DE2622245A1 - Discharge state indicator for sulphur sodium cells - with voltmeter across auxiliary anode and sulphur cathode - Google Patents

Abstract

The discharge state of a Na/S battery for trucks which has a solid electrolyte sepng. the S-cathodes from the Na-anodes is determined by providing some of the cells with a second Na-anode. This forms with the cathode a potentiometric cell. A voltmeter connected to it indicates the no-load voltage of the cell which is function of the state of discharge. This is simple method of indicating the state of discharge of such a battery, even when loaded by current consumers. The storage capacity of the battery is not detrimentally affected and it is easily possible to apply a remote indication.

Description

Device for determining the state of discharge of an electrical

chemical battery.

The invention relates to a device for determining the duck SeS state of an electrochemical battery, in particular / electric vehicle battery based on sodium and sulfur, with storage cells, their alkali metal anodes are separated from the sulfur cathodes by solid electrolytes.

As is known, batteries based on alkali metal / sulfur are used operated at high temperatures with molten electrodes. A consolidation must be achieved here the sulfur or the alkali metal polysulfide can be avoided, because with changes in state Internal voltages often occur in these electrodes, which affect the solid electrolyte can destroy. This is especially true for batteries in electric vehicles Significance of which a high level of operational safety is required.

For this reason, sodium / sulfur-based batteries are used usually only such an operating interval is used at temperatures of around 300 0C, that of a stoichiometric composition of the sulfur electrode of about Na2S20 im loaded State of the battery up to about Na2S2.8 when discharged State corresponds. It has now been shown that between the discharge state one Battery and its open circuit voltage, especially in the vicinity of a discharge point, which is still permissible with regard to the solidification of the sulfur, a connection consists. For example, the open circuit voltage of a sodium / sulfur cell is a Discharge by 20 "each, at which the sulfur cathode reaches a composition of Na2S5, about 2.08 V. In the event of a further discharge, this voltage drops approximately linearly down to a value of 1.78 V, the sulfur cathode having a composition of Na2S2.8.

The invention is based on the object of providing a device of Specify the type mentioned at the beginning, which it takes advantage of the aforementioned effect allows the state of discharge of an electrochemical battery on the basis of Alkali metal and sulfur also occur during their exposure to electricity consumers easy way to determine. In addition, the device should be designed in this way be that the storage capacity of the battery is hardly affected and a remote display the state of discharge is easily possible.

The solution to this problem is that at least one memory cell is provided with at least one further, second alkali metal anode, which together with the sulfur cathode forms a measuring cell to which a voltmeter for currentless or at least almost currentless measurement is connected to display the open circuit voltage of the storage cell dependent on the state of discharge. The stoichiometry the sulfur cathode of a storage cell is thus based on a measurement of the open circuit voltage monitored so that falling below a limit value, in which a solidification of the sulfur sets in, is avoided and a timely charging the battery can be initiated. By the voltmeter for currentless or at least almost currentless measurement, the measuring cell is practically not loaded, so that a long service life of the second alkali metal anode is ensured. In addition, polarization phenomena of the measuring cell are avoided. As voltage measuring devices For example, the well-known DC voltage compensators can be used for currentless measurement, The well-known ones can also be used as voltmeters for almost currentless measurements Measuring devices with high internal resistance are used.

Such storage cells are preferably used for training as a measuring cell Select which are representative of the discharge status of the entire battery.

Batteries within the meaning of the invention can have any number of Have storage cells, including batteries with only a single storage cell should be recorded.

In order to largely separate the working and measuring circuit from each other, It is recommended that the sulfur cathode of the memory cell has an up in the vicinity of the second alkali metal anode, which is electrically highly conductive Potential dissipation is arranged to which the corresponding pole of the voltmeter connected. The potential dissipation extends here preferably up to to the area of the solid electrolyte.

If several storage cells are designed as measuring cells, it is advantageous to if the measuring cells can be individually connected to the voltmeter. Through this is the discharge status of the individual, located at representative points on the battery Memory cells can be queried individually and one after the other.

If the storage cells are electrically connected in series, then It is advantageous that the measuring cells can also be connected in series and connected to the Voltmeter can be connected.

With this arrangement, the state of discharge can be measured by three measuring cells record as mean value through a single voltage measurement.

In this case, the measuring cells are advantageously via a switching element can be connected to the voltmeter. Vorugstreise serves as a switching element manually operated step switch that allows the measuring cells to be connected individually or in series to be connected to the voltmeter.

For monitoring a battery installed in an electric vehicle it is advantageous if the voltmeter and, if necessary, the switching element are arranged in the driver's cab.

The second alkali metal anode is advantageously in one preferably arranged with 9 -aluminium oxide (X - Al203) formed insulating tube, the lower end of which is sealed with the ion-conducting solid electrolyte and through its upper end, which is also closed, one with the alkali metal in conductive Connected potential discharge, especially in the form of a molybdenum wire, is led to the outside.

In order to minimize the space required for installation in the storage cell to keep, it has proven itself when the insulating tube is preferably round in cross-section has a clear width of about 1.5 to 2 mm.

This further simplifies the structure of the alkali metal anode, that the solid electrolyte has the shape of a plug and is inserted into the insulating tube is.

If the second alkali metal anode is tubular and immersed with its solid electrolyte into the sulfur cathode, it proved to be useful if the immersion depth and the length of the insulating tube are chosen so that the solid electrolyte the sulfur cathode remains in contact with the sulfur even at the lowest level and the potential dissipation not even at the highest level of the sulfur cathode is touched by the sulfur.

Further advantages of the invention emerge from the following description of exemplary embodiments in connection with the drawings, which follow schematically show: FIG. 1 an electrochemical storage battery with three parallel-connected Storage cells, two of which are provided with a device according to the invention Fig. 2 shows an electrochemical battery with three storage cells connected in series, two of which are provided with a device according to the invention and 3 shows the second alkali metal anode in detail and on a larger scale.

The battery shown in Figures 1 and 2 has three each Storage cells 10, 11, 12. Each of these memory cells has one in cross section circular graphite cup 13, from each of which is the sulfur cathode 14 is included. Since sulfur is a bad conductor of electricity, that is Sulfur cathode penetrated by an electrically conductive matrix 15, which in the present Execution example consists of graphite felt and each with the negative, memory cell terminal 16 leading to the outside, for example in the form of a wire stands. | In the sulfur cathode 14, the solid electrolyte 17 is in the form of a bottom closed tube arranged approximately centrally and it is in its upper area 18 locked. The solid electrolyte contains the alkali metal anode 19, which over a centrally arranged potential conductor 20 is connected to the outside space and there forms the positive terminal 21. This potential conductor penetrates here the closure 58 of the graphite cup 13.

In the area of the ring-shaped sulfur cathode 14 there is now another second alkali metal anode 22 arranged, which together with the sulfur cathode a Measuring cell forms. Your potential derivation 23 is led upwards, penetrates the Closure 58 of the graphite cup 13 and forms the positive measuring connection in the outer space 24, 54. Details of the construction of the second alkali metal anode are shown in FIG and will be explained later.

The storage cells 10, 11, 12 of the battery according to Figure 1 are over Lines 25, 26 connected in parallel and provided with connections 271 28 for acceptance the stored electrical energy.

The memory cells 11 and 12 each have second alkali metal anodes 22 are provided, the positive measuring connection 24 each via a line 29, 30 with one stage of the stage switch 31 is connected. The output of the multiple switch is via a line 32 to the positive input terminal of a voltmeter 33 connected with high internal resistance; the. The second, negative terminal of the voltmeter is, as shown in Fig. 1, via the line 59 to the negative ven memory cell connections 16 connected. In order to ensure the coupling between the working and measuring circuit as possible To keep it low, the line 59 is in each case immediately at the exit of the connection 16 from the graphite cup 13 connected, so that the working and measuring current jointly traversed line parts are short.

During operation, if the tap changer is in the appropriate position 31 either the open circuit voltage of the storage cell 11 or 12 with the voltmeter 33 can also be measured by setting the tap changer accordingly switch off the measuring device to protect the second alkali metal anodes. Because the open circuit voltage the state of discharge depends on the stoichiometry of the sulfur cathodes of cells 11 and 12 monitor, so that with certainty the occurrence of solid Phases of the sulfur cathode is avoided and a charging or replacement of the battery can be initiated. Since the power consumption of the voltmeter 33 is insignificant, the second anodes 22 have a long service life even with very low alkali metal volumes. After the alkali metal has been consumed can these second alkali metal anodes 22 by connecting a corresponding one Power source can be recharged or, what is even easier, simply against charged can be exchanged. The second alkali metal anodes 22 are preferred provided in such storage cells that are responsible for the discharge status of the entire battery are representative, e.g. in the case of a battery block with different temperature ranges ~ Storage cells arranged in these areas. cells.

When using the battery in electric vehicles, the voltmeter is used 33 as well as the step switch 31, 38 preferably arranged at the control station, see above that the driver can easily monitor and check the discharge status.

In the exemplary embodiment according to FIG. 2, the memory cells 11 and 12 electrically connected in series and also with second alkali metal anodes 22 provided for the formation of measuring cells. The measuring cells themselves are additional here electrically switchable in series. This allows in addition to the individual, separate measurement the open circuit voltage of the memory cell 11 or 12 is also the common Measurement of an average open circuit voltage of cells 11 and 12. In addition, the Measuring cells each have their own negative potential dissipation 34, 35, which in the Matrix 15 is embedded and extends up to the vicinity of the second anode 22, preferably up to the vicinity of their Festele # trolyte, extends and through the side wall of the graphite cup 13 is led to the outside. In this way will; an extensive separation of work and measuring circuit achieved by practically no two circuits in common Line parts are available. Thus, the open circuit voltage of the memory cells can be measured without any influence from their working current. Preferably the Potentialabfünrungen 34, 35 are each in the area of their penetration of the Graphite cup 13 is provided with an insulating layer, e.g. made of glass, in order to reduce the open circuit voltage To be able to measure the measuring cells either individually or in series, that is Voltmeter 33 via lines 44, 45 to the output of a two-pole step switch 38 connected. The input stages of the first pole of the tap changer are with the digits 40 to 43, the input stages of the second pole with the digits 50 to 53 designated, the stages 40 and 50 are not occupied, so that in this position the multiple switch the measuring device is separated from the measuring cells.

To now adjust the open circuit voltage of the measuring cells either individually or together to be able to detect, is the negative measuring connection 36 to the stages 41 and 43, the negative measuring terminal 37 connected to stage 42. The positive measurement terminal 54 is connected to stage 51, the positive measuring connection 24 to stages 52 and 53. Furthermore, those from the positive measuring connection 54 and those from the negative are in the node 46 Measuring connection 37 outgoing lines connected to one another. Since the lines in Figure 2 are clearly shown, a more detailed designation was dispensed with.

If the tap changer is in the position shown in Figure 2, so, as can be easily seen, the measuring cell arranged in the memory cell 11 connected to the voltmeter 33. Will the step switch on the steps 42 and 52 turned over, the measuring cell of the memory cell 12 is with the voltmeter 33 connected. In the position 43, 53 of the step switch, the measuring cells are the Memory cells 11 and 1 are connected in series and the series voltage is measured by the voltmeter 33 displayed This series voltage represents the mean open circuit voltage of the cells 11 and 12 represent the no-load voltage representative of the state of charge of the battery e.g.

of the memory cells 11 and 12 is thus through a single measurement recorded. Otherwise, the statements made in relation to FIG. 1 also apply here.

In Figure 3 is the one used for measuring the open circuit voltage second alkali metal anode 22 shown in detail and on a larger scale. An insulating tube 47 made of z -aluminium oxide of circular cross-section is below with a plug-shaped solid electrolyte 48 made of ß-aluminum oxide (Al203) and above closed by means of a glass drop 49. To do this the solid electrolyte to hold and close the interior of the insulating tube from the exterior the solid electrolyte 48, as can be seen from Figure 3, with one made of glass powder Soldering 55 is provided. The alkali metal is located in the interior of the insulating tube 47 56, which is taken up by a matrix 57, e.g. in the form of steel wool. The potential derivation 23 in the form of a straight wire made of molybdenum penetrates the glass drop 49 outside and is in intimate contact with the matrix 57 in the interior of the insulating tube. If the storage cells are in operation there is a risk that the sulfur cathode could come into contact with the potential lead 23, this is to be avoided to provide insulation, e.g. in the form of a glass cover, of Eurzschlösser.

The alkali metal serving as anode is removed before the Insulating tube 47 introduced by distillation in a vacuum.

However, it is also possible to use the alkali metal after insertion the anode into the sulfur cathode by means of an electrical charge.

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Claims (14)

Claims Ä I device for determining the state of discharge an electrochemical battery, in particular an electric vehicle battery the base of sodium / sulfur, with storage cells, their alkali metal anodes through Solid electrolytes are separated from the sulfur cathodes, characterized. that at least one memory cell (11, 12) with at least one further, second Alkali metal anode (22) is provided, which together with the sulfur cathode (14) forms a measuring cell to which a voltmeter (33) for currentless or at least almost currentless measurement is connected to display the dependent on the discharge status Beer run voltage of the storage cell. 2. Device according to claim 1, characterized in that in the The sulfur cathode (14) of the storage cell extends into the vicinity of the second alkali metal anode (22) extending, electrically highly conductive potential dissipation (34, 35) is arranged to which the corresponding pole of the voltmeter is connected. (Fig. 2) in 3. Device according to claim 1 or 2, arranged with / several memory cells Measuring cells, characterized in that the measuring cells are individually connected to the voltmeter (33) are connectable. (Fig. T) 4. Device according to claim 3 with connected in series Storage cells, characterized in that the measuring cells can also be connected in series and can be connected together to the voltmeter (33). (Fig. 2) 5. Device according to claim 3 or 4, characterized in that the measuring cells over a switching element (31, 38) can be connected to the voltmeter (33). 6. Device according to one of claims 1 to 5, characterized in that that the voltage of the voltmeter displayed when the battery is discharged is the Brand discharged and the voltage displayed when the battery is charged, the brand "Charged" assigned. 7. Device according to one of claims 1 to 6 for one in one Battery arranged in an electric vehicle, characterized in that the voltage measuring device and optionally the switching element are arranged in the driver's cab. 8. Device according to one of claims 1 to 7, characterized in that that the second alkali metal anode (22) in a preferably with M aluminum oxide (k -Al203) formed insulating tube (47) is arranged, the lower end of which with the ion-conducting solid electrolyte (48) is closed and also through it closed upper end one with the alkali metal (56) in conductive connection standing potential discharge ~ 23), especially in the form of a molybdenum wire is guided outside. (Fig. 3) 9. Device according to claim 8, characterized in that that the insulating tube (47), which is preferably round in cross section, has a clear width of about 1.5 to 2 mm. 10. Device according to claim 8 or 9, characterized in that the solid electrolyte (48) inserted into the insulating tube (47) has the shape of a plug having. 11. Device according to one of claims 8 to 10, characterized in that that glass solder for fastening the solid electrolyte (48) and a glass drop (49) is used to close the upper end of the insulating tube (47). 12. Device according to one of claims 8 to 11, characterized in that that the alkali metal (56) of the second alkali metal anode by an electrically conductive, matrix (57) also conductively connected to the potential conductor (23), e.g. made of metal wool. 13. Device according to one of claims 1 to 12, with tubular, second alkali metal anode, characterized in that the second alkali metal anode (22) with its solid electrolyte preferably vertically into the sulfur cathode (14) dips and is easily exchangeable. 14. Device according to claim 13, characterized in that the Immersion depth and the length of the insulating tube (47) are chosen so that the solid electrolyte (48) is in contact with the sulfur even when the sulfur cathode (14) is at its lowest level remains and the potential derivation (23) even at the highest level of the sulfur cathode is not touched by the sulfur.