Patent Application
20120183847
The field of the invention is current collectors, and especially as it relates to current collectors in bipolar lead acid batteries (BLAB).
It is well-known in the art of lead acid battery manufacture that pure lead has a relatively high resistance to corrosion in sulfuric acid containing electrolytes due to the insulating layer of PbSO4/PbOx (1<x<2) that is formed in the electrolyte. Thus, and at least at first glance it appears desirable to form in a lead battery a positive plate with a grid structure made from pure lead since the PbSO4/PbOx layer acts as semi-permeable membrane and blocks the transport of SO42− and/or HSO4−species. In most cases, the PbSO4/PbOx layer has a thickness of about four microns and tends to stay at that value through the life of a lead acid battery cell, and cells made with pure lead grids experience under most circumstances no corrosion while float-charged.
Where the lead acid battery is a bipolar lead acid battery, it is especially desirable to have a durable and corrosion-resistant substrate. Consequently, pure lead has been considered a prime material for such substrate to capitalize on the protective properties of the PbSO4/PbOx layer. It is known from U.S. Pat. No. 3,806,696 that pure lead grids and pure lead plates can be welded together to provide a composite collector structure in which the resultant weld is of low internal impedance and is relatively thick for increased oxidation and corrosion resistance. Such methods advantageously reduce the resistance at the grid/lead interface. However, lead grid structures from pure lead are unfortunately not suitable for deep cycling applications as the PbSO4/PbOx layer that is formed during operation also acts as an insulator with very high electric resistance, which in turn results in a premature capacity loss of the cell. To avoid such drawbacks, almost all production battery grids are made of various non-welded lead alloys (e.g., Odyssey lead acid battery, containing at least 0.7% Sn in the lead alloy).
It is also known from U.S. Pat. No. 6,620,551 that the collector for a lead acid battery can be formed from a pure lead substrate and an additional surface layer that comprises a Sn-free lead alloy composition (most typically including an alkaline metal or alkaline earth metal). This and all other extrinsic materials discussed herein are incorporated by reference in their entirety. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply. While such collectors may reduce or even entirely avoid the formation of the PbSO4/PbOx layer, other disadvantages nevertheless remain. For example, manufacture of such composite structures will typically require lamination, which tends to be instable over prolonged times. Furthermore, the amount of added alkaline metal or alkaline earth metal is typically relatively high and thus often interferes with material properties of the alloy.
Thus, even though numerous current collectors are known in the art, there is still a need to provide improved current collectors, especially for BLAB.
The present invention is directed to devices and methods for bipolar batteries, and especially bipolar lead acid batteries with substantial improved performance and power-to-weight ratio in which a monolithic current collector combines advantages of improved resistance to oxidation and conductivity.
In one aspect of the inventive subject matter, a bipole assembly for use in a bipolar lead acid battery is contemplated, wherein the assembly includes a monolithic composite current collector that comprises a conductive substrate formed from a first metal composition and an electroformed grid structure. Most preferably, the electroformed grid structure is conductively coupled to a first side of the substrate and formed from a second metal composition.
In especially preferred aspects, the first metal composition is pure lead and the second metal composition is a lead alloy (e.g., alloyed with an alkaline earth metal, an alkaline metal, and/or tin). Contemplated assemblies will also preferably include a non-conductive grid that is coupled to the substrate on a second side of the substrate that is opposite the first side, and a negative active material (NAM) contacting the non-conductive grid and the second side of the substrate. A positive active material (PAM) typically contacts the electroformed grid structure and the first side of the substrate. Where the battery is configured as a deep cycle battery, it is generally preferred that the electroformed, or cast grid structure has a surface area Sgrid, the PAM has a weight WPAM, and that the ratio of WPAM to Sgrid is between 0.65-1.1 g/cm2, and more preferably between 0.8-1.0 g/cm2. While not limiting to the inventive subject matter, it is also contemplated that the substrate may be configured as a composite substrate in which a non-conductive polymer carrier is coupled to the substrate opposite the first side, wherein the polymer carrier has a plurality of openings that allow formation of a conductive path between the substrate and another conductive material located on an opposite side of the carrier.
Therefore, and viewed from a different perspective, a bipolar lead acid battery is contemplated that includes the above bipole assembly, most typically configured as a valve regulated lead acid battery. It is further especially preferred that such batteries are configured as a deep cycle battery.
In another aspect of the inventive subject matter, a method of forming a current collector is contemplated which comprises a step of electroforming a composite structure in which a lead alloy grid and a lead substrate form a monolithic structure. Thus, and viewed from a different angle, a method of forming a bipole assembly for a bipolar lead acid battery may include a step of gradually building a lead alloy grid structure onto a lead substrate or gradually forming a lead substrate onto a lead alloy grid structure to thereby form a monolithic current collector structure.
It is especially preferred that the step of gradually building comprises electroforming, electroplating, vapor depositing, and/or redox depositing. In further contemplated methods, the lead alloy grid structure and the first side of the substrate are coupled to a PAM. Most preferably, deep cycle batteries are formed such that the lead alloy grid structure has a surface area Sgrid, the PAM has a weight WPAM, and the ratio of WPAM to Sgrid is between 0.65-1.1 g/cm2, and even more typically between 0.8-1.0 g/cm2.
It is still further contemplated that a non-conductive grid is coupled to the lead substrate on the side of the substrate that is opposite the side onto which the grid structure is formed, and that a NAM is coupled to the non-conductive grid and the opposite side. While not limiting to the inventive subject matter, it is also preferred that in at least some aspects the lead substrate is configured as a composite substrate in which a non-conductive polymer carrier is coupled to the lead substrate opposite the side onto which the grid structure is formed. In such configurations, the polymer carrier has a plurality of openings that allow formation of a conductive path between the lead substrate and another conductive material located on the opposite side of the carrier.
Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.
The inventors have discovered that various monolithic positive current collectors can be prepared for a BLAB in which the benefits of a Sn/Pb alloy grid and the benefits of a pure lead substrate are combined in an economically and technically desirable manner. Monolithic current collectors of particularly preferred devices and methods are electroformed such that the collector has an alloyed grid (most typically SnPb alloy) portion that is structurally and conductively continuous with a pure lead substrate. Alternatively, the current collectors of further particularly preferred devices and methods are welded composite structures where the alloyed grid (most typically SnPb alloy) is resistance welded to a pure lead substrate to so form the composite collector.
Based on a series of experiments using prefabricated off-the-shelf parts, the inventors discovered that when a pure lead substrate (e.g., thin lead foil with a purity of at least 99 wt % as shown in
In an effort to circumvent the disadvantages associated with the welding process, the inventors discovered that currently known lead and lead alloy electroforming technology (see e.g., U.S. Pat. No. 7,097,754; DSL Dresden Material-Innovation GmbH) can be applied to form monolithic composite structures in which one part of the composite structure (the grid) comprises a lead alloy (e.g., SnPb alloy) and in which another part (the lead substrate) of the composite structure comprises pure lead. Contemplated methods and collectors formed with such methods will not only avoid laborious welding processes to conductively couple a grid to a substrate, but also advantageously allow formation of the composite structure in many configurations and geometries in a highly automated and simple manner.
The term “monolithic” in conjunction with a composite structure is used to mean that the structure will include at least two different materials that are joined to form a continuous interface, wherein the interface does not include a binding material disposed between the different materials, and wherein the interface does not include a physical modification (e.g., heat affected zone or melt zone) of at least one of the two different materials. The term “formed” as used in conjunction with the grid and/or substrate means that the grid and/or substrate is produced in a gradual and additive process where material is added to the nascent grid and/or substrate to so arrive at the final grid and/or substrate structure. Furthermore, the term “pure” in conjunction with the term “lead” refers to lead having a chemical purity of at least 95 wt %, more typically at least 98 wt %, and most typically at least 99.9 wt %.
Consequently, it should be recognized that the inventors contemplate various bipole assemblies for use in bipolar lead acid batteries, and that such assemblies will advantageously include one or more monolithic current collectors in which a conductive substrate is formed from a first metal composition (typically pure lead) and in which a grid structure is formed from a second metal composition (typically a lead alloy). Most preferably, contemplated devices are electroformed, however, various alternative processes are also deemed suitable and include electroplating, vapor deposition, and deposition from a redox reaction (as described, for example, in U.S. Pat. No. 6,548,122). Alternatively, resistance welding (e.g., spot or seam welding) may be used to form the composite current collector structure, which will exhibit almost identical mechanical and electrochemical properties as the aforementioned electroformed and, by definition, monolithic current collector.
With respect to the substrate it is contemplated that the substrate comprises lead or is made entirely from lead and has a generally planar and relatively thin configuration. Thus, in most typical aspects of the inventive subject matter, the substrate is a pure lead foil having a thickness of between about 2 mm and 0.05 mm. The lead substrate may also be modified to include elements other than lead to so increase stability against oxidation, or may be a lead alloy to impart desirable characteristics. It should be noted that where the lead foil is very thin (e.g., equal or less than 0.1 mm), a conductive or non-conductive carrier may be implemented to stabilize the structure. For example, suitable carriers include non-conductive and oxidation resistant polymeric materials (e.g., synthetic polymers such as PVDF, HDPE, and other polymers known in the battery art), but also certain conductive materials such as glassy carbon, Magnelli phase suboxide materials. Where the carrier is non-conductive, it is especially preferred that the carrier includes a plurality of transverse channels that allow inclusion of a conductive material to so allow transfer of electrons from one side of the carrier to the other side (see
In less preferred aspects, metals and metal alloys other than lead and lead alloys are also contemplated. For example titanium, aluminum, lead or plastic substrates can be coated by Sn, SnO2 or Ti4O7 to make them impervious to corrosion. Similarly, it should be noted that the most preferred material for the grid is a binary lead alloy comprising 0.4 to 0.9% Sn with the balance of pure Pb.
Most preferably, and at least in part depending on the choice of materials, it is preferred that at least one of the grid structure and the substrate are electroformed in a process that allows formation of a monolithic composite structure. For example, a template may be structured such that a grid is built by electroforming onto a spindle using a first material (e.g., lead alloy), and that onto the so formed grid structure a pure lead substrate is formed. Of course, it should be noted that the monolithic composite structure may be formed in a reverse manner where the substrate is formed first, and the grid structure is formed in a subsequent step. For example, a mask may be applied to the lead substrate to serve as a template for vapor or electrochemical deposition of the lead alloy grid structure. The exact configuration of the grid structure will depend on the size and configuration of the substrate, and will further depend on the particular use of the battery as further explained below.
Recognizing the critical role of the grid-to-PAM interface under deep cycling duty, an optimization relationship between the weight of PAM (WPAM) and area of the grid (Sgrid) that is in contact with PAM was established in which β is defined as WPAM/Sgrid in a positive half cell. Among other grids produced, especially suitable experimental grids had a β value of between about 0.5-1.3 g/cm2, more preferably between about 0.65-1.1 g/cm2, and most preferably between about 0.8-1.0 g/cm2, whereas a typical SLI (Start, Light, Ignition) battery is considered to have a β value of about 2.5 g/cm2. As used herein, the term “about” in conjunction with a numeral refers to a range of that numeral of +/−10%, inclusive. Furthermore, and unless the context dictates the contrary, all ranges set forth herein should be interpreted as being inclusive of their endpoints, and open-ended ranges should be interpreted to include only commercially practical values. Similarly, all lists of values should be considered as inclusive of intermediate values unless the context indicates the contrary.
In further especially preferred experiments, the grid portion of the collector structure was designed to a β value of about 0.95 g/cm2 (using 42 g of PAM and 44 cm2 total area of grid wires in contact with PAM). Remarkably, in such and the above grids and substrates, sufficient area of the current collecting surfaces was present to achieve uniform distribution of the PAM in contact with the grid wires to improve the utilization of PAM and increase cycle life, particularly for deep cycle operation.
With respect to suitable negative active materials (NAM) it should be appreciated that all known NAM are considered appropriate for use herein. Thus, especially contemplated NAM includes various lead-based pastes. As in other known batteries, the NAM is preferably retained at the substrate using a non-conductive carrier (grid) that is most preferably compression resistant. While not limiting to the inventive subject matter, the non-conductive grid is preferably manufactured from a synthetic polymer that is resistant to acid and oxidative corrosion.
Consequently, the inventors also contemplate numerous bipolar lead acid batteries in which multiple bi-pole assemblies are coupled together in a manner well known in the art. Thus, and in especially preferred aspects, a deep cycle bipolar lead acid battery with highly desirable characteristics can be manufactured. As used herein, the term “deep cycle” in conjunction with the term “battery” refers to a battery that is designed to allow repeated discharge (e.g., greater 20 times) of the battery to 20% of full charge without adverse effects on the battery. Moreover, it should be appreciated that in especially preferred aspects the lead acid bipolar batteries contemplated herein are configured as a valve regulated (recombinant) lead acid battery (VRLA). Consequently, it is preferred that the electrolyte in such batteries may be a gelled electrolyte or absorbed electrolyte (typically using a glass mat).
In a typical experiment, a batch of 12V BLABs was prepared in which the substrates and the grids of the current collectors were welded to each other. These first generation batteries have proven the feasibility and advantages of electroformed composite current-collectors. It is expected that electroformed monolithic current collectors will provide the same or even further improved results. The cycling performance of such BLABs appeared to be steady as can be readily taken from the data below. Moreover, the BLABs demonstrated desirable capacity parameters as can be taken from the data below. Based on these initial experiments and general configurations, the inventors have constructed various additional BLABs with the following characteristics:
Table 1 below depicts general parameters of the active materials while Table 2 below lists various design parameters for the lead substrate and grid. Table 3 below lists the weight of the BLAB components, and Table 4 lists an estimate weight calculation. Finally, Table 5 depicts exemplary performance data of the BLAB.
Typical performance data of a cycle life test of an exemplary 12V bipolar battery prototype made to test the monolithic current collectors are depicted in
It should be apparent to those skilled in the art that many more modifications besides those already described are possible without departing from the inventive concepts herein. The inventive subject matter, therefore, is not to be restricted except in the spirit of the appended claims. Moreover, in interpreting both the specification and the claims, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms “comprises” and “comprising” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced. Where the specification claims refers to at least one of something selected from the group consisting of A, B, C . . . and N, the text should be interpreted as requiring only one element from the group, not A plus N, or B plus N, etc.
This application claims priority to our copending U.S. provisional application with the Ser. No. 61/179,609, which was filed May 19, 2009.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US10/35235 | 5/18/2010 | WO | 00 | 3/7/2012 |
| Number | Date | Country | |
|---|---|---|---|
| 61179609 | May 2009 | US |
