Clamping structure for battery cells

A structure for clamping a plurality of battery cells to prevent deformation thereof, includes a pair of pressure plates positioned against the ends of a stack of battery cells and a plurality of bands which extend around the cells and the end plates to hold the end plates in fixed position with respect to each other. The structure can be used with a plurality of sealed cells of rectangular configuration to pevent expansion of the cells of the type where pressure can build up therein, such as ni-clad rechargeable batteries, and thereby prevent bulging of the electrodes of the cells to injure the same. The pressure plates can be made of steel to also serve as heat sinks during welding of the bands, and the bands can be formed of steel strips which are preferably cinched tight about the cells and welded together. Partitions can be positioned between adjacent cells, with edges welded to the bands to prevent expansion of the cellsin a direction parallel to the pressure plates.

Batteries for use in portable electrical devices often include a plurality 
of cells which are electrically connected to provide the voltage and 
current requirements desired. Such cells may be of rechargeable type 
wherein gasses are developed during charging which cause the build-up of 
pressure in cells which are sealed. Some cells are vented to relieve the 
pressure but substantial cost is involved in providing a venting structure 
which will not allow entry of foreign material into the cell and not allow 
spilling of the electrolyte from the cell. It is almost impossible to 
provide a venting structure which will permit escape of gasses and not 
permit escape of the electrolyte, which is a corrosive and otherwise 
dangerous substance. 
Battery cells have been provided within a rigid housing to hold the 
elements therein against bulging, but to provide such a housing with small 
dimensional tolerances also involves substantial cost. Structures have 
been provided for holding stacks of cells together using bolts with 
pre-loading springs acting on the end cells. These structures are all 
complicated and require additional space about the cells, which is 
undesirable, particularly in batteries used in portable devices. The size 
and cost of the prior devices for holding cells has made the same 
objectionable for many applications. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide a simple and inexpensive 
structure to secure a stack of battery cells. 
Another object of the invention is to provide a clamping structure for a 
stack of rectangular sealed battery cells to prevent deformation of the 
cells in response to the build-up of pressure within the cells. 
A further object of the invention is to provide a clamping structure for a 
stack of battery cells which does not require close tolerances and can be 
formed of simple components so that it can be provided at low cost. 
Still another object of the invention is to provide a prismatic battery 
cell stack with a structure for preventing expansion of the sealed cells 
thereof which does significantly increase the size of the battery unit. 
The clamping structure of the invention is adapted to be used with a stack 
of rectangular sealed battery cells, and includes a pair of pressure 
plates positioned at the ends of the cell stack, and a plurality of bands 
about the stack and the end pressure plates. The bands can be formed of 
steel straps which, in their preferred form, are cinched tight and welded 
together to hold the pressure plates in fixed positions with respect to 
each other. The pressure plates are also formed of steel and can be of a 
thickness and mass to form heat sinks to prevent the heat developed by 
welding of the straps from damaging the cells. Partitions or septums 
formed of sheet steel can be positioned between adjacent cells in the 
stack and have edges welded to the bands to prevent expansion of the cells 
in a direction parallel to the pressure plates. The clamping structure 
prevents bulging of the cells, which would cause separation of the 
electrodes therein, as well as lateral bulging of the stack, which might 
cause the electrodes to shift in position, and ultimately rupture of a 
close fitting battery housing. The structure in its preferred form is 
formed by elements of simple and inexpensive construction and which do not 
require close tolerances, so that the overall cost of the structure is 
very small.

DETAILED DESCRIPTION OF THE DRAWINGS 
In FIG. 1, a plurality of cells 10 of rectangular shape are arranged in a 
stack, with the larger sides of the cells positioned adjacent each other. 
The cells 10 may be of the nickel-cadmium type of known construction, and 
each includes a plurality of electrodes and an electrolyte in a 
sealed-housing. The cells are arranged so that the terminals 11 of 
adjacent cells which are of opposite polarity are next to each other to 
facilitate connection of the cells 10 in series so that the voltages 
thereof are additive. It will be apparent that the cells can be arranged 
in various manners to satisfy the voltage and current requirements 
desired. 
In the preferred form, a pair of pressure plates 12, best shown in FIG. 2, 
are positioned against the larger outer sides of the end cells 10 in the 
stack. The plates 12 may have a size to substantially cover the adjacent 
sides of the cells, and may be formed of steel of a thickness to be 
substantially rigid. A plurality of bands 14 are provided about the cells 
10 and the pressure plates 12. The bands 14 are formed by strips of steel 
having ends 15 and 16 which are cinched tight about the cells 10 and the 
end plates 12, and the ends are overlapped and spot welded, as shown at 
points 18. This forms a pre-tightened band which holds the pressure plates 
12 in fixed position with respect to each other and prevents expansion of 
the cells 10 across the thickness thereof. 
It may also be desired to use partitions or septums 20 between adjacent 
cells to prevent transverse expansion of the cell stack. The septums 20 
have right angle edges 21 and 22 which engage the bands 14, and which are 
spot welded thereto. This further holds the cells against expansion due to 
the build-up of gas pressure therein. 
The pressure plates 12 may have sufficient mass that they also serve as 
heat sinks. This is important during the spot welding (18) of the bands 
14, as it removes the heat generated during welding so that the adjacent 
battery cell 10 is not damaged. During welding of the bands 14 to the 
septums 20, a brass strip can be inserted between the septum and the cell 
to remove heat, so that the cell is not damaged by the heat. 
The clamping structure of the invention has been found to be highly 
effective to prevent damage to the cells, resulting from expansion thereof 
due to the build-up of gasses within the sealed cells, as during charging. 
Any expansion of the cells can cause bulging of the electrodes to impair 
the operation of the cells. 
The structure of the invention in its preferred form is constructed of 
simple and inexpensive components which have no critical tolerances. The 
pressure plates and strips can be cut from sheet steel. The septums can 
also be formed of sheet metal and the edges can be bent by use of a very 
simple tool. Accordingly, the clamping structure can be provided and 
applied to a cell stack at very small cost.