Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
2000-09-28
2003-03-11
Chaney, Carol (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S232000
Reexamination Certificate
active
06531248
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to battery pastes, and, in particular, to battery pastes which contain additives, and to negative and positive active material which can be produced by applying the battery pastes to grids, curing and forming. The invention also relates to a method for introducing the additives into the paste, to plates made by applying pastes made by the method to grids, curing and forming, to formed plates so produced, and to electrochemical cells, including batteries, containing such formed plates. The additives enable the modification of the paste so that positive and negative active material produced therefrom has improved resistance to vibration, and there is increased utilization of active material capacity and, as a consequence, increased initial specific capacity in batteries containing the positive and negative active material, by comparison with batteries made from previously known battery pastes, including ones containing chopped glass fiber strand having an average diameter of about 0.013 millimeter and ones containing glass fibers which are tin coated. In one embodiment, glass microfibers or glass particulates which have such a chemical composition that they release Ni, Pt, Ba, Co, Sb, Bi, Sn and other ions which it is desirable to introduce into positive active material and negative active material are introduced into the battery pastes.
BACKGROUND OF THE INVENTION
The Prior Art
Lead acid batteries are commonly used in many applications such as automobiles, golf carts, wheel chairs, UPS and in telecommunication, where two different kinds of demands are placed on these batteries. In one kind of application the battery is required to stand-by until a need for power arises, while, in the other, the battery is called upon to deliver power periodically, on a more or less regular basis. The former type of application is called “float service” or a stand-by application, while the latter is called cycle service. A golf cart battery, which may be deeply discharged every day, is an example of cycle service. Another recognized battery application is called “SLI”, and is found in automotive service where there are quick demands for start, lighting and ignition of the vehicle.
The lead acid battery has both positive and negative plates, separator, and electrolyte, all packed in a case. The plates of a battery are typically planté, pasted or tubular plates. In Planté plates, lead oxide is generated by direct oxidation of the lead that forms a conducting substrate, or grid. The oxide layer is formed by a large number of charge-discharge cycles. In pasted plates, a paste composed of active materials such as lead oxide (PbO) and metallic lead, called grey oxide or lead dust, is applied to the conducting substrate or grid and “formed” by charging either in a “forming bath” of electrolyte or after the pasted substrate has been assembled with the other components of a battery . In tubular positive plates, either individual tubes or gauntlets of tubes are filled with active material pastes and then formed. The active material is retained by the individual tubes or gauntlets and the current is collected by a central spine which is located interior of the tubes.
In the lead acid battery, lead is used to manufacture both a grid and the active battery paste or material that is applied to the grid in the production of a pasted plate. The lead that is used to make the active material is generally oxidized by one of two mechanical processes, the Barton pot or the ball mill. There are other processes, such as chemical oxidizing of the lead, which can be carried out in rotary tube furnaces, molten litharge furnaces, lead fume chambers and batch furnaces.
In the Barton pot process, a fine stream of molten lead is circulated around the inside of a heated vessel, where oxygen from the air reacts with fine lead droplets or particles to produce an oxide coating around each droplet.
Ball milling is a general term for a large variety of processes that, generically, involve milling large lead pieces in a rotary mechanical mill. With attrition of lead in the mill, lead pieces and then fine metallic flakes are formed; the fine flakes are oxidized to a lead oxide by an air flow in the mill, which also removes the lead oxide particles to a storage silo, where they are collected. The active material which is applied to the grids is a paste which can be made by adding sulfuric acid, water, and various additives, usually called expanders, to the mixture of lead oxides from the storage silo. The other additives may differ depending on whether the paste is for the negative or positive plate. One addition that is made to both positive and negative pastes consists of (floc) fibers, generally of the textile class of organic fibers that are cut to short lengths, and are used in very small amounts, typically of the order of 0.1 percent, based upon the initial oxide weight. Such additives as carbon black, barium sulfate and lignin sulfonates are used in the paste for the negative plates. Paste mixing in general is controlled to achieve a desired paste density, determined using a cup with a hemispherical cavity and by the measurement of paste consistency with a penetrometer. Paste density will be influenced by the total amount of water and acid used in the paste, by the specific identity of the oxide or oxides used, and by the type of mixer used.
Various types of equipment are used in production to paste plates. The control of the pasting of the plate is critical to achieving uniform and consistent performance of the battery. The suitability of the paste for application by this equipment is dependent on the reology of the paste, which is dependent on many factors but is critical to having good processing properties in the plate pasting process. With conventional paste, adding too much acid or water will produce a paste that can not be pasted in conventional commercial plate pasting equipment.
After the plates are pasted, they are cured. For example, “hydroset” cure, which is typically used for SLI plates, involves subjecting the pasted plates to a temperature which, preferably, is between 25 and 40° C. for 24 to 72 hours. The curing is important, especially for the positive plate. During the curing step, the lead content of the active material is reduced by gradual oxidation from about 10 to less than 3 weight percent. Furthermore, the water (about 50 volume percentage) is evaporated. This evaporation must be done quite carefully, to ensure that the volume occupied by the water actually gives rise to porosity and is not lost by shrinkage, which again might lead to the formation of cracks”
1
. The total fluidity of the paste, and, therefore, the proportion of water and acid therein, is critical because a paste with too much fluidity can not be pasted commercially to produce a grid which has an acceptable structural integrity. Fluidity is a key process variable that must be carefully controlled if acceptable plates are to be made, and the fluidity required varies, depending on the type of pasting machine used. For example, a belt paster can be used with a paste having a given fluidity, but an orifice paster requires a paste with a fluidity slightly higher than the given fluidity, and apparatus of the kind used to produce small round cells, where the paste is sprayed (see, for example, U.S. Pat. No. 5,045,086, which discloses a spraying method for applying battery pastes to grids), requires an even more fluid paste. The particle size and surface area per unit of weight of the oxide or oxides pasted influence the fluidity of the paste produced, and must be taken into account in preparing the oxide or oxides for pasting.
1
See, Handbook of Battery Materials/ed. Jurgen O. Besenhard, Wiley-VCH, 1999; ISBN: 3-527-29469, page 167
The plates, after they have been pasted and the paste has been cured, are then formed by either a tank formation process or a container formation process. In tank formation the pasted plates are placed in tanks of fairly dilute sulfuric acid and a direct current is ap
Ferreira Antonio L.
Zguris George C.
Chaney Carol
Fish & Richardson P.C.
Squannacook Technologies LLC
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