Electrochemical cell

An electrochemical cell comprising a relatively thin strip of anode material, first and second electrolyte layers coated on the opposing surfaces of the anode strip, first and second relatively thin strips of cathode material contacting the first and second electrolyte layers, thereby forming a laminate strip with the electrolyte layers and anode strip and a single cathode current conductor strip. The laminate strip is deformed such that both of the first and second strips of cathode material contact the single cathode current conductor strip along substantially the entire length thereof. In one embodiment, the cell takes the form of a spiral, in which the conductor strip is superposed to the laminate strip and the combination is rolled lengthwise, and in another embodiment, the cell takes the form of a stack in which the laminate strip is fan-folded and the conductor strip is fan-folded and inserted between the folds of the laminate strip such that the corners of the folds of the laminate strip are perpendicular to the corners of the folds of the conductor strip. s

BACKGROUND OF THE INVENTION 
The present invention relates to electrochemical cells and, more 
particularly, to nonaqueous cells utilizing a polymer electrolyte. 
Solid-state cells having a lithium anode, a finely-divided metal oxide 
cathode and a polymer electrolyte possess many advantages over other types 
of electrochemical cells. For example, such cells provide a long useful 
service life, possess a relatively high power density, a relatively high 
specific energy--on the order of 200 to 300 Wh/kg--and a relatively high 
specific power--on the order of 600 W/kg. Such cells are also desirable in 
that their polymer-based electrolyte component can be readily and 
inexpensively formed with greatly reduced thickness, and the entire cell 
can be shaped in a number of desirable configurations thereby making the 
cell useful in a wide variety of applications. 
An example of such a cell is disclosed in the publication Advanced Battery 
Development, published in 1984. That cell comprises a lithium foil anode, 
a cathode of finely divided vanadium oxide with carbon black additions 
mixed with electrolyte material, termed a "composite electrode," and an 
electrolyte comprising an ion-conducting polymer consisting of 
poly(ethylene oxide) complexed with the lithium salt LiCF.sub.3 SO.sub.3 
deposited in a thin layer on a nickel foil. 
A laminate, comprising elongate strips of anode material, polymer 
electrolyte, cathode material and current conductor layers is formed into 
a cell by folding the laminate in a "fan-folded" or "concertina" 
configuration. However, in the fan-folded configuration disclosed, the 
stacked segments of the laminate overlie each other such that the segments 
of current conductor contact each other and the segments of anode material 
contact each other on successive segments of the fan-folded laminate. 
In another embodiment, a cell comprises a spiral or "jelly roll" 
configuration in which a laminate comprising a strip of insulator 
material, a strip of anode material, a strip of polymer electrolyte, a 
strip of composite cathode material and a strip of current collector are 
wound into a spiral shape. Successive windings of the aforementioned 
laminate are isolated from each other by the strip insulator segment of 
the laminate. 
Another battery cell construction is disclosed in the article "The Magic of 
MOLI" in the June 1987 issue of QST. That cell includes a molybdenum 
disulfide cathode, a polymer electrolyte and a lithium anode. A laminate 
comprising an anode sandwiched between two electrode layers which, in 
turn, contact two cathode layers is wound in jelly-roll fashion and 
encased in a steel can to form the cell. Strips of metal foil extend 
transversely of the anode and cathode layers and are connected to the 
negative and positive electrodes, respectively, of the resulting battery. 
However, the aforementioned cell designs possess some disadvantages. For 
example, the lithium/vanadium oxide cell designs disclosed show a single 
cathode laminated to each anode strip, and a single current conductor for 
each cathode. Consequently, a portion of the anode strip opposite the 
electrolyte layer is largely unused and adds unnecessarily to the cost, 
weight, and thickness of the resultant cell. It is not currently 
practicable to manufacture lithium anode strips which are sufficiently 
thin to overcome this disadvantage. 
The disadvantage with the MOLI cell is that each cathode requires its own 
current conductor, again adding to the overall weight thickness and cost 
of the resultant cell. Accordingly, a need exists for a lithium battery 
which is relatively inexpensive to manufacture, is efficient in operation 
in that it uses substantially the entire anode strip and is light in 
construction. 
SUMMARY OF THE INVENTION 
The present invention is an electrochemical secondary cell of the 
lithium/vanadium oxide type in which a laminate comprising the anode, two 
layers of polymer electrolyte and two layers of cathode material is formed 
such that a single current conductor strip contacts both layers of cathode 
material. In one embodiment, a single cathode current conductor strip is 
superposed to a laminate strip comprising a single anode strip sandwiched 
between two electrolyte layers and two cathode strips, and the combination 
is wound into a spiral. As a result of the spiral winding, the single 
cathode conductor strip contacts both cathode layers and therefore serves 
a double duty. 
In a second embodiment, the aforementioned cell laminate is fan-folded into 
a stack having a plurality of laminate sections. The cathode conductor 
strip is also fanfolded into a stack which is interleaved between the 
folded segments of the laminate strip and oriented such that the folds of 
the conductor strip are at right angles to the folds of the laminate 
strip. With both embodiments, the cathode conductor strip may be provided 
with tabs protruding sidewardly from a longitudinal edge of the strip and 
spaced along its length. Similarly, the lithium anode may be provided with 
a protruding strip of metal foil, such as nickel, which extends from a 
side of the anode strip opposite that of the cathode tabs. The resultant 
structures are fitted with positive and negative electrodes which are made 
of a conductive material and attached to the appropriate set of tabs. 
In a preferred method of fabricating the spiral or jelly-roll cell, a 
mandrel of nonconducting material is connected to the leading edge of a 
strip of metallic foil, and the foil is wound about the mandrel. 
Simultaneously, a strip of cell laminate is inserted into the nip of the 
roll of foil. As the foil strip continues to be wound about the mandrel, 
it forms the cathode current conductor strip with the cell laminate as 
well as a protective casing. 
Accordingly, it is an object of the present invention to provide a cell 
laminate and current conductor strip structure in which a cathode current 
conductor in the form of a single strip contacts both cathode layers of a 
laminate cell having cathode strips positioned to interact with opposing 
sides of an anode strip; a cell laminate and cathode current conductor 
which can be folded or deformed into a compact structure; a cell laminate 
and cathode current collector combination which is lightweight, thin, and 
relatively easy to manufacture; and a cell laminate and cathode current 
collector which comprises a lithium cell having a high power density. 
Other objects and advantages of the invention will be apparent from the 
following description, the appended claims and the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As shown in FIG. 1, the electrochemical cell of the present invention 
includes a cell laminate, generally designated 10, which comprises an 
anode strip 12, first and second layers of polymer electrolyte 14, 16, 
respectively, and first and second cathode strips 18, 20, respectively. In 
the preferred embodiment, the cell laminate 10 comprises a portion of a 
second cell having an alkali metal foil anode with a thickness of about 75 
microns, an ionically conducting polymeric electrolyte layer containing an 
ionizable alkali metal salt with a thickness of about 25 microns and an 
intercalation cathode layer of a finely divided transition metal oxide 
with a thickness of about 75 microns. 
In a particularly effective embodiment, the anode strip 12 comprises a 
lithium foil and the cathode strips comprise a composite of finely divided 
vanadium oxide (V.sub.6 O.sub.13), carbon black or an electronically 
conductive polymer and solid electrolyte material. The polymer electrolyte 
14, 16 preferably comprises a lithium salt, such as LiCF.sub.3 SO.sub.3, 
dissolved in poly(ethylene oxide), PEO. Alternatively, the active cathode 
component may comprise metal chalcogenides such as NbSe.sub.3, V.sub.2 
O.sub.5, MnO.sub.2, TiS.sub.2 or electronically conducting organic 
polymers such as polypyrrole and polyacetylene. Both the electrolyte 
layers 14, 16 and the cathode strips 18, 20 may be coated onto the anode 
strip 12 by the "doctor blade" continuous casting , solvent evaporation 
technique or by extrusion. 
Although element 10 in FIGS. 1 and 2 is referred to as a cell laminate, it 
should be noted that there are in face two "cells" in the strict sense of 
the term, each having a cathode in an ion exchange relation with an anode. 
However, in the electrochemical cell shown in the figures, the two cathode 
layers are always joined by a single current conductor. 
As shown in FIGS. 1 and 2, the cell laminate 10 preferably includes an 
anode current collector strip 22 which is embedded in the anode strip 12 
along a longitudinal edge thereof and extends sidewardly therefrom. 
Appropriate materials for the strip 22 are nickel, copper other conductive 
metals, conductive polymers and metal-coated polymers. The cell laminate 
10 is superposed to and is joined to a cathode current conductor strip 24, 
which is sized to protrude sidewardly beyond the longitudinal edge 26 of 
the cell laminate 10 opposite the edge containing the anode current 
conductor strip 22. The protruding portion 28 is separated from the 
remainder of the cathode conductor strip 24 by a broken line 30 for 
purposes of illustration. An appropriate material for the strip 24 is 
aluminum, other conductive metals, polymers and metal-coated polymers. 
When placed in position as shown in FIG. 2, the cell laminate 10 and 
cathode strip 22, which together comprise a cell 32, are preferably rolled 
lengthwise to form a "jelly-roll" or spiral configuration, as shown in 
FIGS. 3, 4 and 5. With this configuration, the single cathode current 
conductor strip 24 is able to contact both cathode strips 18, 20 along 
substantially their entire lengths and therefore conduct current from both 
cells to the positive electrode of the associated battery. 
The protruding part 28 of the cathode strip 24 provides a convenient 
positive electrode 33 at one end of the cell 32, and the anode conductor 
strip 22 protrudes from the opposite end of the cell to provide a negative 
electrode 34. 
As shown in FIGS. 3-5, it is also preferable to fabricate the cathode 
conductor strip 24 so that it is longer in length than the cell laminate 
10. Consequently, the cathode conductor strip 24 forms an outer protective 
covering for the cell 32 when formed into the spiral shown in the figures. 
As shown in FIGS. 6(A)-6(C), an alternate spiral cell structure 32' may be 
fabricated utilizing a cylindrical mandrel 35 made of a nonconductive 
material such as nylon. To form the spiral cell 32', the cathode conductor 
strip 24' is attached at an end to the mandrel 35 and wound in a spiral 
about it. The cell laminate 10, with a protruding anode strip 22, is 
inserted into the nip 36 and the cathode conductor strip 24' continues to 
be wound around the mandrel 35 so that the cell laminate 10 itself forms a 
spiral in between the windings of the cathode conductor strip. 
Again, it is preferable that the cathode conductor strip 24' be longer in 
length than the cell laminate 10 so that the finished product, shown in 
FIG. 6(C), includes an outer protective covering of metal. Once the 
cathode conductor strip 24' has been wound about the mandrel 35, and the 
cell laminate 10, the resulting structure includes protruding positive and 
negative electrodes 33', 34' respectively. 
A more conventional positive electrode is formed by slitting the protruding 
portion 28' of the cathode conductor strip 24' into a plurality of tabs 
42, then folding the tabs radially inwardly and connecting them to a 
button 44 made of a conductive material such as nickel and having a 
cylindrical head 46 and shank 48. The shank 48 is attached to the ends of 
the tabs 42 and secured within the mandrel 35. The head 46 then becomes 
the positive electrode 33' of the cell 32'. 
The opposite end of the cell 32' includes a spiral of protruding end 22 in 
which the windings are sealed and separated by an insulating polymer 50. A 
layer of conducting polymer 52 is applied to form a flat negative 
electrode surface. Similarly, the windings of the cathode are sealed and 
separated by an insulating polymer 50. The cell is encased in a jacket 54 
made of a nonconductive polymer. 
An alternate design of the cell 32" is shown in FIGS. 7 and 8. In FIG. 7, 
the cell laminate 10' is fanfolded along its length, thereby forming a 
series of segments 56 joined by creases 58. The anode conductor strip has 
been modified to form a series of protruding tabs 22' extending along one 
longitudinal side of the cell laminate 10', and spaced to extend from 
every second segment 56. 
Similarly, the cathode conductor strip 24" is fanfolded to form a plurality 
of segments 60 in which every other segment has a protruding tab 28'. 
Sequential segments 60 are joined by creases 62. 
As shown in FIG. 8, the cell 32" is formed by interleaving the segments 60 
of the cathode conductor strip 24' with the segments 56 of the cell 
laminated 10'. Consequently, the cathode conductor strip 24" contacts both 
faces of each segment 56 of the cell laminate 10' and therefore contacts 
the surfaces of both cathode strips 18, 20 substantially along their 
entire lengths. 
The resultant structure is substantially in the form of a cube. The creases 
58 of the cell laminate 10' are oriented at right angles to the creases 62 
of the cathode conductor strip 24, and the tabs 22' of the anode strip 12 
are longitudinally aligned with each other, as are the tabs 28' of the 
cathode conductor strip. Accordingly, the anode and cathode tabs 22', 28', 
respectively, may be joined together to form the negative and positive 
electrodes of the resultant cell 32". 
While the forms of apparatus herein described constitute preferred 
embodiments of this invention, it is to be understood that the invention 
is not limited to these precise forms of apparatus, and that changes may 
be made therein without departing from the scope of the invention.