|Title of Invention||
A PROCESS TO ENHANCE THE ELECTROCHEMICAL ACTIVITY OF NATURAL MANGANESE DIOXIDE FOR DRY CELL
|Abstract||The process to enhance the electrochemical activity of natural manganese dioxide for dry cell wherein electrochemical activity of natural manganese dioxide is enhanced by diffusing approximately 0.1 weight percent of dopant having ionic size approximately that of the manganese ion into the crystal lattice of natural manganese dioxide at latter's softening temperature of approximately 450 ° C for approximately 48 hours adapted to lose the thermodynamic stability.|
THE PATENT ACT, 1970
'A PROCESS TO ENHANCE THE ELECTROCHEMICAL ACTIVITY OF NATURAL MANGANESE DIOXIDE FOR DRY CELL "
MATSUSHITA LAKHANPAL BATTERY INDIA LIMITED.
An Indian company incorporated
in India under the Companies Act, 1956
of India having its registered office at
Makarpura, G.I.D.C, Vadodara 390 010
State of Gujarat, India.
The following specification particularly describes and ascertains the nature of this invention and the manner in which it is to be performed: -
This invention relates to a process to enhance the electrochemically activity of natural manganese dioxide for its application in zinc carbon dry cell (here after referred as dry cell).
FIG 1 shows commonly available dry cell especially with cylindrical can shaped zinc anode 1. Against the interior cylindrical surface of the can, a layer of jellified starch 2 containing ammonium chloride and zinc chloride in water as electrolyte. The cathode depolarizer material containing a mixture of natural or / and synthetic artificial manganese dioxide and conductive carboneous material such as acetylene black moistened with liquid electrolyte compressed in the form of bobbin 3 which is placed in contact with starch layer. Centrally placed within the depolarizer material is the rod shaped carbon electrode 4 acting as current collector with its upper end covered with a metal cap 5.
In a dry cell, the depolarizer mix composition decides the service output to be delivered from a fixed volume available in the cylindrical zinc can. The depolarizer mix therefore is designed with a suitable blend of synthetic and naturally occurring manganese dioxide to occupy the above said fixed volume depending on either the consumer requirement or the dry cell with a particular application. The different types of available manganese dioxide used in the above blend are naturally occurring manganese dioxide (hereafter referred as NMD), chemicallytreated or -developed manganese, dioxide. (CMD) and electrochemically deposited manganese dioxide (EMD). The electrochemical activity is higher in EMD and is least in NMD with later price is approximately ten times cheaper. Therefore NMD especially constitutes the larger proportion of cathode mix, for the dry cell manufactured for low to medium current drain applications.
The disadvantage of above considered cathode depolarizer mix is that, if service output performance of dry cell has to be enhanced, then due to fixed volume in the dry
cell, largely constituting NMD has to be substituted with CMD or EMD making the dry cell price expensive.
It has been known through literature that electrochemical activity of natural manganese dioxide can be enhanced either by simply annealing at higher temperature maximum to its softening temperature or by inserting traces of ionic impurities (hereafter referred as dopant) into the manganese dioxide lattice through insitu doping using Mn(N03)2 at its thermal decomposition temperature else by co-deposition of dopant into the crystal lattice during the manufacturing of electrolytic manganese dioxide from either MnS04 or MnCk bath. However, no work or process of solid state diffusion or inserting dopant into a thermodynamically stable form of NMD at its softening temperature has been reported or established.
OBJECT OF THE INVENTION
It is the object of the present invention to disclose the economically viable process of enhancing the electrochemical activity of NMD.
It is the object of the present invention to enhance the electrochemical activity of NMD at its softening temperature by solid state diffusion or insertion of dopant into the crystal lattice of NMD.
SUMMARY OF INVENTION
In accordance to present invention, an economically viable process of enhancing the electrochemical activity of NMD for dry cell is disclosed wherein active NMD was prepared by diffusion of dopant into the crystal lattice of NMD, at the softening temperature of NMD. In the present invention the ionic size of the dopant is approximately of the ionic size of manganese ion for the process to be effective. The insertion of dopant into the crystal lattice of NMD leads to crystal defect such as either replacement manganese ions or occupancy of interstitial sites by the dopant, losing the thermodynamic stability and resulting into dectrochemically active NMD.
DETAILED DESCRIPTION OF THE INVENTIONS
This invention is now described with reference to the example of doping on NMD and its effects on electrochemical activity.
The active NMD sample was prepared by thoroughly mixing NMD and 0.1 wt % (of NMD) of molybdenum based oxide as dopant and followed by subjecting the mixture to heat treatment at the softening temperature of NMD, i.e., 450°C for 48 h in a rotary furnace. The resultant mixture was treated with 7.5 N NH3 by thoroughly stirring for about 30min. to remove the unreacted molybdenum based oxide as ammonium molybdate. The treated oxides (hereafter referred as doped NMD) were then washed with plenty of water and then dried at 110°C, and adequately stored. To compare the effect of electrochemical activity on Molybdenum doped NMD and heating, sample of NMD was subjected to above process without dopant. The resultant oxide (hereafter referred as annealed NMD) was used for comparative study.
The comparison of electrochemical activity between Molybdenum doped NMD with annealed NMD and NMD was evaluated electrochemically through half-cell reaction. The reference voltage was taken against saturated calomel electrode (S.C.E) acting as reference electrode and the working electrode constitutes of the 0.1 g of above manganese dioxide under evaluation in the ratio of 1:10 with carbon black compressed and palletized in circular form for each respective evaluation. The cell was activated by dipping into Lechanche electrolyte (5M NH4CI + 2M ZnCl2) before subjecting to discharge at different constant currents (continuous) of 1, 5 and 10 mA respectively at 25° C. The discharge curves were recorded on a computer controlled potentiostat / galvanostat to a cut-off voltage of 0.00 V vs. SCE (approximately 1.00 V vs. Zn).
FIG 2: Shows the comparative Voltage Vs time curve of Molybdenum doped NMD (marked as A", B" & C") and NMD (marked as A, B & C) at 1, 5, 10 mA constant current regime respectively.
FIG 3: Shows the comparative Voltage Vs time curve of Molybdenum doped NMD (marked as A", B" & C") and annealed NMD (marked as A' B' & C) at 1, 5, 10 mA constant current regime respectively.
Table 1 given below shows different electrochemical parameter evaluated from the voltage vs. time curve.
FIG 2 represents the comparison of variation in discharge duration in terms of mAh and also usable energy (area under the curve) in terms of Jouies/gram for Molybdenum doped NMD and NMD in different constant continuous discharge regime of 1, 5, 10 mA. Time is given in abscissa in seconds and Voltage against SCE in ordinates in mV. Curve A" and Curve A represents the discharge curve of Molybdenum doped NMD and NMD at a discharge rate of 1 mA. Similarly curve B" & Curve B and Curve C" & Curve C represents the discharge curve at 5 and 10 mA respectively.
FIG 3 represents the comparison of variation in discharge duration in terms of mAh and usable energy (area under the curve) in terms of Joules/gram for Molybdenum doped NMD and annealed NMD in different constant continuous discharge regime of 1, 5, 10 mA. Curve A" and Curve A' represents the discharge curve of Molybdenum doped NMD
and annealed NMD at a discharge rate of 1 mA. Similarly curve B" & Curve B' and Curve C" & Curve C represents the discharge curve at 5 and 10 mA respectively.
It is evident from the data in Table 1 given above and FIG 2 that the discharge performance in terms of mAh capacity and usable energy for the Molybdenum doped manganese dioxide sample is significantly improved for all the three discharge regimes of 1,5, and 10mA, compared with NMD sample. This improvement is however not so significant compared to the annealed NMD sample in low and intermediate drain of 1 and 5 mA but a distinct improvement of 9 % and 8.3 % in both usable energy and discharge duration respectively observed during relatively high rate discharge of 10 mA current drain.
An explanation of the observed phenomenon will now be given as follows;
The physico-chemical characterizations of the samples are depicted in Table 2 given below.
It is evident from the Table 2, that the purity of the annealed NMD sample has increased compared with NMD sample due to the loss of combined water by virtue of which the manganese dioxide content has increased. But in Molybdenum doped NMD, purity is marginally lowered compared to that of annealed sample which indicates the feasibility of solid state diffusion at the softening temperature of NMD i.e., 450°C. It is also evident from the Table 2 that tapping density (apparent density) has increased for Molybdenum doped NMD sample compared to annealed NMD and NMD leading to increased surface area and thereby, enhances the number of sites for reaction. Resistivity data further shows that conductivity of Molybdenum doped manganese dioxide sample have increased considerably leading to better discharge performance in relatively high discharge rate.
This invention particularly relates to a process of enhancing the electrochemical activity of NMD for dry cell wherein solid state diffusion made possible on thermodynamically stable NMD at its softening temperature by inserting dopant having ionic size approximately that of manganese ion. The said dopant having ionic size approximately close to manganese ion, for enhancing the electrochemical activity can be Aluminum (Al), Bismuth (Bi), Molybdenum (Mo), Vanadium (V) and Titanium (Ti). The process of doping shall be carried out at the softening temperature of 450°C for 48h.
This invention further state that the doped NMD can be effectively and efficiently used in
relatively heavy discharge rate;
1. The process to enhance the electrochemical activity of natural manganese dioxide for dry cell wherein electrochemical activity of natural manganese dioxide is enhanced by diffusing approximately 0.1 weight percent of dopant having ionic size approximately that of the manganese ion into the crystal lattice of natural manganese dioxide at latter's softening temperature of approximately 450 ° C for approximately 48 hours adapted to lose the thermodynamic stability.
2. The process to enhance the electrochemical activity of natural manganese dioxide for dry cell as claimed in claim 1, wherein dopant having ionic size approximately close to manganese ion wherein dopant can be Aluminum, Bismuth, Molybdenum, Vanadium and Titanium.
3. The process to enhance the electrochemical activity of natural manganese dioxide for dry cell as claimed in claims 1 and 2 as substantially described in the specification herein above and illustrated in the accompanying drawings.
Dated this day of March, 2004.
For Matsushita Lakhanpal Battery India Ltd.
|Indian Patent Application Number||289/MUM/2004|
|PG Journal Number||42/2008|
|Date of Filing||08-Mar-2004|
|Name of Patentee||MATSUSHITA LAKHANPAL BATTERY INDIA LTD.|
|Applicant Address||G.I.D.C. MAKARPURA, VADODARA 390 010, GUJARAT, INDIA.|
|PCT International Classification Number||C25B 4/16|
|PCT International Application Number||N/A|
|PCT International Filing date|