Battery having an integrated flame retardant device

Abstract

The invention relates to a battery (1) having an integrated flame retardant device, wherein the battery (1) has: a cathode layer (2), a separating layer (3), and an anode layer (4), wherein the separating layer (3) is arranged between the cathode layer (2) and the anode layer (4), wherein the separating layer (3) is impermeable to electrons and permeable to at least one positive type of ion, wherein the separating layer (3) has a flame retardant device having at least one glass fibre (30), which comprises a closed cavity (34), and wherein a flame retardant (31) is arranged in the cavity (34). The invention provides a battery (1) which has increased fire resistance.

Description

Battery having an integrated flame retardant device The invention relates to a battery having an integrated flame retardant device. In order to store electric energy for subsequent discharge, batteries or accumulators are used. They enable power to be supplied independently of power supply networks or elec- tric generators. Batteries can also be used to supply electric loads in aircraft. For general use outside aircraft, composite batteries are known and, in their basic form, these have three layers. In this case, a separating layer is arranged between a cathode layer and an anode layer. The cathode layer and the anode layer can comprise a polymer, which is reinforced by carbon fibres. In this case, the fibres of the cathode layer can be coated, e.g. with iron oxide. The separating layer can be composed of a polymer with a reinforce- ment consisting of glass fibres. The separating layer acts as an electric insulator for elec- trons. In this case, lithium ions can pass through the separating layer but electrons cannot. Since the lithium ions are inflammable, the use of lithium ion batteries or accumulators in aircraft is critical since aircraft have only limited extinguishing capacities. In this context, DE 10 2010 041387 A1 or EP 3 053 206 B1, for example, disclose the use of flame retardants in the housing of unstructured lithium ion batteries. However, the lith- ium ion batteries may start to burn within the housing since it is only at the housing of the battery that a fire comes into contact with the flame retardant, that is to say that the hous- ing of the battery may reach high temperatures owing to the flames. This can damage the surroundings of the housing and, in the worst case, can lead to ignition of the materials surrounding the housing. It is therefore the object of the invention to provide a battery which has increased fire re- sistance. . According to the invention, a battery having an integrated flame retardant device is pro- vided, wherein the battery has an anode layer, a separating layer, and a cathode layer, wherein the separating layer is arranged between the cathode layer and the anode layer, wherein the separating layer is impermeable to electrons and permeable to at least one positive type of ion, wherein the separating layer has a flame retardant device having at least one glass fibre, which has a closed cavity, and wherein a flame retardant is arranged in the cavity. By means of the invention, the glass fibres are destroyed and the cavity opened in the case of an increase in the temperature in the battery, with the result that the flame retardant es- capes and develops its flame inhibiting action. The fire risk due to the lithium ions ar- ranged in the battery is thus significantly reduced by the escaping flame retardant. If a source of fire develops in the battery or flashes over to the battery from an external source of fire, the flame retardant escaping through the destruction of the glass fibres can inhibit the fire and, in the ideal case, also extinguish it. Outside a fire incident, the glass fibres re- inforce the separating layer and furthermore act as electric insulators between the cathode layer and the anode layer. The invention is thus provided with multifunctional glass fibres which additionally provide a fire safety function in a simple and space-saving manner. The fire resistance of the battery is thus increased. It is advantageous if the at least one glass fibre has a critical temperature, wherein the glass fibre breaks when the critical temperature is exceeded, and the flame retardant escapes from the cavity. By means of the critical temperature, it is possible to predetermine under precisely what temperature conditions the flame retardant is supposed to escape from the cavity. Further- more, this avoids the need for the glass fibre first of all to melt in order to open the cavity, i.e. for destruction of the glass fibre by a melting process to occur. On the contrary, the glass fibre disintegrates due to internal stresses which arise owing to the temperature dif- ference across the cross section of the glass fibre before the melting point of the glass fibre is reached. In contrast to the melting of the glass fibre, disintegration ensures that the cav- ity within the glass fibre is opened above the critical temperature instead of the molten glass continuing to seal the cavity or resealing it after initial opening in an unfavourable case. It is expedient if the quantity of flame retardant is dimensioned in such a way that a fire in the battery is suppressed after the flame retardant escapes from the cavity. In this way, the quantity of flame retardant can be matched precisely to the boundary con- ditions within the separating layer or the battery, and therefore sufficient flame retardant is available to extinguish a fire in the battery. Furthermore, it is thereby possible to avoid overdimensioning the quantity of flame retardant, and therefore costs for the flame retard- ant can be saved in the production of the battery. It is advantageous if the flame retardant is triphenylphosphate. Triphenylphosphate has proven to be a very effective flame retardant for lithium ion bat- teries. An effective flame retardant for lithium ion batteries is thus provided. Furthermore, the required quantity of flame retardant can be further reduced by the effectiveness of the triphenylphosphate, and therefore additional costs can be saved, at least in production. Thus, in a first illustrative embodiment, it is possible for only a partial quantity of the glass fibres to have a cavity containing flame retardant. As an alternative or in addition, it is also possible to use glass fibres with only very small cavities, thus also making it possible to reduce the overall diameter of the glass fibres. This saves weight and costs. Saving weight is advantageous especially in aircraft construction. It is advantageous if the separating layer comprises a polymer, in which the at least one glass fibre extends as a reinforcing fibre. It is furthermore expedient if the separating layer has a multiplicity of glass fibres having a cavity, which preferably form a glass fibre mat. By providing a multiplicity of glass fibres having a cavity, the flame retardant can be dis- tributed uniformly within the separating layer. An effective fire retardant effect is thereby provided over the entire area of the separating layer. If the glass fibres additionally form a glass fibre mat, it is thereby possible to avoid the formation of empty spaces between the glass fibres which cannot be supplied with a flame retardant. Furthermore, a glass fibre mat increases the stability of the separating layer and hence also of the battery. It is advantageous if the cavity extends along the glass fibre, preferably along the entire glass fibre. In contrast to a cavity which extends over only a short section of the total length of the glass fibre, a cavity which extends along the entire glass fibre makes it possible to provide a fire retardant effect over the entire length of the glass fibre. Since the glass fibre can pro- vide an opening to the cavity containing the flame retardant at every point at which it breaks due to a temperature increase, fire safety is further increased. Furthermore, it is advantageous if the at least one glass fibre has an outside diameter of be- tween 8 μm and 14 μm, preferably between 10 μm and 12 μm. Glass fibres with these outside diameters are strong enough to bring about a reinforcing effect in the polymer of the separating layer. Thinner glass fibres would not have the re- quired reinforcing effect if they were simultaneously supposed to store sufficient flame re- tardant within a cavity to achieve an adequate fire retardant effect. If the glass fibres are too thick, it is not possible to ensure that they open at the correct time in the event of a fire in order to enable the flame retardant to escape from the cavity of the glass fibre. It is advantageous if the cavity has a diameter of between 4 μm and 7 μm, preferably be- tween 5 <semantics>μ<annotation encoding="application / x-tex">\mu< / annotation>< / semantics>m and 6 <semantics>μ<annotation encoding="application / x-tex">\mu< / annotation>< / semantics>m. A cavity with a diameter in this range can hold sufficient flame retardant to develop a flame retardant effect. Moreover, at these diameters, adhesion and cohesion forces are not strong enough to hold the flame retardant in the cavity when the cavity opens. It is advantageous if the cathode layer contains carbon fibres that comprise an iron oxide coating, wherein the carbon fibres are embedded in a polymer in the cathode layer. Furthermore, an aircraft is provided which, according to the invention, comprises at least one battery in accordance with the above description, at least one electric load, and at least one electric lead, wherein the battery is connected to the electric load via the electric lead. ť Thus, an aircraft is provided which can have a rechargeable lithium ion battery for supply- ing electric loads within the aircraft, wherein the battery has increased fire resistance. It is advantageous if the at least one battery is arranged in a cabin panel or a structure, in particular a laminated shell or a frame structure, of the aircraft. Thus, batteries can be distributed in a flexible manner within the aircraft. Furthermore, the batteries can be arranged in a space-saving and yet easily accessible manner in the interior of the aircraft if, for example, they are secured behind a panel. In this way, the batteries can also be arranged close to the electric loads, with the result that just one supply line has to be laid to the battery and it is possible for branching to the electric loads to take place only afterwards. As a result, the structure of an aircraft is significantly simplified and only a small number of electric loads are affected if a battery fails. Furthermore, the elimination of electric leads also makes it possible to save weight. According to the invention, a method for producing a battery having an integrated flame retardant device is furthermore provided, wherein the method has the following steps: a) providing at least one glass fibre having a cavity; b) filling the cavity with a flame retard- ant; c) closing the cavity; and d) arranging the at least one glass fibre in a separating layer of a battery, wherein the separating layer is applied to a cathode layer or an anode layer. The invention is described below with reference to an illustrative embodiment by means of the attached drawing, in which: Figure 1 shows a schematic illustration of a battery having an integrated flame retardant device; Figure 2 shows a schematic illustration of a glass fibre having a cavity and flame retardant; Figures 3a,b show schematic illustrations of glass fibres having a cavity and flame retardant above another, burning layer; Figures 4a,b show schematic illustrations of aircraft with a battery having an inte- grated flame retardant device; and * 6 Figure 5 shows a schematic flow diagram of the method for producing a bat- tery having an integrated flame retardant device. The battery is denoted overall by the reference sign 1 below, as illustrated in Figure 1. The battery 1 comprises a cathode layer 2, a separating layer 3 and an anode layer 4. The separating layer 3 is arranged between the cathode layer 2 and the anode layer 4. In this case, the anode layer 4 comprises a polymer 44, which is reinforced with carbon fi- bres 20. The anode layer 4 can furthermore be connected to a collector layer (not shown), which establishes contact with an electric lead. The cathode layer 2 comprises a polymer 22, which is likewise reinforced with carbon fi- bres 20. The carbon fibres 20 are furthermore provided with a coating 21 of iron oxide. The cathode layer 2 can furthermore be connected to a collector layer (not shown), which establishes contact with an electric lead. The separating layer 3 comprises a polymer 33, which is reinforced with glass fibres 30. Here, the separating layer 3 allows through positive ions, e.g. lithium ions. The separating layer 3 is impermeable to electrons. During the charging process, positive ions pass from the anode layer 4 to the cathode layer 2 through the separating layer 3. The electrons are fed in from outside via the cathode layer 2 to compensate for the charge of the positive ions. During the discharge process, the positive ions pass from the cathode layer 2 to the anode layer 4 through the separating layer 3. Here too, electrons are fed in via the anode layer 4 to compensate for the charge of the positive ions. In this case, as illustrated in Figure 2, the glass fibres 30 have cavities 34, which extend along the entire glass fibre 30. Here, the cavities 34 are closed. Furthermore, the cavities 34 contain a flame retardant 31. The flame retardant 31 can be triphenylphosphate. The glass fibres 30 are woven into a glass fibre mat. Empty spaces between the glass fi- bres 30 are thereby avoided. If all the glass fibres 30 have a cavity 34 containing flame re- tardant 31, the glass fibre mat enables the entire area of the separating layer 3 to be cov- ered with flame retardant 31 from the cavities 34 of the glass fibres 30. Thus, fire re- sistance can be increased over the entire area of the separating layer 3 since glass fibres 30 having cavities 34 which can supply flame retardant 31 when there is a temperature in- crease in the event of fire are arranged at every point of the separating layer 3. The glass fibres 30 are furthermore designed in such a way that they start to break above a critical temperature when there is a temperature increase. This is illustrated in Figure 3a, in which a fire 5 has developed in the anode layer 4. Here, the glass fibres 30 have cracks 32, which extend through the wall of the glass fibre 30 almost as far as the cavity 34. The cracks 32 can arise from internal stresses in the glass fibre 30, caused by temperature dif- ferences between different regions across the cross section of the glass fibre 30. If the crit- ical temperature is exceeded, the walls of the glass fibre 30 open at the cracks 32, opening the cavity 34 of the glass fibre 30. The flame retardant 31 then emerges from the cavity 34 to the outside through the glass fibre 30. Here, Figure 3b illustrates that flame retardant 31 is inhibiting the fire 5 and is about to extinguish the fire 5. Here, the amount of flame retardant 31 is sufficient to enable a fire 5 within the battery 1 to be extinguished. The glass fibres 30 furthermore have an outside diameter of between 10 µm and 12 µm. Thus, the glass fibres 30 have an outside diameter which is dimensioned so that, in the event of a fire, the glass fibres 30 can disintegrate due to the increase in temperature and the cavity 34 within the glass fibre 30 can be opened. The cavity 34 has an inside diameter of from 5 µm to 6 µm. This diameter is adequate to accommodate sufficient flame retardant 31 to increase the desired fire retardant effect. A cross section through an aircraft 6 is illustrated schematically in Figure 4a. Arranged in an interior 63 of the aircraft 6 in this case is a cabin panel 7, which lines the outer wall of the interior 63. In this case, a battery 1 is arranged behind the panel 7. The battery 1 is connected by means of electric leads 62 to electric loads 61 - in this case reading lights. Here, the battery 1 supplies the electric loads 61 via the electric leads 62. . As an alternative or in addition, the battery 1 can be integrated into the panel 7 (not shown). In this case, the battery 1 is part of the panel 7 and can therefore be produced at the same time as the panel 7. It is thereby possible to combine working steps and to save costs in production. Moreover, the battery 1 cannot become detached from the panel 7, and therefore there is no need to check the fastening of the battery 1 during a maintenance pro- cess. It is thereby possible to lower maintenance costs. In this case, the battery 1 can furthermore be electrically connected (not shown) to a gen- erator or a fuel cell or an additional battery which has a significantly higher capacity than the battery 1. This connection is then used to charge the battery 1. Figure 4b likewise shows a schematic illustration of an aircraft 6. In this illustrative em- bodiment, the battery 1 is secured on a supporting structure 8 of the aircraft 6. Here too, the battery 1 is connected to electric loads 61 by means of electric leads 62. The battery 1 supplies the electric loads 61. This battery 1 too can be connected by means of a further electric lead (not shown) to an energy source or an energy storage device which has a larger capacity than that of the bat- tery 1. In this case, the battery 1 can be arranged and / or secured on almost any of the elements of the aircraft structure of an aircraft 6. Thus, the battery 1 can be arranged in a flexible man- ner, as required, in an aircraft 6 and can supply power for electric loads in a decentralized way. Here, the battery 1 has a high fire resistance, which is essential in aircraft construc- tion. Figure 5 shows a schematic illustration of a flow diagram of the method 100 for producing a battery having an integrated flame retardant device. In this case, the method 100 comprises step a), providing 101 at least one glass fibre hav- ing a cavity. Here, the glass fibre can have a diameter of from 10 <semantics>μm<annotation encoding="application / x-tex">\mu m< / annotation>< / semantics> to 12 <semantics>μm<annotation encoding="application / x-tex">\mu m< / annotation>< / semantics>. In this case, the cavity in the glass fibre can have a diameter of from 5 µm to 6 µm. In this case, the cavity can extend over the entire length of the glass fibre. In a second step b), the cavities are filled 102 with a flame retardant. During this process, triphenylphosphate can be fed into the cavity. However, it is also possible to use a differ- ent flame retardant. In a third step c), the cavity is closed. This can be accomplished by melting the ends of the glass fibre, for example, or by heating the ends of the glass fibre and then compressing the ends of the glass fibre, for example. In this way, the flame retardant is trapped in the cav- ity and cannot escape from the cavity. Only if the wall of the cavity is destroyed can the flame retardant escape from the cavity. In a fourth step d), the glass fibre having the cavity is arranged 104 in a separating layer of a battery. In this case, a multiplicity of glass fibres having cavities and flame retardant contained therein can be arranged in a separating layer. The separating layer can further- more comprise a polymer in which the glass fibres are embedded as reinforcing fibres. Furthermore, the glass fibres can be woven into a glass fibre mat which covers the entire separating layer. In this way, the flame retardant in the cavities of the glass fibres can be distributed over the entire separating layer by means of the glass fibres. Furthermore, the stability of the separating layer is increased by the glass fibre mat. Here, the separating layer can be secured on an anode layer or a cathode layer of a battery. If the separating layer is secured on an anode layer of a battery, a cathode layer is arranged and secured on the separating layer. If the separating layer is secured on a cathode layer of a battery, an anode layer is arranged and secured on the separating layer. Here, the separating layer acts as an electric insulator. In this case, the electric insulation is with respect to the electrons. Positive ions can pass through the separating layer. In this ar- rangement, the positive ions can pass backward and forward in both directions between the anode layer and the cathode layer. After production, the battery can be arranged in an aircraft. In this case, the battery can supply electric energy in a decentralized manner at various points in the aircraft. Thus, for . í example, the battery can be arranged behind an aircraft panel. As an alternative or in addi- tion, the battery can be secured on a structure of the aircraft, e.g. in a laminated shell or in the frame structure. . • . - . . • · . • . · • . ·

Claims

1. A battery having an integrated flame retardant device, wherein the battery has: a cathode layer, a separating layer, and an anode layer, wherein the separating layer is arranged between the cathode layer and the anode layer, wherein the separating layer is impermeable to electrons and permeable to at least one positive type of ion, wherein the separating layer has a flame retardant device having at least one glass fibre, comprising a closed cavity enclosed within the at least one glass fibre, and wherein a flame retardant is arranged in the closed cavity within the at least one glass fibre.

2. The battery according to claim 1, wherein the at least one glass fibre has a critical temperature, wherein the at least one glass fibre breaks when the critical temperature is exceeded, and the flame retardant escapes from the closed cavity.

3. The battery according to claim 2, wherein the quantity of flame retardant is dimensioned in such a way that a fire in the battery is suppressed after the flame retardant escapes from the closed cavity.

4. The battery according to any one of claims 1 to 3, wherein the flame retardant is triphenylphosphate.

5. The battery according to any one of claims 1 to 4, wherein the separating layer comprises a polymer, in which the at least one glass fibre extends as a reinforcing fibre.

6. The battery according to any one of claims 1 to 5, wherein the at least one glass fibre of the separating layer is at least one of a plurality of glass fibres of the separating layer.

7. The battery according to claim 6, wherein the plurality of glass fibres form a glass fibre mat.

8. The battery according to any one of claims 1 to 7, wherein the closed cavity extends along the at least one glass fibre.

9. The battery according to any one of claims 1 to 8, wherein the at least one glass fibre has an outside diameter of between 8 μm and 14 μm.

10. The battery according to claim 9 wherein the outside diameter of the at least one glass fibre is between 10 µm and 12 µm.

11. The battery according to any one of claims 1 to 10, wherein the closed cavity has a diameter of between 4 µm and 7 µm.

12. The battery according to claim 11 wherein the diameter of the closed cavity is between 5 µm and 6 µm.

13. The battery according to any one of claims 1 to 12, wherein the cathode layer contains carbon fibres that comprise an iron oxide coating, and wherein the carbon fibres are embedded in a polymer in the cathode layer.

14. An aircraft comprising at least one battery according to any one of claims 1 to 13, at least one electric load, and at least one electric lead, wherein the at least one battery is connected to the at least one electric load via the at least one electric lead.

15. The aircraft according to claim 14, wherein the at least one battery is arranged in a cabin panel or a structure, of the aircraft.

16. The aircraft according to claim 15 wherein the at least one battery is arranged in a laminated shell or in a frame structure, of the aircraft.

17. A method for producing a battery having an integrated flame retardant device, wherein the method has the following steps: a) providing at least one glass fibre having a cavity therein; b) filling the cavity within the at least one glass fibre with a flame retardant; c) closing the cavity; and d) arranging the at least one glass fibre in a separating layer of the battery, wherein the separating layer is applied to a cathode layer or an anode layer.