DE102015005805A1 - Electrolyte with multilayer structure and electrical storage device - Google Patents

Abstract

The invention relates to an electrolyte having a multilayer structure comprising - at least a first electrolyte layer, which is characterized by a first relative permittivity ε1; At least one second electrolyte layer, which is characterized by a second relative permittivity ε2, an interface between the first electrolyte layer and the second electrolyte layer, characterized in that the first relative permittivity ε1 and the second relative permittivity ε2 define a coefficient α and the electrolyte of the first electrolyte layer and the electrolyte of the second electrolyte layer are selected such that at the interface the measure α in the range 0.244 <α <0.5, preferably 0.371 <α ≤ 0.5, particularly preferably 0.436 <α ≤ 0.5, further preferably 0.475 <α ≦ 0.5, particularly preferably 0.488 <α ≦ 0.5, even more preferably 0.494 <α ≦ 0.5, where ε1 is always the lower of the relative permittivities of the adjacent media and ε2 is the higher of the relative permittivities of adjacent media.

Description

The invention relates to an electrolyte with a multilayer structure and to an electrochemical energy store, in particular a battery cell, comprising such an electrolyte. Multi-layered electrolytes are u. a. interesting for lithium ion batteries.

A layered structure of an electrolyte for a lithium-ion battery may consist of several layers of liquid and / or solid electrolyte. In particular, such a structure may comprise two layers (not necessarily identical in composition) of liquid electrolyte and a central layer of solid electrolyte as a separator

Examples of liquid electrolytes are mixtures of ethylene carbonate and ethyl methyl carbonate (EC and EMC) with lithium hexafluorophosphate (LiPF ₆ ) as the conductive salt and propylene carbonate and ethylene glycol dimethyl ether (PC and DME) with lithium bis (trifluoromethylsulphonyl) imide (LiTFSI) as the conductive salt , Since ethylene glycol dimethyl ether is also referred to as 1,2-dimeteroxyethane, the abbreviation DME is also used for this purpose.

Examples of solid electrolytes are: garnet-type systems such as Li _{7 + xy} M ^II _x M ^III _3-x M ^IV _2-y M _y ^V O ₁₂ , in which:
M ^II : divalent cation,
M ^III : trivalent cation;
M ^IV : tetravalent cation,
M ^V : pentavalent cation
is, for example
Lithium Lanthanum Zirconate Li _7-3x Al _x La ₃ Zr ₂ O ₁₂ or
Li _7-x La ₃ (Ta / Nb) _x Zr _2-x O ₁₂ . Further examples are systems with so-called LiSiCon crystal phases Li ₁ -x (M ⁵⁺ , M ³⁺ ) _x M ^{4 + 2-x} (PO ₄ ) ₃ , where M ₅₊ Ta and / or Nb, M ³ + Al , Cr, Ga, Fe and M ⁴ + Ti, Zr, Si, Ge may be. The use of sulfidic electrolytes is conceivable.

Regarding the construction of such systems and the materials involved will be on Jennifer L. Schaefer, Yingying Lu, Surya S. Moganty, Praveen Agarwal, N. Jayaprakash, Lynden A. Archer, Electrolytes for High-Energy Lithium Batteries, Appl. Nanosci. 2 (2012), pp. 91-109 as well as the DE 102 011 013 018 B3 . US 2003 0205467 A1 . US 2009 0317724 directed.

Sulfidic systems are used for example in US 2005 0107239 A1 . US 2009 159839 A or JP 2008 120666 A described.

For the total resistance of an electrolyte with multilayer structure, in addition to the conductivities of the liquid or solid electrolytes involved, the interface resistance between the two types of electrolyte is also decisive.

How this interface resistance can be systematically minimized is not found in the prior art.

From the EP 1134758 A1 has become known a polymer electrolyte which is equipped with a side chain with a large dipole moment. The resulting high relative permittivity increases loudly EP 1134758 A1 the ionic conductivity of the conductive salt dissolved in the polymer matrix. It is further stated that this side chain lowers the interfacial resistance to the electrodes to the same order as known from liquid electrolytes. The reason given for this is the possible better chemical cohesion of electrodes and electrolyte.

From the US 2014/0011101 A1 For example, a lithium-air battery has become known with an ion-conductive solid electrolyte, which may include lithium aluminum germanium phosphate (LAGP), lithium aluminum titanium phosphate (LATP), or lithium titanium silicon phosphate (LATSP). The organic electrolyte used is dimethoxyethane (DME).

Out Tonghuan Yang, Lin Sang, Fei Ding, Jing Zhang, Xingjiang Liu: Three-and four-electrode EIS analysis of water-stable lithium electrode with solid electrolyte plate. In: Electrochimica Acta 81, 2012, p. 179- 185. - ISSN 0013-4686 is a lithium-ion cell with LAGP as a solid electrolyte and ethylene carbonate: Diethylencarbonat: ethyl methyl carbonate 1: 1: 1 has become known as a liquid electrolyte.

The US 2006/01334492 describes an electrolyte with two layers in which the electrolyte is the same in both layers.

The object of the invention is to avoid the disadvantages of the prior art and specify which conditions must be met in an electrolyte with multi-layered structure in order to realize the lowest possible interface resistance.

According to the invention, this object is achieved in that in an intended for use in the room temperature range electrolyte having multilayer structure, comprising at least one electrolyte layer, which is characterized by a relative permittivity ε ₁ , and at least one further electrolyte layer, characterized by a relative permittivity ε ₂ and an interface between the two electrolyte layers, where the two relative permittivities ε ₁ and ε ₂ define a coefficient α = ε ₁ / (ε ₁ + ε ₂ ) and the electrolyte of one electrolyte layer and the electrolyte of the further electrolyte layer are selected such that in that the coefficient at the interface is in the range 0.244 <α ≦ 0.5, preferably 0.371 <α ≦ 0.5, particularly preferably 0.436 <α ≦ 0.5, very particularly preferably 0.475 <α ≦ 0.5, more preferably 0.488 < α ≤ 0.5, even more preferably 0.494 <α <0.5, where ε ₁ is always the lower of the relative permittivities of the adjacent media and ε _{2 is} the higher of the relative permittivities of the adjacent media. This solution is not limited to combinations of liquid electrolytes and / or polymers, but explicitly includes inorganic materials such as glasses, glass ceramics or (polycrystalline) ceramics with a. It is particularly preferred if the α value is α ≈ 0.5, but at least α> 0.436, in particular α> 0.488, ie in the range 0.436 <α ≤ 0.5, preferably 0.488 <α ≤ 0.5. For such a case of almost identical permittivities, a relatively large linear range of the overvoltage of 0.2 V, in particular 1 V, is achieved in the interface region of the different electrolytes.

In fact, the inventors have found that, in the case of an electrolyte with a multilayer structure, the adjacent electrolytes, even if they are glasses, glass ceramics or ceramics, can be considered as dielectric continuums with a conductive salt or conductive oxide distributed therein. This was surprising because it had been expected, in particular for semicrystalline structures, that the individual atomistic skeleton structure plays such a large role that a continuum description is not possible. Also in this case, d. That is, if either of the two adjacent electrolytes or both is a glass, a glass-ceramic or a ceramic, it is preferable to select the same value of relative permittivity for both electrolytes. Since the relative permittivity is temperature- and frequency-dependent, the choice is made for a specific operating point or work area, ie. H. for a specific frequency and / or a specific temperature or a frequency and / or temperature range.

However, frequency-dependent changes in the relative permittivity of the background, ie the matrix material described as a dielectric continuum, are generally limited to individual frequency ranges. As Charles Kittel, Introduction to Solid State Physics, 5th Edition, R. Oldenbourg-Verlag Munich Vienna, 1980, p. 441 , such as Ekaterina I. Igorodina, Maria Forsyth, and Douglas R. MacFarlane, "On the components of the dielectric constant of ionic liquids: ionic polarization?", Phys. Chem. Chem. Phys. 11, 2452-2458 (2009) , it can be seen, relative to the relative permittivity, if one goes on the frequency scale from top to bottom, first the electronic polarizability, ie the mobility of the electron shell relative to the core, then the ionic polarizability, ie the displacement of atoms with partial charges of different sign against each other , then the dipole polarizability, ie the orientation of permanent dipoles, and then the space charge polarizability, ie the migration of ions to the interfaces. The latter is an effect of ionic conduction and therefore does not belong to the above background.

In ion guides made of glass, glass ceramics or ceramics, only the first two contributions and the last one play a role. In order not to count the latter, one goes on the frequency scale from top to bottom and to the extent that one considers both the electronic and the ionic polarizability. This is the case below the infrared range, see Charles Kittel, Introduction to Solid State Physics, 5th Edition, R. Oldenbourg-Verlag Munich Vienna, 1980, p. 441 , such as Ekaterina I. Igorodina, Maria Forsyth, and Douglas R. MacFarlane, "On the components of the dielectric constant of ionic liquids: ionic polarization?", Phys. Chem. Chem. Phys. 11, 2452-2458 (2009) , The relative permittivity is then practically constant up to the frequencies at which the space charge effects begin. This value is used as the relative permittivity of the background. Of course you count z. B. the electronic polarizability of the conductive salt or the Leitoxids with; However, this fact is neglected for ionic conductors made of glass, glass ceramic or ceramic, which can not be easily prepared without the conductive salt or lead oxide.

In the case of liquid electrolytes or polymer electrolytes which can be prepared without conducting salt or lead oxide, the relative permittivity used is the practically constant value which is found below the frequency range in which the dipole polarizability "switches on" (calculated from top to bottom). In the case of polymer electrolytes which can not be prepared without conducting salt or conductive oxide, one must use the sometimes narrow frequency window between the frequency range in which the dipole polarizability "switches on" (from top to bottom) and the onset of space charge polarizability.

If the ideal case according to the invention of the equality of the relative permittivities on both sides of the interface before, the energy level of the charge transport transporting ions, z. Example, in a lithium-ion battery, the lithium ions are determined on the two sides.

Assuming that the energy level of these ions is determined only by the dielectric and interactions with other ions, especially the counterions, are negligible, then the charge transporting ions are located on both sides of the interface in the absence of external stress and activity on both sides also at the same energy level, which in turn is approximately determined by the Born's formula for the free solvation enthalpy. This will be on M. Born, Volume and Hydration Heat of the Ions, Zeitschrift für Physik, No. 1, pp. 45-48 (1920) referenced, whose contents are included in the present application in full.

If an additional voltage difference is applied to the multi-layered electrolyte layer, for example from the outside, then this results according to FIG K. Aoki, Theory of the ion transfer kinetics at a viscous immiscible liquid / liquid interface by means of the Langevin equation, Electrochimica Acta 41, No. 14, pp. 2321-2327 (1996). in that the stress in a thin boundary layer on both sides of the interface drops and there causes an inversely proportional to the interface resistance ion transport.

If there is continuity of relative permittivity at the boundary layer, there is no discontinuity of the electric field at the interface, which is favorable for a minimum interfacial resistance. This will be on K. Aoki, ibid , referenced. Ideally, in multi-layered electrolytes, combinations of different electrolytes, for example, liquid and solid electrolytes are selected in which the relative permittivities for all two (or three, in the case of different liquid electrolytes) materials involved match. The measurement of the relative permittivities, z. According to Application Note 1369-1 "of 28/10/2008 from Agilent, Santa Clara, California, USA. The disclosure of this document is incorporated in full in the present application.

herangezogen. Erfindungsgemäß ist ε₁ die niedrigere der beiden beteiligten relativen Permittivitäten, ε₂ die größere. Für den Idealfall der Übereinstimmung von ε₁ und ε₂, gilt für die Maßzahl α = ½, bei Abweichung von ε₁ und ε₂ wird α kleiner.As a measure of the degree of correspondence of the relative permittivities or dielectric constants, the inventive measure α

used. According to the invention ε _{1 is} the lower of the two relative permittivities involved, ε ₂ the larger. For the ideal case of the correspondence of ε ₁ and ε ₂ , for the measure α = ½, with deviation of ε ₁ and ε ₂ , α becomes smaller.

It is particularly preferred if the materials having the first and the second permittivity ε ₁ , ε ₂ are different materials, preferably a solid electrolyte and a liquid electrolyte.

wobei die Stromdichte j₀ eine Konstante ist, die u. a. von der Ladungsträgerdichte und (exponentiell) von der Temperatur abhängt. Diesbezüglich wird wieder auf K. Aoki, Theory of the ion transfer kinetics at a viscous immiscible liquid/liquid interface by means of the Langevin equation, Electrochimica Acta 41, Nr. 14, S. 2321–2327 (1996) verwiesen. ξ ist die normierte Spannung an der Grenzfläche und ξ_eq deren Gleichgewichtswert, den die normierte Spannung annimmt, wenn kein Feld von außen angelegt wird und sich nur (im allgemeinen Fall, in dem die oben angenommene Gleichheit der Energieniveaus und Aktivitäten auf beiden Seiten nicht zwingend gilt) durch Diffusion von Ladungsträgern eine Spannung einstellt. Die Differenz ξ – ξ_eq heißt normierte Überspannung. Für die normierte Spannung an der Grenzfläche gilt:

wobei z die Ladungszahl eines Ladungsträgers ist. Im vorliegenden Beispiel ist z = 1. F ist die Faraday-Konstante, R die Gaskonstante, T die absolute Temperatur, und ϕ_1,2 sind die Potentiale, auf denen die beiden angrenzenden Medien liegen. Die Überspannung (Φ₁ – Φ₂) – (Φ₁ – Φ₂)_eq ergibt sich aus der normierten Überspannung zu

To get the current through the interface, consider the Butler-Volmer equation, such as in K. Aoki, Theory of the ion transfer kinetics at a viscous immiscible liquid / liquid interface by means of the Langevin equation, Electrochimica Acta 41, No. 14, pp. 2321-2327 (1996). disclosed. The disclosure of this document is incorporated in full in the present application. For the current through the interface then applies:

wherein the current density j _{0 is} a constant which depends inter alia on the charge carrier density and (exponentially) on the temperature. In this regard, reference is again made to K. Aoki, Theory of the ion transfer kinetics at a viscous immiscible liquid / liquid interface by means of the Langevin equation, Electrochimica Acta 41, No. 14, pp. 2321-2327 (1996). ξ is the normalized stress at the interface and ξ _{eq is} the equilibrium value that the normalized voltage assumes when no field is applied from the outside and only (in the general case where the assumed equality of energy levels and activities on both sides is not mandatory applies) by diffusion of charge carriers sets a voltage. The difference ξ - ξ _eq is called normalized overvoltage. For the normalized stress at the interface:

where z is the charge number of a charge carrier. In this example, z = 1, F is the Faraday's constant, R is the gas constant, T is the absolute temperature, and _1.2 φ are the potentials at which the two adjacent media are. The overvoltage (Φ ₁ - Φ ₂ ) - (Φ ₁ - Φ ₂ ) _eq results from the normalized overvoltage

The exponential equation (2) can be z. B. develop to the second order. It then follows:

For the case where the relative permittivities ε ₁ , ε ₂ agree, the coefficient α = ½ holds, and Ohm's law is obtained with j ₀ · zF / (RT) as interfacial conductance and the reciprocal as a specific interfacial resistance. If ε ₁ deviates from ε ₂ , ie if α = ½, then the additional term then differs from zero, depending on the sign of the overvoltage, compared to the case α = ½ increased or decreased current, ie a reduced or increased effective interfacial resistance. (With effective interface resistance, we denote the quotient of overvoltage and current, which is formed without regard to the validity of a linear relationship.) The linear range of the curve j against ξ - ξ _eq is thus reduced. Considering a three-layer structure with z. B. a solid electrolyte in the middle and two liquid electrolytes on both sides, so affects in each case at one of the two interfaces of the increased effective interfacial resistance. How big the effect is depends on the voltage conditions, ie on how far the respective overvoltage goes beyond the linear range. Applying a sufficiently large voltage to the three-layer structure, the increased effective interfacial resistance at the interfaces will be expressed in an increased effective resistance of the overall structure. We still notice that the extent of the linear region is temperature-dependent. The larger the temperature, the smaller the square member in (5) relative to the linear member.

For the measured effective interfacial resistance then the above-mentioned temperature dependence of j _{0 also plays} a role.

As an upper bound characterizing the boundary of the linear work area, the case is assumed when, when the first-order term and the second-order term on the right-hand side of (5), j are opposite, reaches a maximum as a function of ζ-ζ _eq . Substituting the values (Faraday constant 96485 C / mol, gas constant 8.314 J / (mol K)) gives a relationship between the overvoltage, where this is the case, and α:

For T = room temperature: Table 1: Minimum value of α as a function of the range of the overvoltage, in which an approximate linearity of the current-voltage curve should be given Size of the linear range of the overvoltage 0.05V 0.1V 0.2V 0.5V 1 V 2 V Minimum value of α 0.244 0.371 0.436 0,475 0.488 0.494

This means that with very different relative permittivities and thus α << 0.5 only small linear ranges are possible. If a linear dependence of the current density j on the overvoltage is to be present, the value of α ≈ 0.5, but at least α ≥ 0.436, preferably α> 0.488, for a linear range of this overvoltage of 0.2 V, in particular 1 V and more, and thus ε ₁ approximately equal to ε ₂ .

Metrologically, this interface resistance is accessible by means of impedance spectroscopy. In impedance spectroscopy, the interface impedance can be deduced because the limit impedance separates from the volume impedances due to the high capacitances associated therewith.

According to the invention, it is therefore provided, in the case of an electrolyte with a multilayer structure intended for use in the room temperature range, comprising at least one electrolyte layer which is characterized by a relative permittivity ε ₁ and at least one further electrolyte layer which is characterized by a relative permittivity ε ₂ Electrolyte of an electrolyte layer and the electrolyte of the further electrolyte layer are selected such that at the interface the coefficient α in the range 0.244 <α ≤ 0.5, preferably 0.371 ≤ α <0.5, particularly preferably 0.436 <α ≤ 0.5, further preferably 0.475 <α ≦ 0.5, particularly preferably 0.488 <α ≦ 0.5, even more preferably 0.49 <α ≦ 0.5, wherein always ε _{1 is} the lower and ε _{2 is} the higher of the relative permittivities of adjacent media. If the electrolyte comprises a multiplicity of electrolyte layers with a multiplicity of interfaces, each of the interfaces having a relative permittivity, the requirement is defined for the dimensional factor α _n = ε _1n / (ε _1n + ε _2n ) defined at each of the plurality of interfaces make sure that the value α _{n is} within the previously defined limits. It is very preferred if the value of α is in the range 0.436 <α ≦ 0.5, in particular 0.488 <α ≦ 0.5. In such a case, a relatively large linear range of the overvoltage is reached in the interface region, wherein the overvoltage to 0.2 V, preferably 1 V linear.

In order to provide the largest possible linear working range over a temperature range of at least -40 ° C to + 85 ° C, preferably -70 ° C to + 100 ° C, it is provided that the temperature-dependent value of α _n for the temperature range - 40 ° C to + 85 ° C, ie from 258 K to 383 K, preferably from -70 ° C to + 100 ° C, ie 228 K to 398 K, which results from (6) by inserting a required linear range to 0.05 V, preferably up to 0.1 V, more preferably up to 0.2 V, most preferably up to 0.5 V, more preferably up to 1 V, still more preferably up to 2 V, resulting inequality 0.5 - 0.256 · T / 298 K. <α _n ≤ 0.5, preferably 0.5 - 0.128 · T / 298 K <α _n ≤ 0.5, particularly preferably 0.5 - 0.064 · T / 298 K <α _n ≤ 0.5, very particularly preferably 0.5-0.025 × T / 298 K <α _n ≦ 0.5, more preferably 0.5-0.012 × T / 298 K <α _n ≦ 0.5, even more preferably 0.5-0.006 × T / 298 K <α _n <0.5. lies. In this case, T is used in the previously indicated temperature ranges in K. The same requirement is not only set for the temperature range, but also for the frequency range in which the electrochemical energy storage is to be used, since the relative permittivity, as previously shown, is also frequency-dependent.

It is particularly preferred if the first electrolyte having the first permittivity ε ₁ is a solid electrolyte and the other electrolyte having the second permittivity ε ₂ is a liquid electrolyte.

The solid electrolyte used is preferably an inorganic material, in particular a glass material or a ceramic material, in particular also a glass ceramic material or a polymer provided with a conductive filler, in particular a powder or granules of inventive glass or inventive glass ceramic or ceramic. Very particularly preferred, in particular for use in the field of electrochemical energy stores, are solid electrolytes comprising Li, for example a lithium aluminum germanium phosphate, a lithium lanthanum zirconate or a system with LiSICon crystal phases, ie. H. Lithium super ionic conductor (LiSICon) crystal phases.

The liquid electrolyte used is preferably a mixture of one or more nonaqueous solvents, in particular a carbonic solvent, with at least one fluoride conducting salt, preferably LiPF ₆ . Examples of suitable solvents are ethylene carbonate, butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), vinylene carbonate (VC), methyl ethyl carbonate (EMC), 1,2-dimethoxyethane (dME), 1,2-diethoxyethane (DEE), γ Butyrolactone (γ-BL), sulfolane, acetonitrile, N-methyl-2-pyrrolidone (NMP), dimethylsulfoxide (DMSO), ethyl acetate (EA), 1,3-dioxolane (DOL), tetrahydrofuran (THF), tetra (ethylene glycol) -dimethyl ether (TEGDME), tri (ethylene glyco) dimethyl (TEGD). The solvents can be used alone or as a suitable mixture. Exemplary blends are EC / DMC in the ratio 50/50 (wt%) or electrolyte blends with ratio EC to (DMC + EMC) <1. LiPF ₆ can be used alone or in combination with other conductive salts. The latter include, by way of example, LiBF ₄ , LiAsF ₆ , LiClO ₄ , LiB (C ₆ H ₅ ) ₄ , LiCH ₃ , SO ₃ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiC (So ₂ CF ₃ ) ₃ , LiAlCl ₄ , LiSiF ₆ Li [(OCO) ₂ ] ₂ B, LiDFOB, LiCl, and LiBr.

The concentration of LiPF ₆ or Leitsalzmischungen compared to the nonaqueous solvents is not limited, but is preferably in the range of 0.1 M (mol / dm ³ ) to 5.0 M (mol / dm ³ , preferably 0.5 M (mol / dm ³ ) to 3.0 M (mol / dm ³ ).

In addition to the electrolyte with a multi-layer structure and minimized interface resistance, the invention also describes an electrochemical energy store, in particular a battery cell, comprising an electrolyte according to the invention with multilayer structure with at least one electrolyte layer which is characterized by a relative permittivity ε ₁ and at least one further electrolyte layer, the is characterized by a relative permittivity ε ₂ , wherein the relative permittivities in the specified range of the coefficient α is from 0.244 to 0.5.

Particular preference is given to an electrochemical energy store which comprises a total of three electrolyte layers, two liquid electrolyte layers and a solid electrolyte layer arranged between the liquid electrolyte layers, wherein the relative permittivities ε ₁ , ε ₂ and ε _{3 of} the three electrolyte layers are chosen such that they substantially coincide and so on electrochemical energy storage is provided with the largest possible linear working range and minimized interface resistances available.

The invention will be described in more detail below without limitation based on the embodiments and the drawings.

Show it:

1a - 1d Nyquist diagrams of an electrolyte with multilayer structure, wherein a lithium-aluminum-germanium-phosphate glass-ceramic is used as a solid electrolyte. The liquid electrolytes used are propylene carbonate (PC) or 1,2-di-methoxyethane (DME) at different temperatures of -40.degree. 1a ), -20 ° C ( 1b ), 0 ° C ( 1c ) as well as 20 ° C ( 1d ) used.

In the 1a to 1d As an exemplary embodiment, two combinations of a lithium-aluminum-germanium-phosphate glass-ceramic (LAGP) and a liquid electrolyte (once PC and once DME) are shown. It is a three-layer structure, wherein the solid electrolyte LAGP between two identical liquid electrolyte - once PC, arranged in the other case DME. The conductive salt in both cases is LiTFSI (1 mole per kg of solvent). With a measurement of the complex impedance (four-point measurement with two measuring electrodes in the two liquid electrolyte zones on one side and on the other side of the solid electrolyte) with an alpha analyzer from Novocontrol (frequency range 0.01 Hz to 20 MHz), the electrolytes with multilayer Construction on the volume resistivity of the solid electrolyte and on the occurrence and size of interface resistances studied. For the principle of four-point measurement, see Mirko Hofmann, Integrated impedance spectroscopy of aerobic cell cultures in biotechnological high-throughput screenings, Dissertation, RWTH Aachen University, Faculty of Electrical Engineering and Information Technology, 2009.

The relative permittivity of propylene carbonate (PC) is 64.4. This will be on Fujinaga, K. Izutsu, "Propylene Carbonate Purification and Tests for Purity Pure and Applied Chemistry 27 No. 1 (1971), pp. 273-280" whose disclosure content is fully included in the present application. The relative permittivity of 1,2-dimethoxymethane (DME) is 7.2. This will be on R. Montadi, M. Matsu, IS Arthur, S.-J. Hwang, "Magnesium Boron Hydride: From Hydrogen Storage to Magnesium Battery", Angewandte Chemie International Edition 51, No. 39 (2012), pp. 9780-9783 in turn, the disclosure content of which is in its entirety included in the present application.

With respect to the temperature dependence of the interfacial resistance, which decreases exponentially with temperature, the frequency-dependent measurements leading to the Nyquist plots are carried out at different temperatures (40 ° C, -20 ° C, 0 ° C, 20 ° C, see d). The lowest temperature of -40 ° C is the lower limit of the temperature scale of -40 ° C to 85 ° C, which is important for automotive applications. The sample dimensions of the electrolyte with one layer of liquid electrolyte / one layer of solid electrolyte / one layer of liquid electrolyte are 2 mm in height and 7.65 mm in diameter.

The loci 1 (Nyquist plots) measured at -40 ° C show two strongly overlapping semicircles 10, 12 at high frequencies as well as further semicircles 14.1 (for the liquid electrolyte DME), which are more strongly separated from the other two, 14.2 (for the liquid electrolyte PC) at low frequencies. The measuring voltage is 0.1 V.

The Nyquist evaluation gives the following resistance or capacitance values for these three semicircles:

The third semicircle 14.1, 14.2 is an expression of the interfacial resistance. As from the different loci in the Nyquist diagrams in the 1a - 1d for the combination of liquid electrolyte DME / solid electrolyte LAGP / liquid electrolyte DME (locus 100) and liquid electrolyte PC / solid electrolyte LAGP / liquid electrolyte PC (locus 200), locus 200 has a more strongly separated semicircle 14.2 and thus a high interfacial resistance, which has a stronger flow-reducing effect the locus 100. According to the invention, this is also expressed in the parameter α. This results in an α = 0.395 for the electrolyte pair DME / LAGP. For the electrolyte pair PC / LAGP α = 0.145. In the first case α is close to 0.5 and thus in the linear range, in the second case far below. The interfacial resistance is greatly increased especially in the mismatched PC / LAGP case.

According to the invention, the relative permittivities are adapted, which in the present case has been achieved by adaptation of the liquid electrolyte to the solid electrolyte and selection of a suitable solvent, namely DME for the solid electrolyte LAGP, results in a low interfacial resistance. This is expressed by an α value which is close to 0.5.

In a further exemplary embodiment, for which, however, no Nyquist diagrams were recorded, the solid electrolyte is LLZO (lithium lanthanum zirconate). The value of the relative permittivity of the solid electrolyte LLZO is 22.4. In order to set α in the range according to the invention, a mixture of PC and DME as solvent is selected as liquid electrolyte and the relative permittivity is set to 22.4. The relative permittivity of the mixture is a weighted average of the individual permittivities.

Thus, the mixture of PC and DME consists of 0.266 parts or 26.6 mole% PC and 0.734 parts and 73.4 mole% DME, respectively, because 0.266 x 64.4 + 0.734 * 7.2 = 22.4. If, for example, 28 mol% PC and 72 mol% DME are mixed instead, a relative permittivity of the liquid electrolyte of 23.216 is obtained. The α value is then 0.491. If, as a further example, 35 mol% PC and 65 mol% DME are mixed, the relative permittivity of the liquid electrolyte is 27.22. The α value is then 0.451.

Conversely, if the relative permittivity of the solid electrolyte to the liquid electrolyte is to be adjusted, this is done by selecting a suitable solid electrolyte.

The invention provides the surprising result to be recognized in the exemplary embodiment that the interface resistance to a liquid electrolyte can also be minimized by simply adapting the relative permittivities for a semicrystalline solid electrolyte.

With the invention, the limits for the permittivities are specified for the first time within which the interfacial resistance is minimized in a multilayer electrolyte and a linear behavior of the current flow through when applying a voltage over a wide temperature range of, in particular -40 ° C to + 85 ° C. the interfaces depending on the voltage can be expected.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of 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.

Cited patent literature

• DE 102011013018 B3 [0005]
• US 20030205467 A1 [0005]
• US 20090317724 [0005]
• US 20050107239 A1 [0006]
• US 2009159839 A [0006]
• JP 2008120666 A [0006]
• EP 1134758 A1 [0009, 0009]
• US 2014/0011101 A1 [0010]
• US 2006/01334492 [0012]

Cited non-patent literature

• Jennifer L. Schaefer, Yingying Lu, Surya S. Moganty, Praveen Agarwal, N. Jayaprakash, Lynden A. Archer, Electrolytes for High-Energy Lithium Batteries, Appl. Nanosci. 2 (2012), pp. 91-109 [0005]
• Tonghuan Yang, Lin Sang, Fei Ding, Jing Zhang, Xingjiang Liu: Three-and four-electrode EIS analysis of water-stable lithium electrode with solid electrolyte plate. In: Electrochimica Acta 81, 2012, p. 179-185. - ISSN 0013-4686 [0011]
• Charles Kittel, Introduction to Solid State Physics, 5th Ed., R. Oldenbourg-Verlag Munich Vienna, 1980, p. 441 [0016]
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Claims (10)

Electrolyte with multilayer structure comprising - at least a first electrolyte layer, which is characterized by a first relative permittivity ε ₁ ; - At least a second electrolyte layer, which is characterized by a second relative permittivity ε ₂ , - an interface between the first electrolyte layer and the second electrolyte layer, characterized in that - the first relative permittivity ε ₁ and the second relative permittivity ε ₂ a measure α

and - the electrolyte of the first electrolyte layer and the electrolyte of the second electrolyte layer are selected such that at the interface the coefficient α in the range 0.244 <α ≤ 0.5, preferably 0.371 <α ≤ 0.5, particularly preferably 0.436 <α ≤ 0.5, more preferably 0.475 <α ≤ 0.5, particularly preferably 0.488 <α ≤ 0.5, even more preferably 0.494 <α ≤ 0.5, where ε ₁ is always the lower of the relative permittivities of the adjacent media and ε _{2 is} the higher of the relative permittivities of the adjacent media. An electrolyte according to claim 1, characterized in that the electrolyte comprises a plurality of electrolyte layers having a plurality of interfaces, wherein for the defined at each of the plurality n of interfaces measure α _n = ε _1n / (ε _1n + ε _2n ) is true that at the interfaces the measure α _n in the range 0.244 <α _n ≤ 0.5, preferably 0.371 <α _n ≤ 0.5, particularly preferably 0.436 <α _n ≤ 0.5, even more preferably 0.475 <α _n ≤ 0.5, more preferably 0.488 <α _n ≤ 0.5, even more preferably 0.494 <α _n ≤ 0.5, where ε _1n is always the lower of the relative permittivity of the adjacent media and ε _{2n is} the higher of the relative permittivities of the adjacent ones Media is. Electrolyte according to claim 2, characterized in that for all interfaces n substantially the measure α _{n is the} same. Electrolyte according to one of claims 1 to 3, characterized in that the electrolyte of the first electrolyte layer is a solid electrolyte and the electrolyte of the second electrolyte layer is a liquid electrolyte. Electrolyte according to one of claims 1 to 4, characterized in that the measured value α or the dimensional numbers α _n for all temperatures T in the temperature range -258 K to +383 K, preferably 228 KC to 398 K in the range 0.5 - 0.256 · T / 298 K <α ≦ 0.5, preferably 0.5-0.128 × T / 298 K <α ≦ 0.5, more preferably 0.5-0.064 × T / 298 K <α ≦ 0.5, very particularly preferably 0.5-0.025 × T / 298 K <α ≦ 0.5, more preferably 0.5-0.012 × T / 298 K <α ≦ 0.5, even more preferably 0.5-0.006 × T / 298 K < α ≤ 0.5 is or lie. Electrolyte according to one of claims 4 to 5, characterized in that the solid electrolyte comprises one of the following materials: - an inorganic material, in particular - a glass material or - a glass ceramic material or - a ceramic material - and an organic material, in particular one with a conductive filler provided polymer. An electrolyte according to claim 6, which comprises solid electrolyte Li, in particular a lithium aluminum germanium phosphate, a lithium lanthanum zirconate or a system with Lisuper ionic conductor (LiSICon) crystal phases. An electrolyte according to any one of claims 4 to 7, characterized in that the liquid electrolyte is a mixture of one or more non-aqueous solvents, in particular a carbonic solvent with at least one fluoride conducting salt, preferably LiPF ₆ . Electrochemical energy store, in particular battery cell comprising an electrolyte with multilayer structure according to one of claims 1 to 8. Electrochemical energy store according to claim 9, characterized in that the battery cell comprises at least three electrolyte layers, two liquid electrolyte layers and a disposed between the two liquid electrolyte layers solid electrolyte layer.

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