Novel Carbon Compositions, Methods Of Production, And Use

Abstract

An improved electrode material for electrical energy storage devices is provided by heating a carbonaceous material to provide a charred residue, then treating this charred residue in a fused salt bath under reducing and oxidizing (in the absence of oxygen) conditions. The resulting material contains occluded salts and these may, in a preferred embodiment, be removed.

Description

This invention relates to novel carbon compositions; and to methods of production. Also, this invention relates to an energy storage device utilizing one of the novel carbon compositions of the present invention as an important component thereof.

CARBON COMPOSITIONS DEFINED

Carbonaceous or carbonizable materials are plentiful in natural form. When these materials are heated in the absence of air, several products can be formed depending upon the conditions such as temperature, pressure and the like that are used. The products that can be produced include diamond, graphite, cokes and chars.

The carbon compositions of this invention are prepared from those of the above several products which have had a thermal history within the range of about 500.degree. C. to about 1,250.degree. C. Particularly useful precursors are chars prepared by heating carbonaceous or carbonizable materials to a temperature in the range from about 500.degree. C. to about 1,250.degree. C.

Carbonaceous or carbonizable materials occur in many forms including wood, coal, petroleum, pitch, and the like. However, low-temperature-produced chars prepared from these plentiful substances contain many undesirable impurities, introduced either by absorption, absorption, chemical occlusion or other, which render them relatively useless for many applications including those hereinafter described.

Therefore, these low-temperature carbon chars must be refined and treated to remove the impurities, and/or have materials added to them either after on concomitantly with purification, to thereby convert them to a more highly useful form. The resulting, unique carbon compositions and a method for their formation constitute an important part of the present invention and provide a substantial advance to the art.

APPLICATIONS - ENERGY STORAGE DEVICES

The novel carbon compositions contemplated by the present invention contain many potential applications including chemical reaction catalysts, sensing elements for electrical control units for both industrial and home utility, and as electrodes in energy storage systems, batteries, capacitors, fuel cells, and the like.

One especially interesting and important use for novel carbon compositions produced in accordance with the present invention is as an ion absorber and electron conductor in an electrical energy storage device where carbon electrodes have heretofore been used.

In accordance with the present invention, a particular application of the novel carbon compositions is as electrodes in novel single and multicell capacitor-battery energy storage devices.

The novel capacitor-battery storage device possesses the known functional advantages of conventional chemical storage batteries and conventional capacitors but not of their disadvantages.

Specifically, a conventional capacitor is able to store energy quickly -- on the order of seconds or at most minutes for charging, but suffers the disadvantage that it stores very little energy per unit size. Conversely, a chemical battery is able to store larger amounts of energy per unit size, but suffers the disadvantage of a relatively slow charging rate.

The capacitor-batteries, as contemplated by the present invention, provide both the quick energy storage characteristic of the conventional capacitor, and the high-level energy storage characteristic of the conventional chemical storage battery. Thus, capacitor-batteries have the advantageous characteristics of both conventional capacitors and conventional chemical storage batteries but none of the major defects of these devices. Accordingly, the capacitor-battery device is quickly rechargeable to high levels of energy storage for greater utility than either the conventional capacitor or the conventional chemical storage battery.

CONTRIBUTION TO THE ART

Therefore, a unique electrode for use in capacitor-battery storage devices and a novel capacitor-battery energy storage device utilizing such electrode as a component part thereof would also provide a substantial advance to the art.

Accordingly, it is an important object of the present invention to provide novel carbon compositions.

A further object is to provide a method for producing novel carbon compositions, wherein precursor, activatable chars are converted to "modified" structures having unexpected utility in the modified state.

A further object is to provide novel electrodes for electrical energy storage devices.

A further object is to provide a novel capacitor-battery energy storage device.

A further object is to provide a novel electrical capacitor-battery utilizing as an electrode or electron-conducting component, a novel carbon composition of invention.

A further object is to provide a method for producing novel carbon compositions involving oxidation and reduction of precursor, activatable chars in molten salt electrolytes, whereby materials from the molten salt electrolytes are adsorbed into the carbon structures to render them more highly useful than activatable chars not so treated.

A further object is to provide a novel electrical capacitor-battery storage device utilizing an electron conductor of novel carbon composition in combination with a fused salt electrolyte wherein the novel carbon composition is partially produced by pre-use cycling in the cell to cause the occlusion therein of certain elements of the molten salt to produce unexpectedly active electron storage members, surpassing in capacity the prior art analagous members of carbon, wherein it was postulated that surface area was the principal factor contributing to high levels of energy storage.

Other objects of this invention will appear in the following description and appended claims, reference being had to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views.

FIG. 1 is a graph illustrating electrode capacity phenomena that have been discovered in accordance with the present invention;

FIG. 2 is an isometric view, partly broken away in section, of capacitor-battery storage cell made according to the present invention;

FIG. 3 is an isometric view of a bipolar electrode unit, usable in a cell of the type shown in FIG. 2;

FIG. 4 is a graph illustrating electrode capacity phenomena obtained in the run of example 6;

FIG. 5 is a graph illustrating electrode capacity phenomena observed in the preconditioning of a carbon material to produce products within the scope of the present invention in accordance with example 7, wherein the sweep was made first in the more negative direction;

FIG. 6 is a graph illustrating electrode capacity phenomena observed in the preconditioning of a carbon material in accordance with example 7a wherein the sweep was made first in the more positive direction; and

FIG. 7 is a graph illustrating electrode capacity phenomena observed in the preconditioning of a carbon material in accordance with example 7b, wherein the carbon was previously treated by vapor phase chlorination.

Before explaining the present invention in detail it is to be understood that the invention is not limited in its application to the particular construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced and carried on in various ways. Also, it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

THE NOVEL CARBON COMPOSITION AND ITS PRODUCTION

The novel carbon compositions of the present invention can be characterized by the terminology "selected carbon polymers". Further, the novel carbon compositions of the present invention can be identified by chemical analysis, and also perhaps equally importantly, as will be discussed hereafter, by the method of production inasmuch as the chemical analysis and method of production seem to be inextricably intertwined with one another.

Still further, it should be pointed out that the novel carbon compositions of the present invention exist in two forms:

1. The form in which it has electrochemically associated with it certain ingredients from a molten salt bath produced by cycling at a predetermined voltage range in such bath. This cycling converts the carbon into an unexpectedly easily reversible charge collector of unusually high capacity over an unexpectedly broad potential span as the result of the electrochemical association with it of certain constituents from the molten bath.

2. The form wherein the carbon compositions has been desalted following the electrochemical-cycling treatment, with the resultant retention of the unique carbon structure that has been developed during the cycling, irrespective of the occlusion therein of component parts of the salt.

Chemical analysis. The quantitative chemical analysis of the electrochemically reacted material, with salt from a molten bath of sodium chloride and potassium chloride, is as follows:

PERCENT __________________________________________________________________________ CONSTITUENT BROAD SPECIFIC __________________________________________________________________________ Na 10-13 11.7 K 18-21 19.6 Cl 29-31 29.0 C Balance

The quantitative chemical analysis of the carbon material of invention, made by desalting the above material, is as follows:

CONSTITUENT PERCENT __________________________________________________________________________ C 87.56 H <0.10 Cl 5.51 Ash 1.52 O 5.31 (by difference) Surface Area 256 square meters per gram.

DEFINITIONS

Oxidation: In the present invention, oxidation is used in the broad sense to denote the increase in positive valence or decrease in negative valence of any element in a substance. On the basis of the electron theory, oxidation is a process in which an element loses electrons. In a narrower sense, oxidation means the chemical addition of oxygen to a substance.

Reduction: In the broad sense, reduction is the decrease in positive valence or the increase in negative valence of an element. In the narrow sense, reduction means the decrease in the oxygen content, or the increase in the hydrogen content, of a substance.

Definitions taken from Handbook of Chemistry, Lange, 10th edition, 1961, McGraw-Hill Book Company, Inc.

THE METHOD OF PRODUCTION

Basically, the steps involved in the method are as follows:

Step I. Heating a carbonaceous or carbonizable material in a nonoxidizing atmosphere at a temperature in the range of about 500.degree. to about 1,250.degree. C. to form a char.

It has been found that carbons in accordance with the present invention can be made of activated petroleum coke, wood char, activated sodium lignosulfonate char, activated bituminous coal, polyvinylidene chloride char, polyacrylonitrile char and the like. The feature which is common to all of these materials is their low temperature of preparation. None of these carbons has been heated above about 1,100.degree. C.

A lower limit can be set on the temperature of preparation because the carbon must be conducting. Conductivity in chars or carbonized materials ordinarily begins around 600.degree. or 700.degree. C., although in certain specific instances, for example polyvinylidene chloride char, conductivity becomes appreciable at temperatures around 500.degree. C. In a definitive sense then, any polymer carbon that has been prepared between the temperatures of about 500.degree. C. and about 1,250.degree. C. is to be included within the scope of the present invention.

In general, these carbons can be characterized by their X-ray diffraction patterns, which are distinctly different from graphite. Graphite is characterized by very sharp diffraction lines, while the low-temperature polymer carbons are characterized by very diffuse diffraction bands. In fact, in many instances, very flat diffraction patterns which indicated very low crystallite concentration are obtained. Upon heat treatment, the flat patterns of the low-temperature carbons are gradually converted in stages to the crystalline graphite type of diffraction pattern.

Slightly higher temperature carbons, which begin to show a substantial organization as evidenced by their diffraction patterns do not exhibit sufficient capacity to be economically attractive and could not compete with low-temperature carbons.

Step II. The selected charcarbon is next pressed and bonded into electrode form.

Step III. The charcarbon is then treated by both oxidation and reduction to remove therefrom certain occluded impurities such as ash, oxygen, nitrogen, etc. to produce a selected carbon polymer. This can be done by:

A. oxidizing first, reducing, and then reoxidizing to produce the selected carbon polymer; or

B. reducing first and then oxidizing to produce the selected carbon polymer.

Oxidizing as contemplated above is to be understood as a reaction conducted in a nonoxygen-containing atmosphere, such as a chlorine gas treatment of the charcarbon in a closed chamber.

In accordance with the present invention, the oxidation-reduction operation can be conducted by cycling the charcarbon electrode in an electrochemical cell or equivalent environment. Although a cell containing a LiCl--KCl eutectic melt has given good results, other molten salt electrolytes can be used. This cycling accomplishes a two-fold effect on the carbon material as follows:

1. It modifies the structure of the porous carbon material in an unexpected, and as yet unexplained way to produce a novel material of high electrical charge-holding capacity.

2. It produces an electrochemical reaction between the carbon and the fused eutectic in which the electrical conditioning is effected.

It is to be noted with respect to this exemplary step of the method that a selected voltage range is chosen to produce the unexpected structure. Therefore, in detail, step III of the exemplary method is as follows:

The carbon from step II is immersed in a fused lithium chloride-potassium chloride eutectic melt or equivalent electrolyte, at a temperature in the range of about 350.degree. C. to about 850.degree. C.

The carbon is for this purpose connected to a source of electrical current and is thus made an electrode in a circuit, another electrode also being immersed in the electrolyte to provide a complete circuit.

Thereafter, the electrode is charged in both positive and negative directions. In the positive direction, the carbon is charged to at least - 0.3 volt with respect to chlorine evolution. From a practical point of view this can be extended to the point at which halogen evolution becomes prohibitive. Then in the negative direction, the carbon is charged to at least -2 volts with respect to chlorine evolution. The negative side can be extended to the -3-volt level.

The order in which these reactions are carried out is not to be considered limiting.

Charging the carbon in the positive direction apparently removes oxygen from the polymer as carbon oxides, both carbon monoxide and carbon dioxide. Hydrogen would also be stripped from the electrode as HCl in a chloride melt or as HBr in a bromide melt.

It is not certain what the effect is when taking the carbon in the negative direction, but an electrochemical reaction does occur between the melt and the chlorinated carbon at some point between about -1.5 and -2.3 volts. Subsequent reoxidation, when accomplished, puts the carbon in condition for use as an electrode.

These steps amount to electrochemical oxidation and reduction of the carbon and are effective to remove all of the oxygen and most of the ash, leaving a novel carbon polymer structure.

Both oxidation and reduction must be accomplished in order to put the carbon into the unique compositional form. Thus, oxidation alone, as by charging the electrode in one direction, still requires reduction by charging the electrode in the reverse direction.

Relative to the foregoing electrochemically treated product, it is to be clearly understood that the product is distinctly different from simple mixtures of the melt and the carbon.

When conditioned in this way, electrodes having characteristic capacities are obtained. Although the detailed characteristics of the capacity curve depend upon the source of the char, the general characteristics of the curve are common, as shown in FIG. 1. Thus, there is a zero point of charge which appears somewhere in the vicinity of - 0.7 volt, a maximum capacity in the neighborhood of - 1.8 to -2 volts, and frequently, with a shoulder in the neighborhood of -1 to -1.5 volts.

Between zero volts and the zero point of charge, the charge storage is probably as an electrical double layer, involving primarily adsorption of the anions. From the zero point of charge to more negative potentials, the adsorptions appear to be specific. The shoulder between -1 and -1.5 volts may correspond to removal of covalently bound chlorine, and the maximum at about -1.8 to about -2 volts would correspond to the specific adsorption of alkali metal ions.

EXAMPLES

The following examples relate to specific runs made in accordance with the present invention.

EXAMPLE I

Petroleum Coke

6 to 14 mesh activated petroleum coke, obtained from the Matheson Coleman Bell Company was pulverized to 200-320 mesh and 200 milliliters of the powdered coke was mixed with 75 milliliters of Durez resin No. 16470 (obtained from the Durez Plastics Division of Hooker Chemical Company). The mixture was cast into a block and dried overnight in an oven at a temperature of 40.degree. C. The oven temperature was the raised to 60.degree. C. for an additional 24 hour period. The dried block was then packed in a granular coke in an electric furnace and baked in an atmosphere of argon for a period of 20 hours. The temperature program for this 20-hour period was 2 hours at 245.degree. C., then 81/2 hours at 245.degree. C., then 2 hours up to 845.degree. C., then 3 hours at 845.degree. C., and finally 4 1/2 hours to below 235.degree. C.

The baked block subsequently was removed from the furnace. A rectangular piece of carbon 1 .times.1/2 .times.1/4 inch was cut from the block and used as a test electrode in an electrochemical cell. The electrolyte in the cell was molten lithium chloride - potassium chloride eutectic. Other electrodes in the cell included a graphite tube, bubbling chlorine, used as a chlorine reference electrode, and a lithium-10percent aluminum electrode used as the working electrode or anode.

The temperature of the cell was maintained at 500.degree. C.

The carbon polymer electrode was initially charged to 0 volta and maintained there for a period of 2 hours. The electrode potential was then adjusted to -3 volts over a period of 1 hour and then brought again to 0 volt over a similar period.

The electrical properties of the novel carbon material so formed were characterized using a potentiostatic sweep method with the results shown in FIG. 1 and table I. --------------------------------------------------------------------------- TABLE I --------------------------------------------------------------------------- PETROLEUM COKE CAPACITY

Electrode Capacity within Zone __________________________________________________________________________ Zone (meq./cc.) __________________________________________________________________________ I 0.4 II 0.06 III 0.4 IV 2.2 V 2.8 d=0.785 g./c.c. __________________________________________________________________________

The general characteristics of the capacity curve based on these data are typical of the polymeric carbon charge exchange electrodes produced and conditioned in this manner in accordance with the present invention.

The test results of several runs proved that a maximum energy storage of nearly 20-watt minute from a cell using electrodes made from activated petroleum coke can be obtained when:

1. The carbon electrode is charged in the positive direction first;

2. The conditioning is carried out at the comparatively high temperature (525.degree. C.); and

3. The conditioning is carried out over approximately a 2.8-volt range.

Typical data are set forth in the following table:

Direction Energy Temperature of Delivery at 250 .degree. C. First Charge (Watt Min.) __________________________________________________________________________ 450 + 19.0 - 17.1 525 + 19.9 - 18.8 __________________________________________________________________________

EXAMPLE II

Sodium Lignosulfonate Char

One hundred milliliters of Green Label Brer Rabbit Molasses was placed in a No. 3-AUS 1-quart Baker-Perkins dough mixer and the mixer heated by means of the steam jacket until the molasses flowed freely. Small amounts of N-BC4567 Filtchar (a sodium lignosulfonate char obtained from the West Virginia Pulp and Paper Company) were added and mixed with the molasses until the mixture was not sticky to the touch and did not cling tenaciously to the sides of the mixer. The temperature of the mixer was raised to drive off sulfur dioxide and more Filtchar added to maintain the desired consistency. Water was evaporated from the mixture until a semidry rubbery mixture was obtained.

This mixture was further dried in the Baker-Perkins dough mixer until it broke up into fairly small granular particles. The mixture was then transferred to a drying oven and dried for a period of 2 days at a temperature of 230.degree. F. The dried particles were then pulverized in a hammermill (running at 16,000 r.p.m. using a fine (0.02-inch diameter) round hole screen. The resulting powder was mixed with one-quarter of its weight of additional filtchar and this mixture was compressed into a block at a temperature of 150.degree. F. and a die pressure of 8 tons per square inch. The dried block was packed in granular coke in an electric furnace and heated in an atmosphere of argon gas for a period of 45 hours. The heating-cooling cycle was on an automatic 30.degree. curve program with a maximum temperature of 780.degree. C.

A pair of electrodes measuring 1 .times. 1/2.times. 1/4inch were cut from the baked block and inserted in a cell similar to that described in example 1.

One of the carbon electrodes was used to produce a composition of the present invention while the other was used as a working electrode.

The test electrode was charged initially to 0 volt for a period of 2 hours and subsequently to -3 volts and back to 0 volt over a period of 2 hours.

Then, the capacitance of this polymeric carbon electrode was measured by the potentiostatic sweep method with results similar to those shown in FIG. 1. The results are listed in table II below. --------------------------------------------------------------------------- TABLE II --------------------------------------------------------------------------- SODIUM LIGNOSULFONATE CHAR CAPACITY

Electrode Capacity within Zone __________________________________________________________________________ Zone (meq./cc.) __________________________________________________________________________ I 0.7 II 0.4 III 0.9 IV 2.6 V 2.5 d=0.56 g./cc. __________________________________________________________________________

The general characteristics of the specific capacitance curve of the sodium lignosulfonate char are similar to those obtained with the petroleum coke polymeric carbon electrode of example 1. The curve is subject to substantially the same theoretical interpretations.

EXAMPLE III

Bituminous Coal Char

30-S Coal Tar Pitch (obtained from the Barrett Division of Allied Chemical Company) was mixed with dry ice and pulverized to a fine powder, mixed with more dry ice and screened to give a 200 to 320 mesh powder pitch. This was mixed with an equal amount of Bituminous Coal Char (obtained from the Pittsburg Chemical Company) and compressed to a block at a temperature of 90.degree. C. at a pressure of less than 300 pounds per square inch to give a block volume of 80 percent of the loose mixture volume.

The block was packed in granular coke in an electric furnace and heated at a temperature of 500.degree. C. for a period of 36 hours, then at a temperature of 1,000.degree. C. for a period of 18 hours and finally cooled from 1,000.degree. C. to room temperature over an 18 hour period.

A rectangular piece measuring 1 .times.1/2 .times. 1/4 inch was cut from the baked block and used as a test electrode in an electrochemical cell similar to that described in example 1. However, both the reference electrode and the working electrode were graphite tubes contained in a larger Pyrex tube.

Bottled chlorine gas was bubbled through the graphite tube of the reference electrode.

The electrolyte was potassium chloride - lithium chloride eutectic. The temperature of the eutectic was maintained at 450.degree. C.

After initial charging of the last electrode to 0 volt and maintaining it there for 2 hours, the electrode was subsequently returned to -3 volts, and then back to 0 volt over a period of 2 hours. Thereafter, the capacity of the resulting carbon composition was determined by the potentiostatic sweep method and the results, again, were substantially as shown in FIG. 1 of the drawings. The actual capacity figures are listed in table III following. --------------------------------------------------------------------------- TABLE III --------------------------------------------------------------------------- BITUMINOUS COAL CHAR CAPACITY

Electrode Capacity within Zone __________________________________________________________________________ Zone (meq./cc.) __________________________________________________________________________ I 0.3 II 0.2 III 0.3 IV 1.3 V 2.2 d=0.82 g./cc. __________________________________________________________________________

EXAMPLE IV

Cocoanut Char

An electrochemical cell was constructed using a block of carbon obtained from the Pure Carbon Co., St. Mary's, Pa., and designated as Purebon FC--13, having an average particle size of about 30 microns. The block of carbon was 1/2 .times. 1/8 .times. 1 inch and was used as a test electrode in an electrochemical cell.

A second electrode of equivalent size was fabricated from lithium-18 percent aluminum alloy.

The two electrodes were placed in lithium chloride - potassium chloride eutectic and connected through an external circuit such that the cell could be charged to maximum voltage and discharged at constant current. The cell was operated with the eutectic maintained at a temperature of 425.degree. C.

The lithium-18 percent aluminum electrode has a potential of -3.36 volts at the 425.degree. C. temperature of the eutectic. Thus, when a cell comprising carbon and aluminum-lithium electrodes is charged to 3.36 volts, the carbon electrode will be at 0 volt. When the cell is discharged to 0.36 volt across the cell, the carbon electrode will be at -3 volts.

Accordingly, after this cell was assembled, it was discharged from its initial voltage of 1.8 volts to 0.36 volts. Thereafter, the cell was reversed and charged to 3.36 volts. The current at which this operation was conducted was 500 milliamperes.

The cell was operated for approximately 15 hours, or approximately 30 cycles.

Thereafter, a chlorine reference electrode was inserted into the system and the electrical properties of the carbon material formed by the electrical cycling were characterized using the potentiostatic sweep method as in the prior examples. The results were again similar to those presented in FIG. 1. The results are tabulated in table IV following. --------------------------------------------------------------------------- TABLE IV --------------------------------------------------------------------------- PUREBON FC-13 CAPACITY

Electrode Capacity within Zone __________________________________________________________________________ Zone (meq./cc.) __________________________________________________________________________ I 0.7 II 0.4 III 0.8 IV 3.0 V 4.0 d=0.90 g./cc. __________________________________________________________________________

EXAMPLE 5

Cocoanut Char

A series was run in which six cells were constructed. Each cell consisted of a chlorine reference electrode and two carbon electrodes fabricated from Purebon FC-13 having the dimensions 1/2 .times. 1/4 .times. 1 inch.

The temperature of operation was 450.degree. C.

The electrolyte was lithium chloride - potassium chloride eutectic.

The cells were each operated for about 15 hours on a cycling schedule which consisted of charging to 3 volts across the cell under constant voltage and then discharging to 1 volt across the cell at a constant current of 500 milliamperes.

At the end of the 15 hour schedule, each of the cells was charged fully. Thereafter, each cell was discharged to a predetermined voltage across the cell. Different cells were discharged to different voltage levels to provide a spread over a range corresponding to substantially the full working potential range of the electrodes.

The exact potential of each electrode was then measured with respect to the chlorine reference electrode. The two test electrodes were withdrawn from each cell and analyzed for lithium, potassium, and chloride ion content, using extraction and precipitation techniques. The balance was assumed to be carbon. The analytical results are set forth in table V following. ##SPC1##

The data set forth in table V shows that over the entire range of potential of the electrodes, the occluded components from the molten eutectic electrolyte are present in substantially the same ratio at all times. However, the total amount of occluded materials in the electrodes from the eutectic, increases slightly with decreasing potential of the electrode.

EXAMPLE 6

Hardwood Char

A cell was assembled using a test electrode prepared from a commercial carbon obtained from the Purebon Carbon Company, St. Mary's, Pa., designated Purebon FC-50, having an average particle size of about 75 microns. The electrode was 1/2 .times. 1/4 .times. 1 inch. The cell also included a working electrode of lithium-18 percent aluminum, and a chlorine reference electrode. Lithium chloride - potassium chloride eutectic was used as the electrolyte and was maintained at a temperature of 450.degree. C.

The test carbon electrode was first charged to -3 volts and subsequently taken to 0 volt over a period of 21/2 hours on a sweep potentiostat.

On the fifth cycle the data of table VI were obtained. --------------------------------------------------------------------------- TABLE VI --------------------------------------------------------------------------- PUREBONS FC-50 CAPACITY

Electrode capacity within Zone __________________________________________________________________________ Zone (meq./cc.) __________________________________________________________________________ I 1.5 II 0.6 III 0.9 IV 4.6 V 4.7 d.times.0.84 g./cc. __________________________________________________________________________

The capacity versus potential data obtained during the fifth cycle are plotted in graph form in FIG. 4 of the drawings. As shown in FIG. 4, the forward sweep from 0 volt to -3 volts on the test carbon electrode is represented by the solid line. The reverse sweep from -3 volts to 0 volt is represented by the dotted line.

The graph demonstrates the complete reversability of a reaction which occurs at -1.8 volts on the forward sweep. Thus, the capacity increases sharply at this point on both the forward and reverse sweeps.

A similar reaction occurs at -2.8 volts. However, the peak at that point is not sufficiently sharp to be observed on the reverse sweep.

THE METHOD OF PRODUCTION-- FURTHER INSIGHT

Insight into the method of production has been obtained by carrying out the preconditioning steps on the raw carbon with a controlled potential sweep apparatus. Results of several experiments show clearly that the carbon compositions of the invention are clearly different from either the starting materials or simple mixtures thereof. These conclusions are demonstrated conclusively by the following examples.

EXAMPLE 7

SWEEP FIRST IN MORE NEGATIVE DIRECTION

A cell was constructed as in example 6, using a test electrode of Purebon FC-50 carbon, obtained from the Pure Carbon Company, St. Mary's, Pa. The cell also included a lithium-18 percent aluminum working electrode and a chlorine reference electrode. Lithium chloride - potassium chloride eutectic was the electrolyte, and the temperature of operation was 450.degree. C.

The carbon test electrode was operated on the potentiostatic sweep apparatus at a rate of 10 millivolts/minute starting at 1.3 volts which was the initial potential of the cell. The sweep was made first in the more negative direction.

The results of this run are shown in FIG. 5 where the potential of the electrode is plotted as the abscissia, and the instantaneous amount of reaction is plotted on the ordinate as capacity in milliequivalents per gram of original carbon material per volt of sweep.

At the onset of the sweep, no reaction occurs. However, at a potential slightly more positive than -2 volts, a reaction begins which increases sharply at -2.5 volts and passes through its maximum rate at -2.7 volts.

On reversal, a slowly diminishing reaction is observed which causes the current to increase in magnitude, maximizing at -1.85 volts. The amount of reaction then decreases to near zero and begins to rise sharply again at -0.8 volt. Between this potential and 0 volt a gas was evolved from the test electrode.

The gas was collected, analyzed on infrared apparatus, and found to be composed of substantially equal amounts of carbon monoxide and carbon dioxide.

Upon discharging this electrode, there is a rapidly diminishing reaction passing through a minimum at -0.6 volt and then rising slowly, showing appreciable reaction in the -1 to -1.5-volt region, zone III.

A larger reaction occurs in the region -1.5 to -2.3 volts, zone IV.

A small peak occurs in the region of about -2.7 volts, zone V.

Subsequent cycling of this electrode was constant, and essentially the same as shown in FIG. 4.

EXAMPLE 7a

SWEEP FIRST IN MORE POSITIVE DIRECTION

FIG. 6 illustrates the results of a run on the order of that conducted in example 7, but with the exception that the sweep was made first in the more positive direction.

In this run, no reaction occurred until the carbon electrode reached the potential of -0.3 volts, at which point an abrupt reaction began. During this abrupt reaction, a gas was also evolved that was analyzed and found to be made up of approximately equal parts of carbon monoxide and carbon dioxide.

This reaction is essentially irreversible as evidenced by the reverse sweep of FIG. 6, where the current drops rapidly to zero. Nothing happened until the electrode potential had reached -1.6 volts. At this point a slow reaction began which accelerated at about -2.2 volts and reached a maximum at -2.35 volts. This reaction then dropped rapidly and a second maximum occurred at -2.8 volts.

The reverse sweep was very similar to the reverse sweep of example 7, as shown in FIG. 5, but showed a slightly larger reaction in the -1.75-volt region and slightly less reaction in the -0.8-volt region.

EXAMPLE 7b

CHLORINE TREATMENT

Further insight into the method of production can be obtained by treating a raw carbon electrode in an atmosphere of chlorine gas for a period of 1 hour at room temperature. The carbon used was Purebon FC-50.

The results obtained from a cell constructed using this material as a test electrode are shown in FIG. 7.

In this run the reaction was similar to that of example 7, as shown in FIG. 5, except that the peak which occurred at -2 volts in example 7, FIG. 5, is shifted to -2.35 volts and is substantially enhanced.

The peak that occurred at -2.8 volts in example 7, FIG. 5, is virtually nonexistent in this run, FIG. 7.

In toto, these results show that this portion of the carbon composition synthesis, i.e. taking the raw carbon to 0-volt results in the removal of oxygen from the carbon polymer structure and the replacement of the oxygen with a chlorine structure. This reaction may be represented by the following equations.

1. A-O+Cl.sup.- CO, CO.sub.2 +ACl wherein A represents a raw carbon material.

where B represents a new carbon structure.

Apparently this reaction proceeds with near perfect stoichiometry, i.e., two atoms of chlorine replace one atom of oxygen.

Either the chlorine structure or the oxygen structure can be reduced at sufficiently negative potential to produce a totally new material. The chlorine structures are reduced at -2.35 volts while the oxygen structures are reduced at -2.8 volts. These reductions are essentially irreversible. At no time during subsequent cycling are reaction maxima observed that could correspond to these same reactions.

Apparently it does not matter whether the chlorine structure is reduced or the oxygen structure is reduced, because in the end, the same novel carbon material is produced.

This may be restated as follows: Thus, the carbon can be reduced electrochemically by charging it to -3 volts; and then oxidizing it by charging it to 0 volt. Alternatively, it may be oxidized by charging to 0 volt and then reduced by charging it to -3 volts.

As a further alternative, if desired, the carbon can first be oxidized in a chlorine atmosphere and then reduced in an electrochemical cell. Presumably this could be extrapolated to a process taking place entirely outside a cell as long as proper energetics for the reactions could be maintained.

Novel carbon structure B, in the equation above, must still be oxidized to 0 volt or greater, preferably in an electrochemical cell, to produce the final compositions of the present invention. After such treatment, the novel product produced is then reversible on continued cycling, as in an electrochemical storage application.

THE POSSIBILITY OF OTHER SALT COMPOSITIONS AS REDUCTANTS FOR THE CARBON POLYMER

The electrochemical treatment as described in the foregoing examples can be carried out in electrolytes other than lithium chloride - potassium chloride eutectic. However, for reasons that will become apparent, this particular electrolyte is preferred. The primary requirement for the electrolyte is that it must support a wide potential span. Furthermore, the range between about -0.2 volt and about -2.0 volts with respect to chlorine evolution must be readily attainable in the electrolytes under consideration.

At least in principle, the electrolyte need not be a fused salt. Thus, although particular solvents have not been discovered to date, the reactions of the present invention can conceivably be carried out in a nonaqueous solvent containing dissolved lithium or potassium chlorides, for example.

Further, the electrolytes may be other than the eutectic compositions. For example, novel carbon compositions within the scope of the present invention have been prepared successfully in molten potassium chloride as well as molten lithium chloride. In each of these cases, similar reactions were observed and similar products were obtained.

Within the extended scope of the invention the reaction may be carried out, at least to a degree, in fluoride and bromide melts, in addition to chloride melts. Iodide melts do not at present appear to be operable.

The chloride electrolyte is preferred for two reasons:

1. The carbon electrode is not attacked at an appreciable rate at the most positive potentials attainable; and

2. The attainable positive voltage in chloride melts is sufficient to oxidize the carbon structure.

Fluoride melts can be used to oxidize the carbon, but at potentials near -0.3 volts, perfluorocarbons begin to be evolved.

Bromide melts, on the other hand, do not allow a sufficient degree of oxidation of the carbon structures to give the highest yields of the desired products.

The cationic components of the melt may be any or all of the alkali metals (Group Ia of the Periodic Table), the alkaline earth metals (Group IIA) or the members of Group IIIb including the members of the rare earth and actinide contraction series. These materials have in common the property that the cation will not be discharged at an iron or other inert cathode at potentials greater than -2 volts with respect to chlorine. Thus, salts containing these cations will not be decomposed under the conditions of operation of the present invention.

These conclusions are substantiated by the following examples:

EXAMPLE 8

An electrochemical cell was constructed using two electrodes made from Purebon FC-13 carbon of 1/2 .times. 1/4 .times. 1 inch-dimension. The cell also included a chlorine reference electrode.

The electrolyte was molten potassium chloride.

The temperature of operation was 850.degree. C.

The cell was operated on a 0 to -3.3-volt span across the cell on a schedule consisting of a constant voltage charge and constant current at 500 milliamps discharge over a 15 hour period (overnight).

At the end of this schedule, the carbon electrode that had been maintained positive throughout the cycling was connected as a test electrode to the sweep potentiostat while the electrode that had been maintained most negative was connected as the working electrode.

The cell was then cycled between 0 and -2.5 volts at a rate of 20 millivolts per minute. The results are presented in composite table VII, presented below example 14.

EXAMPLE 9

A cell as in example 8 was constructed and cycled in the same manner.

The electrolyte was lithium chloride and the operating temperature was 700.degree. C.

The results are recorded in composite table VII.

EXAMPLE 10

A cell as in example 8 was constructed and cycled in the same manner.

The electrolyte was lithium chloride - barium chloride eutectic and the operating temperature was 650.degree. C.

The results are recorded in composite table VII.

EXAMPLE 11

A cell as in example 6 was constructed. This comprised a test electrode of Purebon FC-13 carbon 1/2 .times. 1/4 .times. 1 inch, an anode of lithium - 18 percent aluminum and a chlorine reference electrode.

The electrolyte was 32 weight percent lithium chloride, 17 weight percent cesium chloride, and the balance potassium chloride.

The operating temperature was 450.degree. C.

The cycling was the same as in example 8.

The results are presented in composite table VII.

EXAMPLE 12

A cell as in example 8 was constructed and cycled in the same manner.

The electrolyte was lithium chloride-- potassium chloride eutectic.

The operating temperature was 700.degree. C.

The results are presented in composite table VII.

EXAMPLE 13

A cell was constructed as in example 6, see example 11.

This comprised a test electrode of Purebon FC-13 carbon 1/2 .times. 1/4 .times. 1 inch.

The electrolyte was 31 weight percent lithium chloride, 51 weight percent potassium chloride, and the balance was rubidium chloride.

The operating temperature was 450.degree. C.

The cycling was carried out as in example 8.

The results are presented in composite table VII.

EXAMPLE 14

This is a comparison to example 12.

A cell as in example 8 was constructed and cycled in the same manner.

The electrolyte was 50 percent lithium chloride - 50 percent potassium chloride instead of a lithium chloride - potassium chloride eutectic, as in example 12.

The operating temperature was 700.degree. C.

The results are presented in composite table VII. ##SPC2##

SUMMARY OF THE RESULTS SHOWN IN TABLE VII

Table VII affirms the point made above that a broad range of cationic components can be used in the electrolyte to provide practical and similar operation.

The following examples relate to further extensions relative to the salt compositions. Example 15 shows that the carbon can be cycled first in a chloride eutectic and then transferred to a bromide eutectic with analogous results. Example 16 shows that an operation performed entirely in a bromide eutectic produced an electrode having the same capacity as in the chloride then bromide operation of Example 15.

EXAMPLE 15

An electrochemical cell was constructed using Purebon FC-13 carbon as a test electrode of 1/2 inch.times. 1/4 inch.times. 1 inch-dimensions. The anode was fabricated of lithium-18 percent aluminum alloy.

The electrolyte was lithium chloride - potassium chloride eutectic and the operating temperature was 450.degree. C.

The electrodes were connected through an external circuit such that the cell could be charged to maximum voltage and discharged at a constant current. The cell was operated on a constant voltage charge to 3.36 volts across the cell and discharged at a constant current of 500 milliamperes down to a level of 0.5 volt across the cell.

The cell was cycled for 15 hours (overnight) approximately 30 cycles. Then the discharge for record purpose was taken at 500 milliamperes.

The electrodes were then withdrawn from the electrolyte and transferred to fresh electrolyte consisting of a lithium bromide - potassium bromide eutectic. Note that this is an all bromide eutectic.

The cell was then cycled according to the same schedule. However the charging voltage was reduced to 3.0 volts.

After cycling for 4 hours, a trace of voltage versus time was made for the record.

The results are shown in composite table VIII.

The capacities as reported in table VIII for zones II, III and IV were obtained by integrating the area beneath the discharge curve, using as reference, the potential of the lithium-aluminum working electrode.

The capacities of the test electrode were similar in both electrolytes but values were somewhat lower in the bromide electrolyte.

It was observed that the distribution within specific zones was somewhat different. In the bromide electrolyte, zone II gained capacity at the expense of zone III. This could have certain advantages in some applications particularly in an energy storage device. ##SPC3##

EXAMPLE 16

A cell was constructed essentially as in example 15 bromide--that the entire operations was carried out in lithium bromide potassium bromide eutectic. The cycling range was between 0 and -3 volts at 450.degree. C.

The cell was cycled for about 15 hours and then a discharge curve was taken for record.

The results are shown in table VIII, above.

The capacity in zone IV was the same as for the electrode of example 15. Thus, an electrode prepared and operated in lithium bromide - potassium bromide eutectic, had the same capacity as an electrode prepared in lithium chloride-- potassium chloride eutectic but operated in lithium bromide-- potassium bromide eutectic.

It will be noted that the capacity in zones II and III was however significantly reduced by comparison.

Even with these minor differences however, the similarity is clearly evident.

CONCLUSIONS

The foregoing runs comprise part of a substantial series.

Temperature Range

The results show that the temperature at which the reactions of the present invention can be conducted extend over a substantial range. Similar products have been produced at temperatures from about 400.degree. C. to about 850.degree. C. Temperatures of about 400.degree. C. to about 500.degree. C. are generally preferred for reasons of economy.

Also, the results show that best energy storage results are produced by first charging in the positive direction to about -0.3 volt relative to chlorine evolution, and subsequently cycling between about 0 volts and about -2.8 volts relative to chlorine evolution.

After about 5 to 6 cycles, the carbon reaches a steady state.

Ash content of the carbon does not appear to have either an advantageous or detrimental effect on the energy storage capacity.

THE NATURE OF THE CHARGED CARBON IN VIEW OF THE EXAMPLES

The method which is most useful for the study of a carbon structure in a fused salt is a potentiostatic sweep method in which the voltage impressed across the electrode with respect to a reference is continuously and linearly changed as a function of time. The current required to bring the system to the instantaneous potential is a direct measure of the differential capacitance of the test electrode.

The capacity measured includes the double-layer capacity along with any pseudocapacity due to reactions which occur either in the carbon surface which could be considered as a part of the double layer, or between constituents of the melt and the electrode surface.

In the carbon structures of the present invention, the primary reactions involve ions of the melt with the carbon substrate in the region of the electrical double layer.

At the extreme end of the stability range of the melt, reactions do occur at carbon electrodes which result in loss of adsorbed material from the electrode into the melt. In this region, the double-layer concept of material storage does not apply.

In FIG. 1 of the drawings accompanying this application, there is illustrated the capacity curve obtained with a pressed activated petroleum coke material according to example I. This particular carbon shows to some degree all of the possible regions of appreciable variation in the capacity curve as a function of electrode potential.

The units of the vertical or capacity axis of FIG. 1 are farads per milliliter of electrode.

The horizontal or potential axis varies from the chlorine evolution point at 0 volts to -3 volts relative to chlorine evolution.

The vertical dotted lines in FIG. 1 divide the curve into five regions, the exact nature of which are at present unknown. However, reasonable speculation is believed possible as follows:

I. The first zone, at the left side of the curve probably represents the pseudocapacity and double-layer capacity of chloride ion on the electrode surface.

II. The second region conforms to published capacity values for carbon in cryolite, i.e. about 15-20 microfarads per cm..sup.2 and includes the zero point of charge. (from "Fused Salts", McGraw Hill, 1964, H. A. Laitinen and R. A. Osteryoung, P. 271).

This area II is perhaps the only region in which truly pure double-layer absorption is involved.

III. The third region involves a slight prominence in the curve and may correspond to the desorption of covalently bound chloride.

IV. The fourth region is a region of significant alkali metal adsorption occurring near -1.8 to -1.9 volts.

V. The fifth region shows another strong adsorption that occurs at -2.7 volts.

If the assumption is valid that region III corresponds to chloride desorption, then regions IV and V correspond to excess alkali on the carbon surfaces - or electrochemically reacted and infused into the actual carbon structure.

By integrating the area beneath the capacity curve for voltage intervals from chloride desorption to the more negative regions, the numbers of adsorbed ions can be calculated. These numbers then can be related to the number of atoms present in the carbon electrode to give a relative population of the carbon atoms per adsorbed ion. This gives an indication of the surface density of charge.

Calculated in the manner indicated, the -1.9-volt maximum in zone IV corresponds to 46 carbon atoms per ion. At the -2.8 maximum of zone V there is a correspondence to 12 carbon atoms per ion. In terms of concentrations, these figures correspond to about 1.5 and 3.5 milliequivalents per cc. respectively.

The following general statements illustrate the unique aspects of the present invention.

Not all carbons perform in the manner indicated to produce the novel compositions of the present invention. For example, a graphitic carbon fails to produce adsorption of the type shown in FIG. 1 of the drawings. Source materials from which effective electrodes are produced, if heated above 1,250.degree. C. are not effective. Therefore, carbons produced by heat treatments not exceeding about 1,250.degree. C. are necessary as starting materials for the present invention.

These selected carbons all perform generally in accordance with the showing of FIG. 1. Some of the carbons fail to show a pronounced peak at 2.8 volts in region V; however, they all show substantially similar adsorption.

The quantity of charge in the 1.9-volt region varies somewhat as does the magnitude of the shoulder in the region of chloride desorption.

From the foregoing, it will be observed that possible minor variations in products falling within the scope of the present invention are therefore possible. The variations appear to depend upon the source of the carbon raw materials from which the novel products are made.

USES FOR THE PRODUCTS OF INVENTION

One of the most important uses for the carbon materials of the present invention is set forth in the latter part of this specification, e.g., an electron conductor, functioning in the nature of an electrode, for an electrical energy storage cell. Extremely high storage capacities have been displayed by the novel carbon products of the present invention in this type of use.

Further uses include: reagents in chemical reactions, catalysts for chemical reactions, and the like. These materials would function in chemical reactions as reducing agents and possibly as metallation agents. Thus, the reduction of ketones, aldehydes, etc., should occur in a highly specific fashion using these alkali-containing carbons.

Transmetallation, or the formation of alkyl or aryl lithiums from Grignard reagents or possibly by direct metallation, also seem likely.

These materials are also eligible as catalysts for base-catalyzed reactions particularly. Variation in basicity of these different voltage regions is quite large. For example, the first would correspond to roughly the pH of an alkoxide ion while the second peak would be approaching the basicity expected from a phenyl negative ion. From these latitudes of possible basicities, the latitude of reactions and the selectivity of the reactions which could be promoted are quite large.

Further applications for the novel carbon materials of the present invention would include electrodes for use in systems other than fused halides in which the pretreatment is conducted. This contemplates that the fused salt residues be removed by simple solvents. The desalted electrodes would be useful in other electromechanical energy storage systems using nonaqueous solvents or lower decomposition potential salt mixtures.

THE ENERGY STORAGE CELL ASPECT

In accordance with the present invention, use is made of the novel carbon structures alluded to above as electron conductors in energy storage cells. Thus, the use in accordance with the present invention is that of forming an electron conductor and ion-gathering surface for exposure in a nonconducting electrolyte.

It is not proposed that the novel carbons of the present invention function in accordance with the prior art theory of surface area. At the present, it is not known what the phenomenon involved is. However, it has been found that an unexpectedly high storage capacity for electrical energy is provided by utilizing a novel carbon of this invention as an electron conductor, with the carbon forming an interface component with a nonelectron-conducting medium, such as a fused salt electrolyte.

In accordance with the present invention, electrical energy is stored to an unexpectedly high order of magnitude substantially greater than that of conventional capacitors of comparable size.

Further, in accordance with the present invention it has been discovered that a greatly extended feedout of energy is provided -- as distinguished from the short, high-peak surge provided when a capacitor substantially instantaneously discharges. Thus, useful power output, of long duration, is provided by the present invention, as distinguished from the quick-surge-type pulse produced by the discharge of a capacitor.

By operating in accordance with the present invention, an electrolyte is used that makes it possible to store high-current densities and at the same time materially decrease the size of an electrical energy storage device as compared to the size of a capacitor necessary to store the same amount of energy.

THE NOVEL STORAGE CELL: FIGS. 2 and 3

Referring now more particularly to FIG. 2, there is shown an electrical energy storage cell embodying an electrode made by the present invention.

A container 10 provides a housing for the unit and serves as a storage reservoir for the fused lithium chloride - potassium chloride eutectic used as the electrolyte in the system. Suitable, the container 10 is fabricated of a heat-resistant material capable of withstanding the fused eutectic. This material must be inert relative to the eutectic, of course, and materials such as a nonporous graphite, sheet steel, sheet nickel, stainless steel alloys, ceramics, alumina, etc., will function in this application.

Since the cell illustrated operates at or above the fusion temperature of the lithium chloride - potassium chloride eutectic, means must be provided for maintaining the temperature at the levels indicated. Any suitable heating means can be utilized, such as immersion heaters or the like. For purposes of exemplary illustration, there is shown in FIG. 2 a resistance heater, designated by the reference numeral 12. If it be assumed that the container 10 is made of an electrically conducting material, it would be understood that the heater 12 must be spaced from it by an insulator. Accordingly, a layer 14 of insulating cement is placed over the outside surface of container 10 prior to the application of the heater 12. Heater 12 suitable comprises a continuous nichrome wire in coil form, wound about the container 10, over the cement layer 14, and thereby spaced from contact with the container 10. It will be understood that the heater 12 could be comprised of flat strip-type resistance units as well as the coiled wire mentioned.

To conserve heat within the unit, there is conveniently and preferably provided an external insulation sheath 16 of suitable material, such as asbestos or the like.

In the embodiment of FIG. 2, there is provided a pair of electrodes 18 and 20. At least one of the members 18 and 20 is made from a novel carbon composition of the present invention. The electrodes 18 and 20 are maintained in spaced relationship relative to one another by means of a separator member 22. This separator member 22 is suitably formed of a porous nonconductor such as asbestos cloth. Being porous, the member 22 is readily permeated by the ion-containing and conducting medium 11, namely the lithium chloride - potassium chloride molten eutectic. It is to be understood that any nonconducting, inert spacing material that is also pervious to the passage of the liquid eutectic can be used for the function of the asbestos cloth unit discussed.

Electrical energy current collectors 24 are provided in intimate contacting relationship with the electrodes 18 and 20. The current collectors 14 suitably are formed from graphite compressed into plates. Leads 26 and 28 are connected to and extend from the current collectors 24. These are adapted to be connected either to a charging circuit or to a load such as an electric motor or the like to impart power thereto. It is to be understood that the invention is not limited to the use of graphite in the current collectors 24; accordingly, tantalum metal and the like can be used to serve the current-collecting function.

The current 24 are intimately contacted with or joined to the electrodes 18 and 20. This provides an ideal electrical connection for proper functioning of the unit.

To provide an assembled unit, it will be understood that the electrodes 18 and 20 and the separator member 22 can be fastened together by any suitable means as nonconducting bolts extending through the assembly.

THE ELECTROLYTE

As has been pointed out before, the novel carbon structures of the present invention are derived by an electrochemical oxidation-reduction reaction. This is done in an environment of the energy storage cell illustrated in FIG. 2, which utilizes as one of its components a suitable molten salt of the nature previously set forth.

A particularly useful salt mixture is composed of lithium chloride and potassium chloride with the lithium chloride being present at a level of 58.5 mol percent and the potassium chloride being present at a level of 41.5-mol percent. This is a eutectic composition and is functionally operable in a temperature range of 350.degree. C. to 1,000.degree. C. This material has a low specific resistivity, 0.6 ohm cm. at 450.degree. C., which produces a low internal resistance of the cell.

THE NATURE OF THE ELECTRODES AND THEIR ULTIMATE PRODUCTION IN SITU IN A STORAGE CELL

As has been indicated above relative to the unique carbon compositions of the present invention, a step in their production as regards the inclusion therein of at least portions of the molten salt, comprises electrochemical charging or treatment of the charcarbon composition after it has been fashioned into the shape of an electrode and actually placed either in an environment simulating an energy storage cell or in an actual storage cell.

The treatment comprises the cycling of the electrode over the voltage range from about -0.3 volt relative to chlorine evolution to about -3 volts relative to chlorine evolution. As has been previously mentioned, this imparts a unique character to the carbon material and at the -2.7-volt level a very strong adsorption phenomenon for electron storage takes place. This region is the region of significant alkali metal adsorption; and also a region occurs near -1.8 to -1.9 volts, indicating a strongly adsorptive phenomenon.

MULTIPLE COMPONENT STORAGE CELLS

FIG. 2 illustrates a single cell unit of the present invention. In the extended scope of invention, these units lend themselves to connection or association with other cells of similar construction to produce higher capacity units. Within the scope of the invention, these plural cells can be connected in parallel or in series.

THE BIPOLAR CELL ASPECT

This is illustrated in FIG. 3 of the drawings.

In FIG. 3, a unit of the bipolar-electrode-type is illustrated in its basic form. A number of cells constructed as shown in FIG. 3 may be further assembled, by repetition, to provide an electrical storage device of high capacity, applicable to the propulsion of stationary prime movers, or to vehicles of the automotive type, and the like.

Referring further to FIG. 3, it will be noted that the bipolar electrode 30 in the center of the unit is of greater thickness than the spaced electrodes 32 and 34 that flank the center electrode. The reason is that the center electrode 30 functions actually as a dual electrode and its storage capacity in volumetric measurement is therefore equivalent to the two electrodes 32 and 34.

The outer or flanking electrodes 32 and 34 are maintained in spaced relationship away from the center electrode 30 by nonconducting spacer elements 36. As indicated above, these may be formed from a material such as asbestos cloth. An electrical tapoff is provided from the central dual electrode 30 by means of a lug portion 38 that extends above the top edge, a marginal edge, thereto. A graphite bolt 40 or equivalent is used to provide an electrical connector.

Electrical infeed-outfeed to the flanking electrodes 32 is provided by means of lug portions 42 that extend beyond the top edge, or one marginal edge thereof. The lug portions 42 are interconnected electrically by means of a graphite spacer or bridge member 44. A graphite bolt 40 extends through aligned holes in the elements 42, 44, 42 to hold those parts in assembled relationship, providing electrical connection.

From the foregoing it will be observed that an insert of the type shown in FIG. 3 actually comprises two cells connected in parallel, with the intermediate plate 30 functioning as a common electrode.

It will be evident that any number of these inserts can be assembled in either individual compartments or side-by-side contacting relationship to produce higher energy storage units.

In this regard, a sandwich construction can be produced wherein all of the intermediate electrodes are of the double-thickness type, characterized by element 30 in FIG. 3. Only the outside units would be singles. Thus, in the intermediate portion of a stacked sandwich, all of the double-thickness units would function as bipolar electrodes.

From the foregoing it will be understood that the cell units of the present invention lend themselves to connection with cells of similar construction either by connection of a number of cell units in parallel or in series, or by utilization of a stack of electron conductors where the individual electron conductors in the stack are separated by nonconducting spacers, preferably of thin cross section for maximum storage per unit volume. Thus the intermediate electron conductors act in the bipolar capacity, cumulatively adding their respective outputs as if connected in series.

Claims

What is claimed is:

1. A porous, electrically conductive, carbon polymer char body having a zero point of charge at about -0.7 volt, a maximum cation storage capacity in the range of about -1.8 to about -2 volts, a strong adsorption for both alkali metal ions and electron storage at about -2.7 volts, said char containing electrochemically associated therewith at least one cationic component selected from the group consisting of alkali metals, alkaline earth metals, rare earth metals and mixtures of at least two thereof and at least one anionic halogen selected from the group consisting of chlorine, bromine and fluorine, said electrochemically associated char being characterized by its ability to reversibly collect high-capacity charges over a broad electrical potential.

2. An electrical energy storage cell comprising a container for a fused metal salt electrolyte, a fused metal halide salt electrolyte maintained at a temperature ranging from about 350.degree. C. to about 1,000.degree. C. said halide selected from the group consisting of chlorine, bromine and fluorine, means for maintaining said temperature, and a plurality of electrodes immersed in said electrolyte at least one of said electrodes comprising a porous, electrically conductive polymer char body according to claim 1.

3. A char body as in claim 1 wherein said cationic component includes alkali metal.

4. A char body as in claim 3 wherein said halogen is chlorine.

5. A char body as in claim 3 wherein said cationic component is alkali metal.

6. A char body as in claim 5 wherein a plurality of alkali metal cationic components are associated with said char.

7. A char body as in claim 6 wherein said alkali metal cationic components are sodium and potassium.

8. A char body as in claim 7 having the following approximate concentration of components:

9. A char body as in claim 6 wherein said alkali metal components are lithium and potassium.

10. A char body as in claim 9 wherein said halogen is chlorine.

11. A char body as in claim 10 having the following approximate concentration of components.

12. A method of making a porous, electrically conductive, carbon polymer char body comprising heating a substantially carbonaceous material at temperatures ranging between about 500.degree. C. and about 1,250.degree. C. to convert said material to a porous polymeric carbon char body having diffuse x-ray diffraction bands and low-crystallite concentration and then in any order electrochemically reducing and electrochemically oxidizing said char body, said oxidation being conducted in a nonoxygen-containing medium, by immersing said body in molten salt of halogen anion selected from the group consisting of chlorine, bromine and fluorine and at least one cation selected from the group consisting of alkali metals, alkaline earth metals, rare earth metals and mixtures thereof, said salt being maintained at temperatures of about 350.degree. C. to about 850.degree. C. and electrically charging said immersed body to at least -2 volts in the negative direction relative to chlorine evolution to effect said reduction and charging said immersed body to at least -0.3 volt in the positive direction relative to chlorine evolution to effect said oxidation.

13. A method as in claim 12 wherein said salt is comprised of the chloride of a plurality of alkali metals including potassium.

14. A method as in claim 12 wherein said charging in the negative direction is to from -2 to -3 volts relative to chlorine evolution.

15. A method as in claim 12 including removing a substantial proportion of said cations by desalting the resulting char body.