California Institute of Technology

Other

Bipolar Power Corporation

The United States of America As Represented by the Administrator of the

Atlantic Richfield Company

John J Rowlette

Jack Y Josefowicz

Thomas J Clough

John W Sibert

James E Graf

The Battery Plates with Self-Passivating Iron Cores and Mixed Acid Electrolyte disclosed and claimed in this patent application solve the problems encountered by previous attempts to construct practical bipolar plates for lead-acid batteries. One of the preferred embodiments of the present invention comprises a novel combination of a self-repairing substrate (12) surrounded by a lead coating (16a & 16b) resulting in a bipolar plate (10A) which is nearly three times lighter than its pure lead counterpart. Since this innovative plate incorporates a core or substrate (12) that is self-passivating under the electrical potential and highly acidic conditions found in the lead-acid battery, any pinholes, gaps, or flaws in the lead coatings (16a & 16b) are naturally resealed. Another preferred embodiment utilizes a coating of a semi-conducting metal oxide (18), such as fluorine-doped stannic oxide, on the positive side of the bipolar plate (10B) instead of lead, which further reduces the weight. The self-passivation of the central core is enhanced by combining phosphoric or boric acid with the sulfuric acid electrolyte used in the battery.

Battery plates with self-passivating iron cores and mixed acid

The Battery Plates with Lightweight Cores disclosed and claimed above solve the problems encountered by previous attempts to construct practical bipolar plates for lead-acid batteries. The preferred embodiment (10) includes a thin, lightweight, inexpensive metal core (12) with very high thermal and electrical conductivity. The lower or negative side (12b) of the core (12) is covered with a negative side protective layer (16) which defends the core (12) from an acidic environment. The upper or positive side (12a) of the core (12) is covered with a positive side protective layer (18) which safeguards the core (12) from a hostile oxidizing electrochemical environment. In the preferred embodiment, the core (12) is aluminum, the negative side protective layer (16) is lead and the positive side protective layer (18) is doped stannic oxide. Intermediate layers (14a & 14b) of copper or nickel may be placed between the core (12) and the negative and positive protective layers (16 & 18) to promote adhesion. Various alternative embodiments (20, 32, 42) that employ different combinations of materials are described in the specification. The invention may be implemented using positive and negative side seals (58 & 68).

Battery plates with lightweight cores

The battery system and process of the present invention enables the increase of the specific energy of the lead-acid battery by using new starting pastes which will allow significantly higher utilization efficiencies of the positive and negative pastes. The invention enables the increased utilization efficiency of both electrodes, to thereby increase the specific energy of the battery. Two paste combinations have been found to be advantageous. First, a battery has at its positive terminal, a lead sulfate (PbSO.sub.4) paste and at its negative terminal, a tribasic lead sulfate (3PbO'PbSO.sub.4 'H.sub.2 O). In a second combination, a paste of lead sulfate (PbSO.sub.4) is used at the positive electrode and while a monobasic lead sulfate (PbO.PbSO.sub.4), is applied to the negative electrodes.

Utilization efficiencies by using high sulfate starting materials

The Lightweight Battery Plates disclosed and claimed in this patent application solve the problems encountered by previous attempts to construct practical bipolar plates for lead-acid batteries. One of the preferred embodiments of the present invention comprises a novel combination of a self-repairing substrate (12) surrounded by a lead coating (16a & 16b) resulting in a bipolar plate (10A) which is nearly three times lighter than its pure lead counterpart. Since this innovative plate incorporates a core or substrate (12) that is self-passivating under the electrical potential and highly acidic conditions found in the lead-acid battery, any pinholes, gaps, or flaws in the lead coatings (16a & 16b) are naturally resealed. Another preferred embodiment utilizes a coating of a semi-conducting metal oxide (18), such as fluorine-doped stannic oxide, on the positive side of the bipolar plate (10B) instead of lead, which further reduces the weight. Alternative embodiments may utilize aluminum or aluminum alloy substrates, which can further lighten the plate but will forfeit its self-repairing quality.

Lightweight battery plates

An apparatus [10] is disclosed for a lightweight bipolar battery of the end-plate cell stack design. Current flow through a bipolar cell stack [12] is collected by a pair of copper end-plates [16a,16b] and transferred edgewise out of the battery by a pair of lightweight, low resistance copper terminals [28a,28b]. The copper terminals parallel the surface of a corresponding copper end-plate [16a,16b] to maximize battery throughput. The bipolar cell stack [12], copper end-plates [16a,16b] and copper terminals [28a,28b] are rigidly sandwiched between a pair of nonconductive rigid end-plates [20] having a lightweight fiber honeycomb core which eliminates distortion of individual plates within the bipolar cell stack due to internal pressures. Insulating foam [30] is injected into the fiber honeycomb core to reduce heat transfer into and out of the bipolar cell stack and to maintain uniform cell performance. A sealed battery enclosure [ 22] exposes a pair of terminal ends [26a,26b] for connection with an external circuit.

Lightweight bipolar storage battery

The power characteristics of a lead-acid battery are improved by incorporating a dispersion of 1 to 10% by weight of a thermodynamically stable conductivity additive, such as conductive tin oxide coated glass fibers (34) of filamentary glass wool (42) in the positive active layer (32) carried on the grid (30) of the positive plate (16). The avoiding of positive plate reversal to prevent reduction of the tin oxide is accomplished by (a) employing an oversized positive plate and pre-charging it; (b) by pre-discharging the negative plate; and/or (c) by placing a circuit breaker (26) in combination with the plates (16, 18) and terminals (22, 24) to remove the load when the voltage of the positive plate falls below a pre-selected level.

Lead-acid battery construction

A liquid-impermeable plate (10) having through-plate conductivity with essentially zero resistance comprises an insulator sheet (12) having a series of spaced perforations (14) each of which contains a metal element (16) sealingly received into the perforation (14). A low-cost plate can readily be manufactured by punching a thermoplastic sheet (40) such as polypropylene with a punching tool (52), filling the apertures with led spheres (63) having a diameter smaller than the holes (50) but larger than the thickness of the sheet, sweeping excess spheres (62) off the sheet with a doctor blade (60) and then pressing a heated platen (74) onto the sheet to swage the spheres into a cylindrical shape and melt the surrounding resin to form a liquid-impermeable collar (4) sealing the metal into the sheet.

Bipolar battery plate

The plate (10) comprises a matrix or binder resin phase (12) in which is dispersed particulate, conductive tin oxide such as tin oxide coated glass fibers (14). A monopolar plate (11) is prepared by coating a layer (18) of electrolytically active material onto a surface of the plate (10). Tin oxide is prevented from reduction by coating a surface of the plate (10) with a conductive, impervious layer resistant to reduction such as a thin film (22) of lead adhered to the plate with a layer (21) of conductive adhesive. The plate (10) can be formed by casting a molten dispersion from mixer (36) onto a sheet (30) of lead foil or by passing an assembly of a sheet (41) of resin, a sheet (43) of fiberglass and a sheet (45) of lead between the nip of heated rollers (48, 50).

Battery plate containing filler with conductive coating

The unitary electrode (10) comprises a porous sheet (12) of fiberglass the strands (14) of which contain a coating (16) of conductive tin oxide. The lower portion of the sheet contains a layer (18) of resin and the upper layer (20) contains lead dioxide forming a positive active electrode on an electrolyte-impervious layer. The strands (14) form a continuous conduction path through both layers (16, 18). Tin oxide is prevented from reduction by coating the surface of the plate facing the negative electrode with a conductive, impervious layer resistant to reduction such as a thin film (130) of lead or graphite filled resin adhered to the plate with a layer (31) of conductive adhesive. The plate (10) can be formed by casting a molten resin from kettle (60) onto a sheet of glass wool (56) overlying a sheet of lead foil and then applying positive active paste from hopper (64) into the upper layer (68). The plate can also be formed by passing an assembly of a sheet ( 80) of resin, a sheet (86) of sintered glass and a sheet (90) of lead between the nip (92) of heated rollers (93, 95) and then filling lead oxide into the pores (116) of the upper layer (118).

Unitary plate electrode

A liquid-impermeable plate (10) having throughplate conductivity with essentially zero resistance comprises an insulator sheet (12) having a series of spaced perforations (14) each of which contains a metal element (16) sealingly received into the perforation (14). A low-cost plate can readily be manufactured by punching a thermoplastic sheet (40) such as polypropylene with a punching tool (52), filling the apertures with lead spheres (63) having a diameter smaller than the holes (50) but larger than the thickness of the sheet, sweeping excess spheres (62) off the sheet with a doctor blade (60) and then pressing a heated platen (74) onto the sheet to swage the spheres into a cylindrical shape and melt the surrounding resin to form a liquid-impermeable collar (4) sealing the metal into the sheet.

A low maintenance battery comprises a sealed casing (102) having a cavity (204) receiving a stack (108) of monopolar and bipolar plates (110, 112) interspersed with mats (122) of fiberglass felt immobilizing electrolyte and forming a gas path for diffusion of oxygen to the negative electrode (112). The casing contains a single, resealable vent (202). During charging, oxygen generated at the positive plate (110) diffuses through the mat (122) and decomposes at the negative plate (112). The negative plate (112) has a larger capacity than the positive plate (110) to prevent evolution of hydrogen. Voltage potential is increased or decreased by placing one or more bipolar plates (120) in series relation between alternating positive and negative monopolar plates that are connected in parallel to respective positive and negative battery terminals (104, 106). The monoplates (110, 112) are connected in parallel to respective positive and negative battery terminals (104, 106) by way of bus plates (114, 116, 130, 132). The resealable vent permits operation by way of the oxygen cycle which prevents loss of electrolyte. The vent prevents invasion of oxygen from the ambient to discharge negative plates.

Sealed bipolar multi-cell battery

A coulometer for accurately measuring the state-of-charge of an open-cell battery utilizing an aqueous electrolyte. The coulometer includes a current meter (38) for measuring the battery charge/discharge current and a flow meter (42) for measuring the rate at which the battery produces gas during charge and discharge. Coupled to the flow meter is gas analyzer (54) which measures the oxygen fraction of the battery gas. The outputs of the current meter, flow meter and gas analyzer are coupled to a programmed microcomputer which includes a CPU (68) and program and data memories (74), (76). The microcomputer calculates that fraction of charge and discharge current consumed in the generation of gas so that the actual state-of-charge can be determined. The state-of-charge is then shown on a visual display (80).

State-of-charge coulometer

Batteries (50) containing oxidized, discharged metal electrodes such as an iron-air battery are charged by removing and storing electrolyte in a reservoir (98), pumping fluid reductant such as formalin (aqueous formaldehyde) from a storage tank (106) into the battery in contact with the surfaces of the electrodes. After sufficient iron hydroxide has been reduced to iron, the spent reductant is drained, the electrodes rinsed with water from rinse tank (102) and then the electrolyte in the reservoir (106) is returned to the battery. The battery can be slowly electrically charged when in overnight storage but can be quickly charged in about 10 minutes by the chemical procedure of the invention.

Chemically rechargeable battery

A light weight lead-acid battery (30) having a positive terminal (36) and a negative terminal (34) and including one or more cells or grid stacks having a plurality of vertically stacked conductive monoplates (10, 20) with positive active material and negative active material deposited on alternating plates in the cell or grid stack. Electrolyte layers (26, 28) positioned between each monoplate are included to provide a battery cell having four sides which is capable of being electrically charged and discharged. Two vertical positive bus bars (42, 43) are provided on opposite sides of the battery cell for connecting the monoplates (10) with positive active material together in parallel current conducting relation. In addition, two negative bus bars (38, 39) on opposite sides of the battery cell each being adjacent the positive bus bars are provided for connecting the monoplates (20) with negative active material together in parallel current conducting relation. The positive (42, 43) and negative (38, 39) bus bars not only provide a low resistance method for connecting the plurality of conductive monoplates of their respective battery terminals (36, 34) but also provides support and structural strength to the battery cell structure. In addition, horizontal orientation of monoplates (10, 20) is provided in a vertical stacking arrangement to reduce electrolyte stratification and short circuiting due to flaking of positive and negative active materials from the monoplates.

Growing community of inventors

Monrovia, CA, United States of America

John J Rowlette