IL313993A - Secondary electrochemical cell and battery - Google Patents

Description

Secondary Electrochemical Cell and Battery FIELD AND BACKGROUND OF THE INVENTIONThe invention, in some embodiments, relates to the field of batteries andelectrochemical cells, especially secondary batteries and cells.An electrical battery is a device that provides electrical current. A battery comprisesone or more electrochemical cells connected in parallel or series, each cell including apositive electrode (during cell discharge, the cathode of the cell) in electrical communicationwith a positive terminal and a negative electrode (during cell discharge, the anode of the cell)in electrical communication with a negative terminal, the two electrodes separated one fromthe other with a membrane called a separator. The electrodes , the separator and a conductiveelectrolyte constitutes an electrode assembly that is held inside a case, where the positiveterminal and the negative terminal pass through the shell, thereby providing electricalcommunication between the electrodes and outside of the shell.When the two terminals are connected through a circuit, redox reactionsspontaneously occur at the electrodes, generating an electrical current that passes from onecontact to the other contact through the circuit accompanied by flow of ionic charge carriersfrom the negative electrode to the positive electrode in an electrolyte through the separator.Primary cells generate electrical current by irreversible redox reactions.Secondary cells generate electrical current by reversible redox reactions so thatsecondary cells are rechargeable. Known secondary cells include lead–acid, zinc–air, nickel–cadmium, nickel–metal hydride, lithium-ion, lithium iron phosphate, and lithium-ion polymersecondary cells. At the time of this writing, additional secondary cells are being developedincluding lithium-silver, sodium-ion, zinc-bromine, sodium-sulfur and silver-zinc secondarycells.In Figure 1A, a known 18650 lithium-ion secondary cell 10 is schematically depictedin side cross section. Cell 10 is substantially an 18 mm diameter by 65 mm length cylindercomprising a jelly-roll electrode assembly 12 contained inside a shell 14 , jelly-roll assembly 12 comprising a positive electrode layer and a negative electrode layer separated by aseparator layer and an electrolyte. Shell 14 includes a cylindrical can portion 16 with anintegrally-formed bottom 16a and an open top 16b . Open top 16b is sealingly closed bycrimping around a top-cap 18 . Both can portion 16 and top-cap 18 are made of a conductivemetal and are electrically insulated one from the other by a plastic gasket 20 . Top-cap 18 iselectrically connected to the positive electrode layer with a positive tab 22 so that top-cap 18 constitutes the positive terminal of cell 10 . Can portion 16 is electrically connected to thenegative electrode layer with a negative tab 24 so that can portion 16 constitutes the negativeterminal of cell 10 .In Figure 1B, a known 4680 lithium-ion secondary cell 26 is schematically depicted inside cross section. Cell 26 is substantially a 46 mm diameter by 80 mm length cylindercomprising a jelly-roll electrode assembly 12 contained inside a casing 14 . Casing 14 includes a cylindrical can portion 16 with an integrally-formed bottom 16a and an open top 16b . Open top 16b is sealingly closed by crimping around a can-closing disk 28 . An initially-present hole 28a that passes through can-closing disk 28 is sealed by welding. A copper disk 30 is welded to the end of the current collector of the negative electrode layer of electrodeassembly 12 and is also welded to the inside of can portion 16 so that can portion 16 constitutes the negative terminal of cell 10 . An aluminum disk 32 is welded to the end of thecurrent collectors of the positive electrode layer of electrode assembly 12 and is also weldedto the inner face of an electrically conductive positive button 34 . Positive button 34 passesthrough a hole in bottom 16a of can portion 16 and is electrically insulated from can portion 16 by insulating washer 36 , so that positive button 34 constitutes the positive terminal of cell 26 .One of the disadvantages of some electrochemical cells (such as some secondarycells, especially some secondary cells that include lithium) is thermal runaway, theuncontrolled and self-accelerating increase of the temperature inside the shell of anelectrochemical cell. Thermal runaway typically begins with a short circuit or other failure in aelectrochemical cell caused, for example, by physical damage that bends or penetrates theshell; a production defect in a cell component; overcharging; over-discharge; or excessiveheating of the cell. Subsequently in an acceleration stage, reactive components of theelectrode assembly exothermically react with the electrolyte, releasing more heat than isdissipated by the cell together with the release of gaseous reaction products inside the casing.The pressure and the rate of the exothermic reactions increases. Actual thermal runawayoccurs when heating is very rapid for example a rate of 10 °C / minute, typically occurring ata temperature of about 130 °C to about 200 °C , depending on the cell type. The thermalrunaway increases the pressure inside the shell until the side of the shell rupturesaccompanied by ejection of a very hot jet of gases and particulate remnants of the electrodeassembly.

In a battery that includes more than one cell, cells neighboring the failed cell areheated during the acceleration stage and during the thermal runaway and can be physicallydamaged as a result of the shell rupture. Such heating and/or physical damage may triggerthermal runaway in the neighboring cells of the battery and even a chain reaction thatultimately destroys most or all of the cells of the battery. Thermal runaway can lead to failureof a cell or battery and can be accompanied by overheating, release of flammable / toxicgases, fire and explosion.It would be useful to have batteries comprising one or more electrochemical cellsconfigured so that the damage and/or danger caused in the event of thermal runaway orconditions leading up to thermal runaway, are reduced compared to known batteries andcells.

SUMMARY OF THE INVENTIONSome embodiments of the invention relate to electrochemical cells and/or to batteriesthat comprise one or more such electrochemical cells, such a cell configured to release gasfrom inside the shell of the cell when the internal pressure inside the shell is above apredetermined threshold. The cell is thereby configured to mitigate the damaging effects ofthermal runaway in the cell.According to an aspect of some embodiments of the teachings herein, there isprovided a secondary electrochemical cell, comprising:a shell defining a sealed internal volume;contained in the internal volume, an electrode assembly comprising a positiveelectrode, a negative electrode, a separator and an electrolyte;a positive terminal providing electrical communication between the positive electrodeand the outside of the shell; anda negative terminal providing electrical communication between the negativeelectrode and the outside of the shell;the shell having a predesigned weak area such that, when pressure inside the internal volumeis above a predetermined threshold pressure, the weak area is selectively breached forming abreach, allowing release of gas from the internal volume through the breach.In some embodiments, the secondary electrochemical cell is a lithium-ion secondaryelectrochemical cell.In some embodiments, the shell is a rigid shell. Alternatively, in some embodimentsthe shell is a flexible shell.

In some embodiments, the cell is configured so that the release of gas from theinternal volume is accompanied by ejection of at least some of the electrode assembly fromthe internal volume of the cell through the breach.In some embodiments, the release of gas through the breach is in a predetermineddirection.In some embodiments, the predesigned weak area is configured to reseal after therelease of gas.In some embodiments, the predesigned weak area comprises a valve. In some suchembodiments, the valve comprises a one-way valve.In some embodiments, the predesigned weak area comprises a plug blocking a pre-existing hole in the shell, configured so that the breaching of the predesigned weak areacomprises the plug unblocking the hole as a result of excess pressure inside the internalvolume. In some such embodiments, the configuration comprises the plug being configuredto change shape as a result of excess pressure inside the internal volume, the change of shapeleading to the breaching of the predesigned weak area. In some embodiments, theconfiguration comprises the plug being configured to translate relative to the hole as a resultof the excess pressure.In some embodiments, the predesigned weak area comprises a weak portion of theshell and the breaching comprises irreversible damage to the shell.In some embodiments, the cell further comprises a heat-sensitive componentfunctionally associated with the at least one weak area, configured so that the breaching isfacilitated by a physical change of the heat-sensitive component caused by an elevatedtemperature inside the internal volume.In some embodiments, the cell further comprises inside the internal volume, a gas-generating material that generates gas inside the internal volume when the temperature insidethe internal volume passes an activation temperature thereby increasing the pressure insidethe internal volume.In some embodiments, the gas-generating material is an additional componentdifferent from the electrode assembly.In some embodiments, the gas-generating material is a component of the pre-designedweak area. In some embodiments, the weight of the gas-generating material is not less than about1% of the weight of the electrode assembly.

In some embodiments, the gas-generating material comprises at least one member ofthe group of materials consisting of sodium carbonate, ammonium carbonate, zinc carbonate,sodium bicarbonate, potassium bicarbonate, ammonium bicarbonate, azodicarbonamide,potassium allophanate, xylitol pentanitrate, 1,3,5-Trinitro-1,3,5-triazinane, guanidiniumnitrate, ethylene glycol dinitrate and diazomethane and combinations thereof. In some embodiments, the gas-generating material is a solid at 25°C and 100 kPa.In some embodiments, the generation of gas is endothermic.In some embodiments, the generated gas is a fire retardant.In some embodiments, the generation of gas is by thermal decomposition of the gas-generating material.According to an aspect of the teachings herein, there is also provided a batterycomprising at least one secondary electrochemical cell as described herein. In someembodiments, the battery comprises a casing in which the at least one cell is contained, and avolume in the casing not occupied by cells,wherein in at least some of the volume not occupied by cells is a heat sink material,configured to passively absorb at least some of the heat generated by a cell during thermalrunaway, the heat sink material selected from the group consisting of a liquid, a gel and and asolid.

BRIEF DESCRIPTION OF THE FIGURESSome embodiments of the invention are described herein with reference to theaccompanying figures. The description, together with the figures, makes apparent to a personhaving ordinary skill in the art how some embodiments of the invention may be practiced.The figures are for the purpose of illustrative discussion and no attempt is made to showstructural details of an embodiment in more detail than is necessary for a fundamentalunderstanding of the invention. For the sake of clarity, some objects depicted in the figuresare not to scale.In the Figures:Fig. 1A (prior art) schematically depicts a 18650 lithium-ion secondary cell in side Fig. 1B (prior art) schematically depicts a 4680 lithium-ion secondary cell in sidecross section;cross section;Fig. 2 schematically depicts a battery according to the teachings herein in side crosssection, the battery having eight electrochemical cells according to the teachings herein, ofwhich four are depicted; Figs. 3A and 3B schematically depict an embodiment of an electrochemical cellaccording to the teachings herein in side cross section, the cell having a jelly-roll electrodeassembly, in Figure 3A during normal operation and in Figure 3B subsequent to breaching ofa predesigned weak area;Figs. 4A, 4B, 4C and 4D schematically depict four different embodiments ofelectrochemical cells according to the teachings herein in side cross section all comprising agas-generating material inside the internal volume of the shell of the cell, the gas-generatingmaterial being: in Figure 4A the gas-generating material being a powder that has beencompressed into a single solid disk; in Figure 4B the gas-generating material being a powderseparated from the electrode assembly by a partition; in Figure 4C the gas-generatingmaterial being a powder contained inside a metal foil capsule; and in Figure 4D the gas-generating material being a powder held together as a clump with a wax;Figs. 5A and 5B schematically depict an embodiment of an electrochemical cellaccording to the teachings herein similar to a known 18650 lithium-ion secondary cell in sidecross section (Figure 5A) and a view towards a bottom face (Figure 5B);Figs. 6A and 6B schematically depict an embodiment of an electrochemical cellaccording to the teachings herein in perspective view, the cell being a pouch cell having ashell with a weak portion, in Figure 6A during normal operation and in Figure 6B subsequentto breaching of the weak portion of the shell;Figs. 7A, 7B and 7C schematically depict an embodiment of an electrochemical cellaccording to the teachings herein the cell being a pouch cell having two one-way valves aspredesigned weak areas, in Figure 7A in perspective view, in Figure 7B in side cross sectionduring normal operation and in Figure 7C subsequent to breaching of a one-way valve;Figs. 8A and 8B schematically depict an embodiment of an electrochemical cellaccording to the teachings herein in side cross section, the cell having a prismatic shell with apredesigned weak area comprising a hole ordinarily blocked by a pressure-sensitive plug, inFigure 8A during normal operation and in Figure 8B subsequent to breaching of thepredetermined weak area;Figs. 9A and 9B schematically depict an embodiment of an electrochemical cellaccording to the teachings herein in side cross section, the cell having a prismatic shell with apredesigned weak area comprising a hole ordinarily blocked by a temperature-sensitive plug,in Figure 9A during normal operation and in Figure 9B subsequent to breaching of thepredetermined weak areacaused by the plug changing shape as a result of an elevatedtemperature of the cell; and Figs. 10A and 10B schematically depict an embodiment of an electrochemical cellaccording to the teachings herein in side cross section, the cell having a predesigned weakarea comprising a hole ordinarily blocked by a temperature-sensitive plug, in Figure 10Aduring normal operation and in Figure 10B during the process of breaching of the hole causedby portions of the plug vaporizing and/or decomposing as a result of an elevated temperatureof the cell.

DESCRIPTION OF SOME EMBODIMENTS OF THE INVENTIONThe invention, in some embodiments thereof, relate to electrochemical cells and/or tobatteries that comprise one or more such electrochemical cells, such a cell configured torelease gas from inside the shell of the cell when the internal pressure inside the shell isabove a predetermined threshold. The cell is thereby configured to mitigate the damagingeffects of thermal runaway in the cell.The principles, uses and implementations of the teachings herein may be betterunderstood with reference to the accompanying description and figures. Upon perusal of thedescription and figures present herein, one skilled in the art is able to implement the inventionwithout undue effort or experimentation. In the figures, like reference numerals refer to likeparts throughout. Before explaining at least one embodiment in detail, it is to be understood that theinvention is not necessarily limited in its application to the details of construction and thearrangement of the components and/or methods set forth herein. The invention is capable ofother embodiments or of being practiced or carried out in various ways. The phraseology andterminology employed herein are for descriptive purpose and should not be regarded aslimiting.According to an aspect of some embodiments of the teachings herein, there isprovided a secondary electrochemical cell, comprising:a shell defining a sealed internal volume;contained in the internal volume, an electrode assembly comprising a positiveelectrode, a negative electrode, a separator and an electrolyte;a positive terminal providing electrical communication between the positive electrodeand the outside of the shell; anda negative terminal providing electrical communication between the negativeelectrode and the outside of the shell; the shell having a predesigned weak area such that, when pressure inside the internal volumeis above a predetermined threshold pressure, the predesigned weak area is selectivelybreached forming a breach allowing release of gas from the internal volume through thebreach.When a secondary electrochemical cell undergoes thermal runaway, the pressureinside the internal volume of the cell increases due to the increase of temperature and theformation of gases due to vaporization, thermal decomposition and chemical reactions ofsome components of the cell, typically components of the electrode assembly. In prior art secondary electrochemical cells, when the internal pressure is sufficientlyhigh, the side of the shell ruptures releasing gases and cell fragments and potentiallydamaging the surroundings. Prior to the rupture of the shell, the elevated temperature of thecell potentially damages the surroundings. The damage caused by the rupture of the shell andthe elevated temperature can trigger thermal runaway in neighboring cells. In contrast, in cells according to the teachings herein, the predesigned weak area isselectively breached (i.e., portions of the shell that are not a predesigned weak area are notbreached) at a predetermined threshold pressure that corresponds to a temperature that doesnot substantially damage the surroundings, e.g., ignites a fire, melts some object or triggersthermal runaway in a neighboring cell). The temperature that corresponds to thepredetermined threshold pressure is preferably substantially lower than the temperature atwhich shells of prior art shells rupture.Further, a cell of the teachings herein is preferably configured so that the breaching ofthe predesigned weak area does not substantially damage the surroundings, e.g., does notscatter dangerous fragments or damage neighboring cells to the extent that these may betriggered to undergo thermal runaway. Additionally, the release of gas from the internal volume following the breaching of apredesigned weak area removes heat from inside the cell, thereby reducing the temperature ofthe cell, potentially assisting in reducing damage and suppressing thermal runaway. The predetermined threshold pressure is any suitable threshold pressure that allowsrelease of gas through a breach formed by the breaching of predetermined weak area withoutan uncontrolled rupture of the shell as known in prior art cells. Preferably, at thepredetermined threshold pressure the only place gas is released from the internal volume isthrough a breach formed by the breaching of the predetermined weak area. A cell according to the teachings herein is configured with any suitable chemistry,including any suitable known chemistry, for example a lithium-ion secondary electrochemical cell (e.g., lithium polymer, LiCoO, LiFePO, LiMnO, LiMnO, LMR-NMC, LiNiMnCoO, LiAg) and a sodium-ion secondary electrochemical cell. A cell according to the teachings herein has any suitable electrode assembly,including any suitable known electrode assembly structure, for example, jelly-roll electrodeassembly or flat laminated electrode assembly. A cell according to the teachings herein has any suitable shell, including any suitableknown shell. In some embodiments, the shell is a rigid shell, e.g., a rigid cylindrical shell, arigid prismatic cells, a button shell. In some embodiments, the shell is a flexible shell, e.g., apouch cell.In some embodiments, the cell is configured so that the release of gas from theinternal volume is accompanied by ejection of at least some of the electrode assembly fromthe internal volume. An advantage of such embodiments is that the ejection of at least someof the electrode assembly reduces the rate of and even stops the chemical reactions that leadto thermal runaway and assists in dispersing excess heat to the surroundings.In some alternative embodiments, the cell is configured so that only gas and particlesentrained therein are released from the internal volume when the weak area is breached. By preventing escape of large of the large components and fragments of the electrodeassembly from the internal volume of the cell, contamination of the surroundings withpotentially dangerous fragments is reduced.In preferred embodiments, the release of gas (and in some embodiments, at least someof the electrode assembly) is in a predetermined direction. In such embodiments, for use thecell is preferably installed (e.g., in a battery) so that the gas is released in a direction thatavoids or reduces damage to the surroundings, for example, neighboring cells.In some embodiments, once the predesigned weak area is breached, the internalvolume of the cell is no longer sealed. Alternatively, in some embodiments, the predesignedweak area is configured to reseal after the release of gas. In some embodiments, the predesigned weak area comprises a valve. In some suchembodiments, the predesigned weak area comprises a one-way valve. In some embodiments, the predesigned weak area of the shell comprises a plugblocking a pre-existing hole in the shell configured so that the breaching comprises the plugunblocking the hole as a result of excess pressure inside the internal volume therebybreaching the predesigned weak area. In some such embodiments, by excess pressure ismeant any pressure above about 100 kPa, typically near or equal to the predeterminedthreshold pressure. In some such embodiments, the configuring of the shell comprises the plug being configured to change shape as a result of excess pressure inside the internalvolume, the change of shape of the plug leading to breaching of the predesigned weak area.Additionally or alternatively, in some such embodiments, the configuring of the shellcomprises the plug being configured to translate relative to the pre-existing hole as a result ofexcess pressure inside the internal volume, e.g., the plug is physically pushed out of the holeby the excess pressure.In some embodiments, the predesigned weak area comprises a weak portion of theshell and the breaching comprises irreversible damage to the shell at the weak portion, e.g.,tearing, rupturing, cracking, breaking and/or delamination of the weak portion. In some embodiments, the cell further comprises a heat-sensitive componentfunctionally associated with the at least one weak area, configured so that the breaching ofthe weak area is facilitated by a physical change of the heat-sensitive component caused byan elevated temperature inside the internal volume. In some embodiments, the physicalchange of the heat-sensitive component is at least one of losing adhesiveness, at leastpartially melting, at least partially softening, at least partially decomposing, at least partiallyvaporizing and changing shape. In some embodiments, a cell according to the teachings herein further comprisesinside the internal volume, a gas-generating material that generates gas inside the internalvolume when the temperature inside the internal volume passes an activation temperaturethereby increasing the pressure inside the internal volume. The activation temperature ispreferably a temperature that is higher than the desired maximal operating temperature of thecell. For example, some prior art vehicle secondary electrochemical cells are heated to up to°C during charging and some LiFePO cells can operate at temperatures of up to 65 °C. Insome embodiments, the activation temperature of gas-generating material is preferably notless than about 70 °C, not less than about 80 °C and even not less than about 90°C. In someembodiments, the activation temperature is lower than a temperature which damages thesurroundings. For example, in some embodiments, the activation temperature is not greaterthan about 285 °C (the upper limit for thermal resistance of Bakelite®), not greater thanabout 200 °C and even not greater than about 150 °C.In some embodiments, the gas-generating material is an additional componentdifferent from the electrode assembly (inter alia, is not a component of the electrolyte or ofthe separator). In preferred embodiments the predesigned weak area of a cell comprising agas-generating material is breached at a lower (and therefore less dangerous) temperaturethan a substantially equivalent cell with such a gas-generating material as in the latter cell, the predesigned weak area is breached by pressure that results from products of vaporizationand/or decomposition of components of the electrode assembly such as the separator and/orelectrolyte.Any suitable amount of gas-generating material is present inside the internal volume.In some embodiments, the weight of the gas-generating material is not less than about 1%,not less than about 2% and even not less than about 5% of the weight of the electrodeassembly. Additionally or alternatively, in some embodiments the weight of the gas-generating material is not more than about 50% of the weight of the electrode assembly. The gas-generating material is of any suitable phase, e.g., a solid, a liquid, a gel.In some preferred embodiments, the gas-generating material is hygroscopic. As isknown in the art, in some instances water is found inside the internal volume of anelectrochemical cell. In embodiments where the gas-generating material is hygroscopic, inaddition to the other functions, the gas-generating material also functions to absorb and/oradsorb any water that is found inside the internal volume, thereby improving batteryperformance and reducing the chance of thermal runaway. In some embodiments, the gas-generating material is present inside the internalvolume as a particulate material (e.g., a powder). In some such embodiments the particles ofthe material are held together as opposed to being loose particles inside the cell, for example,are confined inside a capsule and/or are held together by an adhesive or similar materialand/or are embedded in a matrix (e.g. a wax) and/or are compressed together.In some preferred embodiments, the gas-generating material is present inside theinternal volume in a high-surface area form. As used herein, the surface area of the low-surface area form of the amount of gas-generating material present in a cell is the surface areaof a non-porous sphere of that amount of gas-generating material. A high-surface area formof the gas-generating material is a form that has a surface area that is not less than 10x andeven not less than 20x of the low-surface area form. A high-surface area form reacts morequickly when the temperature inside the internal volume passes the activation temperatureand, if relevant, is more effective in absorbing / adsorbing water.In some embodiments, a high-surface area can be achieved by distributing the gas-generating material over two or more discrete pieces, e.g.,, at least two, at least three, at leastfour and even at least 6 discrete pieces. The two or more discrete pieces have any suitableshape, for example, spheres, balls, tablets, rods, flakes and polyhedrons. That said, in someembodiments, a high-surface area can be achieved by providing the one or more pieces with ashape that inherently has a high-surface area shape, e.g. a rod or flake.

Additionally or alternatively, in some embodiments, a high-surface area can beachieved by providing one or more pieces that are porous allowing water vapor and gases topenetrate into the one or more pieces. Additionally or alternatively, in some embodiments, a high-surface area can beachieved by providing one or more pieces that are textured, that is to say, the surface of theone or more pieces is not smooth but includes surface-area increasing features such as ridges,grooves, spikes and pores.In some embodiments, the gas-generating material is a solid at 25°C and 100 kPa.In some embodiments, the generation of gas is by thermal decomposition of the gas-generating material.In preferred embodiments, the generation of gas is endothermic. Such embodimentshave the advantage of removing heat from cell, thereby potentially assisting in reducingdamage and suppressing thermal runaway. In some preferred embodiments, the generated gas is non-flammable. In preferredembodiments, the generated gas is a fire retardant, for example, carbon dioxide, water ornitrogen.In some embodiments, the gas-generating comprises at least about 50%, at least about60%, at least about 70% and even at least about 80% by weight of an inorganic salt, forexample a carbonate or bicarbonate. Advantages of some carbonates and bicarbonates is thatthese are non-flammable, thermally decompose to non-flammable products and hygroscopic.In some embodiments, the gas-generating material comprises (and in some embodimentsconsists of) at least one material selected from the group consisting of sodium carbonate,ammonium carbonate, zinc carbonate, sodium bicarbonate, potassium bicarbonate,ammonium bicarbonate, azodicarbonamide, potassium allophanate, xylitol pentanitrate,1,3,5-Trinitro-1,3,5-triazinane, guanidinium nitrate, ethylene glycol dinitrate anddiazomethane and combinations thereof. In some embodiments, the gas-generating comprise a combination of potassiumbicarbonate and sodium bicarbonate, preferably at a ratio of from about 100:19 to about100:14 (w/w), similar or identical to Purple-K.In some embodiments, the gas-generating material comprises a decomposition-temperature lowering additive. For example, sodium carbonate ordinarily decomposes at550°C but in the presence of additives such as CaO and Ca(OH) the decompositiontemperature is lower. material Name CAS Nr. phase at STP decomposition [°C] gases released NaCOsodium carbonate 207-838-8 solid 550°C CO(NH)COammoniumcarbonate506-87-6 solid 58°C CO, NH, HO ZnCOzinc carbonate 3486-35-9 solid 140°C CONaHCOsodiumbicarbonate144-55-8 solid 80°C CO, HO KHCOpotassiumbicarbonate298-14-6 solid 100-200°C CO, HO NHHCOammoniumbicarbonate1066-33-7 solid 60°C CO, NH, HO CHONazodicarbonamide 123-77-3 solid 225°C N, CO, CO, NHKCHNOpotassiumallophanate26479-35-solid 270°C CO, CO, NH CHNO xylitol pentanitrate 147-16-0 solid 163°C CO, HO, N, O CHNO 1,3,5-trinitro-1,3,5-triazinane 121-82-4 solid 170°C CO, HO, N, O CHNO guanidiniumnitrate 506-93-4 solid 240°C HO, N CHNO ethylene glycoldinitrate628-96-6 liquid CO, HO, N, O CHNdiazomethane 334-88-3 liquid 100°C N TABLE 1: Exemplary Gas-Generating Materials According to an aspect of some embodiments of the teachings herein, there is alsoprovided a battery comprising at least one secondary electrochemical cell according to theteachings herein. In Figure 2, a battery 38 according to the teachings herein is depicted in side crosssection, battery 38 comprising a battery casing 40 having a casing box 40a and a casing lid 40b containing eight secondary electrochemical cells 42 according to the teachings herein. InFigure 3, only four of the eight secondary electrochemical cells 42 are depicted, cell 42a , 42b , 42c and 42d .In some embodiments of a battery, there is a volume that is not occupied by cellsinside the battery casing, in some instances between neighboring cells. In Figure 2, there is avolume 44 not occupied by cells 42 inside battery casing 40 . In some embodiments, the volume not occupied by cells is empty. In some embodiments, present in at least some of thevolume not occupied by cells are temperature-controlling conduits (e.g., conduits fortransporting a cooling / heating fluid in proximity of the cells allowing the cells to bemaintained in a close to ideal temperature range by heating or cooling. Additionally oralternatively, in some embodiments present in at least some of the volume is a heat sinkmaterial, confirmed to passively absorb at least some of the heat generated by a cell duringthermal runaway, the heat sink material selected from the group consisting of a liquid, a geland a solid. In some embodiments, the heat sink material fills at least 20%, at least 40% andeven at least 60% of the volume of battery case that is not occupied by some other solidcomponent. In some embodiments, a heat sink material is selected from the group consistingof water or a hydrogel. In some embodiments, a heat sink material is a non-explosive non-flammable solid material that thermally decomposes at a decomposition temperature, therebyabsorbing heat. In preferred such embodiments, the decomposition produces a non-flammablegas, for example one or more of water, carbon dioxide and/or nitrogen. In preferred suchembodiments, the decomposition temperature is not less than about 60 °C, not less than about°C and even not less than about 75 °C. Additionally or alternatively, in preferred suchembodiments, the decomposition temperature is not greater than about 200 °C, not greaterthan about 150 °C and even not greater than about 120 °C. In some such embodiments, such asolid material comprises or consists of a material selected from the group consisting of aninorganic material, a carbonate, a bicarbonate, sodium bicarbonate, potassium carbonate, zinccarbonate and combinations thereof.In some embodiments, a battery according to the teachings herein that comprisesmore than one secondary electrochemical cell according to the teachings herein is configuredso that selective breaching of a weak area of the cell leads to disconnection of that cell fromthe battery contacts while preserving the connection of at least one other cell with the batterycontacts. As a result, a breached cell does not lead to total failure of the battery, rather thebattery continues to function with some remaining functioning cells.

A single secondary electrochemical cell 42 such as found in battery 38 is depicted inside cross section in Figure 3A (during normal use) and in Figure 3B (after breaching of thepredesigned weak area). Like known secondary electrochemical cells, cell 42 comprises:a shell 46 defining a sealed internal volume 48 ;contained in internal volume 48 is an electrode assembly 12 (a jelly-roll electrodeassembly) comprising a positive electrode, a negative electrode, a separator; and an electrolyte (typically a liquid or gel comprising an organic solvents, electrolyte salts(e.g., lithium ion) and additives);a positive terminal 50a providing electrical communication between the positiveelectrode of electrode assembly 12 and the outside 52 of shell 46 ; anda negative terminal 50b providing electrical communication between the negativeelectrode of the electrode assembly and the outside 52 of shell 46 .Shell 46 has one predesigned weak area 54 such that, when pressure inside internalvolume 48 is above a predetermined threshold pressure, weak area 54 is selectively breachedto form a breach, allowing release of gas from internal volume 48through the breach to theoutside 52 of shell 46 .Cell 42 is a lithium polymer secondary electrochemical cell.Shell 46 of cell 42 is a rigid cylindrical shell. In cell 42 , shell 46 includes two parts: an upper part 46a and a lower part 46b .Upper part 46a defines most of internal volume 48 . Upper part 46a is substantially aright cylinder that has a closed proximal end 46c (through which terminals 50a and 50b pass)and an open distal end 46d . Lower part 46a is substantially a plug having a cylindrical shape with two outerdiameters: a wide distal portion 46a which has an outer diameter identical to that of upperpart 46a and an narrow proximal portion 46f that that has an outer diameter allowing narrowproximal portion 46f to slide into open distal end 46d of upper part 46a to a snugly matedstate.In the mated state which is the ordinary state for operation of cell 42 , depicted inFigure 3A, internal volume 48 is sealed and the seam between upper part 46a and lower part 46b constitutes predesigned weak area 54 .When the pressure inside internal volume 48 increases above a predeterminedthreshold, for example resulting from a high internal temperature caused by thermal runaway,the pressure pushes lower part 46b away from and out of upper part 46a in an axialtranslation motion, thereby selectively breaching shell 46 . Open distal end 46d of upper part 46a of shell 46 constitutes a breach through which gas from internal volume 48 is released,see Figure 3B. Concurrently with the release of gas, the gas also ejects components ofelectrode assembly 12 (the central part of the spiral that constitutes the jelly-roll of electrodeassembly 12 and is not anchored to closed proximal end 46c of upper part 46a of shell 46 byterminals 50a and 50b ). As can be seen when studying Figure 2 in light of Figure 3B, therelease of gas and ejection of components of electrode assembly 12 is in a predetermined direction, axially away from terminals 50a and 50b towards lid 40b of battery casing 40 . Insuch a way, when predesigned weak area 54 of cell 42 is breached, ejected components ofelectrode assembly 12 and released gas do not damage or substantially contaminate thesurroundings including neighboring cells, instead pushing lid 40b off of box 40a of batterycasing 40 . In some embodiments of cell 42 , upper part 46a and lower part 46b of shell 46 arefashioned to snugly fit so that the parts are held together by friction with a force that isovercome by the predetermined threshold pressure.In some alternative embodiments, the two shell parts 46a and 46b are held togetherand sealed by a heat-sensitive material, for example, a heat-sensitive adhesive or athermoplastic polymer such as polyethylene, that is present in the interface between the twoparts. A high internal temperature inside internal volume 48 causes the heat-sensitive materialto soften (for polyethylene at between about 80° - 120° C) and even melt (for polyethylene atbetween about 120° - 130° C). In such embodiments, the force required to separate parts 40a and 40b at normal operating temperatures of less than 60° is relatively high, but the softeningand/or melting of the heat-sensitive material reduces the force required to breach predesignedweak area 54 and to push lower part 46b out of upper part 46a to be equivalent to the forceapplied by the predetermined threshold pressure.Additionally or alternatively, in some alternative embodiments of cell 42 , at least aportion of upper part 46a of shell 46 , for example open distal end 46d thereof, is configuredto deform when the pressure in internal volume 48 is elevated from normal but is not greaterthan the predetermined threshold pressure. Such deformation is such as to reduce the frictionthat keeps upper part 46a and lower part 46b in a mated state, for example is outwardexpansion (e.g., increase in diameter) of open distal end 46d of upper part 46a whichconfiguration can include the choice of material from which upper part 46a of shell 46 ismade and the thickness thereof. Optionally, narrow proximal portion 46f of lower part 46b ofshell 46 is additionally configured to be resistant to any such deformation.

Cell 42 depicted in Figures 3A and 3B is devoid of a gas-generating material insideinternal volume 48 that is not a component of electrode assembly 12 . Consequently, thepressure inside internal volume 48 substantially increases only when the temperature insideshell 46 is sufficient to generate gases, for example, by vaporizing and/or thermally-decomposing components of electrode assembly 12 .

Gas-generating materialIn Figures 4A, 4B, 4C and 4D are depicted embodiments of a cell according to theteachings herein that are substantially similar to cell 42 depicted in Figures 3A and 3B butcomprise a gas-generating material that is different from the electrode assembly inside theinternal volume, the gas-generating material being a component configured to generate gasinside the internal volume when the temperature inside the internal volume passes anactivation temperature. Such generation of gases thereby increasing the pressure inside theinternal volume so that predesigned weak area 54 is selectively breached at a lowertemperature than a comparable cell devoid of the gas-generating material.In Figure 4A, a cell 56 comprises as a gas-generating material 58 , a solid gas-generating material such as an inorganic salt (e.g., sodium carbonate, ammonium carbonate,zinc carbonate, sodium bicarbonate, potassium bicarbonate, ammonium bicarbonate andcombinations thereof) compressed into a single solid disk. At an activation temperature (thatis conducted to gas-generating material 58 inside internal volume 48 or through the walls ofthe shell), gas-generating material 58 thermally decomposes (typically endothermically),releasing a gas inside internal volume 48 . In some such embodiments, instead of a singledisk, the gas-generating material is distributed among two, three or even more distinct units,e.g., pellets, balls, disk, rods, in order to increase the surface area and potentially to increasethe rate of gas generation when the activation temperature is reached.In Figure 4B, a cell 60 comprises a powder (e.g., azodicarbonamide, potassiumallophanate or xylitol pentanitrate) as a gas-generating material 58 behind a partition 62 , e.g.,a sheet or foil of a metal (e.g., aluminum) or of a polymer (polycarbonate, polyethylene). Atan activation temperature, gas-generating material 58 thermally decomposes, rupturingpartition 30 and releasing a gas inside internal volume 48 . In some preferred suchembodiments, partition 62 is permeable to water vapor (e.g., a fabric such as Nomex fabric)and gas-generating material 58 is hygroscopic (e.g., a carbonate or a bicarbonate) where theholes in the fabric are such that particles of gas-generating material 58 cannot pass partition 62 but water vapor can pass partition 62 to be absorbed /adsorbed by gas-generating material 58 . In Figure 4C, a cell 64 comprises a powder (e.g., azodicarbonamide, potassiumallophanate or xylitol pentanitrate) or a liquid (e.g., Guanidinium nitrate or 1,3,5-Trinitro-1,3,5-triazinane) as a gas-generating material 58 contained inside a metal foil capsule 66 . Atan activation temperature, gas-generating material 58 thermally decomposes, rupturingcapsule 34 and releasing a gas inside internal volume 48 .

In Figure 4D, a cell 68 comprises a powder (e.g., of ammonium carbonate, zinccarbonate, sodium carbonate, ammonium carbonate) as a gas-generating material 58 whichparticles are aggregated together into a clump 70 with the help of a wax. The specific waxand the specific gas-generating material are selected so that the activation temperature is nearthe melting point of the wax.

Breaching of a weak portion of a shellIn some embodiments, the predesigned weak area comprises a weak portion of theshell and the breaching comprises irreversible damage to the shell at the weak portion, e.g.,tearing, rupturing and/or delamination.A first such an embodiment is a cell 72 depicted in Figure 5A in side cross sectionand Figure 5B a view towards a bottom face 74 of a can portion 16a of a shell 46 . Cell 72 issubstantially similar to a known 18650 lithium-ion secondary cell such as cell 10 depicted inFigure 1. Unlike cell 10 , cell 72 comprises, as a predesigned weak area 54 , grooves 76 engraved (or otherwise applied) to bottom face 74 of can portion 16a of shell 46 of cell 72 .Grooves 74 are sufficiently deep so that at a predetermined threshold pressure in internalvolume 48 , bottom face 74 selectively breaks at grooves 76 , thereby breaching predesignedweak area 54 , allowing the release of gas through the thus-formed breach. A second such embodiment is a cell 78 depicted in perspective view in Figures 6A(during normal use) and 6B (after breaching of the predesigned weak area). Cell 78 is similarto a prior art flexible pouch cell having a flat laminated electrode assembly. Unlike prior artpouch cells where the two faces of the shell of the cell are adhered one to the other along theentire periphery to avoid any rupture, in cell 78 a specific small part of a periphery 80 of shell 46 is a predesigned weak area 54 . When the pressure inside the internal volume of shell 46 is above a predeterminedthreshold pressure, weak area 54 delaminates to allow selective breaching allowing release ofgas from the internal volume in a predetermined direction, see Figure 6B.A person having ordinary skill in the art is able to make a weak area on a portion of aperiphery of the shell of a cell, for instance, by more-weakly securing the two faces of thepouch cell at the weak area during manufacture of the shell, or by weakening a specified areaafter manufacture, e.g., by perforation or heat treatment. As with all other suitable embodiments of a cell of the teachings herein, cells wherethe predesigned weak area comprises a weak portion of the shell and the breaching comprises irreversible damage to the shell at the weak portion may or may not additionally comprise agas-generating material inside the internal volume as described above.

One-way valveIn Figures 7A (perspective view during normal use), 7B (side cross section duringnormal use) and 7C (side cross section during release of gas from the internal volume) isdepicted a cell 82 . Cell 82 is similar to a prior art flexible pouch cell having a flat laminatedelectrode assembly 12 . Cell 82 comprises two one-way duckbill check valves 84 (forexample, made of high-temperature resistant silicone rubber) that provide one-way fluidcommunication from an internal volume 48 to the outside 52 and which constitute the twopredesigned weak areas 54 of cell 82 . As known in the art of valves, a duckbill check valve issubstantially a tube that is ordinarily biased to a collapsed state (Figure 7A) that preventsretrograde fluid flow (from outside 52 into internal volume 48 ). When the pressure insideinternal volume 48 is above a predetermined threshold pressure (that pushes apart the "lips"of check valves 84 ), weak area 54 is selectively breached allowing release of gas from theinternal volume in a predetermined direction. Due to the narrowness of the lumen of check valves 84 , predesigned weak areas 54 ofcell 82 are configured to allow only the release of gas and possibly small particles entrainedin the gas, but not other contents of internal volume 48 , to prevent the contents of internalvolume 48 of cell 82 from contaminating the surroundings when weak area 54 is breached. In some such embodiments, duckbill check valves 84 are configured to reseal once thepressure inside internal volume 48 is less than the threshold pressure. Some embodiments similar to cell 82 include other types of one-way valves, forexample, reed valves comprising a metal reed.As with all other suitable embodiments of a cell of the teachings herein, cellscomprising a one-way valve may or may not additionally comprise a gas-generating materialinside the internal volume as described above.

Pressure-sensitive plugA secondary electrochemical cell 86 is depicted in Figure 8A (side cross sectionduring normal use) and in Figure 8B (side cross section with excess pressure inside theinternal volume). Cell 86 comprises a rigid prismatic shell 46 , a laminated electrode assembly 12with a pressure-sensitive plug 88 blocking a pre- existing hole 90 as the predesigned weakarea 54 of cell 86 . Pressure-sensitive plug 88 is configured to change shape as a result of excess pressure inside an internal volume 48 . Specifically, pressure-sensitive plug 88 comprises a high-temperature resistant silicone rubber sleeve 88a and apolytetrafluoroethylene (PTFE) pin 88b . During normal use, as depicted in Figure 8A, pin 88b is located inside sleeve 88a ,outwardly-expanding sleeve 88a to anchor pressure-sensitive plug 88 firmly inside hole 90 ,in a manner analogous to a wall anchor. As depicted in Figure 8B, when the pressure inside internal volume 48 equals orexceeds a predetermined threshold pressure, the pressure translates pin 88b outwards,pushing pin 88b out of sleeve 88a . Since the outwards pressure applied to sleeve 88a by pin 88b is reduced as a result of the translation, sleeve 88a changes shape by contractinginwardly, thereby reducing the frictional force between sleeve 88a and the walls of hole 90 .As a result, the pressure inside internal volume 48 is sufficient to translate pressure-sensitiveplug 88 outwards, pushing pressure-sensitive plug 88 out of hole 90 , thereby breaching weakarea 54 and allowing the release of gas from internal volume 48 . As with all other suitable embodiments of a cell of the teachings herein, cellscomprising a pressure-sensitive plug may or may not additionally comprise a gas-generatingmaterial inside the internal volume as described above.

Temperature-sensitive shape-changing plugIn some embodiments, a cell according to the teachings herein comprises a heat-sensitive component functionally associated with a predesigned weak area, configured so thatthe breaching of the predesigned weak area is facilitated by a physical change such aschanging shape of the heat-sensitive component caused by an elevated temperature inside theinternal volume.In Figures 9A (side cross section during normal use) and 9B (side cross section whenelevated temperature and excess pressure is inside the internal volume), a cell 92 comprises arigid prismatic shell 46 with a temperature-sensitive plug 94 blocking a pre-existing hole 90 as the predesigned weak area 54 of cell 92 . Temperature-sensitive plug 94 is configured tochange shape as a result of elevated temperature inside an internal volume 48 . Specifically,temperature-sensitive plug 94 is a plug comprising a shape-memory alloy componentconfigured to transform from a blocking shape to a breached shape at a transition temperaturethat corresponds to the predetermined threshold pressure. Suitable shape-memory alloysinclude Ni-Ti-Hf-Zr shape-memory alloys designated LEW-TOPS-130 from NASA's Glenn Research Center which can be designed to have a transition temperature from about 100°C toabout 300°C.During normal use, as depicted in Figure 9A, temperature-sensitive plug 94 is locatedinside hole 90 in the blocking shape, thereby sealing hole 90 to prevent the passage of gasesthrough hole 90 into and out of internal volume 48 .As depicted in Figure 9B, when the temperature inside internal volume 48 increasessufficiently (e.g., as a result of thermal runaway), gas is formed inside internal volume 48 . Ata predetermined transition temperature that corresponds to the predetermined thresholdpressure of cell 92 , temperature-sensitive plug 94 changes from the blocking shape to thebreached shape. The pressure inside internal volume 48 translates temperature-sensitive plug 94 outwards, pushing plug 94 out of hole 90 , thereby breaching predesigned weak area 54 and allowing the release of gas from internal volume 48 . As with all other suitable embodiments of a cell of the teachings herein, cellscomprising a temperature-sensitive plug may or may not additionally comprise a gas-generating material inside the internal volume as described above.

Temperature-sensitive vaporizing / decomposing plugIn some embodiments, the cell comprises a heat-sensitive component functionallyassociated with the at least one weak area, configured so that the breaching of the weak areais facilitated by a physical change of the heat-sensitive component such as at least partiallydecomposing and/or at least partially vaporizing which also leads to a change in shape of theplug and preferably leads to generation of gas inside the internal volume of the cell. In somesuch embodiments, the cell comprises a gas-generating material as discussed above, the gas-generating material being a component of the pre-designed weak area.In Figures 10A (side cross section during normal use) and 10B (side cross sectionimmediately prior to breaching of a predesigned weak area 54 ), is schematically depicted acell 96 according to the teachings herein. Cell 96 is similar to a known 4680 lithium-ionsecondary cell such as cell 26 depicted in Figure 1B. Predesigned weak area 54 of cell 96 comprises a temperature-sensitive decomposing plug 98 at least partially made of a gas-generating material 98a as described above contained inside an outer shell 98b , plug 98 blocking a pre-existing hole 90 . During normal use, as depicted in Figure 10A, temperature-sensitive decomposingplug 98 is located inside hole 90 , thereby preventing the passage of gases through hole 90 into and out of internal volume 48 of cell 96 .

When the temperature inside internal volume 48 increases sufficiently (e.g., as a resultof thermal runaway), gas-generating material 98a of 98 vaporizes and/or decomposes asdescribed for the gas-generating materials discussed above, releasing gas inside internalvolume 48 , see Figure 10B When a sufficient portion of gas-generating material 98a isvaporized/decomposed so that the predetermined threshold pressure of cell 96 is reached, theremaining gas-generating material 98a is translated out of hole 90 together with outer shell 98b ofplug 98thereby breaching predesigned weak area 54 and allowing the release of gasfrom internal volume 48 .

Unless otherwise defined, all technical and scientific terms used herein have the samemeaning as commonly understood by one of ordinary skill in the art to which the inventionpertains. In case of conflict, the specification, including definitions, takes precedence. As used herein, the terms "comprising", "including", "having" and grammaticalvariants thereof are to be taken as specifying the stated features, integers, steps orcomponents but do not preclude the addition of one or more additional features, integers,steps, components or groups thereof. As used herein, the indefinite articles "a" and "an" mean"at least one" or "one or more" unless the context clearly dictates otherwise. As used herein, when a numerical value is preceded by the term "about", the term"about" is intended to indicate +/-10%. As used herein, a phrase in the form "A and/or B"means a selection from the group consisting of (A), (B) or (A and B). As used herein, aphrase in the form "at least one of A, B and C" means a selection from the group consistingof (A), (B), (C), (A and B), (A and C), (B and C) or (A and B and C).It is appreciated that certain features of the invention, which are, for clarity, describedin the context of separate embodiments, may also be provided in combination in a singleembodiment. Conversely, various features of the invention, which are, for brevity, describedin the context of a single embodiment, may also be provided separately or in any suitablesubcombination or as suitable in any other described embodiment of the invention. Certainfeatures described in the context of various embodiments are not to be considered essentialfeatures of those embodiments, unless the embodiment is inoperative without those elements.It is appreciated that certain features of the invention, which are, for clarity, describedin the context of separate embodiments, may also be provided in combination in a singleembodiment. Conversely, various features of the invention, which are, for brevity, describedin the context of a single embodiment, may also be provided separately or in any suitablesubcombination or as suitable in any other described embodiment of the invention. Certain features described in the context of various embodiments are not to be considered essentialfeatures of those embodiments, unless the embodiment is inoperative without those elements.Although the invention has been described in conjunction with specific embodimentsthereof, it is evident that many alternatives, modifications and variations will be apparent tothose skilled in the art. Accordingly, it is intended to embrace all such alternatives,modifications and variations that fall within the scope of the appended claims. Citation or identification of any reference in this application shall not be construed asan admission that such reference is available as prior art to the invention.Section headings are used herein to ease understanding of the specification and shouldnot be construed as necessarily limiting.

Claims (25)

1. CLAIMS:1. A secondary electrochemical cell, comprising:a shell defining a sealed internal volume;contained in said internal volume, an electrode assembly comprising a positiveelectrode, a negative electrode, a separator and an electrolyte;a positive terminal providing electrical communication between said positiveelectrode and the outside of said shell; anda negative terminal providing electrical communication between said negativeelectrode and the outside of said shell;said shell having a predesigned weak area such that, when pressure inside said internalvolume is above a predetermined threshold pressure, said weak area is selectively breachedforming a breach, allowing release of gas from said internal volume through said breach.

2. The secondary electrochemical cell of claim 1, being a lithium-ion secondaryelectrochemical cell.

3. The cell of any one of claims 1 to 2, wherein said shell is a rigid shell.

4. The cell of any one of claims 1 to 2, wherein said shell is a flexible shell.

5. The cell of any one of claims 1 to 4, configured so that said release of gas from saidinternal volume is accompanied by ejection of at least some of said electrode assembly fromsaid internal volume through said breach.

6. The cell of any one of claims 1 to 5, wherein said release of gas through said breach isin a predetermined direction.

7. The cell of any one of claims 1 to 6, wherein said predesigned weak area isconfigured to reseal after said release of gas.

8. The cell of any one of claims 1 to 7, wherein said predesigned weak area comprises avalve.

9. The cell of claim 8, wherein said valve comprises a one-way valve.

10. The cell of any one of claims 1 to 6, wherein said predesigned weak area comprises aplug blocking a pre-existing hole in said shell, configured so that said breaching of saidpredesigned weak area comprises said plug unblocking said hole as a result of excesspressure inside said internal volume.

11. The cell of claim 10, wherein said configuration comprises said plug being configuredto change shape as a result of excess pressure inside said internal volume, said change ofshape leading to said breaching of said predesigned weak area.

12. The cell of any one of claims 10 to 11, wherein said configuration comprises said plugbeing configured to translate relative to said hole as a result of said excess pressure.

13. The cell of any one of claims 1 to 6, wherein said predesigned weak area comprises aweak portion of said shell and said breaching comprises irreversible damage to said shell.

14. The cell of any one of claims 1 to 13, further comprising a heat-sensitive componentfunctionally associated with said at least one weak area, configured so that said breaching isfacilitated by a physical change of said heat-sensitive component caused by an elevatedtemperature inside said internal volume.

15. The cell of any one of claims 1 to 15, further comprising inside said internal volume,a gas-generating material that generates gas inside said internal volume when the temperatureinside said internal volume passes an activation temperature thereby increasing the pressureinside said internal volume.

16. The cell of claim 15, wherein said gas-generating material is an additional componentdifferent from said electrode assembly.

17. The cell of any one of claims 15 to 16, wherein said gas-generating material is acomponent of said pre-designed weak area.

18. The cell of any one of claims 15 to 17, wherein the weight of said gas-generatingmaterial is not less than about 1% of the weight of said electrode assembly.

19. The cell of any one of claims 15 to 18, wherein said gas-generating materialcomprises at least one member of the group of materials consisting of sodium carbonate,ammonium carbonate, zinc carbonate, sodium bicarbonate, potassium bicarbonate,ammonium bicarbonate, azodicarbonamide, potassium allophanate, xylitol pentanitrate,1,3,5-Trinitro-1,3,5-triazinane, guanidinium nitrate, ethylene glycol dinitrate anddiazomethane, and combinations thereof.

20. The cell of any one of claims 15 to 19, wherein said gas-generating material is a solidat 25°C and 100 kPa.

21. The cell of any one of claims 15 to 20, wherein said generation of gas is endothermic.

22. The cell of any one of claims 15 to 21, wherein said generated gas is a fire retardant.

23. The cell of any one of claims 15 to 22, wherein said generation of gas is by thermaldecomposition of said gas-generating material.

24. A battery comprising at least one cell of any one of claims 1 to 23.

25. A battery of claim 24, comprising a casing in which said at least one cell is contained,and a volume in said casing not occupied by cells,wherein in at least some of said volume not occupied by cells is a heat sink material,configured to passively absorb at least some of the heat generated by a cell during thermalrunaway, said heat sink material selected from the group consisting of a liquid, a gel and anda solid.