Advanced graphite additive for enhanced cycle-life of lead-acid batteries

Abstract

An Advanced Graphite, with a lower degree of ordered carbon domains and a surface area greater than ten times that of typical battery grade graphites, is used in negative active material (NAM) of valve-regulated lead-acid (VRLA) type Spiral wound 6V/25 Ah lead-acid batteries. A significant and unexpected cycle life was achieved for the Advanced Graphite mix, where the battery was able to cycle beyond 145,000 cycles above the failure voltage of 9V, in a non-stop, power-assist, cycle-life test. Batteries with Advanced Graphite also showed increased charge acceptance power and discharge power compared to control groups.

Claims

1. An energy storage device, comprising: an electrode comprising lead; an electrode comprising lead dioxide; a separator between the electrode comprising lead and the electrode comprising lead dioxide; an aqueous solution electrolyte containing sulfuric acid; and a carbon-based additive comprising graphite having a specific surface area of approximately 100 to 900 m.sup.2/g, wherein the carbon-based additive is a disordered carbon additive in negative active material with (i) crystallinity of 60% or lower, (ii) degradation onset temperature of 650 C. or lower; and (iii) degradation temperature range of a minimum 170 C. or higher, and further wherein the carbon-based additive has (i) between about 20 and 40 percent microporous carbon particles of the total amount of carbon-based additive by weight; (ii) between about 60 and 70 percent mesoporous carbon particles of the total amount of carbon-based additive by weight; and (iii) between about 0 and 10 percent macroporous carbon particles of the total amount of carbon-based additive by weight.

2. The energy storage device of claim 1, wherein the carbon-based additive has a specific surface area of substantially 100 to 550 m.sup.2/g.

3. The energy storage device of claim 1, wherein the carbon-based additive has a specific surface area of substantially 100 to 350 m.sup.2/g.

4. The energy storage device of claim 1, wherein the carbon-based additive has a specific surface area of substantially 100 to 250 m.sup.2/g.

5. The energy storage device of claim 1, wherein the carbon-based additive is mixed with a negative, dry, unformed paste having a surface area greater than 3 m.sup.2/g.

6. The energy storage device of claim 4, wherein the concentration of the carbon-based additive relative to the paste is approximately 0.3 to 6% by weight.

7. The energy storage device of claim 4, wherein the concentration of the carbon-based additive relative to the paste is approximately 0.3 to 3% by weight.

8. The energy storage device of claim 4, wherein the concentration of the carbon-based additive relative to the paste is approximately 0.3 to 2% by weight.

9. The energy storage device of claim 1, wherein the carbon-based additive is used in a paste for a negative plate of battery and has a total pore volume of greater than about 0.2 cm.sup.3/g with a predominant pore size of less than 20 .

10. The energy storage device of claim 1 wherein the carbon-based additive is used in a paste for a negative plate of battery and has a total pore volume of greater than about 0.2 cm.sup.3/g with a predominant pore size of 20 -500 .

Description

DESCRIPTION OF THE DRAWINGS

(1) The patent application file contains at least one drawing executed in color. Copies of this patent application publication with color drawing(s) will be provided by the U.S. Patent and Trademark Office upon request and payment of the necessary fees.

(2) These and other advantages of the present invention will be readily understood with reference to the following specifications and attached drawings wherein:

(3) FIG. 1a is a graph representing the extent of periodic graphene layers compared by two-dimensional, wide-angle X-ray diffraction;

(4) FIG. 1b is a graph representing the extent of periodic graphene layers compared by thermogravimetric analysis for the standard, battery-grade graphite and Advanced Graphite used in this work;

(5) FIG. 1c is a chart depicting wide-angle X-ray diffraction and thermogravimetric analysis results of standard, battery-grade graphite and Advanced Graphite;

(6) FIG. 1d is a chart depicting initial characterization of spiral 6V/25 Ah modules;

(7) FIG. 2a is a graph representing pore-volume distribution calculated by density functional theory (DFT) method for standard, battery-grade graphite;

(8) FIG. 2b is a graph representing pore-volume distribution calculated by density-functional theory (DFT) method for Advanced Graphite;

(9) FIG. 3a is a bar graph representing regenerative-charge acceptance;

(10) FIG. 3b is a bar graph representing peak power for 6V/24 Ah modules containing (i) no-carbon, standard, negative mix; (ii) negative mix with 1% by weight standard graphite and 1 wt % standard carbon black; and (iii) negative mix with 2% by weight-advanced carbon at different state-of-charges (SoC) at 25 C.;

(11) FIG. 4 is a graph representing charge current at 500th microcycle (end-of-test unit) in micro-hybrid dynamic charge acceptance test (mDCAT) for (i) no-carbon, standard, negative mix; (ii) negative mix with 1% by weight standard graphite and 1% by weight standard carbon black; and (iii) negative mix with 2% by weight advanced carbon with batteries at 80% SoC;

(12) FIG. 5 is a graph representing end of discharge voltage for (i) negative mix with 1% by weight standard graphite and 1 wt % standard carbon black; and (ii) negative mix with 2% by weight-advanced carbon at 60% state-of-charges (SoC) and 2.5% depth-of-discharge (DoD) at 25 C. on non-stop, power assist cycle life;

(13) FIG. 6 is a diagram of an example prismatic lead-acid battery capable of carrying out the present invention;

(14) FIG. 7 is a diagram of an example spiral-wound lead-acid battery capable of carrying out the present invention;

(15) FIG. 8 is a diagram demonstrating a method of preparing an Advance Graphite paste and battery electrode;

(16) FIG. 9a shows a graph of discharge capacity for batteries with standard negative mix with no carbon and batteries with advanced graphite containing negative mix;

(17) FIG. 9b shows a graph of EN Cold cranking test results for batteries with standard negative mix with no carbon and batteries with advanced graphite containing negative mix;

(18) FIG. 10a shows a graph of dynamic charge acceptance testing performed at 70% state of charges (SoC) with charge voltage of 13.5, 14.0 or 14.4 V for batteries with standard negative mix with no carbon and for batteries with advanced graphite containing negative mix;

(19) FIG. 10b shows a graph of dynamic charge acceptance testing performed at 80% state of charges (SoC) with charge voltage of 13.5, 14.0 or 14.4 V for batteries with standard negative mix with no carbon and for batteries with advanced graphite containing negative mix;

(20) FIG. 10c shows a graph of dynamic charge acceptance testing performed at 90% state of charges (SoC) with charge voltage of 13.5, 14.0 or 14.4 V for batteries with standard negative mix with no carbon and for batteries with advanced graphite containing negative mix;

(21) FIG. 11 shows a graph of end of discharge voltages and discharge capacities in VDA 17.5% DoD test for batteries with standard negative mix with no carbon and for batteries with advanced graphite containing negative mix;

(22) FIG. 12a shows a graph of discharge capacity (C20 rate) test results for batteries with standard negative mix with no carbon and for batteries with advanced graphite containing negative mix;

(23) FIG. 12b shows a graph of reserve capacity test results for batteries with standard negative mix with no carbon and for batteries with advanced graphite containing negative mix;

(24) FIG. 12c shows a graph of EN Cold cranking test results for batteries with standard negative mix with no carbon and for batteries with advanced graphite containing negative mix; and

(25) FIG. 13 shows a graph of discharge capacities as % of rated capacity over 50 cycles of Repeated reserve capacity test for batteries with standard negative mix with no carbon and for batteries with advanced graphite containing negative mix.

DETAILED DESCRIPTION

(26) Exemplary embodiments of the present invention will be described hereinbelow with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail because they would obscure the invention in unnecessary detail.

(27) A graphitic carbon with a greater degree of defective sites in regular graphene layers is disclosed herein. Lower regularity of graphitic layers results in an Advanced Graphite with a highly advantageous surface area, e.g., about 100-900 m.sup.2/g, as compared to typical numbers of between 10-30 m.sup.2/g. A carbon based additive (e.g., Advance Graphite) would preferably have a surface area between 20 and 750 m.sup.2/g with a more preferred range of about 20-450 m2/g or 20-550 m.sup.2/g. However, a most preferred range would be about 100-900 m.sup.2/g, 100-550 m.sup.2/g, 100-350 m.sup.2/g or 100-250 m.sup.2/g. A suitable off-the-shelf Advanced Graphite substitute may include, for example, CyPbrid I and CyPbrid II. CyPbrid I, available from Imerys Graphite and Carbon (www.timcal.com), is a high purity graphite (<0.22% ash) with a specific surface area of 280-300 m.sup.2g. Alternatively, carbon nanotubes may be used as a carbon-based paste additive. Carbon nanotubes are hexagonally shaped arrangements of carbon atoms that have been rolled into molecular-scale tubes of graphitic carbon. Carbon nanotubes have been constructed with length-to-diameter ratio of up to 132,000,000:1, therefore yielding a very high surface area to volume ratio. In other alternate exemplary embodiments, one of the following can be used in negative active paste: an admixture of crystalline carbon, like graphite, carbon nanotube or graphene and amorphous carbon, like carbon black or activated carbon; or heat and/or mechanically treated crystalline carbon, like graphite, carbon nanotube or grapheme, among others.

(28) During research and development of the Advanced Graphite and Advanced Graphite paste, a number of experimental methods and devices were employed: (i) the structures of graphite powder samples were analyzed using X-ray diffraction; (ii) degradation behavior was examined using a thermogravimetric analyzer; and (iii) surface area and pore-size distribution were probed using a surface area analyzer. Powder X-ray diffraction was performed using a Siemens D5000 X-Ray Diffractometer operated at 20 kV, 5 A. Thermogravimetric analysis (TGA) was performed using a TA instruments TGA Q500 by heating the graphite powder sample up to 1,000 C. at the rate of 20 C./min. Surface area and pore-size distribution were measured using nitrogen gas adsorption on a Micromeritics Tristar 3020. Data were analyzed using Brunauer, Emmett, and Teller (BET) and density functional theory (DFT) methods.

(29) Referring first to FIG. 2a, a graph representing pore-volume distribution calculated by the DFT method for a standard, battery-grade graphite is shown, while FIG. 2b represents the pore-volume distribution for Advanced Graphite.

(30) FIG. 2a shows that the pore volume for standard graphite is relatively low (less than 4.510.sup.3 cm.sup.3/g) for the entire range of pores measured for nitrogen gas adsorption with a wide pore range distribution. As a result, the surface area of standard graphite is relatively low, thus restricting electrolyte access, resulting in an active material with lower charge acceptance.

(31) FIG. 2b, by contrast, shows that Advanced Graphite has a much higher pore volume for pore widths (0-800 ) with a peak of 0.05 cm.sup.3/g with predominantly micro (less than 20 ) and meso (20-500 ) porosity. Depending on the batch, Advanced Graphite may further contain a trivial amount of macro (greater than 500 ) pore widths, typically between 0 and 10%. Advanced Graphite with predominantly micro and meso porosity has a total pore volume approximately 3 times greater than standard graphite (0.2 cm.sup.3/g for advanced graphite vs. 0.065 cm.sup.3/g for standard graphite). As a result, the surface area of standard graphite is much greater, thus allowing electrolyte access, resulting in an active material with higher charge acceptance. To test and compare the Advanced Graphite against various negative pastes, spiral wound 6V/25 Ah modules and prismatic 14.4V/78 Ah valve-regulated lead-acid (VRLA) type absorbed glass mat (AGM) batteries were assembled with three different compositions of negative paste, including (i) a control negative mix having no additional carbon; (ii) a negative mix with 1%-by-weight standard graphite and 1%-by-weight, standard carbon black; and (iii) a negative mix with 2% by weight Advanced Graphite. AGM batteries, instead of using a gel or liquid electrolyte, use a fiberglass like separator to hold the electrolyte in place. The physical bond between the separator fibers, the lead plates, and the container make AGMs spill-proof and the most vibration and impact resistant lead-acid batteries available today. Even better, AGM batteries use almost the same voltage set-points as flooded cells and thus can be used as drop-in replacements for flooded cells.

(32) Initial characterization of the modules included 20-hour capacity (discharge at 1.2 A to 5.25V at 25 C.), reserve capacity (discharge at 25 A to 5.25V at 25 C.) and cold cranking (discharge at 400 A to 3.6V at 18 C.). After each test, the modules were recharged at 6 A/7.2V/20 h+4 h/0.6 A. For the sake of accuracy during the testing, battery weights, internal resistance, and low-rate and high-rate discharges for each group were equivalent at onset. The average results for the initial characterizations of the modules of the three groups of modules are summarized in FIG. 1d. FIG. 1d clearly show that all batteries had comparable initial performance parameters, thus suggesting that any change in performance during the testing would be due to the various paste additives, and not variations in the battery construction.

(33) In hybrid electric vehicle applications, the power on discharge for a battery and the charge acceptance power are of great importance. Discharge power determines the degree of achievable electrical boosting during the acceleration period, while the charge acceptance affects the degree of utilization of the regenerative braking energy during the deceleration step. To simulate the different conditions in which the battery can work in the vehicle, the tests were conducted at different State-of-Charge's (SoC) ranging from 20% to 100%. A constant voltage of 16V was used for 5 seconds at 25 C. for charge acceptance power while a voltage of 10V was used for 10 seconds at 25 C. for discharge power measurement.

(34) A Micro-hybrid dynamic charge acceptance test (mDCAT) was performed on prismatic batteries at 80% SoC. The test cycle included multiple micro-cycles with different discharge currents (i.e., discharge at 48 A for 60 s, discharge at 300 A for 1 s, rest for 10 s, charge at 100 A to 100% SoC, discharge at 7 A for 60 s and rest for 10 s) including a high current pulse. The test cycle included a total of 500 microcycles with 6 hour rest time.

(35) Power-assist, cycle life tests were also performed to determine the influence of the three different negative plate formulations in the evolution of capacity, voltage, and internal resistance under partial state-of-charge cycling. The profile used for testing was based on the European Council for Automotive R&D (EUCAR) procedure for Hybrid Electric Vehicles (HEV) and had to be repeated 10,000 times (on one unit) with the battery at 60% SoC and 2.5% depth-of-discharge.

(36) The evolution of end voltage, capacity, weight loss, and internal resistance is recorded every 10,000 cycles. The battery was rested for 6 hours after every 10,000 cycles to allow the electrolyte to stabilize. At end of discharge, a voltage of 5V (per 6V module) reached along the cycling, or a battery capacity under 50% of initial value, was considered battery failure criteria. From previous Advanced Lead-Acid Battery Consortium (ALABC) reports, power-assist cycle life in the range 200,000-220,000 cycles has been obtained for different NAM formulations that included additions of different types of graphites and combination carbon black and graphite in the range 1%-1.5%. A non-stop, power-assist, cycle-life test, in which the battery is cycled continuously without rest step at 10,000 cycle intervals, has been devised to simulate real life test conditions. This test helps in differentiating the various grades of carbons that produced similar test in a standard, EUCAR, power-assist cycle-life test.

(37) The results show the negative mix with 2% by weight Advanced Graphite greatly outperformed both the standard negative mix and the negative mix with 1% by weight Standard Graphite and 1% by weight Standard Carbon Black. In reviewing the results, a wide-angle X-ray diffraction (WAXD) was used to determine the regularity of carbon structures. Diffraction peaks at a specific angle appeared due to constructive interferences from X-rays diffracted from periodic crystal structures. For graphite, the only periodic structure is the arrangement of graphene sheets in the z-direction. The distance between these carbon layers is a constant 3.35 . Diffraction from these sheets (002 plane) of graphite results in a diffraction peak at 226.

(38) A crystalline solid consists of regularly spaced atoms (electrons) that may be described using imaginary planes. The distance between these planes is called the d-spacing, where the intensity of the d-space pattern is typically directly proportional to the number of electrons (atoms) that are found in the imaginary planes. Every crystalline solid will have a unique pattern of d-spacing (also known as the powder pattern), which may be analogous to a fingerprint for a solid. The peak position and d-spacing remains constant for all grades of graphite, while intensity of the peak varies based on the amount of defects present in the sample, quantified by crystallinity percentage of the sample. Carbon black (and activated carbon) has no peak due to the absence of periodic structure. Full width at half maximum (FWHM) of a peak is a measure of crystal size distribution, whereas a smaller FWHM (narrow peak) corresponds to smaller distribution of crystal sizes. Surface area is, in general, inversely related to crystallinity percentages (lower defects in carbon, lower surface area).

(39) WAXD and TGA results for standard battery grade graphite, as well as the Advanced Graphite of the present application, are provided in FIGS. 1a through 1d. Diffraction peak position (226), as well as d-spacing (3.4 {acute over ()}), for two grades were consistent with diffraction patterns from graphene layers. The peak intensity for the disclosed Advanced Graphite was about 70% of standard battery grade graphite, indicating greater defects on graphite structures. The chart in FIG. 1c represents a comparison of the wide-angle x-ray diffraction and thermogravimetric analysis results of standard battery grade graphite and Advanced Graphite.

(40) As indicated in FIG. 1c, Advanced Graphite also has a lower crystallinity percentage (60%) and a wider full width at half maximum (FWHM) value (0.79) (i.e., larger size distribution) compared to standard graphite, yielding higher defective carbon sites. The lower crystallinity percentage indicates higher defects in the Advance Graphite structure, providing a significantly greater surface area. Advanced Graphite's surface area was found to be over ten times greater than the surface area of standard graphite (330 m.sup.2/g versus 21 m.sup.2/g). Despite the higher surface area, the positive attributes of advanced graphite remained virtually unchanged. For example, according to the thermogravimetry tests, both standard graphite and Advanced Graphite had comparable degradation values, indicating that, unlike high surface area carbon black and activated carbon, the graphite will not degrade as much over time. Essentially, Advanced Graphite combines the stability of standard graphite with the high surface area of carbon blacks and activated carbons in a single carbon-based additive.

(41) Advanced Graphite also onsets degradation at a lower temperature as compared to standard graphite, resulting from the presence of higher amorphous carbons and/or defective carbon sites (as seen in FIG. 1b). FIG. 1a is a graph representing the extent of periodic graphene layers compared by two-dimensional, wide-angle x-ray diffraction, while FIG. 1b represents the extent of periodic graphene layers compared by thermogravimetric analysis for the standard battery grade graphite and Advanced Graphite of the present invention. Wider degradation window for Advanced Graphite is consistent with wider FWHM result obtained from WAXD, indicating large crystal size distribution.

(42) The charge acceptance power and power discharge at different SoC (at a constant 25 C.) are presented in FIGS. 3a and 3b for modules containing: (i) no-carbon, standard-negative mix; (ii) negative mix with 1% by weight standard graphite and 1 wt % standard carbon black; and (iii) negative mix with 2% by weight advanced carbon. FIG. 3a is a bar graph representing regenerative charge acceptance (watts), while FIG. 3b is a bar graph representing peak power (watts) for 6V/24 Ah. The data was collected at different state-of-charge (SoC) values, ranging from 20% to 100% with 20% intervals. For reference, FIG. 1d is a chart depicting the comparable initial characterization of three spiral 6V/25 Ah modules used in the test.

(43) Referring first to FIG. 3a, the graph indicates that a standard, graphite-carbon mix generally shows a higher charge acceptance as compared to both the no-carbon control mix and Advanced Graphite mix. The performance of the standard, graphite-carbon mix may be attributed to the presence of smaller-particulate, high surface area, carbon black.

(44) In FIG. 3b, by contrast, the graph clearly indicates that the Advanced Graphite mix consistently yields the highest discharge power at all state-of-charge levels. The graph also shows the drastic drop in discharge power for the no-carbon, control mix and standard, graphite-carbon mix as the SOC decreases from 100% to 20%. The Advanced Graphite mix's outstanding performance may be attributed to the higher electrical conductivity of Advanced Graphite as compared to the standard graphite/carbon black mix. Remarkably, maximum improvement was observed at 20% SoC, where the Advanced Graphite mix showed more than 35% and 25% improvement over the control battery (no-carbon mix) and standard, graphite-carbon mix, respectively.

(45) A micro-hybrid dynamic charge acceptance test (mDCAT) was performed on prismatic batteries (e.g., a battery that is prismatic, or rectangular, in shape rather than cylindrical) at 80% SoC to determine charge acceptance capability of batteries in hybrid electric vehicle (HEV) application at high rate partial state-of-charge (SoC) conditions. Charge current at 500th micro-cycle or end of test unit for different batteries at 25 C. is presented in FIG. 4. The results show higher charging current representing higher charge acceptance for both carbon-containing groups compared to standard, no-carbon batteries. The control batteries reached end-of-test condition after 13 units of cycling (6,500 cycles), while carbon-containing batteries continued to cycle beyond 10,000 cycles, representing longer cycle life.

(46) The EUCAR, power-assist, cycle-life test is an important test for hybrid electric vehicle (HEV) applications carried out to simulate the power performance of batteries under partial state-of-charge cycling. The profile used for testing contains a test unit that repeats 10,000 times with the battery at 60% SoC and 2.5% depth-of-discharge. The battery rests for a few hours after 10,000 cycles for the electrolyte to stabilize in the battery before further testing. This rest step in power-assist cycle-life tests does not typically represent actual use conditions. Therefore, a non-stop, power-assist, cycle-life test was devised, whereby the battery was cycled without rest until it reached failure condition. The non-stop, power-assist test also helps to differentiate various carbon groups that perform alike when rested after every 10,000 cycles.

(47) Results of the non-stop, power-assist test is presented in FIG. 5, which shows the standard, graphite-carbon mix (1% by weight standard graphite and 1% by weight standard carbon black and a negative mix with 2% by weight advanced carbon)the best performing group from previous resultsreaching failure condition below 20,000 cycles. A significant and unexpected cycle life was achieved for the Advanced Graphite mix (2% by weight Advanced Graphite), where the battery was able to cycle beyond 145,000 cycles above the failure voltage of 9V. This important advancement in cycle life is the result of combining two important attributes of additiveshigher surface area and higher electrical conductivity in a single graphite (i.e., Advanced Graphite).

(48) Elimination of carbon black, with its inferior mechanical stability, from the negative paste mix, a typical additive to improve surface area and enhance charge acceptance, results in a robust battery that may be cycled efficiently over an extended period of time.

(49) Advanced Graphite, with ordered structures that are inert to electrochemical reactions during charge-discharge cycles and with surface area of at least ten times greater than typical battery-grade natural or synthetic graphites, is an ideal candidate for lead-acid battery application. The use of this Advanced Graphite will advance the capabilities of valve-regulated, lead-acid battery to compete with other chemistries for HEV application.

(50) FIG. 6 illustrates a prismatic lead-acid battery 600 configured to accept an Advanced Carbon paste. As seen in the diagram, the lead-acid battery comprises a lower housing 610 and a lid 616. The cavity formed by the lower housing 610 and a lid 616 houses a series of plates that collectively form a positive plate pack 612 (i.e., positive electrode) and a negative plate pack 614 (i.e., negative electrode). The positive and negative electrodes are submerged in an electrolyte bath within the housing. Electrode plates are isolated from one another by a porous separator 606 whose primary role is to eliminate all contact between the positive plates 604 and negative plates 608, while keeping them within a minimal distance (e.g., a few millimeters) of each other. The positive plate pack 612 and negative plate pack 614 each have an electrically connective bar travelling perpendicular to the plate direction that causes all positive plates to be electrically coupled and negative plates to be electrically coupled, typically by a tab on each plate. Electrically coupled to each connective bar is a connection post or terminal (i.e., positive 620 and negative post 618). The Advanced Carbon paste of the present application may be pressed in to the openings of grid plates 602, which, in certain exemplary embodiments, may be slightly tapered on each side to better retain the paste. Although a prismatic AGM lead-acid battery is depicted, the Advance Carbon additive may be used with any lead-acid battery, including, for example, flooded/wet cells and/or gel cells. As seen in FIG. 7, the battery shape need not be prismatic, it may be cylindrical, or a series of cylindrical cells arranged in various configurations (e.g., a six-pack or an off-set six-pack).

(51) A carbon containing paste may be prepared having an optimum viscosity (260-310 grams/cubic inch) and penetration (38-50). The carbon paste may then be applied to a lead alloy grid that may be cured at a high temperature and humidity. In cylindrical cells, positive and negative plates are rolled with a seperator and/or pasting papers into spiral cells prior to curing. Once cured, the plates are further dried at a higher temperature and assembled in the battery casing. Respective gravity acid may be used to fill the battery casing. Batteries are then formed using an optimized carbon batteries formation process (i.e., profile). The formation process may include, for example, a series of constant current or constant voltage charging steps performed on a battery after acid filling to convert lead oxide to lead dioxide in positive plate and lead oxide to metallic lead in negative plate. In general, carbon-containing negative plates have lower active material (lead oxide) compared to control plates. Thus, the formation process (i.e., profile) for carbon containing plates is typically shorter.

(52) FIG. 7 illustrates a spiral-wound lead-acid battery 700 configured to accept an Advanced Graphite paste. As in the prismatic lead-acid battery 600, a spiral-wound lead-acid battery 700 comprises a lower housing 710 and a lid 716. The cavity formed by the lower housing 710 and a lid 716 houses one or more tightly compressed cells 702. Each tightly compressed cell 702 has a positive electrode sheet 704, a negative electrode sheet 708 and a separator 706 (e.g., an absorbent glass mat separator). AGM batteries use thin, sponge-like, absorbent glass mat separators 706 that absorb all liquid electrolytes while isolating the electrode sheets. A carbon containing paste may be prepared having an optimum viscosity (260-310 grams/cubic inch) and penetration (38-50). The carbon paste may then be applied to a lead alloy grid that may be cured at a high temperature and humidity. In cylindrical cells, positive and negative plates are rolled with a seperator and/or pasting papers into spiral cells prior to curing. Once cured, the plates are further dried at a higher temperature and assembled in the battery casing. Respective gravity acid may be used to fill the battery casing. Batteries are then formed using an optimized carbon batteries formation process.

(53) The Advanced Graphite paste may be prepared using one of many known processes. For example, U.S. Pat. No. 6,531,248 to Zguris et al. discusses a number of known procedures for preparing paste and applying paste to an electrode. For example, a paste may be prepared by mixing sulfuric acid, water, and various additives (e.g., Advance Graphite and/or other expanders), where paste mixing is controlled by adding or reducing fluids (e.g., H.sub.2O, H.sub.2SO.sub.4, tetrabasic lead sulfate, etc.) to achieve a desired paste density. The paste density may be measured using a cup with a hemispherical cavity, penetrometer (a device often used to test the strength of soil) and/or other density measurement device. A number of factors can affect paste density, including for example, the total amount of water and acid used in the paste, the specific identity of the oxide or oxides used, and the type of mixer used. Zguris also discusses a number of methods for applying a paste to a battery electrode. For example, a hydroset cure involves subjecting pasted plates to a temperature (e.g., between 25 and 40 C.) for 1 to 3 days. 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 (i.e., about 50 volume percentage) is evaporated.

(54) FIG. 8 is a flow chart demonstrating a method of preparing an Advanced Graphite paste and applying it to a battery electrode. To form the paste, paste ingredients (e.g., Advanced Graphite, graphite, carbon black, lignin derivatives, BaSO.sub.4, H.sub.2SO.sub.4, H.sub.2O, etc.) are mixed 800 until a desired density (e.g., 4.0 to 4.3 g/cc) is determined. The carbon containing paste may be prepared by adding lead oxide, one or more carbon expanders and polymeric fibers to a mixing vessel, with mixing of the materials for 5-10 minutes using a paddle type mixer (800). Water may be added (x % more water than regular negative paste mix for every 1% additional carbon) with continued mixing. A carbon paste (e.g., a paste containing Advance Graphite) would preferably contain 0.3-6% carbon-based additive by weight with exemplary ranges of about 1-4% or 1-3%. Other exemplary embodiments describe a carbon paste would contain about 0.3-6%, 0.3-3%, 0.3-2% or 0.3-1.5% carbon-based additive by weight.

(55) Once the carbon containing paste has been prepared, sulfuric acid may be sprinkled into the mixing vessel with constant stirring; and mixing may be continued for additional 5-10 minutes (802). Viscosity and penetration of the resulting carbon paste may be measured and water may be added to the paste to attain necessary visosity (804). This carbon containing paste may then be applied to lead alloy grid (806) followed by curing at high temperature and humidity (808). In cylindrical cells, the positive and negative plates are rolled with a seperator and/or pasting papers into spiral cells before curing. Cured plates are further dried at higher temperature. Dried plates are assembled in the battery casing; and respective gravity acid is filled into the battery casing (810). Batteries are then formed using an optimized carbon batteries formation profile (812).

(56) Additional Examples follow:

Example 1

(57) Group L3 70 Ah Micro-hybrid flooded (MHF) prismatic type batteries were assembled with two different compositions of negative paste: standard negative mix with no additional carbon; and negative mix with 1.3 wt % Advanced Graphite

(58) A standard paste-mixing recipe was used for standard positive and standard negative control pastes. Additional graphite containing carbon additive was added to the negative paste mix for advanced graphite containing plates. Advanced graphite containing paste was prepared by adding lead oxide, one or more carbon expanders and polymeric fibers to a mixing vessel, followed by mixing of the materials for several minutes using a standard batch paste mixer. Additional water was used for advanced graphite containing paste. Sulfuric acid was sprinkled into the mixing vessel with constant stirring and the mixing was continued for an additional time.

(59) Viscosity and penetration of the resulting carbon paste was measured, and optionally, water was added to the paste to attain the desired viscosity. This carbon-containing paste was then applied onto a lead alloy grid, followed by curing at high temperature and humidity. Similar procedures were followed for standard positive and standard negative plates using standard paste recipe, paste mixing, pasting and curing process. The dried plates were assembled in the battery casing with standard seperators; and standard specific gravity acid was filled into the battery casing specific to MHF batteries. Batteries were then formed using an optimized carbon battery formation profile. Formed batteries were subjected to various electrochemical tests below.

(60) Initial characterization of group L3 batteries included a 20-hour discharge capacity test and a EN cold cranking test. After each test, the modules were recharged at conditions recommended for the battery type. These tests were performed to determine the responses of battery to slow as well as to fast discharge conditions.

(61) FIG. 9a shows a graph of discharge capacity for batteries with standard negative mix with no carbon and batteries with advanced graphite containing negative mix. FIG. 9b shows a graph of EN Cold cranking test results for batteries with standard negative mix with no carbon and batteries with advanced graphite containing negative mix FIGS. 9a and 9b show that both standard batteries with no additional carbon as well as batteries with 1.3% advanced graphite additive meet or exceed the L3 group battery specification for discharge capacity (70 Ah) and EN CCA test specification of 7.5V at 10 seconds and 9.0V at 40 seconds.

(62) Charge acceptance test was performed to determine the ability of battery to accept charge at a partial state of charge (PSoC) conditions. The battery was initially discharged at C/20 rate to get the battery to 70, 80 or 90% state of charge (SoC). After the battery voltage stabilized at that PSoC, battery was charged with a constant voltage. Current drawn by batteries during this charge step was monitored and recorded. The charge current that a battery accepted during this test depended on surface area of the negative active material and electrical conductivity of the electrodes. Charge acceptance varied with charge voltage, as well as SoC, of the battery. Charge voltages of 13.5, 14.0 and 14.4 V were used to determine the charge acceptance of batteries at 70, 80 or 90% SoC (FIGS. 10a, 10b and 10c).

(63) Advanced graphite-containing batteries showed higher charge acceptance, compared to standard batteries with no carbon, at all charge voltage and at all SoC. Differences in charge acceptance for standard and advanced graphite containing batteries appear to be higher at higher test voltages. Similar differences in charge acceptance were observed at all state-of-charges. Charge acceptance decreased for both groups at lower test voltages.

(64) Standard batteries with no carbon, and batteries with advanced graphite additives, were then subjected to 17.5% depth of discharge (DoD) test according to the Verband der Automobilindustrie (VDA) performance specification for enhanced flooded batteries. One unit (approximately 1 week) of 17.5% DoD testing consists of a discharge capacity test done after 85 chargedischarge micro-cycles, with 17.5% depth of discharge swing performed on a battery at 50% state of charge. FIG. 11 shows that a significant and unexpected cycle life was achieved for the advanced graphite mix where the battery was able to cycle more than 1000 cycles (13 to 14 weeks), while the standard batteries failed around 750 cycles (less than 9 weeks). This important advancement in cycle life is the result of combining two important attributes of additiveshigher surface area and higher electrical conductivity in single graphite. Addition of this advanced graphite results in a robust battery that could be cycled efficiently over an extended period of time.

(65) Discovery of this advanced graphite, with ordered structures that are inert to electrochemical reactions during charge-discharge cycles and with surface area of at least 10 times greater than typical battery grade natural or synthetic graphites, is a vital step for lead acid battery application. Use of this Advanced Graphite represents a significant advance for the capabilities of valve-regulated lead acid battery as compared with other chemistries for HEV application.

Example 2

(66) Group LN5 92 Ah Advanced glass mat (AGM) type prismatic batteries were assembled with two different compositions of negative paste. Tests were conducted with regard to batteries having no additional carbon standard negative mix for reference, as well as negative mix with 0.3 wt % Advanced Graphite. A standard paste-mixing recipe was used for standard positive and standard negative control pastes. Additional graphite-containing carbon additive was added to the negative paste mix for advanced graphite-containing plates. The dried plates were assembled in the battery casing with standard AGM seperators; and standard specific gravity acid was filled into the battery casing specific to AGM batteries. Formed batteries were subjected to various electrochemical tests, as is described below.

(67) Initial characterization of group LN5 batteries included a 20-hour discharge capacity test (FIG. 12a), a Reserve capacity test (FIG. 12b) and a EN cold cranking test (FIG. 12c). After each test, the modules were recharged at conditions recommended for the battery type. These tests were performed to determine the responses of battery to slow, medium and fast discharge conditions. FIGS. 12a, 12b and 12c show that both standard batteries with no additional carbon, as well as batteries with 0.3% advanced graphite additive, meet or exceed the LN5 group battery specification for discharge capacity (92 Ah), reserve capacity (160 minutes) and EN CCA test specification of 7.5V at 10 seconds and 9.0V at 40 seconds.

(68) Repeated reserve capacity test is a cycle life test performed to predict the durability of lead acid batteries. The batteries are cycled at reserve capacity rate (25 A discharge) 50 times. Discharge capacities are monitored and recorded over 50 cycles for both standard and advanced graphite batteries. FIG. 13 shows a graph of discharge capacities as % of rated capacity over 50 cycles of Repeated reserve capacity test for batteries with standard negative mix with no carbon and for batteries with advanced graphite containing negative mix. FIG. 13 show that Advanced Graphite containing battery increases cumulative energy capacity over 50 cycles of repeated reserve capacity test by about 10%, when compared to standard battery. This increase is observed for an average of 3 batteries from each group. This advancement in cycle life is the result of combining two important attributes of advanced graphite additive-higher surface area and higher electrical conductivity in single graphite.

(69) The individual components shown in outline or designated by blocks in the attached Drawings are all well-known in the battery arts, and their specific construction and operation are not critical to the operation or best mode for carrying out the invention.

(70) While the present invention has been described with respect to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

(71) All U.S. and foreign patent documents, all articles, brochures, and all other published documents discussed above are hereby incorporated by reference into the Detailed Description of the Preferred Embodiment.