DUAL CHEMISTRY HYBRID BATTERY SYSTEMS
FIELD OF THE INVENTION:
[0001] This invention relates to hybrid battery systems, and particularly to hybrid battery systems having a high power, low impedance battery in parallel with a high energy battery, where the batteiy chemistries of the two component batteries are different.
BACKGROUND OF THE INVENTION:
[0002] Hybrid battery systems are becoming known, and are or will be finding more acceptance in various configurations and situations where battery power is required, either as a prime energy source - such as in many kinds of portable electrical equipment of all sorts, power tools, telephones, computers, and the like - as well as in traction vehicles of all sorts, and in stand-by situations. In all configurations of hybrid battery systems, there is a parallel arrangement of two disparate batteries, one of which is typically a high power battery, or a supercapacitor, and the other of which is a high energy battery. Each has its own charge and discharge characteristics, its own impedance characteristics, and its own contribution to the provision of power to the load. In many instances, the high energy battery may be called upon to recharge the high power battery, even during ongoing load requirements being placed on the hybrid battery system. [0003] Typically, the kind of load requirements that are being contemplated are those which are pulsed loads, as opposed to steady state loads; moreover, the kind of load is such that it may have periods of high energy requirements and longer periods of low energy requirements, all of which are expected to be satisfied by the hybrid battery system.
[0004] The combination of two rechargeable batteries which deliver an enhanced performance as a "tuned" system is quite simple in concept. As noted, one unit is designed to have a relatively low ampere hour capacity, but it will have the capability of high power delivery. The other unit will have greater ampere hour capacity - sometimes, much greater - and it is designed to maximize energy density.
[0005] Put together, such a hybrid battery system can offer a number of specific advantages as power sources for devices that have variable or "pulse" load profiles. Those advantages include the following:
• Higher overall energy density. • High pulse capability without truncation of life times of the constituent battery units. Greater service life.
• Higher safety levels for more volatile high energy density batteries. [0006] Also, as noted, hybrid battery systems contemplate the use of supercapacitors as well as the use of high power batteries. However, there are certain advantages to be gained by using low ampere hour capacity rechargeable batteries instead of supercapacitors. One of those advantages is, of course, the higher available ampere hour capacity for high current delivery from a battery as opposed to a supercapacitor. Moreover, sustained pulses are possible from a rechargeable, high power battery as opposed to a supercapacitor, due to the prospect of the depletion of the capacitive charge storage of the battery, and Faradaic energy arising from the electrochemical reaction in the battery.
[0007] This is particularly important when it is considered that the demand for pulsed energy does not necessarily allow sufficient time for immediate recharge of the high power pulse device - the supercapacitor or high power battery. Moreover, in such instances as when a portable computer is being started at the same time as the onset of wireless communication through an associated modem and/or mobile telephone, for
example, there may be a sustained high current drain as the hard drive of the computer is spun up and wireless communication is initiated. The concern is, of course, that the energy requirements that are placed on such as a supercapacitor may be greater than the ampere hour capacity of the supercapacitor to deliver. [0008] Still further, it is now becoming known that there are a number of combinations of rechargeable chemistries that may be possible in the configuration of a hybrid battery system. Thus, by pairing or combining the highest power density batteries and the highest energy density batteries, the greatest performance benefits may be achieved. For example, a high energy nickel zinc battery may be combined with a high power density lead acid battery; or a high energy density lithium polymer battery may compliment a high power nickel zinc battery or a nickel metal hydride battery, or a lead acid battery.
[0009] However, the chose of a particular system must contemplate the
"electrochemical" compatibility of the constituent batteries, as well as the complexity of the electronic management system for the hybrid battery configuration. By referencing the electrochemical compatibility, it is meant that care must be taken in interfacing batteries that have different chemistries which have distinct thermodynamic signatures. Each battery has unique voltage ranges associated with its conditions of charge, discharge, and very little electrochemical activity. Also, the voltage ranges for those various conditions may vary quite considerably from battery to battery.
[0010] However, those voltage ranges for various conditions of batteries can be modified either chemically, or by battery design, so as to fine tune battery compatibility. [0011] It must be noted, however, that an even easier, and more readily available approach, may be arrived at by varying the number of cells in each battery. Careful matching of the numbers of cells will ensure appropriate load sharing and efficient transfer of charge between two parallel battery strings.
[0012] Of course, the relative impedances of two batteries, and their relative capacities, must also be considered.
[0013] Several arrangements may be contemplated, where the operation and responsibility of one or the other of the constituent battery units in a hybrid battery 5 system may vary, depending on the purposes to which the hybrid battery system is to be put. They include the following sets of circumstances, which are discussed in greater detail hereafter;
• A configuration where the energy battery maintains the power battery fully charged over its entire operational range.
.0 • A configuration where the energy battery maintains the power battery fully charged over most of its operational range.
• A configuration where the energy battery maintains the power battery fully charged only when the energy battery itself is fully charged.
• A configuration where the energy battery is not capable of recharging [ 5 the power battery over the entire voltage range of operation of the hybrid battery system. [0014] A number of various hybrid battery system configurations are contemplated by the present invention, having differing electrical couples with respect to the high power battery and the high energy battery. Examples of such hybrid battery 20 systems configurations, having different chemistries - that is having different electrical couples - of the high power battery and the high energy battery, are described in greater detail hereafter.
SUMMARY OF THE INVENTION:
25 [0015] In accordance with one aspect of the present invention, there is provided a plurality of hybrid battery system configurations. However, it will be noted that the present invention is particularly directed to dual chemistry hybrid battery systems; and
to that end, the present invention teaches a hybrid battery system which comprises a high power, low impedance battery in parallel with a high energy battery. [0016] The high power, low impedance battery, and the high energy battery, have substantially equal terminal voltages when they are each fully charged, and at rest. [0017] However, the ampere hour capacity of the high energy battery to a predetermined cutoff voltage is at least twenty times the ampere hour capacity of the high power battery to the same cutoff voltage.
[0018] The electrical couples of the high power battery and the high energy battery are different one from the other. [0019] Indeed, the electrical couples of the high power battery and the high energy battery may be chosen from the group of pairs of electrical couples consisting of lead acid and nickel zinc batteries, lead acid and lithium ion batteries, lead acid and lithium polymer batteries, nickel zinc and lithium polymer batteries, nickel metal hydride and lithium polymer batteries, and carbon nickel oxide and nickel zinc batteries.
[0020] In the case where the pair of electrical couples is carbon nickel oxide and nickel zinc, the carbon nickel oxide batteiy may comprise carbon impregnated into a nickel foam substrate, and the nickel electrode is a compressed pasted nickel oxide electrode having a thickness in the range of 0.007 to 0.012 inches. [0021 ] In that case, the carbon electrode of the carbon nickel oxide battery may be doped with a doping material chosen from the group consisting of bismuth oxide, iron hydroxide, and combinations thereof.
[0022] Typically, the number of cells in the high power battery differs from the number of cells in the high energy batteiy.
BRIEF DESCRIPTION OF THE DRAWINGS:
[0023] The novel features which are believed to be characteristic of the present invention, as to its structure, organization, use and method of operation, together with further objectives and advantages thereof, will be better understood from the following drawings in which a presently preferred embodiment of the invention will now be illustrated by way of example. It is expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention. Embodiments of this invention will now be described by way of example in association with the accompanying drawings in which: [0024] Figure 1 is a simple circuit showing a hybrid battery system in series with a load;
[0025] Figure 2 is a simple circuit showing several additions to the circuit of
Figure 1; [0026] Figure 3 is a composite set of curves showing the effect of coupling a lead acid power battery with a nickel zinc energy battery, compared with the performance of the nickel zinc battery alone; and
[0027] Figure 4 is a further composite curve showing the effect of coupling a carbon nickel oxide battery with a nickel zinc battery, compared with the nickel zinc battery alone;
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS: [0028] The novel features which are believed to be characteristic of the present invention, as to its structure, organization, use and method of operation, together with further objectives and advantages thereof, will be better understood from the following discussion.
[0029] Each of Figures 1 and 2 shows a typical configuration of a hybrid battery system 10 and 12, respectively. Each of these hybrid battery configurations comprises
a low impedance, high power battery 20 connected in parallel with a high energy battery 22. In each case, the hybrid battery configuration 10 or 12 is shown in series with a load 14.
[0030] The hybrid battery configuration 12 also includes a DC to DC converter 16, in series with a switch 18 which may function to put the DC to DC converter into the circuit between the high energy battery 22 and the high power battery 20, in the manner described hereafter. A pair of diodes 24, which may also be Field Effect Transistors, are shown; one or either of which may function at any time, in the manner described hereafter. [0031] The ampere hour capacity of the high energy battery 22, to a predetermined cutoff voltage, is typically at least twenty times the ampere hour capacity of the high power battery 20, to the same cutoff voltage.
[0032] However, the electrical couples of the high power battery 20 and of the high energy battery 22, are different one from the other. [0033] Various examples of disparate pairs of electrical couples of the high power battery and of the high energy battery, respectively, are as follows, each of which is described in greater detail hereafter;
Lead acid high power battery and nickel zinc high energy batteiy. Lead acid high power battery and lithium ion high energy batteiy. • Lead acid high power battery and lithium polymer high energy batteiy.
Nickel zinc high power battery and lithium polymer high energy battery. Nickel metal hydride high power batteiy and lithium polymer high energy battery. • Carbon nickel oxide high power battery and nickel zinc high energy battery.
[0034] It will also be noted, as examples only, that the number of cells in the high power battery 20 may differ from the number of cells in the high energy battery
22. Examples of such configurations are given below.
[0035] Several types of conditions for varying configurations of hybrid battery systems, in keeping with the present invention, have been noted above. Specific examples are now given.
[0036] The first type of configuration is that in which the high energy battery will maintain the high power battery fully charged over its entire operational range.
Reference is made to Examples 1, 2, 3, and 4, as follows;
Example 1 Lead Acid/Lithium Ion
5 Cell Lead Acid 3 Cell Lilon Battery Voltage
Example 3 Nickel Zinc/Lithium Polvmer 8 Cell NiZn 4 Cell Li Polymer Battery Voltage
[0037] Each of these examples show the effect, in various dual chemistry hybrid battery configurations, of the changes in battery voltage over the entire operational range of the hybrid battery. Referring to Example 4, over the normal discharge and charge range of the lithium polymer battery - that is, from 3.7 volts to 4.2 volts - the high power battery operates in such a voltage range that it is always fully charged. In the case of Example 4, in particular, the available pulse energy is derived from the double layer capacity of the high power battery. The Faradaic current of the high power battery is accessed only in cases of long high current pulses, or in the event of extremely high current drains.
[0038] In all of these examples, pulse energy is available over the discharge life of the energy battery. However, in cases where overcharging of the power battery 20
is likely, a diode or FET 24 may be inserted into one or both arms of the hybrid battery configuration, as shown in Figure 2.
[0039] Another condition is the situation where the high energy battery 22 will maintain the high power battery 20 fully charged over most of its operational range.
In this case, reference is made to Examples 5 and 6.
Example 5 Lead Acid/Nickel Zinc
6 Cell Lead Acid 8 Cell NiZn Battery Voltage
[0040] Here, it is seen that the high energy battery will operate with minimal external influence so as to maintain the power battery fully charged over most of its discharge range. However, in the latter stages of discharge, the voltage of the high energy battery may be insufficient to charge or to rapidly replenish the power batteiy. [0041] In that case, the power battery must be actively charge from the high energy battery through a DC to DC converter during the nonpulse periods.
[0042] Again, reference is made to Figure 2, where it can be seen that switch
18 can be operated during the non pulse periods of the load 14, so as to supply energy from the high energy battery 22 through the DC to DC converter 16 to the high power battery 20.
[0043] Alternatively, the power battery 20 may be sized with an appropriate reserve capacity that it is sufficient to deliver the remaining pulse energy without recharge. This, of course, would normally result in a significantly higher cost for the hybrid battery configuration.
[0044] Yet another situation where a hybrid battery may be employed is that when the high energy battery maintains the high power battery fully charged only when the high energy battery, itself, is fully charged.
[0045] In this case, reference is made to Example 7. Here, the high energy battery does not have the capability of recharging the high power battery over much of its discharge range. Such a hybrid battery may be functional, for example, in automotive starting situations where charge flow is directed to the power battery preferentially. Otherwise, unless the high power battery 20 is sized to deliver the pulse loads without recharge, there is a need for DC to DC conversion as shown in Figure 2. Example 7 Lithium Polymer/Nickel Metal Hydride
12 Cell NiMH 4 Cell Li Polymer Battery Voltage
[0046] Yet another situation for dual chemistry hybrid battery systems, in keeping with the present invention, is the case when the high energy battery is not
capable of recharging the high power battery over the entire voltage range of operation. Here, reference is made to Example 8. Example 8 Nickel Zinc/Lithium Polymer lO Cell Zn 4 Cell Li Polymer Battery Voltage
[0047] It will be seen that both batteries, in this case, must be charged independently, or the high energy battery will be utilized to charge the high power battery using DC to DC conversion. Such a configuration may be particularly applicable in a situation where the high energy battery 22 will replenish the high rate battery 20 tlirough the DC to DC converter 16, and where the high power battery 22 is the conduit for all current which is supplied to the load 14.
[0048] Other tests of dual chemistry batteries in keeping with the present invention are discussed below, with reference to Figures 3 and 4.
[0049] First, turning to Figure 3 , two discharge voltage characteristic curves are illustrated over a period of time. It is seen that the battery voltage axis ranges up to 8 volts, and the time axis in Figure 3 is over 801 seconds.
[0050] A first voltage discharge characteristic is shown at 32, and it is representative of the terminal voltage of a nickel zinc battery when operated on its own, in a situation to be described hereafter. The curve 34 is the discharge voltage characteristic of a hybrid battery system, which comprises the same nickel zinc batteiy together with a lead acid batteiy.
[0051] The configuration in this case was a dual chemistry hybrid battery system which comprised a three cell high power lead acid battery in parallel with a four
cell high energy density nickel zinc battery. However, as noted the nickel zinc battery was first tested on its own.
[0052] The pulse load was a 300 mA current for 1.2 millisecond, with a 4 millisecond rest between pulses. The nominal voltage of the two batteries was 6 volts. [0053] It will be seen that up to about 500 seconds, the voltage excursions of the nickel zinc battery alone, as shown in curve 32, were quite profound. Also, at about
400 seconds, a cutoff voltage of 5 volts was being reached.
[0054] On the other hand, it is seen in curve 34 that because of the lower impedance of the lead acid battery, the voltage excursions of the hybrid battery were relatively small up to about 500 seconds. This is because the low impedance of the lead acid battery permitted such relatively small voltage excursions during pulse applications. However, below a battery voltage of about 5.8 volts, the lead acid battery was unable to be recharged, and the pulse response returned to normal - at about 500 seconds. On the other hand, up to a 5 volt cutoff voltage - a quite normal cutoff voltage for a nominal 6 volt battery - there was between 50% and 100% increase in run time.
[0055] Turning now to Figure 4, another set of curves is shown at 42 and 44.
In this case, curve 42 is representative of the terminal voltage characteristic of a nickel zinc battery alone; curve 44 is representative of the terminal voltage excursions of a hybrid battery system. It is seen that the terminal voltage in this case ranged from about
7 volts up to above 9 volts, over a time period of about 27 minutes.
[0056] The dual chemistries involved in this hybrid battery system are a high power, thin film, carbon nickel oxide battery, together with a nickel zinc high energy battery. [0057] The manufacture of the high power, thin film, carbon nickel oxide battery comprised impregnating carbon into a highly conducting nickel foam substrate.
The nickel electrode was formed in a conventional pasted technology, except that it was
compressed so as to have a film thickness in the range of 0.007 inches to 0.012 inches - typically, 0.010 inches.
[0058] The utilization of such a high power, carbon nickel oxide battery, avoids certain difficulties with respect to lead acid batteries, such as the interface stability,
5 sulphation of the battery under discharge conditions, and the like.
[0059] Various carbon nickel oxide batteries were manufactured, including some in which the carbon electrode had doping material added to it. The doping material was an electroactive material such as bismuth oxide, iron hydroxide, or combinations thereof. The use of this additional electroactive material permitted
.0 delivery of more than double layer capacity charge.
[0060] The tests shown in Figure 4 were with respect to a seven cell carbon nickel oxide battery having bismuth oxide doping material in the carbon electrode. The nickel zinc battery was a five cell battery, having a capacity of approximately 80 milliampere hours. The useful capacity of the carbon nickel oxide battery, in the
[ 5 voltage range of 7 to 9 volts, was about 3 milliampere hours.
[0061] The nickel zinc battery, and the hybrid battery configuration, were each subjected to a 400 milliampere pulse having a pulse duration of 1.2 milliseconds and a 4 millisecond rest between pulses. It is seen from Figure 4 that the pulse response is much greater for the nickel zinc battery alone, as seen by the height of the voltage
20 excursions shown in curve 42.
[0062] More significantly, the pulse response of the hybrid battery system did not fade as the discharge of the battery proceeded.
[0063] Thus, to a 6.3 volt cutoff voltage, there was a 100% increase in run time, as is clearly seen in Figure 4.
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