DICKINSON, Enders (Inc.3601 Clover Lan, New Castle Pennsylvania, 16105, US)
WESTREICH, Philippe (Inc.3601 Clover Lan, New Castle Pennsylvania, 16105, US)
SUN, Wei (Inc.3601 Clover Lan, New Castle Pennsylvania, 16105, US)
ROMEO, Mike (Inc.3601 Clover Lan, New Castle Pennsylvania, 16105, US)
BUIEL, Edward (Inc.3601 Clover Lan, New Castle Pennsylvania, 16105, US)
DICKINSON, Enders (Inc.3601 Clover Lan, New Castle Pennsylvania, 16105, US)
WESTREICH, Philippe (Inc.3601 Clover Lan, New Castle Pennsylvania, 16105, US)
SUN, Wei (Inc.3601 Clover Lan, New Castle Pennsylvania, 16105, US)
ROMEO, Mike (Inc.3601 Clover Lan, New Castle Pennsylvania, 16105, US)
| WHAT IS CLAIMED IS: 1. An energy storage device, characterized by: at least one negative electrode comprising an active material comprising lead, at least one positive electrode comprising lead dioxide, a separator between the at least one negative electrode and the at least one positive electrode, and an aqueous electrolyte comprising sulfuric acid, characterized in that the at least one negative electrode comprises: a porous carbon material having a surface area in a range of 150 to 1000 m2/g; and less than 0.1 wt% lignin based on the weight of the active material. 2. An energy storage device as in Claim 1 , characterized in that the at least one negative electrode comprises 0.1 wt.% to 5.0 wt% carbon material, based on the weight of the active material. 3. An energy storage device as in Claim 1 , characterized in that the at least one negative electrode comprises 2.0 wt.% to 5.0 wt% carbon material, based on the weight of the active material. 4. An energy storage device as in Claim 1, characterized in that the at least one negative electrode comprises less than 0.05 wt% lignin based on the weight of the active material. 5. An energy storage device as in Claim 1, characterized in that the at least one negative electrode comprises from more than 0.0 wt.% to less than 0.1 wt% lignin based on the weight of the active material. 6. An energy storage device as in Claim 1, characterized in that the carbon material has a surface area in a range of 200 to 750 m2/g. 7. An energy storage device as in Claim 1, characterized in that the carbon material has a surface area in a range of 200 to 500 m2/g. 8. An energy storage device as in Claim 1 , characterized in that the at least one negative electrode further comprises barium sulfate. 9. A negative electrode, characterized by: an active material comprising lead; less than 0.1 wt% lignin based on the weight of the active material; and a porous carbon material having a surface area in a range of 150 to 1000 m2/g. 10. A negative electrode as in Claim 9, characterized by 0.1 wt.% to 5.0 wt% carbon material, based on the weight of the active material. 11. A negative electrode as in Claim 9, characterized by 2.0 wt.% to 5.0 wt% carbon material, based on the weight of the active material. 12. A negative electrode as in Claim 9, characterized by less than 0.05 wt% lignin based on the weight of the active material. 13. A negative electrode as in Claim 9, characterized by more than 0.0 wt.% to less than 0.1 wt% lignin based on the weight of the active material. 14. A negative electrode as in Claim 9, characterized in that the carbon material has a surface area in the range of 200 to 750 m2/g. 15. A negative electrode as in Claim 9, characterized in that the carbon material has a surface area in the range of 200 to 500 m2/g. 16. A negative electrode as in Claim 9, characterized in that the negative electrode further comprises barium sulfate. |
IN NEGATIVE ELECTRODE
This PCT international application claims priority to U.S. provisional application 61/254,824, filed on 26 October 2009, and U.S. provisional application 61/288,376, filed on 21 December 2009, both in the U.S. Patent and Trademark Office.
I. Technical Field The present invention is directed to an energy storage device, such as a lead acid battery, having at least one negative electrode comprising an active material comprising lead, a carbon material having a surface area in the range of 150 to 1000 m 2 /g, and less than 0.1 wt% lignin based on the weight of the active material. II. Background Of Invention
Hybrid electric vehicles (HEVs) require much higher charging characteristics for batteries compared to conventional automobiles, and conventional lead acid batteries do not exhibit good charge characteristics (also referred to as charge acceptance). The use of lead acid batteries in conventional automobiles are used to start the vehicle at an origination point and then only serve to stabilize the voltage of the power net in the vehicle until the vehicle arrives at a destination point.
Micro hybrid vehicles (uHEVs) are different from conventional vehicles, as they are designed to shut the engine off when the vehicle comes to a stop. The engine is then restarted immediately before the vehicle begins moving again. As a result, the lead acid battery is forced to discharge during the period the engine is off to provide support for electrical loads in the vehicle and discharge at a high rate to start the vehicle. This will happen many times during a normal trip as opposed to only once for a conventional vehicle. The lead acid battery therefore will discharge many times and be required to charge quickly in order to replenish the charge depleted during the stop event to allow the vehicle to complete another stop-start event. This new requirement for lead acid batteries is difficult to achieve, as their conventional design allows for discharges up to 1000A, but charging up to only 20A for prolonged periods of time.
Mild hybrid electric vehicles (mHEVs) feature all of the same requirements as uHEVs, but also can have the additional requirement that they can be charged at high rates during regenerative braking events.
III. Summary of Invention An energy storage device includes at least one negative electrode comprising an active material comprising lead, at least one positive electrode comprising lead dioxide, a separator between the at least one negative electrode and at least one positive electrode, and an aqueous solution electrolyte comprising sulfuric acid. The at least one negative electrode further comprises a porous carbon material having a surface area in the range of 150 to 1000 m 2 /g and less than 0.1 wt% lignin based material, based on the weight of the active material.
As used herein "substantially", "generally", "relatively", "approximately", and "about" are relative modifiers intended to indicate permissible variation from the
characteristic so modified. It is not intended to be limited to the absolute value or characteristic which it modifies but rather approaching or approximating such a physical or functional characteristic.
References to "one embodiment", "an embodiment", or "in embodiments" mean that the feature being referred to is included in at least one embodiment of the invention. Moreover, separate references to "one embodiment", "an embodiment", or "in embodiments" do not necessarily refer to the same embodiment; however, neither are such embodiments mutually exclusive, unless so stated, and except as will be readily apparent to those skilled in the art. Thus, the invention can include any variety of combinations and/or integrations of the embodiments described herein.
In the following description, reference is made to the accompanying drawings, which are shown by way of illustration to specific embodiments in which the invention may be practiced. The following illustrated embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. It is to be understood that other embodiments may be utilized and that structural changes based on presently known structural and/or functional equivalents may be made without departing from the scope of the invention.
IV. Brief Description Of The Drawings
FIG. 1 is a schematic drawing of an energy storage device according to an exemplary embodiment of the present invention.
FIG. 2 is a diagram showing a Dynamic Overcharge 2C Partial-State-of-Charge algorithm.
FIG. 3 is a graph showing Test Results for a Standard Vaive Regulated Lead Acid Battery (VRLA) versus an uHEV VRLA according to an exemplary embodiment of the present invention using the algorithm of FIG. 2.
V. Detailed Description of Invention The present invention is directed to an energy storage device, for example, a lead acid battery. The discussion below is directed to a valve regulated lead acid (VRLA) battery, but the present invention is not so limited and also applies to other kinds of energy storage devices, such as hybrid energy storage devices, ultracapacitors, and supercapacitors.
According to a particular embodiment of the present invention illustrated in FIG. 1, an energy storage device 1 comprises at least one positive electrode 5, at least one negative electrode 10, at least one separator 15, a casing 20, a negative terminal 25, and a positive terminal 30. In the illustrated embodiment, the energy storage device has two negative electrodes and three positive electrodes. The energy storage device further comprises an acid electrolyte, for example sulfuric acid.
In specific embodiments, the at least one positive electrode comprises lead dioxide. The separator may comprise a material suitable for use with the acid electrolyte, and may comprise a woven material or a felted material. In specific embodiments, the separator may comprise an absorbent glass mat (AGM) or polyethylene.
The at least one negative electrode comprises an active material comprising lead (e.g., a sponge-type lead), and a current collector grid comprising metallic lead. According the present invention, the at least one negative electrode has a limited Iignin or lignosulfonate content.
Lignin causes lead sulfate in a negative electrode to grow into large crystals that are less soluble than smaller lead sulfate crystals and which are present for more cycles when lignin is not present. Lead sulfate must dissolve first in order for a battery to accept charge and recharge when the battery is charged. Hence, the use of lignin increases the growth of the lead sulfate crystals, reduces solubility of lead sulfate, and reduces the dynamic charge acceptance of VRLA batteries.
In specific embodiments, the at least one negative electrode comprises 0.0 to 0.1 wt.% lignin, for example, less than 0.1 wt.% lignin, preferably less than 0.05 wt.% lignin, based on the weight of the active material. The minimization or elimination of the lignin material in a negative electrode is contrary to conventional practices that always include lignin in order to maintain high surface area of a lead active material. Failure to do so, results in poor discharge capacity which would result in failure to start a vehicle.
The energy storage device of the present invention overcomes this disadvantage by the using a carbon expander in the at least one negative electrode that does not cause the lead sulfate crystal structure to grow and, as a result, increases the charge acceptance of the battery without the loss of the batteries discharge capabilities. The carbon expander also acts to retain the high surface area of the lead active material.
Carbon materials with too low of a surface area (less than 150 m 2 /g) tend to not maintain a high charge acceptance of the battery and only show increase in relative performance compared to a control of 1.21. Carbon materials with too high a surface area (greater than 1000 m 2 /g) exhibit good initial performance in terms of charge acceptance, but fail to meet cycle life requirements because this type of carbon eventually hydrogenates and becomes an insulator (i.e., fails to continue to conduct electrodes). Thus, according to specific embodiments of the present invention, the at least one negative electrode comprises a carbon materia! having a surface area in the range of 150 to 1000 m 2 /g, for example 200 to 750 m 2 /g, which provides both the advantages of improved charged acceptance and longevity in terms of cycle life. High surface area carbon may have a tendency to hydrogenate and become highly resistive. Therefore, a range of 200 to 500 m 2 /g is preferable for advanced lead acid batteries for high charge acceptance applications. The surface area of the carbon material may be measured by using a BET method.
In specific embodiments, the carbon material comprises a porous carbon material. In specific embodiments, the amount of carbon in the at least one negative electrode may be in the range of from 0.1 wt.% to 5 wt.%, for example from 2 wt.% to 5 wt.%, based on the weight of the active material of the negative electrode.
In specific embodiments, the at least one negative electrode may also comprise barium sulfate. The barium sulfate may be present in an amount of 0 to 1 wt.%, for example, 0.1 to 1 wt.%, based on the weight of the active material.
Typical flooded and valve regulated (VRLA) lead acid batteries (such as EN-L5 size batteries) can only sustain charge at a rate of 20 A. VRLA batteries according to the present invention can accept up to 45 A of current, which is 2.25 times greater than what is currently commercially available (as shown in FIGS. 2-3).
The present invention is illustrated by the following non-limiting embodiments. EXAMPLE 1
Lead acid batteries were cycled using a Dynamic Charge Acceptance Test
Procedure (DCA) that simulates micro hybrid (uHEV) and mild hybrid (mHEV) electric vehicle battery conditions and that is used to evaluate the Partial State of Charge (PSOC) cycling performance.
This procedure was accomplished by using a simple PLC (Programmable Logic Controller)-based algorithm, where the amount of overcharge is iteratively determined for each successive cycle based on a specific rest voltage following the charge from the previous cycle. If the State-Of-Charge (SOC) of the battery is decreasing based on the rest voltage, the charge time is increased for the following cycling. If the opposite is true, the charge time is decreased.
A schematic of this dynamic overcharge algorithm is shown in FIG. 2, in which TOCV represents Top of Charge Voltage; PCRV represents Post Charge Rest Voltage; EODV represents End of Discharge Voltage; and PDRV represents Post Discharge Rest Voltage. FIG. 2 shows the algorithm for a lead acid battery with a nominal 10 A C-rate.
FIG. 3 shows the results (charge time and current plotted against cycle number) of cycling both conventional, standard lead acid batteries and lead acid batteries according to the present invention using the DCA Test Procedure of FIG. 2 (Dynamic HEV Cycling at 80% SOC (-19 Ah versus -13 Ah), PDRV Setpoint ( 2.60 versus 12.69); and to 20,000 cycles). Data shown in FIG. 3 correspond to Battery 1a and Battery 3 in the Table discussed below.
As shown in FIG. 3, the valve regulated lead acid battery (VRLA) of the present invention charges with more than 2 times the charging current of a conventional VRLA battery. Both the conventional VRLA and the VRLA battery of the present invention were made to the same dimension and have the same battery construction except for the composition of the negative electrode. EXAMPLE 2
As shown in the Table below, the performance of VRLA batteries based on dynamic charge acceptance testing (DCAT) of FIG. 2 is shown for negative electrodes having carbon materials with different surface areas.
As seen in the Table, a VRLA battery according to the present invention with carbon having a surface area of 260 m 2 /g exhibits improved relative performance.
VI. Industrial Applicability An energy storage device (e.g., lead acid battery) is provided. The energy storage device is particularly suitable for hybrid vehicles and other energy storage
applications.
Although specific embodiments of the invention have been described herein, it is understood by those skilled in the art that many other modifications and
embodiments of the invention will come to mind to which the invention pertains, having benefit of the teaching presented in the foregoing description and associated drawings. It is therefore understood that the invention is not limited to the specific embodiments disclosed herein, and that many modifications and other embodiments of the invention are intended to be included within the scope of the invention. Moreover, although specific terms are employed herein, they are used only in generic and descriptive sense, and not for the purposes of limiting the description invention.