Semi-interpenetrating polymer networks as separators for alkali metal batteries.

Abstract

The present invention relates to a solvent-free solid electrolyte for an alkali metal solid-state battery, comprising an alkali metal conductive salt and a semi-interpenetrating polymer network (sIPN) of a crosslinked polymer and a non-crosslinked polymer, wherein the semi-interpenetrating polymer network comprises a non-crosslinked polymer selected from the group consisting of polyethylene oxide (PEO), polycarbonate (PC), polycaprolactone (PCL), chain-end-modified derivatives of these polymers, or a mixture of at least two of these components, and the crosslinked polymer is polyethylene glycol dimethacrylate (PEGdMA). The present invention also relates to a method for producing the solid electrolyte, and to an alkali metal battery comprising the solid electrolyte of the present invention.

Description

[Technical Field]

[0001] The present invention relates to a solvent-free solid electrolyte for an alkali metal solid-state battery, comprising an alkali metal conductive salt and a semi-interpenetrating polymer network (sIPN) of a crosslinked polymer and a non-crosslinked polymer, wherein the semi-interpenetrating polymer network is a non-crosslinked polymer selected from the group consisting of polyethylene oxide (PEO), polycarbonate (PC), polycaprolactone (PCL), chain end modified derivatives of these polymers, or a mixture of at least two of these components, and the crosslinked polymer is polyethylene glycol dimethacrylate (PEGdMA). The present invention also relates to a method for producing the solid electrolyte, and to an alkali metal battery comprising the solid electrolyte of the present invention. [Background technology]

[0002] Rising user demands for sustainability and mobility have significantly changed the landscape of decentralized energy storage in recent decades. Previously, the size, weight, and very limited electrical capacity of batteries significantly limited their technical availability. However, the use of alkali-metal-based energy storage systems, such as lithium secondary batteries, has significantly expanded the range of possible applications. Since their market introduction in the early 1990s, lithium-ion batteries have made mobile applications such as smartphones and laptops suitable for mass use. Furthermore, continuous developments have improved their energy density and application reliability. These optimization steps have contributed to the fact that lithium-ion batteries are now being considered as stationary energy storage devices for decentrally generated electricity in both private and industrial applications. Furthermore, these innovative energy storage systems are the basis for new, climate-friendly transport concepts in the field of electromobility.

[0003] In the field of alkali metal batteries, various technological concepts have been pursued to improve ease of use and storage capacity. For example, one way to optimize the safety and energy density of Li-metal batteries is to use solid electrolytes. Because polymer electrolytes have lower gravimetric densities than oxide- and sulfide-based solid electrolytes, this battery configuration could, in principle, relatively easily achieve improved gravimetric energy and power densities. In addition, polymer-based designs can exhibit ease of fabrication and good wettability of sulfide- or oxide-based composite electrodes. Here, the basic requirements are that the polymer electrolyte is compatible with both the alkali metal and the cathode material, exhibits uniform wettability of both electrodes, and allows alkali metal deposition on the anode.

[0004] The patent literature also provides several examples of alkali metal battery designs using polymer-based solid electrolytes.

[0005] For example, International Publication No. 2014 147648 A1 discloses a highly ion-conductive electrolyte composition. Specifically, this publication discloses a semi-interpenetrating polymer network and its nanocomposite as a quasi-solid / solid electrolyte matrix for power generation, storage, and transmission devices, particularly hybrid solar cells, capacitors, electrochemical systems, and flexible devices. The two or three components of the semi-interpenetrating polymer network electrolyte composition include (a) a polymer network having a polyether backbone (component I), (b) a low-molecular-weight linear, branched, or hyperbranched polymer, or any binary combination of such polymers, preferably with non-reactive end groups (component II and / or component III, forming a ternary semi-IPN system), (c) an electrolyte salt and / or a redox couple, and, optionally, (d) a pure or surface-modified nanostructured material to form the nanocomposite.

[0006] WO 2015 043 564 A1 discloses a method for manufacturing at least one electrochemical cell of a solid-state battery including a mixed conductive anode, a mixed conductive cathode, and an electrolyte layer disposed between the anode and the cathode, the method comprising: fabricating or providing a mixed conductivity anode; fabricating or providing a mixed conducting cathode; The surface of at least one of the two electrodes is fabricated by an additional manufacturing process to provide a layer near the surface of the electrode with an electronic conductivity of 10 in the direction perpendicular to the electrochemical cell. 8 and then assembling the anode and cathode together to form a solid-state battery, with the surface modification layer of at least one of the electrodes being disposed at the interface between the anode and the cathode as an electrolyte layer, thereby electrically isolating the mixed conducting electrodes; Includes. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2014 / 147648 [Patent Document 2] International Publication No. 2015 / 043564 Summary of the Invention [Problem to be solved by the invention]

[0008] Such solutions known from the prior art may leave room for further improvement, particularly with regard to increasing the reproducibility of the charge / discharge process, especially in the low-temperature behavior of secondary batteries.

[0009] The object of the present invention is to at least partially overcome the drawbacks known from the prior art, in particular to provide a solution that improves the charge / discharge stability, even when repeatedly cycled, as well as the electrical conductivity at low temperatures. [Means for solving the problem]

[0010] According to the present invention, the problem is solved by a solid electrolyte having the features of claim 1. According to the present invention, the problem is further solved by a method having the features of claim 6 and by a battery according to claim 9. Preferred embodiments of the invention are set out in the dependent claims, the description or the drawings, whereby further features mentioned or shown in the dependent claims or in the description or drawings are, individually or in any combination, subject to the invention, unless the context clearly indicates otherwise.

[0011] According to the present invention, a solid electrolyte for an alkali metal solid-state battery is proposed. The solid electrolyte comprises at least an alkali metal conductive salt and a semi-interpenetrating polymer network (sIPN) of a crosslinked polymer and a non-crosslinked polymer. The semi-interpenetrating polymer network comprises 50 to 80 wt% of a non-crosslinked polymer selected from the group consisting of polyethylene oxide (PEO), polycarbonate (PC), polycaprolactone (PCL), chain-end-modified derivatives of these polymers, or a mixture of at least two of these components, and 20 to 50 wt% of polyethylene glycol dimethacrylate (PEGdMA) as a crosslinked polymer. The solid electrolyte is composed of 90 to 100 wt% of the alkali metal conductive salt and the sIPN, and the solid electrolyte is solvent-free. Surprisingly, it has been found that a solvent-free solid electrolyte having the sIPN structure and the above-described composition has unexpectedly good electrical and mechanical properties. Batteries using these solid electrolytes exhibit particularly stable charge / discharge characteristics, suggesting that alkali metal insertion and removal during cycling is achieved without severe damage to the polymer network. Furthermore, it is believed that dendrite growth can be particularly suppressed, thereby achieving stable electrical characteristics even with repeated cycling. This can contribute to the stable behavior of alkali metal batteries, and overall, to both extended battery life and improved electrical performance. Another advantage is that alkali metal batteries can reproducibly maintain their electrical performance even at very low temperatures. This broadens the thermal operating window of alkali metal batteries, particularly toward lower temperatures, thereby improving their ease of use. Furthermore, such solid electrolytes offer the advantage of safely handling higher voltages and currents through the solid electrolyte, thereby ensuring safe operation of alkali metal batteries under more difficult electrical conditions. Without being bound by theory, it is believed that the polymer electrolytes of the present invention combine a highly amorphous alkali ion conductive phase with improved mechanical stability.Both factors result in higher operational reliability, more reproducible charge / discharge behavior, and a wider temperature range of application. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 shows the average capacity and standard deviation of the battery using pure PEO solid electrolyte. [Figure 2] FIG. 2 shows the average capacity and standard deviation of the battery using a PEO / PEGdMA solid electrolyte (PEGdMA 45% by weight based on PEO). [Figure 3] FIG. 3 is a graph showing the normalized specific capacitance of a solid electrolyte (PEO / PEGdMA) according to the present invention and a solid electrolyte (PEO) that is not a solid electrolyte according to the present invention. [Figure 4] FIG. 4 shows the normalized specific capacity at 40° C. (△) and 60° C. (●) of a battery using a solid electrolyte according to the present invention as a function of charge / discharge cycling. [Figure 5] FIG. 5 shows DSC thermograms (temperature range −100° C. to 100° C., 10 K / min) of the solid electrolyte (45 wt. % PEGdMA) according to the present invention with different EO:Li ratios. [Figure 6] FIG. 6 shows the conductivity of a solid electrolyte according to the invention (45 wt % PEGdMA) as a function of the EO:Li ratio and as a function of temperature. [Figure 7] FIG. 7 shows the voltage behavior over time of a battery using a solid electrolyte according to the invention (45 wt. % PEGdMA) in the NMC622 / / PEO+PEGdMA / / Li arrangement at 60° C. and a specific charge current of 15 mA g-1 as a function of different numbers of Li conductive salts. [Figure 8] FIG. 8 shows the voltage behavior over time of a cell using NMC622 / / PEO+PEGdMA / / graphite as the anode. [Figure 9]FIG. 9 shows the voltage behavior over time of a battery using NMC622 / / PEO+PEGdMA / / LTO as the anode. [Figure 10] FIG. 10 shows the electrical characteristics of a battery using a sIPN of polycaprolactone and PEGdMA (45 wt % based on PCL) in the configuration NMC622 / / polycaprolactone+PEGdMA / / Li at 60°C, plotting voltage as a function of specific capacity. [Figure 11] FIG. 11 shows the electrical characteristics of a battery using a sIPN of polycaprolactone and PEGdMA (45 wt % based on PCL) in the configuration NMC622 / / polycaprolactone+PEGdMA / / Li at 60 °C, showing the voltage curves as a function of time at a specific charge current of 15 mA g-1. DETAILED DESCRIPTION OF THE INVENTION

[0013] The solid electrolyte of the present invention is a solvent-free solid electrolyte for alkali metal solid-state batteries. A solid electrolyte is also called a solid-state electrolyte, a solid body electrolyte, or a solid ion conductor. A solid electrolyte has a coherent polymer support structure and alkali metal ions embedded therein, which are mobile within the polymer matrix of the solid electrolyte. The mobility of ions in the solid electrolyte allows for the flow of electric current. Solid electrolytes are electrically conductive but exhibit lower electronic conductivity than metals. An alkali metal solid-state battery has at least two electrodes and a solid, specifically, non-flowable, electrolyte disposed between the electrodes. In addition to these components, a solid-state battery may have other layers or sheets. For example, a solid-state battery may have other layers between the solid electrolyte and the electrodes. The electrical properties of an alkali metal solid-state battery are based on the redox reaction of alkali metals, i.e., metals in the first main group of the periodic table. Specifically, alkali metals can be lithium, sodium, or potassium.

[0014] The solid electrolyte comprises at least one alkali metal conductive salt and a semi-interpenetrating polymer network (sIPN) of a crosslinked polymer and a non-crosslinked polymer. The mechanical framework of the solid electrolyte, and its strength, is formed by the network of two different polymers. A semi-interpenetrating polymer network is a network composed of two different polymer species. One polymer can be crosslinked to form a three-dimensional network by forming covalent bonds between monomers, while the other polymer is held together purely by ionic or van der Waals interactions, without functional groups. The two polymer components can, at least in principle, be separated from each other by a washing process. Due to the fact that the crosslinked polymer is crosslinked by functional groups only after a physical mixing process with the non-crosslinked polymer, the two components physically interpenetrate and together form a semi-interpenetrating network. The other component of the solid electrolyte is an alkali metal conductive salt, which is "dissolved" in or bound to the network, but according to the present invention, this is not considered a component of the polymer network but a component of the solid electrolyte.

[0015] The semi-interpenetrating polymer network contains 50% to 80% by weight of a non-crosslinked polymer selected from the group consisting of polyethylene oxide (PEO), polycarbonate (PC), polycaprolactone (PCL), chain-end-modified derivatives of these polymers, or a mixture of at least two of these components. Thus, the semi-interpenetrating polymer network composed of two polymer components has PEO, PC, PCL, or a mixture of these components as the main weight component. Each of the non-crosslinked polymers may have a substituted chain end.

[0016] PEO refers to a monomer having the following structural formula:

[0017] [ka]

[0018] wherein the index n may suitably be selected from 10 to 120,000. The radicals R may each independently be hydrogen or a substituted or unsubstituted alkyl or aryl radical. The substituted or unsubstituted alkyl or aryl radical may have a carbon number from C1 to C20 and may further have non-bridging functional substituents such as halogen, NH3, NO2, etc.

[0019] Polycarbonate is a compound having the following structural formula:

[0020] [ka]

[0021] where the index n may suitably be chosen between 3 and 120000. The radicals R at the chain ends correspond to the definitions given above. 1 The group represents an aromatic or aliphatic C1-C15 group.

[0022] Polycaprolactone refers to a compound having the following structural formula:

[0023] [ka]

[0024] where the index n may suitably be chosen between 3 and 120000. The R residues at the chain ends correspond to the definitions given above.

[0025] In addition to the non-crosslinked polymer, the semi-interpenetrating polymer network contains 20 to 50% by weight of polyethylene glycol dimethacrylate (PEGdMA) as a crosslinking polymer. The weight data here refer to the two polymer components, in that the weight proportion of PEGdMA in the polymer network is at most equal to the proportion of the non-crosslinked component. When calculating the weight fraction, the weight fraction of the alkali metal conductive salt is not taken into account, since the formation of the semi-interpenetrating polymer network is essentially determined by the polymer components. PEGdMA is understood to be a monomer having the following structure:

[0026] [ka]

[0027] where the index n can suitably have a value between 5 and 1000. The monomer has two methacrylic functional groups, which are responsible for cross-linking the various monomers.

[0028] The weight fractions of the crosslinked polymer and the non-crosslinked polymer in the sIPN can total 100% by weight. According to the present invention, the semi-interpenetrating polymer network can have no greater amounts of other monomer / polymer components than the listed polymer components. A greater amount would be, for example, more than 5% by weight based on the crosslinked and non-crosslinked polymers listed above. In a preferred embodiment, in addition to the alkali metal conductive salt and the specific crosslinked and non-crosslinked polymers, no further monomers or polymers are included in the structure of the solid electrolyte.

[0029] According to the present invention, the solid electrolyte is composed of 90% by weight or more and 100% by weight or less of an alkali conductive salt and an sIPN. It has been found to be particularly effective for batteries containing the solid electrolyte of the present invention to have the most uniform and reproducible charge / discharge characteristics possible when the solid electrolyte is composed of no components other than a crosslinked polymer, a non-crosslinked polymer, and a conductive salt. Specifically, the solid electrolyte may be solvent-free. Furthermore, the solid electrolyte may not contain additional components intended to increase the solubility of the alkali metal conductive salt or to provide additional mechanical stability to the semi-interpenetrating polymer network. This design is particularly useful for maintaining the amorphous structure of the semi-interpenetrating polymer network, which may contribute to the most stable conductivity possible even at low temperatures.

[0030] In another preferred embodiment of the solid electrolyte, the non-crosslinked polymer may be polyethylene oxide, and the molar ratio of ethylene oxide units to alkali ions, represented by the EO / Li ratio, may be 5 to 15 in the solid electrolyte. The above-mentioned ratio of ethylene oxide units to alkali ions in the solid electrolyte has been found to be particularly suitable for achieving the highest possible conductivity even at relatively low temperatures. This ratio allows for relatively high ion mobility and only slightly disrupts the mechanical structure of the semi-interpenetrating polymer network, thereby achieving not only improved conductivity but also highly reproducible charge / discharge processes. The calculation of this ratio takes into account the EO units in the crosslinked polymer and the EO units in the non-crosslinked polymer. The respective amounts can be determined by methods known to those skilled in the art. For example, the ion concentration can be measured by ICP after dissolving the network. The number of EO units can be measured, for example, by HPLC or GC, after cleaving the covalent bonds of the crosslinked polymer, if necessary. Preferably, the ratio can be 8 to 13 inclusive, and even more preferably, 9 to 12 inclusive.

[0031] Furthermore, in preferred embodiments of the solid electrolyte, the thickness of the solid electrolyte may be between 20 μm and 60 μm. Surprisingly, the solid electrolyte according to the present invention has been shown to exhibit excellent mechanical stability even at very thin membrane thicknesses. These layer thicknesses are sufficient to provide highly reproducible electrical behavior over many charge / discharge cycles. This allows for very compact and durable designs. Overall, layer thicknesses of up to 250 μm, preferably up to 200 μm, and even more preferably up to 150 μm, may be achieved.

[0032] In a preferred embodiment of the solid electrolyte, P N / P V The non-crosslinked polymer P in the sIPN, expressed as a ratio N and cross-linked polymer P V The weight ratio of the non-crosslinked polymer to the crosslinked polymer may be greater than or equal to 2 and less than or equal to 2.5. Such a weight ratio of the non-crosslinked polymer to the crosslinked polymer has been shown to be particularly mechanically stable and to result in a favorable amorphous structure, which allows for sufficient electrical conductivity of the solid electrolyte even at low temperatures.

[0033] In a preferred embodiment of the solid electrolyte, the average molecular weight of PEGdMA may be 300 g / mol to 1000 g / mol. This range of crosslinkable polymer chain lengths preferentially stabilizes the resulting semi-interpenetrating polymer network. Longer PEGdMA chains may result in reduced mechanical strength. Shorter chains also result in reduced mechanical strength, likely due to insufficient crosslinking of the shorter chains. In even more preferred embodiments, the average molecular weight of PEGdMA may be 4500 g / mol to 900 g / mol, or even 600 g / mol to 850 g / mol.

[0034] In a further preferred embodiment of the solid electrolyte, the solid electrolyte may be a solid electrolyte for a Li solid-state battery, and the alkali metal conductive salt may be a mixture of at least two different lithium salts. Using a mixture of different conductive salts can improve the electrical properties of the solid electrolyte of the present invention. Suitable combinations of Li structures can be selected from, for example, LiTFSI + LiFTFSI, LiTFSI + LiFSI, LiTFSI + LiBF4, LiTFSI + LiBOB, LiTFSI + LiDFOB, LiDFOB + LiBF4, or suitable combinations thereof. Furthermore, the solid electrolyte may contain other additives, such as fluorine-based additives that can inhibit aluminum dissolution in other battery components, or SEI additives that can be used to stabilize the anode boundary layer.

[0035] Further, according to the present invention, there is provided a solvent-free method for producing an alkali metal battery solid electrolyte comprising a semi-interpenetrating polymer network, the method comprising: a) preparing a homogeneous solution of an alkaline conductive salt, a polymerization initiator, and a crosslinkable polymer having at least two crosslinkable groups; b) mixing the solution obtained from step a) with a non-crosslinkable polymer to obtain a homogeneous mixture; c) compressing the homogeneous mixture obtained from manufacturing step b) to form a non-crosslinked sheet membrane; d) crosslinking the membrane obtained in production step c) to obtain a solid electrolyte; Surprisingly, it has been found that a homogeneous solid electrolyte can be obtained by purely mechanical solvent-free preparation, and that it also exhibits excellent mechanical and electrical properties. Without being bound by theory, it is believed that the mechanical solvent-free preparation is well suited to providing an amorphous semi-interpenetrating network with a low crystalline fraction, which has a positive effect on the electrical conductivity and temperature dependence of the solid electrolyte.

[0036] The manufacturing step a) involves preparing a homogeneous solution of an alkaline conductive salt, a polymerization initiator, and a cross-linkable polymer. The homogeneous solution can be formed by purely mechanical mixing or stirring of the three components. Possible definitions of conductive salts and cross-linkable polymers have already been given above. Suitable polymerization initiators are chemicals known to those skilled in the art that can decompose into, for example, radicals upon a change in environmental variables, thereby cross-linking the cross-linkable polymer. Possible environmental variables include, for example, temperature or energy input via irradiation with light of various wavelengths. Thus, possible initiators are compounds that decompose into radicals either by heat or irradiation. This manufacturing step a) is carried out in such a way that the initiator does not react.

[0037] The process step b) involves mixing the solution obtained from step a) with a non-crosslinkable polymer. This process can be carried out, for example, by purely mechanical mixing or kneading the mixture. The usual time required to obtain a homogeneous mixture can be, for example, in the range of 1 to 2 hours.

[0038] The manufacturing step c) involves compressing the mixture obtained in the manufacturing step b). Compression can be performed using a press, for example, at a pressure ranging from 0.1 to 200 MPa for a time ranging from 30 minutes to 3 hours. Typically, the thickness of the mixture can be reduced by 10% to 100%, preferably 20% to 80%, through the compression step. This reduction in thickness can result in a mechanically stable yet sufficiently porous network after polymerization, thereby exhibiting excellent mechanical and electrical properties. Without being bound by theory, this is thought to be due to the absence of traces of solvent in the resulting network. This may contribute to improving the reproducibility of the charge / discharge process.

[0039] The manufacturing step d) involves crosslinking the membrane obtained in the manufacturing step c) to obtain a solid electrolyte. Crosslinking of the membrane can be achieved by changing the environmental conditions that stimulate the initiator to form radicals. For example, the membrane can be exposed to high temperatures in a heating oven. Optionally, the crosslinked membrane can be dried by further temperature treatment under normal pressure or in vacuum to remove traces of water.

[0040] In a preferred embodiment of the method, Li-TFSI can be used as the solvent-free alkali metal conductive salt in production step a), azoisobutyronitrile (AIBN) can be used as the polymerization initiator, PEGdMA can be used as the crosslinkable polymer having at least two crosslinkable groups, and PEO can be used in production step b). These components allow the method of the present invention to contribute to the production of solid electrolytes for long-life batteries with reproducible charge / discharge kinetics. Additionally, the batteries exhibit a wider temperature range over which particularly effective electrical properties can be achieved. Specifically, this temperature range is shifted to lower temperatures.

[0041] In a further embodiment of the method, the polymerization initiator can be incorporated in the process step b) instead of in the process step a). In addition to incorporating it in the process step a), it is also possible to incorporate the polymerization initiator into the mixture in the process step b). This can reduce undesired reactions of the initiator in the process step a) and shift the temperature range of the process to a higher temperature.

[0042] Further, according to the present invention, there is provided a solid polymer electrolyte produced by the method according to the present invention. The advantages of the solid electrolyte according to the present invention are explicitly mentioned in the advantages of the method according to the present invention. Without being bound by theory, it is believed that the solvent-free production makes it possible to change the proportion of amorphous regions, which may result in improved conductivity or longer life of batteries containing the solid polymer electrolyte according to the present invention.

[0043] Further, according to the present invention, there is provided an alkali metal battery comprising an anode, a cathode, and a solid electrolyte disposed between the anode and the cathode, the solid electrolyte being the solid electrolyte according to the present invention. The advantages of the alkali metal battery according to the present invention are explicitly mentioned in the advantages of the method according to the present invention and the solid polymer electrolyte according to the present invention. The battery as a whole may have other layers in addition to the components described.

[0044] In the embodiment of the Li metal battery, the positive electrode of the alkali metal battery can be made of materials for all-solid-state lithium ion batteries or materials for lithium metal batteries. x Mn y Co z O2 (NMC), LiCoO2 (LCO), LiFePO4 (LFP) or LNi x Mn y In addition, the positive electrode may further include a binder, an electronically conductive material that enhances electronic conductivity, such as acetylene black, carbon black, graphite, carbon fiber, and carbon nanotubes, and an electrolyte material, particularly a polymer or solid electrolyte, that enhances ionic conductivity, as well as other additives.

[0045] All-solid-state lithium battery materials can be used as the negative electrode of an alkali metal battery in one embodiment as a Li-metal battery. The electrode layer can include active materials suitable for anodes, such as transition metal composite oxides, amorphous carbon, or graphite. In addition, the negative electrode can further include a binder, such as polyvinylidene fluoride (PVDF), polyethylene glycol (PEG), or a combination of alginate and finely divided silicon, an electronically conductive material to increase electronic conductivity, and an electrolyte material, particularly a polymer or solid electrolyte, to increase ionic conductivity, as well as other additives. However, pure lithium, such as in the form of Li foil, or an alloy of lithium with indium, gold, zinc, magnesium, or aluminum can also be suitably used as the negative electrode. Other suitable negative electrodes for all-solid-state lithium-ion batteries include graphite electrodes, silicon-based electrodes, silicon-carbon composites, titanium oxide, and lithium metal electrodes.

[0046] In a preferred embodiment of the battery, the battery may be a Li-metal battery, and the battery may have at least one high current or high voltage electrode. Due to the improved mechanical and electrical properties of the solid electrolyte, the solid electrolyte of the present invention is particularly suitable for the electrically highly demanding applications mentioned above. The high current electrode is a 100 mAhg -1 The electrode can deliver a specific capacity exceeding 1000 kJ / cm² with a charging time of 15 hours or less. The high-voltage electrode can deliver a final charging voltage of 4 V or more.

[0047] In a further preferred embodiment, the solid electrolyte of the present invention can be used in electrochemical devices. Electrochemical devices may include primary and secondary batteries as well as fuel cells or capacitors. Furthermore, the solid electrolyte of the present invention can be used as a layer for improving the electrical contact ("wettability") of electrodes in electrochemical devices. [Example]

[0048] Working Example: I. Preparation of solid electrolyte Ia Solvent process using the example of Li solid electrolyte (state of the art) Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, 0.878 g) was dissolved in acetonitrile (6 g) along with PEGdMA (0.450 g) and the radical initiator azoisobutyronitrile (AIBN, 0.047 g, 2 wt%). The solution was added to a container containing polyethylene oxide (PEO, 1 g, 300 kg / mol) and stirred at room temperature for 4 hours. The mixture was applied to a Mylar film using a doctor blade. The film was allowed to dry in a fume hood for at least 30 minutes. The film was polymerized under a nitrogen stream at 80°C for 1 hour and then dried in a vacuum for at least 12 hours. A wet film thickness of approximately 1.5 mm was required to produce a polymer layer approximately 150 μm thick.

[0049] Solvent-free process using the example of Ib Li solid electrolyte - Variant A The conductive salt LiTFSI (0.878 g) was stirred with PEGdMA (0.450 g) and the radical initiator AIBN (0.047 g, 2 wt%) for 1 hour until a clear solution was formed. The solution was spread on top of PEO powder (1 g, 300 kg / mol) and mixed for 10 minutes at 1000 rpm using a magnetic stirrer. The components were allowed to agglomerate. The mixture was sandwiched between two Mylar films using a 100 μm spacer and repeatedly compressed and folded using a laboratory press at 25 kN for 30 minutes. The mixture was finally compressed to the desired thickness and polymerized between the Mylar films under nitrogen flow at 80 °C for 1 hour. Optionally, the film was then dried in vacuum for 12 hours.

[0050] Solvent-free process using the example of Ic Li solid electrolyte - Variant B The conductive salt LiTFSI (0.878 g) was added to a mortar along with PEO powder (1 g, 300 kg / mol) and homogenized for 10 minutes. The resulting gum was sealed in a pouch bag film and stored at 60 °C for 2 days. A solution of PEGdMA (0.450 g) and the radical initiator AIBN (0.047 g, 2 wt%) was prepared with stirring for 1 hour. The solution was vacuum-sealed in a pouch bag along with the previously prepared PEO-LiTFSI material and stored for 24 hours. The mixture was sandwiched between two sheets of Mylar film using a 100 μm spacer and repeatedly compressed and folded using a laboratory press for 30 minutes. The mixture was finally compressed to the desired thickness and polymerized between the Mylar films under nitrogen flow at 80 °C for 1 hour. Optionally, the film was then dried in vacuum for 12 hours.

[0051] Solvent-free process using the example of Id Li solid electrolyte - Variant C The conductive salt LiTFSI (0.878 g) was placed in a mortar with PEO powder (1 g, 300 kg / mol) and homogenized for 10 minutes. A solution of PEGdMA (0.450 g) and the radical initiator AIBN (0.047 g, 2 wt%) was prepared with stirring for 1 hour. The solution was also placed in the mortar and homogenized for at least 10 minutes. The mixture was sandwiched between two Mylar films using a 100 μm spacer and repeatedly compressed and folded using a laboratory press for 30 minutes. The mixture was finally compressed to the desired thickness and polymerized between the Mylar films at 80 °C for 1 hour under nitrogen flow.

[0052] II. Battery Cell Structure Unless otherwise specified, measurements of the battery types according to the present invention were carried out on solid electrolytes produced by a solvent process. The electrical properties of solid electrolytes according to the present invention produced by a solventless process may have a high amorphous content. For use in lithium metal batteries, circular pieces of polymer film with a layer thickness of 100 μm were punched out to resemble a separator and inserted between the lithium metal electrode and the positive electrode. The electrical properties of the lithium metal batteries thus produced were tested at different temperatures (60°C, 40°C).

[0053] III. Electrical characteristics IIIa. Specific Capacity as a Function of Charge / Discharge Cycles 1 and 2 show the normalized specific capacity of a lithium metal battery according to the present invention and a lithium metal battery other than the present invention as a function of charge / discharge cycles. Normalized to a theoretical capacity of 176 mAh / g. The battery structure is as follows: cathode: NMC622; anode: Li; charging current (each tripled): 7.5 mA g -1 , 15mA g -1 , 30mA g -1 , 75mA g -1 , 150mA g -1 , 300mA g -1 , 750mA g -1 , 7.5mA g -1 , voltage range 3.0~4.3V, specified solid electrolyte with EO:Li ratio 15:1; temperature 60℃.

[0054] Figure 1 shows the average capacity and standard deviation for batteries using a pure PEO solid electrolyte, and Figure 2 shows the average capacity and standard deviation for batteries using a PEO / PEGdMA solid electrolyte (45 wt% PEGdMA based on PEO). Each case shows the average and standard deviation of measurements for five different batteries. Comparing Figures 1 and 2 reveals that the standard deviation of the specific capacity for the batteries of the present invention is significantly smaller than that for the batteries using a pure PEO solid electrolyte. This suggests that the charge / discharge process of the batteries of the present invention is highly reproducible. It is likely that the metal ion calation / intercalation process disrupts the mechanical structure of the solid electrolyte of the present invention less than that of the pure PEO solid electrolyte. Without being bound by theory, the improved electrical stability of the solid electrolyte of the present invention may be due to the suppression of dendrite growth during the charge / discharge process in the mechanically stabilized solid electrolyte of the present invention.

[0055] IIIb. Constant current charging / discharging 3 shows the normalized specific capacity of a solid electrolyte (PEO / PEGdMA) according to the present invention and a solid electrolyte (PEO) other than the solid electrolyte according to the present invention. The experimental setup specifications were as follows: Cell type: 2032 button cell, Electrodes: NMC622 (Targray) Li (Albemarle); Electrolyte as shown; EO:Li ratio: 15:1; Test procedure: 1×C / 20, 100×C / 10; Voltage range: 3.0-4.3 V; Temperature: 60°C; Active material ≈ 4 mg.

[0056] Comparison of data for the solid electrolyte of the present invention with data for solid electrolytes other than the solid electrolyte of the present invention shows that the solid electrolyte of the present invention has a significantly longer service life than a pure PEO solid electrolyte, and in particular, the use of the solid electrolyte of the present invention improves charge / discharge characteristics and reproducibility.

[0057] IIIc. Temperature dependence of normalized specific capacity as a function of charge / discharge cycling 4 shows the normalized specific capacity of a battery using a solid electrolyte according to the present invention at 40° C. (△) and 60° C. (●) as a function of charge-discharge cycles. The specific capacitance curves show that the solid electrolyte according to the present invention has excellent stability, especially at low temperatures, with only a very small decrease in specific capacitance.

[0058] IIId. Amorphous phase Figure 5 shows DSC thermograms (temperature range -100°C to 100°C, 10 K / min) of the solid electrolyte (45 wt% PEGdMA) according to the present invention with different EO:Li ratios. By increasing the Li salt concentration in the solid electrolyte to 10:1, the crystalline portion on the solid electrolyte can be suppressed. Therefore, a highly amorphous solid electrolyte with improved electrical properties can be obtained.

[0059] IIIe. Conductivity Figure 6 shows the conductivity of a solid electrolyte (45 wt % PEGdMA) according to the present invention as a function of EO:Li ratio and as a function of temperature. The instrument setup was as follows: EIS; frequency range: 1 MHz to 1 Hz; temperature range: 0 °C to 70 °C; battery: button cell 2032; sample height: 100 μm; sample diameter: 15 mm (circular); blocking electrode: stainless steel.

[0060] 6 shows that the battery according to the invention using the solid electrolyte according to the invention has an ionic conductivity at 40° C. and an EO:Li ratio of 1:10, comparable to that at 60° C. Thus, the low temperature behavior of the solid electrolyte according to the invention is significantly better than the electrical behavior of the pure PEO solid electrolyte.

[0061] IIIf. Use of two different Li conductive salts Figure 7 shows the charge transfer coefficients of NMC622 / / PEO+PEGdMA / / Li arrangements at 60°C and a specific charge current of 15 mA g as a function of different numbers of Li conductive salts. -1Figure 1 shows the voltage behavior over time of a battery using a solid electrolyte (45 wt % PEGdMA) according to the present invention. This figure shows that the use of two Li salts (LiTFSI and LiFTFSI) improves the voltage increase over time compared to a solid electrolyte using only one conductive salt. This figure shows that the use of two Li salts (LiTFSI and LiFTFSI) improves the voltage increase over time compared to a solid electrolyte using only one conductive salt (LiTFSI).

[0062] IIIg. Electrode Figures 8 and 9 show the cell voltage as a function of time using different anodes. Figure 8 uses the NMC622 / / PEO+PEGdMA / / graphite configuration, and Figure 9 uses the NMC622 / / PEO+PEGdMA / / LTO configuration. The orders show that failure-free operation is possible for cells using NMC622 and anodes other than metallic lithium.

[0063] IIIh. sIPN containing polycaprolactone Figures 10 and 11 show the electrical properties of a battery using a polycaprolactone and PEGdMA sIPN (45 wt % based on PCL) in the configuration NMC622 / / polycaprolactone+PEGdMA / / Li at 60 °C. Figure 10 shows voltage as a function of specific capacity, and Figure 11 shows voltage as a function of time at a specific charge current of 15 mA g. -1 4 shows the voltage curve at

[0064] These figures show that even when PCL is used as a component of an sIPN, a stable and electrically suitable solid electrolyte can be obtained, making it suitable for use in batteries.

Claims

1. A solid electrolyte for an alkali metal solid state battery, comprising: the solid electrolyte comprises at least one alkali metal conductive salt and a semi-interpenetrating polymer network (sIPN) of crosslinked and non-crosslinked polymers; The semi-interpenetrating polymer network is Polyethylene oxide (PEO), polycarbonate (PC), polycaprolactone (PCL) , a chain end modified derivative of these polymers, or a mixture of at least two of these components, the non-crosslinked polymer is 50% by weight or more and 80% by weight or less, and The cross-linked polymer is polyethylene glycol dimethacrylate (PEGdMA) in an amount of 20% by weight or more and 50% by weight or less, The solid electrolyte is composed of 90% by weight or more and 100% by weight or less of the alkali metal conductive salt and the sIPN, and the solid electrolyte is solvent-free.

2. 2. The solid electrolyte of claim 1, wherein the non-crosslinked polymer is polyethylene oxide, and the solid electrolyte has a molar ratio of ethylene oxide units to alkali ions, expressed by an EO / Li ratio, of 5 or more and 15 or less.

3. A solid electrolyte as described in claim 1 or 2, wherein the solid electrolyte is a solid electrolyte for a Li solid state battery, and the alkali metal conductive salt is a mixture of at least two different lithium salts.

4. A solid electrolyte layer comprising the solid electrolyte described in any one of claims 1 to 3 and having a thickness of 20 μm or more and 60 μm or less.

5. 1. A solvent-free method for preparing an alkali metal battery solid electrolyte comprising a semi-interpenetrating polymer network (sIPN), comprising: a) preparing a homogeneous solution of an alkali metal conductive salt, a polymerization initiator, and polyethylene glycol dimethacrylate (PEGdMA) as a crosslinkable polymer having at least two crosslinkable groups; b) mixing the solution obtained from step a) with a non-crosslinkable polymer selected from the group consisting of polyethylene oxide (PEO), polycarbonate (PC), polycaprolactone (PCL), chain end modified derivatives of these polymers, or a mixture of at least two of these components to obtain a homogeneous mixture; c) compressing the homogeneous mixture obtained from step b) to form a non-crosslinked sheet membrane; d) crosslinking the membrane obtained in the production step c) to obtain a solid electrolyte, The semi-interpenetrating polymer network contains 50% by weight or more and 80% by weight or less of the non-crosslinked polymer and 20% by weight or more and 50% by weight or less of polyethylene glycol dimethacrylate (PEGdMA) as the crosslinked polymer, the solid electrolyte is composed of 90% by weight or more and 100% by weight or less of the alkali metal conductive salt and the sIPN, and the solid electrolyte is solvent-free.

6. 6. The method according to claim 5, wherein in the preparation step a), Li-TFSI is used as the solvent-free alkali metal conductive salt, azoisobutyronitrile (AIBN) is used as the polymerization initiator, and PEGdMA is used as the crosslinkable polymer having at least two crosslinkable groups, and in the preparation step b), PEO is used.

7. 7. The method according to claim 5 or 6, wherein the polymerization initiator is incorporated in production step b) instead of production step a).

8. 4. An alkali metal battery comprising an anode, a cathode, and a solid electrolyte disposed between the anode and the cathode, wherein the solid electrolyte is the solvent-free solid electrolyte of claim 1.

9. 9. The battery of claim 8, wherein the battery is a Li metal battery and includes at least one high-current or high-voltage electrode, the high-current electrode being capable of delivering a specific capacity of greater than 100 mAhg −1 in a charge time of 15 hours or less, and the high-voltage electrode being capable of delivering a final charge voltage of 4 V or greater.

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