Polycarbonate-based semi-interpenetrating polymer networks as separators for use in alkali metal batteries.

Abstract

The present invention relates to a solid electrolyte for an alkali metal solid-state battery, the solid electrolyte comprising a mixture of two alkali metal conductive salts and a semi-interpenetrating polymer network (sIPN) of a crosslinked polymer and a non-crosslinked polymer, the semi-interpenetrating polymer network comprising 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, and 10 to 50% by weight of a crosslinked polymer, a polycarbonate of a crosslinkable polyalkyl carbonate monomer having 2 to 15 carbon atoms, based on the single monomer, the single polyalkyl carbonate monomer having two crosslinkable groups, which may be substituted or unsubstituted, selected from the group consisting of acrylic, methacrylic, epoxy, vinyl, isocyanide, or a mixture of two different groups. The present invention also relates to an alkali metal battery having the solid electrolyte of the present invention.

Description

[Technical Field]

[0001] The present invention relates to a solid electrolyte for an alkali metal solid-state battery. The solid electrolyte comprises a mixture of two alkali metal conductive salts and a semi-interpenetrating polymer network (sIPN) of a crosslinked polymer and a non-crosslinked polymer. The semi-interpenetrating polymer network contains 50 wt.-% 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. The crosslinked polymer also contains 10 wt.-% to 50 wt.-% of a polycarbonate of a crosslinkable polyalkyl carbonate monomer having 2 to 15 carbon atoms, based on a single monomer. The polyalkyl carbonate monomer may be substituted or unsubstituted and has two crosslinkable groups selected from the group consisting of acrylic, methacrylic, epoxy, vinyl, isocyanide, or a mixture of two different groups thereof. The present invention also relates to an alkali metal battery having the solid electrolyte. [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 them suitable for mass use in mobile applications such as smartphones and laptops. Furthermore, continuous developments have improved their energy density and application reliability. These optimization steps, for example, 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 addition to batteries using liquid electrolytes, polymer-based solid-state batteries using high-viscosity "solid" electrolytes are also known. The optimum operating temperature for these types is typically in the range of around 60 °C, but there is a need to extend the operating temperature range to lower temperatures, for example, around 40 °C, or even down to around 20 °C. The most common representative of this class of electrolyte is polyethylene oxide (PEO), which uses at least one lithium-conducting salt and is assumed to be oxidatively unstable (above 3.9 V vs. Li / Li+), but is a standard that is inexpensive and readily available. Because PEO is easy to process and can be easily produced on an industrial scale, much effort has been devoted to the production of PEO-based polymer electrolytes. Typically, lithium iron phosphate (LFP) is used for the cathode, and LFP is used because this electrode material is sufficiently compatible with PEO.

[0004] When PEO is used as a polymer electrolyte, repeated charge / discharge cycles can cause battery cells to short circuit, even at voltages above 3.9 V and operating temperatures of 60 °C. Furthermore, in high-voltage electrodes, such as NMC (lithium nickel manganese cobalt) electrodes, the charge state between the electrolyte and the electrode becomes uneven, further increasing the undesirable situation. Furthermore, the combination of PEO and conductive salts is known to exhibit various crystalline and amorphous phases without additives, potentially resulting in uneven lithium ion transport. These factors hinder the widespread commercial use of solid electrolytes in electrodes with a wide temperature range and high voltages.

[0005] Several improvements in alkaline solid electrolytes have been described in the patent literature. For example, WO 2014 147 648 A1 discloses highly ion-conductive electrolyte compositions. In particular, this document discloses highly ion-conductive electrolyte compositions of semi-interpenetrating polymer networks and nanocomposites thereof as quasi-solid / solid electrolyte matrices for power generation, storage, and delivery devices, particularly hybrid solar cells, accumulators, capacitors, electrochemical systems, and flexible devices. The binary or ternary 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 two-component combination of such polymers, preferably with non-reactive end groups (components II and / or III, forming a ternary semi-interpenetrating polymer network); (c) an electrolyte salt and / or a redox couple; and, optionally, (d) a pure or surface-modified nanostructured material for forming a nanocomposite.

[0006] WO 2015 043 564 A1 discloses a method for manufacturing at least one electrochemical cell of a solid-state battery comprising a mixed conducting anode, a mixed conducting cathode and an electrolyte layer disposed between the anode and the cathode, the method comprising the following steps: - manufacturing or providing a mixed conductivity anode; - preparing or providing a mixed conducting cathode; - The surface of at least one of the two electrodes is made such that the electron conductivity perpendicular to the cell in the layer near the surface of the electrode is 10 8 modifying the film by additional process steps to reduce the film thickness to less than S / cm; and - thereafter, assembling the negative electrode and the positive electrode, with the surface modification layer of at least one of the electrodes as an electrolyte layer disposed at the interface between the negative electrode and the positive electrode to electrically isolate the mixed conducting electrodes, thereby forming a solid-state battery. [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 have the potential for further improvement, especially with regard to increasing the reproducibility of the charge / discharge process of alkaline secondary batteries. 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 which results in improved charge-discharge stability even after repeated cycling. [Means for solving the problem]

[0009] According to the present invention, this problem is solved by a solid electrolyte having the features set forth in claim 1. According to the present invention, this problem is further solved by an alkali metal battery as set forth in claim 9. Preferred embodiments of the invention are set forth in the dependent claims, the description or the drawings, whereby the further features set forth or shown in the dependent claims or the description or the drawings may, individually or in any combination, constitute objects of the invention, unless the context clearly dictates otherwise.

[0010] According to the present invention, there is provided a solid electrolyte for an alkali metal solid state battery, the solid electrolyte comprising a mixture of two types of alkali metal conductive salts and a semi-interpenetrating polymer network (sIPN) of a crosslinked polymer and a non-crosslinked polymer, the semi-interpenetrating polymer network comprising 50 wt. % or more and 80 wt. % or less 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 the crosslinked polymer comprises 10 wt. % or more and 50 wt. % or less of a polycarbonate of a crosslinkable polyalkyl carbonate monomer having 2 to 15 carbon atoms, based on the single monomer, as the crosslinked polymer, the single polyalkyl carbonate monomer may be substituted or unsubstituted and has two crosslinkable groups selected from the group consisting of acrylic, methacrylic, epoxy, vinyl, isocyanide, or a mixture of two different groups thereof.

[0011] Surprisingly, it has been found that combining the above-described structure of a solid electrolyte made from a semi-interpenetrating polymer network based on crosslinked polycarbonate and non-crosslinked PEO with a dual-conducting salt leads to significantly improved properties of the resulting solid electrolyte. This solid electrolyte exhibits significantly improved mechanical stability, in contrast to pure PEO-based solid electrolytes. The high mechanical stability of the dual-conducting salt means that the electrical properties of the solid electrolyte and its batteries are significantly more reproducible than those of batteries made solely with polyethylene oxide or a single-conducting salt. Therefore, the number of cycles achievable under the same electrical conditions and the battery life are significantly improved by the structure according to the present invention. Another advantage of this solid electrolyte is its improved proper operation at lower temperatures. Without being bound by theory, the nearly equal polarity of the polycarbonate used according to the present invention relative to the PEO appears to be crucial for the excellent miscibility, which results in a particularly homogeneous mixture and ultimately leads to the formation of a stable, homogeneous network. At the same time, the carbonate group exhibits weak coordination properties with alkali ions, which means that the alkali ions of the conductive salt are mainly coordinated to the added alkali ion conductive polymer electrolyte, e.g., PEO, and are not retained in the relatively inflexible carbonate backbone of the network former. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 shows the results of Li plating / stripping experiments as a function of time for a battery assembly not according to the invention. [Figure 2] FIG. 2 shows the results of galvanostatic cycling of a battery assembly not according to the invention as a function of time. [Figure 3] FIG. 3 shows the results of Li plating / stripping tests as a function of time for cell assemblies not according to the invention and for cell assemblies according to the invention using a dual salt electrolyte. [Figure 4]FIG. 4 shows the results of galvanostatic cycling as a function of time for a cell assembly not according to the invention and a cell assembly according to the invention using a dual-salt electrolyte. [Figure 5] FIG. 5 shows the results of the mechanical stability test (cell structures not according to the invention and according to the invention as a function of pressure deformation). DETAILED DESCRIPTION OF THE INVENTION

[0013] The solid electrolyte of the present invention is a solid electrolyte for use in alkali metal solid-state batteries. Solid electrolytes are also referred to as solid electrolytes, solid electrolyte ion conductors, or solid ion conductors. A solid electrolyte has a coherent polymer support structure with alkali metal ions embedded therein, which are mobile within the polymer matrix of the solid electrolyte. Electrical current can be passed through the movement of ions in the solid electrolyte. While solid electrolytes are electrically conductive, their electronic conductivity is significantly lower than that of metals. An alkali metal solid-state battery has at least two electrodes and a solid, particularly a non-flowing, electrolyte disposed between the electrodes. In addition to these components, the solid-state battery may also contain other layers or sheets. For example, the solid-state battery may contain other layers between the solid electrolyte and the electrodes. The electrical properties of alkali metal solid-state batteries are based on the redox reaction of alkali metals, i.e., metals in the first main group of the periodic table. Examples of alkali metals that can be used include lithium, sodium, and potassium.

[0014] The solid electrolyte of the present invention comprises a mixture of two different alkali metal conductive salts. The alkali metal conductive salt essentially consists of an alkali metal cation and an inorganic or organic anion. To form a mixture of two different alkali metal conductive salts, it is sufficient that the two conductive salts have the same cation but different anions. In this respect, the solid electrolyte of the present invention can contain only one cation species, for example, lithium, but, in contrast, it can also contain two different anions. The amounts of the two different alkali metal conductive salts used do not have to be equimolar. It is also possible to use the two different alkali metal conductive salts at different concentrations. Within the meaning of the present invention, a mixture of two different alkali metal conductive salts exists when one of the two alkali metal conductive salts constitutes at least 10 mol %, preferably 15 mol %, and more preferably 20 mol % of the total amount of alkali metal conductive salts.

[0015] Possible anions can be selected from the group consisting of hexafluorophosphate, perfluorophosphate, tetrafluoroborate, tris(pentafluoroethyl)trifluorophosphate, trifluoromethanesulfonate, bis(fluorosulfonyl)imide, bis(fluoromethanesulfonyl)imide, bis(perfluoroethanesulfonyl)imide, bis(oxalate)borate, difluoro(oxalate)borate, bis(fluoromalonato)borate, tetracyanoborate, dicyanotriazolate, dicyanotrifluoromethylimidazole, dicyanopentafluoroethylimidazole, fluorosulfonyl(trifluoromethanesulfonyl)imide, or a mixture of at least two of these components. Furthermore, at least one of the conductive salts used may contain an anion with a crosslinkable functional group, such as a methacrylic acid group.

[0016] Solid electrolytes contain semi-interpenetrating polymer networks (sIPNs) of cross-linked and non-cross-linked polymers. The basic mechanical structure of solid electrolytes is formed by the network of two different polymers, which provides the electrolyte with strength. A semi-interpenetrating network is composed of two different polymers. One polymer is cross-linked by forming covalent bonds between monomers, allowing it to form a three-dimensional network, while the other polymer lacks functional groups and is held together purely by ionic or van der Waals interactions. The two polymer components can, at least in principle, be separated from each other by a washing process. Because cross-linking of the functional groups of the cross-linkable polymer occurs only after a physical mixing process with the non-cross-linked polymer, the two components physically interpenetrate and together form a semi-interpenetrating polymer network. Other components of the solid electrolyte are alkali metal conductive salts, which are present "dissolved" within the network or bound to the network, but are considered, according to the present invention, as components of the solid electrolyte and not as components of the semi-interpenetrating polymer network.

[0017] The semi-interpenetrating network contains 50% by weight or more and 80% by weight or less 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 network composed of two polymer components has PEO, PC, PCL, or a mixture of these as the main weight component. These polymers, which cannot be crosslinked within the network and are not crosslinked, can each have their chain ends substituted with functional groups.

[0018] PEO refers to a monomer represented by the following structural formula: [ka]

[0019] Here, the index n may suitably be selected from 10 to 120000. The radicals R may each independently be hydrogen or a substituted or unsubstituted alkyl or aryl radical. The substituted or unsubstituted alkyl or aryl radicals may have a carbon number of C1-C20 and may further have non-bridging functional substituents such as halogen, OH, NH3, NO2, and the like.

[0020] Polycarbonate is a compound represented by the following structural formula: [ka]

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

[0022] Polycaprolactone refers to a compound represented by the following structural formula: [ka]

[0023] Here, the index n can be suitably chosen from 3 to 120000. The residues R at the ends of the chain correspond to the definition given above.

[0024] As a further component, the semi-interpenetrating polymer network (sIPN) contains 10 wt. % or more and 50 wt. % or less of a polycarbonate of a crosslinkable polyalkyl carbonate monomer having 2 to 15 carbon atoms, based on the individual monomers serving as crosslinked polymers. Thus, the crosslinkable component of the semi-interpenetrating network is composed of carbonate monomers that can crosslink with each other via functional groups in the monomers. In this way, an insoluble covalently crosslinked structure can be formed within the semi-interpenetrating network, enhancing the mechanical stability of the network. Preferably, the carbonate monomer has two crosslinkable groups, particularly two crosslinkable end groups. However, it is also possible for the carbonate monomer to have more than two functional groups. Note that the weight ratios given above are for the components of the semi-interpenetrating network and do not include the solid electrolyte portion introduced via the alkali metal conductive salt. Possible polycarbonate-based monomers are, for example, linear or branched alkyl polycarbonates with up to 15 carbon atoms between the carbonate groups. The molecular weight of the polyalkyl carbonate monomer can range from 100 g / mol to 5000 g / mol in the uncrosslinked, unfunctionalized state.

[0025] The polyalkyl carbonate monomer may be substituted or unsubstituted and may be composed of two crosslinkable groups selected from the group consisting of acrylic, methacrylic, epoxy, vinyl, isocyanide, or a mixture of two different groups. Thus, the polyalkyl carbonate monomer may carry additional functional groups such as OH, NH, or CHO. However, in addition to this general substitution of the monomer backbone, the polyalkyl carbonate monomer also contains at least two crosslinkable functional groups from among those listed above. These functional groups allow for the formation of covalent bonds between individual polycarbonate monomers.

[0026] In a preferred embodiment of the solid electrolyte, the weight fraction of cross-linked polymer relative to non-cross-linked polymer in the sIPN can be 20 wt.-% or more and 40 wt.-% or less. The concentration and miscibility of each component play an important role in generating a well-stabilized sponge-like structure of the network former within the polymer film. Therefore, significantly higher reproducibility is observed from the above-mentioned concentration range of polycarbonate network former (PEO-based) above 20 wt.-% compared to the pure PEO conductive salt standard. Furthermore, the overall decrease in conductivity due to the use of polycarbonate network former can be compensated for by increasing the salt content to the extent that no capacity loss due to increased cell resistance occurs at 60 °C compared to the pure PEO-conductive salt combination.

[0027] In a preferred embodiment of the solid electrolyte, the molecular weight of the polyalkyl carbonate monomer is 100 g / mol or more and 3500 g / mol or less. Studies of different chain lengths of the polyalkyl carbonate monomer have shown that shorter chain lengths of the polyalkyl carbonate monomer result in improved electrochemical performance. Apparently, shorter chain lengths increase the stability of the sIPN, thereby avoiding squeeze-induced short circuits in battery assemblies using the solid electrolyte of the present invention.

[0028] In a preferred embodiment of the solid electrolyte, the polyalkyl carbonate monomer may be selected from the group consisting of linear or branched, substituted or unsubstituted polyethylene, polymethylene, polypropylene, polybutylene, polyhexylene carbonate, or a mixture of at least two components thereof. Examples of these polyalkyl carbonate monomers include polyethylene carbonate (PEC), polypropylene carbonate (PPC), or polytrimethylene carbonate (PTMC), each of which may have a molecular weight ranging from 500 g / mol to 5000 g / mol. Preferably, the molecular weight of the polyalkyl carbonate monomer may range from 500 g / mol to 2000 g / mol. These alkyl polyalkyl carbonate monomers can provide particularly favorable mechanical properties of the matrix and particularly favorable electrical properties of the solid electrolyte.

[0029] In a preferred embodiment of the solid electrolyte, each polyalkyl carbonate monomer can carry two identical functional groups, which can be methacrylic groups. Introducing symmetrical functionality into the polyalkyl carbonate monomer via two methacrylic groups has proven particularly suitable for obtaining mechanically stable semi-interpenetrating networks. In this regard, each monomer carries two methacrylic groups, preferably two terminal methacrylic groups. The special mechanical stability of the resulting semi-interpenetrating network can significantly improve the lifespan of the solid electrolyte.

[0030] Within the preferred range of solid electrolyte characteristics, the mixture of two different alkali metal conductive salts can include at least alkali (fluorosulfonyl) (trifluoromethanesulfonyl) imide (FTFSI) and alkali bis(trifluoromethanesulfonyl) imide (TFSI) salts. This combination of both alkali metal conductive salts has been found to be particularly suitable for obtaining long-life, highly efficient batteries. This solid electrolyte exhibits excellent electrical conductivity, significantly extending the period until electrical failure of battery assemblies using this solid electrolyte. A particularly suitable mixture of both conductive salts contains between 0.1 wt.-% and 5 wt.-% FTFSI and 15 wt.-%-60 wt.-% TFSI, based on the weight of the sIPN containing the conductive salts. In particular, the proportion of both conductive salts can be between 5 wt.-% and 70 wt.-% based on the weight of the sIPN containing the conductive salts. Furthermore, conductive salts with crosslinkable anions have proven particularly advantageous because they can counteract excessive deformation of the sIPN due to electrostatic interactions between the sIPN and the immobilized anions. The use of crosslinkable conductive salts in sIPNs constructed according to the present invention is particularly advantageous because their addition further supports the formation of a highly amorphous cationic conductive polymer phase. The formation of such mechanically stable amorphous structures is not feasible with prior art compositions.

[0031] In another preferred embodiment of the solid electrolyte, the weight ratio of alkali (fluorosulfonyl) (trifluoromethanesulfonyl) imide (FTFSI) to the sum of the weights of the sIPN and the additional conductive salt components (the weight of alkali FTFSI divided by the weight of the sIPN and the additional conductive salt) is 0.005 or more and 0.1 or less. When the ratio of FTFSI to the sIPN containing the additional conductive salt is within this range, the electrical properties of the solid electrolyte are particularly good and a long life is obtained. In a further preferred embodiment, this ratio is 0.01 or more and 0.075 or less. The carbonyl groups of the network former have an overall weaker affinity for Li+ in the electrolyte than the linear PEO polymer, thereby preferentially coordinating Li+ with the linear PEO polymer. This allows for the use of lower salt concentrations compared to pure polyether or polyethers as network formers at the same salt concentration.

[0032] In a further preferred embodiment, the solid electrolyte may be a solid electrolyte for Li-solid-state batteries. Due to the improved mechanical and electrical properties of the solid electrolyte, the solid electrolyte according to the present invention is particularly suitable for electrically highly demanding applications in lithium-based battery types.

[0033] The present invention also provides an alkali metal battery comprising an anode, a cathode, and a solid electrolyte disposed between the anode and the cathode, characterized in that the solid electrolyte is 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 process according to the present invention and the solid polymer electrolyte according to the present invention. The battery may generally have other layers in addition to the mentioned components.

[0034] The positive electrode of an alkali metal battery, in a Li-metal battery embodiment, can be made of solid-state lithium-ion or lithium-metal battery materials. In this regard, the electrode layer can include an active material such as LiNiMnCozO2 (NMC), LiCoO2 (LCO), LiFePO4 (LFP), or LNiMnO4 (LNMO). Additionally, the positive electrode can further include a binder, an electronically conductive material for enhancing electronic conductivity, such as acetylene black, carbon black, graphite, carbon fiber, or carbon nanotubes, an electrolyte material for enhancing ionic conductivity, particularly a polymer or solid electrolyte, and other additives.

[0035] In a preferred embodiment of the alkali metal battery, the battery may be a Li metal battery, and the battery may have at least one high current or high voltage electrode. This suitability is due to its particularly high mechanical strength and the fact that the solid electrolyte is also suitable for use with high current or high voltage electrodes. The high current electrode can provide up to 100 mAhg with a charging time of 15 hours or less. -1 The high voltage electrode can provide an end-of-charge voltage of 4 V or more.

[0036] In a further preferred embodiment, the solid electrolyte according to the present invention can be used in electrochemical devices. Electrochemical devices can include primary and secondary batteries as well as fuel cells or capacitors. Furthermore, the solid electrolyte according to the present invention can be used in electrochemical devices as a layer for improving the electrical contact ("wetting") of electrodes.

[0037] In addition to applications as polymer electrolyte separators in lithium metal batteries where the polymer electrolyte of the present invention is in direct contact with the cathode, it can also be used in sulfide-based solid electrolyte batteries. This electrical concept can also be applied to oxide-based ceramics, where the polymer electrolyte can function as a wetting aid for the lithium metal side. It is also possible to use multiple different polymer layers on the anode and cathode. Instead of thermal radical polymerization, photopolymerization, in which polymerization is initiated by ultraviolet light irradiation, is also possible. The addition of short-chain polyethylene glycol derivatives can also enable lower operating temperatures. The sIPN of the present invention can also be used to finish other coating substrates, such as siloxide paper, polyethylene / polypropylene films, PTFE, or chemical surfaces such as glass and modified glass.

[0038] Example I. Preparation of solid electrolyte Fabricate sIPN for Li batteries. Ia Synthesis of polycarbonate network formers. The synthesis of the polycarbonate network former is carried out under inert gas. 10 g of poly(1,6-hexanediol) carbonate diol (Mw = 1000 g / mol) is dissolved in dry dichloromethane (100 mL). Approximately 0.5 g of magnesium sulfate is added to dry the polycarbonate, and the mixture is stirred overnight. The mixture is filtered to remove the magnesium sulfate. Next, DMAP (4-(dimethylamino)pyridine) (0.001 mol% per terminal hydroxyl group) and triethylamine (2 equivalents based on terminal hydroxyl groups) are added. The mixture is cooled to 0 °C with stirring, and methacryloyl chloride (1.2 equivalents based on terminal hydroxyl groups) is carefully added. The reaction mixture is stirred at room temperature for 3 days. The crude product is washed five times with 2 M aqueous hydrochloric acid (5 x 50 mL) to extract polar reactants and by-products from the organic phase. A separatory funnel is used for phase separation. The organic phase was dried over magnesium sulfate and the solvent was removed under reduced pressure. The product was dried under vacuum at RT for several days. The dried product was stored under inert gas.

[0039] Ib Preparation of sIPNs according to the invention. A conductive salt blend with a molar ratio of 13 parts Li-TFSI (0.289 g) to 1 part Li-FTFSI (0.018 g) was dissolved in 3 mL of acetonitrile or THF along with polycarbonate (poly(1,6-hexanediol) carbonate dimethacrylate) (0.125 g) and the radical initiator AIBN (azobisbutyronitrile) (0.018 g) as the solvent, followed by the addition of PEO powder (0.5 g). The conductive salt-to-polymer ratio mixture was stirred for several hours to achieve complete homogenization, after which it could be applied to Mylar film at essentially any thickness by film casting. The solvent was evaporated in a fume hood, and the resulting polymer film was polymerized under a nitrogen stream at 70 °C for 1 hour and then dried overnight under vacuum. The solid electrolyte thickness could be anywhere from 1 μm to 500 μm.

[0040] IC battery manufacturing For use in lithium metal battery cells, circular pieces of the polymer film, 200 μm high and 17 mm in diameter, were die-cut and used as separators between a lithium metal electrode and a positive electrode consisting of 91 wt.-% LiNi0.6Mn0.2Co0.2O2, 4 wt.-% carbon black, and 5 wt.-% PVdF. The lithium metal battery cells were tested at 60 °C.

[0041] The electrochemical behavior of the battery assembly according to the present invention and the battery assembly not according to the present invention is shown in Figures 1 to 5, which are as follows. FIG. 1 shows the results of Li plating / stripping experiments on a battery assembly not according to the invention as a function of time. FIG. 2 shows the results of galvanostatic cycling of a cell assembly not according to the invention as a function of time. FIG. 3 shows the results of Li plating / stripping tests as a function of time for cell assemblies not according to the invention and for cell assemblies according to the invention using a dual salt electrolyte. FIG. 4 shows the results of galvanostatic cycling as a function of time for a cell assembly not according to the invention and a cell assembly according to the invention using a dual salt electrolyte. FIG. 5 shows the results of a mechanical stability test (for a battery structure not according to the invention and a battery structure according to the invention) as a function of pressure deformation.

[0042] Figure 1 shows the voltage response of a Li-Li battery using two electrolyte-free s-IPNs. The two Li electrodes were alternately used as the positive and negative electrodes for 1 hour at a constant current of 50 μA / cm2, and the Li was transferred from one electrode to the other through the electrolyte. The battery failed after a relatively short time of 100 hours, due to a short circuit.

[0043] Figure 2 shows the voltage behavior of a conventional galvanostatic cycle of a Li-NMC622 cell using a PEO and polycarbonate polymer electrolyte, but with only one conductive salt (Li-TFSI) at a concentration of 30 wt.-% of the total weight of the s-IPN. This cell also exhibits time-dependent errors, as evidenced by noise in the voltage curve.

[0044] Figure 3 shows the voltage curves of Li plating / stripping experiments as a function of time, one for a cell setup according to the present invention and one for a cell setup without the present invention. The same Li-Li cell assembly was run with the same s-IPN, but once with Li-FTFSI / Li-TFSI as the "dual salt" electrolyte and once with Li-TFSI alone as the electrolyte, according to the present invention. It can be clearly seen that the dual salt approach using Li-FTFSI and Li-TFSI provides significantly longer, failure-free operation. Without being bound by theory, we speculate that the combination of the s-IPN with Li-FTFSI and Li-TFSI stabilizes the Li electrode.

[0045] Figure 4 shows the galvanostatic cycling results of Li-NMC622 batteries with different solid electrolyte compositions. When PEO and Li-TFSI were used alone (PEO12LiTFSI), the battery cells showed defects already early in the cycling process, likely due to short circuits. When PEO was used as the sole polymer and only another lead salt was added (LiFTFSI+PEO12LiTFSI), no significant improvement in electrical behavior was observed, and the cells were destroyed within a short time. Adding carbonate salts to Li-FTFSI in PEO12LiTFSI without forming a semi-interpenetrating network, i.e., without cross-linking the individual polycarbonate monomers, also did not improve electrical behavior. On the other hand, only the combination of the two electrolytes (Li-FTFSI and TFSI) to form a semi-interpenetrating network of PEO and cross-linked polycarbonate exhibited error-free cycling over the measurement period.

[0046] Figure 5 shows mechanical stability testing of solid electrolytes according to the present invention and those without. The use of a solid electrolyte according to the present invention, which has a sIPN of crosslinked polycarbonate and uncrosslinked PEO, significantly improves compressive strength compared to the PEO network alone. Compressive strength was measured using a compressibility testing device that compresses a 2 mm high, 18 mm diameter polymer sample between two stainless steel plates at a constant feed rate of 20 μm / min and measures the force required. This improved compressive strength, combined with the dual-salt approach, is believed to be the reason for the improved Li compatibility and error-free cycling of Li-NMC622 cells.

Claims

1. A solid electrolyte for an alkali metal solid state battery, comprising: The solid electrolyte comprises a mixture of two types of alkali metal conductive salts and a semi-interpenetrating polymer network (sIPN) of a crosslinked polymer and a non-crosslinked polymer, the semi-interpenetrating polymer network comprising: The composition contains 50% by weight or more and 80% by weight or less 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 As the crosslinked polymer, a crosslinked polycarbonate of a crosslinkable polyalkyl carbonate monomer having 2 to 15 carbon atoms is contained in an amount of 10 to 50% by weight, The polyalkyl carbonate monomer may be substituted or unsubstituted and has two crosslinkable groups selected from the group consisting of acrylic, methacrylic, epoxy, vinyl, isocyanide or a mixture of two different groups thereof.

2. 2. The solid electrolyte of claim 1, wherein the weight fraction of crosslinked polymer relative to non-crosslinked polymer in the sIPN is 20 wt.-% or more and 40 wt.-% or less.

3. 3. The solid electrolyte according to claim 1, wherein the molecular weight of the polyalkyl carbonate monomer is 100 g / mol or more and 3500 g / mol or less.

4. 4. The solid electrolyte according to claim 1, wherein the polyalkyl carbonate monomer is selected from the group consisting of linear or branched, substituted or unsubstituted polyethylene, polymethylene, polypropylene, polybutylene, polyhexylene carbonate, or a mixture of at least two components thereof.

5. 5. The solid electrolyte according to claim 1, wherein each of the polyalkyl carbonate monomers has two identical functional groups, and the functional groups are methacrylic groups.

6. 6. The solid electrolyte according to claim 1, wherein the mixture of two kinds of alkali metal conductive salts comprises a salt of alkali (fluorosulfonyl) (trifluoromethanesulfonyl) imide (FTFSI) and an alkali bis (trifluoromethanesulfonyl) imide (TFSI).

7. One of the two types of alkali metal conductive salts is alkali(fluorosulfonyl)(trifluoromethanesulfonyl)imide (FTFSI), 7. The solid electrolyte according to claim 1, wherein the weight of the FTFSI divided by the sum of the weights of the sIPN and the further conductive salt is 0.005 or more and 0.1 or less.

8. 8. The solid electrolyte according to claim 1, wherein the solid electrolyte is a solid electrolyte for a Li solid state battery.

9. 9. An alkali metal battery comprising a negative electrode, a positive electrode, and a solid electrolyte disposed between the negative electrode and the positive electrode, wherein the solid electrolyte is the solid electrolyte according to claim 1.

10. 10. The battery of claim 9, wherein the battery is a Li-metal battery, and the battery has at least one high current or high voltage electrode.

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