Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Separator – retainer – spacer or materials for use therewith
Reexamination Certificate
2002-03-04
2004-08-03
Weiner, Laura (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Separator, retainer, spacer or materials for use therewith
C429S204000, C429S145000, C429S225000, C429S228000
Reexamination Certificate
active
06770401
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an improved lead acid battery element containing a metal impurity inhibiting micronized porous powder polymeric additive, which is added to the negative active material and/or battery separator to inhibit the detrimental effects of certain metal cations on the efficiency of a lead acid battery, particularly the negative plate battery element.
Further the present invention relates to a recombinant battery separator element having a micronized porous powder polymeric additive having an average particle size less than 3 microns. In brief the separator battery elements include the addition of the micronized metal impurity inhibiting additive to the separator of a valve regulated recombinant lead acid battery to inhibit the adverse effects of contaminant metal on the negative plate battery element.
Further the present invention relates to a silica filled polymeric separator having a micronized porous powder polymeric additive having an average particle size less than 3 microns associated with the polymeric separator. In brief the separator battery element includes the addition of the micronized polymeric additive to the polymeric separator to inhibit the detrimental effects of certain metal cations on the negative plate of the lead acid battery.
Further the present invention relates to a negative plate battery element having a metal impurity inhibiting micronized porous polymeric additive associated with the negative active material. In brief the negative plate element includes the addition of a micronized polymeric additive having an average particle size less than 3 microns to the negative active material to inhibit the detrimental effects of certain metal cations on the efficiency of the lead acid battery.
Metal impurities can be introduced into a lead acid battery through the use of the many materials used in its manufacture. For example, metal impurities can be introduced with the lead and lead oxides used in the manufacture of the active material, the materials of construction including the lead grids, alloying agents, electrolyte and water. Nearly all metallic impurities, if they are nobler than lead, have a smaller hydrogen overvoltage. Therefore the metals increase hydrogen evolution even if they are deposited in trace concentrations on the surface of the negative plates. These metals cause a continued gas evolution even after charging is completed. Hydrogen is evolved on the deposited metal with low hydrogen overvoltage. Metals can greatly increase the gassing of the negative plate, the order of their influence ranked highest to lowest is as follows: Pt, Au, Te, Ni, Co, Fe, Cu, Sb, Ag, Bi and Sn. The presence of 0.3 ppm of platinum in the acid can cause a doubling of the self-discharge rate. Tin can produce this effect at 0.1-wt %. Freshly deposited antimony is especially active. Besides the discharge of the negative plates with concomitant hydrogen evolution, these materials also move the end of charge voltage of the negative plates toward more positive values. Because the hydrogen overvoltage decreases with temperature, the self-discharge increases through these reactions.
Antimony is often added to grid lead in order to make the lead more fluid and more easily cast into the shapes necessary for storage battery grids. Further, it also hardens the resulting casting so that it can be further processed in the plant without damage. For deep cycle applications, positive grids with 4 to 6 percent antimony are used for forming a permanent low resistance interface with the positive active material.
Antimony in the grid metal produces a definite effect on the charge voltage characteristics of the fully charged battery. The higher the antimony percentage in the grid metal, the lower the charge voltage and conversely, as the antimony is decreased so the charge voltage increases until pure lead is attained, which produces the highest voltage on charge.
Products from corrosion reactions including antimony from the positive grids slowly go into solution in the electrolyte and from there it is believed to electroplate onto the surface of the negative plates. Some metal ions plate out on the negative such as Au, Pt, Hg, Ag, Cu, Sb while others such as Fe, Cd, Zn, Mn, Na, Ca do not. Multivalent metals that do not deposit are shuttle ions which discharge the positive plate, become oxidized, travel to the negative, discharge the negative plate, are reduced, and return to the positive to continue the process. The combination of local action in the electrodes and shuttle ions effects increase self-discharge and causes poor battery shelf life and incomplete recharging. With metal deposition and the lowering of the battery voltage, a constant voltage charger increases the amount of overcharge, increases positive plate polarization and therefore grid corrosion which reduces the life of the battery.
Metal impurities can be particularly detrimental in valve regulated lead acid batteries (VRLA) operating on the oxygen recombination principal. A number of metal impurities can exert a deleterious effect on the performance of VRLA batteries by affecting one or more of the performance requirements of the VRLA batteries such as by increasing oxygen evolution at the positive electrode, increasing hydrogen evolution at the negative electrode, inhibiting full recharge of the negative electrode, increasing negative plate self discharge and increasing the amount of water lost by the battery in this electrolyte limited system. Typical examples of metals that are particularly deleterious in VRLA batteries are arsenic, antimony, cobalt, chromium, nickel, iron, silver, platinum and tellurium. Furthermore, by enhancing oxidative degradation, trace minerals may have an adverse effect on the life of the negative plate expander.
Negative self-discharge has been identified as a chronic problem with VRLA batteries. Further, it has been shown that negative self-discharge does not appear to exist in batteries constructed with ultra-pure battery materials. Evaluations have shown that the spontaneous gassing occurs on the negative plate due to impurities. Gassing rates from negative plates can vary greatly, some negative plates generating twenty times more gas than others due to metal impurities. The use of recycled lead, with its trace impurities, presents a challenge to equal the performance of limited and expensive ultra-pure materials.
The lead acid battery presents an extremely difficult environment in which to control the adverse effects of metal deposition. One of the major environmental design factors, which has to be taken into consideration, is the varying sulfuric acid molarities and battery potentials (voltages) that occur during the charge and discharge reactions in a lead acid battery. For example, the sulfuric acid concentration in deep discharge applications can change from 38-wt % sulfuric acid on charge to 8-wt % sulfuric acid on discharge. Further, the electrochemical potential of both plates will change as the battery is discharged.
From an additive design standpoint the additive must bind metal ions at the varying acid molarities and voltage conditions during the charge/discharge cycles of the battery and such binding of the metal must be substantially irreversible as the acid molarities and electrochemical potentials change. The design for irreversibly binding of a metal ion is particularly difficult as the hydrogen ion concentration increases during the charge sequence of a battery where the hydrogen ion favors release of the metal ion.
The battery environment of changing acid molarity and battery potentials also can affect the ionic form of the metal ion both from the standpoint of valance and even polarity, i.e., cation or anion. In the battery environment the additive has to selectively and permanently bind the particular ionic form in order to minimize its detrimental effect. The battery environment also provides an environment where an intermediate soluble lead ion may be formed during the conversion of solid lead to insoluble lead
Ensci Inc.
Uxa Frank J.
Weiner Laura
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