Intensification of ion exchange in lithium batteries

The contact area of the anode of lithium batteries with the electrolyte is substantially increased by deposition of minute lithium particles on the anode base layer to form an irregular layer in contact with the electrolyte which reduces the manufacturing cost and increases the contact area which increases the ion exchange between the lithium particles and the electrolyte.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to ion exchange intensification in lithium batteries 
by increasing the anode contact area with the electrolyte. 
2. Description of the Prior Art 
Lithium and some other electrochemical devices or batteries whether they be 
of the liquid or solid state type characteristically use anodes formed 
from layers of metal. In lithium batteries for example it is common to 
form the anode by depositing a foil of lithium onto a base foil of nickel 
or other metal. 
Lithium is a very difficult material to work with, it must be kept from 
water, it can be highly toxic to those exposed to it, and it also has a 
low melting point and corrodes upon contact with the air. 
It is known in the manufacture of plates for lead acid batteries to form a 
paste containing particles of lead and a carrier material. The lead 
composition is then applied to a grid and allowed to dry, which produces 
plates having cavities therein which increases the electrolyte contact 
area and improves performance. The manufacture of such plates is described 
in the publication entitled Lead Acid Batteries by Hans Bode, published by 
John Wiley & Sons, New York, N.Y. 1977, Pages 102-244. While plates having 
the described characteristics are produced by the paste method, this 
method can not be used with lithium due to its considerably different 
nature, and the required handling characteristics. 
In the prior art approach to forming the anode of lithium batteries, 
lithium is extruded or rolled into thin sheets, which are then 
mechanically pressed against a base foil to form the anode. With the multi 
stage handling required it is difficult to prevent the lithium from 
becoming contaminated, and due to its inherent characteristics it is 
difficult to bond the lithium with the base foil so that the resultant 
product is often not satisfactory and separations may occur. 
The surface of extruded or rolled lithium foil is relatively smooth and 
flat, and after fabrication various layers of electrolyte and cathode 
materials are deposited thereon to form an electrochemical cell or device, 
which can be of the type described in our prior U.S. Pat. No. 4,576,883. 
During battery operation ions are exchanged between the electrolyte and the 
lithium layer of the anode in contact therewith. The ion exchange is 
limited by the contact area between the lithium foil and the electrolyte. 
While the advantages of lithium batteries are well known the difficulties 
in their manufacture and the cost/efficiency have limited their 
acceptance. The need exists for a better method of manufacturing the 
anodes, and a more efficient anode in terms of cost and performance. 
SUMMARY OF THE INVENTION 
It has now been found that the structural soundness and the contact area 
for ion exchange between the anode and electrolyte in lithium batteries 
may be considerably increased by the use of a novel anode construction. In 
particular, the invention is directed towards converting lithium into 
minute particles and depositing the particles on the base layer of an 
anode whereby the deposited particles form one or more porous layers onto 
which the electrolyte is placed with a resultant contact area 
substantially greater than that obtained with the conventional flat 
contact surface.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
A lithium battery of the solid state type consists of at least an anode 
layer, a cathode layer and a polymer dielectric layer. The three-layer 
structure, in the form of a sheet, roll tape, etc. forms a simple cell or 
battery. Such structures can also employ various additional layers, 
including current conducting backing layers, insulating layers, and/or 
bipolar electrode connections. Such simple batteries may be connected or 
combined in stacks to form multicell electrochemical devices. 
The cathode and electrolyte layers may be produced from the appropriate 
polymer film using the well known so-called "doctor-blade" technique, 
wherein a solution of the polymer (or polymer compounded with inorganic 
material) is prepared in a suitable solvent and cast as a film onto a 
sheet, for example, of waxed paper which passes beneath a fixed reservoir 
positioned at one end of a flat platform. The front face of the reservoir 
is adjustable in height and the setting of the gap between the 
doctor-blade and the paper sheet determines the thickness of the cast 
film. Evaporation of the solvent causes a uniform reduction in film 
thickness by an amount which is dependent on the concentration of the 
solution. 
The polymeric electrolyte composition can be formed by compounding a 
lithium salt and a polymeric material such as a polyethylene oxide. The 
mixture may be deposited as a film directly onto the cathode layer of the 
cell by the doctor-blade technique referred to previously. This leads to 
good reproducibility of the electrolyte layer, which is optimally in the 
order of 25 micrometers. The cathode layer may be formed of a thin layer 
of polymer spheres which contain an active cathode material such as 
vanadium oxide at their core which is encapsulated with a conductive 
polymer of well known type. As described in our prior U.S. Pat. No. 
4,567,883 such material is formed into an emulsion and applied as a thin 
film to the appropriate substrate layer by the doctor-blade technique as 
previously described. 
The anode layer customarily used in prior art lithium batteries was 
composed of a lithium or lithium/aluminum metal foil mechanically bonded 
to a base metal layer such as nickel. 
Referring now more particularly to the drawings the anode layer 10 of the 
battery is shown with a base layer 11 which is of any suitable metal with 
nickel being a preferred material, and which has a plurality of particles 
12 of lithium thereon. 
The anode layer is prepared by fabricating the base layer 11 by any well 
known technique such as extruding, casting or rolling. The base layer 11 
is then placed in a chamber (not shown) that has had the humidity removed 
so that it is as close to zero as possible. 
Lithium is melted and while molten is deposited onto the layer 11 in very 
small droplets or particles 12, 12A, 12B and 12C and which is applied as 
the base layer passes beneath the deposition structure. The lithium may be 
formed into particles 12, 12A, 12B and 12C by any suitable means such as, 
for example, by the airless paint spraying technique whereby molten 
lithium is fed onto a rotating cone disc (not shown) from which it is 
discharged in fine mist or droplet form. The molten lithium retains its 
shape as it falls from the sprayer onto the layer of nickel 11 and forms a 
layer 13. The droplets 12, 12A, 12B and 12C of lithium bond to the nickel 
layer 11, and may also bond to each other. 
The droplets 12 are illustrated as being of spherical shape, the droplets 
12A are of triangular shape, the droplets 12B are of square shape and the 
droplets 12C are of irregular shape. The sizes and configuration of the 
droplets are dictated by the desired product and their characteristics 
will be apparent to any person skilled in the art. 
Polymer electrolyte may then be applied to the layer 13 to form a layer 14 
onto which additional layers (not shown) may be placed as required. The 
resultant structure as shown in FIG. 2 is an irregular porous layer where 
it is apparent that there exists sufficient space between the particles 
12, 12A, 12B and 12C for the electrolyte layer 14 to penetrate and to 
contact them forming an electronic network or grid through and across the 
anode. 
It will thus be seen that the desired characteristics have been achieved.