U.S. patent application number 10/978226 was filed with the patent office on 2005-08-04 for electrochemical cell recharging system.
Invention is credited to Tsai, Tsepin, Vartak, Aditi.
Application Number | 20050170245 10/978226 |
Document ID | / |
Family ID | 25250627 |
Filed Date | 2005-08-04 |
United States Patent
Application |
20050170245 |
Kind Code |
A1 |
Vartak, Aditi ; et
al. |
August 4, 2005 |
Electrochemical cell recharging system
Abstract
A rechargeable electrochemical cell system is provided. The
system includes a plurality of cells, wherein each cell is
comprised of a first electrode, a second electrode, and a third
electrode electrically isolated from the second electrode. The cell
system may be discharged upon application of a load across a
discharge circuit, which is formed from the first electrodes and
the second electrodes. The cell may be recharged upon application
of a voltage across a recharging circuit, which is formed of at
least one of the first electrodes and at least one of the third
electrodes.
Inventors: |
Vartak, Aditi; (Lake
Mohegan, NY) ; Tsai, Tsepin; (Chappaqua, NY) |
Correspondence
Address: |
REVEO, INC.
3 WESTCHESTER PLAZA
ELMSFORD
NY
10523
US
|
Family ID: |
25250627 |
Appl. No.: |
10/978226 |
Filed: |
October 29, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10978226 |
Oct 29, 2004 |
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09827982 |
Apr 6, 2001 |
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6811903 |
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Current U.S.
Class: |
429/209 ;
320/112; 320/116; 320/126; 429/149; 429/61; 429/9 |
Current CPC
Class: |
H01M 10/42 20130101;
H01M 10/44 20130101; H01M 12/06 20130101; H02J 7/0013 20130101;
H01M 10/441 20130101; H01M 10/4264 20130101; Y02E 60/10 20130101;
H02J 7/0045 20130101; Y10S 429/90 20130101 |
Class at
Publication: |
429/209 ;
429/009; 429/149; 429/061; 320/112; 320/116; 320/126 |
International
Class: |
H01M 014/00; H02J
007/00; H01M 004/00 |
Claims
1-37. (canceled)
38. A rechargeable electrochemical cell system comprising: a
plurality of rechargeable cells, each rechargeable cell including a
first electrode, a second electrode, and a third electrode
electrically isolated from the second electrode; wherein the
plurality of cells are configured for being discharged upon
application of a load across the first electrodes and the second
electrodes, and wherein each cell is configured for being
independently recharged upon application of the voltage across the
first electrode and the third electrode of each cell in isolation
from the other cells.
39. The rechargeable electrochemical cell system as in claim 38,
wherein each second electrode is in isolation from the voltage
across each corresponding first electrode and third electrode when
the cell is recharged.
40. The rechargeable electrochemical cell as in claim 38, wherein
the isolation is effectuated by a transformer, a power supply, a
capacitor, a switch, or a combination comprising at least one of
the foregoing.
41. The rechargeable electrochemical system as in claim 38, wherein
the voltage for recharging is applied by one or more
transformers.
42. In the rechargeable electrochemical cell system as in claim 41,
wherein the transformer comprises a single primary winding and a
plurality of secondary windings, each secondary winding associated
with a third electrode of a corresponding cell.
43. The rechargeable electrochemical cell system as in claim 42,
further comprising a switching power converter coupled to a power
source in operable connection with the primary winding.
44. The rechargeable electrochemical cell system as in claim 43,
wherein the switching power converter comprises a MOSFET
device.
45. The rechargeable electrochemical cell system as in claim 43,
wherein the power source is controlled by a control unit.
46. The rechargeable electrochemical cell system as in claim 45,
wherein the control unit comprises an oscillator.
47. The rechargeable electrochemical cell system as in claim 42,
further comprising a diode between at least one pair of the
secondary windings and the third electrode.
48. The rechargeable electrochemical cell system as in claim 42,
further comprising a rectifier between at least one pair of the
secondary winding and the third electrode.
49. The rechargeable electrochemical cell system as in claim 38,
wherein the voltage across the first electrode and the third
electrode is provided from a power supply.
50. The rechargeable electrochemical cell system as in claim 49,
further comprising a cell conditioning unit between the power
supply, and the recharging circuit of each cell in the system.
51. The rechargeable electrochemical cell system as in claim 50,
wherein the cell conditioning unit comprises a device selected from
the group consisting of a switching power converter, a battery
parameter monitor, a signal conditioning system, a rectifier, a
filter, and combinations comprising at least one of the foregoing
devices.
52. The rechargeable electrochemical cell system as in claim 38,
wherein the voltage is applied across the recharging circuit with a
capacitor.
53. The rechargeable electrochemical cell system as in claim 52,
wherein the capacitor is connected across the recharging circuit
via a switch between the capacitor and the first electrode and the
switch between the capacitor and the third electrode.
54. The rechargeable electrochemical cell system as in claim 38,
wherein the cell is recharged upon application of a selective
voltage across one or more selected recharging circuits.
55. The rechargeable electrochemical cell system as in claim 38,
wherein at least a portion of the plurality of cells are arranged
in series.
56. The rechargeable electrochemical cell system as in claim 38,
wherein at least a portion of the plurality of cells are arranged
in parallel.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to electrochemical cells, and
particularly to electrochemical cells that employ separate charging
and discharging electrodes.
[0003] 2. Description of the Prior Art
[0004] Electrochemical power sources are devices through which
electric energy can be produced by means of electrochemical
reactions. These devices include metal air electrochemical cells
such as zinc air and aluminum air batteries. Certain metal air
electrochemical cells employ an anode comprised of metal particles
that are fed into the cell and consumed during discharge. Metal air
cells include an anode, an air cathode, and an electrolyte. The
anode is generally formed of metal particles immersed in
electrolyte. The cathode generally comprises a semipermeable
membrane and a catalyzed layer for reducing the oxidant, generally
oxygen. The electrolyte is an ionic conductive but not electrically
conductive material.
[0005] Metal air electrochemical cells have numerous advantages
over traditional hydrogen-based fuel cells. In particular, the
supply of energy provided from metal air electrochemical cells is
virtually inexhaustible because the fuel, such as zinc, is
plentiful and can exist either as the metal or its oxide. Further,
solar, hydroelectric, or other forms of energy can be used to
convert the metal from its oxide product back to the metallic fuel
form. Unlike conventional hydrogen-oxygen fuel cells that require
refilling, the fuel of metal air electrochemical cells is
recoverable by electrically recharging. The fuel of the metal air
electrochemical cells may be solid state, therefore, it is safe and
easy to handle and store. In contrast to hydrogen-oxygen cells,
which use methane, natural gas, or liquefied natural gas to provide
as source of hydrogen, and emit polluting gases, the metal air
electrochemical cells results in zero emission. The metal air cells
operate at ambient temperature, whereas hydrogen-oxygen fuel cells
typically operate at temperatures in the range of 80.degree. C. to
1000.degree. C. Metal air electrochemical cells are capable of
delivering higher output voltages (1-3 Volts) than conventional
fuel cells (<0.8V).
[0006] One of the principle obstacles of metal air electrochemical
cells is related to charging the cell, i.e., transformation of
electrical energy to chemical energy, particularly after discharge,
i.e., transformation of chemical energy to electrical energy.
Ideally, charging and recharging should proceed nearly reversibly,
be energy efficient, and result in minimum physical changes to the
cell that may limit the operable life of the cell.
[0007] Therefore, it would be desirable to provide a rechargeable
electrochemical cell and a recharging system that is efficient and
minimizes cell component degradation.
SUMMARY OF THE INVENTION
[0008] The above-discussed and other problems and deficiencies of
the prior art are overcome or alleviated by the several methods and
apparatus of the present invention, wherein a rechargeable
electrochemical cell system is provided. The system includes a
plurality of cells, wherein each cell is comprised of a first
electrode, a second electrode, and a third electrode electrically
isolated from the second electrode. The cell system may be
discharged upon application of a load across a discharge circuit,
comprised of the first electrodes and the second electrodes. The
cell may be recharged upon application of a voltage across a
recharging circuit, comprised of at least one of the first
electrodes and at least one of the third electrodes.
[0009] The above-discussed and other features and advantages of the
present invention will be appreciated and understood by those
skilled in the art from the following detailed description and
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Numerous other advantages and features of the present
invention will become readily apparent from the following detailed
description of preferred embodiments when read in conjunction with
the accompanying drawings, wherein
[0011] FIG. 1(a) is a schematic representation of an
electrochemical cell using a single electrode for charging and
discharging operations;
[0012] FIG. 1(b) is a schematic representation of an
electrochemical cell incorporating a separate charging electrode
for charging operations;
[0013] FIG. 2(a) is a symbolic representation of the cell depicted
in FIG. 1(a);
[0014] FIG. 2(b) is a symbolic representation of the cell depicted
in FIG. 1(b);
[0015] FIG. 3 schematically shows discharging and recharging of a
typical battery cell;
[0016] FIG. 4 schematically shows discharging and recharging of a
system of typical battery cells;
[0017] FIG. 5 schematically shows discharging and recharging of a
battery cell using the structure and system herein;
[0018] FIG. 6 schematically shows discharging and recharging of
battery cells using embodiments of the structure and system
herein;
[0019] FIG. 7 is an exemplary circuit diagram of a recharging
system of battery cells using an embodiment of the structure and
system herein;
[0020] FIG. 8 schematically shows a system of battery cells using
another embodiment of the structure and system herein;
[0021] FIG. 9 schematically shows a system and discharging and
recharging operation of battery cells using a further embodiment of
the structure and system herein; and
[0022] FIG. 10 is an exemplary circuit diagram of a recharging
system of battery cells using an additional embodiment of the
structure and system herein;
[0023] FIG. 11 is an example of a transformer that may be used in
various embodiments of the structure and system herein;
[0024] FIG. 12 is an example of a plurality of transformers that
may be used in various embodiments of the structure and system
herein; and
[0025] FIG. 13 is an exemplary circuit diagram of a parallel system
of battery cells using an additional embodiment of the structure
and system herein.
DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS
[0026] A rechargeable electrochemical cell system is provided. The
system includes a plurality of cells, wherein each cell is
comprised of a first electrode, a second electrode, and a third
electrode electrically isolated from the second electrode. The cell
system may be discharged upon application of a load across a
discharge circuit, which is formed from the first electrodes and
the second electrodes. The cell may be recharged upon application
of a voltage across a recharging circuit, which is formed of at
least one of the first electrodes and at least one of the third
electrodes.
[0027] Referring now to the drawings, an illustrative embodiment of
the present invention will be described. For clarity of the
description, like features shown in the figures shall be indicated
with like reference numerals and similar features as shown in
alternative embodiments shall be indicated with similar reference
numerals.
[0028] FIG. 1(a) is a schematic representation of an
electrochemical cell 10 (wherein the symbol is represented in FIG.
2(a)). Electrochemical cell 10 may be a metal oxygen cell, wherein
the metal is supplied from a metal anode 12 (typically a negative
electrode) and the oxygen is supplied to an oxygen cathode 14
(typically a positive electrode). The anode 12 and the cathode 14
are maintained in electrical isolation from on another by a
separator 16, and are maintained in ionic conduction with an
electrolyte. The electrolyte may be an alkaline media such as a
solution in which the anode 12 is submersed. Alternatively, the
electrolyte may be imbibed within the anode 12. Further, the
electrolyte may be formed within the separator 16.
[0029] During discharge, oxygen from an oxidant source (not shown)
is used as the reactant for the air cathode 14 of the metal air
cell 10. When oxygen reaches the reaction sites within the cathode
14, it is converted into hydroxyl ions together with water. At the
same time, electrons are released to flow as electricity in the
external circuit. The hydroxyl travels through the separator 16 to
reach the metal anodes 12. When hydroxyl reaches the metal anode
(in the case of an anode 12, for example, comprising zinc), zinc
hydroxide is formed on the surface of the zinc. Zinc hydroxide
decomposes to zinc oxide and releases water back to the alkaline
solution. The reaction is thus completed.
[0030] The anode reaction is:
Zn+4OH.sup.-.fwdarw.Zn(OH).sub.4.sup.2-+2e (1)
Zn(OH).sub.4.sup.2-.fwdarw.ZnO+H.sub.2O+2OH.sup.- (2)
[0031] The cathode reaction is:
1/2O.sub.2+H.sub.2O+2e.fwdarw.2OH.sup.- (3)
[0032] Thus, the overall cell discharge reaction is:
Zn+1/2O.sub.2.fwdarw.ZnO (4)
[0033] During recharging operations, consumed anode material (i.e.,
oxidized metal), which is generally in ionic contact with the
cathode 14, is converted into fresh anode material (i.e., metal)
and oxygen upon application of a power source (e.g. more than 1-2
volts for metal-air systems) across the cathode 14 and consumed
anode material.
[0034] The anode 12 may be any conventional anode for a metal air
or metal oxygen cell. Typically, it provides an oxidizable fuel
source including metal particles and an ionic conductor.
Additionally, a current collector is also typically provided in
electrical contact with the anode 12 to facilitate connection
thereto. Further, one or more additional constituents such as
binders or additives, are also optionally included. Preferably, the
formulation optimizes ion conduction rate, density, and overall
depth of discharge.
[0035] The metal constituent may comprise mainly oxidizable metals
such as zinc, calcium, lithium, magnesium, ferrous metals,
aluminum, and combinations and alloys comprising at least one of
the foregoing metals. These metals may also be alloyed with
constituents including, but not limited to, bismuth, indium, lead,
mercury, gallium, tin, cadmium, molybdenum, tungsten, chromium,
vanadium, germanium, arsenic, antimony, selenium, tellurium,
strontium, and also additives such as polysaccharide and
sorbitol.
[0036] The electrolyte generally comprises alkaline media in which
the anode 12 may be submersed. Preferably, sufficient electrolyte
is provided to maximize the reaction and depth of discharge. The
electrolyte generally may comprise ionic conducting materials such
as KOH, NaOH, other materials, or a combination comprising at least
one of the foregoing electrolyte media.
[0037] The oxygen supplied to the cathode 14 may be from any oxygen
source, such as air; scrubbed air; pure or substantially oxygen,
such as from a utility supply, local system supply, or an on site
oxygen manufacturing system; or any other processed air.
[0038] Cathode 14 may be a conventional air diffusion cathode which
generally must be a bi-functional electrode in rechargeable cell
configurations. For example, a cathode may generally comprise an
active constituent and a carbon support, along with suitable
connecting structures, such as a current collector. Of course,
higher current densities may be attained with suitable cathode
catalysts, oxidants, and formulations. The bi-functional
characteristics of the cathode 14 allow it to function both during
discharging and recharging operations. An exemplary air cathode is
disclosed in copending, commonly assigned U.S. patent application
Ser. No. 09/415,449, entitled "Electrochemical Electrode For Fuel
Cell", to Wayne Yao and Tsepin Tsai, filed on Oct. 8, 1999, which
is incorporated herein by reference in its entirety. Other air
cathodes may instead be used, however, depending on the performance
capabilities thereof, as will be obvious to those of skill in the
art.
[0039] The carbon used is preferably chemically inert to the
electrochemical cell environment and may be provided in various
forms including, but not limited to, carbon flake, graphite, other
high surface area carbon materials, or combinations comprising at
least one of the foregoing carbon forms. The cathode current
collector may be any electrically conductive material capable of
providing electrical conductivity and optionally capable of
providing support to the cathode 14. The current collector may be
in the form of a mesh, porous plate, metal foam, strip, wire, foil,
plate, or other suitable structure. In certain embodiments, the
current collector is porous to minimize oxygen flow obstruction.
The current collector may be formed of various electrically
conductive materials including, but not limited to, nickel. nickel
plated ferrous metals such as stainless steel, and the like, and
combinations and alloys comprising at least one of the foregoing
materials. Suitable current collectors include porous metal such as
nickel foam metal.
[0040] A binder is also typically used in the cathode 14, which may
be any material that adheres substrate materials, the current
collector, and the catalyst to form a suitable structure. The
binder is generally provided in an amount suitable for adhesive
purposes of the diluent, catalyst, and/or current collector. This
material is preferably chemically inert to the electrochemical
environment. In certain embodiments, the binder material also has
hydrophobic characteristics. Appropriate binder materials include
polymers and copolymers based on polytetrafluoroethylene (e.g.,
Teflon.RTM. powder or emulsions such as and Teflon.RTM. T-30
commercially available from E.I. du Pont Nemours and Company Corp.,
Wilmington, Del.), sulfonic acid (e.g., Nafion.RTM. commercially
available from E.I. du Pont Nemours and Company Corp.),
polyvinylidene fluoride (PVDF), polyethylene fluoride (PEF), and
the like, and derivatives, combinations and mixtures comprising at
least one of the foregoing binder materials.
[0041] The active constituent is generally a suitable catalyst
material to facilitate oxygen reaction at the cathode 14. The
catalyst material is generally provided in an amount suitable to
facilitate oxygen reaction at the cathode 14. Suitable catalyst
materials include, but are not limited to: manganese and its
compounds, cobalt and its compounds, platinum and its compounds,
and combinations comprising at least one of the foregoing catalyst
materials.
[0042] To electrically isolate the anode 12 from the cathode 14,
the separator 16 is provided between the electrodes. In the cell 10
herein, the separator 16 is disposed on the anode 12 to at least
partially contain the anode constituents. Separator 16 may be any
commercially available separator capable of electrically isolating
the anode 12 and the cathode 14, while allowing sufficient ionic
transport between the anode 12 and the cathode 14. Preferably, the
separator is flexible, to accommodate electrochemical expansion and
contraction of the cell components, and chemically inert to the
cell chemicals. Suitable separators are provided in forms
including, but not limited to, woven, non-woven, porous (such as
microporous or nanoporous), cellular, polymer sheets, and the like.
Materials for the separator include, but are not limited to,
polyolefin (e.g., Gelgard.RTM. commercially available from Dow
Chemical Company), polyvinyl alcohol (PVA), cellulose (e.g.,
nitrocellulose, cellulose acetate, and the like), polyethylene,
polyamide (e.g., nylon), fluorocarbon-type resins (e.g., the
Nafion.RTM. family of resins which have sulfonic acid group
functionality, commercially available from DuPont Chemicals,
Wilmington, Del.), cellophane, filter paper, and combinations
comprising at least one of the foregoing materials. The separator
may also comprise additives and/or coatings such as acrylic
compounds and the like to make them more wettable and permeable to
the electrolyte. Further, the separator 16 may comprise a
solid-state membrane, such as described in copending, commonly
assigned U.S. Pat. No. 6,183,914, entitled "Polymer-based Hydroxide
Conducting Membranes", to Wayne Yao, Tsepin Tsai, Yuen-Ming Chang,
and Muguo Chen, filed on Sep. 17, 1998, which is incorporated
herein by reference in its entirety; U.S. patent application Ser.
No. 09/259,068, entitled "Solid Gel Membrane", to Muguo Chen,
Tsepin Tsai, Wayne Yao, Yuen-Ming Chang, Lin-Feng Li, and Tom
Karen, filed on Feb. 26, 1999, which is incorporated herein by
reference in its entirety, and U.S. patent application Ser. No.
09/482,126, entitled "Solid Gel Membrane Separator In Rechargeable
Electrochemical Cells", to Muguo Chen, Tsepin Tsai, and Lin-Feng
Li, filed on Jan. 11, 2000, which is incorporated herein by
reference in its entirety.
[0043] Referring now to FIG. 1(b), a rechargeable metal air cell
110 is shown (wherein the symbol is represented in FIG. 2(b)). The
cell 110 includes a negative electrode 112 and a discharging
electrode 114 in ionic contact. Further, a charging electrode 115
is disposed in ionic contact with the negative electrode 112, and
electrically isolated from the cathode 114 with a separator 116 and
electrically isolated from the negative electrode 112 with a
separator 117. Since the charging electrode 115 is present, the
cathode 114 may be a mono-functional electrode, e.g., formulated
for discharging while the charging electrode 115 is formulated for
charging. Further, with the use of the charging electrode 115, the
cathode 114 may be operated primarily during discharging
operations, and more preferably only during discharging operations.
This allows the cathode 114 to achieve longer lifetimes and attain
higher reliability during the lifetime. Furthermore, this allows
use of materials otherwise not applicable in bi-functional
electrodes.
[0044] In operation, consumed anode material (i.e., oxidized
metal), which is in ionic contact with the charging electrode 115,
is converted into fresh anode material (i.e., metal) and oxygen
upon application of a power source (e.g. more than 1.2 volts for
metal-air systems) across the charging electrode 115 and consumed
anode material. The charging electrode 115 may comprise an
electrically conducting structure, for example a mesh, porous
plate, metal foam, strip, wire, plate, or other suitable structure.
In certain embodiments, the charging electrode 115 is porous to
allow ionic transfer. The charging electrode 115 may be formed of
various electrically conductive materials including, but not
limited to, copper, ferrous metals such as stainless steel, nickel,
chromium, titanium, and the like, and combinations and alloys
comprising at least one of the foregoing materials. Suitable
charging electrodes include porous metal such as nickel foam
metal.
[0045] Referring to FIGS. 3 and 4, recharging and discharging for a
single cell (FIG. 3) and a plurality of cells (FIG. 4) are
represented. During discharging, the current generally flows in
series from the cathode through the load to the anode due to the
electrochemical reaction. During recharging, the current generally
flows in the opposite direction, from the current source to the
cathode, causing electrochemical reaction to convert the metal
oxide into metal.
[0046] FIG. 5 represents recharging and discharging for a cell
including a charging electrode. During discharging, the current
flow is similar to that of cells without a charging electrode.
However, during recharging, current flows though the charging
electrode and the anode. Current flow through the cathode is
preferably eliminated, as it causes degradation of the cathode
structure, thus decreasing performance of the cathode and cell.
[0047] Referring now to FIG. 6(a)-6(c), discharging and recharging
operation of a plurality of cells each including a charging
electrode is schematically depicted. FIG. 6(a) represents
discharging, wherein the current flows across the load and the
plurality of cells. FIG. 6(b) represents one embodiment of a system
for recharging the cells, wherein current from a charging device is
applied across the charging electrodes and the anodes. During
recharging, current is isolated from the air cathodes, which is
accomplished by a one pole two way switchable circuit between an
anode of one cell and a charging electrode and cathode of another
cell. Accordingly, when a switch is in one position the anode is
connected to the cathode of an adjacent cell and the circuit is
configured for discharging operations. When the switch is switched
to the other position, the anode is connected to a third electrode
of the adjacent cell and a cell circuit is configured for
recharging operations. The switches may be any conventional switch
capable of handling the desired current and/or voltage. Suitable
switches include, but are not limited to, mechanical switches,
semiconductor switches, or molecular (chemical) switches.
[0048] In another embodiment, and referring now to FIG. 6(c), the
system provides a continuous discharging path (e.g., without any
switches between the cells). Each cell is charged by a discrete
power source which is isolated from the power source associated
with other cells. Therefore, no current passes through cathode
during charging operations. Additionally, the discharging path may
remain connected during charging operations (e.g., as opposed to
the system in FIG. 6(b) wherein the discharging path is
disconnected during charging). Furthermore, discrete charging
allows for a controlled voltage application across each cell. In
this configuration, absence of a switching circuit in the discharge
path minimizes various detriments associated with typical switches
or switching circuits. Such detriments include increased internal
resistance due to the contact resistance of the switches, power
loss and heat generation during discharging, and inefficiencies
associated with the switch driving mechanism.
[0049] The isolated charging voltage (with or without switches) may
be effectuated with a system of transformers, capacitors, switches,
power supply systems, microprocessor systems, software systems, and
combinations comprising at least one of the foregoing apparatus.
Further, while the isolated charging voltages are depicted as being
applied to individual cells, other schemes may be desirable, such
as applying isolated charging voltages to groups of cells in
various combinations. Different methods of individual and isolated
cell charging are proposed are shown in FIGS. 7, 8, and 9.
[0050] Referring to FIG. 7, an embodiment of a cell system 700
employing an individual and isolated charging voltage system is
illustrated. System 700 includes a plurality of cells 702 including
a discharging electrode 704, a charging electrode 706, and a
negative electrode 708. During discharging operation, the cells 702
produce energy through the discharging electrodes 704 and the
negative electrodes 708. During recharging operation, discrete
voltages are applied across charging electrodes 706 and the
negative electrodes 708, which does not affect discharging
electrodes 704.
[0051] The discrete charging voltage is applied through a system of
current transformers, preferably high frequency high current
transformers, with a single primary 712 and multiple secondary
windings 710 associated with each cell 702 through a diode 718. The
primary is driven by switching power converter and control unit 714
which may contain pulse width modulation (PWM) control circuit and
various switching converter topologies including, but not limited
to, flyback converter, forward converter, push pull converter, half
wave bridge converter, full wave bridge converter etc. In one
embodiment, PWM circuitry is used to maintain proper duty cycle for
adjusting output parameters suitable for optimal charging of each
cell. A power source 716 is coupled to the circuit, which could be
AC or DC depending on voltage, current and space constrains of the
application. A diode or rectifier 718 is used to provide rectified
directional flow of current.
[0052] FIG. 8 represents another embodiment of an isolated charging
system 800. During discharging operation, the cells 802 produce
energy through the discharging electrodes 804 and the negative
electrodes 808. During recharging operation, discrete voltages are
applied across charging electrodes 806 and the negative electrodes
808, isolated from the discharging electrodes 804 of other cells.
In this system charging of each cell is controlled by a cell
conditioning unit 820. The cell conditioning unit 820 may contain
various systems 814 such as PWM control circuitry; various
switching converter topologies including, but not limited to
flyback converter, forward converter, push pull converter, half
wave bridge converter, and full wave bridge converter; battery
parameters monitor (which can provide battery parameters to
external monitoring circuit); PWM control circuitry (to allow
charging parameters to be adjusted for optimal performance);
software systems; microprocessor systems; or any combination
comprising at least one of the foregoing systems. The cell
conditioning unit 820 further includes a signal conditioning unit
818 coupled to the charging electrode circuit (i.e., the negative
electrodes 808 and the charging electrode 806). For example, the
signal conditioning unit 818 may comprise one or more rectifiers,
regulators, filters, etc., or combinations thereof, for proving
directional and noise free charging. A unit 822 provides feedback
to the control and monitoring circuit of battery parameters and
battery condition including, but not limited to, charging voltage,
current, temperature, etc. The feedback circuit contains an
isolating circuit which could be optical or magnetic. A power
source 816 may be AC or DC depending on voltage, current and space
constraints of the application.
[0053] FIG. 9 shows a switched capacitor charging circuit 900.
During discharging operation, the cells 902 produce energy through
the discharging electrodes 904 and the negative electrodes 908.
During recharging operation, voltages are applied across charging
electrodes 906 and the negative electrodes 908, isolated from the
discharging electrodes 904 of other cells. Charging is carried out
in two steps. In a first step (identified in FIG. 9 as (a))
switches 912 are closed and switches 910 are opened thereby
charging capacitors 914 from power supply 916. In a second step
(identified in FIG. 9 as (b)) switches 912 are opened and 910 are
closed thus charging the respective cell through charge that has
been stored in the capacitor. These steps are repeated at a
frequency best suited for charging the capacitor and charging the
cell system. Capacitor type and value is selected based on factors
including but not limited to charging time and switching frequency.
The switches 910 and 912 may be controlled by one or more suitable
control devices (not shown), as will be apparent to one skilled in
the art. The switches may be any conventional switch capable of
handling the desired current and/or voltage. Suitable switches
include mechanical switches and semiconductor switches.
[0054] FIG. 10 illustrates another exemplary embodiment of a system
1000 for charging of metal-air cells. During discharging operation,
each cell 1002 produces energy through a discharging electrode 1004
and a negative electrode 1008. During recharging operation, voltage
is applied across each cell 1002 through a charging electrode 1006
and the negative electrode 1008, isolated from the discharging
electrodes 1004 of other cells. A single primary 1012 and multiple
secondary 1010 transformer was constructed using a low profile
(dimensional), high frequency, and high current flat transformer
module. A flat transformer identified as FTI-12X2A-1B available
from Flat Transformer Technology Corp., Costa Mesa, Calif. was used
for this purpose. This transformer has an output capacity of 1 to
20 volts and up to about 20 amperes at frequencies in the range of
hundreds of kilohertz. Construction of one such module is shown in
FIG. 11 as a transformer 1109. An assembly of four such modules is
shown in FIG. 12, wherein the individual transformers 1209 are
electrically isolated from each other with suitable insulators
1240. The primary was wound through the cores of the plurality of
transformers 1209. A rectifier 1018 may be used for rectification
of the secondary output waveform. The assembly of the
transformer(s) and the rectifiers 1018 may be enclosed in a
shielding box 1020 to avoid magnetic interference. An oscillator
1014 contains timers (e.g., LM555 timers) as an oscillator
switching device coupled to a MOSFET 1015 (e.g., at frequency of
400 KHz). R4 and R5 control the duty cycle of the waveform, which
in turn controls the charging current.
[0055] A further alternative system 1300 is depicted in FIG. 13. A
plurality of cells 1302 are arranged in parallel. The discharging
circuit remains connected during recharging of the cells 1302 via
the recharging voltage source 1350, which may comprise any of the
systems described herein (e.g., switched, power supply,
transformer, capacitor, etc.).
[0056] With the recharging system and cell using the recharging
system described herein, various benefits are derived. The life and
reliability of the discharging electrodes may be substantially
increased since voltage is minimally, or more preferably not at
all, applied across the discharging electrode and the negative
electrode during recharging operations. Isolated charging increases
charging efficiency and allows for a controlled voltage application
across each cell. In certain configurations, wherein use of
switches is minimized, internal resistance due to the contact
resistance of the switches is decreased, as is heat generation
during recharging and discharging, as well as other inefficiencies
associated with the switch driving mechanism. Further, application
of discrete and isolated voltages may be controlled and directed to
certain cells or groups of cells within a system.
[0057] While preferred embodiments have been shown and described,
various modifications and substitutions may be made thereto without
departing from the spirit and scope of the invention. Accordingly,
it is to be understood that the present invention has been
described by way of illustrations and not limitation.
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