Shunt Current Elimination for Series Connected Cells

The subject invention is related to U.S. Pat. No. 4,197,169, entitled: SHUNT CURRENT ELIMINATION AND DEVICE, issued Apr. 8, 1980, and to copending U.S. patent applications, Ser. Nos. 97,194; 122,193; 122,706; and 144,679, respectively filed on Nov. 26, 1979; Feb. 19, 1980; Feb. 19, 1980; and Apr. 28, 1980; all are assigned to a common assignee.

The teachings of these inventions are meant to be incorporated herein by way of reference.

This invention relates to a method and apparatus for the elimination of shunt currents in electrochemical systems having a plurality of cells connected in series electrically and hydraulically.

The phenomenon of shunt currents is well known and occurs in electrically connected series cells. Shunt currents are a result of conductive paths through the electrolyte shared by adjacent groups of cells of the system.

The elimination of shunt currents has been recently described with respect to systems having a plurality of cells that are electrically connected in series and hydraulically connected in parallel. The shunt currents in such systems can be effectively eliminated or reduced by passing a protective current through a common manifold of the system, in a direction the same as the shunt currents and of a proper magnitude to effect elimination. The above teaching is the subject of U.S. Pat. No. 4,197,169, entitled: Shunt Current Elimination and Device; issued: Apr. 8, 1980; inventors: Markus Zahn, Patrick G. Grimes, and Richard J. Bellows.

Some of the teachings of this patent apply to the present invention and inasmuch as they provide an understanding, are meant to be incorporated herein by way of reference.

The invention for which Letters Patent is presently sought involves the elimination and/or reduction of shunt currents in electrochemical systems having a hydraulic series configuration, i.e. electrochemical systems wherein the cells are hydraulically connected at least in part in series, and do not necessarily enjoy the convenience of a common electrolyte-carrying manifold.

Such configured systems have severe shunt current effects. Shunt currents in such systems are not easily eliminated due to the lack of commonality of the hydraulic pathways.

The invention pertains to a method and device for eliminating and/or reducing shunt currents in electrochemical systems having a plurality of cells that are electrically connected at least in part in series, and are hydraulically connected at least in part in series.

Hydraulic series connected cells have shared electrolyte in the intercell conduits connecting adjacent cells. Such shared electrolyte gives rise to electrical electrolytic pathways between the adjacent cells, which paths allow shunt currents therebetween.

The electrochemical systems of this invention have at least two adjacent intercell conduits, which are inventively connected by an electrical bypass. Shunt currents which are created in the shared electrolyte of these intercell conduits is effectively reduced by passing a protective current through the electrical bypass in a direction the same as the shunt currents and of a magnitude which will reduce, if not eliminate them.

The electrical bypass may be in the form of an electrical conductor or a porous, electrolytically conductive electrolyte-carrying plug disposed or connected across the adjacent intercell conduits.

For purposes of this invention, the term shared electrolyte shall mean that portion of the electrolyte contained in an area of commonality to the adjacent cells; the electrolyte being a physical continuum between such cells.

The electrochemical systems of this invention may be those wherein the electrolyte is static within the system or is circulated through the system, as shown in the U.S. patent to Venero, No. 4,105,829.

As used herein the term "electrochemical devices" or "electrochemical systems" shall be meant to include but not limited to photoelectrochemical devices such as water photolysis cell devices, photogalvanic cell devices, liquid solar cell devices and to include other electrochemical devices such as batteries, fuel cell devices, chloralkali cell devices, metal-air devices, sea water batteries, electrolyzers, electrochemical synthesizers, and electrowinning devices, as well as other devices employing cathodes, anodes, electrodes and common electrolytes, ionic conductors and plasmas including bipolar and monopolar multicell devices, and including devices having a plurality of electrolytes (e.g. catholytes and anolytes).

It is an object of the invention to provide an improved method and device for shunt current elimination and/or reduction in electrochemical systems having a plurality of cells that are electrically and hydraulically connected in series;

It is another object of this invention to provide a method and device for shunt current elimination in hydraulically series connected cells of an electrochemical system, wherein an electrical bypass is provided between adjacent intercell conduits, and a protective current is applied thereto.

These and other objects of the invention will be better understood and will become more apparent with reference to the following detailed description considered in conjunction with the accompanying drawings briefly described below:

FIG. 1 illustrates in schematic form a typical monopolar electrochemical system of the type having a plurality of cells hydraulically connected in series and which generates shunt currents.

FIGS. 1a through 1d are alternate embodiments of the invention, showing in schematic form various ways of arranging for an electrical bypass with protective current being applied thereto;

FIG. 2 is a schematic view of a typical bipolar electrochemical system of the type having a plurality of cells hydraulically connected in series and which generates shunt currents;

FIG. 2a is a schematic view of the invention as applied to the bipolar system of FIG. 2;

FIG. 3 is a schematic diagram of the electrochemical system of FIG. 2 utilizing another embodiment of the invention; and

FIG. 4 is an electrical analogue of the electrochemical system shown in FIG. 1.

Generally speaking, respective monopolar and bipolar electrically connected battery systems as typically shown in FIGS. 1 and 2, will develop shunt currents (arros 5) in the electrolyte of the intercell conduits 11 between the cells 2, 4, 5, 8, 10, etc. The electrolyte shared by adjacent cells 2;4, 4;6, and 6;8 etc. respectively, disposed in the interconnecting conduits 11, gives rise to shunt currents between each cell pair.

If an electrical bypass 20 (FIGS. 1a-1d and 2d) is placed across the intercell conduits 11 of the hydraulic series connected systems, and the appropriate protective currents are passed across the electrical bypass 20, shunt currents can be reduced or eliminated. These protective currents are applied in the direction of the resulting shunt currents and are of sufficient magnitude to reduce or null the shunt currents. These protective currents pass through the alternate regions of electrolyte 19 and electrical bypass connectors 20 (FIGS. 1a-1d and 2d). The electrical bypass connector 20 may be an electrolyte-containing porous plug 25, as shown in FIGS. 1d or 2d, which plugs 25 are fluidically connected across respective adjacent intercell conduits 11, and which allow ions to pass therethrough, but which restrict electrolyte flow. Membranes (not shown) can also serve a similar purpose.

The electrical bypass 20 can also be an electrical conductor 26 to which current is directly applied via electrodes 22 and 24 (typical), as shown in FIGS. 1a through 1c. FIGS. 1a and 1c illustrate alternate ways to electrically connect the bypass conductors 20. Redox reactions will occur at the points of contact between the electrodes 22 and 24 and the (typical) electrolyte in the intercell conduits 11.

The voltage drop through the electrolyte in the intercell conduits 11 should approximate or equal the voltage of the cell beneath it, which is Vo+IR.sub.e, wherein Vo is the open circuit cell voltage, I is the current, and R.sub.e is the effective internal resistance of each cell. Reference should be made to the electrical circuit of FIG. 4, which is the analogue of the battery system of FIG. 1.

The resistance through each intercell conduit 11 is given as L.sub.m, such that the current Sm in each conduit is:

The same current passes through the electrical bypass 20, whose resistance is given as C.sub.m, such that the current V.sub.c through the bypass 20 is:

The current across the entire system of FIG. 1, from electrodes 28 to 30 is then (with N even) given as: ##EQU1##

This is the same condition for the electrically series connected cells with parallel hydraulic connections as shown in aforementioned U.S. Pat. No. 4,197,169. Therefore, the power requirements will be the same for either system configuration.

The power requirements for hydraulically series connected systems may be reduced by making C.sub.m less resistive than L.sub.m by using electronic conductors as short paths for C.sub.m. Power requirements may thus be reduced by as much as one-half.

The protective scheme of this invention may also be extended to the system configuration using tunnels 32 as depicted in FIG. 3, and as previously described in U.S. patent application Ser. No. 97,194.

There can be two methods of shunt conduction: through the electrolyte in the conduit, or additionally through the conduit walls (if they are conductors).

Modern practice uses a plastic pipe conduit walls. Older practice has sometimes used metal pipes with or without glass interruptors to increase the resistance.

The foregoing teachings can be applied to either case. Also, the aforementioned teachings can apply to a system comprising of multiple sets of cells, each set having cells connected hydraulically in parallel, with each set connected hydraulically in series.

The foregoing may include devices such as a magnetohydrodynamic device wherein the electrolyte is a hot gas plasma ionic conductor. For purposes of definition, therefore, electrolyte is herein meant to include plasmas.

Having thus described this invention, what is desired to be protected by Letters Patent is presented in the following appended claims.