CA1270296B

CA1270296B - Electric energy storage devices

Info

Publication number: CA1270296B
Application number: CA615,557A
Authority: CA
Inventors: Dwight R. Craig
Original assignee: Individual
Current assignee: Individual
Priority date: 1989-11-10
Filing date: 1989-11-10
Publication date: 1990-06-12
Anticipated expiration: 2007-06-12

Abstract

ELECTRIC ENERGY STORAGE DEVICES
ABSTRACT OF THE DISCLOSURE
This invention relates to novel type eletrochemical devices such as capacitors or batteries, among other devices which have high capacitance or power to volume or weight ratios, or which have other valuable characteristics, and which are characterized by the practical use of one or more phenomena, including pseudocapacitance, "kinetic reversibility"
(passage of approximately equal and substantial charge or discharge currents at about the same rate), "coulombic revers-ibility" (passage of substantially equal numbers of coulombs in charging and discharging of the device), distinguish-able energy states of electrodeposited species on surfaces, creation of surface layers, electrochromic effects, negative differential resistance, and frequency multiplying effects which occur during, or as a result of, the formation or modification of an electrodeposited layer or layers on, or separation of charges in doubly layers in, one or more elec-trodes and/or as a result of the reaction(s) occurring be-tween electrode and electrolyte.

Description

ELEÇTKIC ENE~GY STORAGE DEVICES
B~CKGROUNI~ OF T~IF_I,NV,~NTION
The his~ory ~ el.ectrochemical energy s~or~g~ ~evices, especlally capacitors ~Ind batteries~ hns involved attempts S to reduce the ~ize, illcluding both weight and volume, and to incr~ the electric~1 ener~y storage c~p~city while at the satne time increasitlg the voltage re~uired ~or dl-electric bre~kdown~ The occurrence under certain condi-tions o large electrochemical capacitance including 10 pseudoeapaeitanee is ~ell establlshed, bu~ prior to this invention~ no slgnificant praetieal dev~ces or appllca-tions having a high degree of "kinetic reversibility"
have been madeO Recent technvlo~ical advances in eapae-itors have included aluminum electrolytic capacitors, tantalum capacitors, ancl ceramie among others ~ all of which are film-type capa~ it~rs D Recent advances ln bat-tery design have lnclu~ed improvement in l~fe, efficiency and ener~y den~i~y by making available improved lead acid, Y

~27(:~2~6 nickel c~dmlum, nlck~?l zinc, ~nd various pr~lnary cells all o which sre inherell~ly over-voltage device~ l~mi~ed by electrode polarizAtionO ~lowever, although many of the ~evice3 ~mbr~cing the recent technologicnl advances have filled a need, there continues to be a requirement or eficient high power density devices which wi~hstand ~he rigors o continuous u~e ~nd virtually unlimi~ed cyclin~
in electricnl Cil'CUitS. Thls inven~ion provldes ~uch devices which shall be reEerred to herein as Supercapacl~ors.

SUM~Y O~ 'l'HE INVENTION
This invention relates to a novel type of electro-chemlc~l device such as ~ cap~cltor or a batt~ry ~nd more pnr~iculArly ~o t~le pr~ctic~l use of ~n electrochemic~l sys~em exhibiting a higll de~ree of pseudocapacitarlce, "klnetic reversibility," and/or "coulomblc rever~ibility,"
with which is sometimes as~oci~ted a capacitance, among o~;her characteristics, arislng ~rom the passage of charge that accompanies the change o~ potential of a sultable electrode. The devlces of this inven~ion also permlt taking advantage of the energy storage capaclty ~ormed by a pair of spaced electrodes immersed in an ionized elec-trolyte (that is, double-layer capacltance and the geo-metrlc dielectrlc cap~-itance).

7~ 9~

In accordance with the invention an electrical energy device, in particular, a storage device, comprises at least one rechargeable electrochemical cell, which comprises at least two electrodes, at least one electroly-te and a container therefor.
A-t least one of -the electrodes has a surface which comprises an active electrochemical material of a defined characteristic.
This characteristic can be identified by reference to the voltammogram which results from electron transfer between the active electrochemical material and the elec-tro-lyte, which vol-tammogram has charge/discharge curve trace sections in substantially "mirror image" form.
The characteristic can also be defined by reference to the pseudocapacitance resulting from the afore-men-tioned electron trans~er, or by reference to the "kinetic revers-ibility" resulting from such electron transfer.
The device may comprise a single such rechargeable cell or a plurality of such cells.
In another aspect of the invention there is pro-vided a process for storing electrical energy in such a device having a system based on positive and negative electrodes and the electrolyte which comprises: a) charging the device by introducing an electrical current through the electrodes, b) maintaining a potential on the device below the continuous reaction voltage of the system, until a desired charge is obtained, and c) discharging the resulting stored electrical energy for a desired applica-tion or use of the electricity.

~7~

The ac-tive electrochemical material is typically a metal or a metal compound or a mixture of metals, metal compounds or of me-tal(s) and me-tal compound(s).
Preferably the active electrochemical ma-terial is selected from the group consisting of: metals selected from the group consisting of ruthenium, rhodium, tantalum, cobalt, iridium, molybdenum, nickel, vanadium and tungsten; oxides, sulfides, hydrides, ni-trides, phosphides and selenides of said metals; the sulfides of iron and lead; and mixtures 10 thereof.
DESCRIPTION O~_THE INVENTION
The supercapacitor ls an electrochemical cell or combination oE cells comprising at least two elec-trodes, an electrolyte, and a container therefor.
The electrodes typically have a surface or are composed of one or more o:E the following materials: the metals ruthenium, tantalum, rhodium, iridium, cobalt, nic]cel, molybdenum, tungsten and vanadium, the oxides, sulfides, hydrides, nitrides, phosphides and selenides of the metals;
20 the sulfides of iron and lead; and mixtures thereof.
The electrolyte may be acidic or basic or neutral, aqueous or nonaqueous, for example, sulfuric acid or potassium hydroxide or sodium sulfate. A suitable container is used to house the preceeding components.

~z70296 In addition, the supercapacitor may advantageously employ a separator be-tween the electrodes. Ion permeable membranes, hydrophilic plastic films, glass, paper, felt, and cellulosics are all suitable depending on the par-ticular application and device.
Current collector grids or meshes may be employed in the electrode assembly if desired.
The supercapacitor is an electrochemical cell or combination of cells characterized by 1) the formation and/or reactivity of an electrodeposited layer or layers on one `` ~.;~7~Z~

or more electrodes, ~tl~/or by Z) the type of re~ction occurrin~ between electrode ancl electrolyte, ~nd/or by 3) the separation of ch~r~es across double layers, These chAracteri~tic processes occur in a poten~ial range ~hrough-out which no con~inu~us reaction occurs of An electrode orelectrolyte in the SySt~lll. They E~lve rise to one or more o a multiplicity of l~henomena ineludinK~ but not limited to, pseudocap~cit~nce, "kinetic reversiblity," "~oulombic reversibility," dlstinguishable energy states of electro-clepo~ltecl species on surEaces, creation of surEace layers~el~ctrochromic ~fec~s, neg~v~ dlffer~ntial resistance, ~nd .ErQcluency multiplylng e~ccts. These characteristic processes are us~able io m~ny ways~ sone of which will be ~escribed in more clet~ll her~in~ter and in ~he ex~mples ~nd description o~ the drawings.
A large f~mily of devic~s is conceived which employ these basic characteristic processes. Examples of ~hese are electronic-capncitor-like devices; battery-type devices; passive negative dierent~Ml resistance devices;
20 passive frequency collversioTl devlces; electrochromic de-vices; data processing memories; gaseous, liLIUid, and solid material separatlon devic~s and systems; and passive devices exhibiting constant reac~ance vsrsus frequency, which devlces may ut 11 ize ~ne or more of the characteristic~
clescribed ~n the prevl.ous p~r~graph, ~,;270~96 The electrochellllca1 cells used for these ~pplications m~y be produced in varivus forms, such as plane electrode cells; "~elly-rolll' cells; porous eLectrode cells; slurry systems; fluldiæec3-~ed e1ectrodes; endless belt electrodes;
transparent or opaque electrodes ~nd housings; liquid, solid, or g~seous elec~rolytes; etc~, depending on the nature oE the device. Furthermore 9 in several of the forRgoing devices o~ tl~is inv~ntion which take advantage o~ the electrodeposition or reac~ion tha~ occurs at under-1~ potential, I hav~ foun~ that the ~lements o the me~ls dis-~lt)~s~d m~y be usecl ~ls ~le~trocles. For ex~lm~)le, in cl~t~ pro-cesslng m~ory device upl)lications, metals ~uch ~s platinum, gol~l, or iridium mi~h~ be preerred el~ctrode m~terinls because they exhibit a one-to~one rclationship between the met~l adsorben~ ~oms and the hydrogen (or other) electro-deposited ~toms, th~reby allow~ng for a memory density approaching the sur~ce denslty of metal atoms in the sur-face (which is on the order of 1015 per square centimeter).
Also, in solid ma~erial sel)arfltion devices such as in the sel~ara~ion of met~lllic le~d, the le~d can be electro-deposited from aqueous solution (lead chloride~ onto a metallic substrate electrode, preferably gold, such electro~
deposition of lead being preferential to other ions and reversible with respect to voltage on this electrode 9 thereby permltting sel)a~ tion or reEining of lead with the 2g6 - ~ -use of minimal amounts oE electrical energy.

DESCI~IPTION OF D~WINGS
Figur~ 1 ls a volt~ ogram show~ng oxygen and hydrogen electroadsorption and electrodesorption on platinum sur-5 faces at potentials less than those required for gas evolu-tion.
Fi~ure 2 i8 a voltauuno~ram in aqueous solu~ion of ruthenium oxide, In ole~trode material pre~erably employed in this inventioll.
Figtlre 3 is a vol~ammoglam in aqu~ous ~olution o a mixture o~ ruth~niu~ n~ ~n~alum oxides which i~ ~ mixed metal oxidc electrocle mater:Lal also advantageously employed in thi~ invention.
~ is;ure 4 1~ s~ill allother voltammogram in aqueous 901u-15 tiOII o another material, nan)ely, molybdenum oxide 9 whichis also employed in certain devices o~ ~his inventlon.
Fi~.ure 5 is a vol~allunogram o~ tungsten oxide ln . aqueous solution.
Figure 6 is a voltanullogram o~ nickel oxide in aqueous 20 solution.
Figure 7 is a monopolar p~r~l~el plate structure ca-pacitor in accordance wi th this invention.
Figure 8 is B monopola~ "jelly-roll" ~structure capac-itor in accordanc~ with this invention.

Figure 9 ls a more det~lled view of the b~sic struc-ture o the c~p~citor of ~hls invention which is a pre-ferred embodiment.
~igure 10 is a di~gr~mm~tic sketch of a bat~ery of this inven~ionO

DETAILE~ ~ESCI~IPTION OF T~IE INVE~TI~N
, , . . , , , . ., .. .. ~ .
The phenomena which are s~ novelly employed in ~h~
dev~ces o~ this invention are ~he resul~ ~f certain reac-t~on~ which occur ~n some electrochemical cells. An ex-ample o~ pseudoc~p~citance occur~ in the deposition andiorli~a~ion o hydro&~rl und oxygen on pl~t:Lnum sur~ace~ at po~entl~lls le85 tt~ lo~ req~ired ~or g~s evolution~ The vol~alllmv~ram~ of Figure~ 1 through 6 were obt~ine~ by use o~ the procedure described ~enerally in M~ er~ rle-cr~
~ by Bockris und ~eddy on page 1316.
Fig~lr~ 1 ~not an actual voltan~mogram) depicts oxygen electroadsorption (area A3 9 oxygen electrodesorptlon (area B), hydrogen electroadsorption ~srea C) 7 and hydrogen electrodesorption (area D)~

2() The area between the curve an(l the x-axis represents the charge delivered to or accepted from ~he electrode (O ~ i~dt) O In tllis c~se" as the voltage is cycled, the electrode i6 altern~ely charged and dlsch~rged, fir~t as hydrogen is electro~ld.~,r~ed and electrodesorbed, then as ~71D2~

oxy~en ~s electro~dsor~e~ and el ~trodesorbed. The name given ~o the char~e/discharge phenomenon is "p~eudo-cal)acitance, ~ since iL ~ehaves like a capacitance, bu~
the s~orage o~ charKe involve~ a Farad~ic proces~, rather th~n an electrostatic one. Electrochem~stry literature tells U8~ that this pseudocapacitance is n~t a real capaci-tance, since it will not hold ~ charge, but this inven-tion mak~s ~se o~ 1~ as a storage means. (See Bockri~
and ~eddy, Modern ~.lectrochemistrY, P0 10~7.) lU Xn ~he case referre~ to above (Fl~ure~ the cou-lom~ic charge (~ d~) durin~ electroadsorption in ~he oxygen reglon ls sub~tarltially th~ ~atlle a~ the coulombic di~charge ~uring elec~rodesorption. The .~ame is true for ~.he hydrog~n region, taken sep~rately from the oxygen an~, o~ cour~e, for the total reaction~ taken over the voltage range 0 to approximately 1~3 volts RHE. Th$s bal~nce of coulombic charge and coulombic discharge shall be re-f erred to herein as "coulombic revers-lbillty . "
In Figure 1, the electro~dsorption and electro~
20 desorption of oxygen occur at di~ferent vol~ages " and their current traces are oE dlfferent shapes. The electroo adsorption and electrodesorption of hydrogen, on the other hand, occur at apl)rox~mately the same volt~e and produce curves th~ are approximate "mirror lmages, " F~ gure 2 is 25 R volt~mmogram of a preferred electrode material o this )Z96 lnven~ion, i~., ruth~lliulll oxid~, From Figure ~ it esn be seen ~.hat all sections of the urve show approximate "mirror images" with respect to the voltage axis. Repre-sentative "mlrror lm~ges" in this context are shown in Figures 2 through 6I This "Inirror image" phenomenon shall be referred to herein ~s "kinetic reversibili~y" while the non~"mirror im~ge" ~uch as the oxygan el~ctro~dsorption-desorption in Figure 1 shall be re~erred ~o as "kinetic nonreversibility" or partial reversibility. Systems that are "kineticslly reversible" show very hi~h electrical e~iciency, si.nce they return charge at the same volt~ge at wh~ch they receive i~. System~ that are "kinetically nonreversible" ~re les~ ef~icient, since they are charged at a differen~ voltage thsn that at whicll they are dis-charged.
Referring ngain to Figure 1, in the hydrogen regionwe ~ee three curren~ peaks between the voltages oE 0.4 and 0.0 RHE~ cor~espond~ng, it is believed~ to the electro-~dsorption and electrodesorption of hydrogen at (probably) d~ferent ~itQS on ~he pla~inum surace. We also see less-well-defined peaks in the oxygen region where it is be-lieved that oxygen is simil~rly adsorbed and desorbed.
Colncident with these re~cti.on~ is observed ~ change of entropy and a heat oF a~sorption or desorption of the 9~

hy~rogen and oxygen ~nd of othe~ specie~ whlch may occupy the site 9 such ax organic impuri~ies or water molecules.
Thus there ~re in thes~ re~ctions dis~ing~lishable energy states of various electro~eposited speciex on the sur-~aces o~ the substr~tes.
Further to analyses rel~ting to Figure 1, it is nowbelieved that the electr~orp~io~ oÇ hydrogen on platinum produces a surface monolayer oE hydrogen, while the e:Lectro-sorption o~ oxygc~rl can produce multiple surace layers oE
oxy~en or oxide.
In th~ cre~tioll o ~om~ surfacca layers, such ~S oxldes on ruth~niutn~ un~c!r th~ l)roper condition~ we observe ~
change in th~ optlcul ~Ippe~r~tlce or re1ectivi~y ~f t~e surEace.
lS ReEerring once morc to Figure l, we observe th~t 9 for ex~mple, the portlon oE ~he hydrogen desorptlon curve at about 0.35 volts RHE shows ~ reduction of current with ~n increase in voltage. This represents a negative d i~feren-~ial resistance characteristic which occurs in ~he systems o~ this invention. Also, the are8 at o.o to 0O4 volts KHE
shows three cycles of current or on~-half cycle of voltage, which frequency-rnultiplying characte~istic occurs in the systems oE this inventior10 The unique ch~racteristics exhibited in the systems o this invention, including "Lc~neLic reversibility~"

~.2~

"coulombic rever~ibility, " distinguishabl~ energy st~te~
o elec~rodeposit:ion, creation of surfsce ~reas, electro-chromic ef:~ects, ne~,cnt ive di~f~erentiul re~.istance, ~Ind I~recluency multiplyi~ e~ s are ~?mploye~l in t:h~ ~lecLrical 5 enerf~y devices rei èrred t:o herein.
In order for this invention to be more readLly under-stc70d and to describe th~ many varla~iorl~ that may be émployed in each of the components, thls invention will now be de~ailed usin~ a c~pacitor as ~n example; ~owever, 10 this is not to be construed a~ llmitirlg tlliS invention.

T~IE F:LECT~OI)E
. ..
Th~3 electrodcs oE t:hl~ invenl~ion~ ~h-3ir cornl~osition;
pr~ap~ra~lon, D.ncl a~q~em~ly in th~3 Sup~rcap~ci~or devices of thi~s lnven~ioll ar~ cri~ic~ll to ob~a$nillg the superior per-fonm~nce in el~ctrical nl~d physical characteristics of thedevices to be exemplified herelnafter. I have found that in order to maximize the reduction in ~ize, including volume and weight ratios, to the energy storage capacity an-l to optimize the combined efects o~ pseudocapacitance, 20 double-layer c~pacitarlce and "kinetic reversibility," it is desirable to employ an electrode ma~erial having a voltammogram of substan~lally syn~letrical current traces in the oxidation and reductlon cyclesJ Materials th~t may advant~geous ly be employed are ruthenium oxides and ~27~9~;

mixtures o rutheniulll with t~ntalutn ~nd/or iridiuln~ pre-erably a 50-50 mole percent RuTaOx or such a ~nix~ure with amoun~s of iridiulll æuch as E~u~ SIrO ~5~ra~ 5x ()ther electrode materlals such as previously described 5 m~y be employed, i~ being pre~erable that their voltammo-grams show subs~cant i~l "kinetic revers ibility" such as that ~hown in Figures 2 ~ 3, 4, 5, or 6 ~
When employing rut~enium as the elec~rode material, the ruthenium con~ent may be varied over wi~e ranges aY
shown when m~xe~ with> lor axample~ tantalum, or irldiuln.
The ollowing data in Table I illu~trat:es a mea~ured var-iation in c~pacitaIlce per unit geotIletric area ag~inst mole percen~ of ruthenlurll irl ttle electrode mate~rlal whell mixed with tantalum.

lS TABLE I
C~p~C i~A~ 5~it i Mo ~ 5~ 5~ F~cm 0.045 0~1 2.0 2.8 1.6 0.8 The poro~ity o the electrode is another factor that contributes to optlmiz~tion of results or dev~ces o this ~nven~ion, In gener~ll 9 poroglty i~ de~irabl~ in order to maximi~e the energy stor~ge density, or capacitance per unit volume. Howev~r~ ~roper control of the porosity will also allow control of the intPrnal resistunce and oE the reaction rate (by controlling the access time of the elec-trolyte ~o the electrode), ~hus providing a mea%ure o~
control over the capacit~nce versu~ ~requency ch~lr~cte~-istic. This can be ~ontrolled to the extent oE providing capacitance which varie~ inv~rsely wi~h fresluency, ~hus allowing productioll of a constant reac~ance devic~, as ~oel~-tioned herelnbe~ore.
The thicknes~ of the oxide coating is still another ~lCtOr ~at a~eC~9 t:llc perEorm~lnce and char~c~eristlcs o~ the Supercap~cito~ o~ thi~ invention. Generully, the capacit~nce varies wi~h the thicknes~ of the ruthenium oxide coating so that by vnrying the thickness o~ the coa~ing~ the capacitance per unit area may be controlled~
Using the thermal oxidation technique (see Ho ~. Beer, South African Patent 662.667 (1966) and 680.034 (1968)) a thick and uniform ruthenium oxide fonmation wns obt~ined.
This coating was tenaclous and further did not exhibit any flaking or other unde~irable characteristics.
In additi~n, I have found th~t the purity of the metals or metal cvmpoul~s u~ed in the preparation of the 25 electrodes can have a ~ignificant eEfect on the perEor~nance gl,z~

o the device~ For ex~ ple, it is obvious th~t the wrong type of metallic impurl~y in a capacitor or other device uslng a metal electrode would produce a galvAnic corrosive ~ction which would deterlorate the elec~rode and probably increa~e ~he le~k~ge curren~ of ~he devlee. In general, I prefer a purity o 99 percent ~r bettér~ but certRin systems can toler~te high percen~ages of impurit~es with-out detrimental eEfect. In ~ome c~ses, additives c~n even be beneflcial, as ln the case oE, e.g., tantalum oxide addltion to ruthenium oxide (see T~lble I)~ In ~hi~ c~se, addition o S0 pereen~ tantalum oxide n~aximized the spec-ific c~pacitance oE the ~evice~
Various proces~es ~nd techniclues may be employed in the preparation of the electrode. Among those methods which I have ~ound sati~acto~y are: thermal prepar~tion of ~he selected mAterial, e.g., nlthenium-tantalum mixed oxides; electrochemically gener~ted ruthenium oxide; and pressed pelle~ electro~e preparation~ ~ncluding the use of binders, e.g. 9 1eflon pow~er, ~f desired, O~her methods of preparing a ruthenlum oxide electrode may be employed, or example ? precursor or impr2gn~tion tech-niques. In the examples which follow, specific details will be given concerlling the preparatiorl of electrodes in connec~ion with the d~ta obt~ined in specific experimen~s and with preerred embodi!llents of this invention.
* Trade Mark ~%70Z9G

TH~ ELI~~OLY~C
The elec~oly~es which may be used in the Superc~pac-itor of this inve!ltion may be acidic, alkaline, or neutral, aqueous or nonaqueous, I have used, succ~ssfully, elec-trolytes v~rying in ptl rom (-) 1 to (~) 14, takirlg lnto ~ccount, of cour~e, the chemical s~ability o ~he elec-trode ln the electrolyte, pH ~ec~s the specific capac~
lt~rlce o-~ the device, with the ~mount varying with the electrode ~nd wi~h the ~lectroly~e. Examples of electro-lytes employed ~re: NaOH, H2S04, KOH, HCL, NaCl03, NazS04,and K2S0~. Sol~.cl or gAs~c)us electrolytes may, of course, ul~o be u~ed provide~ the active Lon~ are compatible wit~
the electrode ad~orption or renc~lon process~

Figure 7 111UBtr~e~ one o~ sn~ny possible con~igura-tions o~ a monopolar type of cap~ci~or tha~ can be made using concepts described in ~his invention. Electrodes~
o various sizes and sh~pes, may be used, having been previously coated with active materials such as ruthenium oxide. The~e electrodes are provided with conduc~ive tabs for current conduction to nnd ~rom the electrodes. The electrodes are then s~cked, alternating electrode (l) which may be positive and electrode (2) which is negative and u~ing a ~u1table sep~rator (3) to preven~ shorting of electrode~ nd (2). The le~d t~bs (4) ~re brought out-side the casin~ (5) through a suitable hole (6) in the end c~p (7), and tab6 (4) from the multiple eleckrodes (1) nnd (2~ may be g~thered together by welding. After insertion 5 o the electrolyte (8), t:he assembly may then be drawn li~htly together by u~e o~ a turnbuckle~tyl~e of casing (5) and ~ecesses (lQ). Elec~rolyte l~kage may be prevent~
by the use of a suit~ble se~l~nt (9). This assembly ~nay be hooked up ln a plur~lity of unlts to produce a capncl~or o any given capacity~
Figure 8 repL-esents anotiler possible con~ig,uratiosl o~
a monopolar typc oE caplcitor, popularly texmed ~ elly-roll" typ~. Her~ two electrocles (1~ and (2), coated with An ~ppropriate a~t:ive m~ter~nl ~uch ~s ru~henium oxide (no~
15 shown) ar e preven~ed ~rom shor~lng by interl~aving a sult-able sepArator (3), and ~re rolled up in "~elly-roll"
~ashion a~ shown. Tabs (4) are extended from each of the electrodes through the ca~ing (5), and aft~r insertion of a suitable electrolyte (8), the holes t6) are plugged wlth a suitable sealant (9).
The Supercapacitors of this invention have much larger capacitance per unit volume than aluminum electrolytic capacitor~. For ex~lmple~ an experin~ental capacitor pro-duced in accordance wit~l t~is invention ~nd o~ the de~ign shown in Figure 9 o~ 6 volt~ and 109000 ufd was 1/10 the Z9~

phy~ical size o a ~tand~rd ~on~erci~l ~luminum ~lectrolyte capacitor of the same voltage ~nd capacitance. Another model of the s~me desi~n yielded 1/30 the physical ~lze of the commercial cap~citor. To achieve the high energy density c~pacitor (s-nall volume ~nd light weight) it is preferable to optinlize not only the electrode ma~erial, the electrolyte, ~nd the sep~rators, when u~?d, but ~lso the physical conEiguration, stacking, end ~ecmlnals, an~ the container or c~se, t~l~reby permi~tin~ improvemen~ in physical siz~.
Figures 7, 8, ancl 9 illustrate various configur~ions ~or capncitors of t:his inv~ntion. In ~he Supercapacitor shown in Fi~,ur~ ~3, the clectrodes (1) ~Ind (2) ~re 10 mil.
thick substr~te titanium co~ted witll R~T~0x ~nd ~he sl)acer-gaskets (11) are 15 nlil, thick Viton. This is pressuresealed, preventing electrolyte leakage and shun~ cu~rent losses. The cnse se~lant (9) i~ electrolyt0 re3istant compound such as epoxy resin coated over the assembled stack. The case cylinder (5) may be a plas~ic such as Kovar9 polyethylene, or polypropylene. The end caps (7) are copper and the wires ~re spo~ welded to the two end electrodes (1) ~nd (2).
The ~ssembly procedure comprises stacking (a) the oxide coated electrodes which are oxide Eree on their ~5 edges so th~t they will seal when assembled~ (b) the end * Trade Mark ~%~7~Z~

electrodes which are oxide coated on one side and w~ich have their le~d wires spot welded, and (~) the Viton g~s-k~ts, The stack so Eormed is im~er~ed in ~he electrolyte under vacuum. The ~tack is removed from the electrolyte pressure sealed. The stack is t:hen coat~d wit~l insu].~tor compound su~h as epoxy resln by forcing the resin through the opening (13~ and out: t:hrough the exit (14), The concept oE thi~ lnvention may b~ employed, for ex~lmple, in bltteLies Lor use in ~owering pacem~kers Eor implant~tion in hulllAns wh~re regulation oE heartbeat is re~lulred. Sinc~ this battcry is el~lctricnlly rechargeable, it would be rechur~d ~y inductance from outside the body, thus peL~nittin~; recharging without remov~l Erom the bodyi, (Present: bMt:terieq or t~liS use are not rechargeable el~c-tric~lly and must ~e replaced about every five to sevenyears by a surgical process.) Further~ thls recharging would be done at periods ~horter than the above-mentioned ive to seven ~e~rs 9 allowing much smaller batteries to be used. Furt~er, with batteries of this invention, ex tremely long life and a very great number of cycles can be realized, thus eliminating the need for any further surgery, once the initi~l implantatlon is accomplished.
This battery is partieularly well suited to this applica-~ion because of its sn~all ~ize, lts lon~ cycle liEe, and it9 rechargeability.

~.~7~

In ~nother application, this battery would be used for utility load~levelling by charging a great number of cell~d (connected in ~ suitable serles-parallel arr~ngement) at night over, Bay, ~ ten-hour l~eriod when the load demand in a utility power-~eneration station is low. These bat-terie~ would then be ~isch~lrged a~ the pe~k load deman~
hours o the dAy, thus ~llowin~ a rel~tively const~nt power-generation level to be used by the utility. ~ther advsntages also derive ~rom this practice and are well-known to those ac~luainted wi~h load-levellin~ technology.
Thig battery 19 particularly well-suited to this ~echnology b~c~u~e o i~ hi~h char~c-to~iHcharge eE~iciency and its very long cycle lie.
~is~ure lO lllustl~tes a ~-ypical one-cell batterv o~
this invention. Electrocle~ ~l) and t2~ are, in this c~se, porous slus~s Oe rutheniulll oxi~e pow~er, prevented Erom shorting one to the other by a suit~ble separa~or, and enclosed in a casin~ (in this case m~de of an insulatin~
materlal, althou~rll the electrod2 and leads could easily be insulated erom the casin~ i~ the casini~, were made of metal or other conductlve material). Either electrode can be considered us the positive electrode with this desi~n~
and the battery can be char~recl alternately in one polarity and ~hen in the opposite pol~rity without damaf~e.

~,2~ 6 A list o~ characteristics of the battery o~ this invention is given below:
1. A very ~ligh round trip (char~e-dischar~e) efficiency 2. Very long life

3. Very great cycle life

4. ~llgh power density

5. Very hl~,h chMr~,e and di~charge r~es

6. Capacity substMntially inv~riant with hi~h dis-charge ra~es

7. Shalll~w ~n~ deep c~ischarge capabllity without afectin~ etillles . Reasollable energy density 9. Eleatrlc~lly recharK0~ble (secondary type) 10. Simple construc~ion, black box type Table II gives ~he performance ch~racteristics of Supercapacitors m~de as de~cribed ~bove. The following exAmples are given to urther illustrate this in~ention;
however ~ they are not lntended to limit the scope thereo.

Z~6 \BLF, I I
Ex~lnple I Exulnple II
l~evice Type Cay~citor C~pacitor Elec trode S ~. Fc~rm T~lerln~11y formed ~'ellet b. Composition TflRu()x Ku02 ~lectrolyt~ :~ . 5 M l~2~4 3 . 5 M H2S()~
Pol~lrity ~3ipol~r/N~>npol~r Sin~le ~:ell/Nonpol~r Vol~lmc 5.O C1113 (). 5 cm3 (~ppr.) Capaei~anc~ 10,()~)0 uEcl (~5 Fd To ler~nce ~ o t~ SL~/o Vol~flR~ 6 V l V
ESK 80 InJL
AA~sembly See l~i~ul e '3 See t; i~ur~a 10 a. 10 mil. gaskets Separator b. 1 mil. Ti substrates c, Screw assembly Figure 9 shows a 3 volt capacitor o t similar cons truc t ion .

THE ELECTRICAL ANI) OPERi~TING C~I~R~CTERISTICS
_ . , . , . _ , OF DEVICES OF THIS INVENTION
_____ ~_ The electricnl characteristlc~ of the rechargeable electrochemical cells of this invention are more re~dily untlerstood by reference ~o the :Irawings in Figures 2 ~qo2~

- 2~ -t~rough 6 whlch ~how volt~ mogr~ms of v~rious electrode/
electrolyte combinatit)lls or systems embr.aced wlthin this invention. Once the device has been char~e~ by applying ~ voltage to its ~erminals and ~he device is disconnected rom its volt~g~ source, no current will be flowing and the voltsge o~ th~ posi~ive electrode will be ~t th~ higl vclt~ nd o~ ~he ~urve ~ hown in ~lgure 2 (poin~ A).
When npplying ~n electrlcal loa~ ~cross the termlnals, curren~ flows ~nd traces the p~th o.~he curve in ttle lower sec~ion below the horixon~al axis along the path , C, D, un~il the ~lectrode is ~ully discharged which 1~ shown ~It pOillt 1), When ch~r~ing the ~evlcQ, ~he current ~or the ~o~i~ive c~rod~ trace~ e curve ~n th~ upper 9ec~i~n ~bove the 5 1Xi9 along the path D~ F., F, A. The other electrode has substan~ially the same electrical characteristics, which can be depicted in ~ simllar m~nner, except th~t the current flow is the opposite, ~hat is, discharging along path G~ H~ E9 D and charging along path D, C, J, G. Thus the devices of this lnvention possess the unique feature of maximizing the use o~ "kinetic reversibility." This is also shown by Figure 2 because the amount of current flowing during char~e of the ~evice is subs~antially ~he same, but oE opposite ~ign, ~s the current 10wing during discharge oE the ~evice u~ the same poten~ial. This is 2~36 especially true ~or ~hose systen)s having curves in thc charge/discharge cycle which have the forms o close~
"mlrror im~ges." T~le ide~l ~;ystem ~or ~n electronic cap~c-i~or is ~e~)icted as Ll~e broken line rect~ngle for l~'igure 2 for the electrode/electrolyte system described. It can re~ldily be seen that t~le nctual curve closely approximates the ideal.
The deviccs of tl~is inven~ion which ~mploy "kinetic rever6ibllity," tlave ~:he ad~i~lonal a~v~n~u~e ~hAt the capacitnnce of an electronic cspacitor (or the capacity o~
a b~ttery) c~n ~;e controll~d by the electrical or ~)hoto~ctive bias ~e.g., D.C. workillg voltage level) ilnpressed on the device. F'o~ ex~mple, in re~rrin~ ~o ~igure 4, the ins~n-taneous capacitance clepends on the height o the curve above the x~axis ~t the lns~ntaneous volta~eO Slnce this height varies with the positlon alon~ ~he x-ax~s, i~ can be seen that the capacit~nce can be controlled by operating the device at a higher or lower voltage, This voltage level can be effected by the use of any oE a number of features ~0 such as multiple electrodes or electrodes oE difEerent eEfec-tive reactivity (for example 9 different volumes or surface areas).
The electrochemical renctions that take place in ~he rnetals from the m~terials of this lnvention are not fully known, however3 some o the elec~rode m~terials known to be c~pable of exis~ing ln ~I Llurulity of t~xidation st~te6 such as the oxides oE ruthetlium, tungsten, molybdenum9 and cobalt are among those which are pre~erred Eor capacitor devices. It is importan~ in operating ~he devices o~ this invention not to apply a voltage across its terrninals that causes contlnuous reaction of the electrolyte and to keep it below the r~n~e w~ere there is any ~gl~ific4nt arnount oE evolution o~ oxy~en or hydrogen.at tlle electrodes or dissolution of the elcc~.rodes ~hemselves.
Al~hou~h my inventioll h~s been describecl with respect to speci~ic examples, lllus~rations, and certain preferred en~hocllment~ thereof, I do not in~nd that my invention should be thereby con~trued ~g being limitecl in scope except ns expressly cdefined in the ~ppended claims.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An electrical energy storage device comprising at least one rechargeable electrochemical cell, said at least one electrochemical cell comprising at least two electrodes, at least one electrolyte and a container therefor, at least one of said electrodes having a surface comprising an active electrochemical material, having a voltammogram resulting from electron transfer between said active electrochemical material and said at least one electrolyte whose charge/discharge curve trace sections are in substantially "mirror image" form.

2. An electrical energy storage device in accordance with claim 1, wherein said electrodes are separated by a separator.

3. An electrical energy storage device in accordance with claim 2, wherein said separator is selected from the group consisting of: ion permeable membranes, hydrophilic plastic films, glass, paper, felt and cellulosic material.

4. An electrical energy storage device in accordance with claim 1, 2 or 3, wherein said surface comprises at least one electrodeposited layer of a said active electrochemical material.

5. An electrical energy storage device in accordance with claim 4, wherein said active electrochemical material is selected from the group consisting of metals, metal compounds and mixtures thereof.

6. An electrical storage device in accordance with claim 4, wherein said active electrochemical material com-prises at least one member selected from the group consisting of:
i) a metal selected from the group consisting of ruthenium, rhodium, tantalum, cobalt, iridium, molybdenum, nickel, vanadium and tungsten, ii) oxides, sulfides, hydrides, nitrides, phosphides and selenides of metals of said group i), iii) sulfides of iron, and iv) sulfides of lead.

7. An electrical energy storage device comprising at least one rechargeable electrochemical cell, said at least one electrochemical cell comprising at least two electrodes, at least one electrolyte and a container therefor, at least one of said electrodes having a surface comprising an active electrochemical material which in said at least one electrolyte exhibits pseudocapacitance or kinetic reversibility resulting from electron transfer between said active electrochemical material and said at least one electrolyte.

8. An electrical energy storage device in accordance with claim 7, wherein said electrodes are separated by a separator.

9. An electrical storage device in accordance with claim 7 or 8, wherein said active electrochemical material comprises at least one member selected from the group con-sisting of:

i) a metal selected from the group consisting of ruthenium, rhodium, tantalum, cobalt, iridium, molybdenum, nickel, vanadium and tungsten, ii) oxides, sulfides, hydrides, nitrides, phosphides and selenides of metals of said group i), iii) sulfides of iron, and iv) sulfides of lead.

10. An electrical energy device comprising at least one rechargeable electrochemical cell, said at least one electrochemical cell comprising at least two electrodes, at least one electrolyte and a container therefor, at least one of said electrodes having a surface comprising an active electrochemical material which in said at least one electrolyte exhibits pseudocapacitance resulting from electron transfer between said active electrochemical material and said at least one electrolyte.

11. An electrical energy device comprising at least one rechargeable electrochemical cell, said at least one electrochemical cell comprising at least two electrodes, at least one electrolyte and a container therefor, at least one of said electrodes having a surface comprising an active electrochemical material which in said at least one electrolyte exhibits "kinetic reversibility"
resulting from electron transfer between said active electro-chemical material and said at least one electrolyte.

12. An electrical energy device comprising at least one rechargeable electrochemical cell, said at least one electrochemical cell comprising at least two electrodes, at least one electrolyte and a container therefor, at least one of said electrodes having a surface comprising an active electrochemical material which in said at least one electrolyte exhibits pseudocapacitance and "kinetic reversibility" resulting from electron transfer between said active electrochemical material and said at least one electrolyte.

13. An electrical energy device in accordance with claim 10, 11 or 12, wherein said electrodes are separated by a separator.

14. An electrical device in accordance with claim 10, 11 or 12, wherein said active electrochemical material comprises at least one member selected from the group consisting of:
i) a metal selected from the group consisting of ruthenium, rhodium, tantalum, cobalt, iridium, molybdenum, nickel, vanadium and tungsten, ii) oxides, sulfides, hydrides, nitrides, phosphides and selenides of metals of said group i), iii) sulfides of iron, and iv) sulfides of lead.

15. An electrical energy device in accordance with claim 13, wherein said active electrochemical material comprises at least one member selected from the group consisting of:
i) a metal selected from the group consisting of ruthenium, rhodium, tantalum, cobalt, iridium, molybdenum, nickel, vanadium and tungsten, ii) oxides, sulfides, hydrides, nitrides, phosphides and selenides of metals of said group i), iii) sulfides of iron, and iv) sulfides of lead.

16. A device in accordance with claim 1, 2, 3, 5, 6, 7, 8, 10, 11, 12 or 15, wherein both electrodes are characterized by a surface active electrochemical material composed of the same substance.

17. A device in accordance with claim 13, wherein both electrodes are characterized by a surface active electrochemical material composed of the same substance.

18. A device in accordance with claim 1, 2, 3, 5, 6, 7, 8, 10, 11, 12 or 15, wherein the active electrochemical material is composed of an oxide or a mixture of oxides of the same or of different metals.

19 A device in accordance with claim 13, wherein the active electrochemical material is composed of an oxide or a mixture of oxides of the same or of different metals.

20. A device in accordance with claim 18, wherein the active electrochemical material is an oxide of ruthenium.

21. A device in accordance with claim 18, wherein the active electrochemical material is a mixture of oxides of ruthenium and tantalum.

22. A device in accordance with claim 18, wherein the active electrochemical material is an oxide of molybdenum.

23. A device in accordance with claim 18, wherein the active electrochemical material is an oxide of tungsten.

24. A device in accordance with claim 1, 2, 3, 5, 6, 7, 8, 10, 11, 12 or 15, wherein the active electrochemical material is a metal.

25. A device in accordance with claim 24, wherein the metal is iridium.

26. A device in accordance with claim 1, 2, 3, 5, 6, 7, 8, 10, 11, 12 or 15, wherein the at least one electrolyte is a liquid.

27. A device in accordance with claim 1, 2, 3, 5, 6, 7, 8, 10, 11, 12 or 15, wherein the at least one electrolyte is a solid.

28. A device in accordance with claim 1, 2, 3, 5, 6, 7, 8, 10, 11, 12 or 15, wherein the at least one electrolyte is a gas.

29. A device in accordance with claim 26, wherein the liquid is an aqueous inorganic acid.

30. A device in accordance with claim 29, wherein the aqueous inorganic acid is sulfuric acid.

31. A device in accordance with claim 26, wherein the liquid is an aqueous base.

32. A device in accordance with claim 31, wherein the aqueous base is caustic soda.

33. A device in accordance with claim 26, wherein the liquid is an aqueous neutral salt.

34. A device in accordance with claim 33, wherein the aqueous neutral salt is sodium sulfate.

35. A battery in accordance with claim 1, 2, 3, 5, 6, 7, 8, 10, 11, 12 or 15.

36. A capacitor in accordance with claim 1, 2, 3, 5, 6, 7, 8, 10, 11, 12 or 15.

37. An electrical energy storage device in accordance with claim 1, 2, 3, 5, 6, 7 or 8, wherein the voltammogram has a "mirror image" charge/discharge trace of substantially varying height at different voltages.

38. A process for storing electrical energy in an electrochemical device in the form of a system comprising positive and negative electrodes, electrolyte and a container therefor, wherein at least one of said electrodes has a surface comprising an active electrochemical material having a voltammogram resulting from electron transfer between said active electrochemical material and said at least one electrolyte whose charge/discharge curve trace sections are in substantially "mirror image" form, which comprises:

a) charging the device by introducing an electrical current through the electrodes, b) maintaining a potential on the device below the continuous reaction voltage of said system, until a desired charge is obtained of stored electrical energy, and c) discharging the stored electrical energy for a desired application or use of the electricity.

39. A process according to claim 38, wherein in said system said electrodes are separated by a separator.

40. A process according to claim 38 or 39, wherein in said system said surface comprises at least one electro-deposited layer of said active electrochemical material.

41. A process according to claim 40, wherein said active electrochemical material comprises at least one member selected from the group consisting of:
i) a metal selected from the group consisting of ruthenium, rhodium, tantalum, cobalt, iridium, molybdenum, nickel, vanadium and tungsten, ii) oxides, sulfides, hydrides, nitrides, phosphides and selenides of metals of said group i), iii) sulfides if iron, and iv) sulfides of lead.

42. The process of claim 38, 39 or 41, comprising repeating the charge cycle after discharge in order to recharge the device for continuous or subsequent use.

43. The process of claim 38, 39 or 41, wherein said active electrochemical material exhibits a pseudocapacitive characteristic.

44. The process of claim 38, 39 or 41, wherein the voltammogram has a "mirror image" charge/discharge trace of substantially varying height at different voltages, and wherein the device is operated at different voltage levels to control the electric energy storage capacity.