GB2101394A

GB2101394A - Safety means or electrochemical cells

Info

Publication number: GB2101394A
Application number: GB08216226A
Authority: GB
Inventors: Matzliach Babai; Jonathan R Goldstein
Original assignee: Tadiran Israel Electronics Industries Ltd
Current assignee: Tadiran Israel Electronics Industries Ltd
Priority date: 1981-06-18
Filing date: 1982-06-03
Publication date: 1983-01-12
Also published as: FR2508241B1; JPS584261A; GB2101394B; DE3222294C2; DE3222294A1; FR2508241A1; IL63120A; IL63120A0

Abstract

There are provided safety means for high energy density electrochemical cells, comprising in combination mechanical venting means and a liquid or gaseous additive compatible with the cell constituents which additive undergoes a steep pressure increase when the cell temperature is increased, and high energy density electrochemical cells of the type comprising a helically wound electrode of the alkali metal or alkaline earth metal type, with a carbon or inert metal current collector, a non-aqueous electrolyte of the inorganic oxyhalide or thiohalide solvent, with a solute dissolved therein, provided with venting means and an additive as defined above.

Description

SPECIFICATION Electrochemical cells The present invention relates to novel highenergy electromechanical cells provided with means for the prevention of the explosion of same when exposed to abuses such as external or internal shorting or disposal of in fire.

The miniaturization of electric and electronic devices has led to the development of reliable high-energy density electromechanical cells or batteries which can be stored over prolonged periods of time, and which can be safely operated over a wide range of temperatures. Recently developed electromechanical cells fulfilling such requirements comprise highly active anode materials such as lithium or calcium or the like, a non-aqueous liquid depolarizer material, a suitable salt dissolved in said depolarizer, and an inert carbon or similar cathode current collector.

Amongst cells which have been commercialized there are to be mentioned cells having a lithium anode, a carbon current collector, a non-aqueous electrolyte such as thionyl chloride, and a dissolved salt like lithium aluminium chloride.

Various similar cells have been described which make use of related depolarizers such as sulfuryl chloride, chromyl chloride, vanadium oxytrichloride, phosphorus oxychloride, thionyl bromide, selenium oxychloride and the like. Cells of the lithium/thionyl chloride/lithium aluminum tetrachloridelporous carbon type are commercially available in a lower power configuration, i.e. a bobbin configuration which is characterized by a comparatively low surface area of the anode and the cathode. Such cells are comparatively safe under conditions of abuse.

Similar cells, of the high power density type, with large-surface-area electrodes such as those with a spirally wound configuration are much more dangerous under conditions of abuse. Particularly severe modes of abuse are short-circuitry and external heating when the cell internal components reach a critical temperature above the melting point of the lithium anode. This is likely to happen when such high-energy density cells are exposed to external short-circuiting or internal short-circuiting which may occur unintentionally or intentionally upon compression of such cells or any other deformation thereof.

Internal shorts may create a hot-spot where the critical temperature is exceeded, thus causing the cell to explode. U.S. Patent No. 4,184,010 discloses electrochemical cells provided with a vent adapted to relieve internal pressures reaching about 350 psi. Such vents are likely to be adequate for external shorting, but probably not for internal shorting and for abuse by fire disposal. If for example a nail penetrates the frame of such cell, the resulting internal shorting is likely to cause conditions where the response of such a pressure vent is not adequate.

Summary of the invention: The present invention relates to a safety device for use with high energy density cells of the type where abuse may cause explosion of the cell due, for example, the heating of an internal component above a certain critical temperature. The novel safety device is not restricted to a specific type of cell or cell configuration, and it can be effectively used with different cells which are likely to explode when exposed to conditions of internai-or external short-circuiting or which are liable to explode when disposed of, in a fire.

The novel device according to the present invention comprises a pressure vent adapted to respond when a certain predetermined pressure is reached, and a cell provided with a substance having a high coefficient of change of pressure upon change of temperature. Said added component is preferably a gas or pressurized liquified gas which undergoes a rapid and abrupt change of pressure upon being exposed to a change of temperature. The vent is of the mechanical type; it can be a burst-disk or a weakened structure of the cell casing adapted to open when a certain internal pressure is reached.

When such gas or liquified gas is contained in such cells, same has to be compatible with all the other components of the cell. Generally the novel cells will be pressurized, i.e. the internal pressure of the cell at ambient temperature will be above atmospheric pressure. The gas or liquified gas ought to have a rapid change of pressure upon increase of temperature, and thus when the temperature increases there is rapidly reached a predetermined pressure which is adequate to burst the mechanical pressure seal. When the vent is opened, the contents of the cell are rapidly released, and this also causes a certain degree of cooling due to the Joule-Thompson effect.The pressure at which the vent will be burst open can be predetermined, and generally this will be about 350 psi. (23 atmospheres) The material added to the cell, which provides the desired steep rise of internal pressure with increase of temperature must be compatible with the components of the cell. It is advantageous to use a substance which will improve the performance of the cell: thus for example there is advantageously added a material which acts as supplementary cathodic depolarizer to the oxyhalide or thiohalide main depolarizer used in certain type of cells. It is advantageous to use gases which are easily liquified or even solidified, and these may be easily introduced into such cells during manufacture.Amongst substances suitable for the intended use there may be mentioned sulfur dioxide, chlorine, nitrogen dioxide, sulfur hexafluoride, fluorinated hydrocarbons or other inorganic or organic substances fulfilling the physical and chemical requirements. The material added must be chosen in such manner as to be compatible with the constituents of the electromechanical cell and have the physical characteristics required over the range of storage and use temperatures of such cells.

The cell casing is provided with a vent or pressure relief port which are adapted to relieve abruptly the internal pressure when a certain value of pressure is reached. The vent is designed to rupture abruptly when the predetermined pressure is reached, thus providing a large enough opening for the expulsion of the cell contents without any explosion of the cell. As an example, a vent fulfilling the requirements for venting the cell content comprises a groove of predetermined size and depth within the cell wall which will rupture when there takes place in the cell a certain predetermined pressure, and which is large enough to vent the fluid content of the cell upon rupturing. The remaining wall thickness, angle of the groove and material determine the bursting pressure and venting characteristics.

It is clear that the shape, size and configurations of the vent, bursting disc or groove are a matter of choice, and that these depend on the overall size of the cell and on the desired speed of venting in case of a mishap. The basic features of the invention are the combination of venting means and of an additive which results in an abrupt increase of pressure upon increase of internal temperature of the cell.

The weakened structure serving as pressure vent can be a groove of about 1 to 5 mm length and about 0.2 to 1 mm width, depending on the cell size, of a wall thickness of about 0.33 mm to 0.07 mm.

The structure will be such that it will burst before a predetermined pressure is reached. This is about 600 to 700 psi. (40 to 70 atmospheres) There may also be used a metal member in the bottom member of the cell, which is held in said bottom member by a glass to metal seal and which metal chamber will be ejected before such predetermined pressure is reached.

The invention is illustrated by the following examples, which are to be construed in a nonlimitative manner.

Example 1: Four D-size cells were produced having a lithium anode, a carbon anode current collector and an electrolyte comprising thionyl chloride and lithium aluminum tetrachloride, with electrodes each having the dimensions of 40 cm by 4.2 cm, having a glass separator between same, and spirally wound. These components were inserted into a nickel-plated cold-rolled steel container provided with a groove serving as a vent of 2 mm length by 0.25 mm width, with a remaining wall thickness of the casing of 0.05 mm. The groove was terminated at both ends by V-shaped incisions. The lithium anode was connected via a nickel tab to the container, while the carbon current collector was connected to a centrally mounted nickel fill tube acting as positive in the cell cover, insulated by a glass-to-metal seal. The cover is welded to the top of the cell.The cells were filled via the fill tube with an electrolyte of 50 wt-% sulfur dioxide in thionyl chloride containing 1.2 M lithium aluminum tetrachloride.

After filling the tube was crimped and welded to provide a hermetic seal. The internal pressure of such a cell under ambient temperature is about 28 to 42 psi. The four cells were disposed of in fire and all vented quietly without any explosions.

Similar cells without sulfur dioxide exploded when disposed of in the fire.

Output not adversely affected.

Example 2: Eight cells were produced as in Example 1, but in 4 of these there was introduced 60 wt-% sulfur dioxide in thionyl chloride and in the other 4 no sulfur dioxide at all. The cells were crushed between two metal plates using an air-driven piston in the direction perpendicular to the cylindrical container of the cell, i.e. perpendicular to the electrode stack, crushing the cell to 50% of the initial diameter. The cells containing sulfur dioxide vented quietly while those without SO2 exploded.

Example 3: Eight cells were produced according to Example 1, with 60 wt-% sulfur dioxide in thionyl chloride containing 1.2 M LiAICi4. Eight similar cells were produced but without sulfur dioxide. A 3 mm nail was thrust through the cells perpendicular to the longitudinal axis, with a pneumatic press. All the cells with SO2 vented quietly whilst all the cells without SO2 exploded.

Example 4: A cell produced according to Example 1, but with 50 wt-% sulfur dioxide in thionyl chloride containing 1.2 M LiAICI4, was discharged via a 1.5 ohm resistor and gave 4.8 Ah to a 2 V cut-off voltage. A second cell without sulfur dioxide gave 5.0 Ah to 2 V cut-off.

Claims

1. Safety means for high energy density electrochemical cells, comprising in combination mechanical venting means and a liquid or gaseous additive compatible with the cell constituents which additive undergoes a steep pressure increase when the cell temperature is increased.

2. Safety means according to claim 1, wherein the mechanical venting means comprise a valve or a groove in the cell casing, of suitable size and thickness, so as to burst when a predetermined pressure is reached.

3. Safety means according to claim 1 or 2, for use in lithium anode or calcium anode cells with thionyl chloride or a similar oxychloride or thiochloride electrolyte, wherein the additive is selected from sulfur dioxide, chlorine, nitrogen dioxide, sulfur hexafluoride and fluorinated hydrocarbons.

4. A high energy density electrochemical cell of the type comprising a helically wound electrode of the alkali metal or alkaline earth metal type, with a carbon or inert metal current collector, a non-aqueous electrnlyte of the inorganic oxyhalide or thiohalide type, with a solute dissolved therein, provided with mechanical venting means and an additive compatible with the cell constituents, which additive undergoes a steep pressure increase when the cell temperature is increased.

5. An electrochemical cell according to claim 4, wherein the anode is lithium anode, the current collector is made of porous carbon and the electrolyte comprises thionyl and dissolved lithium aluminum tetrachloride.

6. An electrochemical cell according to claim 4 or 5, wherein a groove of about 1 to 5 mm length by 0.2 to 1 mm width is provided with a wall thickness of about 0.03 to 0.07 mm.

7. A cell according to claim 6, wherein the additive is sulfur dioxide which comprises about 20 to 70 weight per cent of the electrolyte.

8. A cell according to claim 7, wherein the additive is sulfur dioxide, comprising 40 to 60 wt % of the electrolyte.

9. A cell, according to any of claims 4 to 8, wherein the venting means are adapted to burst before the pressure exceeds about 600 psi.

10. A cell according to any of claims 4 to 9, wherein the venting means are adapted to burst before a pressure of 200 psi is exceeded.

1 1. A cell according to any of claims 4 to 10, provided with venting means and an additive with steep rise of pressure versus temperature, substantially as hereinbefore described.

12. An electrochemical cell, substantially as hereinbefore described and illustrated by the foregoing Examples.

13. Safety means for high energy density electrochemical cells, substantially as hereinbefore described and illustrated by the foregoing Examples.