Primary alkali metal cell with cyanocycloalkane additive

Abstract

The invention relates to a primary cell comprising: at least one anode wherein the at least one anode comprises an alkali metal as active anode material; at least one cathode, wherein the at least one cathode comprises an active cathode material; an electrolyte wherein the electrolyte comprises at least one additive wherein the at least one additive is a cyanocycloalkane of formula (I) wherein y represents a cycloalkane having at least 3 and at most 15 C atoms. # imgabs0 # (I).

Description

[0001] The present invention relates to a primary cell, which comprises: at least one anode having an alkali metal as an active anode material; at least one cathode comprising an active cathode material; and an electrolyte, wherein the electrolyte comprises at least one additive.

[0002] "Primary cell" is a term for a battery that is not rechargeable (in the sense that the electrochemical reaction that occurs during use is irreversible). In contrast, the electrochemical reaction of a secondary cell can be reversed by passing an electric current into the cell, thereby regenerating the corresponding chemical reactants.

[0003] From an ecological point of view, a battery comprising at least one secondary cell is particularly advantageous. However, primary cells play an important role when charging is impractical or impossible, such as during military combat, rescue missions or in implantable medical devices. Another and perhaps the most important benefit of primary cells, especially for use in implantable medical devices, is that they are immediately ready even after long storage times because they exhibit a much lower self-discharge rate. Therefore, primary cells are the preferred battery type for applications that require stable performance over long periods of time. In addition, primary batteries exhibit superior specific energy.

[0004] The use of an anode comprising an alkali metal as an active anode material is considered advantageous for the theoretically achievable properties of a primary cell, such as high nominal voltage, high specific capacity and low self-discharge. In particular, lithium and sodium exhibit extremely high theoretical specific capacities (Li: 3860 mAh / g, Na: 1165 mAh / g), low densities (Li: 0.59 g / cm 3 ; Na: 0.97 g / cm 3 ) and negative electrochemical potentials (Li: -3.04 V; Na: -2.71 V, relative to the standard hydrogen electrode).

[0005] In the case of lithium, the reduction and oxidation reactions are as follows:

[0006] Reduction: Li + + e - → Li 0

[0007] Oxidation: Li 0 → Li + + e -

[0008] However, alkali metals are highly reactive and form a passivation layer at the anode surface due to reaction with the unit cell electrolyte. This passivation layer is known as the solid-electrolyte interphase (SEI) and significantly affects the performance of the unit cell. Since the formation of the SEI is inevitable, the SEI needs to be sufficiently stable and electrically insulating to prevent further degradation reactions. However, the typically low ionic conductivity of the SEI results in an increase in the impedance within the unit cell. As a result, the discharge voltage and the battery capacity are reduced, which becomes a problem especially in use within medical devices.

[0009] In addition, alkali metal unit cells are characterized by another problem, as the formation and deposition of metallic alkali metals (such as lithium) can occur on the anodic surface or the inner surface of unit cell components including the lid, the casing, the collector, or the cathode pin. If the potential of the corresponding component is lower than the deposition potential of the corresponding alkali metal (e.g., U < 0 V, relative to Li / Li + ), then the formation of metallic alkaline deposits occurs. In this context, the term "inner surface of the unit cell" encompasses the surfaces of internal components (including but not limited to the lid, the casing, or the current collector of the unit cell) that are in contact with or may come into contact with the electrolyte. This is especially a problem in lithium metal unit cells.

[0010] A variety of reasons can lead to this situation, for example, due to a local increase in the Li + ion concentration in the electrolyte. If the locally increased lithium concentration moves towards the current collector or other accessible inner surface elements with an anodic potential, excessive lithium ions can deposit onto the lithium metal. In addition, an increase in the ohmic resistance can lead to a reduced anodic potential, for example, if the electric conductivity of the electrode or the ionic conductivity of the electrolyte deteriorates. Lithium deposition occurs in an irregular granular or dendritic form. In the worst case, the positive and negative compounds of the unit cell are bridged, resulting in an internal short circuit.

[0011] To reduce lithium deposition and prevent bridging between the negative and positive components by lithium clusters, the isolation of internal passive components (such as covers, housings, and contact parts) is often employed.

[0012] For example, EP3319145A1 describes a cathode contact component surrounded by a plastic insulating component. The insulating component is mainly made of polyethylene (PE), ethylene chlorotrifluoroethylene (ECTFE or Halar); ethylene tetrafluoroethylene (ETFE), polypropylene (PP) and / or polytetrafluoroethylene (PTFE). Since they are non-conductive, they prevent the bridging of lithium clusters between the negative electrode component and the positive electrode component.

[0013] Instead of separate components, US7,482,093B1 provides an electrode pack and a cathode contact piece completely surrounded by an anode assembly and a housing. This provides more complete insulation, although through significant accumulation.

[0014] From US2014 / 0335394A1, the use of glass wool is known, which increases the distance between the negative electrode passive component and the positive electrode passive component. In addition, the tortuosity of the insulating material effectively prevents the "straight-line" dendritic growth of lithium clusters.

[0015] However, in any case, the insulation of the internal passive components by plastic insulating components results in a reduction in the volume of the active components for both the anode volume and the cathode volume. Therefore, the energy density of the unit cell is reduced. In addition, plastic insulating components can indeed prevent the bridging of lithium clusters between the negative electrode component and the positive electrode component, but they do not avoid lithium deposits.

[0016] Therefore, alternative attempts are aimed at changing the amount of electrolyte. In this context, US7,432,001B1 teaches that an excess of electrolyte at the anode (especially at its edge) leads to lithium deposition. This excess and thus the deposits can be prevented by reducing the amount of electrolyte. However, a reduction in the amount of electrolyte in the battery may lead to uneven discharge of the cathode, which in turn has a negative impact on the performance of the battery. For use in medical devices, the resulting uncertainty means that such batteries cannot be easily used.

[0017] Other attempts to minimize the described risks of lithium deposition and bridging between lithium clusters are based on adding additives to the electrolyte.

[0018] For example, US9,190,696B2 discloses a highly concentrated non-aqueous electrolyte containing a lithium-conductive salt and an ionic liquid. The high concentration of conductive salt forms a quasi-solid electrolyte in the highly viscous ionic liquid, which should prevent the bridging of lithium clusters between the negative electrode component and the positive electrode component.

[0019] US2017 / 0179532A1 discloses an electrolyte for a metal secondary battery (such as a rechargeable lithium or sodium battery) containing a halogen-containing material (such as a metal halogen and / or a halogen complex). The addition of halogen enables the uniform electrodeposition of metals such as lithium or sodium on the anode and can prevent the formation of metal dendrites on the anode surface.

[0020] US2015 / 0349380A1 treats a rechargeable lithium-sulfur battery having an electrolyte additive according to the formula MX, where M corresponds to a transition metal and X corresponds to an anion. The disclosed electrolyte additive can form a stable passivation layer (also known as a solid electrolyte interface film) on the metal anode and prevent the formation of lithium dendrites.

[0021] However, what all three of these additives have in common is that they do not prevent lithium deposition at high currents, such as in ICD applications.

[0022] From the article by F, Ding et al., J. Am. Soc. 2013, 135, 4450 - 4456, electrolyte additives (such as CsPF 6 、RbPF 6 、ZnPF 6 、or RbPF 6 ) are known for rechargeable lithium metal batteries (such as lithium batteries, sodium batteries, magnesium metal batteries, and zinc-lust batteries). The addition of Cs + 、Rb + 、Al 3+ 、Zn 2+ 、Ga 3+ 、Un 3+ and Sn 2+ should prevent the chaotic growth of dendrites. However, electrolytes based on ionic liquids have worse ionic conductivity than non-aqueous battery electrolytes.

[0023] In addition, US9,112,361B2 teaches a combination of multiple parameters for preventing and / or reducing lithium dendrite growth in a lithium secondary battery. First, a special electrolyte composition is provided having an electrolyte additive (especially lithiated polyphenoxy-polyethylene glycol) and a fluorinated surfactant. In combination, ripple current charging is foreseen rather than constant current and / or constant voltage charging. At the same time, special programming of the battery management system (BMS) ensures that the temperature, current, and voltage in the unit cell are limited, with particular attention paid to maintaining a cold atmosphere in the battery and minimizing transient current and voltage. Due to the high concentration of conductive materials in the electrolyte, the conductivity of the electrolyte is reduced, which can lead to deterioration of battery performance.

[0024] Finally, there are some methods in the optimization of the electrolyte for secondary unit cells. US7,871,721B2 describes an electrolyte solvent for secondary lithium ion batteries, which contains aliphatic mononitrile (R-C≡N), where R is linear C 1 -C 15 alkane. Thereby, at (very) low and high temperatures, the protection of the cathode surface and the stability of the electrolyte during the charge / discharge cycle are both improved.

[0025] From US6,333,425B1, malononitrile salts or malononitrile ionic compounds are known as electrolyte additives for lithium secondary batteries to improve the ionic conductivity of the electrolyte. The compound contains an anionic part combined with at least one cationic part, where M is hydronium ion, nitrosonium - NO + 、ammonium - NH 4+ 、metal-type cation with valence m, organic cation with valence m or organometallic-type cation with valence m.

[0026] In US9,666,906B2, a mixture of specific nitrile solvents and dinitrile solvents (such as acetonitrile, propionitrile, butyronitrile, pivalonitrile, hexanenitrile, malononitrile, succinitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelaonitrile and sebaconitrile) is taught to be blended into a high-voltage electrolyte to make it stable during charging.

[0027] However, none of these methods involve primary unit cells. Therefore, the additives known in the prior art are not related to the above problems.

[0028] Therefore, the object of the present invention is to provide a primary alkali metal unit cell suitable for medium-current applications and / or high-current applications, while concomitantly suppressing the deposition of the corresponding alkali metal and cathode material on the anode surface and the inner surface of the unit cell formulation.

[0029] This object is achieved by a primary alkali metal unit cell having the features of current claim 1.

[0030] The primary unit cell according to claim 1 comprises: at least one anode, wherein the at least one anode contains an alkali metal as the active anode material; at least one cathode, wherein the at least one cathode contains an active cathode material; and an electrolyte, wherein the electrolyte contains at least one additive.

[0031] The at least one additive is a cyanocycloalkane of the following formula

[0032]

[0033] Among them, y represents a cycloalkane having at least 3 and at most 15 carbon atoms.

[0034] Surprisingly, the adverse lithium deposition can be eliminated by means of this additive. In the absence of the additive, the concentration of lithium ions on the electrode surface increases because the diffusion of lithium in the active particles is slower than the transport of lithium ions in the electrolyte. In other words, the mass transport of lithium particles in the active particles is the rate-determining step.

[0035] In addition, if there is an excess of electrolyte at the electrode edge, the Li ions diffuse via a circuitous and no longer direct path. The turning of the Li ions increases the Li concentration at the staggered electrode edge and then leads to Li deposition. Generally, the lithium anode is connected to the cover and the housing. If there is an excess of electrolyte between the electrode assembly and passive components (such as the housing, the cover, the anode contact component, the cathode pin), the lithium concentration will increase there and lead to lithium deposition.

[0036] Against this background, the present invention can prevent lithium deposition and / or reduce lithium dendrites by means of an electrolyte additive for a lithium metal battery, and extend the life of an implantable battery because it has been found that adding an additive to the electrolyte of a primary alkali metal unit cell effectively inhibits the deposition of the alkali metal on the anode surface and other inner surfaces of the unit cell. This observation can be explained by the stabilization of the formation of the SEI, even in high-rate and high-current pulse discharge applications.

[0037] Therefore, the advantages provided by the present invention are that it not only prevents the bridging of lithium clusters between the negative electrode component and the positive electrode component, but also prevents the formation of lithium dendrites on the metal-type components. In addition, the action of the electrolyte additive prevents the deposition of lithium throughout the interior of the battery.

[0038] It has been found to be advantageous if y represents a cycloalkane compound in a given structural formula. Particularly preferred are the following compounds:

[0039]

[0040] .

[0041] Each of these residues R 1 , R 2 , R 3 , R 4 , R 5 , R 6 and R 7 can each be defined as a hydrogen atom or a C 1 -C 4 alkyl group. Thus, R 1 , R 2 , R 3 , R 4, R 5 , R 6 and R 7 are independent of each other. On the one hand, it is advantageous that due to symmetry and more restricted rotation, the melting and boiling points of cycloalkanes are higher than those of comparable normal alkanes. On the other hand, the cyclic system has a stabilizing effect.

[0042] In certain embodiments, the cyano cycloalkane is selected from compounds of the following formula:

[0043] .

[0044] In other words, the groups R 1 -R 7 each correspond to a hydrogen atom. Thus, the cycloalkane corresponds to the most well-known, stable and easily accessible compounds.

[0045] Supplementary or alternatively, the cycloalkane compound is directly linked to the nitrile such that the running index a in the general form has the value 1. This corresponds to the following formula:

[0046] .

[0047] This has the advantage that virtually no steric effects come into play. In addition, the compounds can also be synthesized particularly easily. This applies in particular to the formulas given in claims 2 and 3, which are still valid in the special case of a = 1 and should be explicitly disclosed:

[0048]

[0049] .

[0050] wherein R 1 , R 2 , R 3 , R 4 , R 5 , R 6 and R 7 are independently defined as a hydrogen atom or a C 1 -C 4 alkyl. The resulting compounds show the advantages over the more general formulas described above in a particularly pronounced manner. For cycloalkanes without any allyl groups, the most positive effects are shown:

[0051] .

[0052] According to an embodiment, in the electrolyte, the at least one additive (i.e., a cyano cycloalkane) has a concentration of 0.0005 mol / l - 2 mol / l, preferably 0.005 mol / l - 0.4 mol / l, and most preferably 0.05 mol / l - 0.3 mol / l. At concentrations below 0.0005 mol / l, the beneficial effects of the cyano cycloalkane are hardly noticeable, while concentrations above 2 mol / l do not result in any further significant reduction in lithium deposition.

[0053] In addition to the cyano cycloalkane as an additive, the electrolyte contains at least one solvent and may further contain at least one conductive salt.

[0054] Suitable electrolytes include, but are not limited to, non-aqueous (preferably aprotic) solvents such as esters, ethers, and dialkyl carbonates (especially tetrahydrofuran, methyl acetate, diethylene glycol dimethyl ether (bis(2-methoxyethyl) ether), triethylene glycol dimethyl ether (tris(2-methoxyethyl) ether), tetraethylene glycol dimethyl ether (tetrakis(2-methoxyethyl) ether), 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-2-methoxyethane, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, or mixtures thereof), or cyclic carbonates, cyclic esters, cyclic amides (especially propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyrolactone, N-methylpyrrolidone, or mixtures thereof). Suitable electrolytes also contain polar non-aqueous solvents such as acetonitrile, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, or mixtures thereof.

[0055] The conductive salt is preferably an inorganic alkali metal salt, where the alkali metal cation is the same as the active anode material. Suitable anions are PF 6 - 、BF 4 - 、AsF 6 - 、SbF 6 - 、ClO 4 - 、O 2 - 、AlCl 4 - 、GaCl 4 - 、SCN - 、SO 3 (C 6 F 5 ) - 、C(SO 2 CF 3 ) 3 -, N(SO 2 CF 3 ) 2 - and SO 3 CF 3 - etc. In a preferred embodiment, the concentration of the conductive salt in the electrolyte is between 0.5 and 2.0 mol / l, preferably between 0.8 and 1.5 mol / l.

[0056] In a preferred embodiment, the alkali metal used as the active anode material is sodium metal, sodium alloy, lithium metal or lithium alloy, preferably lithium or lithium alloy. Anodes based on sodium, lithium and their alloys are particularly suitable due to their high theoretical specific capacity and negative electrochemical potential. In addition, both of these alkali metals are inexpensive and readily available (compared to their heavier homologues).

[0057] The shape of the anode is not limited to a specific form. Preferably, the anode is in the form of a sheet or foil that is at least conductively connected to a metallic anode current collector, for example by pressing or welding. Further embodiments include disc-shaped, cylindrical, rod-shaped or pleated (folded) anodes.

[0058] The cathode is preferably a solid material and may comprise a metal, metal oxide, mixed metal oxide, metal sulfide, carbonaceous compound or a mixture thereof.

[0059] In a further embodiment of the present invention, the active cathode material is MnO 2 , silver vanadium oxide (SVO), copper silver vanadium oxide (CSVO), V 2 O 2 , TiS 2 , CuO 2 , Cu 2 S, FeS, FeS 2 , CF x (fluorocarbon), Ag 2 O, Ag 2 O 2 , CuF, Ag 2 CrO 4 , CuO, copper vanadium oxide or a mixture thereof, preferably MnO 2 .

[0060] If desired, a binder material is added to the active cathode material during the preparation of the cathode. The binder typically comprises 1.0 - 5.0 wt% of the total cathode material mixture. Suitable materials include powdered fluoropolymers, such as polytetrafluoroethylene or polyvinylidene fluoride.

[0061] In addition, one or more additives for improving the cathode conductivity, including graphite or carbon black, can be added to the cathode material. Preferably, these additives account for 1.0 to 15.0% by weight of the total cathode material mixture.

[0062] Preferably, the cathode is conductively connected to a metallic cathode current collector, which can be in the form of a thin sheet of metal foil. Suitable materials are selected from, but not limited to, titanium, gold, stainless steel, cobalt nickel, molybdenum, or steel alloys.

[0063] Within the scope of the present invention, a number of primary unit cells are combined into a battery. A battery generally includes at least one electrochemical unit cell, and multiple unit cells can be combined in series and / or parallel circuits. In this document, the terms unit cell, primary (alkali metal) unit cell, primary (alkali metal) battery, and battery are considered collective terms and, where applicable, can be used interchangeably.

[0064] In a preferred embodiment, the primary unit cell is a lithium metal battery comprising: at least one anode having lithium as the active anode material, and at least one cathode having MnO 2 as the active cathode material. This combination is particularly attractive because of the aforementioned advantages of lithium combined with MnO 2 MnO 2 is a highly stable and low-cost material with a high potential capacity. Although the nominal voltage of 3.0V is lower than that of, for example, lithium thionyl chloride (3.6V), Li-MnO 2 achieves significantly higher currents (up to 5A continuous load and up to 10A pulse load).

[0065] Lithium MnO 2 unit cells are based on the insertion of Li + ions into the MnO 2 lattice. The underlying redox reaction is as follows:

[0066] Anode: Li 0 → Li + + e -

[0067] Cathode: Mn IV O 2 + Li + + e - → LiMn III O 2

[0068] Total: Li 0 + MnO 2 → LiMnO2

[0069] For the Li / CF x unit cell, the following reactions occur:

[0070] Anode: xLi + xS → xLi + .S + xe

[0071] Cathode: CF x + xLi + .S + xe → C(Li + .S-F - ) x

[0072] Total: CF x + xLi + .S + xe → C(Li + .S-F - ) x

[0073] Therefore, S represents one or more solvent molecules coordinated with each Li + ion.

[0074] Upon formation, the graphite intercalation compound (GIC) intermediate then decomposes into the final discharge products:

[0075] C(Li + .S-F - ) x → C + xLiF + xS

[0076] To avoid internal short circuits, the electrodes are separated by a separator made of an electrically insulating material that is also chemically inert, i.e., does not react with the anode or cathode materials and the electrolyte. Nevertheless, when wetted by the electrolyte, the separator allows the diffusion of ions, i.e., Li + ions to diffuse from the anode to the cathode during discharge. Suitable materials are polyolefins (e.g., polyethylene or polypropylene), or fluoropolymers (e.g., polyethylenetetrafluoroethylene), etc. Preferably, the separator is in the form of a membrane.

[0077] The unit cell assembly is arranged within a housing that is compatible with the materials of the anode, cathode, and electrolyte. The housing may comprise materials such as titanium, aluminum, or stainless steel, etc.

[0078] The present invention further includes the use of a primary alkali metal unit cell having a cyanocycloalkane additive as a battery in an implantable battery or an implantable medical device. A cardiac pacemaker, a leadless pacemaker, an implantable cardioverter defibrillator (ICD), a cardiac loop recorder, a drug delivery pump, or a nerve stimulator are examples of battery-powered active implantable medical devices.

[0079] Accordingly, the present invention further includes an implantable battery or an implantable medical device that includes the primary alkali metal unit cell according to the present invention.

[0080] In particular, pacemakers and ICDs rely on a battery that allows for the continuous delivery of pulses, even after long periods of inactivity. If an acute cardiac event is detected, a high-current pulse is delivered to prevent possible cardiorespiratory arrest. Even when operated under such adverse conditions, the primary unit cell according to the present invention neither exhibits a significant amount of undesirable lithium deposition nor a voltage delay.

[0081] The development, advantages, and application possibilities of the present invention also become apparent from the following description of the examples and the drawings. All features described and / or shown in the drawings, either alone or in any combination, form the subject matter of the present invention, regardless of whether they are included in the claims or their back references.

[0082] The following examples illustrate the present invention, but the present invention is not limited by and not restricted to these examples. All examples are shown in Table 1.

[0083] Primary lithium metal MnO 2 and CF x unit cells were used as a model system to determine the effect of cyanocycloalkanes on lithium deposition and voltage. The cathode contains MnO 2 as the active cathode material, and the MnO 2 is mixed with graphite (3 wt% of the total composition) and carbon black (2 wt% of the total composition) as conductive additives and polytetrafluoroethylene (3 wt% of the total composition) as a binder. The anode contains metallic lithium.

[0084] Table 1: Composition of the electrodes

[0085]

[0086] Basically, the electrolyte contains LiClO 4 (1 mol / l) in a mixture of 1,2-dimethoxyethane, ethylene carbonate, and propylene carbonate (ratio 4:4:2 (volume / volume)). Different additives were added to show the effect.

[0087] Table 2: Overview of the test distribution for different variants

[0088]

[0089] To promote the deposition of metallic lithium on the electrodes and on metallic passive components (such as the lid or the surface of the housing), the HR cells and the MR are loaded with 25 pulses per day (current density: 39 mA / cm²; pulse duration: 10 s; interval between pulses 15 s) until 1 V (similar to the example given in US 7,432,001 B1). Then, the cells are opened and the area of the lithium deposits on the lid area is determined using a microscope. The results obtained are interpreted based on the attached drawings.

[0090] In the attached drawings:

[0091] Figure 1 is a graph showing an exemplary pulse discharge curve of a primary cell according to Test 1,

[0092] Figure 2 is a graph showing an exemplary pulse discharge curve of a primary cell according to Test 2,

[0093] Figure 3 is a graph showing an exemplary pulse discharge curve of a primary cell according to Test 3,

[0094] Figure 4 is a graph showing an exemplary pulse discharge curve of a primary cell according to Test 4,

[0095] Figure 5 is a graph showing an exemplary pulse discharge curve of a primary cell according to Test 5,

[0096] Figure 6 is a graph showing an exemplary pulse discharge curve of a primary cell according to Test 6,

[0097] Figure 7 shows the amount of lithium deposited in a comparison of Test 1 and Test 2,

[0098] Figure 8 shows the amount of lithium deposited in a comparison of Test 3 and Test 4, and

[0099] Figure 9 shows the amount of lithium deposited in a comparison of Test 5 and Test 6.

[0100] Figures 1-6 The curves depicted in show the pulse discharge curves of the primary cells according to Tests 1 - 6.

[0101] First, it should be explained byFigure 1 Let's discuss the obtained results in detail. Among them, the initial average voltage is about 1.7V. Subsequently, it increases after about 20mAh to reach a maximum value of about 2.0 to 2.05V. During the initial pulse train, this initial increase can be correspondingly explained by the gradual formation of the discharge products of conductive graphite (CF x . In addition, for all unit cells, especially for Figure 5 and 6 the high-rate unit cells among them, a relatively sharp drop is observed. This observation can be attributed to the excessive deposition of metallic lithium, resulting in the bridging of the anode of the unit cell and another metallic component. Therefore, the unit cell is depleted due to an internal short circuit.

[0102] After reaching its maximum value, the measured voltage initially only drops slowly, thus resulting in a long and small linear drop between 20 and 150mAh. During this plateau phase, the output of the unit cell remains predictable. After 140mAh, the voltage drops below the initial voltage, and moreover, after 150mAh, the drop in voltage subsequently accelerates until it reaches a cut-off voltage of 1.0V at about 1700 to 1800mAh, which indicates the end of the life of the corresponding unit cell.

[0103] In x which represents the measurement results of medium-rate unit cells of Li / CF Figure 2 , the same behavior can be found. However, the medium-rate unit cells of Li / CF x do not contain any additives and at least the additives according to the present invention.

[0104] It immediately becomes clear that the presence of the cyano cycloalkanes according to the present invention can repeatedly result in almost the same behavior for each individual unit cell (i.e., there are only small differences in the individual discharge curves).

[0105] The comparison of Tests 3 and 4 (medium-rate unit cells of Li / MnO 2 ) shows the same basic picture (even though the specific values here are somewhat different), because only a very small maximum appears near 10mAh and the drop starts near 100mAh until it reaches 1.0V at 150mAh.

[0106] For Figure 5 and 6 the Li / MnO 2 high-rate unit cells depicted in Tests 5 and 6, it is obvious that a plateau above 2.4V appears between 100 and 1000mAh, while the lower limit of 1500V is reached at 1800mAh.

[0107] Figure 7 , 8 and 9 show the total amount of lithium deposited on the inner cover surface, inner housing surface, and contact assembly of the unit cells according to Tests 1 - 6. Each of these three figures always shows a comparison of a specific unit cell with and without an additive. Specifically, Figure 7 shows a comparison of Li / CF X medium rate unit cells with and without an additive, Figure 8 shows a comparison of Li / MnO 2 medium rate unit cells with and without an additive and Figure 9 shows a comparison of LiMnO 2 high rate unit cells with and without an additive.

[0108] In all cases, the beneficial effect of the additive immediately becomes clear. While the primary unit cells characterized by a cyanocycloalkane show hardly any lithium deposition even after the test period, the comparative unit cells 16 - 20 (and thus the exceeding cells) show at least ten times the deposition.

[0109] The results presented clearly show that the cyanocycloalkane used as an electrolyte additive according to the invention strongly reduces or even prevents the deposition of metallic lithium on the inner surfaces of the primary unit cells. In addition, bridging of lithium clusters between the negative and positive components is reliably avoided and thus battery short - circuiting is avoided.

Claims

1. A primary unit cell, comprising: at least one anode, wherein the at least one anode comprises an alkali metal as an active anode material; at least one cathode, wherein the at least one cathode comprises an active cathode material; an electrolyte, wherein the electrolyte comprises at least one additive, characterized in that the at least one additive is a cyano cycloalkane of the following formula , where y represents a cycloalkane having at least 3 and at most 15 carbon atoms.

2. The primary unit cell according to claim 1, characterized in that the cyano cycloalkane is selected from compounds of the following formula wherein R 1 , R 2 , R 3 , R 4 , R 5 , R 6 and R 7 are each independently a hydrogen atom or a C 1 -C 4 alkyl group.

3. The primary unit cell according to claim 2, characterized in that the cyano cycloalkane is selected from compounds of the following formula 。 4. The primary unit cell according to any one of the preceding claims, characterized in that the at least one additive is a cyano cycloalkane of the following formula , where y represents a cycloalkane having at least 3 and at most 15 carbon atoms.

5. The primary unit cell according to any one of the preceding claims, characterized in that, in the electrolyte, the at least one additive has a concentration of 0.0005 mol / l - 2 mol / l, preferably 0.005 mol / l - 0.4 mol / l, and most preferably 0.05 mol / l - 0.3 mol / l.

6. The primary unit cell according to any one of the preceding claims, characterized in that the active cathode material is a solid material, the solid material comprising a metal, a metal oxide, a mixed metal oxide, a metal sulfide, a metal fluoride, a carbonaceous compound or a mixture thereof, preferably comprising MnO 2 , silver vanadium oxide (SVO), copper silver vanadium oxide (CSVO), V 2 O 2 , TiS 2 , CuO 2 , Cu 2 S, FeS, FeS 2 , CF x , Ag 2 O, Ag 2 O 2 , CuF, Ag 2 CrO 4 , CuO, copper vanadium oxide or a mixture thereof, particularly preferably comprising MnO 2 .

7. The primary unit cell according to any one of the preceding claims, characterized in that the primary unit cell is a lithium metal battery, the lithium metal battery comprising at least one anode having lithium as an active anode material and at least one cathode having MnO 2 or CF x as an active cathode material.

8. The primary unit cell according to any one of the preceding claims, characterized in that the electrolyte comprises at least one solvent and may further comprise at least one conductive salt, in particular esters, ethers, dialkyl carbonates, acetonitrile, dimethyl sulfoxide, dimethylformamide, dimethylacetamide or mixtures thereof.

9. The primary unit cell according to claim 8, characterized in that the electrolyte comprises at least one conductive salt.

10. The primary unit cell according to claim 9, characterized in that the electrolyte comprises at least one inorganic alkali metal salt, a conductive salt, wherein the alkali metal cation is the same as the active anode material.

11. The primary unit cell according to claim 9 or 10, characterized in that the concentration of the conductive salt in the electrolyte is between 0.5 and 2.0 mol / l, preferably 0.8 - 1.5 mol / l.

12. The primary unit cell according to any one of the preceding claims, characterized in that at least one separator is arranged between the anode and the cathode.

13. Use of the primary unit cell according to any one of the preceding claims as a battery in an implantable battery or an implantable medical device.

14. An implantable battery, comprising the primary unit cell according to any one of claims 1 - 12.

15. An implantable medical device, comprising the primary unit cell according to any one of claims 1 - 12.

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