FI63500C - LADDNINGSBAR ELEKTRISK ACKUMULATORCELL MED MINST EN ZINKANOD - Google Patents

Description

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Sweden-Sweden (SE) 7508110-9 (71) Aktiebolaget Tudor, S-172 8l Sundbyberg, Sweden-Sweden (SE) (72) Otto von Krusenstierna, Stockholm, Mats Reger, Akersberga,

Sweden i-Sverige (SE) • (7 ^) Oy Borenius & C: o Ab (5¾) Rechargeable electric battery cell with at least one zinc anode - Laddningsbar elektrisk accumulatorcell med minst en zinkanod

The invention relates to an electric battery cell with at least one cathode and at least one zinc anode. There is a septum or spacer between the cathode and the anode, in addition to which the cell contains an alkali electrolyte with a zinc concentration so high that when the battery cell is fully charged, the electrolyte contains solid zinc oxide. The anode and / or spacer member are adapted to oscillate in or parallel to the plane of the electrode.

The zinc anodes in the alkali electrolyte are already known in combination with various cathodes, e.g. cathodes containing nickel oxide and silver oxide. Zinc anodes have several advantages, e.g., high half-cell potential, high power-to-weight ratio, and low cost, compared to alternative anode materials. However, there are some problems associated with the use of zinc anodes, particularly with respect to cell life and the need for large amounts of electrolyte. These problems are related to the special properties of the zinc in the early electrolyte. Zinc electrodes are so-called. soluble electrodes, i.e., in connection with the discharge reaction, zinc forms electrolyte-soluble reaction products which leave the electrode. Zinc is primarily formed by zincate ions, which can then further react in the electrolytes. This produces zinc oxide, which is much less soluble in the electrolyte than zinc oxide, so that zinc oxide precipitates as a solid. The main reactions associated with zinc electrode discharge and zinc oxide precipitation are

Zn + 40H "= Zn (OH) 42" + 2e "

Zn (OH) 2 s ZnO + H 2 O + 20H "

Other reactions and other types of ions occur, but the above are completely predominant and are sufficient for this presentation.

The problems with zinc electrodes are due to the fact that when zinc re-precipitates on the electrodes, zinc dendrites are widely formed, which tend to grow up to the counter electrode and then short-circuit the cells. This is also facilitated by the tendency of the zinc material to accumulate at the edges of the electrode, and in particular at the lower edge, so that redistribution to the active material on the surface of the electrode takes place during the charging and discharging cycles.

Various methods have been tried to solve these problems. The use of semipermeable membranes between zinc electrodes and counter electrodes has become very common. These membranes are so dense that the protruding growth of zinc dendrites is hampered. Numerous additional materials, both organic and inorganic, have been tried in the electrolyte, membrane and electrodes. These efforts have led to significant improvements in cells equipped with zinc electrodes, but the results are still unsatisfactory. Various attempts have also been made to influence the redistribution of the active material on the electrode surface. One way is to construct the cell in such a way that flows and diffusion in the electrolyte are prevented as much as possible, in order to cause the zinc to reprecipitate on the same surfaces from which the zinc dissolves during discharge. However, this quite significantly restricts access to the electrolyte, the consequences of which are illustrated below. Another way to solve the problem of distribution of the active material is to pump the electrolyte so that it circulates in the cell. However, this requires price-increasing and space-consuming auxiliary systems with pumps, piping, etc.

3 63500

Zinc electrodes also tend to passivate. The mechanisms leading to this and their causes have not been fully elucidated, but the presence of zinc oxide particles in the active zinc material is generally thought to be an essential cause of passivation. These particles isolate some parts of the zinc material from participating in electrochemical processes, resulting in an increase in the load on other parts of the electrode. To avoid this phenomenon as thoroughly as possible, the amount of electrolyte has been kept so high that the zinc released from the electrode may be present in the electrolyte dissolved. This has led to the need for relatively large amounts of electrolytes, but still it has not been possible to completely avoid the precipitation of zinc oxide. Zincate ions decompose slowly to form zinc oxide. The reaction mechanisms have not been fully elucidated, but as a result of this decomposition, the formation of zinc oxide in the electrolyte cannot be completely avoided. The electrolyte can be strongly supersaturated with sinate ions and this method is used in battery cells, but the electrolyte levels are still too high. In order to remove the zinc oxide inevitably present in the electrolyte, e.g. proposed recirculation of electrolyte from pumping through a filter in which zinc oxide would be filtered out.

The invention relates to a chargeable electric battery cell having at least one zinc anode and an alkaline electrolyte, and in which the anode and / or the spacer element between the anode and the cathode are adapted to oscillate in the plane of the electrode or parallel thereto. The difficulties associated with efforts to keep the electrolyte free of zinc oxide have been explained above. However, this is theoretically possible in known cells and is probably also practically possible in fully charged, relatively new cells. Such cells are of course not within the scope of the invention, since according to a characteristic feature of the invention the total amount of zinc in the cell corresponds to at least 200 g of zinc oxide per liter of electrolyte, the zinc concentration of the electrolyte being so high that It has proved possible to use in the cells according to the invention electrolytes # which contain zinc oxide in very large amounts, even to such an extent that the electrolyte is poorly flowable due to its consistency. The electrolyte contains at least 200 g of zinc oxide, preferably 250 to 400 g of zinc oxide per liter of electrolyte when the cell is discharged. However, zinc oxide levels greater than 600 g / l have been successfully tested. Particularly good results have been obtained in the case where the oscillating component is provided with eliminations which cause the electrolyte to be pumped between the electrodes. This means that the electrolyte performs both a reciprocating motion and a consequent motion which results in a circulating flow between the upper and lower parts of the electrode surfaces.

Fig. 1 shows a cell according to the invention and Fig. 2 shows conceivable different embodiments of a spacer for vibrating between the electrodes of the cell. In the cell shown in Figure 1, the anodes are arranged to oscillate. The spacer member shown in Figure 2 has an outer edge 1, a fastening member 2 and spacer strips 3, 4, 5 and 6. These strips, which are suitably, though not necessarily, made identical throughout the spacer member, may be one of the four different embodiments shown in the figure. This causes, in addition to the reciprocating movement of the electrolyte, a "net flow" directed either upwards or downwards. The oscillation frequency is suitably 1 ... 500 Hz and the amplitude is selected with respect to this so that the linear velocity of movement at least at some point in the upward and downward movement is about 20 cm / sec. The amplitude is suitably about 4 mm and the frequency about 50 Hz.