Title of Invention


Abstract This invention relates to a cathode for aqueous secondary cells. It consists of a nickel plaque having a coat of poly aniline having oligomeric phthalocyanine incorporated therein. The invention also includes a cell having the above referenced cathode and a zinc anode separated by a sheet or film impregnated with aqueous zinc sulphate solution. A method of making the cathode is also included in the invention.
Full Text

This invention relates to a cathode for an aqueous secondary cell. The invention also includes an aqueous secondary cell incorporating the cathode of this invention.
Polymer cells having electrochemically synthesised polypyrrole doped with tetrafluoroborate as a positive electrode is known in the art. 0.5 molar solution of lithium tetrafluoroborate in propylene carbonate is the electrolyte and lithium foil is used as a the other electrode. Though the overall performance of these cells are excellent, the energy density is lower than the theoretical value. Further, to avoid increase of viscosity due to decrease in ion concentration in the electrolyte, during discharge operations, solvent concentration has to be regulated and maintained in excess.
Yet another rechargeable polyaniline - lithium battery known in the art has polyaniline doped with tetrafluoroborate as anode and lithium alloy as negative electrode. A mixture of lithium tetrafluoroborate, propylene carbonate and 1,2 methoxy ethane is the electrolyte solution used in such cells. As self discharge of these batteries is about 15% in 90 days, they are found to be no match to conventional Ni-Cd batteries in power delivery.
Performance of polyaniline batteries in combination with Zn or PbOi electrode have also been studied. The cells in which Zinc was used showed a maximum output capacity of 108Ah and an energy density of lllWh/kg polymer. In order to keep high coulombic efficiency, the charging depth is

maintained at less than 80%. Further, the polymer electrode must also be kept free of exposure to high anodic potential in order to achieve long term stability. The negative electrode of Pb02 showed high coulombic efficiency of >95% even after 4000 repetition of charge - discharge cycles, even when exposed to high anodic potentials. However, the use of lead compounds is highly detrimental from the environmental point of view.
Prior art discloses the use of monomeric metallo and metal free phthalocyanine compounds as cathode and acetylene black as current collector cathode with lithium disc as anode and 1 molar lithium perchlorate in propylene carbonate as electrolyte. Cells having polymeric phthalocyanines as cathode are also known in the art. However, phthalocyanines exhibit electrocatalytic activity towards decomposition of the solvent namely propylene carbonate when the cut off voltage exceeds 1 V.
From above prior art disclosure, it has become abundantly clear that the hitherto known batteries having conducting polymers as one of the electrodes and lithium or lithium containing alloy as the counter electrode have many limitations.
An aprotic solvent is conventionally used to dissolve the electrolyte. A further disadvantage is the passivation of lithium with a layer of lithium carbonate. In aqueous batteries using polyaniline alone as cathode deeper and higher charging current density were reported resulting in lowering of current efficiency and cycle stability.

In order to overcome the above discussed drawbacks, a secondary cell that works in aqueous medium having a cathode of oligomeric phthalocyanine incorporated polyaniline coated on a nickel plaque in combination with Zinc as the anode has been developed. The cathode in accordance with the invention affords high energy density and cycle stability. Yet another advantage of this invention is the secondary cell made in accordance with the invention does not use any toxic substances such as lead, cadmium and their derivatives.
Oligomeric metallo phthalocyanine incorporated polyaniline as cathode in rechargeable aqueous cells achieves these objectives. Oligomeric metallo]
phthalocynine incorporated poly aniline is prepared by blending the individual/
polymers in any desired ratio
Oligomeric phthalocyanato cobalt containing carboxy terminal is prepared by reported method. The method involves heating benzene 1,2,4,5 tetracarboxylic dianhydride with cobalt sulphate in presence of urea and other catalysts namely ammonium chloride and ammonium molibdate at 180°C in nitrobenzene medium for 12 hrs. The product is purified by repeated washing with

methanol followed by boiling with alkali and precipitation by dilute hydrochloric acid. The precipitate was filtered, washed and dried in vacuum at 50 -60*^0. This is referred to as PPC for brevity.
Known oxidative polymerisation of aniline in aqueous hydrochloric acid using ammonium persulphate as the oxidising agent resulted in the production protonated form of the emeraldine base namely emeraldine hydrochloride. The reaction is carried out at 0*^0 or below. The polymer obtained is dried under vacuum and is found to have a structure - [CgH^NH - CgH^NH-CgH^N = CgH^N^]^"*" 201"". This polymer is herein referred as PANI. These two polymers vis. PPc and PANI are made into a fine powder separately and are mixed in the solid state in the desired weight ratio. Dimethyl formamide may be used as the mixing medium. A nickel plaque of the desired dimension is then made by sintering nickel powder with expanded nickel mesh. The pasty mass of PPC and PANI is coated on the nickel plate and is then allowed to dry. The coated electrode may then be weighed to ascertain the weight of the coating.
The cathode for an aqeuous secondary cell according to this invention comprises a nickel plaque provided with a coating of polyaniline incorporated with oligomeric phthalocyanine thereon.

This invention also includes a method of making a cathode for an aqueous secondary cell comprising mixing oligomeric phthalocyanine and polyaniline and coating the same on nickel plate consisting of a nickel film or sheet sintered with metallic nickel and subsequently drying the same.
An aqueous secondary cell is obtained with the help of zinc foil as the anode. Preferably Zinc foil of 0.2mm thickness having dimensions of 25 x 5.0 cm^ used in conjunction with a cathode having a nickel plaque of 2.5 x 5.0cm^.
The Zinc foil and the polymer coated nickel plaque were pressed together with a filter paper or the like permeable sheet or film as a separator in between them. The separator has previously been soaked in O.IM aqueous solution of ZnS04.
This invention also includes an aqueous secondary cell which comprises a Zinc anode in conjunction with a cathode consisting of a nickel plate provided with a coating of polyaniline incorporated with oligomeric phthalocynanine, said anode and cathode being separated by a separator containing aqueous Zinc sulphate solution.

Cells made with PANI and PPo in the ratio of 1:0.5 by weight exhibit an initial open circuit voltage of 1.28V These cells discharged a constant current of 0.9KiA/cffi . The following equations explains the electrochemical reaction taking place in the cell.
-C6H4NH-C6H4NH-C6H4-N=C6H4=N- + 2H^ +2e- =
-CeH4 NH- CeH4 NH- C,H, -NHCeH, -NH 1
Ci2oH4oN32 032Co4.8H20+4e- - C,,,H,,N,,Co,'- m^O 2
The charge delivered is calculated on the basis of equations 1 and 2.

Table I shown herein below shows t voltage, charge capacity and energy density of t by using different weight ratios of PANI and PPc
Table 1. Effect of PPc content on the cell/parameters )

RANI PPc OCV Charge Energy rechargeable
ratio by (V) capacity density cycles
weight % mAh** Ah/Kg+
PAN! 1.24 5 10 nil
90:10 1.22 5 10 one
80:20 1.22 12.5 25 two
66.6:33.3 1.24 25 50 six
** calculated ba sed on the time taken to run a 3 00mA motor (cu rrent density ^
6mAcm^) I

Table II shovn hereinbelow shows the comparison of experimentally observed oapaoiter . theoritioall. calculated value ^^^ the calls having cathodes with different proportions of PAHI and PPc.
Table 2 Theoretical and experimental capacities of the cells containing different proportions of PANI and Ppc

\ * at current strength of 0.9mA/cm^; t in non-aqueous systems; ** Studies were done in aqueous solution (.1M ZnS04 ). There is no need to expel oxygen from the system

PANI- Theo. Exptal. Max. Stability
PPc ratio Capacity Capacity Charging
bywt% (Ah/Kg) (Ah/Kg) Voltage (V)
PANI 123.8 123.8* 1.3 Good in
(100%) oxygen free atm.
PANI 148.1 148.0* 1.2 Good in
(EB) oxygen free atm.
80:20 106.7 106.0 1.4 Good**
66.6:33.3 95.5 95.1 1.5 Good
50:50 80.9 58 1.5 ** Good

It is observed that cells with PANI alone performed well only in an oxygen free atmosphere. The charge for 5g of PANI-PPc containing Ig of Pani and 0.5g of PPc is calculated as i [(96500 X 4/2819.6 ) x 0. .5 + (96500 x 2/433) x 1 = 514.18 coulombs (Molecular weight of PPc is 2819.6 and that of PANI is 433 ]. The cell is then charged at constant current of 0.9mA/om . The cell potential increased rapidly at 1.4V. After attaining a value of 1.4V the increase in cell voltage was not steep. A total charge of 514 coulombs was involved in this step. Immediate discharge of the cell to a voltage of 0.65V liberated 514 coulombs of charge indicating a 100% current efficiency. When the charged cell is left open, it discharges slowly and reaches the open circuit value within half an hour and then remains constant for a long time. The charge -discharge characteristics are retained on continuous cycling indicating that no degradation of the polymer occured during the continuous cycling. If the discharging is done immediately after charging the current efficiency was found to be 100%. The maximum capacity of the cell was calculated based on equations 1 & 2 is 95.5 Ah/kg { (96500 x 4/3600) x 0.33/2819.6 } + {(96500 x 2/3800) X 0.67/433 } for the particular composition of PANI-PPc. The experimentally observed charge of 514 coulombs involved in the 0.9mAcm discharge reaction given corresponds to a capacity of 95.5 Ah/kg based only on the weight of PANI-PPc. This value agrees very well with the experimentally observed value.

The above details indicate that the cells developed by , [US/ provides stable and efficient secondary battery that work in an aqueous media. These cells are repeatedly recyclable/and has 100% efficiency in aqueous medium even in the presence of oxygen «»> stable performance is exhibited upto the termination charging of voltage 1.4V though at higher charging voltages of the cell, the charge capacity and energy density increases at the expense of recyclability.
The cell performance is independent of the
concentration of Zinc sulphate and it does not require
maintenance of excess solvent to avoid increase in ion
Though this invention has been described herein above with specific embodiments, obvious equivalents and modifications known to persons skilled in the art are within its scope and that of the appended claims.

1. A cathode for an aqueous secondary cell comprising a nickel plaque provided with a coating of polyaniline incorporated with oligomeric phthalocyanine thereon.
2. The cathode as claimed in claim 1, wherein said nickel plaque consists of an expanded nickel mesh sintered with nickel powder.
3. The cathode as claimed in claims 1 or 2, wherein said coating consists of powdered polyaniline and oligomeric phthalocyanine dispersed in dimethylformamide.
4. The cathode as claimed in claims 1 to 3, wherein the ratio of oligomeric phthalocyanine to polyaniline in the coating is of 1:0.5 wt ratio.
5. The cathode as claimed in claims 1 to 4, wherein said nickel plaque has a dimension of 2.5 x 50 cm .
6. A method of making a cathode for an aqueous secondary cell comprising mixing oligomeric phthalocyanine and polyaniline and coating the same on nickel plate consisting of a nickel film or sheet sintered with metallic nickel and subsequently drying the same.
7. An aqueous secondary cell comprising a zinc anode in conjunction with a
cathode Consisting of a nickel plaque provided

with a coating of polyaniline incorporated with oligomeric phthalocyanine said anode and cathode being separated by a separator containing aqueous zinc sulphate solution.
8. The cell as claimed in claim 7, wherein the separator
is a permeable film of sheet and is impregnated with an aqueous
zinc sulphate solution.
9. The cell as claimed in claim 8, wherein said aqueous
zinc sulphate solution has a strength of 0.1M.
10. A cathode for an aqueous secondary cell substantially
'^ as herein described.
11. A method of making a cathode for an aqueous secondary
■J cell substantially as herein described.
12. An aqueous secondary cell substantially as herein


1166-mas-1999 abstract.pdf

1166-mas-1999 claims.pdf

1166-mas-1999 correspondence-others.pdf

1166-mas-1999 correspondence-po.pdf

1166-mas-1999 descripition(completed).pdf

1166-mas-1999 form-1.pdf

1166-mas-1999 form-19.pdf

1166-mas-1999 form-26.pdf

1166-mas-1999 form-3.pdf

Patent Number 240393
Indian Patent Application Number 1166/MAS/1999
PG Journal Number 20/2010
Publication Date 14-May-2010
Grant Date 07-May-2010
Date of Filing 03-Dec-1999
# Inventor's Name Inventor's Address
PCT International Classification Number H01M10/08
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA