2 FIELD OF THE INVENTION:The present invention relates to flooded flat plate type lead acid battery used in automotive applications, and more particularly to composition of the paste used to make negative electrode in these batteries.BACKGROUND OF THE RELATED ART:Lead Acid batteries are being used throughout the world in various types of applications such as automotive, industrial, power back up etc. The recent advancements in automotive segment are forcing severe challenges to lead acid batteries from its rival storage technologies like lithium ion batteries. While lead acid batteries are highly recommended because of their cost benefit, their usage in advanced technologies has certain limitations under partial state of charge conditions and colder climates. The important parameters under consideration for automotive batteries are charge acceptance, cold cranking and cyclic life. The main failure modes of lead acid batteries in these conditions are negative plate sulfation and positive grid corrosion. While these parameters affect the cyclic life of the battery and charge acceptance, the negative active material composition greatly affect the cold cranking behavior and also initial charge acceptance.Traditionally, the electrodes are prepared by four steps namely grid casting, paste mixing, pasting and curing. The precursors for negative active material called as paste are manufactured by mixing lead oxide, binder, carbon black, barium sulfate, vanisperse, sulfuric acid and demineralized water. The paste is then pasted onto the grids and cured & dried under controlled humidity and temperature. Then positive and negative plates are sandwiched with separator in between them and assembled. The electrolyte i.e. sulfuric
3 acid is filled and initial charging i.e. formation is done which converts cured material into electrochemically active materials lead dioxide in positive and spongy lead in negative. Several studies have been done to overcome the failure modes of lead acid batteries by means of active material additives, alternate grid materials, electrolyte additives. Very few are successful and the negative plate failure is still a challenging one for lead acid battery industry. Electrode preparation particularly negative electrode plays a vital role in the performance of the battery. The composition of the active material is one of the important factors to be considered for optimum battery performance. Thus there is a need for a novel composition for the negative active material which helps in improving performance of the battery especially charge acceptance and cyclic life without affecting cold cranking behavior.SUMMARY OF THE INVENTIONAs said in background of the art, an objective of the present invention is to improve the charge acceptance and cyclic life of the flooded plate lead acid battery used in automotive application. This is achieved by introducing a high surface area and conductive carbon black of the concentration of about 0.15-0.2% in negative paste composition and one of an aqueous polymeric binders such as polyvinylidene difluoride (PVDF), Polyvinyl acetate (PVA) etc in the range of 25-30ml diluted in 2lit of DM water. The surface area of the said carbon black is around 1400-1500m2/g . The objective of this invention is to optimize the paste mixing recipe using the above said carbon and binder in such a way that there is no impact on cold cranking behavior of
4 the battery. Other embodiment of the present invention is to derive the paste mixing process with above said recipe to maintain the paste density and porosity. DETAILED DESCRIPTIONOne embodiment of the present invention provides composition of a paste used for making negative electrode of flooded plate type lead acid battery. The negative electrode paste formula consists of the following raw materials by weight percentage per weight of lead oxide used: 8.2-8.5% of sulfuric acid (specific gravity at 25°c of 1.395-1.405), 0.195-0.205% of Modacrylic fiber, 0.15-0.2% of high surface area and conductive carbon black, 0.55-0.65% of barium sulphate, 0.25-0.35% of lignin, 11-12% of demineralised water. One of aqueous polymeric binders from PVDF/PVA in the range of 25-30ml diluted in 2lit of DM water is also added at the end of the process. The unoxidized free lead content of lead oxide powder is in the range of 25-30%. The surface area of the above said carbon black ranges from 1400-1500m2/g.Another embodiment of the present invention provides the preparation of the negative active material paste consisting above ingredients. The dry materials such as lead oxide, modacrylic fiber, carbon black, barium sulphate and vanisperse are mixed in anautomatic mixer for 3-5minutes, deminerlized water is added into the mixer and wet mixing is done for 2-3 minutes. Sulfuric acid is added to the mixer slowly for a period of 17-18minutes with cooling system or exhaust switched on after 50°c. Final mixing is done with exhaust and cooling system for about 5-7minutes and the paste peak temperature is
5 maintained at 60-64°c. The above said polymeric binder is added and mixed for 2-3min. Then the apparent density of the paste is measured and adjusted to 4.40 to 4.45 g/cm3.The above pastes are pasted on to lead-calcium alloy based grids and are cured by conventional 3BS low temperature curing method. The plates are assembled along with conventional positive plates to make 12V-35Ah batteries . Diluted Sulfuric acid is filled and conventional formation is done. The control batteries are made with conventional carbon black and paste recipe. Then both of these batteries are subjected to electrical testing such as charge acceptance, cold cranking and light load endurance cycling test as per JISD5301 standard. The batteries prepared with above said process performed better than conventional batteries and there is improvement of about 10% in charge acceptance and 12-15% incyclic life. There is much impact on cold cranking performance of the battery. The overall effect of the invention can be seen from the results shown in the below graphs. 3.4 3.5 3.6 3.7 3.8 3.9 4 ControlInvention 10th min current (A)Charge Acceptance
6 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 CLAIM1.A negative paste composition for negative electrode in a lead acid battery comprises of by weight percentage per weight of lead oxide: - 8.2-8.5% of sulfuric acid having a specific gravity at 25°c of 1.395-1.405, - 0.195-0.205% of Modacrylic fiber,- 0.15-0.2% of high surface area and conductive carbon black, - 0.55-0.65% of barium sulphate, - 0.25-0.35% of lignin, 11-12% of demineralised water and- 25-30ml of one of a polymeric binder such as PVDF/PVA diluted in 2lit of DM water. 2.A negative paste composition for negative electrode in a lead acid battery as claimed in claim 1, wherein the percentage of unoxidized lead in 25-30%3.A negative paste composition for negative electrode in a lead acid battery as claimed in claim 1, wherein the surface area of the carbon black is 1400-1500m2/g 4.The method of preparation of a negative paste composition for negative electrode in a lead acid battery as claimed in claim 1, comprising the steps of -mixing the dry materials such as lead oxide, modacrylic fiber, carbon black, barium sulphate and lignin in an automatic mixer for 3-5minutes,
8 -adding deminerlized water into the mixer and wet mixing for 2-3 minutes, -adding Sulfuric acid to the mixer slowly for a period of 17-18 minutes with cooling system or exhaust switched on after 50°c. -final mixing with exhaust and cooling system for about 5-7minutes wherein the paste peak temperature is maintained at 60-64°c. -adding polymeric binder and mixing for 2-3min, and -measuring and adjusting the apparent density of the paste to 4.40 to 4.45 g/cm3.5.A lead acid battery made with negative electrode consisting of paste composition according to claim 1 and the said paste prepared according to claim 4.