U.S. patent application number 11/035967 was filed with the patent office on 2006-01-26 for safety device for a sealed cell.
This patent application is currently assigned to SAFT. Invention is credited to Claude Gilabert, Dominique Ligeois, Jonac Philippe, Gerard Rigobert.
Application Number | 20060019150 11/035967 |
Document ID | / |
Family ID | 34947472 |
Filed Date | 2006-01-26 |
United States Patent
Application |
20060019150 |
Kind Code |
A1 |
Rigobert; Gerard ; et
al. |
January 26, 2006 |
Safety device for a sealed cell
Abstract
A safety device for a sealed cell (1) comprising alternating
positive and negative electrodes respectively connected to positive
and negative current output terminals (6, 7) placed in a container
(2) having an end (3) that is closed by a wall. The wall of the
closed end presents thinning (13) adapted to be torn by excess
pressure inside the container, and the thinning is adapted, on
being torn, to interrupt electrical conduction between the
electrodes of one polarity and the corresponding current output
terminal. The device of the invention is simple in design, is
capable of operating at low pressures, and over a wide range of
pressures, and acts as a circuit interrupter without decreasing the
current density that flows in the electrical circuit.
Inventors: |
Rigobert; Gerard; (Fargues
St Hilaire, FR) ; Gilabert; Claude; (Le Pian Medoc,
FR) ; Philippe; Jonac; (Gradignan, FR) ;
Ligeois; Dominique; (St Loubes, FR) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
SAFT
|
Family ID: |
34947472 |
Appl. No.: |
11/035967 |
Filed: |
January 18, 2005 |
Current U.S.
Class: |
429/56 ;
29/623.2; 429/61 |
Current CPC
Class: |
H01M 50/545 20210101;
H01M 2200/20 20130101; Y02P 70/50 20151101; H01M 50/572 20210101;
Y02E 60/10 20130101; H01M 50/107 20210101; H01M 10/0587 20130101;
Y10T 29/4911 20150115; H01M 50/3425 20210101; H01M 10/0431
20130101; H01M 50/10 20210101; H01M 50/578 20210101; H01M 50/116
20210101; H01M 10/052 20130101; H01M 50/103 20210101 |
Class at
Publication: |
429/056 ;
429/061; 029/623.2 |
International
Class: |
H01M 2/12 20060101
H01M002/12; H01M 10/04 20060101 H01M010/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 23, 2004 |
FR |
0408182 |
Claims
1. A safety device for a sealed cell comprising alternating
positive and negative electrodes respectively connected to positive
and negative current output terminals, the electrodes being
disposed in a container presenting an end that is closed by a wall
presenting thinning adapted to be torn by excess pressure inside
the container, the thinning being adapted, on being torn, to
interrupt electrical conduction between the electrodes of one
polarity and the corresponding current output terminal.
2. A safety device according to claim 1, in which the thinning
constitutes a zone of weakness in the wall at the closed end.
3. A safety device according to claim 1, in which the end closed by
a wall supports the current output terminals.
4. A safety device according to claim 1, in which a cover placed on
an open end of the container supports the current output
terminals.
5. A safety device according to claim 1, in which the tear is
adapted to interrupt electrical conduction between the positive
electrodes and the positive current output terminal.
6. A safety device according claim 1, in which the tear is adapted
to interrupt electrical conduction between the negative electrodes
and the negative current output terminal.
7. A safety device according to claim 1, for a cylindrical format
sealed cell.
8. A safety device according to claim 1, for a prismatic format
sealed cell.
9. A safety device according to claim 1, for a cell operating with
pressures inside the container lying in the range 4 bars to 20
bars.
10. A safety device according to claim 9, wherein the pressures
inside the container lie in the range 8 bars to 12 bars.
11. A safety device according to claim 1, in which the thickness of
the thinning represents substantially 20% of the thickness of the
wall at the closed end of the container.
12. A safety device according to claim 1, including a rim of the
closed end wall, said rim being adapted to prevent the electrodes
being ejected in the event of the thinning being torn.
13. A method of manufacturing a safety device for a sealed cell,
the method comprising the steps consisting in: providing a
container presenting an end that is closed by a wall; stamping the
wall at the closed end so as to create thinning suitable for being
torn by excess pressure inside the container; placing a stack of
positive and negative electrodes inside the container; connecting
the electrodes to current output terminals so that tearing the
thinning interrupts electrical conduction between the terminals of
one polarity and the corresponding current output terminal; and
closing the cell in sealed manner.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a safety device for a
sealed cell. It also covers a method of manufacturing such a
device.
[0002] A sealed electrochemical cell (or "battery") comprises in
conventional manner an electrochemical stack made up of alternating
positive and negative electrodes on either side of separators
impregnated in electrolyte. Each electrode is made up of a metal
current collector supporting an electrochemically active material
on at least one of its faces. Each electrode is electrically
connected to a current output which provides electrical continuity
between the electrode and an external application with which the
cell is associated. The stack of electrodes is placed in a
container that is closed in sealed manner by a cover.
[0003] The invention relates to sealed cells of the nickel cadmium,
nickel metal hydride, and lithium ion types. These cells may be of
cylindrical format or of rectangular format (also known as
prismatic format). They constitute cells that are rechargeable,
also known as secondary cells or as accumulators.
[0004] A cell is generally designed to operate under so-called
"nominal" conditions, i.e. within given ranges of temperature,
current, and voltage. When a sealed cell is used outside the
nominal conditions, for example in the event of accidental
overcharging, or a short circuit, or temperature higher than the
maximum operating temperature, etc., there is a danger of
explosion. This is because such situations lead to the electrolyte
heating and to electrolyte vapor being formed. An accumulation of
such vapor inside the container increases the internal pressure of
the cell and that can lead to the container bursting violently and
to chemical compounds being sprayed out that are harmful and
corrosive for the environment and for people situated nearby.
[0005] Safety devices exist that prevent gas from accumulating
inside the container of a sealed cell and that enable the gas to be
exhausted when the internal pressure exceeds a predetermined
value.
[0006] Known safety devices are generally constituted by valves.
U.S. Pat. No. 5,523,178 describes a valve for a cell. That valve
nevertheless presents the drawback of being complex in design. When
valves are simple in design they suffer from the drawback of
opening only at pressures that are high or opening only over a
narrow range of pressures.
[0007] Furthermore, it is necessary for a cell safety device also
to possess a circuit interrupter function suitable for electrically
and irreversibly isolating apparatus connected to the cell. Known
valves do not perform this circuit interrupter function. A specific
electrical device must be provided for performing the circuit
interrupter function when the valve is activated.
[0008] There therefore exists a need for a safety device for a
sealed cell which is simple in design, suitable for low pressures,
and capable of operating over a wide range of pressures. There also
exists a need for a safety device that acts simultaneously as a
circuit interrupter.
[0009] An object of the present invention is to solve the
above-mentioned problems.
SUMMARY OF THE INVENTION
[0010] To this end, the invention provides a safety device for a
sealed cell comprising alternating positive and negative electrodes
respectively connected to positive and negative current output
terminals, the electrodes being disposed in a container presenting
an end that is closed by a wall presenting thinning adapted to be
torn by excess pressure inside the container, the thinning being
adapted, on being torn, to interrupt electrical conduction between
the electrodes of one polarity and the corresponding current output
terminal.
[0011] According to a characteristic, the thinning constitutes a
zone of weakness in the wall at the closed end.
[0012] According to a characteristic, the end closed by a wall
supports the current output terminals.
[0013] According to a characteristic, a cover placed on an open end
of the container supports the current output terminals.
[0014] In embodiments, the tear is adapted to interrupt electrical
conduction between the positive electrodes and the positive current
output terminal or between the negative electrodes and the negative
current output terminal. Depending on the application, the sealed
cell is cylindrical in format or prismatic.
[0015] According to a characteristic, the sealed cell operates with
the pressure inside the container lying in the range 4 bars to 20
bars, and preferably in the range 8 bars to 12 bars.
[0016] According to a characteristic, the thickness of the thinning
represents substantially 20% of the wall thickness at the closed
end of the container. According to a characteristic, a rim of the
wall of the closed end is adapted to prevent the electrodes being
expelled in the event of the thinning being torn.
[0017] The invention also provides a method of manufacturing a
safety device for a sealed cell, the method comprising the steps
consisting in: [0018] providing a container presenting an end that
is closed by a wall; [0019] stamping the wall at the closed end so
as to create thinning suitable for being torn by excess pressure
inside the container; [0020] placing a stack of positive and
negative electrodes inside the container; [0021] connecting the
electrodes to current output terminals so that tearing the thinning
interrupts electrical conduction between the terminals of one
polarity and the corresponding current output terminal; and [0022]
closing the cell in sealed manner.
[0023] Other characteristics and advantages of the invention appear
on reading the fowling description given by way of example and with
reference to the FIGS.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a longitudinal section view of a sealed lithium
ion cylindrical cell provided with a safety device of the
invention; and
[0025] FIGS. 2A and 2B are respectively a longitudinal section view
and a cross-section view of the safety device of the invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
[0026] The invention provides to a safety device for a sealed cell.
The cell comprises alternating positive and negative electrodes
respectively connected to positive and negative current outlet
terminals. The electrodes are disposed in a container presenting
one end that is closed by a wall. The wall of the closed end
presents thinning (i.e. a portion of reduced thickness) suitable
for being torn by excess pressure inside the container. On being
torn, the thinning is adapted to interrupt electrical conduction
between the electrodes of one polarity and the corresponding
current output terminal.
[0027] Thus, in the event of the pressure inside the cell exceeding
a predetermined threshold value, the thinning tears and serves to
exhaust the gas, thereby preventing the cell from exploding. The
device also acts as a circuit interrupter by simultaneously
interrupting electrical conduction between the electrodes of one
polarity and the corresponding current output terminal.
[0028] A preferred embodiment of the invention is described below
by way of example.
[0029] FIG. 1 is a longitudinal section view of a sealed
cylindrical lithium ion cell provided with a safety device of the
invention.
[0030] The cell 1 comprises a container possessing a cylindrical
wall 2 closed at one end by an end wall 3 and open at its opposite
end 4. A cover 5 is placed on the open end. It supports current
output terminals 6 and 7. One of the current output terminals, in
the example described the positive terminal 6, is welded to the
cover. The other current output terminal, in the example described
in the negative terminal 7, passes through the cover. It is secured
thereto by any suitable means such as screw-fastening or crimping.
A gasket 8 insulates the negative current output terminal 7
electrically from the cover.
[0031] An electrochemical stack 9 constituted by a winding of
positive and negative electrodes with a separator is disposed in
the container about a hollow shaft 10 which serves as a gas
chimney. A connection strip 11 connects the positive electrodes of
the stack to the end wall of the container, the walls of the
container being electrically conductive and connected to the cover.
Another connection strip 12 connects the negative electrodes of the
stack to the negative current output terminal. A ring-shaped gasket
14 is placed between the electrochemical stack and the end wall of
the container. It provides electrical insulation so as to prevent
electrical contact being made between the edge of a negative
electrode in the stack and the wall of the container that is
connected to the positive electrode, since that could give rise to
a short circuit.
[0032] In the invention, the closed end 3 constituted by the end
wall of the container presents thinning 13. This thinning is
adapted to be torn by excess pressure inside the container. In the
example shown, when the thinning tears it is adapted to interrupt
electrical conduction between the positive electrodes and the
positive current output terminal. FIG. 2B shows that the thinning
is circular in shape with a diameter constituting about 75% of the
diameter of the container for a cell that is cylindrical. The
thickness of the thinning is about 20% of the thickness of the wall
at the closed end of the container. The thinning that is
implemented constitutes a zone of weakness in the closed end, and
it tears under gas pressure. The thickness of the thinning can be
adjusted as a function of the looked-for opening pressure and the
mechanical strength of the container. The material of the container
is preferably aluminum. Alternatively, nickel-plated steel or
copper could be used. Depending on the thickness of the thinning,
an opening pressure lying in the range 4 bars to 20 bars can be
obtained. The thickness of the thinning is preferably selected so
that the opening pressure lies in the range 8 bars to 12 bars. The
safety device is thus suitable for operation at low pressure and
over a broad range of pressures. The non-deformed portion of the
closed end wall forms a rim 15 that serves to prevent the
electrochemical stack being expelled in the event of the thinning
being torn.
[0033] One possible method of manufacturing a cell of the invention
is described below. This description refers to a cylindrical
cell.
[0034] A thinning 13 is made in a portion of the wall of the closed
end 3 of the container by stamping the container material in a
press.
[0035] A gasket 14 is inserted in the end of the container. It
covers the thinning and the rim at the closed end. It is made of a
material that withstands high temperatures such as polyetherimide
(PEI).
[0036] Thereafter the electrochemical stack is made. The positive
electrode is constituted by a current collector, which may be an
aluminum foil, covered in an active material constituted by a
lithium-containing oxide of transition metals such as LiCoO.sub.2,
LiNiO.sub.2, LiMnO.sub.2, LiMn.sub.2O.sub.4, or a mixture
thereof.
[0037] The negative electrode is constituted by a current
collector, which may be a copper foil, covered in an active
material constituted by a material in which lithium can be inserted
reversibly, such as graphite, coke, vitreous carbon, or carbon
black.
[0038] The separator may be a polyolefin. At least one positive
electrode, at least one separator, and at least one negative
electrode are superposed to form the electrochemical stack 9. The
electrochemical stack is wound around the hollow shaft 10 made of
aluminum. The positive and negative electrodes are bonded to their
plane connections. A connection strip of plane shape is preferred,
but any type of connection could be envisaged.
[0039] The electrochemical stack 9 carrying its connections is
inserted into the container 2. The electrodes and the separators
are impregnated and the container is filled with electrolyte under
reduced air pressure inside the container. The electrolyte is
constituted by a lithium salt dissolved in an organic solvent. The
container is closed in sealed manner by welding a cover 5 to the
open end 4 of the container, which cover is fitted with current
output terminals 6 and 7.
[0040] The operation of the safety device is described below.
[0041] The thinning 13 created in the closed end 3 of the cell
constitutes a zone of weakness. When the wall at the closed end is
not strong enough to withstand the pressure of electrolyte vapor,
the thinning tears. The pressure is exhausted through the tear and
the pressure inside the cell drops to atmospheric pressure.
Simultaneously with the appearance of the tear, electrical
conduction between the plane connection of the positive electrode
11 and the wall of the container 2 is interrupted, thereby
interrupting the supply of power to the electrical load. When the
thinning is torn in part only, excess pressure is exhausted, but
the circuit-interrupting function is not provided. Current flow in
the electrical circuit needs to be interrupted by an operator.
[0042] The safety device is simple in design and combines the
functions of a valve and of a circuit interrupter. It does not
require any additional parts that need to be assembled to make the
cell, thereby giving the safety device a high degree of
reliability.
[0043] The safety device of the invention also presents the
advantage of not reducing the density of the current flowing in the
electrical circuit as happens when series-connected circuit
interrupters are used. The thickness selected for the thinning is a
compromise between the largest possible section in order to pass
current and the smallest possible section in order to ensure that
the thinning tears.
[0044] The safety device is thus well adapted to high-power
applications (e.g. hybrid vehicles), in which high current
densities are used.
[0045] Another advantage of the invention lies in the fact that the
electrochemical stack is retained inside the container in the event
of the thinning being torn suddenly, since the rim 15 at the closed
end prevents the electrochemical stack from being ejected. The
opening created by tearing the thinning is too narrow to allow the
electrochemical stack to pass through. The risks of dangerous
chemical substances being sprayed out is thus limited.
[0046] The present embodiment and the drawings should be considered
as being presented by way of non-restricted illustration, and the
invention is not limited to the details provided herein, but can be
modified while remaining within the ambit and the scope of the
accompanying claims. In particular, the end of the container that
is closed by a thinned wall may be the end that supports the
current output terminals.
* * * * *