U.S. patent application number 15/882126 was filed with the patent office on 2020-09-03 for flexible micro-battery.
The applicant listed for this patent is Johnson & Johnson Vision Care, Inc.. Invention is credited to Jean-Francois Audebert, Jonathan Howarth, Zachary Kanner, Leonard Pagliaro, Serena Peterson, Lawrence Edward Weinstein.
Application Number | 20200280026 15/882126 |
Document ID | / |
Family ID | 1000005031120 |
Filed Date | 2020-09-03 |
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United States Patent
Application |
20200280026 |
Kind Code |
A9 |
Audebert; Jean-Francois ; et
al. |
September 3, 2020 |
FLEXIBLE MICRO-BATTERY
Abstract
Designs, strategies and methods for forming micro-batteries are
described. In some examples, ultrasonic welded seals may be used to
seal battery chemistry within the micro-battery. In some further
examples, the micro-battery is encapsulated by a copper film where
at least a portion of the copper film is formed by electroless
plating.
Inventors: |
Audebert; Jean-Francois;
(Falls Church, VA) ; Kanner; Zachary; (Framingham,
MA) ; Pagliaro; Leonard; (Bowie, MD) ;
Weinstein; Lawrence Edward; (Silver Spring, MD) ;
Peterson; Serena; (College Park, MD) ; Howarth;
Jonathan; (Baltimore, MD) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Johnson & Johnson Vision Care, Inc. |
Jacksonville |
FL |
US |
|
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20180159094 A1 |
June 7, 2018 |
|
|
Family ID: |
1000005031120 |
Appl. No.: |
15/882126 |
Filed: |
January 29, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15326161 |
Jan 13, 2017 |
10593911 |
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PCT/US15/41365 |
Jul 21, 2015 |
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15882126 |
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62487262 |
Apr 19, 2017 |
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62026851 |
Jul 21, 2014 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 2/0207 20130101;
H01M 2/0275 20130101; H01M 4/661 20130101 |
International
Class: |
H01M 2/02 20060101
H01M002/02; H01M 4/66 20060101 H01M004/66 |
Claims
1. An electrochemical micro-battery comprising biocompatible cell
components including: an anode current collector; a cathode current
collector; an anode extending along an arcuate path; a generally
planar cathode extending along the arcuate path, wherein the anode
is positioned above the cathode; a separator positioned between the
anode and the cathode, wherein the separator extends along the
arcuate path; an electrolyte positioned generally surrounding the
anode, the cathode and the separator to provide ionic conductivity
between the anode and the cathode; flexible packaging generally
surrounding the anode, the cathode, the cathode current collector,
the separator, and the electrolyte, wherein the anode collector
extends through the flexible packaging along a first vector along
the arcuate path, and the cathode collector extends through the
flexible packaging along a second vector along the arcuate path; an
encapsulating copper layer surrounding the flexible packaging,
wherein one of the anode collector or the cathode collector is not
surrounded by the encapsulating copper, and wherein at least a
portion of the copper layer is deposited to the flexible packaging
with electroless plating.
2. A method of manufacturing a micro-battery comprising: obtaining
a cathode collector; attaching a cathode to the cathode collector
with a conductive adhesive; obtaining an anode collector; obtaining
an anode; stacking the cathode collector, the cathode, the anode,
the anode collector, and a separator, wherein the separator lies
between the cathode and the anode; surrounding the stack with a
first and second flexible plastic sheet; welding the first and
second flexible plastic sheets to each other with a first
ultrasonic weld, wherein the first ultrasonic weld surrounds the
stack along a first portion of two sides, wherein a second portion
of the two sides comprises a fill port for the micro-battery;
filling an electrolyte within the fill port; welding the second
portion of the two sides of the first and second flexible plastic
sheets, wherein the welding of the second portion seals the fill
port; depositing an electroless plated layer of copper along a
portion of the micro-battery.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This patent application claims the benefit of U.S.
Provisional Patent Application No. 62/487,262 filed Apr. 19, 2017
and is a continuation in part of U.S. patent application Ser. No.
15/326,161, filed Jan. 13, 2017, which in turn claims the benefit
of U.S. Provisional Application No. 62/016,851 filed Jul. 21, 2014.
The contents of each are herein incorporated by reference.
BACKGROUND OF THE INVENTION
Field of the Invention
[0002] The present invention generally relates to an
electrochemical battery, and more particularly to a biocompatible
micro-electrochemical cell.
Description of the Related Art
[0003] Recently, the number of medical devices and their
functionality has begun to rapidly develop. These medical devices
may include, for example, implantable pacemakers, electronic pills
for monitoring and/or testing a biological function, surgical
devices with active components, contact lenses, infusion pumps, and
neurostimulators. Added functionality and an increase in
performance to many of the aforementioned medical devices have been
theorized and developed. However, to achieve the theorized added
functionality, many of these devices now require self-contained
energization means that are compatible with the size and shape
requirements of these devices, as well as the energy requirements
of the new energized components.
[0004] Some medical devices may include electrical components such
as semiconductor devices that perform a variety of functions and
may be incorporated into many biocompatible and/or implantable
devices. However, such semiconductor components require energy, and
thus energization elements may preferably also be included in such
biocompatible devices. The topology and relatively small size of
the biocompatible devices may create challenging environments for
the definition of various functionalities. In many examples, it may
be important to provide safe, reliable, compact and cost-effective
means to energize the semiconductor components within the
biocompatible devices. Therefore, a need exists for biocompatible
energization elements formed for implantation within or upon
biocompatible devices where the structure of the millimeter- or
smaller-sized energization elements provides enhanced function for
the energization element while maintaining biocompatibility.
[0005] One such energization element used to power a device may be
a battery. When using a battery in biomedical type applications, it
may be important that the battery structure and design accommodate
aspects of biocompatibility. Therefore, a need exists for novel
examples of forming biocompatible batteries for use in
biocompatible energization elements that may have significantly
improved containment aspects.
[0006] There are several micro-batteries which have been developed,
some of which are designed to be implantable or otherwise
associated with a medical or other device that require a power
source for operation. For purposes of this specification, a
micro-battery is defined by its relatively small dimensions.
Specifically, at least one dimension (that is the length, width or
thickness of the battery) shall be less than one millimeter (1.0
mm), and a second dimension shall be less than one centimeter (1.0
cm), whereas the volume of the micro-battery shall be less than
0.003 cc or three thousandths of a cubic centimeter.
[0007] It is possible to prepare batteries with these dimensions by
additive manufacturing, by winding the electrodes, or by picking
and placing active materials into place. These batteries can be
made in a variety of shapes, including cylindrical, prismatic, or
arcuate shapes. When biocompatible materials are used for the
miniaturized power source, the power source is biocompatible. For
example, carbon-zinc batteries, with a zinc salt electrolyte, zinc
negative electrode, and manganese dioxide positive electrode can be
biocompatible.
[0008] There exists a need for a micro-power supply that is
biocompatible, may be used in medical and other small devices, and
that is capable of repeated or continuous operation by providing
required energy while the device is being, bent, flexed or
otherwise manipulated and after such manipulation.
SUMMARY OF THE INVENTION
[0009] Accordingly, improved, flexible micro-batteries and designs
for use in biocompatible energization elements have been disclosed.
Micro-batteries used in ophthalmic medical devices may have unique
and challenging requirements such as the need for mechanical
robustness, a degree of flexibility, and biocompatibility. A
contact lens using a micro-battery may require the battery to
possess the qualities of the lens by having a long shelf life,
having a measure of flexibility and maintaining integrity and
operability after being manipulated, It may also need to be
biocompatible for the period starting with lens manufacturing
through the usage lifetime of the lens. This period exposes the
micro-battery to the saline solution within the lens, either
directly or through an intermediate layer, and the micro-battery
may need not only maintain its capacity and ability to provide the
required power to the lens, but also be adequately sealed to
prevent leaching of the battery components. The dimensions of a
micro-battery make isolation of the battery components particularly
challenging as the surface area to volume ratio of the
micro-battery may be very high.
[0010] The micro-battery may be stored within an ophthalmic lens
for years, with the lens containing the micro-battery stored inside
of a sealed package filled with a saline packing solution. This
storage environment is similar to being stored in sterile saline
solution in which the ophthalmic lens is immersed. This storage
condition and the environment of an ophthalmic lens or other device
in standard conditions may require that the micro-battery be
designed to tolerate a given environment without failure due to
water ingress through the packaging into the interior of the
micro-battery which may also lead to swelling. The micro-battery
packaging may have a measurable level of permeability. Osmotic
pressure differences may, therefore, be created which may direct
water to migrate into the micro-battery interior. Often,
conventional battery electrolytes are non-aqueous and do not
tolerate moisture contamination, or are highly concentrated acidic
solutions (for example, zinc chloride) or basic solutions, such as
potassium hydroxide. Use of an electrolyte with a low salt
concentration may be a possible solution to reduce the osmotic
pressure difference between the electrolyte and packing solution
surrounding a lens containing the micro battery.
[0011] Another issue related to biocompatibility and osmotic
pressure is the pH of the electrolyte. Typically, aqueous battery
electrolytes may not be biocompatible. In a typical alkaline
battery, the potassium hydroxide electrolyte is strongly alkaline
to increase ionic conductivity. In a carbon zinc or LeClanche cells
the acid pH of the electrolyte may strongly influence hydrogen gas
production on the zinc surface. Strongly acidic or basic
electrolytes are not biocompatible. Many typical corrosion
inhibitors such as mercury are not biocompatible either.
[0012] Many micro-batteries, especially those mass-produced or
those needing biocompatibility are encased in rigid exteriors.
Their rigidity typically does not allow such batteries to be
utilized in flexible devices. Furthermore, the rigid casing design
limits the dimensions of the battery which are possible, since a
minimum casing thickness is required to maintain rigidity.
[0013] Batteries utilizing conductive traces require both flexible
traces and flexible substrates on which to support the trace. Such
flexibility is not found in materials compatible with an oxidizing
battery environment. Instead, the batteries of the prior art are
typically constructed to be generally immobile after being
manufactured. Movement of the battery may adversely affect
connections, sealing of the exterior and otherwise affect the
proper operation of the battery.
[0014] One general aspect includes a biomedical device including an
electroactive component, a biocompatible battery, and a first
encapsulating layer. The first encapsulating layer encapsulates at
least the electroactive component and the biocompatible battery. In
some examples, the first encapsulating layer may be used to define
a skirt of a contact lens, surrounding internal components of an
electroactive lens with a biocompatible layer of hydrogel that
interacts with the user's eye surface. In some examples the nature
of the electrolyte solution provides improvements to the
biocompatibility of the biomedical device. For example, the
composition of the electrolyte solution may have lowered
electrolyte concentrations than typical battery compositions. In
other examples, the composition of electrolytes may mimic the
biologic environment that the biomedical device occupies, such as
the composition of tear fluid in a non-limiting example.
[0015] According to one aspect of the present invention, an
electrochemical micro-battery with biocompatible components is
provided that comprises an anode, which may be cylindrical,
extending along a first vector and a generally planar cathode
extending along a second vector. The second vector is generally
parallel to said first vector, and the cathode is disposed from the
anode by a predetermined space. A cathode collector is in
electrical contact with the cathode and extends along the second
vector. In an aspect, the cathode collector is positioned within
the cathode. The electrochemical micro-battery may also includes an
electrolyte positioned generally surrounding both the anode and the
cathode and positioned within the predetermined space to provide
ionic conductivity between the anode and cathode.
[0016] In an aspect, the electrochemical battery may further
comprise an anode current collector, wherein the anode and the
anode current collector are bonded in electrical communication. The
anode and the anode current collector are positioned to extend
along the first vector in a first stacked arrangement, and the
cathode and said cathode current collector are bonded in electrical
communication, and are positioned to extend along the second vector
in a second stacked arrangement. The first stacked arrangement and
the second stacked arrangement are separated relative to each other
by the predetermined space. A separator may be positioned between
the first stacked arrangement and the second stacked arrangement
within the predetermined space.
[0017] Packaging may generally surround the anode, cathode, cathode
collector and the electrolyte. Terminal ends of the anode may
extend through the packaging along a first vector, and the cathode
collector may also extend through the packaging along a second
vector. The packaging may have a generally uniform thickness. The
packaging may be customized and accommodate an electrochemical
battery cell which is formed into a desired shape in three
dimensions. The packaging may prevent water and oxygen migration
through said packaging. In an aspect, the packaging may comprise a
polymer coated with a metal oxide. The water vapor transmission
rate of the packaging may be less than 1 g/m2-day when measured at
between 85 and 100% relative humidity and between 20 and 40 degrees
Celsius. Thus, in an electrochemical micro-battery, with a volume
equal to or less than three cubic millimeters (3.0 mm3), having an
interior space which is encapsulated by biocompatible packaging,
which in one aspect is positioned in ion communication with a
bodily fluid, or an artificial bodily fluid such as saline
solution, the packaging may act to inhibit mass transfer between
the interior space and the bodily fluid or saline solution.
[0018] The electrochemical micro-battery may be shaped in all three
dimensions. In some examples, the electrochemical micro-battery may
include a planar shape as well as a shape wherein both a first
vector and a second vector are arcuate, and wherein the first
vector and second vector are concentric to each other.
[0019] The electrochemical micro-battery may also include an anode
made of zinc. In an aspect of the invention the anode may be a zinc
wire. The cathode of the present invention comprises manganese
dioxide, a conductive additive material, and a binder. The cathode
collector may comprise a wire shaped metal such as titanium and may
be positioned adjacent or alternatively within the cathode. In an
embodiment where the cathode collector is positioned within the
cathode, the diameter of the anode may equal the thickness of the
cathode, so that the thickness of the electrochemical cell equals
the anode diameter in addition to the packaging thickness.
[0020] The first electrochemical cell of the micro-battery may
operate as a single cell or be connected to a second
electrochemical cell in series or parallel to the first
electrochemical cell. In the series embodiment, the anode of the
first electrochemical cell may be electrically connected to the
cathode collector of the second electrochemical cell. The anode of
the electrochemical cell may be welded to the cathode collector of
the second electrochemical cell to form a mechanically secure and
electrically communicating connection. The micro-battery cells may
be independently packaged or the packaging of the first
electrochemical cell and the packaging of the second
electrochemical cell may be joined as to form a contiguous package.
In an aspect, when the second electrochemical cell is connected in
series to said electrochemical cell, the anode of the
electrochemical cell is electrically connected to a cathode
collector of said second electrochemical cell, and the packaging of
the electrochemical cell and the packaging of the second
electrochemical cell are joined as to form a contiguous package. In
an aspect wherein the anode of the electrochemical cell further
includes an anode collector in electrical communication with the
anode of the electrochemical cell, the anode collector extends out
of the electrochemical cell and extends into the second
electrochemical cell, and wherein the anode collector is
electrically connected to the cathode of the second electrochemical
cell, and wherein the packaging of the electrochemical cell and the
packaging of the second electrochemical cell are joined as to form
a contiguous package.
[0021] In an aspect, the volume of the electrochemical battery may
be equal to or less than three cubic millimeters (3.0 mm3). The
anode may have a length extending along the first vector, and a
width and thickness extending perpendicular to said first vector,
wherein the width is greater than the thickness, and the ratio of
the length to the width is greater than twenty to one (20:1). The
cathode may have a length extending along the second vector, and a
width and thickness extending perpendicular to the second vector,
the width is greater than said thickness, and the ratio of the
length to the width is greater than ten to one (10:1).
[0022] In an aspect, the interior space of the micro-battery may
comprise an aqueous neutral electrolyte solution, such as zinc
acetate. The concentration of the zinc acetate in the electrolyte
may comprise less than ten weight percent of said electrolyte (10
wt %). The pH of the electrolyte may be between 6 and 8, wherein
the packaging is positioned in ionic communication with a saline
solution, the difference between the osmotic pressure of the
electrolyte relative to the osmotic pressure of the saline solution
is less than ten atmospheres (10 atm). The anode may comprise zinc
and the cathode may comprise manganese dioxide. The anode current
collector and the cathode current collector may each comprise
titanium, tantalum, platinum or other electrically conductive,
flexible, biocompatible material. The anode may include both zinc
powder, and a zinc article such as zinc foil extending the length
of the battery, wherein the zinc powder is in electrical
communication with the zinc article.
[0023] The micro-battery may be constructed according to a method
comprising the steps of: forming a cathode having a length and
thickness, wherein the ratio of the length to the thickness is
equal to or greater than 50:1; attaching the cathode to a cathode
collector which extends the length of the cathode to form a cathode
assembly; forming an anode having a length and thickness, wherein
the ratio of the length to the thickness is equal to or greater
than 50:1; distribute an aqueous electrolyte around both the anode
and the cathode assembly to enable ionic communication between the
cathode and anode; and placing the cathode assembly, the
electrolyte and the anode within a first and second portion of
thermoplastic packaging. The first and second portions may envelop
all of the electrolyte, a portion of the cathode assembly and a
portion of the anode to form a battery interior bounded by sides of
the battery interior, except to enable an end portion of the
cathode assembly and anode to extend out of the battery interior at
both a first and second end of the micro-battery; sealing the
battery interior by heating the first and second portions of the
packaging along the length of the battery interior sides, and
sealing the battery interior at the first and second end of the
micro-battery by sealing the packaging around the extending anode
and cathode assembly; and removing packaging external to the sealed
micro-battery. In an aspect of the method, the first and second
portions of the packaging may be placed within an ultrasonic
welder, and the ultrasonic welder may seal the first and second
portions of the packaging around the battery interior by sealing
the packaging, and cutting the packaging at the seal in one step.
In an aspect, a separator may be inserted between the anode and
cathode. In another aspect, the anode is attached to an anode
collector, and the anode collector is positioned to extend out of
the battery interior at both the first and second ends of the
micro-battery.
[0024] These and other features, advantages, and objects of the
present invention will be further understood and appreciated by
those skilled in the art by reference to the following
specification, claims, and appended drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is an exemplary cross-sectional view of an
electrochemical battery cell taken along a normal to the vector L
(length);
[0026] FIG. 2 is an exemplary cross-sectional view of the
electrochemical battery cell taken along plane normal to the vector
H (height);
[0027] FIG. 3 is an exemplary cross-sectional representational view
of the electrochemical battery cell of the present invention;
[0028] FIG. 4 is an exemplary perspective view of the
electrochemical battery cell with the packaging portion
exploded;
[0029] FIG. 5A is an exemplary perspective view of the packaging
portion of the electrochemical battery cell, according to one
embodiment;
[0030] FIG. 5B is an exemplary perspective view of the packaging
portion of the electrochemical battery cell, according to another
embodiment;
[0031] FIG. 6 is an exemplary cross-sectional view of the
electrochemical battery cell of the present invention disposed in
an ultrasonic welding fixture depicting a method of sealing the
exterior packaging;
[0032] FIG. 7 is an exemplary cross-sectional view of the shaped
battery package illustrating two cells in series in an arcuate
shape;
[0033] FIG. 8 is an exemplary cross-sectional view of the shaped
battery package showing two cells in series in an arcuate shape and
highlighting how the cells are electrically connected;
[0034] FIG. 9 is an exemplary enlarged section of the electrical
connection between the two cells of the shaped battery package
depicted in FIG. 8;
[0035] FIG. 10 is an exemplary exploded view of the electrochemical
battery cell showing two cells in series in an arcuate shape, and a
laser weld beam for sealing the cell packaging;
[0036] FIG. 11 A is an exemplary perspective view of substrate used
to prepare the present invention in the illustrative example;
[0037] FIG. 11B is an exemplary perspective view of an interim form
of the cathode and cathode collector assembly of the present
invention as described in the illustrative example;
[0038] FIG. 11C is an exemplary perspective view of the cathode and
cathode collector assembly of the present invention as described in
the illustrative example; and
[0039] FIG. 11D is an exemplary perspective view of the present
invention as prepared in the substrate as described in the
illustrative example.
DETAILED DESCRIPTION OF THE INVENTION
[0040] Methods of forming flexible micro-batteries with improved
biocompatibility are disclosed in the present application. In the
following sections, detailed descriptions of various examples are
described. The descriptions of examples are exemplary embodiments
only, and various modifications and alterations may be apparent to
those skilled in the art. Therefore, the examples do not limit the
scope of this application. In some examples, these biocompatible
batteries may be designed for use in, or proximate to, the body of
a living organism.
Glossary
[0041] In the description and claims below, various terms may be
used for which the following definitions will apply:
[0042] "Anode" as used herein refers to an electrode through which
electric current flows into a polarized electrical device. The
direction of electric current is typically opposite to the
direction of electron flow. In other words, the electrons flow from
the anode into, for example, an electrical circuit.
[0043] Battery as used herein refers to an electrochemical power
source which consists of a single electrochemical cell or a
multiplicity of electrochemical cells, suitably connected together
to furnish a desired voltage or current. The cells may be primary
(non-rechargeable) or secondary (rechargeable) cells.
[0044] "Binder" as used herein refers to a polymer that is capable
of exhibiting elastic responses to mechanical deformations and that
is chemically compatible with other energization element
components. For example, binders may include electroactive
materials, electrolytes, polymers, etc. In some examples, binder
may refer to a substance that holds particles and/or
particles+liquid together in a cohesive mass.
[0045] "Biocompatible" as used herein refers to a material or
device that performs with an appropriate host response in a
specific application. For example, a biocompatible device does not
have toxic or injurious effects on biological systems.
[0046] "Cathode" as used herein refers to an electrode through
which electric current flows out of a polarized electrical device.
The direction of electric current is typically opposite to the
direction of electron flow. Therefore, the electrons flow into the
cathode of the polarized electrical device, and out of, for
example, the connected electrical circuit.
[0047] "Coating" as used herein refers to a deposit of material in
thin forms. In some uses, the term will refer to a thin deposit
that substantially covers the surface of a substrate it is formed
upon. In other more specialized uses, the term may be used to
describe small thin deposits in smaller regions of the surface.
[0048] "Electrode" as used herein may refer to an active mass in
the energy source. For example, it may include one or both of the
anode and cathode.
[0049] "Energized" as used herein refers to the state of being able
to supply electrical current or to have electrical energy stored
within.
[0050] "Energy" as used herein refers to the capacity of a physical
system to do work. Many uses of the energization elements may
relate to the capacity of being able to perform electrical
actions.
[0051] "Energy Source" or "Energization Element" or "Energization
Device" as used herein refers to any device or layer which is
capable of supplying energy or placing a logical or electrical
device in an energized state. The energization elements may include
batteries. The batteries may be formed from alkaline type cell
chemistry and may be solid-state batteries or wet cell batteries
including aqueous alkaline, aqueous acid or aqueous salt
electrolyte chemistry or non-aqueous chemistries, molten salt
chemistry or solid state chemistry. The batteries may be dry cell
(immobilized electrolyte) or wet cell (free, liquid electrolyte)
types.
[0052] "Fillers" as used herein refer to one or more energization
element separators that do not react with either acid or alkaline
electrolytes. Generally, fillers may include substantially water
insoluble materials such as carbon black; coal dust; graphite;
metal oxides and hydroxides such as those of silicon, aluminum,
calcium, magnesium, barium, titanium, iron, zinc, and tin; metal
carbonates such as those of calcium and magnesium; minerals such as
mica, montmorollonite, kaolinite, attapulgite, and talc; synthetic
and natural zeolites such as Portland cement; precipitated metal
silicates such as calcium silicate; hollow or solid polymer or
glass microspheres, flakes and fibers; and the like.
[0053] "Functionalized" as used herein refers to making a layer or
device able to perform a function including, for example,
energization, activation, and/or control.
[0054] "Mold" as used herein refers to a rigid or semi-rigid object
that may be used to form three-dimensional objects from uncured
formulations. Some exemplary molds include two mold parts that,
when opposed to one another, define the structure of a
three-dimensional object.
[0055] "Power" as used herein refers to work done or energy
transferred per unit of time.
[0056] "Rechargeable" or "Re-energizable" as used herein refer to a
capability of being restored to a state with higher capacity to do
work. Many uses may relate to the capability of being restored with
the ability to flow electrical current at a certain rate for
certain, reestablished time periods.
[0057] "Reenergize" or "Recharge" as used herein refer to restoring
to a state with higher capacity to do work. Many uses may relate to
restoring a device to the capability to flow electrical current at
a certain rate for a certain reestablished time period.
[0058] "Released" as used herein and sometimes referred to as
"released from a mold" means that a three-dimensional object is
either completely separated from the mold, or is only loosely
attached to the mold, so that it may be removed with mild
agitation.
[0059] "Stacked" as used herein means to place at least two
component layers in proximity to each other such that at least a
portion of one surface of one of the layers contacts a first
surface of a second layer. In some examples, a coating, whether for
adhesion or other functions, may reside between the two layers that
are in contact with each other through said coating.
[0060] "Traces" as used herein refer to energization element
components capable of connecting together the circuit components.
For example, circuit traces may include copper or gold when the
substrate is a printed circuit board and may typically be copper,
gold or printed film in a flexible circuit. A special type of trace
is the current collector. Current collectors are traces with
electrochemical compatibility that make the current collectors
suitable for use in conducting electrons to and from a cathode or
anode of an electrochemical cell.
[0061] There may be other examples of how to assemble and configure
batteries according to the present invention, and some may be
described in following sections. However, for many of these
examples, there are selected parameters and characteristics of the
batteries that may be described in their own right. In the
following sections, some characteristics and parameters will be
focused upon.
[0062] Referring to FIG. 1 and FIG. 2, there is shown two different
cross sectional representations of an exemplary electrochemical
battery cell 100 according to one embodiment. FIG. 1 is a cross
section representation along a plane normal to the vector L
(length) and FIG. 2 is a cross section representation along a plane
normal to the vector H (height).
[0063] The electrochemical battery cell includes a cylindrical
anode 110 which extends along the length of the electrochemical
battery cell and serves as the negative electrode. More
specifically, the anode 110 extends along a vector parallel to the
length vector L shown in FIG. 2. In this embodiment, the anode 110
is generally cylindrical in shape and circular in cross section.
The diameter of the anode 110 is small enough and its aspect ratio
(length to width ratio) is large enough to enable flexibility of
the anode 110. The diameter may be sized large enough to
accommodate the absence of any current collector. As the
electrochemical battery cell discharges, reactive material from the
anode may electrochemically react and go into solution. As the
anode reactive material leaves the anode, the surface of the anode
may pit or otherwise change and a general decreasing diameter may
be realized. The remaining anode material may remain contiguous to
remain capable of acting as an anode current collector throughout
its length and as such may be capable of conducting electrons from
the anode out of the electrochemical battery cell.
[0064] As may be described again below in more detail, in some
examples the anode 110 is positioned on one side of the
electrochemical battery cell in this embodiment adjacent the
exterior first and second packaging portions 140 and 150. The first
packaging portion 140 and the second packaging portion 150 are
disposed relative each other to form a cell interior 160. The
packaging portions are manufactured from a material that may be
bonded or otherwise sealed to itself. The packaging portion
material may also be flexible and capable of enclosing all
components located within the cell interior 160.
[0065] In some examples, the electrochemical battery cell further
includes a cathode 120 which also extends along the length of the
electrochemical battery cell and serves as the positive electrode.
More specifically, the cathode 120 extends along a vector parallel
to the length vector L shown in FIG. 2. In this embodiment, the
cathode 120 is generally planar and rectangular in cross section.
The cathode may be positioned in electrical contact with a cathode
current collector 130, and in this embodiment, may be attached onto
the cathode current collector 130. This arrangement of coating the
cathode 120 onto a flexible conducting current collector 130
provides a flexible cathode construction that remains coherent
while the electrochemical battery cell 100 is twisted, bent or
otherwise contorted. As the electrochemical battery cell
electrochemically discharges, reactive material from the cathode
120 may electrochemically react and possibly expand. The cathode
may be designed to accommodate such expansion by being made with an
appropriate porosity and by being made from appropriate ingredients
that accommodate any such expansion. Such accommodation may enable
the cathode 120 to maintain adhesion with the cathode current
collector 130 and otherwise remain coherent.
[0066] The cathode 120 and the cathode current collector 130 are
shown positioned and supported on the second packaging portion 150
and at a position opposed to the anode 110 within the cell interior
160. Although the sizes of the anode 110 and the cathode 120 shown
in FIG. 1 and FIG. 2 are not necessarily to scale, the relative
positions of the anode and cathode are gapped by a predetermined
space 170. The dimensions of the predetermined space within the
cell interior may be important to ensure the anode and cathode do
not make direct contact with each other which would cause a battery
short circuit. The dimension may also not be so large as to prevent
effective ionic charge diffusion which directly relates to the rate
capability of the electrochemical battery cell. Although in
alternative embodiments, a permeable membrane battery separator may
be used, the cell construction of the present embodiment obviates
the need for added manufacturing complexity and expense of adding
such a component.
[0067] The cathode 120 and the anode 110 ionically communicate via
an electrolyte 180 which is positioned such that both the anode and
cathode may ionically communicate with the electrolyte material.
The electrolyte 180 may allow the flow of electric charge between
the anode 110 and the cathode 120. The electrolyte 180 may be a
liquid, gel or semi-solid provided that it is flexible and capable
of moving within the cell interior 160 while performing its task of
providing ionic diffusion between the anode 110 and cathode
120.
[0068] The electrons generated by the electrochemical battery cell
100 may be conducted from the cell via an anode collector tab 190.
This anode collector tab 190 may be affixed to an end of the anode
110 to be in electric communication with the anode 110. The anode
collector tab 190 provides a shape appropriate extension of the
anode 110 so that the cell interior 160 may be appropriately
sealed, with both the anode 110 and cathode 120 electrically
communicating exterior of the cell interior 160 and both first and
second packaging portions 140 and 150. The position of the anode
collector tab 190 in FIG. 1 and FIG. 2 is shown intermediate the
anode 110 and the first packaging portion 140. As may be seen, this
positioning may add height or a protrusion to the electrochemical
battery cell 100 and an alternative position may be preferred to
avoid increasing these dimensions. The anode collector tab 190 is
shaped relative to what it may be connecting to in a device. This
shape may be selected by one skilled in the art to create an
electrically secure connection between the anode tab and the
device.
[0069] Although not shown in the embodiment of FIG. 1 and FIG. 2,
both the anode collector tab 190 and the cathode current collector
130 may extend beyond the respective ends of the anode 110 and the
cathode 120. These extending portions of the anode collector tab
190 and the cathode current collector 130 enable more efficient
sealing of the cell interior 160. The first and second packaging
portions 140 and 150 may be both sealed to each other to seal the
cell interior 160 from the exterior or the electrochemical battery
cell 100, and sealed around the anode collector tab 190 and the
cathode current collector 130 which extend exterior the sealed
first and second packaging portions 140 and 150. As such, the anode
collector tab 190 becomes the negative exterior contact for the
electrochemical battery cell 100, and the cathode current collector
130 becomes the positive exterior contact for the electrochemical
battery cell.
[0070] In operation, when a load (not shown) is electrically
connected to both the anode collector tab 190 and the cathode
current collector 130 to form a circuit, the anode 110 releases
electrons via the anode collector tab 190 to the negative exterior
contact while simultaneously releasing ions into the electrolyte
180. The cathode 120 accepts the electrons flowing from the circuit
through the positive exterior contact and the cathode current
collector 130 and electro chemically reacts to equilibrate the
chemical potential of the electrochemical battery cell. The present
arrangement of the electrochemical battery cell 100 may effectively
operate while in torsion, while being bent, or otherwise
manipulated.
[0071] The electrochemical battery cell 100 shown in FIG. 1 and
FIG. 2 may be electrically and mechanically coupled in series with
an identical cell as shown in FIG. 3. In FIG. 3, there is shown a
first electrochemical battery cell 200 and its respective negative
end portion 201. The first electrochemical battery cell 200
possesses an anode 210, a cathode 220 and an anode collector tab
290. Also, shown in FIG. 3 is a second electrochemical battery cell
300 and its positive end portion 301. The second electrochemical
battery cell also has an anode 310, a cathode 320 and a cathode
current collector 330. As shown in FIG. 3 the anode collector tab
290 of the first electrochemical battery cell 200 is connected to
the cathode current collector 330 of the second electrochemical
battery cell 300 at connection point 399. This mechanical and
electrical coupling arrangement creates a multi-cell battery with
two electrochemical battery cells in series to provide an effective
voltage twice that of each individual cell. Alternative coupling
arrangements may be used to create parallel and other multi-cell
batteries using two or more cells.
[0072] The respective packaging portions 240 and 340, and 250 and
350 are shown joined to form a contiguous exterior surface or may
be manufactured as single packaging portions. However as may be
described in more detail the respective cell interiors 260 and 360
are preferably segregated. In FIG. 4, there is shown an alternative
view of the two batteries in series 400. A first electrochemical
battery cell 401 is electrically and mechanically coupled to a
second electrochemical battery cell 402. Both the first
electrochemical battery cell 401 and the second electrochemical
battery cell 402 have respective anodes 410 and 411, and respective
cathodes 420 and 421. Each cathode is associated with and
electrically coupled to a cathode current collector, and the first
electrochemical battery cell cathode 420 is associated with first
electrochemical battery cell cathode current collector 430, and the
second electrochemical battery cell cathode 421 is likewise
associated with a second electrochemical battery cell cathode
current collector (not shown). The second electrochemical battery
cell anode 411 is electrically and mechanically associated with a
second electrochemical battery cell anode collector tab 490 which
is also electrically and mechanically associated with the first
electrochemical battery cell cathode current collector 430 at
connection point 499.
[0073] The two electrochemical cells in series are surrounded on
the cathode side by a first packaging portion 440 which extends the
length of the two cells in series but is terminated at a first end
403 to enable the second electrochemical battery cell cathode
current collector to overhang the first packaging portion. At a
second end 404, the first packaging portion is similarly terminated
to enable the first electrochemical battery cell anode collector
tab 491 to extend beyond the second end. A second packaging portion
450 similar in length and width to the first packaging portion 440
is positioned adjacent the anode side of the two batteries in
series and the cell interior 460 may be sealed by associating the
first packaging portion 440 and second packaging portion adhesively
or by welding in a manner that allows both the second
electrochemical battery cell cathode current collector and the
first electrochemical battery cell anode collector tab to extend
beyond the packaging portions to enable them to be in electrical
communication with an external load (not shown).
[0074] It may be preferred to segregate the cell interior 460 into
individual cell interiors associated with each electrochemical
battery cell. This may be done by providing a divider adjacent the
connection point 499. Referring to FIG. 5A there is shown a
packaging portion 500 that may be used to provide the cell interior
segregation of this embodiment. The packaging portion 500 includes
a divider 510 which may be affixed to the packaging portion at a
segregation spot 520 on the packaging portion. The divider 510 may
be configured to act as a dam between two electrochemical battery
cells in series to prevent ionic conduction and convective flow
between the cells. The divider 510 may be laser welded to the
packaging portion and then again laser welded when the packaging
portion 500 is sealed relative a second packaging portion via laser
welding or an alternative connecting method. In an alternative
embodiment, the divider may be affixed via alternative joining
methods such as ultrasonic welding, or heat welding methods.
[0075] In FIG. 5B, there is shown an alternative embodiment of
providing segregation of the cell interior. A packing portion 550
includes a divider 560 at a segregation spot 570 on the packaging
portion. The divider 560 may be secured to the packaging portion
and a second packaging portion via adhesive and more preferably via
UV-cured adhesive. The first and second packaging portions may be
sealed relative each other at their peripheries and the divider 560
adhesively secured to both packaging portions to provide the
segregation of the cell interior.
[0076] In FIG. 6, there is shown a cross-sectional view of an
alternative embodiment of the electrochemical battery cell 600. In
this embodiment, the electrochemical battery cell 600 possesses a
cylindrical shaped electrochemical battery cell cathode current
collector 630, which is shown positioned between the
electrochemical battery cell cathode 620 and a first packaging
portion. Although not shown, the electrochemical battery cell
cathode current collector may alternatively be disposed entirely
within or partially within the cathode 620. An anode 610 is located
within the cell interior 660 at a predetermined distance 670 from
the cathode 620. The cell interior is filled with electrolyte (not
shown) to provide required ionic conductivity between the anode and
cathode electrodes.
[0077] A method of joining both the first packaging portion 640 and
the second packaging portion 650 along their respective peripheries
may be described using FIG. 6. The electrochemical battery cell 600
may be placed within an ultrasonic welding fixture which is shown
representatively in cross section surrounding a portion of the
electrochemical battery cell 600. The ultrasonic welding fixture
comprises both an ultrasonic welding horn 691 and an ultrasonic
welding anvil 692. The electrochemical battery cell 600 is placed
within the fixture and the ultrasonic welding horn 691 is brought
into contact with the first packaging portion 640 at the locations
where a weld is desired. In this methods embodiment, a weld is
desired both at the anode side of the electrochemical battery cell
601 and at the cathode side of the electrochemical battery cell
602. A controlled pressure is applied by the fixture to the
electrochemical battery cell bringing together the first packaging
portion 640 and the second packaging portion 650. The ultrasonic
horn is vibrated at a frequency appropriate for the material at the
desired amplitude for a predetermined amount of time that is
required to weld the first and second packaging portions. The
controlled pressure may be maintained for a second predetermined
time to allow the packaging portions to fuse.
[0078] Prior art ultrasonic welding of plastics takes place with
the motion of the ultrasonic horn largely perpendicular to the
plane of the items being joined (for the side seal, along vector H
shown in FIG. 2), and this may result in a wide joint which may be
objectionable. In some examples, when the motion of the ultrasonic
horn is largely in the same plane as the side seal (for the linear
side seal, a plane extending along vector L shown in FIG. 2), a
relatively narrower seal may be achieved. The vector of the horn's
motion is in the same plane as the edge of the package being
sealed. For nonlinear side seams (for example, arcuate side seams),
the horn's motion relative to the side seam may vary at different
positions along the side seam, but may remain in the same plane as
the packaging being welded.
[0079] Excess packaging may be mechanically trimmed at ends 693 and
694, for example, by laser-cutting, ultrasonic cutting, tool-die
degating, or waterj et cutting) such that the packaging portions
exterior the weld is removed. Alternatively, ultrasonic weld time
may be extended to cut the sealed ends 693 and 694 while sealing
the packaging portions. Once the packaging portions have been
welded along the periphery thus sealing the electrochemical battery
cell, the second controlled pressure is removed and the ultrasonic
welding horn is retracted. By this joining process, many
electrochemical battery cells may be consecutively sealed.
[0080] The present electrochemical battery cell configuration is
not restricted to a linear, planar construction, and instead may be
constructed in multiple shapes and sizes according to various
embodiments. The components of the electrochemical battery cell, as
well as the packaging, may be used to shape the electrochemical
battery cell to its desired shape.
[0081] In FIG. 7 there is shown the electrochemical battery cell
1000 in an arcuate shape. In this embodiment, two electrochemical
battery cells are connected in series. A first electrochemical
battery cell 1001 is both electrically and mechanically connected
to a second electrochemical battery cell 1002 at a connection point
1099. Both the first and second electrochemical battery cells are
shown resting on a first packaging portion 1040. Although not
shown, a second packaging portion is associated with the first
packaging portion to form a contiguous exterior packaging exterior
for the electrochemical battery cell.
[0082] The first electrochemical battery cell 1001 includes an
anode 1010 and a cathode 1020. The cathode is positioned in
electrical communication with a first electrochemical battery cell
cathode current collector 1030. The second electrochemical battery
cell 1002 similarly includes an anode 1011, and a cathode 1021. The
cathode 1021 is positioned adjacent and in electrical communication
with a second electrochemical battery cell cathode current
collector 1031. Both the anodes 1010 and 1011 possess associated
anode collector tabs which are both electrically and mechanically
connected to an anode end to conduct electrons.
[0083] At connection point 1099, there is shown an electrical and
mechanical connection between the first electrochemical battery
cell anode collector tab 1090 and the second electrochemical
battery cell cathode current collector 1031. The connection may be
welded or alternatively made so that electricity may flow between
both the first and second electrochemical battery cells, and so
that it provides a measure of strength so that the electrochemical
battery cell 1000 is fixed in the desired shape.
[0084] Each of these components in the electrochemical battery cell
extend along parallel arcuate paths or vectors. For example, the
anode 1010 and the anode 1011 extend along an arcuate vector the
length of which is approximately the length of the electrochemical
battery cell 1000. The cathode 1020 and the cathode 1021 extend
along a separate arcuate vector which extends in parallel to the
anode vector. The electrochemical battery cell 1000 may be
configured in the shown planar C-shape, or the arcuate shape may be
non-planar such as frustoconical or shaped to extend about a
spherical segment such as in the body of a contact lens. The shape
may be maintained by the rigidity of the components or
alternatively by inclusion of a structural portion which would be
included within the electrochemical battery cell but not be an
active component of the electrochemical reaction. For example, a
die cut titanium foil may be placed within the cell interior and
intermediate the first and second packaging portions. The foil
structural portion would act to maintain the desired shape of the
electrochemical battery cell while not significantly increasing the
non-active volume of the electrochemical battery cell.
[0085] In FIG. 8, there is shown a top sectional view of an
alternative embodiment of the electrochemical battery cell 1100. In
this embodiment, the electrochemical battery cell 1100 possesses a
cylindrical shaped electrochemical battery cell cathode current
collectors 1130 and 1131, which is shown positioned between the
electrochemical battery cell cathode 1120 and 1121 and a packaging
portion (not shown). Although not shown, the electrochemical
battery cell cathode current collector may alternatively be
disposed within or partially within the cathodes 1120 and 1121. The
wire shaped cathode current collectors in combination with the wire
shaped anodes provide a structural rigidity which obviates the need
for any non-active structural portion. The two electrochemical
battery cells 1101 and 1102 that comprise the electrochemical
battery cell 1100 are electrically and mechanically connected at
connection point 1199.
[0086] The wire shaped first electrochemical battery cell anode
1110 and the second electrochemical battery cell cathode current
collector 1131 may be joined by an ultrasonic weld as shown in FIG.
9. A compressive force holds the first electrochemical battery cell
anode 1110 and the second electrochemical battery cell cathode
current collector 1131 together while the ultrasonic welding
fixture 1198, which is representatively shown, acts to weld the two
wire shaped components to form a mechanically connected joint 1197.
Alternatively, the joint 1197 may be created using resistive
welding of another joining technique to create an electrically
communicating and mechanically sound joint. Another joining method
useful to encapsulate the electrochemical battery cell is laser
beam welding.
[0087] In FIG. 10, the electrochemical battery cell 1100 is shown
assembled with mechanically connected joint 1197 already formed and
divider 1196 created to segregate the cell interior of the first
and second electrochemical battery cells. A first and second
packaging portion 1140 and 1141 of equal size are placed with their
peripheries aligned and compressed to create a pressurized
periphery along the entire periphery of the packaging portions.
This may be done in a fixture which creates the pressurized
periphery at the same time, or sequentially with a moving jig or
fixture. While the periphery is compressed, a laser weld beam may
be passed along the electrochemical battery cell (in the direction
shown by vector W 1194) and the compressed periphery that passes
through the laser weld beam is welded by being melted and then
joined during re-solidification. The laser fires many heating
pulses per second forming separate overlapping spot welds that form
a seam along the packaging portion periphery. So as not to cause
local heating of the cell interior, battery components and
electrolyte an appropriate laser wavelength is chosen. For
polypropylene packaging material, 800 nm laser light is
preferred.
[0088] Another embodiment of the electrochemical battery cell 1 100
in FIG. 8 may be described with an alternative anode construction.
In this embodiment, the two electrochemical battery cells 1101 and
1102 that comprise the electrochemical battery cell 1100 are
electrically and mechanically connected by sharing a common
component. The anodes 1110 and 1111 each additionally comprise an
anode current collector which is electrically conductive. The
active anode material is then disposed onto or adjacent each anode
current collector to be in electrical communication, while
maintaining physical contact with the anode current collector. The
use of such an anode current collector enables it to also be used
as a cathode collector in an adjacently connected cell. For
example, the electrochemical battery cell anode current collector
(not shown) of the first electrochemical battery cell 1101 may
extend into the second electrochemical battery cell and be used as
the cathode current collector 1131 of the second electrochemical
battery cell. By use of this common cell component, the first
electrochemical battery cell 1101 and the second electrochemical
battery cell 1102 are electrically and mechanically connected
without the need for any weld or joint.
EXAMPLES
[0089] The compositions and processes described here, and ways to
make and use them are illustrated in the following examples.
Example 1
[0090] Substrate Preparation
[0091] A polycarbonate block was cut into sections. First and
second slots 2010, 2011 (each approximately
0.325-inch-long.times.0.008-inch-deep.times.0.0393-inch-wide) were
milled from the surface of the block 2000 as shown in FIG. 11 A. A
channel 2020 (between 0.007'' wide and 0.01'' wide) was then cut
intermediate the first and second slots 2010 and 2011, connecting
the two larger slots in line. Each finished slot is used to hold a
cell.
[0092] Cathode Preparation
[0093] A cathode sheet was prepared with a composition of 10% by
weight of carbon black (e.g. ACE Black AB100 from Soltex, Houston,
Tex., 83-85% by weight of fine electrolytic manganese dioxide (e.g.
Tronox of Stamford, Conn.) and the balance (5-7%) by weight PTFE
(e.g. 60 wt % dispersion of PTFE in water, available as TE3859 from
Dupont Polymers (Wilmington, Del.)--has 60.6%>solids in batch,
5.7%>wetting agent) The sheet was prepared by combining the
carbon black and manganese dioxide in a mixing container, and
mixing at 1,000 RPM for 3 minutes in a Thinky mixer Model Number
ARM-310 from Thinky of Laguna Hills, Calif. Then, roughly 1.05
grams of de-ionized water per gram of manganese dioxide was added
to the mixing container, which was again mixed at 1,000 RPM for 3
minutes. Then, the PTFE was added, and mixed at 200 RPM in the
mixer to disperse the PTFE, and then at 1,500 RPM to fibrillate the
PTFE, forming a coherent mass.
[0094] The resulting coherent mass was then kneaded until the
viscosity increases to the point where the material stiffness is
increased and the material is formable. Pieces of battery packaging
laminate consisting of a heat-resistant polymer outer layer, inner
aluminum foil core, and heat-sealable polymer inner layer (e.g.
packaging from Ultra Flex Corporation, Brooklyn, N.Y. The packaging
consists of a 0.001'' polyethylene heat-sealable layer on one side,
a 48 gauge (0.0005'') PET film on the other, and a 0.000316''
aluminum foil layer in between the two) were cut, and folded
lengthwise in half with the heat-resistant layer on the outside.
Pieces of the coherent mass were broken off, and placed on the
inside of the packaging folded lengthwise. The coherent mass was
rolled down using a jeweler's mill; the material was periodically
folded back on itself to enhance the fibrillation and bonding, and
at times the material was rotated 90 degrees in position against
the packaging to avoid its spilling out over the edge. Sheets of
roughly 150 micron thickness were prepared in this manner from the
cathode mix. This sheet was removed from the packaging material,
placed on a weigh boat, and air-dried at room temperature for a few
hours. Finally, the sheet was dried at 60.degree. C. between a few
hours and overnight.
[0095] Electrolyte Formulation
[0096] The electrolyte was first prepared using a mixture of 1.9 M
NH4Cl and 0.63 M CaCl2 In deionized water.
[0097] A gelled electrolyte was then prepared, as follows: an
amount of electrolyte was added to a beaker containing a stir bar.
This beaker was covered to prevent evaporation, and heated and
stirred on a stirring hot-plate until boiling. De-ionized water was
then added to replace the water which had evaporated as determined
by weighing. Sufficient agar was added to the beaker to produce a
mixture containing 97% by weight of the electrolyte, and 3% by
weight of agar. The electrolyte with agar was stirred on the
hotplate until the agar dissolved, then de-ionized water was added
to replace the water which had evaporated. The mixture was then
stirred and allowed to cool to room temperature, forming a soft,
cloudy gel.
[0098] Anode
[0099] Commercial pure zinc wire (e.g. (0.006'' pure zinc 99.95%
wire from California Fine Wire of Grover Beach, Calif.) was
obtained.
[0100] Cathode-Current Collector Assembly Procedure
[0101] Strips of cathode material roughly 7 mm long were cut from a
roughly 150 .mu..eta. thick piece of cathode material using a
blade. Then, thinner strips up to 3 mm or so wide (but at least 600
.mu..eta. wide) were cut from these strips. Short lengths (roughly
2 cm to 10 cm) of 0.002 inch diameter titanium wire (e.g. 0.050 mm
99.8% pure, hard temper titanium wire from Goodfellow of
Coraopolis, Pa.) were cut from a roll, and their ends were attached
to a plastic weigh boat with a small dot of epoxy, which was
allowed to cure. The assembly of the cathode is illustrated in FIG.
11B. The cathode strips 2040 were placed beneath the wire 2050
glued at one end 2051, and the wire was held taut over the strip.
With the wire held taut, a conductive glue coating (e.g. prepared
containing a polymeric binder and graphite flakes e.g. TIMCAL E-LB
1020, from Timcal of Westlake, Ohio). After the conductive coating
was dried enough to hold the wire 2050 to the surface of the
cathode sheet 2040, the end of the wire held taut was released.
After the coating was dried in air for a few hours, the wire was
cut away from one end 2051 of the assembly using a blade, the other
end of the wire was trimmed to a shorter length, and the cathode
strip 2040 was cut to a width of between 400 and 800 .mu..eta.--see
FIG. 11C.
[0102] Cell Assembly Procedure
[0103] The cathode-current collector assembly was glued into the
plastic substrate 2000 as shown in FIG. 11D using the conductive
coating/glue. The cathode-current collector assembly 2030 was set
in place with the wire facing down, to enable wetting the cathode
strip 2040 later. The cathode-current collector assembly 2030 was
first attached at the end 2012 of the slot 2010; the
cathode-current collector assembly 2030 was then flexed away from
the wall of the slot, additional conductive glue applied along the
wall, and the cathode-current collector assembly 2030 pressed
against the wall of the slot. If excess cathode material was
present which would prevent clearance between the zinc wire 2060
inserted later and the cathode, the excess material was removed.
Lengths of the zinc wire approximately 1.5 centimeters were cut and
straightened. They were placed in the slot 2010 and extended out
the open end of the cell; a small amount of epoxy was applied to
hold the wire in place. Then, epoxy was applied across the channel
opening of the slot, and polyimide tape (e.g. Kapton Brand) was
placed over the opening of the slot until the epoxy had cured. At
that point, the polyimide tape was removed. Then, electrolyte was
applied to cover the slot, and allowed to soak into the cathode. An
absorbent paper wipe was then used to remove all of the electrolyte
from the slot and the area of the substrate surrounding the slot,
except for that absorbed within the cathode. Gelled electrolyte was
then added to fill the slot. A piece of polyimide adhesive tape
(e.g. Kapton Brand) was placed over the top of the slot including
the end; this tape would normally extend end-to-end with two cells
vertically in place.
[0104] Then, two-part epoxy was used to cover over top of the
polyimide tape, and also to cover the ends of the block where the
wires exit the slot. Once the epoxy was cured, the polycarbonate
substrate was secured. Then, smooth-jawed alligator clips were used
to clip onto the wires (titanium and zinc) coming out of the cells,
taking care not to short the cells. Insulator was placed between
the clips to prevent them from touching. The insulators were
removed after the epoxy had gelled, but before it was fully
hardened. The cells were tested using ordinary battery test
equipment.
[0105] Table 1 is the performance and general description of the
electrochemical battery cell which was prepared as described in
Example 1.
TABLE-US-00001 TABLE 1 Capacity 1.40 .mu.A-h at 10 .mu.A Resistance
~800-1500.OMEGA.(typical) at 100 .mu.A Cell dimensions (slot 0.325
inch long .times. 0.008 inch deep x 0.0393 in substrate) inch wide
(~0.03 inch wide)-roughly 8.3 mm .times. 200 .mu.m .times. 1 mm
(~1.7 .mu.L) Open Circuit Voltage 1.5 V (nominal)
Example 2
[0106] Zinc Powder Anode
[0107] An anode using zinc as a bound powder was prepared. Zinc
powder (e.g. EEF grade from Umicore, Belgium) was prepared using
PTFE (from TE3859 dispersion) as a binder, and using Acetylene
Black (AB100%) as a conductive filler, with a composition of 5%
acetylene black, 5% PTFE, and 90% zinc by weight. 20 grams of zinc
were mixed by hand with 1.11 grams of acetylene black using a
plastic spatula to form a visually homogeneous mixture. This
mixture was then mixed using a Thinky ARM-310 mixer for three
minutes at 1000 RPM with 9 grams of de-ionized water. Then, 1.85
grams of 60% PTFE (TE3859) dispersion were added to the mixture,
which was mixed for three minutes at 200 RPM to disperse, then
three minutes at 1000 RPM to fibrillate to form a coherent mass.
This coherent mass was then kneaded and rolled between pieces of
battery packaging (from Ultra Flex Corporation, Brooklyn, N.Y. The
packaging consists of a 0.001'' polyethylene heat-sealable layer on
one side, a 48 gauge (0.0005'') PET film on the other, and a
0.000316'' aluminum foil layer in between the two). As with the
cathode sheet preparation, pieces of this laminate were cut, and
folded lengthwise in half with the heat-resistant layer on the
outside. Pieces of the coherent mass were broken off, and placed on
the inside of the packaging folded lengthwise. The coherent mass
was rolled down using a jeweler's mill; the material was
periodically folded back on itself to enhance the fibrillation and
bonding, and at times the material was rotated 90 degrees in
position against the packaging to avoid its spilling out over the
edge. Sheets of roughly 150 micron thickness were prepared in this
manner from the cathode mix. This sheet was removed from the
packaging material, placed on a weigh boat, and air-dried at room
temperature for a few hours. Finally, the sheet was dried at
60.degree. C. between a few hours and overnight.
[0108] Strips of the anode material approximately 300 microns
wide.times.150 microns thick.times.7-8 mm long were cut out, and
then attached using the conductive glue (Timcal E-LB 1020) to 50
micron titanium wire current collectors (e.g. from Goodfellow,
Coraopolis Pa.), as was done using for the cathode.
[0109] A cathode sheet consisting of 10 wt % acetylene black (AB
100), 5 wt % PTFE (from TE3859 dispersion), and 85% fine Mn02
(Tronox) was prepared as described in Example 1. Strips of material
roughly 10 mm wide.times.150 .mu..eta. thick were cut from this
sheet. Pieces of titanium foil were cut, and transparent tape was
applied to leave an approximately 7 mm wide strip of bare foil.
This foil was then painted over with conductive glue, and a strip
of the cathode sheet was pressed in while the glue was still wet.
After drying for roughly two hours to overnight at 60.degree. C.,
the foil was removed from the oven, and cut into strips and
inserted into an experimental holder; these strips with attached
cathode acted as the counter-electrode. The experimental sample
holder had a piece of zinc foil used as a quasi-reference
electrode, the bound zinc sheet attached to the 50.mu. titanium
wire acting as the working electrode, and the titanium foil with
cathode sheet attached was the counter electrode. All three
electrodes were together in a glass vial containing 1.9 M NH4Cl and
0.63M CaCl2 in de-ionized water electrolyte. A test was performed
on three samples, consisting of alternating open-circuit periods of
30 seconds with pulses of 5, 10, and 100 .mu.A applied to the
working electrode, followed by an open-circuit period of 30
seconds. The internal resistance of each electrode was taken as the
average of the resistance determined from the voltage drop at the
beginning and end of the 100 .mu.A pulse. The three samples had
resistances of 101, 183, and 145.OMEGA..
Example 3
[0110] Sealed Micro-Battery Construction
[0111] Forming Cell Components:
[0112] The cell components of the micro-battery assembled in this
example are further described by the dimensions and other physical
properties in Table 2.
TABLE-US-00002 TABLE 2 Micro-battery dimensions 10 mm in Length,
1.1 mm in width, 0.25 mm in thickness Micro-battery volume 2.75
cubic millimeters or 0.00275 cc Anode dimensions 7 mm in Length,
0.15 mm in width, 0.075 mm in thickness Cathode dimensions 7 mm in
Length, 0.55 mm in width, 0.12 mm in thickness Anode collector
thickness 0.03 mm in thickness Cathode collector thickness 0.03 mm
in thickness Electrolyte Volume 0.000642 cc Separator thickness
0.030 mm Packaging (each layer) 0.025 mm thickness
[0113] Preparing Cathode Sheet:
[0114] The cathode is prepared as follows. First, the dry powders
are mixed using a Waring laboratory blender. Mn02 (Tronox fine) and
BP2000 carbon black (Cabot) are mixed in a 500 g: 20.83 g ratio
(24:1).
[0115] Once the powders have been blended, they are then
transformed into a wet blend together with PTFE. The overall blend
composition is 24.27% dry powders (as mentioned above), 66.50%
de-ionized water, 4.86% Triton X-100 solution, and 4.37% solution
(DISP30, 60 wt % PTFE). The wet blend is then filtered using a
Buchner funnel under vacuum.
[0116] After the solid mass has been prepared, it is repeatedly
rolled using a jeweler's press, pasta roller, or similar to
fibrillate the PTFE chains further. After each rolling step except
for the last, the solid mass is re-constituted to prepare for the
next step.
[0117] A custom motorized roller setup is used to transform the
dough into a freestanding sheet. The material is fed through the
rollers a number of times, folding the material back onto itself
each time, and the gap between the rolls is reduced until the gap
is 0.12 mm. After this, the material is allowed to air-dry.
[0118] After the cathode is in the form of a freestanding sheet,
this sheet is then attached to a current collector using an
adhesive (such as EB-012 sold by Henkel, or E-LB 1020 sold by
Imerys). The titanium foil current collector may be roughened by,
for example, immersion in a boiling 10 weight % oxalic acid
solution for ten minutes. After roughening, the titanium foil is
removed, rinsed with de-ionized water, and allowed to dry
thoroughly.
[0119] An Epilog FiberMark 50 W pulsed Ytterbium fiber laser is
used to cut titanium foil (10 micron thickness) into strips which
are 400 .mu..eta. wide. The strips of cathode material are cut to
the desired width, and coated with EB-012 on one side. The coated
side of the cathode material is pressed onto the cut titanium.
Afterwards, the laser is used to cut the titanium and cathode into
individual freestanding components.
[0120] An electrolyte gel is prepared consisting of 25 wt % zinc
acetate, 0.2 wt % ammonium acetate with the balance water, gelled
with 6 wt % CMC (GA07 Walocel).
[0121] If desired, the cathode strip may be laminated to a
separator. To accomplish this, a cathode strip on titanium is
coated with electrolyte get and a piece of separator (25 .mu.m
thick Dreamweaver Silver.TM., available from Dreamweaver
International, Greer, S.C.) slightly wider than the cathode is
placed on top of the gelled electrolyte. The cathode and separator
are placed between two pieces of FEP (fluorinated ethylene
propylene) film, and the entire stack is then placed between two"
thick brass shim pieces. The stack is then run through an Apache
AL-13P laminating machine so that the cathode and separator are
mechanically bonded together.
[0122] The anode consists of a piece of zinc foil which is cut to
size using a technique such as laser or ultrasonic cutting.
Optionally, the zinc may be glued to a piece of roughened titanium
foil using a conductive adhesive prior to cutting; the roughened
titanium foil serves as the current collector for the anode. The
glue used may be a carbon-filled thermoset resin such as Atom
Adhesives AA-Carb 61. In the case where a thermoset resin is used,
it is applied to either the zinc or the titanium. It is also
possible to apply a thermoplastic resin paste, ink, or coating,
such as Creative Materials (Ayer, Mass.) 107-25, to one side of a
zinc strip and a titanium piece, and then to apply heat and
pressure to join the two together.
[0123] In some cases, it is desirable to have two cells in series
sharing a current collector, which acts as the anode current
collector for the first cell and the cathode current collector for
the second cell. In this case, the anode is attached to one part of
the current collector as described above while the cathode is
attached to the other side of the current collector, allowing bare
current collector on either end to enable feedthroughs.
[0124] Coated Film:
[0125] Coated packaging film refers to a polymeric film adjacent to
a film with a higher barrier than that of the polymeric material,
and where the said higher barrier film is formed on the polymeric
film or resides on an adjacent layer. The ceramic film may be
silicon oxide, aluminum oxide, titanium oxide, aluminum, gold,
titanium, or the like, and the film may be formed by CVD,
sputtering, plasma deposition, sol-gel, and the like. Optionally,
the coated film may include alternating layers of polymer and
higher barrier film deposited onto the initial higher barrier film.
A preferred example of the packaging film used is Ceramis CPP-004
(CelPlast, Toronto, Canada), which is polypropylene coated with a
silicon oxide barrier layer.
[0126] Packaging the Cell:
[0127] In general, the cell is normally sealed between two pieces
of polymer film, either coated or uncoated, which form the top and
bottom of the packaged cell. The first step in manufacturing the
cell is to lay down the cathode and cathode collector onto the
package, so that the cathode collector is in place on the package.
It is helpful to mechanically hold the cell components in place
during sealing, so that they do not shift to cause a short or
interfere with the sealing process. For example, it is possible to
attach the cell components to one of the packaging films using a
lightly tacky pressure sensitive film, such as 3M 80 spray adhesive
or Krylon Easy-Tack. One may also envision using a mechanical clamp
of some fashion to hold the cell components in place during the
sealing process. Once the cathode and collector are in place, the
cathode is wetted with electrolyte. The cathode may optionally be
laminated to a separator prior to cutting; if this is not the case,
a piece of separator is mechanically placed on top of the wet
cathode, and if necessary more electrolyte is applied.
[0128] At this point, the anode, (and optionally the anode
collector; the combination may be referred to as the anode
assembly) is then added to the cell. If the cathode is not
laminated to a separator as described above, the anode assembly may
be placed beside the cathode, and separated from the cathode by the
separator to prevent electrical shorting. Alternatively, whether or
not the cathode is laminated to a separator, the anode assembly may
be placed on top of the cathode and separator. In either case, it
is preferable for the separator to be wider than the cathode (or,
in the case where the cathode is laminated to the separator, equal
in width to the cathode), and for the anode assembly to be narrower
than the cathode. Once the anode, cathode, and separator are in
place, the cell is ready to be sealed, together with the top layer
of packaging.
[0129] The cell package has two kinds of seals--"feedthroughs," and
"sides." Feedthroughs are located on the shorter axes of the cell,
while sides are located on the longer axes of the cell (where said
axes may be linear, arcuate, or some other shape.) The functional
difference between feedthroughs and sides is that sides only need
to act as a hermetic seal, while feedthroughs need to act as a
hermetic seal and also enable an electrical terminal or terminals
to extend through them. If the shorter axis of the cell is very
small (for example less than 1.5 mm wide but generally greater than
300 microns wide), sides need to be much narrower than feedthroughs
to prevent an unacceptable internal volume loss. In general, the
sides may be between 20 .mu..eta. wide and 200 .mu..eta. wide,
dependent on the length of the shorter cell axis. At the same time,
it is possible to add material to the thickness of the feedthrough
(such as a dry film, coating, or adhesive) to ensure that the
feedthrough is hermetic even though it has to go around the current
collectors. It is acceptable to have the feedthrough seal occupy a
greater length, because of its location on the longer axis of the
cell which is generally at least 4 mm long.
[0130] Positioning of the electrodes relative to the seams is
critical when dealing with such small components. In general, the
position of the side seams and electrodes may be within 5% of the
width of the battery. For example, for a 1 mm wide battery
electrode and side seam positions would have a tolerance of less
than about .+-.0.05 mm. For the length of the battery, the
tolerance of the position of the bare part of the terminal which
goes through the feedthrough, the feedthrough adhesive, and the
feedthrough sealing mechanism may have a tolerance of roughly 25%.
For example, for a 1 mm wide seal the positioning may be within
.+-.0.25 mm. Note that the width of the bare terminal (the cathode
collector which is not coated with cathode material, and the anode
collector which is not covered by the anode) may extend the length
of the feedthrough seam.
[0131] Thus, different sealing methods are needed for the sides and
the feedthroughs. For sealing of the sides, ultrasonic welding is
preferred. Prior art ultrasonic welding of plastics takes place
with the motion of the ultrasonic horn largely perpendicular to the
vector of the seal, and this results in a wide joint which is
objectionable. If the oscillation motion of the ultrasonic horn is
predominantly in the same plane as the packaging material, a
relatively narrower seal may be achieved.
[0132] Alternatively, laser welding has been used to produce a seal
width of under 40 .mu..eta..
[0133] After welding the side seams, it is necessary to cut through
the packaging film around the sides in order to separate out the
battery package. In some cases, it is possible to simultaneously
weld and cut the side seams. For example, it is possible to
simultaneously seal and cut plastic films with a seal width of
under 50 .mu..eta. using ultrasonic welding when the direction of
the vibration is nearly parallel with the plane of the packaging
material. The vector created by the direction of sealing, which in
the case of the side seal is along the length of the battery
package. However, in certain cases it may be preferable to seal the
side seams in a first step, and then use another step to remove the
packaged cell from the packaging film. This second step may utilize
waterjet cutting, ultrasonic cutting, laser-cutting, tool-die
degating, or the like.
[0134] For the feedthrough, it is necessary to completely close off
the package around the current collector that extend through the
packaging. Because the active materials do not extend into the
feedthrough area, it is possible to add appreciable thickness to
the packaging within this area. For example, for a cell which is
250 microns thick with 25 micron packaging, roughly 200 microns of
material may be added to the feedthrough area to enhance
sealing.
[0135] A first alternative is to coat the current collectors and/or
the packaging with a polymer latex, such as Dow Hypod, Mitsui
Chemipearl, Aquaseal X 2088, or Joncryl prior to heat sealing.
Another alternative is to add a dry polymer film, such as is
manufactured by Fastel, to the seal area. A heat sealable polymer
may also be applied (for example, by screen printing) to the inner
surface of the packaging as a dispersion. Yet another alternative
is to apply a tacky film, such as Asphalt, Conseal 1400 (Fujifilm
Hunt), or Henkel PM040 to the packaging and/or current collectors
in the feedthrough area to enhance heat-sealing, or apply a curable
thermoset adhesive, such as a two-part adhesive, a heat-cured
adhesive, or a UV-cured adhesive, in the feedthrough area. For some
embodiments, it may be necessary to cut through the adhesive for
the feedthrough while welding the sides; this may be accomplished
by ultrasonic welding, which is known to remove contamination from
the weld area. This is because it is necessary for the feedthrough
seal to seal around the terminals of the cell, without any
gaps.
[0136] In some cases, the feedthrough adhesive (polymer latex, heat
seal film, tacky film, or thermoset adhesive) may be applied before
the pressure sensitive adhesive described above, and in some cases
it may be applied after, depending on the properties of the heat
seal adhesive. In the case of using a curable adhesive, once the
heat seal adhesive is in place, the sides of the cell may be sealed
using a technique such as ultrasonic welding or laser welding using
a fixture to substantially exclude electrolyte from the side seal,
followed by curing the adhesive in place to create the
feedthrough.
Example 4
[0137] To reduce the ingress of water into or out of the cell, the
osmotic pressure difference between the cell and its surroundings
may be reduced. The osmotic pressure may be approximated using the
Morse Equation, P=.SIGMA.inMnRT, where P is the osmotic pressure, T
is the absolute temperature, R is the ideal gas constant, Mn is the
concentration in moles per liter of the nth component of the
mixture, and in is the number of ions per formula unit obtained
upon dissolution of the nth component of the mixture. The
difference in osmotic pressure between two solutions may be
expressed as the difference in P, as defined above. Preferably,
this difference may be less than 25 atmospheres, or more preferably
less than 11 atmospheres.
[0138] We prepared an electrolyte solution of 25 wt % zinc acetate
and 0.2 wt % ammonium acetate with the balance comprising
de-ionized water (referred to as the "stock solution"). We also
produced two diluted electrolyte solution which may be referred to
as the 6.25% zinc acetate solution (1:3 ratio from stock solution)
and 1.8% zinc acetate solution (1:13 ratio from stock solution).
The solution which the battery is stored in proximity to is a
saline solution with a composition of 0.824% sodium chloride,
0.893%) boric acid, 0.23% sodium borate, and 0.01% sodium
ethylenediamine tetraacetate (EDTA) by weight, with the balance
comprising de-ionized water; this may henceforth be referred to as
"packing solution." An additional electrolyte was made comprising
0.822% sodium chloride, 1.463% boric acid, and 0.011% sodium borate
by weight, which may henceforth be referred to as "modified packing
solution." The osmotic pressure relative to the packing solution as
calculated using the Morse Equation is given below in Table 4.
[0139] Test Results for Different Solutions
[0140] Cells were prepared to establish performance of the various
electrolytes. Each cell used a piece of card stock as a backing to
provide stiffness, and the packaging consisted of a 0.001''
polyethylene heat-sealable layer on one side, a 48 gauge (0.0005'')
PET film on the other, and a 0.000316'' aluminum foil layer in
between the two (Ultra Flex Corporation, Brooklyn, N.Y.). To enable
heat sealing of the battery, pieces of dry heat sealable polymer
film (Fastel Adhesives & Substrate Products) were used, with a
window of 9 mm.times.1 mm cut out of one piece within the cell to
hold the battery components. The anode was cut out of 0.075 mm
thick zinc using an Epilog Fibermark laser; said anode was
comprised of a strip which was 0.25 microns wide. The cathode was
prepared as described earlier with a composition of 85% Mn02, 10%
carbon black, and 5% PTFE by weight. The cathode was laminated to a
cut titanium piece as described above. For these tests, the cathode
was 400 .mu..eta..+-.5% wide.times.130 .mu..eta..+-.5%
thick.times.8.5 mm.+-.0.5 mm long. The anode and cathode were
placed into the window in the dry heat sealable film such that they
were not in physical contact with each other.
[0141] To fill the cells, electrolyte was added to wet the cathode.
Gelled electrolytes prepared by mixing the electrolytes above with
between 1.8 and 5% by weight Walocel GA07 (Dow Chemical Company)
were added to fill the window within the dry film, and the cell was
packaged using heat sealing, with packaging film on both sides of
the cell. The cells were tested using a VMP3 (Bio-Logic) with a
test protocol of a 20 .mu.A constant current discharge down to a
cutoff voltage of 0.9V. The internal resistance was measured as the
voltage drop obtained from an initial 20 .mu.A pulse lasting three
seconds prior to discharging the battery.
[0142] In addition to electrochemical data, gassing data were
obtained to semi-quantitatively establish projected shelf life in
the various electrolytes. Gassing was obtained by cutting 0.075 mm
thick zinc into 0.13 mm wide strips using an Epilog Fibermark
laser, which were added to glassware designed to obtain gassing
rates. This glassware consists of a volumetric flask filled with
electrolyte solution, which is in contact with the zinc strips.
This flask is sealed with a wax-coated glass stopper. A graduated
section is attached and open to the neck of the volumetric flask,
with an opening exposed to ambient atmosphere; when hydrogen gas is
evolved it collects below the wax-filled section, which forces
electrolyte up into the graduated section, allowing the gassing
rate to be determined by measuring the position of the electrolyte
in the graduated section at different times. The wide portion of
the flask was held in a heated bath held at 45.degree. C., and the
gassing rate was determined based on the rise in electrolyte in the
graduated section. Because zinc corrosion is one of the major
factors impacting shelf life in carbon-zinc batteries, the gassing
rate may be taken as a proxy for shelf life assuming that zinc
corrosion is the main factor limiting shelf life. Data is
summarized in Table 3 below. As the cathode is the electrode
limiting capacity, data are normalized volumetrically to a cathode
size of 400 .mu..eta..times.8 mm.times.130 .mu..eta.. Each data
point is the average of ten cells tested. Notably, for those
solutions containing zinc acetate the pH increases with decreasing
concentration, while gassing rate decreases, and a substantial
capacity is retained. Furthermore, gassing is low in packing
solution and modified packing solution, even in the absence of
zinc.
TABLE-US-00003 TABLE 3 Open- Osmotic Gassing circuit pressure,
Capacity, rate, mL/g- Electrolyte pH voltage Resistance, .OMEGA.
atmospheres .mu.A-h day Stock 5.94 1.530 1080 75 180 0.798 solution
6.25% Zinc 6.27 1.518 1312 10 160 0.521 acetate solution 1.8% Zinc
6.79 1.511 2431 -5.0 90 0.500 Acetate Solution Packing 7.52 1.419
5040 0 80 0.158 Solution Modified 6.04 1.513 2840 1.8 120 0.189
Packing Solution
[0143] Exemplary Component Compositions
[0144] A wide variety of compositions may be used in the
electrochemical battery cell. Any combination of components would
be selected for electrochemical compatibility, and for the ultimate
use of the electrochemical cell. For example if biocompatibility is
required, components would be thus selected.
[0145] Approval of medical devices by regulatory agencies require
that a biocompatibility assessment be conducted to assure safety of
the device or material Biocompatibility classification is thus
obtained by testing according to certain guidelines, including ISO
0.10993, "Biological Evaluation of Medical Devices," and the japan
Ministry of Health, Labour and Welfare (MHLW) `Testing Methods to
Evaluate Biological Safety of Medical Devices," Notice from the
Office Medical Devices. The testing of the biocompatibility of a
device is intended to demonstrate that the device may not, either
directly or through the release of its material] constituents: (i)
produce adverse local or systemic effects; (ii) be carcinogenic; or
(iii) produce adverse reproductive and developmental effects. Some
materials have been well characterized chemically and physically in
the published literature and in the marketplace and have a long
history of safe use. Such materials may be considered biocompatible
and are thus preferred. Materials that are used in medical device
batteries may affect a human eye by touch, leak from the battery
due to, for example, an accident or an improper sealing of the
battery. Use of biocompatible materials minimizes any risk of such
complications occurring if the leaking or leached materials make
contact with the eye or other human tissues.
[0146] The anode is the electrode component which is oxidized in
the electrochemical battery reaction. In one embodiment, the anode
comprises zinc as the active component in the form of a contiguous
wire or thin cylinder. The zinc is preferably battery grade in that
it is free from impurities generally understood by those skilled in
the art to promote corrosion and other undesirable side reactions
in the battery. The zinc may also be alloyed with alloys such as
bismuth, indium, calcium, or aluminum to increase shelf life. Lead
in small amounts has also been shown to be an effective zinc alloy
material. Although thought of as non-biocompatible, the lead stays
within the zinc grain boundaries and is not dissolved in the
electrolyte. Thus, such added lead may not create a
biocompatibility issue. The anode wire also acts to collect the
electrons flowing from the anode and transport them out of the
electrochemical battery cell. To accomplish this dual role, excess
anode is preferably added to the battery to ensure the anode
remains contiguous. Zinc powder may be used as an alternative anode
material as is shown in Example 2.
[0147] The cathode is the electrode component which is reduced in
the electrochemical battery reaction, and when the electrochemical
battery cell is placed in a circuit with a load, the cathode
attracts electrons from the circuit. The preferred cathode material
may be manganese dioxide which is mixed with a conductor additive
and binder to form a cathode mix. It may be preferable to include
as much manganese dioxide in the cathode mix to maximize the
capacity of the electrochemical battery cell and to reduce the
necessary size of the cathode. The amount of cathode in the
electrochemical battery cell is determined relative the anode and
its active amount. The molar amounts of each the anode and cathode
are determined so that the cell reaction may be accomplished for
the desired duration. The form of the cathode is planar in one
embodiment, but may be cylindrical in an alternative embodiment.
The cylindrical cathode may be extruded or otherwise shaped while
being formed.
[0148] The conductor is used to enable electron flow between
cathode particles and from and to the cathode current collector.
The amount of conductor is preferably minimized to accomplish this
task as there is little benefit to adding excess conductor.
Conductors appropriate are graphite, expanded graphite, acetylene
black, carbon black, and other conductors known by those skilled in
the art. Preferably acetylene black is used in the present
invention as it provides the cathode mix a desired level of
electrolyte absorptivity.
[0149] Binder is used in the cathode mix to provide structure to
the cathode throughout the electrochemical battery cell life. The
binders ability to provide this structure may not be altered by the
electrolyte or by the expansion of the manganese dioxide. Preferred
binders include particulate Teflon.RTM. (PTFE) emulsion which may
be fibrillated during mixing of the cathode mix.
[0150] The cathode mix electrically communicates with the cathode
collector, and the purpose of the cathode collector is to both
electrically communicate electrons to and from the cathode but to
also provide structure to the electrochemical battery cell. A
titanium wire is the preferred structure for the cathode collector
as it adequately conducts and has the required rigidity in small
diameters. Titanium mesh, titanium ribbon, expanded mesh, braided
wire all are alternative cathode collector materials.
[0151] Electrolyte is selected for compatibility with the reactive
electrode materials. For the zinc anode and a manganese dioxide
cathode, a LeClanche electrolyte, or ammonium chloride NH4Cl
solution, zinc chloride ZnCl, zinc acetate and mixture thereof, are
one embodiment. For dilute solutions, acetate electrolytes, which
contain zinc acetate and optionally other acetates such as ammonium
acetates, are preferred due to zinc chloride's solubility behavior.
Salines, such as sodium chloride NaCl, magnesium chloride MgCl2 and
potassium chloride KCl solutions together with additives such as
sodium borate, boric acid and sodium ethylenediamine tetraacetate
may alternatively be used. For the gelled electrolyte,
carboxymethyl cellulose, agar, or an alternative gelling agent may
be used. The gelling agent is to increase the viscosity of the
electrolyte so that it remains within the cell at a location where
it is useful, namely between the anode and cathode.
[0152] The gelled electrolyte may be located throughout the cell
interior of the electrochemical battery cell, and is most
preferably located between the anode and cathode which are disposed
relative each other by a predetermined distance. This predetermined
distance may be calculated by those skilled in the art, but the
distance may allow for tolerances necessary to prevent short
circuits caused by the anode and cathode coming in contact with
each other. As there is no separator or other physical barrier
between the electrodes, a practical distance is necessary in this
embodiment. The gelled electrolyte viscosity does act to hinder
movement of the electrodes and its placement between the electrodes
both acts to enable ionic communication and to prevent movement of
the electrodes towards each other. The gelled electrolyte may also
enhance biocompatibility, by providing a physical barrier around
the electrodes. Particles moving from the electrodes are caught in
the gelled electrolyte and prevented from moving away from the
electrochemical battery cell or towards the other electrode. In
another embodiment a thin barrier may be placed between the anode
and cathode to prevent relative contact. The thin barrier may be
made of a separator material or an ionically conductive and
electronically insulating material.
[0153] An anode tab may be mechanically connected to the anode so
that it may electrically transport created electrons from the anode
to the negative terminal of the electrochemical battery cell. Using
an extension of zinc wire for this purpose may corrode or otherwise
affect biocompatibility. Therefore titanium or other corrosive
resistive conductive materials are appropriate to extend the anode
through any packaging material to provide the required external
electron conduit.
[0154] The electrochemical battery cell may be enclosed in a
packaging material to enclose the cell components to enhance shelf
life, restrict ionic, oxygen, and water migration into and out of
the cell, and to ensure biocompatibility. As the packaging material
is inert and plays no role in the performance of the battery,
minimizing the thickness and amount of the material is preferred. A
material that is inert and does not interfere with the cell
reactions is also preferred as is a material that is easily formed
into a contiguous exterior around the entire electrochemical
battery cell while enabling sealing of the terminal electrodes
which necessarily penetrate the packaging and protrude from the
packaging. The packaging material is also preferably easily formed
and sealed by high speed manufacturing processes. Pigmentation of
the packaging material may also be desired and this requirement may
inform the packing material selection.
[0155] Polypropylene may be preferred as a packaging material in
that it may be easily weldable via a variety of processes including
heat, ultrasonic and laser welding. In addition, polypropylene may
be adhesive--bondable and available in a variety of thicknesses and
densities. In addition, polypropylene may be impervious to the
preferred electrolyte compositions and may contribute to
biocompatibility. Alternative biocompatible polymers such as
polyurethane, poly-vinylpyrrolidone, silicone elastomers,
polyethylene, polytetrafluoro ethylene,
poly-(p-phenyleneterephthalamide), polyvinyl chloride,
polypropylene, polyolefins, polyesters, polyacrylates (including
polymethacrylates).
[0156] The battery exterior or the exterior surface of the
packaging material may also be coated to further render it
biocompatible. Appropriate biocompatible coatings may include
phosphorylcholine and poly-para-xylylenes, such as paralene C.
[0157] The coated film used as a packaging material may serve at
least two barrier functions, in addition to acting to maintaining
the physical integrity of the battery. The film may prevent
migration of salt ions, to prevent the loss of electrolyte ions in
the event that the battery is surrounded by liquid. The film may
also retard water transport, to prevent swelling of the battery.
For the case where the battery is enclosed in a sealed package
prior to use, the prevention of oxygen transport is not a critical
need; however, those skilled in the art will recognize that the
same sorts of coatings used to retard moisture transport may also
substantially retard oxygen transport.
[0158] Within the packaging industry, permeability to water of a
material or device is normally measured by subjecting one side of a
barrier film to a given relative humidity while keeping the other
side dry, for example by purging with dry gas, while maintaining a
constant temperature, and measuring the water transmitted across
the film from the side with controlled relative humidity to the dry
side expressed in terms of water vapor transmission rate (WVTR),
with units of mass/area*time at a given temperature and relative
humidity. For example, the units may be expressed as g/m2-day at
temperature in degrees Celsius and relative humidity.
[0159] For the preferred embodiment, the WVTR of the packaging may
be less than 1 g/m2-day, or more preferably less than 0.1 g/m2-day,
or still more preferably less than 0.02 g/m2-day, where said WVTR
is measured at between 85 and 100% Relative Humidity and between
20.degree. C. and 40.degree. C. Instruments for performing such
tests are available from, for example, MOCON Inc. (Minneapolis,
Minn.)
[0160] It may be noted, however, that conventional WVTR
measurements may only measure moisture transport normal to the
barrier film, i.e. through whatever barrier coating may be present.
Given a sealed package, however, it is possible for moisture to
transport through the seam, i.e. parallel to the plane of the
barrier film. This may be especially relevant where the seam of the
package is particularly narrow, for example less than 100 microns
wide. Thus, the barrier property of the polymer film itself, rather
than the coating, dominates the transport behavior of the side
seam, which may make a nontrivial contribution to overall moisture
transport into and out of the battery particularly for very small
batteries, for example those with a package having a surface area
of 0.5 cm2 or less. Therefore, it is preferable for the WVTR of the
polymer to be less than 10 g/m2-day, or more preferably less than 5
g/m2-day at a thickness of 25 microns, a temperature between
20.degree. C. and 40.degree. C., and a relative humidity between 85
and 100%.
[0161] Sealing methods for the packaging material include the
described ultrasonic and laser beam welding. Alternative sealing
methods include heat welding and the use of biocompatible
adhesives.
Additional Electrolyte Formulations
[0162] In some examples, an improvement in gassing of
microbatteries may be obtained by using more highly purified
chemicals (substituting 99.99% pure zinc acetate for 98% pure zinc
acetate in our electrolyte formulation.) Additional improvements
may be obtained by adding zinc chloride to a zinc acetate based
electrolyte which may also increase battery capacity significantly.
In some examples, this may be because of the enhanced utilization
of water and/or the reduced water content in the discharge products
when zinc chloride is incorporated into the electrolyte.
Polymer Package Mechanical Integrity
[0163] In some examples, a dry polymer film adhesive may provide a
reproducible, mechanically strong bond with convenient
manufacturing. In some examples, further improvement may be
obtained by using a heat sealable tape, comprised of polypropylene
or modified polypropylene on both sides of a polyester core. Such
materials may be applied in place of dry heat sealable polymer
film. In some examples a tape used to adhere terminals of
lithium-ion batteries to polypropylene heat sealable packaging,
available from Targray may be used. This tape may provide a
reproducible, strong mechanical bond between the current collectors
and the polypropylene film packaging.
[0164] An alternative dry heat sealable tape example may include a
tape intended for adhering lithium ion battery terminals to
polypropylene packaging. This tape may be obtained from MTI, For
each of the exemplary heat sealable tapes, it may be possible to
ultrasonically seal the sides of the package through the tape prior
to heat sealing the terminals, such that the sides of the cell were
joined together including in the region with the heat sealable
tape.
[0165] The bond between the heat sealable tape and the packaging
film may be improved by adjusting conditions for etching of the
titanium used in the electrode contacts. In some examples, it may
be useful to etch titanium by immersing it for ten minutes in a
boiling solution of 10 weight percent oxalic acid in water. In some
other examples, two additional protocols for etching--a
hydrofluoric acid based etch, and a hydrogen peroxide based etch;
may provide enhanced adhesion of titanium to polypropylene. In some
examples, improvement in bonding may be determined by a burst test
(weight was placed on a heat sealed polypropylene package with one
of the sides having a piece of the etched titanium with the
aforementioned heat sealable tape positioned on both sides of the
titanium between the titanium and the plastic packaging).
[0166] In some examples, Titanium foil may be cleaned by wiping its
surface with isopropanol. The resulting cleaned foil may then be
placed onto a series of plastic rods on a perforated substrate. The
foil may be immersed in a pickling solution containing 35 g/L 40 wt
% hydrofluoric acid, 23.6 g/L sodium sulfate, and 350 g/L
concentrated nitric acid, with the balance water. Subsequently, the
titanium may be rinsed with tap water. Then, the etched titanium
may be placed in a phosphate conversion bath comprised of 53 g/L
trisodium phosphate, 21 g/L potassium fluoride, and 32 g/L 40%
hydrofluoric acid solution for approximately two minutes for
example. The titanium may then be rinsed and placed in a vessel
filled with de-ionized water in a water bath held at 65.degree. C.
for a time period such as fifteen minutes. The titanium may then be
removed from the bath and dried in a drying oven prior to use.
[0167] In some examples, a hydrogen peroxide based etch may be
performed with a modified RAE etch.sup.i. The chemical composition
of the etch formulations may be varied, for example where etching
solutions may be formed with 2% by weight sodium hydroxide, and 1%,
2%, or 3% by weight of hydrogen peroxide, with the balance
de-ionized water. Subsequently, the solution may next be held in a
beaker in a water bath maintained at 60.degree. C. Titanium foil
may next be wiped with isopropanol for cleaning, and then racked
onto a series of plastic rods on a perforated substrate. The foil
may then be etched in one of the solutions for 5-20 minutes, then
removed and rinsed with de-ionized water. The cleaned foil may next
be allowed to dry in an oven.
[0168] Superior bonding conditions may be observed by
electrochemical testing performed by holding a sample of
cleaned/etched titanium foil at 1.55V against a piece of zinc foil
in an electrolyte solution including approximately 6.25% zinc
acetate, 0.5% ammonium acetate, and 10 ppm In.sup.3+ added as
indium sulfate.) It may be noted that the titanium etched with 1%
hydrogen peroxide as described may draw significantly less current
than unetched titanium. This may perhaps be due to a formation of
an oxide layer on the titanium surface during the hydrogen peroxide
etch, which may be called anodization.
[0169] In some examples, a titanium current collector may be
modified in the region where it is heat sealed resulting in
improvements of the mechanical integrity of the heat seal. In some
examples, the improvement may enables staking of heat seal tape
through the battery, reinforcing it. In some examples, the results
of modification by cutting holes in the terminus of the electrodes
may be tested by manually pressing on packaged cells near the
cathode terminal using a metal poking tool. In some examples,
qualitatively improved strength may be observed for cells with two
types of perforated cathode titanium current collectors than with
unperforated titanium cathode current collectors. The cells with
the perforated current collectors remained intact, while the cells
with the unperforated current collectors leaked electrolyte when
pressed. This may imply that the mechanical integrity of a battery
cell package may be enhanced by the perforation, which may lead to
increased shelf life.
Filling and Sealing Methods
[0170] As mentioned previously, one may use ultrasonic welding to
exclude electrolyte from a side seal. Also noted was the
possibility of using laser welding with an appropriate fixture to
accomplish a similar result. In some configurations, however, the
use of ultrasonic welding to seal a wet cell (a cell with
electrolyte present) may be problematic. The cell may not be able
to seal completely. Perhaps this may be because of an interaction
of the ultrasonic energy from the horn with the electrolyte within
a small, enclosed space creating localized pressure variations
which may damage the seal, particularly around the terminals.
[0171] In some examples, improvement may be achieved by changing
from a one-stage weld to a two-stage weld. In such an example,
where the majority of the cell perimeter was welded for a dry cell
using heat seals for the ends and an ultrasonic seal on the
perimeter, the cell was filled, and then the remaining small open
portion of the cell perimeter was sealed ultrasonically. Then the
cell may be degated, and the leads cleared of excess plastic flow
from heat sealing using a small knife.
Use of Adhesives to Hold Components in Alignment
[0172] In some examples, it may be helpful to temporarily hold
components in place, so that they do not move out of alignment in
subsequent steps. While mechanical clamping may be a solution, this
may have an issue in that it requires gripping in multiple
locations, and requires special fixturing for each step. In some
examples, a solution may involve using pressure sensitive
adhesives, such as 3M 75 to hold components in place. In some
examples, using a mixture of 0.5 wt % sodium carboxymethylcellulose
(Walocel 2000 GA 07, Dow) may help to ensure that the cathode,
separator, and anode are aligned with each other when stacked,
while still enabling electrolyte conduction.
[0173] In some examples, the solution may also include using very
small dots of nonconductive pressure sensitive adhesive (3M 75)
between layers. The adhesives may be applied by any number of
conventional methods, such as brushing or spraying as an aerosol
(for example, using a preformulated aerosol can or using a
conventional airbrush), with the use of a template or stencil if
necessary.
Improved Package Barrier Strength and Mechanical Strength Through
Electroless Plating
[0174] In some examples, a narrow side seam in the battery package
may create a region with poor barrier properties, enabling the
transport of moisture and gaseous species into and out of the cell.
Conventional batteries packaged in laminates ("pouch cells") may
have much wider seams on all sides. For example, the side seal of a
pouch cell may be larger than the entire width of a micro-battery
(2-4 mm per side, vs under .about.1 mm width for a micro-battery).
The wider seams, which may not be possible to incorporate in a
small micro-battery, may act as an effective moisture and gas
barrier due to width. Thus, an alternative solution is needed for
barrier strength with very narrow seams.
[0175] In some examples, a solution may involve overcoating the
micro-batteries with a conformal barrier layer using electroless
plating. There may be a range of techniques available for creating
a conformal hermetic barrier coating. Overcoating a miniaturized
carbon-zinc batteries, however, may present special challenges. The
presence of moisture within the battery electrolyte combined with
the imperfect barrier properties of the package may mean that there
may be a continual flux of moisture through the packaging to the
surface of the battery. This flux may act to contaminate the
surface. Furthermore, the imperfect packaging may enable outflow of
moisture. Furthermore, limits may be imposed by the melting point
of the plastic packaging (roughly 160.degree. C. for polypropylene)
which may limit the temperate possible for any coating method.
[0176] Vacuum techniques such as sputter deposition and thermal
evaporation which require a clean surface for deposition may also
be inferior for overcoating micro-batteries due to the continual
flux of moisture to the surface. And, atomic layer deposition may
be unsuitable for the same reason. Other techniques such as sol gel
coating and chemical vapor deposition may require exposure to
temperatures which may damage the battery.
[0177] In some examples, a desirable solution for improving barrier
effectiveness and mechanical strength may involve electroless
plating as a technique for creating a conformal barrier coating.
Electroless plating is a conventional technique, which can deposit
a conformal metal layer onto a conducting or nonconductive coating.
Electroless plating baths have been developed for depositing metals
such as nickel, copper, and tin onto plastic surfaces. The
electroless plated metal may then be further plated using
electroless plating or electroplating with a wide variety of
metals, including nickel, copper, tin, gold, silver, cadmium, and
rhodium. In some cases, because of cost, corrosion, and/or
mechanical concerns, it may be desirable to use a layered structure
incorporating more than one electroplate layer.
[0178] The coating may be made arbitrarily thick, and may
mechanically reinforce the battery in addition to acting as a
barrier. This mechanical reinforcement may force hydrogen out the
sides of the cell, reducing or eliminating bulging due to hydrogen
gas generation during zinc corrosion. To avoid the creation of a
short circuit between the battery terminals due to plating, it may
be necessary to mask one or both terminals using a nonconductive
material during the plating process.
[0179] In some examples a layer may be formed with electroless
plating where electroless plating and/or electroplating may be used
to create a roughly 1 mil (25 microns) conformal copper coating on
them. Platers' tape may be used to mask both terminals of these
batteries during plating to avoid short circuiting the batteries
during the plating processing.
[0180] The tape may next be removed from the terminals, and then
the batteries may be aged at room temperature at 50% relative
humidity. In order to make a comparison similar cells which had not
been copper plated were aged under the same conditions. The cells
were intermittently monitored by having their open-circuit voltage
measured and their resistance established by passing three pulses
of 20 .mu.A for 100 milliseconds. The cells may be deemed to have
failed when their resistance was over 20 k.OMEGA., as compared to
under 5 k.OMEGA. for a fresh cell. The electroless plated cells may
show significant improvement in lifetime over comparison non-plated
cells.
Anode Reinforcement:
[0181] In some examples, it may be observed that when sealing
micro-battery cells, the anode can bend, resulting in corrosion. To
remedy this, In some examples the anode may be reinforced by
bonding it to titanium foil using a conventional epoxy (JB-Weld
plastic adhesive.)
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