DE102010033020A1 - Lithium-air battery with high oxygen saturation - Google Patents

Abstract

The invention relates to a secondary lithium-air battery system that has a high power output and reversibility. Such a battery system is constructed in layers from a lithium anode (3), a cathode (4), a separator (5) arranged between the anode (3) and the cathode (4), which is permeable to lithium ions, and a separator ( 5) and the cathode (4) wetting electrolyte (6), a contact area (10) through which the electrolyte (6) interacts with oxygen, as well as electrodes (7) and (8) and a housing (19) in which there is at least the contact area (10). According to the invention there is compressed air in the housing (19), as a result of which a higher oxygen saturation is achieved in the electrolyte. For this purpose, the battery system (1) advantageously has a pump (16) by means of which the air is compressed. The lithium-air battery system is particularly suitable for motor vehicles.

Description

The invention relates to a secondary lithium-air system according to the preamble of patent claim 1.

In addition to lead-acid batteries, secondary batteries (ie rechargeable batteries) are lithium ion batteries (Li-ion battery) and nickel-metal hydride batteries (Ni-MH battery) for vehicle traction and other mobile power supplies ( especially for electrical appliances such as laptops, mobile phones, etc.). used. The energy density of these systems has a systemic limitation (current Li-ion batteries: 180 Wh / kg, Ni-MH batteries: 80 Wh / kg). When used in motor vehicles, the range achievable with these systems currently remains below 100 km. Even in the event that the theoretically possible energy density of these systems could be achieved, their range would still not be able to reach that of vehicles with internal combustion engines. Lithium-ion batteries are therefore more suitable for short-distance operation, for example in pure city vehicles, or in hybrid systems in combination with a conventional internal combustion engine or a fuel cell. In the long term, therefore, alternative battery systems must be developed, which enable a much longer range. A further improved solution in terms of the maximum achievable energy density lithium-air cells represent. The maximum achievable with these cells energy densities are above 12,000 Wh / kg at a voltage of 2.91 V ( SD Beatti, Journal of The Electrochemical Society 156 (1) A44-A47 ; KM Abraham, Journal of the Electrochemical Society 143 (1), p. 1 ; JP 002008112724 . JP 002008198590 . US 020080176124 ).

The underlying chemical reaction is the conversion of lithium with atmospheric oxygen: 4Li + O ₂ → 2Li ₂ O (E = 2.91 V)

In organic solvents, the reaction proceeds only to the peroxide: 2Li + O ₂ → Li ₂ O ₂ (E = 3.1V)

Secondary lithium-air cells, however, so far have too low reversibility, so they are not used so far. Only the use of the primary (ie non-rechargeable) lithium-oxygen cells for use in small devices or for military applications has so far been successfully operated ( US Patent 5,510,209 (1996) ; http://www.yardney.com/Lithion/Documents/PaprAD-JD-KMA.pdf ).

In contrast to primary lithium-air cells, which are operated with aqueous electrolyte, a cyclability of the cells is achieved with organic electrolyte, ie chargeability by extensive reversibility of cell reactions. However, the current lithium-air cells still have only limited reversibility. The limited cycle capability is determined inter alia by the catalyst used on the cathode side and the structure of the cathode, but also by impurities and degradation and Passivierungserscheinungen the lithium anode. Up to now, capacity losses in the range of more than 10% have occurred per charge / discharge cycle ( A. Debart, Journal of Power Sources 174 (2007), p. 1177 ). Out US-A 2005/0175894 . WO 2007/062220 and US 6432584 For example, there is known an improvement in reversibility wherein the metallic lithium electrode is coated with an ion-conductive inorganic protective layer (e.g., P ₂ O ₅ , GeO ₂ , TiO ₂ , ZrO ₂ , Al ₂ O ₃ , LiHfPO ₄ , NASICON (Sodium Super Ionic Conductor), Sodium Super Ionic Conducting Glass, Li ₅ La ₃ Ta ₂ O ₁₂ or LIPON (Lithium Phosphorus Oxynitride)) to the separator. The protective layer prevents the reaction of lithium with water, which enters the cell with the reaction air, and the oxidation of the lithium anode by atmospheric oxygen. Particularly suitable as the electrolyte are aprotic solvents, preferably also combinations of solvents having donor properties with solvents having acceptor properties.

As the cathode common air electrodes are used in lithium-air cells, as z. B. in zinc-air batteries or even in fuel cells. They usually consist of several layers starting with a porous water-repellent Teflon / graphite layer, the actual catalyst layer and a stromableitenden film, which is usually made of nickel. The catalyst layer is usually a mixture of metal oxides, e.g. As MnO ₂ , porous graphite powder and a binder. In addition to MnO ₂ , it is also possible to use metal phthalocyanines with Co, Fe, Mn and / or Cu and also highly disperse platinum or platinum / ruthenium, silver and ruthenium oxide as catalyst.

In addition to the limited reversibility, the strong temperature dependence of the energy and power density compared to lithium-ion cells is a problem of current lithium-air cells ( Read, JJ Electrochem. Soc. 2002, 149, A1190-A1195 ).

Another major problem of the lithium-air cell is the pronounced polarization of the charging / discharging curves as well as the large difference between the charging and discharging voltage, which leads to considerable losses in efficiency. ( A. Debart, Journal of Power Sources 174 (2007), p. 1177 ).

From the WO 2009/117496 A For example, a lithium-oxygen battery system is known that operates with air or with pure oxygen. This battery system has a special encapsulation around the cell, which serves the fire protection. A protection against deflagration of the battery is achieved in that when operating with air only as much air is sucked through the encapsulation of the cell, as is necessary for operation. As a result, a pressure build-up in the enclosure is reliably prevented, which in the case of deflagration the lithium is only a very small amount of oxygen available. When operating with pure oxygen, it is stored in a pressure bottle and recirculated. As soon as an undesired increase in pressure is registered with this system, the oxygen from the cell casing (encapsulation) is pumped back into the oxygen tank by means of a pump. As a result, the system is operated under a constantly low oxygen pressure in order to have as little oxygen as possible in the event of deflagration in the battery system.

From the US 2009/0053594 A For example, a lithium-air battery system is known in which the cell is packaged in a bag that is filled with oxygen. This results in a closed system operating at atmospheric pressure.

The invention has for its object to provide a secondary lithium-air battery system with improved reversibility and / or higher power output. The task also includes a method for operating such a lithium-air battery system.

This object is achieved with a lithium-air battery system according to claim 1. With regard to the method, the object is achieved with the measures of claim 7. The subclaims show particularly advantageous embodiments.

The secondary lithium-air battery system according to the invention is particularly suitable for use in automobiles and is based on an oxygen enrichment in the electrolyte, which acts as an oxygen carrier. This oxygen enrichment is achieved by a relative to the ambient air pressure increased air operating pressure.

According to the present invention, the electrolyte is charged with oxygen by compressed air. In this case, a constant pressure is adjustable, but in particular, the application of compressed air in response to the respective load request to the cell.

X_s,2

= Löslichkeit des Gases

P

= Druck des Gases über der Lösung.

According to Henry's law, the solubility of an ideal gas is proportional to its pressure over the solution: X _{s, 2} = K * p

X _{s, 2}

= Solubility of the gas

P

= Pressure of the gas over the solution.

Thus, by doubling the oxygen pressure also approximately a doubling of the oxygen concentration in electrolytes and thus a considerable improvement of the oxygen cathode can be achieved. In addition, an improvement in the development of potential dead zones in the pores of the electrode is achieved by the pressure increase, so that the conditions for the electrochemical processes in the cell are ensured even in areas of the cathode, which would be inactive without this pressure increase.

Advantageously, the operating pressure of the cell is at least temporarily increased to at least 1.5 bar, preferably at least 1.9 bar. Depending on the safety requirements and the surrounding of the battery system, the pressure is increased to a maximum of 3 bar, and higher, if the housings are designed accordingly. All pressures are absolute values. This pressure range represents an economical operating range, whereby an increase in pressure by 1 bar (operating pressure 2 bar absolute) achieves an increase in output of approximately 20% could. Too high operating pressures also counteract the associated loss of efficiency by the pump.

In principle, the compressed air for operating the cell can also be provided from a compressed gas cylinder, in particular for mobile use and also for reasons of economy, it is advantageous if a pump is used as compressed air supplier. The use of a fan as a pump is possible, but advantageously a compressor is used, which compresses the ambient air to the required operating pressure. The system overhead required by the use of a pump is significantly overcompensated by the higher recoverable energy gain from the lithium-air battery system.

Advantageously, a control is provided according to the invention, by means of which the increased operating pressure is generated during a discharge process. By means of the control, the operating pressure can advantageously be set in accordance with the discharge conditions, that is, a higher operating air pressure is set for higher required discharge flows. About the control can be advantageously withdrawn in a charging process of the cell, the increased air operating pressure again, in particular, this is set by means of the control of the air operating pressure to the ambient pressure. The easiest way to reduce this pressure is carried out via a preferably controlled or regulated valve. As a result, the pressure reduction can be done quickly and controlled. By reducing the pressure is advantageously achieved that the resulting oxygen during charging of the battery system can degas more easily and on the reduced oxygen concentration in the electrolyte, a higher charging current is possible.

The increased air operating pressure is advantageously set by means of the control current controlled, that is, for high required currents and a high operating pressure is provided. As a result, the system works very economically, since at low currents required the energy cost to increase the operating pressure is saved. Advantageously, the increase of the operating air pressure by means of the control alternatively or additionally also time-controlled, that is only a short time (0.1 to 5 seconds) after the request for an increased current output from the cell, the pressure is increased. This ensures that at very short-term power requirements from the cell not equal to the pump is put into operation, whereby the pump is operated more economically.

In principle, to reduce the pressure in the system, the pump can also be operated in the opposite direction, that is, be used for suction. However, the use of the valve for pressure reduction has proven to be particularly advantageous since it can be used to reduce the pressure in the system to ambient pressure with minimal energy expenditure and, in particular, very quickly, as a result of which charging of the battery system with increased currents is possible very quickly and on the other hand, the reliability of the system is increased.

Since the pressure buildup and degradation in the electrolyte can under certain circumstances also result in degassing of oxygen outside the contact region, via which the exchange takes place between the battery system and the air, it is particularly advantageous to recirculate the electrolyte as described below.

For this purpose, the battery system according to the invention with an (optional) reservoir is used, which is in flow communication with the cathode and / or the separator, wherein preferably takes place an active circulation of the electrolyte and / or a separation of the contact region of the cathode and the cathode.

As a result, an even higher oxygen availability is achieved for the cathode, since the input described oxygen demand during discharge of the battery system precludes a limited solubility and diffusion of oxygen in the electrolyte. Due to this limited oxygen supply to the cathode, the previous lithium oxygen cells according to the prior art have not been suitable for high performance requirements, but only for the medium to low power range. In particular, at a power output (current density) of more than 100 mA / cm ² breaks the cell voltage dramatically in the known lithium-oxygen cells.

An essential component of the invention is therefore also the use of electrolytes with an improved oxygen solubility and / or improved oxygen diffusion. This also leads to an improvement (reduction) of the cathode overvoltage at high current densities and prevents the above-described collapse of the cell voltage at higher current densities. According to the invention, an oxygen solubility of at least 0.5 mmol / l, preferably of at least 0.8 mmol / l and in particular of at least 1.1 mmol / l particularly advantageous, since this the current density of the cathode can be significantly increased. The same applies to the oxygen diffusion rate, which according to the invention is advantageously at least 0.5 × 10 ^-5 cm ² s ^-1 , preferably at least 0.8 × 10 ^-5 cm ² s ^-1 and in particular 1.1 × 10 ^-5 cm ² s ^{. 1} is.

According to the invention, a liquid oxygen-transferring electrolyte is used in the battery system, which serves on the one hand as an oxygen collector (oxygen harvesting) and on the other hand as a reaction medium for the cell reaction (reduction medium). The required oxygen can be provided in more or less pure form, in particular, the oxygen uptake from the air, wherein the air can be previously conditioned, ie in particular a cleaning, CO ₂ reduction and / or dehumidification is subjected.

Suitable electrolytes are in particular ionic liquids. The electrolytes according to the table have proven to be useful here electrolyte Diffusion coefficient D _O2 × 10 ^-5 [cm ² s ^-1 ] Saturation concentration C _O2 [mM] EMIBF ₄ 1.7 ± 0.2 1.1 ± 0.2 PMIBF ₄ 1.3 ± 0.2 0.97 ± 0.05 BMIBF ₄ 1.2 ± 0.2 1.1 ± 0.1

Such electrolytes are known from Dun Zhang, Takeyoshi Okajima, Futoshi Matsumoto, Takeo Osaka, Electroreduction of Dioxygen in 1-n-alkyl-3-methylimidazolium tetrafluoroborate Room-Temperature Ionic Liquids in Journal of The Electrochemical Society, 151 (4) D31-D37 (2004). EMIBF ₄ stands for 1-ethyl-3-methylimidazolium tetrafluoroborate, BMIBF ₄ for the corresponding 1-n-propyl compound and PMIBF ₄ for the corresponding 1-n-butyl compound. The use of such electrolyte is advantageously carried out with an inorganic (ceramic) separator, in particular a multi-layered separator, which is not penetrated by the electrolyte (z. B. Separion ^® from the company Crearis), since these interactions with oxygen and / or water, which is is in the electrolyte, and the lithium anode can be effectively suppressed. Although it is also possible to use electrolytes which bring about lesser interactions of this type, in most cases such electrolytes also have a lower diffusion coefficient for oxygen or a lower saturation concentration for oxygen. These interactions cause a deterioration of the reversibility, ie an irreversible reaction with the lithium.

In addition to the electrolytes already mentioned, it is also possible to use others, in particular based on ionic liquids. According to the invention, the electrolyte may be a solution, and preferably the electrolyte contains at least one ionic liquid, wherein the electrolyte should have a low melting point, in particular below -20 ° C, so that the battery remains operational even at minus temperatures. Furthermore, the electrolyte should preferably have a low viscosity to ensure good flowability through the cathode. A third important criterion for the electrolyte is its electrical conductivity, which should be as high as possible to ensure a low internal resistance of the cell and a good transport of the ions.

Suitable ionic liquids are, in particular, those with an organic onium ion (in particular based on nitrogen-ammonium) and at least one anion that corresponds to the anion of the lithium salt used in the lithium battery. These ionic liquids can easily dissolve lithium salts, are non-or hardly inflammable, and have low viscosities. Such ionic liquids can be used directly as such or in combination with other ionic liquids as well as dissolved in organic solvents as the electrolyte solution in the secondary lithium batteries according to the invention. Usual here is the use of lithium hexafluorophosphate in propylene carbonate / dimethylethylene (PC / DME). Other possible representatives of organic solvents are polyglyme, oxolanes, carbonates, 2-fluorobenzene, 3-fluorobenzene, 4-fluorobenzene, dimethoxyethane. The polyglyms are, for example, diethylene glycol dimethyl ether (CH ₃ (OCH ₂ CH ₂ ) ₂ OCH ₃ ), diethylene glycol diethyl ether (C ₂ H ₅ (OCH ₂ CH ₂ ) ₂ OC ₂ H ₅ ), triethylene glycol dimethyl ether (CH ₃ (OCH ₂ CH ₂ ) ₃ OCH ₃ ), and triethylene glycol diethyl ether (C ₂ H ₅ (OCH ₂ CH ₂ ) ₃ OC ₂ H ₅ ). The dioxolanes are, for example, 1,3-dioxolane, 4,5-diethyldioxolane, 4,5-dimethyldioxolane, 4-methyl-1,3-dioxolane, and 4-ethyl-1,3-dioxolane. The carbonates are, for example, methylene carbonate, dimethyl carbonate, propylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, vinylene carbonate, ethylene carbonate, diethyl carbonate. It is also possible to use 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, diethyl ether, sulfolane, methylsulfolane, Acetonitrile, propionitrile, anisole, ethyl acetate and butyl acetate. The solvents mentioned can also be used in mixtures of two or more of the solvents. Also preferred is the use of EC / DMC.

The anode material used is pure lithium, alloyed and / or mixed (intercalation), in particular with carbon and / or silicon, which is applied to an anode conductor (collector electrode). Copper is particularly suitable as the anode conductor because it is not only a good conductive element but also stable with respect to lithium. The arrester is preferably followed directly by the electrochemically active material (cathode) which contains lithium. Other constituents are advantageously various carbon structures, such as artificial graphite, natural graphite, coke, carbon black, and also plastic fibers, etc. Depending on the purpose of use, it is advantageous for the anode to contain one or more metallic elements from the group Al, Si, Sn, Ag, Bi, Add Mg, Zn, In, Ge, Pb and Ti. These metals alloy with the lithium, thereby increasing the safety of the cell. The anode can be built up from a mixture of one or more of these metals as well as the carbon material (one or more), wherein lithium can also be added in the form of a lithium nitrite. Alternatively or additionally, the lithium is generated at the first charge of the cell in the anode. As an anode, the known from lithium-ion batteries ( US 6,605,390 and US 5,958,622 ) Graphite intercalation electrode can be used.

As the lithium salt which is dissolved in the electrolyte, lithium compounds which dissolve in the solvent or the ionic liquid to form lithium ions are suitable. Particularly suitable for this purpose are LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , CH ₃ SO ₃ Li, LiCF ₃ SO ₃ and LiN (CF ₃ SO ₂ ) ₂ , CF ₃ SO ₃ Li , LiCl or LiBr. Again, two or more of the lithium salts can be dissolved. Suitable lithium salts are, in particular, those salts which dissolve to at least 0.6 M in the electrolyte. Advantageously, the concentration of the lithium salt is at least 0.1 M and in particular at least 0.8 M. Solutions are particularly advantageous in the range of 1.5 to 3 M. If the concentration of the lithium salt is too low, the ionic conductivity is also too low. Since the electrolyte serves as a conductive path for the lithium ions from the anode to the cathode and vice versa, a high conductivity is required for a good function of the battery.

The separators used are customary separators made of plastics or ceramics or combinations thereof. The task of the separator is primarily the separation of anode and cathode to provide a lithium-ion conductivity. In addition, the separator may additionally store the electrolyte and / or serve as a barrier to oxygen and water dissolved in the electrolyte. A preferred construction of the separator is in WO 2007/062220 as the so-called PAM (Protective Membrane Architecture, Protected Membrane Architecture) describes. As a plastic structure for the separator is particularly suitable porous PTFE (polytetrafluoroethylene). Due to the electrochemical processes within the cell, it is necessary that the separator is stable to oxidation. Suitable ceramic structures of the separator are materials such as glass-ceramic ion conductors, in particular those based on phosphate, oxide or oxisulfite. Furthermore, Nasiglass, Nasicon (sodium superconducting conductors), Lisicon (lithium superconducting conductors), such as lithium metal phosphates, ceramic alkali metal ion conductors, in particular lithium beta aluminates, sodium beta aluminates, can advantageously be used.

Examples of solid electrolytes are ZrO ₂ , LiHfPO ₄ , Li ₅ La ₃ Ta ₂ O ₁₂ , Li ₅ La ₃ Nb ₂ O ₁₂ , Na ₅ MSi ₄ O ₁₂ (M: rare earths such as Nd, Dy, Gd), Li ₃ PO ₄ .Li ₂ S.SiS ₂ , Li ₂ O.11Al ₂ O ₃ , Na ₂ O.11Al ₂ O ₃ , Na ₅ ZrP ₃ O ₁₂ , Na ₅ TiP ₃ O ₁₂ , Na ₃ Fe ₂ P ₃ O ₁₂ , Li ₅ ZrP ₃ O ₁₂ , Li ₅ TiP ₃ O ₁₂ , Li ₃ Fe ₂ P ₃ O ₁₂ If the separator has a multilayer structure, it is advantageous to have a ceramic on the anode side which is not penetrated by the electrolyte. As a result, the anode remains protected against irreversible damage by oxygen and / or water.

According to the invention, the battery system has an electrolyte reservoir which lies at least predominantly outside the charge exchange path between the anode and the cathode. This is accomplished by placing this reservoir outside the layered structure of the cell. Particularly advantageous is the oxygen accumulation and -Abreicherung of the electrolyte via this reservoir and thus spatially separated from the reaction zone in the cathode. By replacing the oxygen-enriched electrolyte from the reservoir with the cathode, a higher availability of the oxygen at the cathode is achieved, and vice versa, whereby the internal resistance of the cell decreases and higher currents can be taken (discharge) or taken up (charge). The circulation of the electrolyte from the reservoir to the cathode preferably takes place via an external pump. Advantageously, this pump operates continuously, thereby a uniform exchange of the electrolyte is achieved. A positive side effect of the circulation of the electrolyte is a cooling of the reaction zone.

The arrangement of the contact region at the reservoir a simple and effective regeneration of the electrolyte (loading and unloading with oxygen) is achieved. The additional system overhead for this oxygen loading is overcompensated by the significant energy gain of the battery system. Energy densities up to 700 Wh / kg (1000 Wh / l) can be achieved with the system according to the invention. When using a separator which is at least partially penetrated by the electrolyte (additional electrolyte reservoir), the pump is advantageously connected on the pressure side with the cathode material, whereby regenerated electrolyte is conveyed directly into the cathode. As a result, the lithium ion transport is not disturbed by the electrolyte-filled separator. The removal of the electrolyte can be carried out directly from the electrolyte-filled separator and / or advantageously also from the cathode.

The cathode is porous, as is conventional in the art. The electrolyte penetrates the pores of the cathode. The downstream cathode arrester (collector electrode) is usually a nickel mesh or a nickel foil and may preferably also be oxygen permeable, allowing additional oxygen input or output directly to the cathode.

As a catalyst for the cathode is in particular a metal oxide catalyst such as. For example, manganese dioxide and / or nickel oxide used, preferably together with a binder of porous graphite powder and PTFE. In addition to MnO ₂ , it is also possible to use Ni, Co, Fe, Mn and / or Cu phthalocyanines or highly disperse platinum, if appropriate together with ruthenium. Also known from the fuel cell electrodes based on platinum or

Platinum alloys can be used, for. B. the gas diffusion electrodes LT140-E from ETEK (BASF) or RM100 from Gaskatel.

As a contact area for the interaction with oxygen pore structures are advantageously used with the largest possible surface area. Particularly suitable for this purpose are tubes or hoses, since in this way a particularly large surface area can be made available. On the one hand, oxygen-permeable solids can be used as the material, but in particular, membranes are used. In this case, hydrophobic materials are particularly preferred since this reduces the introduction of water into the electrolyte. The material used is preferably PTFE or PVDF (polyvinylidene fluoride). Corresponding membranes are known, for example, under the trademark Gore-Tex. In this case, a temperature difference between the electrolyte and the ambient air is advantageous, wherein the electrolyte preferably has a higher temperature. In particular, the temperature difference should be, at least temporarily, at least 10 K, more preferably at least 15 K, since this may allow any water components of the electrolyte to be more easily removed via the membrane into the ambient air.

The invention will be described in more detail below with reference to figures and exemplary embodiments.

Show it:

1 : the multilayer structure of a cell according to the invention in the battery system; and

2 : a simplified representation of a double cell.

That in the 1 pictured secondary lithium-oxygen battery system 1 is made up of three main components. These major components are a lithium-oxygen electrochemical cell 2 , a reservoir 11 and a circulation pump 12 , The cells have a layer structure of an Anionenableiter 7 (negative collecting electrode) made of copper foil, then an anode 3 containing lithium and a separator 5 from a cathode 4 is disconnected. The cathode 4 stands with her the separator 5 opposite side in contact with a nickel net, which is the Kathodenableiter 8th (positive collecting electrode) forms. The layer structure is as follows:
anode 3 : 30 to 300 mm;
separator 5 : 30 to 150 mm;
cathode 4 : 30 to 300 mm.

About the narrow sides of the cathode not involved in the layer structure 4 is the cell 2 via lines 14 with the reservoir 11 and the circulation pump 12 fluidly connected, wherein the circulation pump 12 pressure side to the catalyst 4 connected. Because the catalyst 4 the higher pressure resistance to the reservoir 11 has, causes the pressure-side connection of the circulation pump 12 to the catalyst 4 a simplified mechanical design of the system 1 , The reservoir 11 has a contact area 10 on the can be set under increased air operating pressure. The contact area 10 is also permeable to oxygen, allowing an exchange of oxygen between the working air pressure and an electrolyte in the reservoir 6 can take place. The electrolyte 6 is about the circulation pump 12 in the catalyst 4 pumped and leaves it on the opposite narrow side of the catalyst 4 , This circulation of the electrolyte 6 causes oxygen depletion or oxygenation in the electrolyte 6 that is in the separator 5 is located, allowing a deactivation of the cathode 4 is minimized by oxygen. The volume of the electrolyte within the cell 2 to the volume of the electrolyte in the pipes 14 , the pump 12 and the reservoir 11 is about 1: 3 to 1:50, depending on the structure.

As a reservoir to achieve a high oxygen exchange rate between the electrolyte and the ambient air, a parallel circuit of Kapillarschläuchen is used, which are formed from the air-permeable membrane. Here are 3 to 50, in particular 5 to 15 connected in parallel hoses of 5 to 15 cm in length suitable for achieving a good compromise between the exchange of oxygen with the ambient air and the required volume of electrolyte. To prevent collapse of the capillary tubes, the system 1 with the circulation pump 12 designed so that the capillary tubes have a sufficient internal pressure. For this purpose, it may also be advantageous to use a throttle at the reservoir outlet, or to reverse the pumping direction.

The cathode conductor 8th may also have a contact area in these embodiments 10a be provided, via which an additional exchange of oxygen with the air operating pressure system is possible.

The separator 5 can be constructed in multiple layers, on the anode side, a ceramic layer 13 is provided, which is either an optimized contact with the anode 3 allows and / or a lithium-ion conductor, which is the electrolyte 6 from the anode 3 locks.

To increase the oxygen content in the electrolyte 6 is with the battery system 1 a housing 19 provided, at least the contact area 10 encloses. The housing is equipped with a compressor pump 16 (suitable manufacturers are Liebherr, Aerospace, Opcon Automotive, Eaton Automotive) connected, which is controllable. The entrance 22 the compressor pump 16 can with a sorbent 20 be connected, which extracts the intake air moisture and / or CO ₂ . Depending on the design of the electrolyte and the contact area 10 can also be dispensed with the sorbent. The housing 19 has an outlet 23 on that with a 2/2-way valve 17 connected is. The 2/2-way valve 17 is spring-loaded closed in the rest position, but can be opened electronically if necessary via a controller. About the controller 18 continue to be the circulation pump 12 and the compressor pump 16 controlled by the controller 18 As input signals of a pressure sensor 24 in the case 19 is arranged as well as the currents of the end charge or charge the cell 2 serve. The control 18 This is set so that they reach the compressor pump when a certain discharge rate is reached 16 puts into operation and increases the pressure with increasing end charge strength. The housing 19 is designed for a pressure of up to 3 bar. Once the cell 2 no power is removed, the controller stops 18 the compressor pump 16 , If neither charging nor final charge takes place or only small threshold values are not exceeded, the controller stops 18 also the circulation pump 12 ,

When the cell 2 from the discharge to the charge, the controller checks 18 over the pressure sensor 24 whether to reduce the oxygen content in the electrolyte 6 a pressure reduction in the housing 19 is displayed. As soon as the discharge current has reached a certain level, the controller opens 18 the 2/2-way valve 17 to the pressure in the housing 19 to reduce. Opening the 2/2-way valve 17 can be clocked for controlled pressure reduction.

In 2 is a simplified battery system 101 with a cell stack 102 shown. The cell stack 102 is here constructed as a double cell, which is a common anode 3 having. Like all layers here is the anode 3 flat, to which two cells via separators 5 with their cathodes 4 connect. The outer cathode arrester 8th are oxygen permeable as contact areas 10a built up. This structure has the advantage that the largest possible contact area 10a with respect to the lateral surface of the cell stack 102 is reached. The anode 3 and the separators 5 have a seal 121 on, which may be formed for example of epoxy.

The cell stack 102 is in a cell case 119 housed, in turn, with the compressor pump 116 , the 2/2-way valve 17 and the pressure sensor 24 fluidly connected. The basic operation of the battery system 101 corresponds to the 1 described, with the exception that on the one hand here the electrolyte 6 is not circulated, but the oxygen loading and discharge of the electrolyte 6 as well as the Oxygen conversion at the cathode 4 with the lithium ions via diffusion, and on the other hand, that is provided as a temporary air tank here a pressure tank. The pump 116 As a result, they can be made smaller in their volume flow, wherein they the pressure tank 125 to the maximum pressure of the housing 119 , or slightly higher, fills up. About the 2/2-way valve 126 can then - if necessary - the housing 119 quickly with compressed air from the tank 125 be filled to the predetermined operating pressure. This achieves the desired air operating pressure in the shortest possible time, even at a lower pumping capacity.

• – der Li-O₂ Batteriezelle, vorteilhaft in Form eines flächigen Stapelaufbaus,
• – optional dem Umwälzkreislauf zur Zirkulation des sauerstofftransportierenden Elektrolyten,
• – optional einem Wärmetauscher zur Regulation der Zelltemperatur (bei Zirkulation des Elektrolyten,)
• – der (optional externen) Vorrichtung zur Sauerstoffanreicherung (Drucksystem), und
• – der Steuerung der Sauerstoffanreicherung.

The systems according to the invention described each consist of five main components:

• - The Li-O ₂ battery cell, advantageously in the form of a flat stack structure,
• Optionally the recirculation circulation for the circulation of the oxygen-carrying electrolyte,
• - optional heat exchanger to regulate the cell temperature (in case of electrolyte circulation,)
• - The (optional external) device for oxygenation (pressure system), and
• - the control of oxygenation.

• 1. Dem Anodenstromkollektor 7 (Anodenableiter) aus Kupfer mit einer Dicke zwischen 0.002 und 0.025 mm.
• 2. Darauf die Lithium-Metall-Anode 3. Diese kann nach dem Zusammenbau der Zelle aus Lithium-Ionen durch Ladung der Zelle gezüchtet werden oder wird als Lithiumfilm oder als Kompositschicht aus Lithium oder einer herkömmlichen Lithium-Legierung (zum Beispiel mit Silizium), Kohlenstoffpartikeln und einem geeigneten Binder, z. B. aus PTFE oder Zellulose, aufgetragen.
• 3. Dem Separator 5, der den direkten Kontakt der oben beschriebenen Anode 3 mit der untenstehenden Kathodenschicht 4 verhindert. In einer einfachen Anordnung besteht der Separator 5 aus einer mechanisch stabilen, 0.025 bis 0.05 mm dicken Schicht eines gewöhnlichen porösen Separators für Lithium-Ionen-Batterien, z. B. CELGARD (Firma Celanese) oder SEPARION (Firma Evonik). In einer bevorzugten möglichen Anordnung besteht der Separator 5 aus einem Mehrschichtsystem 5, 13 mit Kompositstruktur, welches den folgenden Aufbau hat: Eine mechanisch widerstandsfähige, 0.025 mm dicke Schicht eines herkömmlichen porösen Separators für Li-Ionen-Batterien, z. B. CELGARD (Firma Celanese) oder SEPARION (Firma Evonik), zur Kathode hin; und eine 0.005 mm dicke anorganische Schicht, die optimiert ist für die Li-An- und -Ablagerung.
• 4. Der Sauerstoff-Kathode 4, die in einer einfachen Ausführung aus einem 0.250 mm dicken Kohlenstoff-Vlies gebildet ist (mit einer circa 10%-igen Dichte), dessen Fasern mit einer Katalysatorschicht aus Manganoxide beschichtet sind. Die Kathode 4 kann bereits mit den Reaktionsprodukten der Zellentladung (Li₂O₂ oder Li₂O) beschichtet sein. Alternativ kann die Imprägnierung auch nachträglich durch Zugabe der Reaktionsprodukte in den Elektrolyten erfolgen.
• 5. Dem Kathodenstromkollektor 8 (Kathodenableiter), der z. B. aus Nickel, Graphit oder einem leitfähigen Kohlenstoff-Polymer-Kompositmaterial mit einer Dicke von circa 0.05 mm gebildet ist.

In the simplest case, the cells are built up from five layers:

• 1. The anode current collector 7 (Anodenableiter) made of copper with a thickness between 0.002 and 0.025 mm.
• 2. Then the lithium-metal anode 3 , This may be grown after charging the cell from lithium ions by charge of the cell, or as a lithium film or as a composite layer of lithium or a conventional lithium alloy (for example with silicon), carbon particles and a suitable binder, e.g. As PTFE or cellulose, applied.
• 3. The separator 5 , which is the direct contact of the anode described above 3 with the cathode layer below 4 prevented. In a simple arrangement, the separator 5 from a mechanically stable, 0.025 to 0.05 mm thick layer of a conventional porous separator for lithium-ion batteries, z. CELGARD (Celanese) or SEPARION (Evonik). In a preferred possible arrangement, the separator consists 5 from a multi-layer system 5 . 13 composite structure having the following structure: A mechanically resistant, 0.025 mm thick layer of a conventional porous separator for Li-ion batteries, eg. CELGARD (Celanese) or SEPARION (Evonik), to the cathode; and a 0.005 mm thick inorganic layer optimized for Li attack and deposition.
• 4. The oxygen cathode 4 made of a 0.250 mm thick non-woven carbon fabric (with a density of around 10%), whose fibers are coated with a catalyst layer of manganese oxides. The cathode 4 may already be coated with the reaction products of the cell discharge (Li ₂ O ₂ or Li ₂ O). Alternatively, the impregnation can also be done subsequently by adding the reaction products in the electrolyte.
• 5. The cathode current collector 8th (Cathode conductor), the z. B. of nickel, graphite or a conductive carbon-polymer composite material having a thickness of about 0.05 mm is formed.

For the arrangement in a battery stack ( 2 ), the single cells are built one on top of the other layer by layer or in subgroups and then stacked in a parallel circuit.

In an alternative arrangement (not shown), the cell is spirally wound (wound up). In this case, the cell shape is cylindrical, but the internal structure remains layered. It is also possible to construct the cell by folding the layer structure. To obtain a certain voltage, several of these cells can be electrically connected in a series connection.

• – durch entsprechende Serien- oder Parallelanordnung die elektrische Verbindung der Zellen zur Gewährleistung der entsprechenden Batteriespannung und Batteriekapazität gewährleistet,
• – optional den Durchfluss des zirkulierenden Elektrolyten ermöglicht, der zugleich als Sauerstoffträger fungiert, der das Reaktionsmedium an die Kathoden liefert und die Sauerstoffzufuhr bzw. -ableitung ermöglicht.

The cells are encapsulated in a battery case to form a battery pack. The battery case is designed to:

• - Ensures the electrical connection of the cells to ensure the appropriate battery voltage and battery capacity by appropriate series or parallel arrangement,
• - Optionally allows the flow of the circulating electrolyte, which also acts as an oxygen carrier, which delivers the reaction medium to the cathodes and allows the oxygen supply or -ableitung.

After the individual layers of the cell are built up, the porous regions become in the cathode layer 4 and in the separator 5 with the electrolyte 6 filled, which allows both the oxygen uptake, and acts as a lithium ion conductor, and transported the molecular oxygen. To this comes - as already described above - a solution of one or more lithium salts (eg LiPF ₆ , LiCF ₃ SO ₃ , Li [CF ₃ SO ₂ NSO ₂ CF ₃ ], LiAsF ₆ , LiClO ₄ , LiBF ₄ , LiALClO ₄ ) in ionic liquids (eg, N-propyl-N-methylpyrrolidinium bis (trifluoromethanesulfonyl) imide (PYR1n3TFSI), sec-propyl-N-methylpyrrolidinium bis (trifluoromethane-sulfonyl) imide (PYR1sec3TFSI), N- Butyl-N-methylpyrrolidinium bis (trifluoromethane-sulfonyl) imide (PYR1n4TFSI), iso-butyl-N-methylpyrrolidinium bis (trifluoromethanesulfonyl) imide (PYR1iso4TFSI), sec-butyl-N-methylpyrrolidinium bis (trifluoromethanesulfonyl) imide (PYR1sec4TFSI), N-pentyl-N -methylpyrrolidinium bis (trifluoromethane-sulfonyl) imide) or in molecular solvents (eg: ethylene carbonate (EC), propylene carbonate (PC), ethylmethyl carbonate, dimethyl carbonate, dimethyl carbonate, dimethylformamide) or mixtures thereof. The electrolyte may contain the reaction products of the discharge reaction in the form of small particles (which are incorporated into the porous regions of the cathode) or in the form of dissolved molecules.

The system according to the invention is preferably operated with air as an oxygen supplier. However, it is also an operation with preferably enriched oxygen, in particular from a (pressure) tank - as in 2 shown - possible. In this case, the operating pressure is at least 1.5 bar and / or the oxygen is through the valve 126 blown off into the environment. The oxygen enrichment is advantageously carried out via air-N ₂ / O ₂ separation membranes (which are not shown - the filter 20 preferably downstream) from the ambient air. For special applications, the system can also be operated with chemical oxygen suppliers, such as peroxides, in particular hydrogen peroxide.

In one embodiment, the cathode is 20% by weight acetylene black (or graphite powder) and 80% by weight polymer binder (PTFE). The separator with electrolyte consists of 12% polyacrylonitrile (PAN), 40% ethylene carbonate, 40% propylene carbonate and 8% LiPF ₆ , in a thickness of 75-100 microns. The lithium electrode is 50 μm thick.

Good cyclability is achieved with porous cathodes consisting of a-MnO ₂ nanofibers. The addition of larger cations, such as tetrabutylammonium (TBA +), increases the reversibility of the O2 / O2 redox reactions. Lithium oxides passivate the cathode surface and lead to irreversible processes. Therefore, the solubility of the lithium oxides is increased by adding the large cations. A mixture of Li and TBA salts improves the solubility of the lithium oxides in such a way that the necessary reversibility of the oxygen reduction in the lithium-air battery is achieved. The ionic liquids allow optimal adaptation to the reduction of oxygen due to their high flexibility in the structure. They offer high conductivity, high thermal and chemical stability and low flammability, which is essential for the development of safe cells.

A spiral cell (insert according to 1 ) was made of a 1000 mm long, 50 mm wide and 0.025 mm thick copper foil. This was sandwiched between two separator layers, each composed of a 0.005 mm thick layer of cross-linked P (EO) 10-LiFSI-PYR14FSI (FSI = bis (fluorosulfonyl) imide; PYR14 = N-butyl-N-methylpyrrolidinium) coated to 0.025 mm thickness porous layer from Separion (Evonik). The separator layers (992 mm long, 54 mm wide) project laterally beyond the anode (the copper foil) by 2 mm on three sides, so that they can be sealed with a polypropylene liner between them, thus creating a protective covering around the copper foil. The copper strip protruding 10 mm on the fourth side was welded with a copper rod (3 mm diameter and 80 mm long), which serves as a roll-up aid. The supernatant film and the copper rod were then electrically insulated and sealed with an epoxy resin layer.

Two 1000 mm long, 50 mm wide and 0.25 mm thick layers of nonwoven carbon nonwoven fabric (SIGRATHERM from SGL) impregnated with 5 mg / cm ^{2 of} a mixture of Ketjen black (AKZO) and Teflon PTFE-TE3859 fluoropolymerim (Dupont) , Weight ratio 85:15, and 40 mg / cm ² of high purity Li ₂ O were applied to each side of the anode-separator sandwich. Subsequently, a 1020 mm long, 55 mm wide and 0.05 mm thick layer of a highly conductive carbon polymer compost (SIGRAFLEX ™ from SGL) was placed on one side of the sandwich.

This laminate was then rolled up into a cylinder about 20 mm in diameter and placed in a stainless steel tube (SS316). The positive electrode forms either the steel jacket or a separate arrester with insulated steel jacket, the copper rod forms the negative electrode.

The cell was closed with two plastic caps, over which the electrolyte is introduced and circulated. The electrolyte used was 0.1 mol of LiFSI in 0.9 mol of PYR14FSI. Hoses made of PTFE membranes were used for air exchange.

With these systems according to the invention, energy densities of up to 400 Wh / kg or 600 Wh / l based on the cell can be realized.

LIST OF REFERENCE NUMBERS

1

secondary lithium-oxygen battery system

2

electrochemical lithium-oxygen cell

3

anode

4

cathode

5

separator

6

electrolyte

7

anode conductor

8th

cathode conductor

10

contact area

11

reservoir

12

circulating pump

13

multilayer separator

14

cables

16

compressor pump

17

2/2-Wegebentil

18

control

19

casing

20

filter

121

sealing

22

Input pump

23

outlet

24

pressure sensor

116

compressor pump

117

2/2 way valve

119

cell case

125

pressure tank

126

Inlet-2/2-way valve

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

• JP 002008112724 [0002]
• JP 002008198590 [0002]
• US 020080176124 [0002]
• US 5510209 [0005]
• US 2005/0175894 A [0006]
• WO 2007/062220 [0006, 0034]
• US 6432584 [0006]
• WO 2009/117496 A [0010]
• US 2009/0053594 A [0011]
• US 6605390 [0032]
• US 5958622 [0032]

Cited non-patent literature

• SD Beatti, Journal of The Electrochemical Society 156 (1) A44-A47 [0002]
• KM Abraham, Journal of the Electrochemical Society 143 (1), p. 1 [0002]
• http://www.yardney.com/Lithion/Documents/PaprAD-JD-KMA.pdf [0005]
• A. Debart, Journal of Power Sources 174 (2007), p. 1177 [0006]
• Read, JJ Electrochem. Soc. 2002, 149, A1190-A1195 [0008]
• A. Debart, Journal of Power Sources 174 (2007), p. 1177 [0009]

Claims (10)

Secondary lithium-air battery system ( 1 ) with a lithium-air electrochemical cell ( 2 ), comprising a lithium-based anode ( 3 ), a cathode ( 4 ), one the anode ( 3 ) and the cathode ( 4 ) separating separator ( 5 ), which is permeable to lithium ions, a separator ( 5 ) and the cathode ( 4 ) wetting electrolyte ( 6 ), a contact area ( 10 ) over which the electrolyte ( 6 ) in interaction with air, one with the anode ( 3 ) in electrically connected anode arresters ( 7 ), one with the cathode ( 4 ) in electrically connected cathode arrester ( 8th ), and a housing ( 19 ), in which at least the contact area ( 10 ), characterized in that in the housing ( 19 ) At least temporarily, a relation to the ambient pressure increased air operating pressure is provided. Battery system according to claim 1, characterized in that it for the construction of the increased air operating pressure a compressed air supplier, in particular a pump ( 16 ) having. Battery system according to claim 1 or 2, characterized in that the increased air operating pressure by means of a controller ( 18 ) during a discharging process and / or charging the cell ( 2 ) is regulated to a predetermined value. Battery system according to claim 3, characterized in that the increased air operating pressure by means of the controller ( 18 ) timed and / or current controlled depending on a current flow through the cell ( 2 ) is set. Battery system according to one of the preceding claims, characterized in that it is for a reduction of the increased air operating pressure, a valve ( 17 ) having. Battery system according to one of the preceding claims, characterized in that the increased air operating pressure at least temporarily at least 1.5 bar, preferably at least 1.9 bar and in particular at least 2.5 bar (absolute). Method for operating a secondary lithium-air battery system ( 1 ) with a lithium-air electrochemical cell ( 2 ), comprising a lithium-based anode ( 3 ), a cathode ( 4 ), one the anode ( 3 ) and the cathode ( 4 ) separating separator ( 5 ), which is permeable to lithium ions, a separator ( 5 ) and the cathode ( 4 ) wetting electrolyte ( 6 ), a contact area ( 10 ) over which the electrolyte ( 6 ) in interaction with air, one with the anode ( 3 ) in electrically connected anode arresters ( 7 ), one with the cathode ( 4 ) in electrically connected cathode arrester ( 8th ), and a housing ( 19 ) by the contact area ( 10 ), characterized in that in the housing ( 19 ) for a discharging process and / or charging the cell ( 2 ) by means of one of a controller ( 18 ) activated compressed air suppliers ( 16 ) is established compared to the ambient pressure increased air operating pressure. A method according to claim 7, characterized in that the air operating pressure by means of the controller ( 18 ) for a discharge in the cell ( 2 ) and / or for a charging process of the cell ( 2 ) is abgeregelt. A method according to claim 7 or 8, characterized in that the air operating pressure from the controller ( 18 ) depending on a current flow through the cell ( 2 ) is time-controlled and / or current-controlled. Method according to one of claims 7 to 9, characterized in that the increased air operating pressure is at least temporarily set to at least 1.5 bar, advantageously at least 1, 9 bar and in particular at least 2.5 bar (absolute).

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