Chemically machined current collector design

A current collector in the form of a conductive substrate subjected to a special chemical etch on both major surfaces to provide a "basket weave" structure, is described. The basket weave structures has a lattice construction surrounded by a frame and comprising first strand structures intersecting second strand structures to provide a plurality of diamond-shaped openings or interstices bordered by the strands. The strand structures intersect or join with each other at junctions thereby forming the current collector as an integral unit.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to the conversion of chemical energy to 
electrical energy. More particularly, the present invention relates to a 
conductive substrate providing enhanced contact with an electrode active 
material. The improvement in electrode active contact is provided by 
chemically machining selected portions of the opposed major surfaces of 
the conductive substrate. The thusly fabricated substrate is particularly 
useful as a current collector in an electrochemical cell. 
2. Prior Art 
Presently, there are many different techniques for fabricating current 
collectors including subjecting a conductive foil substrate to mechanical 
expansion and perforating a conductive foil. However, mechanically 
expanded metal screens and perforated foils often have burrs which are 
potential contributors to battery shorting. Other typical state-of-the-art 
current collector designs, such as conventional chemical machining 
(etching or milling), electrolytic etching, and conductive foils provided 
with a vapor deposited bonding layer, attempt to increase the contact 
surface area without altering the generally planar configuration of the 
substrate workpiece. Maintaining the substrate having a planar surface 
structure limits the degree to which the contact surface area can be 
increased. In that respect, foil screen designs limit the variety of 
active material that can be contacted thereto. For example, adherence of 
pressed powders or flexible sheets of electrode active material to foil 
screens is virtually impossible. Finally, conventional woven fabric 
collectors are limited to minimum thicknesses required to maintain 
structural integrity. This detracts from improvements in reducing the 
passive volume of the fabric. 
SUMMARY OF THE INVENTION 
The present invention is, therefore, directed to a conductive substrate 
that serves as a current collector having improved contact or intimacy 
with an electrode active material without the problems characteristic of 
the various types of prior art collectors. The present current collector 
is provided by chemically etching a conductive foil to achieve the 
intimacy attributes of pulled mechanically expanded metal screens without 
burrs, to provide enhanced surface roughness characteristics that 
facilitate contact of the current collector with the electrode active 
material, to allow for support flexibility in selection of electrode 
material type, and to optimize reduction in the passive current collector 
material volume. 
Thus, it is an object of the present invention to provide a current 
collector design that achieves increased intimacy between the electrode 
active material and the collector screen, which in turn yields increased 
discharge efficiency. When an electrochemical cell containing electrodes 
built with the present current collector is used to power an implantable 
medical device such as a cardiac defibrillator, this results in higher 
pulse voltages, reduced charging times and provides for increased 
discharge capacity, thereby extending the medical device life. 
Another object of the present invention is to provide a current collector 
design that provides improved rapid delivery of energy capacity and 
prevents cell premature end of life. 
A further object of the present invention is to provide a current collector 
design that allows enhanced electrode flexibility, facilitating winding 
into cells having a jellyroll electrode assembly. 
Another object of the present invention is to provide a current collector 
that decreases the volume of the cell's passive parts, thereby increasing 
the active material content. 
Still another object of the present invention is to provide a current 
collector design that yields thinner finished electrodes facilitating cell 
assembly, and to provide a current collector design that renders wider use 
in applications with pulse amplitude requirements, such as implantable 
medical devices. 
Furthermore, another object of the present invention is to provide a 
current collector that reduces cell internal resistance. The reduction in 
internal resistance is due to an enhanced intimate contact between the 
current collector and the supported electrode active material which 
consequently enables the fabrication of jellyroll electrode assemblies. 
Such electrode assemblies require less current collector leads in 
comparison to prismatic electrodes assemblies. The reduction of current 
collector leads facilitates cell manufacturability by eliminating 
additional joining operations while enhancing cell reliability. 
According to the present invention, these objects are realized by 
chemically etching selected portions of the opposed major surfaces of the 
current collector to provide the screen with a "basket weave" 
configuration. 
These and other objects of the present invention will become increasingly 
more apparent to those skilled in the art by reference to the following 
description and to the appended drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Throughout the various embodiments of the present invention, like parts, 
components, portions or assemblies are assigned like numerical 
designations. 
Turning now to the drawings, FIGS. 1 to 5 show one embodiment of a 
conductive substrate 10 according to the present invention. The conductive 
substrate 10 is particularly useful as a current collector in an 
electrochemical energy storage device and has a generally elongated, 
rectangular shape provided with a perimeter frame 12 and an integral 
interior reticulum or grid structure 14 bordered by the frame. Tabs 16, 18 
and 20 extend from the frame 12, and in the preferred embodiment of the 
conductive substrate 10 are integral therewith. However, if desired, the 
tabs 16, 18 and 20 can be separate parts that are subsequently welded, 
fused or otherwise secured to the conductive substrate 10 at the frame 12 
thereof. The tabs provide for connecting an electrode (not shown) 
comprising the conductive substrate to a cell terminal. Also, the 
conductive substrate 10 may have a shape other than the rectangular one 
shown depending on the construction or configuration of the cell in which 
the substrate will be incorporated. 
FIG. 2 is an enlarged view of the grid structure 14 having a lattice 
construction surrounded by the frame 12 and comprising first strand 
structures 22 intersecting second strand structures 24 to provide a 
plurality of diamond-shaped openings or interstices 26 bordered by the 
strands. The strand structures 22,24 intersect or join with each other at 
junctions 28 thereby forming the grid structure as an integral unit. 
According to the present invention, the grid structure 14 is fabricated by 
the controlled dissolution or corrosion of a sheet-like or foil shaped 
workpiece through contact with an etchant in a chemical machining or 
photochemical machining process. In that respect, the conductive substrate 
10 begins as conductive coil stock (not shown) having generally planar 
opposed major surfaces in an uncoiled, laid flat orientation. The coil 
stock preferably has a thickness of about 0.001 to about 2 millimeters and 
is cut into sheets from which a multiplicity of current collectors will 
subsequently be fabricated in a batch operation. The cut sheets are 
subjected to a precleaning process such as a chromic acid bath to remove 
scale and then run through a pumice slurry that serves to render the 
workpiece sheets having a clean condition, ready for processing after 
being rinsed and dried. 
A dry film resist or mask is then applied to selected portions of each 
major surface of the workpiece to thereby protect the coated surfaces from 
the chemical action of the subsequent chemical machining or photochemical 
machining process. As is well known by those skilled in the art, the 
protective resist is inert to the etchant compounds, is able to withstand 
the heat from etching, adheres well to the workpiece and is easily and 
inexpensively removed after etching. The resist must also be tough enough 
to withstand handling, rigid enough to prevent drooping when undercut, yet 
scribe easily or spray cleanly. Numerous synthetic or rubber-base resist 
materials are available in a wide variety of types and trade names. 
To fabricate the conductive substrate 10, the resist is applied to a first 
major surface of the workpiece in the configuration of the frame 12 and 
the strand structures 22 and then to a second, opposite major surface of 
the workpiece in the configuration of the frame 12 and the strand 
structures 24. Preferably, the resist is applied to the workpiece as a 
photoresist by a photographic technique. Such a process begins with a 
photo-sensitive resist applied to the entire area of each major surface of 
the workpiece followed by air drying or oven baking the resist contacted 
workpiece. Next, contact printing from a workpiece negative of the to be 
produced grid structure 14 is followed by photographic development and 
drying. The workpiece is next moved through an etchant bath or otherwise 
contacted by the etchant solution such as by spraying. In the case of a 
titanium workpiece, for example, the etchant comprises a hydrogen 
fluoride/nitric acid solution. Those skilled in the art will readily 
recognize etchant solutions that are useful with other conductive 
substrate materials useful with the present invention such as molybdenum, 
tantalum, niobium, cobalt, nickel, stainless steel, tungsten, platinum, 
palladium, gold, silver, copper, chromium, vanadium, aluminum, zirconium, 
hafnium, zinc and iron, and the like, and mixtures and alloys thereof. 
To form the present conductive substrate 10, the workpiece with the applied 
resist pattern having the shape of the frame 12 surrounding the grid 
structure 14 is contacted with the etchant for a period of time sufficient 
to etch away from each major surface a thickness of the workpiece material 
somewhat greater than one-half the total thickness of the workpiece. That 
way, those areas not provided with resist on either major surface of the 
workpiece will be completely removed to provide the diamond-shaped 
openings 26. 
As shown in FIGS. 6 to 9, another embodiment of a conductive substrate 10A 
according to the present invention comprises a grid structure 14A wherein 
the workpiece is not contacted with the etchant for a period of time 
sufficient to completely etch away the material bordered by the frame 12 
and the strand structures 22 and 24 to provide the openings 26. Instead, 
the areas where the openings 26 would reside is thinned or reduced in 
thickness but not etched completely through to provide substrate portions 
29 having a thickness substantially less than that of the workpiece 
material. Such a construction might be useful when the fabricated 
workpiece is intended for use as a current collector contacted with an 
electrode active material in a spray coating process, such as described in 
U.S. Pat. No. 5,716,422 to Muffoletto et al., which is assigned to the 
assignee of the present invention and incorporated herein by reference. 
After the workpiece has been chemical machined to the desired extent to 
provide the grid structure 14 (FIGS. 1 to 5) having the diamond-shaped 
openings 26 bordered by the frame 12 and the first and second strand 
structures 22 and 24, or to provide the grid structure 14A (FIGS. 6 to 9) 
having the frame 12 and the strands 22,24 bordering interior substrate 
portions 29 of a reduced thickness, the resist material is removed in an 
aqueous stripping solution. After rinsing and inspection, the individual 
conductive substrates 10 or 10A are cut or otherwise removed from the 
workpiece sheet and are ready for incorporation into an electrochemical 
energy storage device. In particular, the thusly formed conductive 
substrates can be used to fabricate either the anode or the cathode of a 
primary or secondary electrochemical cell or battery. 
As shown in FIGS. 2 to 5, in its finished form, the conductive substrate 10 
has the substantially parallel first strand structures 22 intersecting the 
second strand structures 24 at an angle indicated at 38 of about 90 
degrees to about 15 degrees. Each of the strands 22 provide the first 
major surface of the conductive substrate 10 having a relatively smooth 
outer surface 22A extending longitudinally along the strand 22 length and 
joined to the frame 12 where the resist was located. The cross-sectional 
view of FIG. 3 shows that the outer surface 22A of the first strand 22 
extends to a step 30 that meets a web 32 connecting to an adjacent step 30 
and first strand portion 22. The web 32 is the inner surface of the 
opposite second strand 24 and has a thickness measured to the opposite 
outer strand surface 24A less than one-half that of the total thickness of 
the coil stock workpiece. Similar to that of the steps 30, the web 32 is 
provided with a pitted or roughened surface texture brought about by the 
chemical action of the etchant corroding the workpiece material in the 
selected areas not protected by the resist mask. 
On the second, opposite major surface of the current collector 10, each of 
the strands 24 has a relatively smooth outer surface 24A extending 
longitudinally along the strand 24 length and joined to the frame 12 where 
the resist was located. As shown in FIG. 5, moving in a lateral direction 
across the short axis of any one of the strands 24, the outer surface 24A 
of the second strand extends to a step 34 that meets a web 36 connecting 
to an adjacent step 34 and second strand 24. As with web 32, web 36 is the 
inner surface of the opposite first strand 22 and has a thickness measured 
to the opposite outer strand surface 22A less than one-half that of the 
total thickness of the workpiece. The web 36 and steps 34 also have a 
pitted or roughened surface texture provided by the corrosive action of 
the etchant. 
As shown in FIGS. 6 to 9, the finished conductive substrate 10A comprises 
the grid structure 14A having the substantially parallel first strand 
structures 22 intersecting the second strand structures 24 at an angle of 
about 90 degrees to about 15 degrees. Each of the strands provide the 
first major surface of the conductive substrate 10A having a relatively 
smooth outer surface 22A extending longitudinally along the strand 22 
length and joined to the frame 12 (not shown in FIGS. 6 to 9) where the 
resist was located. The first strand 22 extends to the step 30A (FIG. 7) 
that meets a web 32A connecting to an adjacent step 30A and first strand 
portion 22. While not shown in the drawings, the second strand 24 
similarly extends to a step 34A that meets a web 36A connecting to an 
adjacent step 34A and second strand portion 24. This embodiment of the 
present invention includes substrate portions 29 in lieu of the openings 
26 of substrate 10. In particular, the cross-sectional view of FIG. 8 
shows that the first strand 22 extends to a step 30A that meets a first 
side 29A of the substrate portion 29 connecting to an adjacent step 30A 
and first strand portion 22. The opposite, second side 29B of the 
substrate portion 29 meets the face 24B of a second strand portion 24. The 
cross-sectional view of FIG. 9 shows that the second strand 24 extends to 
a step 34A that meets the second side 29B of the substrate portion 29 
connecting to an adjacent step 34A and second strand portion 24. The 
opposite, first side 29A of the substrate portion 29 meets a face 22B of 
the first strand portion 22. 
Thus, those skilled in the art will realize that the selective chemical 
machining of the workpiece provides the conductive substrates 10 and 10A 
having a "basket weave" configuration provided by the intersecting strands 
22,24. This construction provides for enhanced contact between the 
conductive substrate and the electrode active material, particularly at 
those locations roughened by the corrosive action of the etchant on the 
workpiece. Further, the chemically machined conductive substrates 10, 10A 
do not have burrs which can contribute to short circuit conditions, and 
the portions of the workpiece removed by the etchant provide for increased 
amounts of active materials. 
As is readily apparent from the previous description, the strands 22, 24 of 
substrates 10 and 10A are substantially co-planar with the respective 
first and second major surfaces of the frame 12. However, that is not 
necessary. If desired, the outer surfaces 22A, 24A of the strands 22, 24 
can be recessed somewhat from the first and second major frame surfaces. 
Such a construction directed to another embodiment of a conductive 
substrate 10B according to the present invention is shown in FIGS. 10 to 
12 and requires an additional masking step wherein the opposed major 
surfaces 12A and 12B of the frame 12 are masked first and the interior 
etched, followed by a second masking of the strand pattern and then 
etching as described above. The resulting grid structure 14B comprises 
first strand structures 40 intersecting second strand structures 42 to 
provide a plurality of diamond-shaped openings or interstices 44 bordered 
by the strands. The strands 40, 42 intersect or join with each other at 
junctions 46 thereby forming the grid structure as an integral unit. 
Particularly, each of the strands 40 provide the first major surface of the 
conductive substrate 10B having a chemically machined, roughened outer 
surface 40A extending longitudinally along the strand length to a step 48 
that meets the first major surface 12A of the frame 12. The 
cross-sectional view of FIG. 12 shows that the pitted and roughened outer 
surface 40A of the first strand 40 extends to a step 50 that meets a 
pitted and roughened web 52 connecting to an adjacent step 50 and first 
strand 40. The web 52 is the inner surface of the opposed, second strand 
42. Similarly, each of the second strands 42 provide the second major 
surface of the substrate 10B having a chemically machined roughened outer 
surface 42A extending longitudinally along the strand length to a step 54 
that meets the second major surface 12B of the frame 12. While not shown 
in the drawings, the pitted and roughened outer surface 42A of the second 
strands 42 extends to a step that meets a pitted and roughened web 
connecting to an adjacent step and second strand 42. Again, the web is the 
inner surface of the opposed, first strand 40. The construction of grid 
structure 14B having the chemical machined outer surfaces 40A, 42A of 
respective strands 40, 42 in addition to the connecting web sections 
provides additional treated surface area for enhanced contact to an 
electrode active material. 
Also, while the grid structures 14, 14A and 14B are shown having the 
respective strand structures parallel to each other, that is not 
necessary. Those skilled in the art will understand that the strands need 
not be parallel but can have a variety of shapes including wavy, 
sinusoidal, concentric, zig-zag among a myriad of others. However, 
according to the present invention, the strands and the like are at least 
partially separated from each other by regions of reduced thickness such 
as the webs 32, 36 of substrate 10. It is also contemplated by the scope 
of the present invention that there can be connecting portions (not shown) 
extending between adjacent strands wherein the connections have an outer 
surface substantially co-planar to that of the side-by-side strands. 
Examples of electrode active materials that may be contacted to a "basket 
weave" conductive substrate to provide an electrode according to the 
present invention include metals, metal oxides, metal sulfides and mixed 
metal oxides. While not necessary, the electrode active material is 
preferably coupled with an alkali metal anode. Such electrode active 
materials include silver vanadium oxide, copper silver vanadium oxide, 
manganese dioxide, titanium disulfide, copper oxide, copper sulfide, iron 
sulfide, iron disulfide, cobalt oxide, nickel oxide, copper vanadium 
oxide, and other materials typically used in alkali metal electrochemical 
cells. Carbonaceous materials such as graphite, carbon and fluorinated 
carbon, which are useful in both liquid depolarizer and solid cathode 
primary cells and in rechargeable, secondary cells, are also useful with 
the present conductive substrate. 
Thus, the present invention further comprises taking about 80 to about 99 
weight percent of an already prepared electrode active material in a 
finely divided form and providing a slurry comprising the material. Prior 
to contact with the "basket weave" conductive substrate of the present 
invention, however, the finely divided electrode material is preferably 
mixed with up to about 10 weight percent of a binder material, preferably 
a thermoplastic polymeric binder material. The thermoplastic polymeric 
binder material is used in its broad sense and any polymeric material, 
preferably in a powdered form, which is inert in the cell and which passes 
through a thermoplastic state, whether or not it finally sets or cures, is 
included within the term "thermoplastic polymer". Representative materials 
include polyethylene, polypropylene and fluoropolymers such as fluorinated 
ethylene and propylene, polyvinylidene fluoride (PVDF) and 
polytetrafluoroethylene (PTFE), the latter material being most preferred. 
Natural rubbers are also useful as the binder material with the present 
invention. 
In the case of a primary, solid cathode electrochemical cell, the cathode 
active material contacted to the "basket weave" conductive substrate is 
further combined with up to about 5 weight percent of a discharge promoter 
diluent such as acetylene black, carbon black and/or graphite. A preferred 
carbonaceous diluent is Ketjenblack.RTM. carbon. Metallic powders such as 
nickel, aluminum, titanium and stainless steel in powder form are also 
useful as conductive diluents. 
Similarly, if the active material is a carbonaceous material serving as the 
cathode current collector in a primary, liquid depolarizer cell or a 
carbonaceous counterelectrode in a secondary cell, the electrode material 
preferably includes a conductive diluent and a binder material in a 
similar manner as the previously described primary, solid cathode 
electrochemical cell. 
To form the electrode active slurry, about 94 weight percent of the cathode 
material, regardless of whether it is a carbonaceous material or one or 
more of a mixture of the other previously described cathode active 
materials, is combined in a twin screw mixer with a dispersion of about 0 
to 3 weight percent of a conductive diluent, about 1 to 5 weight percent 
of a powder fluoro-resin binder and a high permittivity solvent such as a 
cyclic amide, a cyclic carbonate or a cyclic ester. 
After mixing sufficiently to ensure that the conductive diluent and the 
binder material are completely dispersed throughout the admixture and to 
otherwise completely homogenize the various constituents, the electrode 
admixture is removed from the mixer as a slurry containing about 14% 
solids, by volume. The step of subjecting the electrode admixture to the 
mixer to form the slurry can also include the addition of a liquid 
electrolyte. The electrode admixture slurry has a dough-like consistency 
and is preferably contacted onto the opposed sides of the "basket weave" 
conductive substrate of the present invention. 
The thusly formed cathode laminate is heated to a temperature of between 
about 80.degree. C. to about 130.degree. C. and more preferably to about 
110.degree. C., for a period of about 30 minutes to about 60 minutes. The 
heating step is preferably carried out under vacuum and serves to remove 
any residual solvent from the cathode material. Heating further serves to 
plasticize the binder material to ensure the structural integrity of the 
newly manufactured electrode laminate. The electrode laminate can then be 
stored for later use, or is immediately useable in an electrochemical 
cell. After drying to remove all residual water from the slurry contacted 
to the conductive substrate, the resulting anhydrous active admixture is 
calendared under a pressure of about 40 tons/inch.sup.2 to laminate the 
active admixture to the "basket weave" conductive substrate of the present 
invention. 
An alternate preferred method for providing an electrode is to form the 
blended electrode active admixture into a free-standing sheet prior to 
being contacted to the present "basket weave" conductive substrate. One 
preferred method of preparing a cathode material into a free-standing 
sheet is thoroughly described in U.S. Pat. No. 5,435,874 to Takeuchi et 
al., which is assigned to the assignee of the present invention and 
incorporated herein by reference. Other techniques for contacting the 
active material to the conductive substrate includes rolling, spreading or 
pressing the admixture thereto. 
Cathodes prepared as described above are flexible and may be in the form of 
one or more plates operatively associated with at least one or more plates 
of anode material, or in the form of a strip wound with a corresponding 
strip of anode material in a structure similar to a "jellyroll". 
The anode is of a metal selected from Group IA, IIA or IIIB of the Periodic 
Table of the Elements, including lithium, sodium, potassium, etc., and 
their alloys and intermetallic compounds including, for example, Li--Si, 
Li--Al, Li--B and Li--Si--B alloys and intermetallic compounds. The 
preferred anode comprises lithium, and the more preferred anode comprises 
a lithium alloy such as a lithium-aluminum alloy. However, the greater the 
amount of aluminum present by weight in the alloy the lower the energy 
density of the cell. 
The form of the anode may vary, but preferably the anode is a thin metal 
sheet or foil of the anode metal, pressed or rolled on a metallic anode 
current collector, i.e., preferably comprising nickel, to form an anode 
component. Preferably, the anode current collector is of the present 
"basket weave" construction. In the exemplary cell of the present 
invention, the anode component has an extended tab or lead of the same 
material as the anode current collector, i.e., preferably nickel, 
integrally formed therewith such as by welding and contacted by a weld to 
a cell case of conductive metal in a case-negative electrical 
configuration. Alternatively, the anode may be formed in some other 
geometry, such as a bobbin shape, cylinder or pellet to allow an alternate 
low surface cell design. 
An electrochemical cell having an alkali metal-containing electrode serving 
as an alkali metal anode, or an alkalated cathode body and a carbonaceous 
counterelectrode according to the present invention further includes a 
separator provided therebetween. The separator is of electrically 
insulative material, and the separator material also is chemically 
unreactive with the anode and cathode active materials and both chemically 
unreactive with and insoluble in the electrolyte. In addition, the 
separator material has a degree of porosity sufficient to allow flow 
therethrough of the electrolyte during the electrochemical reaction of the 
cell. Illustrative separator materials include fabrics woven from 
fluoropolymeric fibers including polyvinylidene fluoride, 
polyethylenetetrafluoroethylene, and polyethylenechlorotrifluoroethylene 
used either alone or laminated with a fluoropolymeric microporous film. 
Other suitable separator materials include non-woven glass, polypropylene, 
polyethylene, glass fiber materials, ceramics, a polytetrafluoroethylene 
membrane commercially available under the designation ZITEX (Chemplast 
Inc.), a polypropylene membrane commercially available under the 
designation CELGARD (Celanese Plastic Company, Inc.) and a membrane 
commercially available under the designation DEXIGLAS (C. H. Dexter, Div., 
Dexter Corp.). 
The electrochemical cell of the present invention further includes a 
nonaqueous, ionically conductive electrolyte which serves as a medium for 
migration of ions between the anode and the cathode electrodes during the 
electrochemical reactions of the cell. The electrochemical reaction at the 
electrodes involves conversion of ions in atomic or molecular forms which 
migrate from the anode to the cathode. Thus, nonaqueous electrolytes 
suitable for the present invention are substantially inert to the anode 
and cathode materials, and they exhibit those physical properties 
necessary for ionic transport, namely, low viscosity, low surface tension 
and wettability. 
Suitable nonaqueous electrolyte solutions that are useful in both primary 
and secondary cells having an alkali metal electrode and a 
counterelectrode of a solid material contacted to a "basket weave" 
conductive substrate preferably comprise a combination of a lithium salt 
and an organic solvent system. More preferably, the electrolyte includes 
an ionizable alkali metal salt dissolved in an aprotic organic solvent or 
a mixture of solvents comprising a low viscosity solvent and a high 
permittivity solvent. The inorganic, tonically conductive salt serves as 
the vehicle for migration of the alkali metal ions to intercalate into the 
carbonaceous material. Preferably the ion-forming alkali metal salt is 
similar to the alkali metal comprising the anode. Suitable salts include 
LiPF.sub.6, LiBF.sub.4, LiAsF.sub.6, LiSbF.sub.6, LiClO.sub.4, 
LiAlCl.sub.4, LiGaCl.sub.4, LiC(SO.sub.2 CF.sub.3).sub.3, LiO.sub.2, 
LiN(SO.sub.2 CF.sub.3).sub.2, LISCN, LiO.sub.3 SCF.sub.2 CF.sub.3, 
LiC.sub.6 F.sub.5 SO.sub.3, LiO.sub.2 CCF.sub.3, LiSO.sub.3 F, LiB(C.sub.6 
H.sub.5).sub.4 and LiCF.sub.3 SO.sub.3, mixtures thereof. Suitable salt 
concentrations typically range between about 0.8 to 1.5 molar. 
In a liquid depolarizer/catholyte cell, suitable active materials such as 
sulfur dioxide or oxyhalides including phosphoryl chloride, thionyl 
chloride and sulfuryl chloride are used individually or in combination 
with each other or in combination with halogens and interhalogens, such as 
bromine trifluoride, or other electrochemical promoters or stabilizers. 
In other electrochemical systems having a solid cathode or in secondary 
cells, the nonaqueous solvent system comprises low viscosity solvents 
including tetrahydrofuran (THF), methyl acetate (MA), diglyme, trigylme, 
tetragylme, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), 
1,2-dimethoxyethane (DME), diisopropylether, 1,2-diethoxyethane, 1-ethoxy, 
2-methoxyethane, dipropyl carbonate, ethyl methyl carbonate, methyl propyl 
carbonate, ethyl propyl carbonate and diethyl carbonate, and mixtures 
thereof, and high permittivity solvents include cyclic carbonates, cylic 
esters and cyclic amides such as propylene carbonate (PC), ethylene 
carbonate (EC), butylene carbonate, acetonitrile, dimethyl sulfoxide, 
dimethyl formamide, dimethyl acetamide, .gamma.-butyrolactone (GBL), 
.gamma.-valerolactone and N-methyl-pyrrolidinone (NMP), and mixtures 
thereof. In the present invention, the preferred alkali metal is lithium 
metal. For a solid cathode, primary cell and a secondary cell, the 
preferred electrolyte is LiAsF.sub.6 or LiPF.sub.6 in a 50:50, by volume, 
mixture of PC/DME. For a liquid depolarizer cell, the preferred 
electrolyte is 1.0M to 1.4M LiBF.sub.4 in T-butyrolactone (GBL). 
The preferred form of a primary alkali metal/solid cathode electrochemical 
cell is a case-negative design wherein the anode is in contact with a 
conductive metal casing and the cathode contacted to the "basket weave" 
conductive substrate serving as the current collector according to the 
present invention is the positive terminal. In a secondary electrochemical 
cell having a case-negative configuration, the anode 
(counterelectrode)/cathode couple is inserted into the conductive metal 
casing such that the casing is connected to the carbonaceous 
counterelectrode "basket weave" current collector according to the present 
invention, and the lithiated material is contacted to a second current 
collector, which also preferably has the "basket weave" configuration. In 
either case, the current collector for the lithiated material or the 
cathode electrode is in contact with the positive terminal pin via a lead 
of the same material as the current collector which is welded to both the 
current collector and the positive terminal pin for electrical contact. 
A preferred material for the casing is titanium although stainless steel, 
mild steel, nickel-plated mild steel and aluminum are also suitable. The 
casing header comprises a metallic lid having an opening to accommodate 
the glass-to-metal seal/terminal pin feedthrough for the cathode 
electrode. The anode electrode or counterelectrode is preferably connected 
to the case or the lid. An additional opening is provided for electrolyte 
filling. The casing header comprises elements having compatibility with 
the other components of the electrochemical cell and is resistant to 
corrosion. The cell is thereafter filled with the electrolyte solution 
described hereinabove and hermetically sealed such as by close-welding a 
stainless steel plug over the fill hole, but not limited thereto. The cell 
of the present invention can also be constructed in a case-positive 
design. 
The following examples describe the manner and process of an 
electrochemical cell according to the present invention, and set forth the 
best mode contemplated by the inventors of carrying out the invention, but 
are not construed as limiting. 
EXAMPLE 1 
Lithium anode material was pressed on nickel current collector screen and a 
cathode admixture comprising, by weight, 94% silver vanadium oxide mixed 
with 3% TEFLON 7A.RTM., 2% graphite and 1% carbon black was prepared. The 
cathode mix was pressed on a flat etched current collector according to 
the prior art, and a "basket weave" current collector according to the 
present invention. The basket weave current collector consisted of a 
diamond design similar to that shown in FIG. 2 wherein the short axis or 
height of the diamond was about 0.036 inches. The cathode current 
collector material was titanium. The prior art flat etched current 
collector was provided by contacting a planar, titanium substrate with an 
acid solution to increase the contact surface area of the current 
collector. 
Three cells having a prismatic cell stack assembly configuration were 
constructed incorporating the prior art (flat etched) cathode and three 
cells having the present invention (basket weave) cathode associated with 
the anode in a jellyroll electrode configuration were built. In both cell 
constructions, two layers of microporous membrane polypropylene separator 
were sandwiched between the anode and cathode. The electrode assemblies 
were then hermetically sealed in a stainless steel casing in a 
case-negative configuration. The cells were activated with the electrolyte 
consisting of 1.0M LiAsF.sub.6 dissolved in a 50:50, by volume, mixture of 
PC and DME with dibenzyl carbonate (DBC) and benzyl-N-succinimidyl 
carbonate (BSC), at a concentration of about 0.05M and 0.005M, 
respectively, added therein. 
A constant resistive load of 2.49 k.OMEGA. was applied to the cells for 17 
hours during an initial predischarge burn-in period. The predischarge 
period is referred to as burn-in and depleted the cells of approximately 
1% of their theoretical capacity. Following burn-in, the cells were 
subjected to acceptance pulse testing consisting of four 10 second pulses 
1.3 amp (19.0 mA/cm.sup.2) with a 15 second rest between each pulse. 
Following acceptance pulse testing, the cells were subjected to accelerated 
pulse testing comprising being discharged under a constant resistance 
(14.7 kg) background load at 37.degree. C. with superimposed pulse trains. 
In particular, each train was applied every 38 days and consisted of a 1.3 
amp (19.0 mA/cm.sup.2) pulse train of four pulses of ten seconds duration 
with 15 seconds rest between each pulse. 
The average discharge readings for the depth-of-discharge, pre-pulse 
potentials, pulse 1 and 4 minimum potentials and internal resistance (DOD) 
during accelerated pulse discharge testing are summarized in Tables 1 and 
2 for the present invention cells (basket weave, jellyroll and thee 
configuration) and the prior art cells (flat etched, jellyroll electrode 
configuration), respectively. The results are also graphed in FIG. 13. In 
particular, curve 110 was constructed from the average pre-pulse voltage 
of the present invention cells, curves 112 and 114 were constructed from 
the average pulse 1 and pulse 4 minimum voltages, respectively, and curve 
116 is the average internal resistance of those cells. In contrast, curve 
120 was constructed from the average pre-pulse voltage of the prior art 
cells, curves 122 and 124 were constructed from the average pulse 1 and 
pulse 4 minimum voltages, respectively, and curve 126 was constructed from 
the average internal resistance of those cells. 
TABLE 1 
______________________________________ 
Internal 
DOD (Avg.) 
P pre 1 P1 min. (V) 
P4 min. (V) 
Resistance (.OMEGA.) 
______________________________________ 
0.000 3.230 
0.020 2.726 2.678 0.424 
0.227 3.142 
0.247 2.653 2.585 0.428 
0.447 2.832 
0.471 2.411 2.354 0.368 
0.649 2.575 
0.663 2.156 2.187 0.298 
0.834 2.539 
0.857 2.084 2.092 0.344 
1.021 2.471 
1.036 1.982 1.932 0.414 
1.171 2.272 
1.189 1.742 1.681 0.455 
1.336 2.051 
1.354 1.408 1.301 0.577 
______________________________________ 
TABLE 2 
______________________________________ 
Internal 
DOD (Avg.) 
P pre 1 P1 min. (V) 
P4 min. (V) 
Resistance (.OMEGA.) 
______________________________________ 
0.000 3.221 
0.020 2.582 2.543 0.522 
0.211 3.158 
0.231 2.472 2.439 0.553 
0.404 2.873 
0.428 2.356 2.308 0.435 
0.603 2.622 
0.624 2.101 2.135 0.374 
0.799 2.557 
0.818 2.007 2.053 0.388 
0.976 2.489 
0.997 1.971 1.947 0.417 
1.126 2.355 
1.153 1.738 1.684 0.516 
1.293 2.113 
1.314 1.506 1.438 0.519 
______________________________________ 
Thus, the improved intimate contact afforded by the basket weave cathode 
current collector of the present invention enables the construction of 
lithium/silver vanadium oxide cells having a jellyroll electrode 
configuration in comparison to the prior art prismatic cells of a similar 
chemistry. The jellyroll cell stack with the basket weave cathode current 
collector configuration in turn results in higher voltage minimums under 
pulse discharge, which reduces voltage recovery back to pre-pulse levels 
and provides for increased energy utilization efficiency, thereby 
extending the medical device life powered by the present invention cell. 
The cells built according to the present invention also exhibit reduced 
internal resistances, in part, brought about by the jellyroll 
configuration which requires less electrode leads, especially for the 
cathode, than the prismatic design. Fewer electrode leads facilitates cell 
manufacturability by eliminating additional joining operation while 
enhancing cell reliability. 
It is appreciated that various modifications to the inventive concepts 
described herein may be apparent to those skilled in the art without 
departing from the spirit and the scope of the present invention defined 
by the hereinafter appended claims.