WO2006092060A1

WO2006092060A1 - Method to improve the performance of lead acid battery

Info

Publication number: WO2006092060A1
Application number: PCT/CA2006/000316
Authority: WO
Inventors: Joey Chung-Yen Jung
Original assignee: Vizon Scitec Inc.
Priority date: 2005-03-04
Filing date: 2006-03-06
Publication date: 2006-09-08

Abstract

The lead acid battery current collector and the method of manufacturing the same includes a reticulated vitreous carbon porous member which is electroplated with a layer of lead-tin-silver composition or a lead-tin-indium composition. The coated base member is then covered with a lead compound which is then cured to produce a lead oxide for the positive electrode and lead for the negative electrode. The thickness of the composition is within the range of 50-350 micrometers.

Description

METHOD TO IMPROVE THE PERFORMANCE OF LEAD ACID BATTERY

Prior Application

This non-provisional application claims the priority of prior U.S. provisional application Serial No. 60/659,033, filed on March 4, 2005.

Technical Field

The invention generally relates to current collectors for lead acid batteries, and more particularly, to a current collector which includes an electrical conductivity layer applied to the surface of reticulated vitreous carbon current collectors, which improves the performance of the lead acid batteries in specific discharge capacity, utilization efficiency of the active mass, discharge/recharge cyclability, and recharging time.

Background of the Invention

The limiting factor for a lead-acid battery being used in hybrid vehicles and electric traction vehicle is the low power and energy density, which is due to the low utilization efficiency (25 to 40 wt%) of the positive and negative electrodes .

Prengaman, in an article titled "Challenges from Corrosion-Resistant Grid Alloys in Lead Acid Battery Manufacturing" from the Journal of Power Services, 9524-233 (2001) , discussed the effect of calcium, tin, and silver content in the positive grids of lead acid batteries with respect to the grid casting manufacturing process . The presence of tin and silver improves the corrosion resistance of the grid. The presence of 1.2% wt of tin enhances battery recharge ability after a deep discharge and extends the overall battery life. The presence of 0.05% silver decreases the rate of corrosion and increases the mechanical properties of the grid.

PCT patent application No. PCT/US02/3067 states that the performance of a lead-acid battery can be improved by increasing the utilization efficiency of the active mass. The utilization efficiency of positive active mass can be improved with a three-dimensional electrode composition by coating a lead- tin alloy layer on the surface of reticulated vitreous carbon. The utilization efficiency of active mass can be improved from 35% to 62%, which dramatically increases the energy density of lead acid battery.

Summary of the Invention

Accordingly, the present invention includes a current collector for a lead acid battery, comprising: a reticulated vitreous carbon base member,- and a coating for the base member of a lead-tin-silver composition, or a lead-tin-indium composition. The present invention also includes a method of manufacturing a current collector for lead acid batteries, comprising the steps of: coating a reticulated vitreous carbon base member with a layer of lead-tin-silver composition or a lead-tin-indium composition; covering the coated carbon member with a lead compound; and curing the lead compound to produce the completed electrode.

Brief Description of the Drawings

Figure 1 is a front view of a lead acid current collector of the present invention.

Figure 2 is a cross -section view of the current collector of Figure 1 along lines A-A. Figure 3 is a close-up view of a portion of the current collector of Figures 1 and 2.

Best Mode for Carrying Out the Invention

The present invention relates to a method of improving the performance, especially cycling performance, power density, utilization efficiency, and recharging time, of lead acid batteries by using a current collector composed of reticulated vitreous carbon coated with a lead-tin-silver alloy and/or lead- tin-indium alloy. More particularly, it relates to the use of lead-tin-silver alloy and/or lead-indium alloy deposited on lightweight, open pore reticulated vitreous carbon to enhance the performance of lead acid batteries via increased utilization efficiency of the active mass, power output, and acceptance of the charging current .

The present invention uses a current collector comprised of reticulated vitreous carbon. The reticulated vitreous carbon has a porosity of 10 to 20 pore per inch, a high specific surface area, and a high void fraction.

The reticulated vitreous carbon is deposited with a layer of lead-tin-silver alloy and/or lead-tin-indium as uniform as possible. Figures 1-3 show the resulting current collector. The collector 10 comprises a lead alloy frame 12 to hold a reticulated vitreous carbon porous base member (10-20 pores/inch, extending through the base member) and a tab 14 for the electrical connection to the collector. The coated vitreous member is shown at 16 in Figures 1 and 2, while the close-up view of Figure 3 shows a more detailed view -of the cross-section of Figure 2, including the vitreous carbon base member 18 beneath the coating, the open pores 20 of the vitreous carbon base member and the deposited coating 22, which covers the base member. The thickness of the deposited lead-tin-silver alloy and/or lead- indium has a range of 50 to 350 μm, depending on the application. The lead-tin-silver coating has a composition of 95% lead, 3.5% tin, and 1.5% silver. The small amount of silver and tin in the lead alloy coating increases the corrosion resistance of the coating during charge/redischarge; hence increases the corrosion resistance of the current collector, which will enhance the current acceptance during recharge. The silver content in the coating will also improve the electrical conductivity of the current collector. The lead-tin-indium alloy has a composition of 95% lead, 3% tin, and 1% indium. The indium content in the coating increases the fatigue strength and corrosion resistance against oxidation occurring when recharging.

The resulting current collector can be used as both the positive and negative current collector in lead acid batteries. To obtain a functional, secondary lead acid battery, the present current collector will be pasted with lead compounds (i.e. lead oxide, lead sulfate). The pasted electrodes will then enter a curing chamber for the lead oxide to adhere onto the current collectors. Once the pasted electrodes are cured, the current collectors are brought into contact with concentrated sulfuric acid and assembled into either flooded or valve- regulated lead-acid batteries. After the forming (initial charging) step, the paste material is converted into the active material (or active mass) which is lead dioxide on the positive electrode and lead on the negative electrode, respectively. When the lead-acid battery is subjected to discharge, both the lead dioxide on the positive electrode and lead on the negative electrode are converted to lead sulfate and current is transferred via the current collector (or grid) to a consumption source (load) . During charge, a DC current is supplied to lead sulfate by the current collector and the active materials are regenerated. Thus, the interaction of a current collector with the active mass is of crucial importance for the functioning of the lead-acid battery.

The current invention results in improved performance of lead acid batteries due to improvement in the following factors: increase in the utilization efficiency of active mass, increase in the specific energy density and power density, increase in the corrosion resistance of the current collector, increase in the electrical conductivity of the current collector, and improvement in the cycle life of the lead acid batteries .

The present invention provides methods for producing the high-performance current collectors, which includes the steps of lead-alloy deposition.

The invention is further described by the following examples .

Example 1: Electro-deposition of lead-tin-silver alloy The lead-tin-silver composition can be deposited on the surface of the reticulated vitreous carbon via the recipes listed in Table 1. Table 1 Electroplating recipe and operating conditions for lead- tin-silver alloy

To electroplate the reticulated vitreous carbon (RVC) , the RVC plate is placed in the electroplating bath and acts as the cathode, while two 80/15/5 (by weight of lead to tin to silver) lead-tin-silver plates of 3.2 mm thickness act as anodes sandwiching the RVC cathode. The distance between the RVC cathode and the lead-tin anode is 3.8 cm. The cathode and anode have similar geometric areas. Following immersion in the electroplating bath, the electrodes are connected to a DC power supply characterized by a maximum voltage and current output of 25 V and 100 A, respectively. The typical electroplating conditions for lead-tin-silver electroplating are shown in Table 1. The coating thickness is adjusted by varying the plating time (typically between 1 and 3 hours) to achieve the goal of weight saving and longer cycle life.

After the electroplating, the plated RVC enters a sequential washing procedure in the following order: distilled water rinse, alkaline wash (0.1 M NaOH) or acid wash (0.1M HC), distilled water wash, acetone wash and acetone dipping. Drying in a nitrogen atmosphere follows the last washing step. The described procedure assures complete removal of the electroplating bath components from the plated surface and minimizes the surface oxidation. The typical content of the coating is 95% lead, 3.5% tin, and 1.5% silver. It is understood that other coating contents can be easily, achieved by adjusting the plating time, current density and/or plating bath composition.

Example 2: Electro-deposition of lead-tin-indium alloy

The lead-tin-indium composition can be deposited on the surface of the reticulated vitreous carbon via the recipe listed in Table 2.

Table 2 Electroplating recipe and operating conditions for lead- tin-indium alloy

To electroplate the reticulated vitreous carbon (RVC) , the RVC plate is placed in the electroplating bath and acts as the cathode, while two 80/15/5 (by weight of lead to tin to indium) lead-tin-indium plates of 3.2 mm thickness act as anodes sandwiching the RVC cathode. The distance between the RVC cathode and the lead-tin anode is 3.8 cm. The cathode and anode have similar geometric areas. Following immersion in the electroplating bath, the electrodes are connected to a DC power supply characterized by a maximum voltage and current output of 25 V and 100 A, respectively. The typical electroplating conditions for lead-tin-silver electroplating is shown in Table 2. The coating thickness is adjusted by varying the plating time (typically between 1 and 3 hours) to achieve the goal of weight saving and longer cycle life.

After the electroplating, the plated RVC enters a sequential washing procedure in the following order: distilled water rinse, alkaline wash (0.1 M NaOH), distilled water wash, acetone wash and acetone dipping. Drying in a nitrogen atmosphere follows the last washing step. The described procedure assures complete removal of the electroplating bath components from the plated surface and minimizes the surface oxidation. The typical content of the coating is 96% lead, 3% tin, and 1% indium. It is understood that other coating contents can be easily achieved by adjusting the plating time, current density and/or plating bath composition.

Example 3: Manufacture of the Lead Alloy Plated Reticulated Vitreous Carbon Current Collector

In this embodiment, reticulated vitreous carbon (RVC) slabs with 10 and 20 pores per inch are used as substrates for grid manufacturing. The RVC slab has dimensions of: 15.2 cm x 15.2 cm x 12.8 mm (height x width x thickness) and was sliced to a preferred thickness of about^' 3.5 mm, using a steel cutter. After slicing, the height and width of the carbon slab is adjusted to the size needed for the particular battery. One of the commonly employed current collector sizes is 12.7 cm x 12.7 cm (height x width) . The sliced vitreous carbon substrate is then uniformly coated with a layer of lead-tin-silver and/or lead-tin-indium alloy by electroplating. The lead-tin-silver and/or lead-tin- indium coating can be applied on the reticulated vitreous carbon via chemical vacuum deposition. In the case of the electroplating method, in order to supply current to the vitreous carbon structure during electroplating, a 2.5 mm thick connector and a 6 cm x 1.3 cm (height x width) lug, both made of 99.8% by weight purity lead, are attached to the reticulated vitreous carbon slab. The lead tab is applied onto the reticulated vitreous carbon by immersing 3 mm of the carbon piece in melted lead at 370⁰C using aluminum molds, followed by rapid cooling by an air-jet. To electroplate lead-tin-silver and/or lead-tin-indium alloy on reticulated vitreous carbon, there are several electroplating bath compositions. The bath compositions and electroplating conditions are described in Example 1 and Example 2. . Following the electroplating, washing and drying steps, the current collector is further processed by replacing the tab and lug, which serves as current feeder during electroplating, with a wider top connecting element. Additionally, three frames are also attached on the sides of the electroplated RVC plate. The process of attaching the new connector and frames is identical to the one described above for attaching the electroplating connector. The material for the battery grid tab and frames is a lead alloy containing 2% by weight of tin. Although a preferred embodiment of the invention has been disclosed for purposes of illustration, it should be understood that various changes, modifications and substitutions may be incorporated in the embodiment without departing from the spirit of the invention which is defined by the claims which follow.

Claims

1. A current collector for a lead acid battery, comprising: a reticulated vitreous carbon base member; and a coating for the base member of a lead-tin-silver composition or a lead-tin-indium composition.

2. The current collector of claim 1, wherein the coated current collector is covered with a lead compound.

3. The current collector of claim 2, wherein the lead compound is a lead oxide or a lead sulfate.

4. The current collector of claim 1, wherein the lead-tin-silver composition comprises approximately 95% lead, approximately 3.5% tin and approximately 1.5% silver.

5. The current collector of claim 1, wherein the lead-tin-indium composition comprises approximately 90% lead, 3% tin and 1% indium.

6. The current collector of claim 1, wherein the thickness of the lead-tin-silver composition or the lead-tin-indium composition is within the range of 50-300 micrometers.

7. The current collector of claim 1, wherein the base member is porous.

8. A method of manufacturing a current collector for lead acid batteries, comprising the steps of: coating a reticulated vitreous carbon base member with a layer of lead-tin-silver composition or a lead-tin-indium composition; covering the coated carbon member with a lead compound; and curing the lead compound to produce the completed collector.

9. The method of claim 8, wherein the thickness of the layer of lead-tin-silver or the layer of lead-tin-indium is within the range of 50-350 micrometers.

10. The method of claim 8, wherein the step of coating is accomplished by electroplating.

11. The method of claim 10, including the step of cleaning the electroplated base member to remove the electroplating bath components from the plated surface .

12. The method of claim 8, wherein the time of electroplating is within the range of 1-3 hours.