Chemistry: electrical current producing apparatus – product – and – Sealed cell having gas prevention or elimation means
Reexamination Certificate
1998-08-03
2004-01-20
Ryan, Patrick (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Sealed cell having gas prevention or elimation means
C429S223000, C429S206000, C429S248000
Reexamination Certificate
active
06680140
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns an industrial type vented cell aqueous electrolyte secondary storage cell requiring no maintenance.
2. Description of the Prior Art
A storage battery is of the “industrial” type if it has a high capacity, greater than 5 Ah and generally in the range 10 Ah to 200 Ah. A storage battery is of the “open” type if it operates at a relative pressure of not more than one bar (pressure difference relative to atmospheric pressure), the maximal operating pressure being fixed by the pressure at which a relief valve opens. An industrial type vented cell storage battery usually has a prism-shape plastics material container which contains plane electrodes. These aqueous alkaline electrolyte storage batteries are usually based on nickel-cadmium (Ni—Cd) and nickel-metal hydride (Ni—MH).
An industrial type vented cell storage battery includes an electrode package comprising a plurality of pairs. Each pair is made up of a positive electrode, a negative electrode and a separator between the positive and negative electrodes that is virtually impermeable to gases. The electrode package is immersed in a free electrolyte the quantity of which is much greater than that strictly required.
The operation of aqueous electrolyte storage batteries causes gases to be released at the end of charging, namely oxygen at the positive electrode and hydrogen at the negative electrode. A vented cell storage battery operates at a low pressure. The gases produced at the end of charging escape via the relief valve, which leads to consumption of the water of the electrolyte. The loss of water is estimated at approximately 0.3 cm
3
per ampere-hour. The storage battery therefore requires regular maintenance, in other words water must be added periodically. The maintenance frequency depends on the conditions of use of the storage battery in the application concerned, in particular the charged capacity.
To limit the frequency of topping up the electrolyte level after periods of operation, semi-flooded cell storage batteries have been developed in which the electrode package is immersed only partly in the electrolyte, which allows oxygen generated at the positive electrode access to the non-immersed part of the negative electrode, and so recombination occurs here (EP-0 070 646).
Under the above conditions recombination is never complete and these storage batteries still require maintenance. Also, the non-immersed part of the negative electrodes is exposed to an oxygen atmosphere which can degrade it.
To eliminate all maintenance sealed cell industrial type storage batteries derived from those previously described have been proposed (EP-0 666 608). A sealed cell storage battery operates at a relative pressure that can be higher than 1 bar. In a sealed cell storage battery the electrode package includes a separator between the negative and positive electrodes that is highly permeable to gases, allowing oxygen generated at the positive electrode access to the negative electrode, and so recombination occurs there. A sealed cell storage battery further includes an oxygen recombination device. The oxygen formed at the positive electrode at the end of charging leads to an increase in the internal pressure of the storage battery which depends on the charging current. Afterwards permanent conditions are established in which all of the oxygen produced at the positive electrode is reduced (or “recombined”). The electrolyte is introduced in limited quantities corresponding to the pore volume available in the components (electrodes, separator, recombination device).
The generation of gases can expel electrolyte from the pores in the electrode. This phenomenon shortens the service life of the battery by precipitating drying out of the electrode package. Document FR-1 012 395 proposes to provide a low-capacity sealed cell Ni—Cd storage battery with a volume in which the electrolyte expelled in this way can collect. The separators dip into the electrolyte and return the electrolyte to the electrode package.
Ni—MH storage batteries have a negative electrode in which the electrochemically active material is a hydridable metal alloy. Operation of the electrode in an aqueous medium means that corrosion of the hydridable alloy is inevitable. This reaction leads to additional consumption of water.
Where the electrolyte is introduced in limited quantities into the pores of the components, corrosion leads to premature drying out of the storage battery: its capacity falls and its service life is shortened. Document JP-8-96833 proposes to add in the lower part of an Ni—MH storage battery a chamber containing the electrolyte and separated from the electrode package by a sealed wall. An extension of the separator at the bottom of the electrode package passes through this wall and enters the chamber.
Although this increases the service life, the capacities of sealed cell storage batteries are lower than those of vented cell storage batteries. This is because, during the first cycles, the electrodes do not have enough electrolyte to reach their maximum efficiency. Subsequent addition of electrolyte will not have any effect on efficiency.
The aim of the present invention is to propose an industrial type vented cell storage battery that does not require any maintenance and whose energy per unit mass, energy per unit volume and the service life are increased over those of an industrial type sealed cell storage battery.
SUMMARY OF THE INVENTION
The present invention consists in an industrial type vented cell storage battery comprising:
an electrode package including at least one positive electrode containing nickel hydroxide, one negative electrode, and one hydrophilic and gas-permeable separator an extension of which beyond the electrode package is in contact with electrolyte contained in a space between the base of the electrode package and the bottom of the container adapted to contain at least part of an excess quantity of alkaline electrolyte, and
an oxygen recombination device.
Industrial type vented cell storage batteries usually have a prism-shape plastics material (polypropylene) container incapable of withstanding a high pressure (greater than 2 bars relative). In the storage battery of the present invention the separator is permeable to gases to allow oxygen generated at the positive electrode access to the negative electrode. The presence of a recombination device is nevertheless essential because it significantly increases the rate of recombination and enables equilibrium to be obtained at a moderate pressure, even when high charging currents are used. The recombination device includes one or more recombination sites connected to the negative polarity at which the reaction occurs. The device preferably includes a spacer in order to provide a constant volume for gas circulation. The device can include a spacer associated with an auxiliary electrode. A recombination system of the above kind is described in document EP-A-0 666 608 published Sept. 8, 1995, for example.
An industrial type vented cell storage battery is flooded with electrolyte to obtain a high electrode efficiency, higher than that observed in a sealed cell storage battery containing a quantity of electrolyte limited to the volume of the pores of the components. The storage battery of the present invention is flooded with electrolyte (i.e. it contains electrolyte in excess quantity) and includes a space capable of containing at least some of this excess electrolyte. The separator in contact with this electrolyte irrigates the electrode package by capillary action.
This space is between the base of the electrode package and the bottom of the container so that an extension of the separator beyond the bottom of the electrode package dips into the electrolyte contained in it. It can be obtained by raising the electrode package relative to the bottom of the storage battery. This arrangement has the advantage that some of the excess electrolyte is under the electrode package, instead of covering it. Acce
Berlureau Thierry
Liska Jean-Louis
Alcatel
Alejandro R
Ryan Patrick
Sughrue & Mion, PLLC
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