FIELD OF THE INVENTION:
The present invention relates to lead acid battery, and more particularly to composition of the paste with the addition of peroxide additive in situ during paste manufacturing to make positive electrode in order to improve the formation efficiency decreases the current input.
BACKGROUND OF THE RELATED ART:
Lead Acid batteries are one of promising energy storage technologies for so many years in various applications. Even though other technologies such as Lithium ion batteries, Nickel metal hydrides etc. are comparatively superior in terms of performance, the preference has been given to lead acid batteries because of their cost and robustness. But recent advances in new storage technologies (with reduced cost) clearly indicate that there is a threat for lead acid batteries.Hence, there is a need for further reduction in the overall cost of manufacturing and improvement of performance of lead acid batteries.
A typical lead-acid battery manufacturing process includes grid casting, paste mixing, pasting, curing, drying, assembly and formation steps. The precursors for positive and negative active material called as paste are manufactured by mixing lead oxide with additives and sulfuric acid. Then these pastes are coated on the positive and negative electrode grids. The prepared so called plates are cured and dried at controlled temperature and humidity. The batteries are assembled with separator placed in between positive and negative plates. Then electrolyte i.e. sulfuric acid, is filled inside the battery and it undergoes a formation step in which a first time charge is applied in order to convert this cured positive & negative paste into electrochemically active porous materials of lead dioxide and spongy lead respectively.
One of the time and energy consuming step in overall lead acid battery manufacturing process is formation. There are so many additives to positive active material studied in order to reduce this formation time and energy. But practically, very few are succeeded in this area due to lacking in production feasibility, additional cost incurred and adverse side effects on performance. Thus there is need for a specialized composition for paste recipe which can speed up the formation process with reduced energy consumption and also improving the performance of the battery.

The US Patent no. 3,194,685 is the closest prior art which relates to a method for manufacturing stable, pre-sulfated, dry active material for both positive and negative lead acid storage battery electrodes.
However, the present invention is totally different due to the addition of an additive of Sodium and Calcium peroxide which in turn becomes respective sulfate and hydrogen peroxide, the hydrogen peroxide in situ oxidize the lead oxide into lead dioxide and free lead into lead oxide, during drying and mixing process which improves formation efficiency and reduces power input.
SUMMARY OF THE INVENTION
As said in background of the art, an objective of the present invention is to reduce the formation cycle time and energy consumption with improved battery performance. This is achieved by introducing a positive paste composition having a novel additive which can play both roles of formation efficiency enhancement and performance improvement.
Another objective of this invention is to optimize the paste mixing recipe in such a way that there is no impact on paste density. The said battery prepared from this paste does not have any affected with side effects.
DETAILED DESCRIPTION
One embodiment of the present invention provides composition of a paste used for making positive electrode of lead acid battery. The positive electrode paste formula consists of the following raw materials by weight percentage per weight of lead oxide having 25-30% of free lead used: 10-11% of sulfuric acid (specific gravity at 25°c of 1.395-1.405), 0.095-0.105% of Modacrylic/Polyester fiber, 0.1-0.2%) of calcium peroxide or sodium peroxide, 11-12%) of de-mineralized water.
Another embodiment of the present invention provides the preparation of the novel paste consisting above ingredients is explained. The dry materials such as lead oxide having 25-30%> free lead, modacrylic fiber and sodium/calcium peroxide are mixed in an automatic mixer for 3-5

minutes, de-mineralized water is added into the mixer and wet mixing is done for 2-3 minutes. Sulfuric acid of 1.400 density is added to the mixer slowly for a period of 17-18minutes and with cooling system or exhaust switched on after 50°c. Final mixing is done with exhaust and cooling system for about 5-7 minutes and the paste peak temperature is maintained at 62-64°c. Then measured the apparent density of the paste and adjusted to 4.15 to 4.25 g/cm and the final dumping temperature to less than 45 ° C.
Above paste is pasted onto lead alloy based grid and then cured at an automatic humidity controlled chamber. The electrode which is prepared in such a way is used as positive electrode and standard negative electrode is used to assemble 12V-35Ah battery which is used for SLI (Starting, Lighting & Ignition) application. A controlled sample is also prepared without adding the novel additive i.e. sodium/calcium peroxide.
Above batteries are filled with dil.sulfuric acid of specific gravity 1.230 and formation is done with standard formation program input for controlled batteries and with 10% reduction in formation input and cycling time for batteries under invention as given in below table. Both the batteries are met the requirement of standard open circuit voltage (12.75-12.85V) and specific gravity (1.290±0.05).
Table 1: Formation Program

S.No Step Control battery Invention

Current Time Capacity Current Time Capacity
1 Stepl 3 1:00 3 3 0:50 2.5
2 Step 2 10 12:00 120 10 10:50 108.3
3 Step 3 0 1:00 0 0 1:00 0
4 Step 4 7 5:00 35 7 4:30 31.5
Total 19 158 17:10 142.3
The batteries are then tested as per JIS D5301 standard for initial capacity. The control battery has delivered 36Ah and battery under invention has delivered 38Ah i.e. approximately 5% improvement in initial capacity. The mechanism behind the improved formation efficiency is explained in the below given chemical reactions.
The sodium peroxide when dissolved in water, it is converted into sodium hydroxide and hydrogen peroxide. Thus formed hydrogen peroxide is utilized in the partial oxidation of lead oxide into lead dioxide. In case of calcium peroxide, the reaction is single step as it does not dissolve in

water. When calcium peroxide reacts with sulfuric acid it releases calcium sulphate and hydrogen peroxide.
Reactions with Sodium peroxide:
Na202 +2H20 = 2NaOH + H202 - (1)
2NaOH + H2S04 = Na2S04 + 2H20 - (2)
H202 + PbO = Pb02 + H20 - (3)
Reaction with calcium peroxide:
Ca02 + H2S04 = CaS04 + H202 - (4)
H202 + PbO = Pb02 + H20 - (5)
The cured active material from this novel concept consists of nonconductive mono or tribasic lead sulphate and conductive lead dioxide compared to the conventional paste recipe consisting only nonconductive materials. Due to presence of this conductive path within the electrode, the utilization of formation charge input is more. Hence, there is no need of slow charging step in the initial formation and there is a reduction of about 8-10% in both formation input charge and time.
The additive of peroxide does not alter the paste consistency and structure, however it improves paste morphology produces more lead mono oxide and tribasic sulfate crystal increases formation efficiency and decreases the current input in formation cycle. The presence of lead dioxide in the cured paste increases the conductivity and accelerates the formation process. So, paste with peroxide additive can improve the formation efficiency by reducing the formation input energy by 20%. Also the peroxide additive can convert the free lead (25-30%) to lead monoxide during paste mixing.
Along with reduced formation cycle time and energy, the batteries made with this new paste formula exhibit improvement of about 5% in initial capacity.
The addition of peroxide additive in positive active material during paste mixing and subsequent curing and drying process leads to the creation of small amount of conductive lead dioxide. The conductive lead dioxide present in the cured paste potentially increases the conductivity of the paste during formation, thus enables the paste to form with less formation input energy compared to without additive sample 0.1% -0.2% of a small addition will show the higher impact on lead dioxide conversion at all levels of formation input energy and adequate conversion is achieved at 5 times rated capacity of formation input energy. Potentially up to 10% of formation input energy can be reduced by the addition of 0.1%-0.2% addition of peroxide additive.

It may be noted that the present invention is not limited to the above embodiments and the invention could be exemplified in many other ways obvious to a person skilled in the art.

We claim:
1. A composition for positive electrode of lead acid battery, comprising:
- 25 to 30 wt% lead;
- 10-11 wt% sulfuric acid;
- 0.095-0.105 wt% of modacrylic/polyester fibre;
- 0.1-0.2 wt% of calcium peroxide or sodium peroxide; and
- 11-12 wt% of demineralised water.

2. The composition as claimed in claim 1, wherein the lead is predominantly in the form of lead oxide.
3. A method for preparing a composition as claimed in claim 1 for positive electrode of lead acid battery comprising the steps of:
a. mixing the dry materials such as lead oxide, modacrylic fiber and sodium/calcium
peroxide in an automatic mixer for 3 to 5 minutes;
b. adding the demineralised water into the mixer and wet mixing is done for 2-3 minutes;
c. adding the sulfuric acid to the mixer slowly for a period of 17-18 minutes
4. The method as claimed in claim 3, wherein mixing is conducted at the temperature from about 62 °C to 64°C.
5. The method as claimed in claim 3, wherein the density of the composition is 4.15 to 4. 25 g/cm3.
6. The method as claimed in claim 3, wherein the final dumping temperature is maintained below the 45°C.