GB2273603A

GB2273603A - Sulphur electrode for electrochemical energy storage cell comprises insulating zone bonded to electron-conductive zone

Info

Publication number: GB2273603A
Application number: GB9326115A
Authority: GB
Inventors: Sigisfredo Maldonado-Zagal
Original assignee: ABB Patent GmbH
Current assignee: ABB Patent GmbH
Priority date: 1992-12-19
Filing date: 1993-12-17
Publication date: 1994-06-22
Anticipated expiration: 2013-12-17
Also published as: GB9326115D0; DE4243211A1; GB2273603B; JPH06283203A

Description

T 1. 2273603 Electrochemical energy storage cell

Description

The invention relates to an electrochemical energy storage cell according to the precharacterizing clause of Patent Claim 1.

Such electrochemical energy storage cells are very suitable as energy sources. They are being used increasingly in the construction of high-energy batteries which are designed for the power supply of electrical vehicles. One example for these energy storage cells are those based on sodium and sulphur, which are rechargeable and have a solid electrolyte consisting of beta-alumina, which separates the anode compartment from the cathode compartment. The cathode compartment of these energy storage cells serves to accommodate a sulphur electrode which is formed by two half-shells or a cylinder and -20 which Is arranged around the outer surfaces of the solid electrolyte.

The prior art discloses sulphur electrodes whose structure corresponds to a two-part design. That zone of the sulphur electrode, which adjoins the solid electrolyte, in formed by an insulating layer, while the layer facing the caning is electron-conductive. The purpose of this bipartition in to ensure that, when the energy storage cell in recharged, the formation of sulphur takes place in the electron-conductive zone, while the sodium polyoulphide collects in the zone of the solid electrolyte. A separation of this type has a beneficial effect on the operation of the sulphur electrode, an recharging of the energy storage cell in thus facilitated. In the case of the energy storage cells disclosed by the prior art, this desirable separation of sulphur and sodium polysulphide in not achieved. This separation does not take place for the reason that, in

2 the known arrangements, the insulating layer does not have a uniform thickness, and its surfaces are not everywhere in intimate contact either with the solid electrolyte or with the electron-conductive zone of the sulphur electrode. Instead there are, at very many points between the insulating layer and the electron-conductive layer or the solid electrolyte, respectively, cavities which impede the rechargeability.

The object of the invention is to expound an energy storage cell which precludes the drawbacks of the known energy storage cells.

Claims

This object is achieved according to the invention by the features of

Patent Claim 1.

Complete bonding of the insulating layer to the is electron- conductive layer of the sulphur electrode is achieved by needling together the two layers. According to the invention, the insulating layer in manufactured from ceramic fibres or glass fibres or a mixture of these fibres. The electron- conductive layer is formed by a graphite felt which is made from polyacrylonitrile or cellulose. The fibres used to fashion the insulating layer are processed to give a web. This in bonded to the graphite felt with the aid of a needling machine. By impregnating the web and the felt with sulphur and subsequent pressing, the sulphur electrode is formed and arranged around the solid electrolyte. When the energy storage cell is heated to its working temperature of 3500C, the sulphur electrode, which had been compressed during its manufacture, expands. This ensures that the entire sulphur electrode comes into intimate contact both with the easing of the energy storage cell and with the solid electrolyte. At the same time it is ensured that the fibres of the insulating layer, which in part are arranged transversely, now align themselves in such a way that they are oriented radially with respect to the longitudinal axis of the solid electrolyte and, in part, completely penetrate the graphite felt. it is possible to ensure, by a suitable choice of the length of the fibres of the insulating layer, that some of these fibres penetrate the graphite felt sufficiently to extend as far as the easing--- of the energy storage cell. Thus, ionconductive paths through the graphite felt are formed. The intimate contact of the insulating layer both with the entire surface of the solid electrolyte and with the entire surface of the graphite felt, and the fact that the graphite felt is penetrated, in part, by the fibres of the insulating layer, ensure that, when the energy storage cell is recharged, the formation of sulphur takes place in the graphite felt and the sodium polysulphide collects in the surface zone of the solid electrolyte.

The invention is described below in more detail with reference to schematic drawings, in which:

Figure 1 shows a detail from an electrochemical energy is storage cell, Figure
2 shown a sulphur electrode fashioned as a halfshell, Figure 3 shown two half-shells positioned against one another, Figure 4 shows a sulphur electrode fashioned like a cylinder.

The electrochemical energy storage cell 1 depicted in Figure 1 is bounded on the outside by a easing 2 which in fashioned like a cup. Inside the caning 2 a solid electrolyte 3 in arranged which likewise has the shape of a cup. The interior of the solid electrolyte 3 serves as the anode compartment. Between the easing 2 and the solid electrolyte, an annular cavity 5 in provided which serves an the cathode compartment. The sulphur electrode 6 in arranged in this annular cavity. An can be aeon with reference to Figure 1, the entire annular cavity 5 In filled by the sulphur electrode. The sulphur electrode 6 can be fashioned In one or two parts. on the one hand there in the possibility of forming the sulphur electrode 6 from two half -shells, of which one in depicted In Figure 2, and two, as Figure 3 shows, are arranged around the solid electrolyte 3. On the other hand.there in the possibility of fashioning the sulphur electrode 6 in the shape of a cylinder, an depicted in 4 rigure 4. The sulphur electrode 6 is fashioned by employing - a -graphite felt fashioned as a mat. This involves graphite based on polyacrylonitrile or cellulose. The size of the mat depends on whether the sulphur electrode is formed by two half-shells 6K or a cylinder 6Z. One of the surfaces of this mat 6M has a web 6V placed upon it. Said web 6V is manufactured from glass fibres or ceramic fibres or a mixture of said fibres 6P. The ceramic fibres 6P are manufactured from alpha- alumina. The glass fibres 6P are manufactured from sodium- or potassium- free glass, especially E-glass or another glass having the same properties. The ceramic fibres and the glass fibres 6P have a diameter of from 8 to 13 =. Their length is chosen to be from 10 to 60 mm, preferably from 35 to 50 mm. The weight per unit area of the web 6V in from 15 to 150 g/m, preferably from 25 to 100 g/m. The web has a thickness of from 0.5 to 1 mm. The f ibres 6P of the web 6V are arranged in such a way that, after the energy storage cell 1 starts to operate, they run perpendicular to the longitudinal axis of the solid electrolyte 3. With the aid of a needling machine, the web 6V in now needled together with the mat 6M in such a way that the surface of the web 6V is in intimate contact with the entire surface of the mat 6M. Then the graphite mat 6M and the web 6V are Impregnated with sulphur and pressed to form a half-shell 6R or, if the size has been suitably chosen, the cylinder 6Z. Then two half-shells 6E or one cylinder 6Z are inserted, as depicted in Figure 4, into the cathode compartment of the energy storage cell 1 depicted In Figure 5. After complete assembly of the energy storage cell 1, which in Figure 5 is depicted only In part, the cell Is heated to a temperature of 3500C in order to start its operation. owing to this thermal action, the half-shells 6E start to expand. The thickness of the graphite mat 6M and the web 6V were chosen during the manufacture of the sulphur electrodes to be such that, upon the operating temperature of the energy storage cell 1 being reached, they expand sufficiently to be in close contact with the solid electrolyte 3 and the casing 2. As can be seen with reference to Figure 5, the graphite felt mat 6M is penetrated by radially aligned fibres 6F of the insulating web 6V. The fibres 6F are selected to be so long that they extend, in part, an far as the casing 2 of the energy storage cell 1. This causes ion-conductive paths to form. With the aid of these it is ensured that, during recharging of the energy storage cell, the sulphur is formed in the zone of the graphite felt 6M, while the sodium polysulphide collects in the surface zone of the solid electrolyte 3.

Patent Claims 1. Electrochemical energy storage cell based on sodium and sulphur, having an anode compartment and a cathode compartment which are separated from one another by an alkali metal ion-conductive solid electrolyte and are bounded, at least zonally, by a metallic easing, there being arranged in the cathode compartment - ' a sulphur electrode which has an insulating zone and an electron-conductive zone 10, characterized in that the adjoining surfaces of the zones - -- and are bonded together without gaps, and in that the electron-conductive zone --- is penetrated, in part, by ion-conductive paths of the insulating zone is 2. Electrochemical energy storage cell according to Claim 1, characterized in that the electron- conductive zone consists of a mat made of graphite felt based on polyacrylonitrile or cellulose.
3. Electrochemical energy storage cell according to either Claim 1 or 2, characterized In that the insulating zone in formed by a web which is made from ceramic or glass f ibres or f rom a mixture of these two fibres.
4. Electrochemical energy storage cell according to Claim 3, characterized in that the ceramic f ibres are manufactured from alpha-alumina.
5. - Electrochemical energy storage cell according to Claim 3, characterized in that the glass fibres are manufactured from chemically resistant C-glass or sodium- and potassium-free glass, E-glass.
6. Electrochemical energy storage cell according to any one of Claims 3 to 5, characterized in that the f ibres -, of the insulating zone have a diameter of from 8 to 13 gm and a fibre length of from 10 to 60 =m, and in that the weight per unit area of the insulating zone -, is. from 15 to 150 g/m and the insulating zone at least has a cloth thickness of from 0.5 to 1 =m.
7. Electrochemical energy storage cell according to any one of Claims 1 to 6, characterized in that the 7 - ion-conductive paths which in paru penetrate the electron-conductive zone are f ormed by the glass and/or ceramic fibres
8. Electrochemical energy storage cell according to any one of Claims 1 to 7, characterized in that the graphite felt mat and the insulating web 1 are needled together over their entire joined-together surface zones.
9. An electrochemical energy storage cell substantially as herein described with reference to the accompanying drawings.