MATIERE ELECTROACTIVE POUR PILES

ELECTROACTIVE MATERIAL FOR POWER CELLS

Abrégé anglais

ABSTRACT OF THE DISCLOSURE:
An electroactive material for power cells,
especially secondary electrochemical power-producing cells.
It is composed of a complex compound of a transition metal
and basic organic ligands, especially Schiff bases dis-
solved in polar organic solvents, water or their mixtures.

Revendications

The embodiments of the invention in which
an exclusive property or privilege is claimed are defined
as follows:
1. A power cell, having an electroactive
material comprised of a complex of a transition metal, wherein
said electroactive material is a complex of a transition
metal and a schiff base dissolved in a polar organic solvent,
water or their mixtures.
2. A power cell according to claim 1,
wherein the transition metal is one of the following
metals: nickel, cobalt, iron, chromium, manganese, copper,
titanium or vanadium.
3. A power cell according to claim 3,
wherein said Schiff base is an ethylenediamine derivative.
4. A power cell according to claim 1, which
is a secondary electrochemical power-producing cell.

Description

~lec~roactiv3 mat~rial Eor pow~r c911s
r~his invention relates to an ~lectroactive matsrial for
power cells, the secondary electrochemical p~wer producing
cells in particulsr,
The operation o~ an electric power cell is based OIl hete-
rog~neous o~idation and reduction reac-tions OI th~ elsctro~
active material,, The release o~ electric energy is possible
only if the di~ference o~ standard electrode potentials o~
the red-ox systems undergoing elec-trode processas in the ano-
dic and cathodic potential rengss is sufficiently high, a~d ~ihen
the current density is su~ficiently hi~h"
During an electrode ~rocess in ~ po~er cell, the electro-
active material is oxidiz~d on anode, and reduced on cathode,
n'ypically used electroactiv~ materials are liquid sodium
for anode and liquid sulfur for cathode in a solid electroly-te,
containing ~.g. sodium ions.
~ he usa of such m3terizls, though, is inconv~nient and
no~ious becau=,e OI, among other r~asons, high to~icit~,~ of
liquid sodium,
In designs 3ccording to U.S. I`atents ~os~ 3791867,
3827910, 3~64167 and a German OfIe~ No. 2937717~ alkali metaLs
or alkali earths metaLs of low slectronega tl~ity are used
~or anode materials in non-aqueous reversible cells~
while the cathodic electroactivs material is compos~d o~ a
.

~i2~
~ixture o halogens or chalcogens fixed in a conductive
matrix. The eleetrolyte used consists of a salt contain-
ing alkali metal or alkali earth metal ions. In many cases
it is necessary to remove the products of electrode reac-
tions from the electrodes or their immediate vicinity,
which hinders the use of these electroactive materials on
larger scale.
In case of the most known power cells, careful
separation of cathodie and anodic 20nes is necessary to
avoid mixing of the electrolytie substances leading to an
irreversible deaetivation of the cell.
In such a known and widely used power cell, as a
reversible lead cell, the electroactive material of both
anode and cathode consists of a Pb ~II/ in 30 % sulfuric
acid solution. During the charging cycle, Pb /II/ is
reduced to Pb /0/ and oxidiæed to Pb /IV/ on anode and
eathode, respectively. Major drawbacks of such a cell are
the heavy weight of the electrodes and highly corrosive
properties of the electrolyte solution.
It was found, that -the electroactive material
for power cells according to the invention displays suffi-
cient difference of standard electrode potentials and low
charging overpotential in relation to the working potential.
It also allows for the use of low-cost ant low-weight
electrode materials and has no metal-corroding properties.
Moreover, it does not deposit on the electrodes, nor
precipitate within the electrode zones~ making the removal
of the products of electrode reactions unnecessary.
The present invention provides a power cell having
an electroactive material comprised of a complex of a transi-
tion metal, wherein said electroactive material is a complex
of a transition metal and a schiff base dissolved in a polar
organic solvent, water or their mixtures.

-- 3 --
The power cell in accordance with the pr~sen-t invention
may be a secondary power cell.
The transiti~n metals used to compose the electroactive
material according to ~he invention are such metals, as:
nickelt cobalt~ iron, chromium, manganese, copperO titanium
and vanadiums
Schiff bases are used as organic liyands, the most advan-
tageDus being the ethylenediamine derivatives.
Denoting the electroactive material according to the in-
vention as MeL jtvie - transîtion metal, L ~ ligand~, it is re-
duced on cathode duriny the power cell char~ing cycle to lvleL .
During the workiny cycle a reversed react~on tal~es place~ Si-
milarly, during the charging cycle MeL is oxidized on anode to
1eL~, and this reaction is reversed dur ng the working cycle.
The cathode and anode reactions are electrochemically re-
versible, i.e. the same electroactive material works as a re-
actant during the charging cycle, and as a product during the
workins cycle on both electrDdes. The rate of both these re-
actions is controlled by the transport rate.
The additional merit of the electroact~ve material accord-
ins to the invention is a relatively lligh energy output froM
a unit of weight, as well as the possibility of application
of the power cell containing such a material in low tempera-
ture conditions. Moreover, mixing the electroactive material
according to the invention contained within the anode and
cathode zone does not result in an irreversible deactivation
of the power cell, allowiny repeated charging.
The subject o~ this invention is closer described in fol-
lowing examples of preferred embodiments, which do not however

limi~ the scope of ~his invention~ The enclosed Fig, l and
Fig. 2 display cyclic voltammetry curves obtained in condi-
~ions described in Examples I and II, respectively.
Example I.
The electrDactivs material for power cells composed of
a csmplex c~mpound o, nickel (Ni(II)) and N, N ~ethylene~bis
(salicylidenoimine)~ salen) di-ssolved in a O.lM ~C2H5)4 NCl04
-(TEAP) solution in N,N-dimethyl~ormamide (DI~F3. The s~lution
was deoxidized by purging with dry nitrogen~ The electrodes
were made o~ platinum wire 0.6 ~m in diameter and 8 mm long,
The cell dia~ram before charging was:
Pt¦Ni(sale~ (O~lM TEAP in Dl~lr)l Ni (salen),(O.l~1 TEAP in DMF)¦Pt
The difference of standard electrode ,ootentials in this
cell was, ~ E~ = 2.46 V.
During charging and work, the ~0 = -l.59 V and
k = 0.71 x lO 2 cm/s on cathode, and Eo = +0.~7 V and
k~ = 0.72 x lO 2 cm~s on anodeO Potential sweep rate, Vp =
= 5~ mV/s, temperature 25 C, Ni (salen) concentration:
2 x lO 311
Stanoard potentials to, relati.ve to saturated calomel
electrode, SC~, v~ere determin2d as arithmetic means of anode
and cathode peal~ poten~ials /Fig. l/, while the standard of
rate constants charge exchange, I~s, were calculated using
Nicholson method /~.nal~ Chem. 44, 19.6;(1955)/ from the re~
lation between the anode and cathode pea!c potentials,
Example IIo
The electroac~ive material f3r power cells ~omposed of
N,N -ethylene-bis (salicylidenoiminate)-cobalt(II)-(Co (salen))
* N,N-bis salicylidene ethylenediamine dianion

- 5 -
dissolved ln O~l~i Tr:,`\P solutiorl :in llc~amethylphospllo-~riami~e
Tile cell dia~ram beFor^ ~he cl~3rgin~ wa~:
Pt¦~o(salen)~(0~1ll T~ P ln ~-lr~lP~ Co (5alen)~(oo~ TE,~P in ~IrlPT)¦
The dirferencs oF s~andard electrode po~entials in this
cell Y~as ~ 0 = 1~35 v,
~ Fter joinin~ the electl~odes ~cnar~in~ and worlc~,
~-0 a le20 V and ks ~ 0~4~ x 10 2 cm~s on ca~hode, and
Eo = ~0 rl5 V~ kS = ~20 x lo 2 cm/5 on anode e
Potentials ~ and rate constan-ts Qf C)larSe exchan~c
were determined as in Fx3Mple ~0
The cyclic voltammetry curve ~i'ig~ 2~ was recorded in
Followiny conditions:
Co(salen) concentraticn: 2 x ~0 3~1
~otential sweep rate: ~0 mV/s
Temperature: 20 C
r