U.S. patent application number 13/396935 was filed with the patent office on 2012-07-12 for method for controlling the charging or discharging process of a secondary battery with auxiliary electrode.
Invention is credited to Murali Ramasubramanian, Robert Spotnitz.
Application Number | 20120176093 13/396935 |
Document ID | / |
Family ID | 40983574 |
Filed Date | 2012-07-12 |
United States Patent
Application |
20120176093 |
Kind Code |
A1 |
Ramasubramanian; Murali ; et
al. |
July 12, 2012 |
METHOD FOR CONTROLLING THE CHARGING OR DISCHARGING PROCESS OF A
SECONDARY BATTERY WITH AUXILIARY ELECTRODE
Abstract
The present invention includes three-dimensional secondary
battery cells comprising an electrolyte, a cathode, an anode, and
an auxiliary electrode. The cathode, the anode, and the auxiliary
electrode have a surface in contact with the electrolyte. The anode
and the cathode are electrolytically coupled. The auxiliary
electrode is electrolytically coupled and electrically coupled to
at least one of the anode or the cathode. Electrically coupled
means directly or indirectly connected in series by wires, traces
or other connecting elements. The average distance between the
surface of the auxiliary electrode and the surface of the coupled
cathode or the coupled anode is between about 1 micron and about
10,000 microns. The average distance means the average of the
shortest path for ion transfer from every point on the coupled
cathode or anode to the auxiliary electrode.
Inventors: |
Ramasubramanian; Murali;
(Fremont, CA) ; Spotnitz; Robert; (Pleasanton,
CA) |
Family ID: |
40983574 |
Appl. No.: |
13/396935 |
Filed: |
February 15, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12119369 |
May 12, 2008 |
8119269 |
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13396935 |
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Current U.S.
Class: |
320/134 |
Current CPC
Class: |
H01M 4/485 20130101;
H01M 10/425 20130101; H01M 4/5815 20130101; H01M 4/13 20130101;
H01M 2004/025 20130101; H01M 10/448 20130101; H01M 10/052 20130101;
H01M 10/48 20130101; H01M 10/058 20130101; H01M 10/0525 20130101;
H01M 10/44 20130101; H01M 10/446 20130101; H01M 10/0445 20130101;
Y02E 60/10 20130101 |
Class at
Publication: |
320/134 |
International
Class: |
H02J 7/00 20060101
H02J007/00 |
Claims
1-27. (canceled)
28. A method for controlling the charging or discharging process of
a secondary battery, the secondary battery comprising an anode, a
cathode and an auxiliary electrode, the method comprising sensing
the voltage of the anode or the cathode relative to the auxiliary
electrode as the battery is charging or discharging and tuning or
stopping the charging or discharging when the voltage of the anode
and/or the cathode exceeds a specified limit relative to the
auxiliary electrode.
29. The method of claim 28 wherein the secondary battery is a
lithium ion battery.
30. The method of claim 29 wherein the anode comprises silicon and
the discharging of the battery is tuned or stopped when the anode
voltage sensed relative to the auxiliary electrode is 0.9V versus
lithium.
31. The method of claim 29 wherein the anode comprises silicon and
the charging of the battery is tuned or stopped when the anode
voltage sensed relative to the auxiliary electrode is 0.1V versus
lithium.
32. The method of claim 29 wherein the charging of the battery is
tuned or stopped when the cathode voltage sensed relative to the
auxiliary electrode is 4.3V relative to lithium.
33. The method of claim 29 wherein the charging of the battery is
tuned or stopped when the anode voltage sensed relative to the
auxiliary electrode is 0V versus lithium.
34. The method of claim 29 wherein, as the battery is charging, the
charging rate of the battery is at least C/100 relative to the
capacity, C, of the anode or cathode being charged.
35. The method of claim 29 wherein, as the battery is charging, the
charging rate of the battery is at least C/50 relative to the
capacity, C, of the anode or cathode being charged.
36. The method of claim 29 wherein, as the battery is charging, the
charging rate of the battery is at least C/20 relative to the
capacity, C, of the anode or cathode being charged.
37. The method of claim 28 wherein the anode comprises silicon.
38. The method of claim 37 wherein, as the battery is charging, the
charging rate of the battery is at least C/100 relative to the
capacity, C, of the anode or cathode being charged.
39. The method of claim 37 wherein the secondary battery is a
lithium ion battery and, as the battery is charging, the charging
rate of the battery is at least C/100 relative to the capacity, C,
of the anode or cathode being charged.
40. The method of claim 37 wherein, as the battery is charging, the
charging rate of the battery is at least C/50 relative to the
capacity, C, of the anode or cathode being charged.
41. The method of claim 37 wherein the secondary battery is a
lithium ion battery and, as the battery is charging, the charging
rate of the battery is at least C/50 relative to the capacity, C,
of the anode or cathode being charged.
42. The method of claim 37 wherein, as the battery is charging, the
charging rate of the battery is at least C/20 relative to the
capacity, C, of the anode or cathode being charged.
43. The method of claim 37 wherein the secondary battery is a
lithium ion battery and, as the battery is charging, the charging
rate of the battery is at least C/20 relative to the capacity, C,
of the anode or cathode being charged.
44. The method of claim 28 wherein, as the battery is charging, the
charging rate of the battery is at least C/100 relative to the
capacity, C, of the anode or cathode being charged.
45. The method of claim 28 wherein, as the battery is charging, the
charging rate of the battery is at least C/50 relative to the
capacity, C, of the anode or cathode being charged.
46. The method of claim 28 wherein, as the battery is charging, the
charging rate of the battery is at least C/20 relative to the
capacity, C, of the anode or cathode being charged.
47. A method for replenishing a secondary battery, the secondary
battery comprising an anode, a cathode, and an auxiliary electrode
containing a source of carrier ions, and the method comprising (i)
sensing the voltage of the anode or the cathode relative to the
auxiliary electrode as the battery is charging or discharging and
optionally storing sensed voltage data in a memory unit and (ii)
replenishing the anode or cathode with carrier ions from the
auxiliary electrode according to the sensed voltage or stored
voltage data.
48. The method of claim 47 wherein the secondary battery is a
lithium ion battery.
49. The method of claim 47 wherein the anode comprises silicon.
50. The method of claim 47 wherein the secondary battery is a
lithium ion battery and the anode comprises silicon.
Description
[0001] The present application claims the benefit of U.S.
Provisional Application 60/928,519, filed May 10, 2007, which is
incorporated herein by reference in its entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to secondary battery cells and
secondary batteries well as methods for producing these devices and
systems incorporating these cells and batteries.
BACKGROUND OF THE INVENTION
[0003] Secondary batteries are a type of rechargeable battery in
which ions move between the anode and cathode through an
electrolyte. Secondary batteries include lithium-ion, sodium-ion,
potassium-ion batteries, and lithium batteries as well as other
battery types. Secondary batteries are often made of many cells
that are grouped together to form the battery. Each cell of a
secondary battery contains an electrolyte, and at least one
cathode, and at least one anode. When the cells are grouped
together to form a battery, the cathodes and anodes of each cell
can be electrically coupled to achieve the desired capacity of the
battery.
[0004] In secondary battery cells, both the anode and cathode
comprise materials into which a carrier ion inserts and extracts.
The process of the carrier ion moving into the anode or cathode is
referred to as insertion. The reverse process, in which the carrier
ion moves out of the anode or cathode is referred to as extraction.
During discharging of a cell, the carrier ion is extracted from the
anode and inserted into the cathode. When charging the cell, the
exact reverse process occurs: the carrier ion is extracted from the
cathode and inserted into the anode.
[0005] Lithium-ion batteries are a popular type of secondary
battery in which the carrier ions are lithium ions that move
between the cathode and the anode thought the electrolyte. The
benefits and the challenges of lithium-ion battery cells are
exemplary of the benefits and challenges of other secondary battery
cells; the following examples pertaining to lithium-ion battery
cells are illustrative and are not limiting. In lithium-ion battery
cells, the lithium ions move from the anode to the cathode during
discharge and from the cathode to the anode when charging.
Lithium-ion batteries are highly desirable energy sources due to
their high energy density, high power, and long shelf life.
Lithium-ion batteries are commonly used in consumer electronics and
are currently one of the most popular types of battery for portable
electronics because they have high energy-to-weight ratios, no
memory effect, and a slow loss of charge when not in use.
Lithium-ion batteries are growing in popularity for in a wide range
of applications including automotive, military, and aerospace
applications because of these advantages.
[0006] FIG. 1 is a cross section of a prior art lithium-ion battery
cell. The battery cell 15 has a cathode current collector 10 on top
of which a cathode 11 is assembled. The cathode 11 is covered by a
separator 12 over which an assembly of the anode current collector
13 and the anode 14 is placed. The separator 12 is filled with an
electrolyte that can transport ions between the anode and the
cathode. The current collectors 10, 13 are used to collect the
electrical energy generated by the battery cell 15 and connect it
to other cells and to an outside device so that the outside device
can be electrically powered and to carry electrical energy to the
battery during recharging.
[0007] For most existing secondary batteries, after the initial
charge there is a significant drop in total overall capacity. For
instance, in a standard lithium-ion battery, the loss in total
charge capacity after the first charge-discharge cycle is about
5-15%. The term "about" as used herein means within plus or minus
15% of the specified value. Moreover, a portion of the capacity of
most existing secondary batteries is lost with each subsequent
charge-discharge cycle. For instance, in a standard lithium-ion
battery, the loss in total charge capacity after each subsequent
charge-discharge cycle is about 0.1%.
[0008] Three dimensional energy battery cells and batteries can
produce higher energy storage and retrieval per unit geometrical
area than conventional two dimensional (or planar) devices.
Three-dimensional secondary batteries also have a decided advantage
in providing a higher rate of energy retrieval than planar
counterparts for a specific amount of energy stored, by means such
as minimizing or reducing transport distances for electron and ion
transfer between an anode and a cathode. These devices can be more
suitable for miniaturization and for applications where a
geometrical area available for a device is limited and where energy
density requirement is higher than what can be achieved with a
planar device. A three-dimensional secondary battery cell can be
one in which any one (or more) of an anode, a cathode, and a
separator are non-planar in nature, and an actual surface area for
such non-planar component is greater than twice its geometrical
surface area. In some instances, a separation between two height
planes on a third dimension should be at least greater than a
periodicity in an x-y plane divided by a square root of two. For
example, for a 1 cm.times.1 cm sample, a geometrical surface area
is 1 cm.sup.2. However, if the sample is not flat but has a groove
in a depth dimension whose depth is greater than one divided by the
square root of two, or 0.707 cm, then its actual surface area would
be greater than 2 cm.sup.2.
SUMMARY OF THE INVENTION
[0009] The present invention includes three-dimensional secondary
battery cells, batteries, and systems of using and methods of
making the same. A secondary battery cell of the present invention
comprises an electrolyte, a cathode, an anode, and an auxiliary
electrode. The cathode, the anode, and the auxiliary electrode each
have a surface in contact with the electrolyte. The anode and the
cathode are electrolytically coupled, meaning that the carrier ions
of the battery can transfer through the electrolyte from the anode
to the cathode and from the cathode to the anode. The auxiliary
electrode is electrolytically coupled and electrically coupled to
at least one of the anode or the cathode. Electrically coupled
means directly or indirectly connected in series by wires, traces
or other connecting elements. The average distance between the
surface of the auxiliary electrode and the surface of the coupled
cathode or the coupled anode is between about 1 micron and about
10,000 microns. The average distance means the average of the
shortest path for ion transfer from every point on the coupled
cathode or anode to the auxiliary electrode.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a cross section of a prior art lithium-ion
battery; and
[0011] FIG. 2 is an illustration of a secondary battery cell of the
present invention;
[0012] FIG. 3 is an illustration of a system of the present
invention including a secondary battery cell of the present
invention;
[0013] FIG. 4 is an illustration of a system of the present
invention including a secondary battery cell of the present
invention;
[0014] FIG. 5 is a plot of cathode potential relative to a lithium
auxiliary electrode versus time from an example of the present
invention;
[0015] FIG. 6 is a plot of anode potential relative to a lithium
auxiliary electrode versus time from an example of the present
invention; and
[0016] FIG. 7 is a plot of the cell voltage and the anode potential
relative to a lithium auxiliary electrode versus time from an
example of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0017] The inventors of the present invention have discovered that
by using the devices and methods of the present invention,
secondary battery cells and secondary batteries can be manufactured
so as to mitigate the problems associated with the loss of capacity
after the initial and subsequent charge/discharge cycles and to
allow for increased control during the cell or battery's
charge/discharge cycles.
[0018] The auxiliary electrode of the present invention can be used
for increasing the capacity of the energy storage device, improving
the control of the rate of charge and/or discharge of the device,
and/or monitoring the performance of the device over time. The
auxiliary electrode of the present invention differs from
conventional reference electrodes in that it is proximate to
substantially all parts of the cathode and/or anode and capable of
passing significant current. Existing auxiliary electrodes are used
as reference electrodes which are not as effective because of the
significant resistance across a single electrode in a conventional
battery. In the present invention, the auxiliary electrode is
proximate to the anodes and/or cathodes of a secondary cell
allowing carrier ion access to substantially all parts of the
cathodes and/or anodes. This allows for a capability of passing
significant current as well as measuring potential more
accurately.
[0019] The present invention includes a three-dimensional secondary
battery cell comprising an electrolyte, a cathode, an anode, and an
auxiliary electrode. The cathode, the anode, and the auxiliary
electrode each have a surface in contact with the electrolyte. The
anode and the cathode are electrolytically coupled, meaning that
the carrier ions of the battery can transfer through the
electrolyte from the anode to the cathode and from the cathode to
the anode. The auxiliary electrode is electrolytically coupled and
electrically coupled to at least one of the anode or the cathode.
Electrically coupled means directly or indirectly connected in
series by wires, traces or other connecting elements. The average
distance between the surface of the auxiliary electrode and the
surface of the coupled cathode or the coupled anode is between
about 1 micron and about 10,000 microns. The average distance means
the average of the shortest path for ion transfer from every point
on the coupled cathode or anode surface to the auxiliary electrode
surface.
[0020] In another embodiment of the secondary battery cell of the
present invention, the average distance between the surface of the
auxiliary electrode and the surface of the coupled cathode or the
coupled anode is between about 5 microns and about 1000 microns. In
another embodiment, the average distance between the surface of the
auxiliary electrode and the surface of the coupled cathode or the
coupled anode is between about 10 microns and about 500
microns.
[0021] FIG. 2 is an illustration of an exemplary embodiment of a
secondary battery cell of the present invention. The cell contains
at least one cathode 20, at least one anode 22, and an auxiliary
electrode 24. Even though the auxiliary electrode 24 is shown as
one piece, it can comprise a plurality of electrode elements or
portions. The cathode 20 can contain a cathode current collector
21. The anode 22 can contain an anode current collector 23. If the
cell contains multiple cathodes 20, the cathodes 20 can be
electrically coupled to each other. If the cell contains multiple
anodes 22, the anodes 22 can be electrically coupled to each other.
The cell contains a separator 25 between the cathode 20 and anode
22. The cell also contains a separator between the auxiliary
electrode and the cathode 20 or anode 22. The separator between the
auxiliary electrode 24 and the cathode 20 or anode 22 can be the
same material as the separator 25 or it can be a different
material. The separator 25 contains an electrolyte that is capable
of transporting the carrier ions of the cell. In the embodiment of
FIG. 2, the auxiliary electrode 24 is electrically coupled to the
cathode 20. The electrical coupling between the auxiliary electrode
24 and the cathode 20 may contain components 27 to sense or control
current or voltage as well as to store information about current or
voltage.
[0022] In another embodiment, the auxiliary electrode is
electrically coupled to the cathode and the cathode comprises a
cathode material, wherein the cathode material is atmospherically
unstable in its carrier-ion-inserted form. Materials that are
atmospherically unstable in their carrier-ion-inserted form are
materials in which the material and/or the inserted carrier ions
react with components in air. For example, lithium inserted in
titanium sulfide reacts with oxygen and water vapor in the air.
Examples of cathode materials that can be unstable in their
carrier-ion-inserted form include titanium sulfides (e.g., titanium
disulfide, TiS.sub.2), molybdenum sulfides (e.g., molybdenum
disulfide, MoS.sub.2) and vanadium oxides (e.g., V.sub.2O.sub.5).
In another embodiment, the auxiliary electrode functions as an
auxiliary cathode. A cathode in combination with an auxiliary
cathode can achieve better performance than the cathode alone. An
example of a cathode and auxiliary cathode with improved
performance is LiMn.sub.2O.sub.4 and
LiNi.sub.0.8Co.sub.0.15Al.sub.0.05O.sub.2 being electrically
coupled together as cathodes. By electrically coupling these two
cathodes together, better cycle life and performance of the battery
can be achieved.
[0023] In another embodiment of the secondary battery cell of the
present invention, the auxiliary electrode can be electrically
coupled to the anode. In an embodiment in which the auxiliary
electrode is electrically coupled to the anode, the auxiliary
electrode can function as an auxiliary anode. An anode in
combination with an auxiliary anode can achieve better performance
than the anode alone. Alternatively, the auxiliary electrode can be
electrically coupled to both the cathode and the anode. In another
embodiment, the anode comprises an anode material, wherein the
anode material is atmospherically unstable in its
carrier-ion-inserted form. Examples of anode materials that are
atmospherically unstable in their carrier-ion-inserted form include
silicon, germanium, carbon, tin, aluminum, mixtures of transition
metals and silicon, and lithium titanate.
[0024] In another embodiment, both the anode and the cathode
comprise materials that are atmospherically unstable in their
carrier-ion-inserted form. Battery cells in which both the anode
and the cathode comprise materials that are atmospherically
unstable in their carrier-ion-inserted form have heretofore been
prohibitively dangerous and/or expensive to manufacture since the
carrier ion of the cell could not be introduced into the cathode or
the anode prior to assembly of the cell. For example, titanium
sulfide/graphite cells are not practical as the cathode/anode
respectively, of conventional lithium-ion cells, because neither
titanium sulfide nor graphite can be used in a lithiated form to
make a cell. However, the use of an auxiliary lithium electrode
makes it possible to use cathode materials like titanium sulfide,
molybdenum sulfide, and vanadium oxide with anodes like silicon,
germanium, carbon, tin, aluminum, mixtures of transition metals and
silicon, and lithium titanate. After assembly and sealing the cell
with all three electrodes the auxiliary electrode can be used to
introduce carrier ions, like lithium-ions, to the anode and/or
cathode.
[0025] The batteries and battery cells of the present invention can
comprise aqueous or nonaqueous electrolytes.
[0026] As shown in FIG. 3, an embodiment of the present invention
relates to a system comprising a secondary battery cell 31 with an
auxiliary electrode oriented as previously described, a sensor 38,
and a controller 39. The sensor 38 senses the voltage of at least
one of the cathode 30 or anode 32 relative to the auxiliary
electrode 34. The sensor 38 is electrically coupled to the cathode
30 or the anode 32 at which the voltage is sensed and to the
auxiliary electrode 34. In FIG. 3, the sensor 38 is shown as
electrically coupled to both the cathode 30 and the anode 32.
However, the present invention also included embodiments in which
the sensor 38 is coupled to only the cathode 30 or the anode 32.
The controller 39 is electrically coupled to the sensor 38 and the
controller 39 can control the voltage or the current in a
load/charge circuit between the cathode 30 and anode 32 according
to the sensed voltage. A load/charge circuit between the cathode 30
and the anode 32 is a circuit that contains the load driven by the
current produced by the battery cell when the cell is discharged or
a circuit through which electrical energy is used to recharge the
cell. The cathode 30 and the anode 32 are electrolytically coupled
through the electrolyte in the separator 35. The auxiliary
electrode 34 is electrolytically coupled to at least one of the
cathode 30 or anode 32 through the electrolyte in the separator
35.
[0027] In FIG. 3, the auxiliary electrode 34 is electrically
coupled to the cathode 30. However, the present invention includes
embodiments in which the auxiliary electrode 34 is electrically
coupled to the anode 32 as well as embodiments in which the
auxiliary electrode 34 is electrically coupled to both the cathode
30 and the anode 32. The electrical coupling between the auxiliary
electrode 34 and the cathode 30 or anode 32 may contain components
37 to sense or control current or voltage as well as to store
information about current or voltage. The components 37 in the
electrical coupling between the auxiliary electrode 34 and the
cathode 32 or anode 30 can be electrically coupled to the sensor 38
and to the controller 39.
[0028] As shown in FIG. 4, an embodiment of the system of the
present invention can comprise a memory unit 40 coupled to the
sensor, wherein the memory unit 40 stores data about the sensed
voltage. The memory unit 40 can be coupled to the controller 39 and
the controller 39 can control the voltage or the current in the
load/charge circuit according to the data stored in the memory unit
40 as well as according to the voltage sensed by the sensor 38.
Using a memory unit 40, the auxiliary electrode of the present
invention can be used to monitor the charge and/or discharge
process of a secondary battery cell by allowing for recognition of
storage device failure modes, recognition in changes of battery
capacity and/or life, programmable notifications of battery end of
life, and so forth.
[0029] The auxiliary electrode 34 of the present invention can be
used to control the rate of charge and/or discharge of the battery
cell. This can be achieved by manufacturing the auxiliary electrode
out of a reference material that can be used to tune and/or stop
the rate of charge and/or discharge. For most existing rechargeable
energy storage devices, discharge is allowed to continue until the
potential difference between anode and cathode reaches a lower
limit based on battery chemistry. However, in some cases it may be
advantageous to stop the discharge at an anode or cathode potential
relative to a constant reference instead of relative to each other.
For instance, in the case of a silicon anode as part of a
lithium-ion battery, the life a silicon anode is reduced and the
silicon anode is not stable if completely discharged. Ideally,
discharge should stop when the silicon anode reaches a voltage of
0.9 V relative to lithium. In a conventional lithium-ion battery,
controlling the voltage of the anode is done indirectly through the
voltage differential between the anode and the cathode in the cell,
the cell voltage. However, the use of an auxiliary lithium
electrode electrically and electrolytically coupled to at least one
of the cathode or anode allows direct monitoring of the anode and
cathode and so the potential of the anode could be directly
controlled and maintained above 0.9 V relative the auxiliary
electrode. Other potential auxiliary electrode materials that could
be used are lithium alloys, carbonaceous materials, lithium metal
oxides and lithium metal phophides.
[0030] In another embodiment of the invention the auxiliary
electrode 34 can act as a means for rapid recharging of the
secondary battery cell. For most existing secondary battery cells,
the rate of charge of the device is set by charging at a constant
current--one that is relatively low to ensure that the
overpotential to the charge carrier back from cathode to anode is
not so high that device degradation occurs--either at the anode or
cathode or both. For example, in a standard lithium-ion battery, if
a driving voltage of 4.3V at the cathode relative to a lithium
reference is exceeded then undesirable side reactions are likely to
occur on the cathode. Similarly, the voltage of the anode must
remain above a certain value. In a standard lithium-ion battery
cell, the anode must remain above 0V relative to lithium or lithium
deposition on the anode will occur. To ensure that these negative
effects at the cathode and anode do not happen, existing secondary
battery cells charge with a battery voltage cutoff of 4.2 V so that
the cathode voltage threshold limit of 4.3V cannot be exceeded and
the anode threshold voltage of 0.1 V cannot be passed. With an
auxiliary electrode, however, the electrode can actually be driven
at a chosen voltage to maximize the current delivery and reducing
charge time. Preferably, the increased current used to charge a
cell of the present invention should correspond to at least a C/100
rate relative to the capacity ("C") of the electrode that is being
charged. It would however, more preferably correspond to at least a
C/50 charge rate and, most preferably at least a C/20 charge
rate.
[0031] FIG. 3 also shows how the auxiliary electrode 34 can act as
a reference electrode to shut off discharge when the voltage of the
anode 32 and/or cathode 30 exceeds a specified limit versus the
auxiliary electrode 34. One embodiment of the invention would
implement this by sensing the voltage at the cathode 30 or anode 32
relative to the auxiliary electrode 34 with a sensor 38. The
controller 39 would isolate the cell from the circuit it was
powering when the predefined voltage limit is exceeded.
[0032] The controller 39 of FIG. 4 can cause the auxiliary
electrode 34 to replenish at least one of the cathode or anode
according to the voltage sensed by the sensor 38. Alternatively,
the controller 34 can cause the auxiliary electrode 34 to replenish
at least one of the cathode or anode according to the data stored
in the memory unit 40 or according to both the voltage sensed by
the sensor 38 and data stored in the memory unit 40.
[0033] To replenish the cathode 30 or anode 32, a current can be
applied between the auxiliary electrode 34 and the cathode 30 or
anode 32. For example, for a lithium-ion secondary battery cell,
using a lithium foil as the auxiliary electrode, applying a current
between the lithium foil and the anode can replenish the capacity
lost in the first cycle and/or subsequent cycles of the cell.
[0034] In an embodiment of the secondary battery cell of the
present invention, the cell has been cycled and the cathode or the
anode has been replenished by the auxiliary electrode.
[0035] The present invention includes methods of preparing a
replenished secondary battery cell comprising: obtaining the
secondary battery cell as described herein; cycling the anode and
cathode of the cell; and replenishing at least one of the coupled
cathode or anode with carrier ions from the auxiliary electrode.
After replenishment, the auxiliary electrode can be removed from
the secondary battery cell. The auxiliary electrode can be removed
to lower the weight or volume of the cell or to improve the
reliability or safety of the cell or battery in which the cell is
integrated.
[0036] Replenishment of the cathode or anode and removal of the
auxiliary electrode prior to final packing of a secondary battery
cell can improve the energy density of the battery cell. After the
first charge and/or discharge cycle the lost energy capacity can be
replenished by way of the auxiliary electrode material diffusing
into the anode and/or cathode (a battery cell cycle is a charge or
discharge of the battery cell). Diffusion of the auxiliary
electrode material can be accomplished by applying a voltage across
the auxiliary electrode and the cathode and/or anode separately to
drive material transfer between auxiliary electrode and anode
and/or cathode, or by other transport phenomenon that will drive
auxiliary electrode material transfer to the anode and/or
cathode.
[0037] If the auxiliary electrode is not removed from the cell, the
replenishment can be done after final packaging and the auxiliary
electrode will be left in the final battery. If the auxiliary
electrode is left in the final packaged battery cell and
corresponding battery, then the battery cell can perform a capacity
replenishment to replenish the capacity fade that occurs over the
course of cycling the battery cell.
[0038] The auxiliary electrode of the present invention can be
formed by placing an electrode made from the desired material in an
inactive area of the battery cell but still electrolytically
coupled to the anode and/or the cathode through separator.
Alternatively, the auxiliary electrode can be formed by depositing
the desired auxiliary electrode material, using techniques such as
electrochemical deposition, electroless deposition, electrophoretic
deposition, vacuum assisted filling, stencil assisted filling, and
so forth.
[0039] The secondary battery cells and systems of the present
invention may be incorporated into secondary batteries. A secondary
battery can be made according to the methods of the present
invention or with the cells and systems of the present invention as
known in the art. See, e.g., Long et. al., Three-Dimensional
Battery Architectures, Chemical Reviews, 2004, 104, 4463-4492; Wang
and Cao, Electrochimica Acta, 51, 2006, 4865-4872; and Nishizawa et
al., Journal of the Electrochemical Society, 1923-1927, 1997;
Shemble et. al., 5.sup.th Advanced Batteries and Accumulators,
ABA-2004.
[0040] A secondary battery of the present invention can comprise a
plurality of the secondary battery cells as described herein,
wherein the cathodes of the plurality of cells are electrically
coupled, the anodes of the plurality of cells are electrically
coupled, and the auxiliary electrodes of the plurality of cells are
electrically coupled.
[0041] The following examples further illustrate the present
invention. These examples are intended merely to be illustrative of
the present invention and are not to be construed as being
limiting.
EXAMPLES
Example 1
Three-Dimensional Battery Cell With Lithium Foil Auxiliary
Electrode As A Reference Electrode
[0042] A three-dimensional battery was constructed from a 1 cm by 1
cm silicon wafer containing two sets of walls, 120 microns tall,
separated by a spacing of 100 microns. One set of walls served as a
cathode and were coated with a paste comprising lithium nickel
cobalt aluminum oxide, Carbon Black, and polyvinylidene difluoride.
The other set of walls served as the anode. The anode and cathode
walls were separated by a porous separator. A third electrode
comprising a lithium metal foil was positioned above the walls and
separated from the walls by a polyolefin separator (Celgard 2325).
By placing the lithium foil on top of the three-dimensional
structure, the lithium foil was electrolytically coupled with all
the anode and cathode walls. The entire assembly was placed in a
metalized plastic pouch, electrolyte added, and the pouch sealed.
The cathode was cycled with respect to the lithium foil. FIG. 5
shows the potential 50 of the cathode relative to the auxiliary
electrode. Then the anode was first cycled with respect to the
lithium foil. FIG. 6 shows the potential 60 of the anode relative
to the auxiliary electrode. Finally, the anode was cycled with
respect to the cathode while monitoring the cell voltage and the
voltage of the anode with respect to the lithium foil auxiliary
electrode. FIG. 7 shows a chart of one full charge/rest/discharge
cycle with plots of both the cell voltage 70 and anode voltage 71
relative to the auxiliary electrode.
[0043] Although the invention has been described with reference to
the presently preferred embodiments, it should be understood that
various modifications could be made without departing from the
scope of the invention.
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