The invention concerns a method for supplying electrical energy, particularly in a vehicle or stationary application, by operating a metal air battery, particularly a lithi- urn air battery, based on a stoichiometric supply of oxygen

The metal air battery is preferably operated with ambient air, or with oxygen from a reservoir or from a synthetic air reservoir, such as a tank.

Electric vehicles, including vehicles with an internal combustion engine such as a range extender to produce electricity on long voyages, hybrid vehicles and derivates thereof become more and more popular due to ecologic reasons, a limited supply of fossil fuels and research advances.

Particularly, a steady stream of advances in battery research has put large numbers of hybrid electric vehicles on city streets and highways. Additional advances are having a similar effect on so-called plug-in hybrids, hybrid automobiles that can be recharged at home. Despite these successes for electrically propelled cars, both types of hybrid vehicles strongly depend on petroleum-fueled internal combustion engines for distance driving.

In order to fully establish electric vehicles in the market, a storage battery of practical size and weight and affordable price is needed that can provide enough electri- cal energy in a single charge for a motorist to drive at least a few hundred miles. In light of these requirements, a focus of the electric vehicle industry in battery research is directed to so-called metal air batteries, which are, for example, described in U.S. patent 5,510,209.

These metal air batteries provide a high theoretical electrical capacity, particularly when the oxygen mass is excluded. This means that the oxygen needed for operating the metal air battery has to be taken from the ambient air instead of supplying it from an oxygen reservoir. When generating power, this oxygen reacts at the cathode of a lithium oxygen cell with lithium to Li0 ₂ and/or Li ₂ 0 ₂ . In this reaction, one mole 0 ₂ releases two moles electrons. Nevertheless, oxygen should not diffuse from the cathode to the anode since it penetrates into the anode electrode degrading the anode.

When ambient air as 0 ₂ -source is utilized to operate a metal air battery in order to achieve the high energy densities desirable for mobile applications such as in vehi- cles, water and preferably also C0 ₂ have to be reliably removed from the ambient air in order to avoid undesired (devastating) reactions in the metal air battery, especially if the battery is a lithium air battery.

Especially when envisaged for automobile applications, the power response of high capacity batteries such as metal air batteries tends to be slow. In particular the max- imum power which can be drawn from such high capacity batteries is not enough to cover peak demands of vehicles, for example when accelerating or climbing an ascending slope. Furthermore, due to the functioning by chemical reaction, a variable control of the output of the high capacity batteries, such as metal air batteries, tends to be difficult since the chemical reaction can be controlled with a certain time-lag only.

In order to be able to better cover variable power rates and enhance the maximum power which can be delivered by an energy storage device, European patent 1 377 477 B1 proposes a power source for supplying electrical power to a driving motor comprising a first rechargeable energy battery and a second rechargeable power battery and a battery controller capable of controlling a substantially continuous recharging of the power battery with electrical energy from the energy battery.

Departing from this prior art, it is an object of the present invention to provide for supplying electrical energy, particularly in a vehicle, wherein the system comprises a metal air battery, particularly a lithium air battery, allowing a safe operation of the metal air battery with a high cycle-lifetime and/or calendar-lifetime. Another object of the present invention is to provide a system capable of covering high power peaks needed to operate electric propulsion of a vehicle while maintaining the high cycle- lifetime and/or high calendar-lifetime. These objects are achieved by a method for supplying electrical energy according to claim 1 and a system for supplying electrical energy according to claim 9. Advantageous embodiments of the present invention are claimed in the depending claims.

The inventive method for supplying electrical energy, particularly in a vehicle, com- prises the following steps: operating a metal air battery, particularly a lithium air battery. The method preferably comprises the further step of determining a demand of oxygen of the metal air battery and controlling an amount of oxygen supplied to the metal air battery by means of stoichiometry.

The inventive system for supplying electrical energy, particularly in a vehicle, com- prises a metal air battery, particularly a lithium air battery. Preferably, the system further comprises a control module being adapted to control an amount of oxygen supplied to the metal air battery by means of stoichiometry.

Preparing or conditioning air in the sense of the invention is applying any system to the air for preparing the same to operate a metal air battery, such as a coarse filter to remove particles from the air.

A module in the sense of the invention is a hardware comprising at least one device and/or software implementing a certain function.

The invention is based on the approach that the amount of oxygen molecules delivered to the cathode of the metal air battery essentially matches the consumption of oxygen needed for releasing a certain electrical power. This avoids a high oxygen 0 ₂ excess (overpressure) which can lead to a diffusion of oxygen through an electrolyte to a negative electrode side. Such a diffusion leads to undesired side- reactions, e.g. with the product Li ₂ 0 ₂ at the anode. As a consequence, the metal air battery, in particular a lithium air battery loses capacity reducing the cycle-lifetime as well as the calendar-lifetime of the metal air battery. With respect to this it has to be noted that the higher the oxygen concentration on the cathode side, the higher the crossover of oxygen from the anode side of the metal air battery.

With the method and system according to the present invention, the concentration of oxygen at the cathode can be reduced to a minimum. This prevents a diffusion of oxygen from the cathode to the anode. Since other measures to prevent such a diffusion within a metal air battery cell can be omitted (such as an oxygen removal membrane), this leads also to a more efficient design of the cell, saving space and weight which is especially important in mobile applications such as in vehicles. In summary, the invention allows a safe operation of the metal air battery while maintaining a high cycle-lifetime and calendar-lifetime.

In a further advantageous embodiment of the inventive method, the metal air battery is operated with ambient air and the amount of oxygen supplied to the metal air battery is based on an oxygen concentration comprised in the ambient air and the method further comprises the step of preparing air being supplied to the metal air battery.

In a further advantageous embodiment of the inventive method, the method further comprises a step of determining a power demand, preferably the power demand of a vehicle, particularly the power demand of an electrical propulsion of the vehicle, wherein the amount of oxygen supplied to the metal air battery and/or concentration of oxygen in the supplied air is controlled at least as a function of the electrical power demand. This embodiment of the present invention is especially advantageous when a quick response to a power demand is desired, such in electrical propulsion in a vehicle. In a further advantageous embodiment of the inventive method, the method further comprises the step of determining, particularly measuring, an oxygen consumption of the metal air battery, when the amount of oxygen supplied to the metal air battery and/or concentration of oxygen in the supplied air is controlled at least is a function of the oxygen consumption. This embodiment applies where an excess of oxygen shall be absolutely avoided at the cathode side of a metal air battery. Thus, the control assures that only an amount of oxygen consumed is replaced by the amount of air supplied.

In a further advantageous embodiment of the inventive method, the method further comprises the step of determining, particularly measuring, an electrical potential supplied by the metal air battery, when the amount of oxygen supplied to the air battery and/or a concentration of oxygen in the supplied air is controlled at least as a function of the electrical potential. In order to avoid an oxygen excess at the cathode side of the metal air battery, it is also possible to determine the consumption of oxygen for generating electrical energy in the metal air battery by the delivered electri- cal potential. This avoids the use of further sensors, such as gas sensors, to determine the consumption.

In a further advantageous embodiment of the inventive method, the method further comprises the step of determining, particularly measuring, oxygen concentration in the ambient air. In a further advantageous embodiment of the inventive method, the method comprises the following steps: supplying a substantial constant first electrical power by the metal air battery, preferably a lithium air battery, wherein the metal air battery is a high capacity battery and supplying a variable second electrical power by a high power battery, preferably lithium ion battery: Preferably, the method comprises the further step of determining the power demand of a load, particularly electrical propulsion, and adapting the supplied electrical power to the electrical power demand of the load.

In a further advantageous embodiment of the inventive method, the method comprises the step of charging high power battery with electrical energy from a high ca- pacity battery, if the power delivered by the high capacity battery is higher than the power demand of the load.

The aspects of the invention and the respective disclosed features with respect to the inventive method are also valid for the aspects of the invention in the respective advantageous embodiments of an inventive system and vice versa. In an advantageous embodiment of the inventive system, the system is operated with ambient air and the control module is adapted to control the amount of supplied oxygen based on an oxygen concentration comprised in the ambient air, further comprising a conditioning module being adapted to prepare air being supplied to the metal air battery. In a further advantageous embodiment of the inventive system, the system comprises a first sensor adapted to determine the power demand, preferably the power demand of a vehicle, particularly the power demand of an electrical propulsion system of a vehicle and the control module is adapted to control the amount of supplied oxygen and/or the concentration of oxygen in supplied air at least as a function of the electrical power demand.

In a further advantageous embodiment of the inventive system, the system further comprises a second sensor adapted to determine, particularly measure, an oxygen consumption of the metal air battery, wherein the control module is adapted to con- trol the amount of supplied oxygen and/or the concentration of oxygen in supplied air at least as a function of the oxygen consumption.

In a further advantageous embodiment of the inventive system, the system further comprises a third sensor adapted to determine, particularly measure, an electrical potential supplied by the metal air battery, wherein the control module is adapted to control the amount of supplied oxygen and/or the concentration of oxygen in supplied air at least as a function of the electrical tension.

In a further advantageous embodiment of the present invention, the metal air battery is a high capacity battery, wherein the system further comprises a high power battery, particularly a lithium ion battery, a super capacitor, or any other electrochemical energy storage device, wherein the high capacity battery and the high power battery form a battery hybrid system in which the high capacity battery is adapted to provide a substantially constant first electrical power and the high power battery is adapted to provide a temporary variable second electrical power, wherein the second electrical power is higher than the first electrical power and/or specific energy density of the high capacity battery is 1 ,5 to 200, preferably 1 ,5 to 50, more preferably 1 ,5 to 10, and most preferably 1 ,5 to 4,5 times higher as the specific energy density of the high power battery. Such battery hybrid system provides a large range of advantages with respect to operating applications where a lot of different power requirements have to be covered, such as in vehicles with electrical propulsion. Further advantageous aspects and examples of the present invention will be apparent from the description of the following figures: Figure 1 shows at least partially schematically a first preferred embodiment of the inventive system installed in a vehicle; and

Figure 2 shows partially schematically a sequence of steps representing a preferred embodiment of the inventive method. Figure 1 shows a first embodiment of an inventive system 1 for supplying electrical energy in a vehicle 6.

The system 1 preferably comprises a metal air battery 2, particularly a lithium air battery. This metal air battery 2 being a high capacity battery is preferably operated in a manner to provide a substantially constant power to the vehicle 6. The oxygen 0 ₂ needed to oxidize the lithium Li when generating electrical energy is taken from the ambient air 3 and/or supplied from a reservoir.

In the case of ambient air 3, a conditioning module 4 prepares the aspirated air 12 for further processing in the system 1 . Such preparation preferably comprises a filtering, at least of coarse particles, hydrocarbons and fine dust, in the ambient air 3 as well as a tempering of the aspirated air 12 if necessary for the further processing.

In a control module 5, the amount of oxygen (13) supplied to the metal air battery and/or concentration of oxygen in air (13) supplied to the metal air battery 2 can be controlled by means of stoichiometry. For this, the concentration of oxygen in the aspirated air 12 or in the gas from a reservoir is preferably measured by a gas sen- sor 15. A control module 5 then preferably controls the amount of oxygen supplied to the metal air battery 2. Preferably a compressor 16 is provided to change the pressure of the supplied air and/or oxygen 13There are several preferred ways of controlling the amount of oxygen supplied: On the one hand, the amount of air supplied to the metal air battery 2 can be controlled, where the amount of oxygen in the air is calculated from the concentration of oxygen in the aspirated air 12 measured by gas sensor 15. On the other hand, it is possible to alter the concentration of oxygen in the supplied air 13, e.g. by lowering the concentration of oxygen with an oxygen consuming process. Furthermore, the amount of oxygen received by the metal air battery 2 can be preferably altered by varying a flow of supplied gas 13, a varia- tion of pressure in the metal air battery 2 and or by a use of membranes to produce an oxygen-enriched supplied gas 13. The so modified gas 13 is then supplied to the metal air battery 2, where the oxygen in the supplied gas 13 reacts at the cathode of the metal air battery 2 with the metal, preferably lithium Li to Li0 ₂ or Li ₂ 0 ₂ releasing electrons which build up a potential for supplying electrical power to a vehicle 6. The exhaust gas 14 of the metal air battery 2 preferably leaves the system 1 and/or the vehicle 6 via an exhaust pipe.

Electrical energy produced by the metal air battery 2 may be used to propel the vehicle 6 by the electrical propulsion 1 1 or may be used to charge a high power battery 10, preferably a lithium ion battery, a super capacitor and/or any other electrochemi- cal energy storage device.

Several sensors 7, 8, 9, 15 are alternatively or cumulatively arranged at different positions of the system 1 in order to generate information useful for controlling an amount of oxygen supplied to the metal air battery 2. A first sensor 7 may be preferably arranged in the power supply of electrical propulsion 1 1 or in the electrical pro- pulsion device 1 1 itself to determine, particularly measure, the power demand of the electrical propulsion 1 1 . Based on this power demand which has to be satisfied by the metal air battery 2, preferably being a high capacity battery, and the high power battery 10, the amount of electrons which have to be released by the metal air battery 2 can be calculated taking into consideration different electric resistances in the system 1 and/or the vehicle 6 and potentially further power consumers in vehicle 6. By a further stoichiometric calculation, the amount of oxygen molecules can be determined which have to be delivered to the metal air battery 2 via the supplied gas 13 to release the desired power. Preferably, the system 1 comprises a microcomputer to perform these actions, which is preferably associated to the control module 5. Based on the needed amount of oxygen molecules in the metal air battery 2, the control module 5 either adapts the concentration of oxygen in a flow of aspirated air 12 and/or adapts the amount of oxygen supplied to the metal air battery 2 in order to meet the oxygen demand.

According to further embodiments of the present invention, corresponding process- es are preferably defined with respect to a second sensor 8 measuring an oxygen consumption of the metal air battery 2 or a third sensor 9 measuring an electrical potential supplied by the metal air battery. The second sensor 8 measures residual oxygen in an exhaust gas 14 of the metal air battery 2. If residual oxygen is present in the exhaust gas 14 of the metal air battery 2, a comparison with an oxygen concentration in the aspirated air 12 measured by a fourth sensor 15 reveals the oxygen consumption of the metal air battery 2. Based on this calculation, control module 5 can adapt the oxygen supply in the supplied gas 13 to the actual consumption of the metal air battery 2 such that no oxygen excess remains at the cathode side in the metal air battery 2 leading to the residual oxygen in the exhaust gas 14. The third sensor 9 is preferably arranged in the electrical circuit 3 of the metal air battery 2 and measures an electrical potential supplied by the metal air battery 2. Based on this electrical potential, the number of electrons released by the metal air battery 2 can be calculated taking into consideration the internal resistance of the metal air battery 2. From this, by means of stoichiometric calculation, the actual consumption of the metal air battery 2 in order to supply the measured electrical potential can be calculated and the control module 5 can adapt the amount of oxygen supplied to the metal air battery 2 accordingly to avoid an oxygen excess at the cathode.

Preferably, the system 1 not only comprises several of the mentioned sensors 7, 8, 9, 15, and the control module 5 is adapted to apply different operation strategies for the metal air battery 2 with respect to the oxygen supply depending on the opera- tional state of the system 1 and/or the vehicle 6.

Figure 2 shows a preferred embodiment of the inventive method 100 to operate a system 1 as specified with respect to Figure 1 . It is evident to the person skilled in the art that the steps shown in Figure 2 may be arranged in a different order. In the inventive method 100, a metal air battery 2, particularly a lithium air battery, is oper- ated, preferably with ambient air, 101 . Therefore, gas 13 being supplied to the metal air battery 2 is preferably prepared, 102. This may comprise a filtering of coarse particles from ambient air 3 by a filter at the in-take of the inventive system 1 but also other processes such as conditioning of the aspirated air 12 in order to reach a certain temperature. Preferably the power demand of the vehicle 6 or the power demand of the electrical propulsion 1 1 of the vehicle 6 is determined 103. Alternatively or additionally, an oxygen consumption of the metal air battery 2 is determined, particularly measured, 104 and/or an electrical potential supplied by the metal air battery 2 is determined, particularly measured, 105. Based on at least one of the determined power demands, the oxygen consumption and the electrical potential, the amount of oxygen to be supplied to the metal air battery 2 is calculated, 106. Based on this calculated demand, the amount of oxygen supplied to the metal air battery 2 is preferably controlled, 107.

Preferably, according to the inventive method 100, a substantial first electrical power is supplied by the metal air battery 2, wherein the metal air battery 2 serves as a high capacity battery, 108. Further preferably, a variable second electrical power is supplied by a high power battery 8, preferably a lithium ion battery, 109. Further preferably, a power demand of a load, particularly electrical propulsion 14 is determined, 1 10 and the supplied second electrical power is adapted to the power of the load, 1 1 1 . Preferably, in the case that the power delivered by the high capacity battery 2 is higher than the power demand of the load, the high power battery 10 is charged with electrical energy generated by the high capacity battery 2.

LIST OF REFERENCE NUMERALS

1 System

2 Metal air battery

3 Ambient air

4 Conditioning module

5 Control module

6 Vehicle

7 First sensor

8 Second sensor

9 Third sensor

10 High power battery

1 1 Electrical propulsion

12 Aspirated air

13 Supplied gas

14 Exhaust gas

15 Fourth sensor

16 Air compressor