether, as in 9A lists
2. b) Compounds comprising diglycidyl ether, as in 9B listed.
3. c) Compounds comprising tri or tertraglycidyl ether, as in 9C listed.
4. d) compounds comprising substituted PSS- (3-glycidyl) propoxy-heptaisobutyl or cyclosiloxanes, as in 9D listed.
5. e) Compounds comprising polyglycidyl ether, as in 9E listed.

In addition, the glycidyl ethers in each of the aforementioned exemplary compounds can also be substituted by oxetane units.

According to the invention, a simple, fast and reliable production process for polymer electrolytes from heterocyclic monomers or oligomers based on epoxy is carried out thermally induced cationic ring-opening polymerizations (CROP) is proposed which, in conjunction with the synergy of at least one lithium salt or a mixture of lithium salts, produces a mechanically stable, standing and ion-conducting membrane.

In contrast to the previously known CROP processes, which are either solvent-based and / or time-consuming, the process according to the invention advantageously uses no solvents and no external catalysts or initiators.

For this purpose, the thermal induction for the ring-opening polymerizations (CROP) can take place, for example, by means of an oven, a heater or else via an infrared source.

Either a class of monomers or dimers or a mixture of different monomers or oligomers can be used for the process according to the invention, as a result of which a crosslinked homopolymer architecture is achieved in the first case and a crosslinked copolymer architecture for the polymeric solid electrolyte membrane in the second case.

The cationic ring opening polymerization can preferably be carried out at variable temperatures between 20 ° C. and 120 ° C. The ring opening polymerization advantageously takes place between 25 ° C. and 100 ° C., in particular between 30 ° C. and 80 ° C.

The polymerization according to the invention takes place relatively quickly - compared to the previously known CROP processes - and can be completed within 10 minutes to 2 hours, preferably even within 15 minutes to 1 hour.

The duration of the process depends on the selected temperature, an elevated temperature generally accelerating the polymerization, and on the lithium salt concentration or the selected ratio of lithium salt to monomer or oligomer.

Since the suitable lithium salts generally have very different molar masses, the addition of lithium salt is not stated in% by weight but preferably as a ratio of ethylene oxide (from the monomer or oligomer) to lithium (from the lithium salt) as (EO: Li) , According to the invention, this is between 100: 1 and 5: 1, preferably between 80: 1 and 10: 1.

At ratios (EO: Li) of 200: 1 or 400: 1, polymerization would also take place, but this would require a much longer reaction time and significantly higher temperatures than are proposed according to the invention.

The rapid polymerization process takes place in the presence of certain amounts of at least one or more suitable lithium salts. Suitable lithium salts in this sense are, for example, lithium tetrafluoroborate (LiBF ₄ ), lithium difluoro (oxalato) borate (LiDFOB), lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ) and lithium bis (fluorosulfonyl) imide (LiFSI), which are based on anions of super acids based.

The polymerization is optimized taking into account various factors such as polymerization time, temperature, conductivity and electrochemical performance.

The amount of suitable lithium salts (individually or as a mixture) required for the complete conversion of monomer to polymer can be determined for each combination of monomer, or oligomer and lithium salt, for example beforehand by a person skilled in the art using RAMAN spectroscopy. The person skilled in the art can likewise optimize the temperature of the corresponding polymerization by means of DSC analysis.

In a particularly preferred embodiment of the method, it is proposed to use a mixture of lithium salts, which consequently leads to an improved degree of crosslinking. For example, it has been found that the degree of crosslinking is particularly high when LiBF _{4 is used} in conjunction with LiDFOB.

The degree of crosslinking is a quantitative measure for the characterization of polymer networks, which is made up of the quotient of the number of moles of crosslinked basic building blocks and the number of moles in total Macromolecular network can calculate existing building blocks. It can be calculated from the gel content test (insoluble content).

A highly cross-linked system should consist of 100% gel or insoluble components. This means that a polymer-crosslinked network is formed after the heating process, which is insoluble in the test solvent.

The production method according to the invention can advantageously be adapted to process conditions, for example by varying the type and the amount of the lithium salt or lithium salts used.

In a particular embodiment of the invention, the polymeric solid electrolyte is polymerized directly on a composite electrode film using the method according to the invention, for example on a LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (NMC111) cathode or a carbon-coated LiFePO ₄ cathode , This regularly results in very good adhesion between the electrolyte and the electrode.

The crosslinked polymer electrolyte (SPE) produced according to the invention regularly has an ionic conductivity between 5.10 ^-6 S cm ^-1 and 1.2.10 ^-4 S cm ^-1 at 30 ° C. on the basis of the solid electrolytes investigated to date. At higher temperatures of 70 ° C, for example, ionic conductivities of more than 1 S cm ^-1 could also be achieved.

Furthermore, these polymer electrolytes show a low glass transition temperature of regularly below -50 ° C.

In addition, the solid polymer electrolytes produced according to the invention have excellent oxidation resistance and very good electrochemical properties, for example a stability window of over 5.5 V against Li / Li ⁺ .

The rapid manufacturing process can be carried out at temperatures between 20 ° C and 120 ° C and in a period of 10 minutes to 2 hours. No solvents or external catalysts are used in all stages of the polymer electrolyte preparation.

In summary, it can be said that within the scope of this invention, the use of the thermally induced CROP process for the production of a solid electrolyte from heterocyclic monomers or oligomers based on epoxy was further developed. The polymer solid electrolytes produced in this way regularly have an ionic conductivity of sometimes more than 0.1 mS cm ^-1 at room temperature (T = 30 ° C.). They show a very good oxidation stability of over 5.5 V against Li / Li ⁺ . They also show excellent cycle stability at elevated temperatures.

The results obtained in the laboratories confirm that the thermally induced solvent-free CROP process proposed according to the invention represents an industrially highly scalable technology with enormous potential as the primary tool for the production of all solid-state electrolytes.

Special description part

Furthermore, the invention will be explained in more detail and with reference to individual exemplary embodiments and some figures. The invention is not restricted to the exemplary embodiments disclosed here. All described and / or illustrated features can manifest themselves individually or in combination in different embodiments.

While the invention was described and illustrated in detail in the following part of the application on the basis of special exemplary embodiments, this description and the figures are only to be considered by the person skilled in the art as an example, without being restrictive. It is to be assumed that a person skilled in the art would and could make further changes and modifications to the following claims within the scope of his specialist knowledge, which are also covered by the scope of protection of the claims. In particular, further embodiments are included within the scope of the invention with each type of combination of the mentioned features of individual exemplary embodiments.

The features of the different embodiments of this invention and their respective advantages will be revealed to a corresponding person skilled in the art when reading the exemplary embodiments set out below in conjunction with the figures.

Production and characterization of polymer electrolytes according to the invention

Unless otherwise stated, all materials were obtained from Sigma Aldrich. A bifunctional oligomer poly (ethylene glycol) diglycidyl ether (PEGDGE, Mn 500) and various lithium salts such as lithium bis (trifluoromethane) sulfonimide (LiTFSI), lithium tetrafluoroborate (LiBF ₄ ) and lithium difluoro (oxalato) borate (LiDFOB) were used during various polymerization stages. The monomers and oligomers were dried under molecular sieves (3Å) and the lithium salts were dried in vacuo before being used in various formulations.

The samples were completely prepared in an environmentally friendly drying room (100 m ² , RH <1% at 17 ° C). For each sample, an oligomer, PEGDGE, was mixed with different amounts of lithium salt. PEGDGE is in liquid form at 25 ° C. The mixture, hereinafter also called the precursor solution, was stirred with a disperser (IKA T25 digital ULTRA-TURRAX®) until a clear solution was obtained. The clear solution was poured between two Mylar foils and dried for 1 hour at 80 ° C. under an argon atmosphere.

The exact formulation of the samples is given in Table 1. For the individual samples, for example, the ratio of PEGDGE to LiBF4 is given as the ratio of ethylene oxide (EO) to lithium (Li) (EO: Li). The respective amounts for the oligomer and the lithium salts are given in% by weight.

After the polymerization was complete, the membranes were cut directly into disks with different diameters and used for further characterization.

The membrane thickness is adjustable. In the membranes used in the examples, it was in each case 50 to 200 μm.

mit W₀ = Anfangsgewicht der Polymermembran und W_e = Nach-Extraktionsgewicht der PolymermembranThe gel content (insoluble fraction) of the thermally crosslinked polymer electrolytes was calculated as follows: The polymer pieces with a known weight were arranged on a thin metal grid film and packed in this by folding. Sealing is done with paper clips. The weight of the metal mesh films and the paper clip is already known and does not change during the test. The polymer in the film was then soaked in acetonitrile for 18 hours. Only the dissolved polymer parts from the metal mesh foil are lost. After the test, the film is opened and the remaining polymer is removed. This was dried at 60 ° C for 3 hours to obtain the polymer weight after the extraction process. The difference in weight was determined and the gel content was calculated using the following formula: $$\text{gel}\left[\text{\%}\right]=\left(1-\left({\text{W}}_0-{\text{W}}_{\text{e}}\right){\text{/ W}}_0\right)*100)$$

with W ₀ = initial weight of the polymer membrane and W _e = post-extraction weight of the polymer membrane

The curing temperature of the reaction mixture and the glass transition temperature (T _g ) of the crosslinked polymer electrolyte were determined by means of differential scanning calorimetry (DSC) with a DSC 2500 (TA device). A polymer sample of known weight was hermetically sealed in an aluminum pan (T _zero ) for DSC analysis. Sample preparation was done in a dry room to minimize moisture absorption and contamination.

In a typical measurement, the polymer samples were heated from 20 ° C to 120 ° C, then cooled to -150 ° C and heated again to 120 ° C. The heating and cooling steps were carried out with a heating and cooling rate of 10 Kmin ^-1 under an Ar flow.

The polymerization details, such as the polymerization initiation temperature (PiT) and the peak polymerization temperature (PpT), were determined from the heating step between 20 ° C and 150 ° C. The glass transition temperature was determined as the mean value of the change in heat capacity which occurs between 150 ° C and 120 ° C during the transition from the glassy to the rubbery state during the second heating step.

The conversion of the liquid reaction mixture into a solid crosslinked polymer electrolyte was investigated by means of Raman spectroscopy (Bruker, RAM II FT-Raman module Vertex 70 FT-IR spectrometer). The peak at 911 cm ^{-1 was} observed, which corresponds to the epoxy ring deformation of the cyclic epoxy ring. The peaks at 911 cm ^-1 and 1255 cm ^-1 disappear as the polymerization progresses. The complete disappearance of the peak indicates a complete conversion of monomer or oligomer to polymer. The Raman instrument was equipped with an Nd: YAG laser source (1064 nm).

wobei I die Schichtdicke der Fläche der Polymerelektrolytprobe, Rb der Volumenwiderstand und A die Fläche der Polymerelektrolytprobe ist.The ionic conductivity of cross-linked polymer electrolytes was determined by means of electrochemical impedance spectroscopy (EIS) with an Autolab (PGSTAT204-FRA32M, Metrohm) potentiostat. A two-cell battery of the button cell type (2032) was assembled by inserting the polymer electrolyte membrane between two stainless steel blocking electrodes (area 1.54 cm ² ). EIS measurements were performed between 0 ° C and 70 ° C at open cell potential (OCP) in the frequency range from 500 kHz to 1 Hz. The button cells were assembled in a dry room and stored in a climatic chamber (BINDER MK-53). Impedance was measured every 10 ° C with the button cells held at each temperature for 2 hours to achieve temperature equilibrium. The ionic conductivity (σ, Scm ^-1 ) was calculated using the following equation: $$\mathrm{\sigma }=\text{I}*{\text{A}}^{-1}*{\text{Rb}}^{-1}$$

where I is the layer thickness of the area of the polymer electrolyte sample, Rb is the volume resistance and A is the area of the polymer electrolyte sample.

The compatibility of the polymer solid electrolytes (SPEs) at the lithium metal interface was determined by observing the development of the impedance spectra of symmetrical Li / SPE / Li cells at open cell voltage (OCV) at 60 ° C.

The oxidation stability of the polymer solid electrolytes was determined by means of linear sweep voltammetry (LSV) from three electrode test cells (ECC-Ref, EL-Cell, Germany) with a VMP3 (Bio-logic, Switzerland) device. Aluminum or stainless steel (SS) was used as the working electrode and lithium as the counter and reference electrode. The reduction stability of the polymer electrolyte membrane was determined by means of cyclic voltammetry (CV) of a 3-electrode ECC reference cell, copper being used as the working electrode and lithium as the counter and reference electrode. A sampling rate of 0.1 mVs ^{-1 was} used in both measurements. The LSV tests were carried out between OCV and 7 V against Li / Li ⁺ , while the CV tests were carried out between OCV and -0.5 V against Li / Li +.

Manufacture of electrodes and electrochemical characterization

Type 2032 lithium metal button cells according to the invention were produced on a laboratory scale, LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (NMC111) or carbon-coated LiFePO ₄ as cathode, lithium metal as anode and the aforementioned polymeric solid electrolytes as Separator were used. A typical cathode comprises 90 wt .-% active material, 5 wt .-% of polyvinylidene fluoride (PVDF) as a binder and 5 wt .-% Super P ^® from TIMCAL as conductive carbon additive. An NMP-based suspension was prepared, which consists of active material, PVDF and Super P in a ratio of 90: 5: 5, the N-methyl-2-pyrrolidone (NMP) from Sigma Aldrich and the polyvinlylidenene fluoride (PVDF), Solef®, obtained from Solvay.

The slip obtained was then poured onto an aluminum foil under a hood and dried at 60 ° C. overnight. The materials were later cut into circular disks with a diameter of 14 mm and dried at 120 ° C. under high vacuum for 12 hours.

The type 2032 lithium button cells were prepared in the dry room using the cell components and their electrochemical properties were examined at 60 ° C during galvanostatic discharge cycles with constant current at different currents using a MACCOR cycler (series 4000). The galvanostatic charging and discharging studies were carried out in the range of 2.5 - 4 V against Li / Li ⁺ for LiFePO ₄ and in the range of 3 - 4.4 V against Li / Li ⁺ for LiNi _1/3 Mn _1/3 Co _{1 / 3} O _{2 performed} by Hunan Shanshan Energy Technology Co. Ltd. Before the investigations, all cells were kept at 60 ° C. for 6 hours.

Results and discussions

Ring opening polymerization reactions usually include positively charged intermediates (CROP), which are used to produce some important industrial polymers, such as polyacetals, polyoximethyls, polytetrahydrofurans, polysiloxanes, polyethyleneimines, polyglycolides, polylactides and polyphosphazenes ^[11] .

So far, Bronsted acids, Lewis acids with co-initiator, carbenium ions, photoinitiators, onium ions and covalent initiators have been used as initiators for an effective CROP reaction. Bortrifourid (BF ₃ ) with its precursor BF ₃ OEt ₂ is one of the most commonly used Lewis acids for CROP. In systems with alcohol, there are opportunities to use various chain transfer agents (CTA) such as. B. add organic units containing functional groups such as carboxylic acids, alcohol, thiol, etc.

In the context of the invention, the lithium salt LiBF _{4 was used} as a Lewis acid generator in the presence of water. It should be noted that water is generally present as an impurity between 1 ppm and 100 ppm even after drying. During the polymerization, hydroxyl groups are formed in the system. Such hydroxyl groups can also give off H ⁺ ions.

In the exemplary embodiment described, no additional alcohol was added as a solvent or external catalysts.

A scheme of the possible initiation reaction with the following crosslinking reaction is in 1 shown. According to the scheme, minor amounts of water present in the precursor as an impurity, or the oligomer itself, which carries acidic protons in each EO repeat unit, can donate a proton to produce the initiating species H ⁺ BF4. As soon as it has absorbed enough energy it can react with an epoxy ring and then the polymerization reaction as in 1 continue shown.

The optimal polymerization temperature and the required salt concentration for an effective conversion of monomers into polymers could be determined in advance by DSC. The precursor solution was prepared by varying the ratio of PEGDGE to LiBF ₄ , each adding 2, 5 or 10% by weight of LiBF ₄ to the liquid PEGDGE and stirring at high shear for a few minutes to give an excellent and readily soluble precursor to obtain. The precursor solution was examined by means of DSC analysis between 20 ° C and 150 ° C. The polymerization exotherm is calculated from the analysis curves of differential scanning calorimetry (DSC). It results from the area under the curve and the software provided by TA devices can calculate it automatically. This was used to calculate the polymerization initiation temperature, PiT, and the peak polymerization temperature, PpT.

2 Figure 3 shows the polymerization initiation temperature (PiT) and the peak polymerization temperature (PpT) for a polymer with a LiBF4 salt concentration of 2, 5 and 10% by weight. The data come from the DSC analysis of the respective precursors between 20 ° C and 120 ° C. The results shown show that an increase in the LiBF ₄ salt concentration from 2% by weight to 10% by weight (decreasing EO: Li ratio) increased the PiT from 90.8 ° C to 44.8 ° C and the PpT reduced from 101.6 ° C to 80 ° C. This indicates that the amount of salt plays a major role in determining the state of polymerization. Taking into account the importance of the polymerization entry temperature and the peak polymerization temperature, an optimal LiBF ₄ salt content was determined for a quick and reliable conversion of 5% by weight and the polymerization temperature was chosen to be 80 ° C., while the polymerization time was set for 1 hour.

In the 2 the ratio of poly (ethylene glycol) diglycidyl ether (PEGDGE) to LiBF _{4 is given} as the ratio of ethylene oxide to lithium (EO: Li), where PEGDGE has one oxygen atom per ethylene oxide repeat unit.

The composition of the solid electrolytes thus produced, which contain LiBF ₄ and LiTFSI as suitable lithium salts, LiDFOB as a further lithium salt and PEGDGE as an oligomer, is given in Table 1 together with their glass transition temperature values (Tg values) and their gel contents. Table 1 sample PEGDGE LiBF ₄ LiDFOB LiTFSI EO: LI Gel content [%] T _g [1C] P95 95 5 40 78.7 -55.8 P90A 90 5 5 29 74.4 -57.2 P85A 85 5 10 22 66.5 -54.8 P80A 80 5 15 17 55.1 -52.0 P75A 75 5 20 14 45.8 -51.7 P82C 82 5 2 13 20 61.2 -

In the 3 The Raman spectra shown for the polymerized membranes P95 and P90A compared to the pure PEGDGE oligomer show the disappearance of the cyclic epoxy peak at 911 cm ^-1 (*) and 1255 cm ^-1 (#).

The polymerization reaction resulted in a free-standing, transparent and tack-free membrane. The polymerization reaction was confirmed by Raman spectroscopy analysis and ensured that the chosen polymerization temperature and time were sufficient for complete ring opening of the cyclic epoxy residues, as in 3 shown. The peaks at 910 cm ^-1 (*) and 1255 cm ^-1 (#) in 3 in arbitrary units (au), disappeared after the polymerization when the precursor solution was kept at 80 ° C for 1 hour. Complete monomer to polymer conversion was achieved in all combinations of oligomer and lithium salts.

The conversion of the bifunctional oligomer PEGDGE into a cross-linked three-dimensional network by the polymerization reaction was further investigated by measuring the insoluble fraction (gel content) in a suitable solvent. In the present case, acetonitrile (ACN) was used as the extraction solution. The results are shown in Table 1. The gel content study showed that the SPE P95 had an insoluble content of 78.7%, which was gradually reduced by an increase in the LiTFSI content. In all cases, however, the insoluble fraction was always over 45% for all membranes tested.

As the salt concentration is increased, the viscosity is also increased regularly, which in turn reduces the mobility of the entire chain, so that the propagation reactions can be slower than that of the P95 precursor. Although the Raman spectra in all SPEs indicate complete ring opening of the epoxy units, the conversion to a cross-linked network was not 100%.

The polymerization reactions were also carried out at 100 ° C. by varying the polymerization time between 15 and 30 minutes. The results at 100 ° C for a polymerization time of 15 minutes and 30 minutes are particularly worth mentioning. The polymeric solid-state electrolyte membrane P80A showed a gel content of 61.8% at 100 ° C. for 15 minutes, the gel content being increased to 64% for the same polymer membrane at a baking time of 30 minutes. Although a higher temperature leads to a better conversion of the oligomer into a cross-linked network, 80 ° C was chosen as the optimal temperature in the present study. In fact, a higher polymerization temperature and longer baking times lead to parasitic reactions such as chain transfer ^[6] and termination of the growing chain, which leads to a lower insoluble content. It can also limit the use of low boiling monomers when co-polymerization is considered.

In a separate study, the addition of a small amount (2% by weight) of LiDFOB to the polymer matrix improved the overall polymerization and achieved a gel content of 61.2%. This confirmed that there is also a synergy between the salts in the polymer electrolyte which, if carefully selected, leads to an increase in performance. However, when 5 wt% LiBF4 in the P80A formulation was completely replaced by LiDFOB, no conversion was achieved. A minimum of 4 hours was necessary to achieve acceptable monomer-to-polymer conversion. Therefore, it seems important to add enough LiBF ₄ to the precursor to make a polymer electrolyte membrane.

The glass transition temperature was analyzed by DSC analysis between -150 ° C and 120 ° C for a number of polymer solid electrolytes (P95 to P75A). The DSC curves for a series of crosslinked solid polymeric electrolytes (P95, P90A, P85A, P80A and P75A) made with different amounts of LiBF ₄ and LiTFSI are shown in 4 shown.

The corresponding glass transition temperature values (Tg values) are listed in table 1. The glass transition temperature was defined as the midpoint of the heat capacity change observed in a DSC trace during the transition from the glassy to the rubbery state. All polymers showed a glass transition temperature well below -50 ° C. This means that at room temperature all polymer solid electrolytes are at least 70 ° C above their respective glass transition temperature, which ensures sufficient segment movement for the polymer chains. However, the analyzes showed an increase in Tg values by increasing the LiTFSI salt content. This effect can result from the coordination of lithium salt with EO units, which increase the viscosity or stiffness of the polymer chains and thus reduce segment mobility. This restricted mobility with an increased LiTFSI content is directly reflected in an increase in Tg values. DSC measurements are an effective means of calculating the proportion of crystallinity in a polymer. In the present case, no melting peaks were observed during the heating cycle between -150 ° C and 100 ° C, which indicates the formation of a highly cross-linked and completely amorphous polymeric solid electrolyte membrane.

The ionic conductivity of the series of crosslinked solid polymer electrolytes (P95, P90A, P85A, P80A and P75A) was calculated from the results of electrochemical impedance spectroscopy (EIS). The lithium salt is added directly to the liquid PEGDGE oligomer to obtain a precursor solution. This precursor is thermally polymerized at 80 ° C. for 1 hour, with no additional steps having been carried out with the addition of solvents or low molecular weight plasticizers.

In 5 an Arrhenius diagram is shown which shows the ionic conductivity versus temperature for a number of polymer electrolytes which were produced with PEGDGE as oligomer and LiBF ₄ , LiDFOB and LiTFSI as lithium salt. It shows the ionic conductivities for a wide temperature range between 0 ° C and 70 ° C.

Generally, an increase in temperature improves ionic conductivity. The highest ion conductivity was observed for the polymer membrane P85A, which had an ion conductivity of more than 0.1 mS cm ^-1 at 30 ° C. The same SPE P85A also showed an ionic conductivity of 1 mS cm ^-1 at 70 ° C. This special composition contains 10% by weight of LiTFSI, 5% by weight of LiBF4 and 85% by weight of PEGDGE. A further increase in the LiTFSI content reduced the ion conductivity. An optimal ionic conductivity was achieved for an SPE with an EO: Li ratio of 22: 1.

It has been observed that an increase in the lithium salt concentration initially increases the ion conductivity, which indirectly indicates that a lower EO: Li ratio is advantageous for a higher Li + ion mobility. When the EO: Li ratio was varied from 40: 1 to 22: 1, an improved ionic conductivity was determined. However, a further increase in the salt concentration, ie a reduction in the EO-Li ratio from 22: 1 to 14: 1, reduced the ionic conductivity to lower values. The increased LiTFSI addition increases the EO to Li ⁺ ion ratio and leads to reduced chain mobility, as the increased glass transition temperature (Tg) shows in the DSC analysis.

The oxidation stability of the polymer solid electrolytes, which were produced with different amounts of LiTFSI and LiBF4, was analyzed by LSV investigations against aluminum working electrodes at 60 ° C. The results are in 6 A) shown. The initial anodic sweep towards higher potential values, the start of a current peak is usually associated with the decomposition (oxidation) of the electrolyte. In the present case, the limit current was set to 1 µA cm ^-2 , and the highest electrochemical stability was achieved through the P95 membrane, up to 7 V vs Li / Li +.

Increasing the LiTFSI salt concentration reduced the oxidation stability. The lowest value was reached for P80A. Even with P80A, the membrane showed an oxidation stability above 5.5 V against Li / Li ⁺ . If one considers the oxidative stability as a parameter for the selection for a membrane with increased stability, then 5.5 V is an important value. The highest values are achieved by the presence of LiBF ₄ salt, which passivates the aluminum by forming AlF ₃ , which in turn reduces the decomposition of the polymer membranes up to 5.5 V. However, it is important to note that an increased amount of LiTFSI always reduces the oxidative stability of the membrane. The oxidation stability was also measured with stainless steel as the working electrode and similar values were observed. This indicates that the prepared solid polymer electrolytes are very stable towards higher potentials. In all cases examined, neat and clean lines between 3.8 and 4.2 V against Li / Li ^{+ were} determined. This means that the polymeric solid electrolytes produced here are extremely pure and there are no impurities or moisture in the system.

Cyclic voltammetry tests were carried out at 60 ° C to assess the reduction stability of the polymer solid electrolytes, which were produced with different amounts of LiTFSI and LiBF4. In all cases, a clear and well-defined lithium plating / stripping reaction was observed over a Cu working electrode, as in 6 shown. Only an irreversible peak was observed at 2.2 V against Li / Li +, which indicates the reduction of the CuO present on the Cu foil surface to Cu2O. Increasing the LiTFSI content improves the total charge deposited during plating and the corresponding current for stripping. This is related to the improved ionic conductivity of the SPEs.

In the 7 the results of a constant current charge / discharge test of a solid-state cell according to the invention made of LiNi _1/3 Mn _1/3 Co _1/3 O ₂ / P80A / Li at 60 ° C. are shown. In the top 7A) the specific capacities at different currents (0.05 C - 1 C) are shown in relation to the number of cycles. The lower one 7B) shows the curves: potential against specific capacity profiles also at 0.05 C to 1 C.

In summary, a number of solid polymer electrolytes were produced within the scope of this invention, which have a low glass transition temperature, an acceptable ionic conductivity and a wide electrochemical stability window. These are encouraging properties for a highly cross-linked polymer electrolyte.

However, a validation with regard to the galvanostatic in the direction of different cathode materials is necessary. In this context, lithium button cells of type 2032 were assembled on a laboratory scale from a LiNi _1/3 Mn _1/3 Co _1/3 O ₂ composite film as cathode, lithium metal as anode and a polymeric solid electrolyte membrane comprising P80A as a separator. First, the P80A solid polymer electrolyte was inserted between the lithium metal anode and the NMC111-based composite cathode in order to evaluate the performance of the electrolyte in the real battery configuration at an elevated temperature of 60 ° C. The electrochemical behavior was investigated with regard to galvanostatic cycles at different currents from 0.05 C to 1 C. A reversible lithium insertion or reinsertion of Li ⁺ ions into and from the NMC111 electrode between 3 V and 4.4 V against Li / Li ^{+ was} observed. This potential window should deliver a specific capacity of 180 mA hg ^-1 . An active mass load of 2.5 mgcm ^-2 was present in each 14 mm cathode disc.

The 7A shows the specific capacity against the number of cycles at different currents. The cell with 0.05 C delivered a first specific discharge capacity of 169.4 mA hg ^-1 with a Coulomb efficiency of the 1st cycle of 90.6%. An increased current reduced the specific capacity, the cell delivering a specific capacity of 111.6 mA hg ^-1 at 0.2 C. The cell showed reproducible potential profiles at different currents, as in 7B shown. The quick charge capability and capacity maintenance are satisfactory. Even after 35 long cycles, the cell delivered a specific capacity of 106.8 mA hg ^-1 at 0.1C, which corresponds to a decrease of less than 35% compared to the initial value at 0.05C. Nevertheless, this is one of the first examples in which a LiNi _1/3 Mn _1/3 Co _1/3 O ₂ -based cathode was cycled at 60 ° C. with a highly cross-linked, fully EO-based polymer solid electrolyte membrane.

In the 8th the results of a constant current charge / discharge test of a further solid-state cell according to the invention made of LiFePO ₄ / P82C / Li at 60 ° C. are shown. In the top 8A) the specific capacities at different currents (0.05 C - 1 C) are shown in relation to the number of cycles. The lower one 8B) shows the curves: potential against specific capacity profiles between 0.05 C and 1 C.

The test cells LiFePO ₄ / P82C / Li were cycled at 60 ° C with different currents from 0.05 C to 1 C. The constant current discharge test was performed between 2.5 V and 4 V against Li / Li ⁺ and excellent Coulomb efficiency and specific capacity were achieved. In the first cycle, the cell delivered a discharge capacity of 160.6 mA hg ^-1 at 0.05 C with a Coulomb efficiency of 98.3%. A Coulomb efficiency of up to 99.8% was achieved in the following cycles. The cell delivered remarkably high performance at high currents and elevated temperatures. In addition, the LFP-based solid-state cell was also tested at 40 ° C, the cell delivering a specific capacity of 155 mA hg ^-1 at 0.05 C current consumption. The preliminary results in this regard are encouraging. They confirm that the polymeric solid electrolyte according to the invention is also stable with respect to lithium metal and that the limitation due to the kinetics is low.

In summary, it can be said that in the context of this invention, a modified thermally induced cationic ring opening polymerization (CROP) was used effectively for the synthesis of a solid electrolyte. No solvents are used in all phases of the polymerization process. Although the optimal polymerization temperature found so far is 80 ° C. and the time until the epoxy ring has completely opened is 1 hour, similar polymerizations are also possible at 100 ° C. in 15 or 30 minutes. The polymerization reaction proposed here is regularly quick and easy. According to the invention, no solvents or additives are neither required nor provided in all phases of the polymerization process.

The polymeric solid-state electrolytes (SPE) produced according to the invention regularly showed a low glass transition temperature, good ionic conductivity (in some cases> 0.1 mS cm ^-1 ) at ambient conditions (30 ° C.) and a broad electrochemical stability window (> 5.5 V against Li / Li ⁺ ).

The results so far of the polymeric solid electrolytes produced according to the invention are promising, in particular the cycle performance compared to LiNi _1/3 Mn _1/3 Co _1/3 O ₂ and LiFePO ₄ electrodes in lithium metal design.

A cell based on NMC111 delivered a specific capacity of 169 mA hg ^-1 at a current of 0.05 C.

The cell according to the invention with LiFePO ₄ as cathode also provided an excellent specific capacity and Coulomb efficiency. The cell delivered a specific capacity of 160.2 mA hg ^-1 at 0.05 C and 102.3 mA hg ^-1 at 1 C, with Coulomb's efficiency reaching over 99.8% after the first cycle.

Interestingly, a LiFePO ₄ - (LFP-) based solid state cell provided a specific capacity of 155 mAhg ^-1 when operated at 40 ° C with a current of 0.05 C. The polymer solid electrolytes (SPE) produced here according to the invention and produced using the CROP process are therefore an important candidate for the development of a fully-fledged lithium metal battery.

1. [1] K. Xu, Electrolytes and Interphases in Li-Ion Batteries and Beyond, Chem. Rev. 114 (2014) 11503 .
2. [2] Z. Xue, D. He, X. Xie, Polyethylene oxide)-based electrolytes for lithium-ion batteries, J. Mater. Chem. A, 3 (2015) 19218 .
3. [3] B. Rupp, M. Schmuck, A. Balducci, M. Winter, W. Kern, Eur. Polym. J. 44 (2008) 2986
4. [4] J. R. Nair, M. Destro, C. Gerbaldi, R. Bongiovanni, N. Penazzi, Novel multiphase electrode/electrolyte composites for next generation of flexible polymeric Li-ion cells, J. Appl. Electrochem. 43 (2013) 137 .
5. [5] T. F. Miller, Z-G. Wang, G. W. Coates, N. P. Balsara, Designing Polymer Electrolytes for Safe and High Capacity Rechargeable Lithium Batteries, Acc. Chem. Res. 50, (2017) 590 .
6. [6] O. Nuyken, S. D. Pask, Ring-Opening Polymerization - An Introductory Review, Polymers 5 (2013) 361 .
7. [7] P. Dreyfuss J. P. Kennedy, Alkyl halides in conjunction with inorganic salt for the initiation of the polymerization and graft copolymerization of heterocycles J. Polymer Sci. 56 (1976) 129 .
8. [8] Y. Miwa, H. Tsutsumi, T. Oishi, Polymerization of Bis-Oxetanes Consisting of Oligo-Ethylene Oxide Chain with Lithium Salts as Initiators, Polymer Journal, 33 (2001) 568 .
9. [9] Y. Miwa, H. Tsutsumi, T. Oishi, New Type Polymer Electrolytes Based on Bis-Oxetane Monomer with Oligo(ethylene oxide) Units, Polymer Journal, 33, (2001) 927 .
10. [10] Y. Cui, X. Liang, J. Chai, Z. Cui, Q. Wang, W. He, X. Liu, Z. Liu, G. Cui, J. Feng, High Performance Solid Polymer Electrolytes for Rechargeable Batteries: A Self-Catalyzed Strategy toward Facile Synthesis, Adv. Sci. 4 (2017) 1700174
11. [11] O. Nuyken, S. D. Pask, Ring-Opening Polymerization-An Introductory Review, Polymers 5 (2013) 361 - 403 .

Literature cited in this application:

1. [1] K. Xu, Electrolytes and Interphases in Li-Ion Batteries and Beyond, Chem. Rev. 114 (2014) 11503 ,
2. [2] Z. Xue, D. He, X. Xie, Polyethylene oxide) -based electrolytes for lithium-ion batteries, J. Mater. Chem. A, 3 (2015) 19218 ,
3. [3] B. Rupp, M. Schmuck, A. Balducci, M. Winter, W. Kern, Eur. Polym. J. 44 (2008) 2986
4. [4] JR Nair, M. Destro, C. Gerbaldi, R. Bongiovanni, N. Penazzi, Novel multiphase electrode / electrolyte composites for next generation of flexible polymeric Li-ion cells, J. Appl. Electrochem. 43 (2013) 137 ,
5. [5] TF Miller, ZG. Wang, GW Coates, NP Balsara, Designing Polymer Electrolytes for Safe and High Capacity Rechargeable Lithium Batteries, Acc. Chem. Res. 50, (2017) 590 ,
6. [6] O. Nuyken, SD Pask, Ring-Opening Polymerization - An Introductory Review, Polymers 5 (2013) 361 ,
7. [7] P. Dreyfuss JP Kennedy, Alkyl halides in conjunction with inorganic salt for the initiation of the polymerization and graft copolymerization of heterocycles J. Polymer Sci. 56 (1976) 129 ,
8. [8th] Y. Miwa, H. Tsutsumi, T. Oishi, Polymerization of Bis-Oxetanes Consisting of Oligo-Ethylene Oxide Chain with Lithium Salts as Initiators, Polymer Journal, 33 (2001) 568 ,
9. [9] Y. Miwa, H. Tsutsumi, T. Oishi, New Type Polymer Electrolytes Based on Bis-Oxetane Monomer with Oligo (ethylene oxide) Units, Polymer Journal, 33, (2001) 927 ,
10. [10] Y. Cui, X. Liang, J. Chai, Z. Cui, Q. Wang, W. He, X. Liu, Z. Liu, G. Cui, J. Feng, High Performance Solid Polymer Electrolytes for Rechargeable Batteries: A Self-Catalyzed Strategy toward Facile Synthesis, Adv. Sci. 4 (2017) 1700174
11. [11] O. Nuyken, SD Pask, Ring-Opening Polymerization-An Introductory Review, Polymers 5 (2013) 361-403 ,

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included for better information for the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Non-patent literature cited

• K. Xu, Electrolytes and Interphases in Li-Ion Batteries and Beyond, Chem. Rev. 114 (2014) 11503 [0111]
• Z. Xue, D. He, X. Xie, Polyethylene oxide) -based electrolytes for lithium-ion batteries, J. Mater. Chem. A, 3 (2015) 19218 [0111]
• B. Rupp, M. Schmuck, A. Balducci, M. Winter, W. Kern, Eur. Polym. J. 44 (2008) 2986 [0111]
• J. R. Nair, M. Destro, C. Gerbaldi, R. Bongiovanni, N. Penazzi, Novel multiphase electrode / electrolyte composites for next generation of flexible polymeric Li-ion cells, J. Appl. Electrochem. 43 (2013) 137 [0111]
• T. F. Miller, Z-G. Wang, G. W. Coates, N.P. Balsara, Designing Polymer Electrolytes for Safe and High Capacity Rechargeable Lithium Batteries, Acc. Chem. Res. 50, (2017) 590 [0111]
• O. Nuyken, S.D. Pask, Ring-Opening Polymerization - An Introductory Review, Polymers 5 (2013) 361 [0111]
• P. Dreyfuss J. P. Kennedy, Alkyl halides in conjunction with inorganic salt for the initiation of the polymerization and graft copolymerization of heterocycles J. Polymer Sci. 56 (1976) 129 [0111]
• Y. Miwa, H. Tsutsumi, T. Oishi, Polymerization of Bis-Oxetanes Consisting of Oligo-Ethylene Oxide Chain with Lithium Salts as Initiators, Polymer Journal, 33 (2001) 568 [0111]
• Y. Miwa, H. Tsutsumi, T. Oishi, New Type Polymer Electrolytes Based on Bis-Oxetane Monomer with Oligo (ethylene oxide) Units, Polymer Journal, 33, (2001) 927 [0111]
• Y. Cui, X. Liang, J. Chai, Z. Cui, Q. Wang, W. He, X. Liu, Z. Liu, G. Cui, J. Feng, High Performance Solid Polymer Electrolytes for Rechargeable Batteries: A Self-Catalyzed Strategy toward Facile Synthesis, Adv. Sci. 4 (2017) 1700174 [0111]
• O. Nuyken, S.D. Pask, Ring-Opening Polymerization-An Introductory Review, Polymers 5 (2013) 361-403 [0111]

Claims (16)

A process for producing a solid polymer electrolyte by a cationic ring opening and polymerization reaction of a precursor solution which comprises at least one lithium salt and at least one liquid heterocyclic monomer or at least one liquid heterocyclic oligomer, characterized in that the ring opening and polymerization reaction is carried out in the absence of a solvent. Procedure according to Claim 1 , in which the ring opening and polymerization reaction is carried out at temperatures between 20 ° C and 120 ° C, advantageously between 60 ° C and 85 ° C. Procedure according to one of the Claims 1 to 2 , in which the ring opening and polymerization reaction is carried out in a period between 10 minutes and 2 hours, advantageously between 15 minutes and 1 hour. Procedure according to one of the Claims 1 to 3 , in which the precursor solution for initiating the ring opening and polymerization reaction at least one lithium salt from the group lithium tetrafluoroborate (LiBF ₄ ), lithium difluoro (oxalato) borate (LiDFOB), lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium bis (fluorosulfonyl ) imide (LiFSI) or a mixture of at least two of these lithium salts. Procedure according to one of the Claims 1 to 4 in which the precursor solution comprises a liquid monomer or oligomer based on epoxy. Procedure according to the previous Claim 5 , wherein the precursor solution comprises poly (ethylene glycol) diglycidyl ether (PEGDGE) as a liquid oligomer. Procedure according to one of the Claims 1 to 6 , wherein the precursor solution comprises the liquid monomer or oligomer and the lithium salt in a ratio of ethylene oxide to lithium (EO: LI) of 100: 1 to 5: 1, preferably in a ratio of 50: 1 and 10: 1. Procedure according to one of the Claims 1 to 7 , in which the precursor solution has lithium salt in a concentration in the range from 2 to 30% by weight, advantageously from 5 to 25% by weight, based on the polymeric solid electrolyte Procedure according to one of the Claims 1 to 8th , in which the production of a polymeric solid electrolyte takes place directly on an electrode. Procedure according to Claim 1 , in which a precursor solution comprising lithium tetrafluoroborate (LiBF ₄ ) and poly (ethylene glycol) diglycidyl ether (PEGDGE) is used as the liquid oligomer with a ratio of ethylene oxide to lithium (EO: LI) of 40: 1 to 20: 1. Solid polymer electrolyte, producible by a method according to one of the Claims 1 to 10 , wherein the polymeric solid electrolyte has a low glass transition temperature of less than - 50 ° C. Solid polymer electrolyte, producible by a method according to one of the Claims 1 to 10 , the polymeric solid electrolyte having an ionic conductivity between 5-10 ^-6 S cm ^-1 and 1.2-10 ^-4 S cm ^-1 at 30 ° C and a broad electrochemical stability window of more than 5 V against Li / Li ⁺ . Solid polymer electrolyte after Claim 11 or 12 comprising at least one lithium salt from the group lithium tetrafluoroborate (LiBF ₄ ), lithium difluoro (oxalato) borate (LiDFOB), lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium bis (fluorosulfonyl) imide (LiFSI), lithium bis (trifluoromethane (Sulfonimide (LiTFSI) or a mixture of at least two of these lithium salts in a concentration in the range from 2 to 30% by weight, advantageously from 5 to 25% by weight, based on the polymeric solid electrolyte. Solid polymer electrolyte after Claim 11 to 13 comprising - 95% by weight of PEGDGE and 5% by weight of LiBF ₄ or, - 90% by weight of PEGDGE, 5% by weight of LiBF ₄ and 5% by weight of LiTFSI, or - 85% by weight of PEGDGE , 5% by weight of LiBF ₄ and 10% by weight of LiTFSI, or - 80% by weight of PEGDGE, 5% by weight of LiBF ₄ and 15% by weight of LiTFSI, or - 75% by weight of PEGDGE, 5% by weight of LiBF ₄ and 20% by weight of LiTFSI, or - 82% by weight of PEGDGE, 5% by weight of LiBF ₄ , 13% by weight of LiTFSI and 2% by weight % LIDFOB. Electrochemical cell, comprising a cathode, an anode and a polymeric solid electrolyte according to one of the Claims 11 to 14 , Electrochemical cell, with a cathode comprising LiNi _1/3 Mn _1/3 Co _1/3 O ₂ or LiFePO ₄ with an anode comprising Li and with a polymeric solid electrolyte according to one of the Claims 11 to 15 ,

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