GB2611077A

GB2611077A - Endothermic composite article

Info

Publication number: GB2611077A
Application number: GB2113730.2A
Authority: GB
Inventors: Xie Yiran; Phillips Jonathan; Brooks Matthew
Original assignee: Morgan Advanced Materials PLC; Morgan Crucible Co PLC
Current assignee: Morgan Advanced Materials PLC
Priority date: 2021-09-27
Filing date: 2021-09-27
Publication date: 2023-03-29
Also published as: GB202113730D0; DE112022003650T5; WO2023047076A1

Abstract

An energy storage device housing comprises an inorganic composite comprising an inorganic binder comprising a layered double hydroxide (LDH) and a plurality of inorganic endothermic particles distributed within the inorganic binder. The endothermic particles are present in a range from 30-98 wt% based upon the total weight of the endothermic particles and the inorganic binder, and the composite has an endotherm of greater than 200 J/g. The sum of endothermic particles and the inorganic binder comprises at least 60 wt% of the total weight of the composite. Also claimed is the inorganic composite material per se. The layered double hydroxide may be a member of one or more of the hydrotalcite, quintinite, fougerite, woordwardite, cualstibite, glaucocerinite, wermlandite and hydrocalumite groups but is preferably Mg6Al2(OH)16CO3.4H2O. It may be an intercalated or hydrophobicised layered double hydroxide. The composite may include up to 40 wt% additives relative to the weight of the inorganic binder, which may comprise an intercalating agent, e.g. sodium gluconate, for intercalation in the layered double hydroxide. The endothermic particles may comprise a coating of the inorganic binder. A method of preparing the material by forming, shaping and drying a paste is also described and claimed.

Description

ENDOTHERMIC COMPOSITE ARTICLE

FIELD OF THE INVENTION

The present invention relates to articles produced from endothermic material and processes for manufacturing thereof. In particular, the invention relates to endothermic energy storage device housing and associated components, including housing for a plurality of lithium ion batteries.

BACKGROUND

Electrical energy storage devices may fail in operation, and this can result in an uncontrolled release of stored energy that can create localized areas of very high temperatures. For example, various types of cells have been shown to produce temperatures in the region of 600-900°C in so-called "thermal runaway" conditions [Andrey W. Golubkov et al, Thermal-runaway experiments on consumer Li-ion batteries with metal-oxide and oliyin-type cathodes RSC Adv., 2014, 4, 3633-3642].

Such high temperatures may ignite adjacent combustibles thereby creating a fire hazard. Elevated temperature may also cause some materials to decompose and generate gas. Gases generated during such events can be toxic and/or flammable, further increasing the hazards associated with thermal runaway events.

Lithium ion cells may use organic electrolytes that have high volatility and flammability. Such electrolytes tend to start breaking down at temperatures starting in the region 130°C to 200°C and in any event have a significant vapour pressure even before breakdown starts. Once breakdown commences the gas mixtures produced (typically a mixture of CO2, CH4, C2H4, C2H5F and others) can ignite. The generation of such gases on breakdown of the electrolyte leads to an increase in pressure and the gases are generally vented to atmosphere; however this venting process is hazardous as the dilution of the gases with air can lead to formation of an explosive fuel-air mixture that if ignited can flame back into the cell in question igniting the whole arrangement It has been proposed to incorporate flame retardant additives into the electrolyte, or to use inherently non-flammable electrolyte, but this can compromise the efficiency of the lithium ion cell [E.Peter Roth et al, How Electrolytes Influence Battery Safety, The Electrochemical Society Interface, Summer 2012, 45-49]. It should be noted that in addition to flammable gases, breakdown may also release toxic gases.

The issue of thermal runaway becomes compounded in devices comprising a plurality of cells, since adjacent cells may absorb enough energy from the event to rise above their designed operating temperatures and so be triggered to enter into thermal runaway. This can result in a chain reaction in which storage devices enter into a cascading series of thermal runaways, as one cell ignites adjacent cells.

To prevent such cascading thermal runaway events from occurring, storage devices are typically designed to either keep the energy stored sufficiently low, or employ enough insulation between cells to insulate them from thermal events that may occur in adjacent cells, or a combination thereof. The former severely limits the amount of energy that could potentially be stored in such a device. The latter limits how close cells can be placed and thereby limits the effective energy density.

There are currently a number of different methodologies employed by designers to maximize energy density while guarding against cascading thermal runaway.

One method is to employ a cooling mechanism by which energy released during thermal events is actively removed from the affected area and released at another location, typically outside the storage device. This approach is considered an active protection system because its success relies on the function of another system to be effective. Such a system is not fail safe since it needs intervention by another system. Cooling systems also add weight thereby reducing the effectiveness of the storage devices for those applications where they are being used to provide motion (e.g. electric vehicles). The space the cooling system displaces within the storage device may also reduce the potential energy density that could be achieved.

A second approach employed to prevent cascading thermal runaway is to incorporate a sufficient amount of insulation between cells or clusters of cells that the rate of thermal heat transfer during a thermal event is sufficiently low enough to allow the heat to be diffused through the entire thermal mass of the cell typically by conduction. This approach is considered a passive method and is generally thought to be more desired from a safety vantage. In this approach the ability of the insulating material to contain the heat, combined with the mass of insulation required dictate the upper limits of the energy density that can be achieved.

A third approach is through the use of phase change materials. These materials undergo an endothermic phase change upon reaching a certain elevated temperature. The endothermic phase change absorbs a portion of the heat being generated and thereby cools the localized region. This approach is also a passive in nature and does not rely on outside mechanical systems to function. Typically, for electrical storage devices these phase change materials rely on hydrocarbon materials such as waxes and fatty acids for example. These systems are effective at cooling, but are themselves combustible and therefore are not beneficial in preventing thermal runaway once ignition within the storage device does occur.

A fourth method for preventing cascading thermal runaway is through the incorporation of intumescent materials. These materials expand above a specified temperature producing a char that is designed to be lightweight and provide thermal insulation when needed. These materials can be effective in providing insulating benefits, but the expansion of the material must be accounted for in the design of the storage device.

Despite the benefits of these solutions, there is increasing demand for more compact and simplified housing articles which have both heat absorbing and heat insulative properties, and articles and compositions for use therein, which are able to control thermal runaway events.

There is an unfulfilled need for a method to limit cascading thermal runaway in energy storage devices that mitigates the problems of previous proposals.

SUMMARY OF THE INVENTION

In a first aspect of the present invention, there is provided an energy storage device housing comprising an inorganic composite comprising: * an inorganic binder comprising a layered double hydroxide (LDH); and * a plurality of inorganic endothermic particles distributed within the inorganic binder, wherein the endothermic particles are present in a range from 30 wt% to 98 wt% based upon the total weight of the endothermic particles and the inorganic binder, and wherein the composite has an endotherm of greater than 200 J/g wherein the sum of endothermic particles and the inorganic binder comprises at least 60 wt% of the total weight of the composite.

The composite of the present invention provides high energy absorptive capacity in combined with good mechanical strength, which the precursor form is capable of being shaped into thin walled articles. The ability to shape the composite into thin wall structures increases design flexibility and enhances the energy absorbing density of the articles facilitating more compact design configurations. As such, the composite is particularly advantageously used for energy storage device housing applications. The housing may be used to separate and/or encompass one or more cells. Other applications include fire retardant products and barriers.

The composite (and endothermic particles) may have an endotherm greater than 300 J/g or greater than 400 J/g or greater than 500 J/g or greater than 600 J/g or greater than 700 J/g. Preferably, the endothermic capacity of the composite is measured below 400°C or below 300°C as it is desirable, for energy storage device is applications, to absorb energy at these lower temperatures to prevent escalation of thermal events to neighbouring energy storage cells.

The composite may have a modulus of rupture of greater than 6.0 MPa or greater than 8.0 MPa or greater than 10.0 MPa or greater than 12.0 MPa.

In one embodiment, the endothermic particles and the inorganic binder comprises at zo least 70 wt% or at least 80 wt% or at least 85 wt% or at least 90 wt% or at least 95 wt% of the total weight of the composite.

In some embodiments, the sum of endothermic particles and the inorganic binder is in the range of 60 wt% or 70 wt% or 80 wt% or 90 wt% to 100 wt% of the total weight of the composite. The remainder of the composite may comprise filler material and/or other additives, such as processing aids or conductivity enhancers.

In one embodiment, the composite comprises: to 95 wt% endothermic particles; 5 to 60 wt% inorganic binder; 0 to 40 wt% filler material.

0 to 10 wt% additives; and In another embodiment, the composite comprises: to 95 wt% endothermic particles; to 30 wt% inorganic binder; 0 to 8 wt% additives; and 0 to 25 wt% filler materials.

In one embodiment, the composite comprises greater than 0 wt% or greater than 1 wt% or greater than 2 wt% additives.

In some embodiments, the additives comprise water proofing agents. The water proofing agents may react and form part of an intercalated LDH, in which case, the 10 water proofing agents forms pad of the inorganic binder, rather than being part of the additive component.

Inomanic binder The inorganic binder may comprise at least 50 wt% or at least 60 wt% or at least 70 wt% or least 80 wt% or at least 90 wt% of the layered double hydroxide.

The composite may comprise between 2.0 wt% to 50 wt% inorganic binder. In some embodiments, the composite comprises between 3.0 wt% and 30 wt% or between 4.0 wt% and 20 wt% or between 5 wt% and 15 wt% or between 6 wt% and 10 wt% inorganic binder. Higher inorganic binder contents may result in a composite in which the gaseous release from the endothermic materials may be inhibited. A lower inorganic binder content may result in a resultant article with insufficient mechanical strength.

A suitable amount of inorganic binder may be determined by calculating the specific surface area of the particles in the composite raw materials and then calculating sufficient inorganic binder to coat the particles to a thickness of 0.02 to 2.0 pm.

The inorganic binder is preferably evenly distributed over the endothermic particles as indicated by EDS/SEM analysis.

However, the amount of inorganic binder may be adjusted to improve mechanical strength and/or moisture resistance of the composite material.

The LDHs may comprise a positive layer of divalent and trivalent cations, and may 30 be represented by the formula [M t.N3+x(H0-)21" [(X6-)xin yH20]", where Xn-is the intercalating anion (or anions).

In some embodiments, M2 = Ca2., Mg2., Mn2., Fe2., Co2., Ni2., Cu2. or and N3 is another trivalent cation, which may be of the same element as M. Fixed-composition phases have been shown to exist over the range 0.2 5 x 5 0.33 and x> 0.5.

Another class of LDH is known where the main metal layer consists of Li+ and Al3+ cations, with the general formula: [Li+A13+2(H0-)5]+ [Li+A13+2(X6-) * yH20]-, where X6-represents one or more anions with total charge -6. The value of y is typically between 0.5 and 4.

In some cases, the pH value of the solution used during the synthesis and the high drying temperature of the LDH can eliminate the presence of the OH-groups in the LDH. For example, in the synthesis of the (Bi0)4(OH)2CO3 compound, a low pH value of the aqueous solution or higher annealing temperature of solid can induce the formation of (Bi0)2003, which is thermodynamically more stable than the LDH compound, by exchanging OH-groups by C032-groups.[4] Naturally occurring (i.e., mineralogical) examples of LDH are classified as members zo of the hydrotalcite supergroup, named after the Mg-Al carbonate hydrotalcite, which is the longest-known example of a natural LDH phase. More than 40 mineral species are known to fall within this supergroup. The dominant divalent cations, M2+, that have been reported in hydrotalcite supergroup minerals are: Mg, Ca, Mn, Fe, Ni, Cu and Zn; the dominant trivalent cations, N/13+, are: Al, Mn, Fe, Co and Ni. The most common intercalated anions are [CO3]2-, [S042-and CI-; OH-, S2-and [Sb(OH)6]-have also been reported. Some species contain intercalated cationic or neutral complexes such as [Na(H2O)6] or [MgSai]°. The International Mineralogical Association's 2012 report on hydrotalcite supergroup nomenclature defines eight groups within the supergroup on the basis of a combination of criteria. These groups are: * the hydrotalcite group, with M Ms. = 3:1 (layer spacing -7.8 A); * the quintinite group, with M2+:M3+ = 2:1 (layer spacing -7.8 A); * the fougerite group of natural 'green rust' phases, with M2+ = Fe2+, M3+ = Fes+ in a range of ratios, and with 02-replacing OH-in the brucite module to maintain charge balance (layer spacing -7.8 A); * the woodwardite group, with variable M2+:M3+ and interlayer [S042-, leading to an expanded layer spacing of -8.9 A; * the cualstibite group, with interlayer [Sb(OH)6]-and a layer spacing of -9.7 A; * the glaucocerinite group, with interlayer [SO4]2-as in the woodwardite group, and with additional interlayer H20 molecules that further expand the layer spacing to -11 A; * the wermlandite group, with a layer spacing of -11 A, in which cationic complexes occur with anions between the brucite-like layers; and * the hydrocalumite group, with M2+ = Ca2+ and M3+ = Al, which contains brucite-like layers in which the Ca:Al ratio is 2:1 and the large cation, Ca2+, is coordinated to a seventh ligand of 'interlayer' water.

In one embodiment, the LDH comprises hydrotalcite (e.g. Mg6Al2(OH)16](CO3) 4H20).

The LDH may be partially dehydrated in the formation of the composite (e.g. with an attributable endotherm of least 50 J/g or at least 100 J/g or at least 200 J/g for 20 TGA/DSC analysis less than 320°C).

In one embodiment, the endothermic particles are encompassed by inorganic binder. By encompassing the endothermic material, the water absorptive properties of the endothermic materials are inhibited, thereby contributing to a composite with reduced water absorptive properties.

In one embodiment, the composite has a weight gain of 5.0 wt% or less or 4.0 wt% or less or 3.0 wt% or less when exposed to an atmosphere of greater than 95% relative humidity for 24 hours.

In some applications, there may be a need to balance the mechanical and energy absorptive properties with the composite density. The density or porosity of the composite may be controlled through the additional of lightweight filler materials.

Porosity may also be increased through the introduction of foaming agents that can be used are surface active substances from the classes of the anionic and non-ionic surfactants or plant, animal, or artificial proteins, such as, e.g., ethoxylates, alkyl glycosides, aminoxides, sodium olefin, fatty alcohols, sodium lauryl sulfate, or ammonium lauryl sulfate. Mechanical agitation may be employed to generate the required level of porosity. Advantageously, the foaming agent combines with the hydrotalcite paste/slurry to generate a predominately closed pore structure, with the hydrotalcite composition, functioning as an inorganic plasticiser, alone or in combination with optional additives.

Gas generating foaming agents such as sodium bicarbonate may also be used to generate a more open pore structure within the composite.

In one embodiment, the density of the composite material is at least 0.5 g/cm3 or at least 0.7 g/cm3 or at least 1.0 g/cm3 or at least 1.2 g/cm3 or at least 1.4 g/cm3. The upper density limit may approach the theoretical density of the composite components, but is typically no more than 4.0 g/cm3 or no more than 3.0 g/cm3.

Inorganic endothermic particles Then inorganic endothermic particles may be comprised of a compound that: a. absorbs heat by releasing water of hydration; b. by going through a phase change; or c. by chemical reaction wherein the chemical reaction requires a net absorption of heat.

The inorganic endothermic particles preferably release gas upon reaching an activation temperature, with the formed gases removing heat and potentially toxic gas away from the thermal runaway event. The inorganic endothermic materials preferably contain metal hydroxyl, hydrous, carbonate, sulphate and/or phosphate components which decompose or react at a designated onset decomposition or reaction temperature with the reaction or decomposition resulting in the absorption of energy. Examples of endothermic materials (Table A) include sodium bicarbonate, nesquehonite, gypsum, sodium nitrate, magnesium phosphate octahydrate, aluminium hydroxide (also known as aluminium trihydrate), hydromagnesite, dawsonite, magnesium hydroxide, magnesium carbonate subhydrate, boehmite, zinc borate, antimony trioxide, and calcium hydroxide. The decomposition or reaction products are preferably non-toxic, such as carbon dioxide and/or water.

The decomposition or reaction products preferably provide an insulative barrier. It will be understood that the mechanical properties of the housing may deteriorate during a thermal runaway event, such that a more porous insulative article remains. For example, aluminium hydroxide will decompose to a porous alumina article as indicated by the formula below: 2A1(OH)3 -/ A1203 + 3H20

TABLE A

Mineral Chemical Formula Decomposition onset temp.

Nesquehonite >MgCO3*3H20 70-100°C Gypsum CaSO4-2H20 60-130°C Magnesium phosphate octahydrate Mg3(PO4)2*8H20 140-150°C Aluminium hydroxide Al(OH)3 180-200°C Hydromagnesite Mg5(CO3)4(OH)2.4H20 220-240°C Dawsonite NaAl(OH)2CO3 240-260°C Magnesium hydroxide Mg(OH)2 300-320°C Magnesium carbonate subhydrate >Mg0-0O2(0.96)H20(0.3) 340-350°C Boehm ite A10(OH) 340-350°C Calcium hydroxide Ca(OH)2 430-450°C The mechanical deterioration of the battery housing is of secondary importance to the objective of preventing propagation of the thermal runaway event and protecting adjacent equipment, as the thermal event is likely to render the battery module inoperable. However, it is desirable that the article retains its integrity to enable the article to still function as an insulative barrier.

The composite may comprise endothermic particles having a particle size distribution with a D50 value of less than 30 pm or less than 20 pm. The inorganic endothermic (and/or filler material) particle size distribution combined with the amount of inorganic binder may be adjusted to control the porosity, mechanical strength and energy absorptive capacity of the composite.

In one embodiment, the composite comprises endothermic particles with bimodal particle size distribution. Bimodal particle particle size distribution may be used to reduced porosity by increasing the packing efficiency of the endothermic particles.

The total (open and closed) porosity of the composite may be in the range of 3 v/v% to 70 v/v% or in the range of 5 v/0/0 to 50 v/v% or 7 v/v% to 30 v/v%. The open or closed porosity may be in the range of 3 v/v% to 60 v/v% or in the range of 5 v/v% to 50 v/v% or 7 v/v% to 25 v/v%.

Filler materials Filler materials may be used to enhance mechanical properties of the material and resultant housing. The filler materials are preferably insert. The filler material may be porous or increase porosity when added to the composite. The filler material may be selected for a large range of suitable material, including, but not limited to perlite, vermiculite, porous ceramic spheres, expanded clay, foamed lightweight geological materials, microporous silica, microporous alumina, inorganic fibres, expanded glass, hollow ceramic or glass spheres, inorganic fibres. The density of the composite may be controlled through the proportion and particle size of the material used.

In some embodiments, the mixture comprises particulate or fibrous inorganic filler. It has been found that small amounts (e.g. less than or equal to 25.0 wt% or less than or equal to 15 wt% or less or equal to 10 wt% or less than or equal to 5 wt%) may enhance mechanical properties whilst still maintaining a high endothermic material density. Fillers of greater than 0.1 wt% or greater or 0.5 wt% or greater pr 1.0 wt% of the total weight of the composite may provide benefits in terms of mechanical properties.

Additives A range of additives known in the art may be incorporated into the mixture including, but not limited to surfactant, shrinkage modifier, gloss modifier, set retarder (e.g. sodium gluconate), water proofing agent, fire retardant, smoke suppressant, impact modifier, cure modifier, viscosity or rheological modifier, wetting agent (surfactant), dispersing agent, plasticiser, antioxidant, foaming agent, lubricant, release agent, gelling agent, tack modifier, flow agent, acid scavenger, defoamer, processing aid, filler, inorganic binder, or a combination thereof.

It will be appreciated that the article may be coated in all or in part to enhance the surface properties in respect to thermal and/or electrical conductivity; smoothness or abrasive; and handleability or any other required functional property.

To enable article designs with greater design options, the use of rheology modifiers, lubricants and/or surfactants are preferably added. The lubricants and/or surfactants coat the endothermic particles surfaces and enable a higher endothermic material content to be injection moulded (or other shaping technique) with sufficient mechanical integrity, whilst enabling thinner wall thicknesses to be achieved The rheology modifier, lubricants or surfactants may be selected from the group consisting of polysaccharide, polysaccharide derivative, protein, stearic acid, protein derivative, hydroxypropyl methylcellulose (HPMC), comprising methyl hydroxyethylcellulose (MHEC), hydroxyethyl cellulose (HEC) or carboxymethylcellulose (CMC), synthetic organic material, hydratable alumina, hydrotalcite, clay (e.g. bentonite), citric acid and polyacrylic acid, layered aluminium silicate (e.g. ArginotecO) and derivatives or combinations thereof.

In one embodiment, the water proofing agent comprises a monoanion of an aliphatic C2-C34 monocarboxylic acid or an equivalent of a dianion of aliphatic C4-044 dicarboxylic acid. In some embodiments, the water proofing agent comprises a fatty acid. Other carbon chains which one or more hydroxide groups may also be used, such as gluconic acid, glucuronic acid, galacturonic acid, iduronic acid, aldonic acid, ulosonic acid, alginic acid, uronic acid, aldaric acid or salts thereof (e.g. sodium alginate or sodium, potassium, calcium or magnesium gluconate). Other suitable waterproofing agents may also be used as known by the person skilled in the art.

In some embodiments the water proofing agent may react with the LDH to form hydrophobicised LDH. In some embodiments the hydrophobicised LDH is an intercalated LDH. In some embodiments, the LDH may be intercalated with a compound comprising a carbon backbone (e.g. C2_60) and a hydroxide group.

Methods of hydrophobicised and/or intercalated LDHs are disclosed in W0201161173 and US5,326,891, which are disclosed herein by reference.

The proportion of additives may be the equivalent to up to 40 wt% or up to 30 wt% or up to 25 wt% or up to 20 wt% or up to 15 wt% or up to 10 wt% or up to 5 wt% of the weight of the inorganic binder. (e.g. 10 wt% additive relative to the binder equates to 1 part by weight additive to 10 parts by weight binder). Higher additive contents may negatively impact the endothermic capacity of the composite, while lower amounts may not deliver the required functionality. In some embodiments, the additives may make up at least 1 wt% or at least 2 wt% or at least 3 wt% or at least 5 wt% of the the weight of the inorganic binder.

In a second aspect of the present invention, there is provide a composite paste 10 comprising * a solution (e.g an aqueous solution) comprising a LDH inorganic binder; and * a plurality of inorganic endothermic particles, wherein the inorganic endothermic particles are present in a range from 30 wt% to 98 wt% endothermic material based upon the total weight of the inorganic endothermic particles and the LDH inorganic binder (measured on a dry basis); and optionally * additives.

The additives may form a complex or be reacted with the LDHs (e.g. intercalated).

The paste is preferably an extrudable paste. Preferably, the extrudable paste is capable of forming thin-walled shaped articles, such as those defined in the third aspect of the present invention.

The composite paste is a precursor to the composite of the first aspect of the present invention.

In a third aspect of the present invention, there is provided a shaped article comprising the composite according the first aspect of the present invention.

The shaped article preferably comprises a thin wall of less than 10.0 mm or less than 5.0 mm or less than 3.0 mm or less than 2.0 mm or less than 1.0 mm. The minimum wall thickness is governed by the required mechanical strength and/or the required energy adsorptive capacity. In one embodiment, the minimal wall thickness is at least 0.2 mm or at least 0.5 mm or at least 1.0 mm.

In one embodiment, the shaped article is an elongated tube. In another embodiment the shaped article is a planar or curved sheet. In another embodiment, the shaped article is in the form of a layer having a thickness of at least 30 pm. The upper limit is typically less than 50 mm or less than 5.0 mm. The layer may be self-supporting or may be adhered to a supporting structure.

In a fourth aspect of the present invention, there is provided a battery housing for the prevention of thermal runaway of a plurality of cells comprising a plurality of elongated tubes of the second aspect of the invention. In one embodiment, the battery housing comprising a plurality of the tubes. The tubes may comprise a variety of energy absorptive capacity to thereby match the thermal runaway risk profile of the battery pack. The tubes may have different thicknesses or density to provide the differing energy absorptive capacity.

In a fifth aspect of the present invention, there is provided a process of manufacturing a shaped article as defined in the third aspect of the present invention comprising the steps of: a Forming a liquid phase comprising LDH inorganic binder; b Adding inorganic endothermic particles to the liquid phase and mixing to form a paste or slurry; c Shaping the paste to form a green shaped article; and d Drying the green shaped article to form the shaped article (e.g an energy storage device housing).

The liquid phase may comprise a solvent, such as water.

The shaping of the paste may be performed via calendering, injecting, casting, extruding, coating, rolling or pressing. In embodiments using casting, a slurry may be formed, which may be cast into a mould to form the shaped article. The shaped article may be self-supporting. The shaped article may be monolithic and/or homogeneous in structure.

In some embodiments, a plurality of green shaped article may be connectedly arranged prior to drying. Within this embodiment, the drying step may result in the binding of the shaped articles together (e.g. tubes).

In some embodiments, one or more shaped articles may be further coated with a functional coating to enhance their functionality (e.g. water resistant, conductive, adhesive, strengthening etc).

To assist the shaping of the paste, a rheology modifier, lubricant or surfactant is added to the paste. The rheology modifier, lubricant or surfactant may be selected from the group consisting of polysaccharide, polysaccharide derivative, protein, protein derivative, fatty acids (e.g. stearic acid) or derivatives thereof, hydroxypropyl methylcellulose (HPMC), comprising methyl hydroxyethylcellulose (MHEC), hydroxyethyl cellulose (HEC) or carboxymethylcellulose (CMC), synthetic organic material, derivatives or combinations thereof.

The green shaped articles is preferably sufficiently dried to substantially remove all of the residual solvent (e.g. water) from the inorganic binder (e.g. less than 1.0 wt% or less than 0.5 wt%). The drying step is preferably conducted above 100°C and below the activation temperature of the endothermic particles. In one embodiment, is the drying step is performed at 110°C for at least 2 hrs or at least 4 hrs or at least 6 hrs. In another embodiment, the drying step is performed at 170°C for at least 2 hrs or at least 4 hrs or at least 6 hrs. The drying time will be dictated by the properties of then endothermic material and the dimensions of the shaped article being dried.

In a sixth aspect of the present invention there is an extruded tube comprising the inorganic composite as defined in the first aspect of the present invention produced by the process as defined in the fifth aspect of the present invention. The composite compositions are particularly suitable for extruding thin walled tubing with high inorganic endothermic material content.

Unless otherwise indicated reference to the LDH inorganic binder is on a dry weight basis (i.e. comprising no free water or other solvent).

Unless otherwise stated, % wt are relative to the total weight of the composite.

For the purposes of the present invention, intercalated LDHs or otherwise hydrophobicised LDHs will be considered part of the inorganic binder.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 is a graph of the Thermal Gravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) of the composite material of the present invention.

Figure 2 is a SEM image of the composite material in Figure 1.

Figure 3 is a photograph of the surface of a foamed elongated tube of the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

In one embodiment of the present invention, a composite material was formed from aluminium trihydrate (ATH) powder and hydrotalcite (Mg6Al2(OH)16CO3.4H20) (HT) in proportions provided indicated in Examples 2 to 4 and CE#1. The hydrotalcite (HT) may be a commercially obtained grade, which may include an additive package.

Materials used: Kimsuma HT4amil powder: Mg6Al2(OH)16CO3.4H20) Aluminium trihydrate particles: (D10 = 3pm; D50 = 14pm; D90 = 46pm, Specific Surface Area = 1.06 m2/g).

Preparation of HT-sodium qluconate paste Treat Kimsuma HT4aTm powder in oven at about 250-350 °C to make HT loose interlayer; Dissolve sodium gluconate in water to form aqueous solution; Put heat treated HT powder into the aqueous solution Stir for 24 hours and form a paste (67.9 wt% water) Preparation of paste for extrusion Dry mix 78 parts by weight (pbw) ATH powder with 5pbw HT powder for 5 minutes Add 15 pbw HT-sodium gluconate paste and mix for 30 minutes Add further 2 pbw water and mix for 30 minutes to form a homogeneous paste for extrusion.

The further water additional may be adjusted to optimize the viscosity of the paste for extrusion.

The homogenous paste was fed into a piston extruder fitted with a tube die for producing a tube of 18mm internal diameter and 0.70 mm wall thickness. The extruded tubes (approximately 1 to 2 meters length) had sufficient green strength to maintain their shape when laid onto a grooved support table. The tube was covered with paper and dried at room temperature for 24 hours, after which the tubes were further dried at 170°C to drive off any remaining residual moisture (i.e. free water). The tube was then cut to the required length (e.g. 65-70 mm).

Example 1

A 18mm internal diameter tube was made as previously described from a green paste comprising about 13 parts by weight water, with the other components provided on a dry basis in Table B:

Table B

Raw formulation Example 1 Typical range ATH powder 89 parts by weight 67 -84 pbw Hydrotalcite 10 parts by weight 15-30 pbw Additives* 1 parts by weight 0.03 to 8 pbw Water 13 parts by weight 8-18 pbw *estimated The TGA (Figure 1) of the final product confirmed that there was no mass change up to 170°C, indicating that there was no residual moisture.

The composition of the final product is provided in Table C. It is noted that the hydrotalcite may comprise other additives derived from the commercial formulation 20 used.

Table C

After drying Example 1 ATH 89 wt% Hydrotalcite 10 wt % Additives* 1 wt % *esfimated A Scanning Electron Microscope (SEM) image of the composite (Figure 2) illustrated that the endothermic particles were coated with a layer of hydrotalcite. The Energy Dispersive Spectroscopy (EDS) analysis confirmed that there is an even distribution of magnesium, aluminium and oxygen over the surface of the composite, indicative of a hydrotalcite layer covering the ATH particles.

The properties of the composite are reported in Table D.

Table D

Properties value Strength (MoR) 14 MPa Moisture absorption 2 wt% Density Bulk Density: 1.89 g/cm3 Apparent Solid Density: 2.09 g/cm3 Open Porosity 9.71% Thermal Conductivity 2.0 W/m*k at (20-170 °C) 0.9 W/m*k at (200 -400 °C) Estimated binder coating thickness 0.04 to 0.09 pm Modulus of Rupture (MoR) The MoR was performed by using 3-point bending test. The sample tested were extruded and dried rods. The diameter of the rods was 2 mm. Typically, the length of the rods were about 60 mm and the span was 40 mm. The typical testing speed used was 1 mm/min. The MoR value is calculated by the maximum load and the dimension of the sample.

Moisture absorption The moisture absorption was performed by measuring the mass of the samples. The mass of the sample was measured. The sample was then kept in a container which has a relative humidity greater than 95 % for 24 -36 hours. The mass of the sample was measured again and the moisture absorption was calculated.

Density and Open Porosity Archimedes' density measurement method was used to identify the density and porosity. The mass of the sample was measured in air. The sample was then submerged in water and the submerged weight were measured. The sample were then dried by using a damp cloth and the mass was measured again in air. The bulk density, apparent solid density and porosity was calculated with the results provided in Table D. A further example was conducted which utilised a foaming agent resulting in an elongated tube with evaluated porosity, as indicated in the photograph of the surface of the elongated tube (Figure 3).

Thermal Conductivity The thermal conductivity was determined by flash diffusivity test. The thickness and mass of the sample was measured. The sample was then coated with graphite for testing. The equipment subjects one side of the sample to a pulse of energy generated by a xenon flash tube and measure the temperature rise on the far side of the sample. The thermal diffusivity, thermal conductivity can then be calculated. The dried sample was tested from 20 °C to 175 °C to obtain the operation temperature range thermal conductivity. The sample was then put in an oven at 250 °C for 4 hours to allow the endothermic material react completely. The sample was put to the thermal conductivity test again from 200 °C to 400 °C to give the thermal runaway temperature range thermal conductivity value.

Estimated binder coating thickness The binder coating thickness was calculated by using the mass ratio between the powder and binder in a dried sample, the density of the binder, and the surface area 30 of the powder. Through the mass ratio between powder and binder and the density of binder, the volume of binder per unit mass of powder can be calculated. The surface area of the powder was tested by BET and provided by the supplier. The volume of binder divided by the surface area of per unit of powder gives the estimated binder coating thickness.

S Assessment of effect of additive addition Formulations were prepared as per Example 1, but with the paste adjusted to contain different quantities of sodium gluconate relative to the HT. The results (Table E) indicate that the sodium gluconate in the range of 1 to 30 wt% of the sodium gluconate and HT composition provide good humidity resistance, as indicated by the water absorption test results, and strength, with improved strength correlating with increased levels of sodium gluconate. Example 2, containing no sodium gluconate (i.e. no intercalation), had a relative high water absorption level and lower strength compared to examples containing sodium gluconate.

Table E: % wt sodium gluconate in HT-sodium gluconate mixture

Example 2 3 4 5

% sodium gluconate in HT 0 1 3 30 Moisture absorption test 5.3 wt% 1.2 wt% 1.6 wt% 1.4 wt% Strength (observed) 0 00 000 0000

Claims

CLAIMS1. An energy storage device housing comprising an inorganic composite comprising: * an inorganic binder comprising a layered double hydroxide (LDH) and * a plurality of inorganic endothermic particles distributed within the inorganic binder, wherein the endothermic particles are present in a range from 30 wt% to 98 wt% based upon the total weight of the endothermic particles and the inorganic binder, and wherein the composite has an endotherm of greater than 200 J/g; and wherein the sum of endothermic particles and the inorganic binder comprises at least 60 wt% of the total weight of the composite.
2. The housing of claim 1, wherein the layered double hydroxide is represented by the formula [M2.1-xN3.x(H0-)2]X. [(Xn-)xin * yH2O]where Xn-is the intercalating anion (or anions).M2+ = Ca2+, Mg2+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+ or Zn2+, and N3+ is another trivalent cation, of the same element as M; 0.2 x 0.33 or x > 0.5.
The housing of claim 2, wherein the layered double hydroxide is a member of one or more of the hydrotalcite group; quintinite group; fougerite group; woodwardite group; cualstibite group; glaucocerinite group; wermlandite group; and the hydrocalumite group.
4. The housing according to any one of the preceding claims, wherein the layered double hydroxide has the formula Mg6Al2(OH)16CO3.4H20.
5. The housing according to any one of the preceding claims, wherein the layered double hydroxide is an intercalated layered double hydroxide or a hydrophobicised layered double hydroxide.
6. The housing according to any one of the preceding claims, wherein the composite comprises 0 to 40 wt% additives relative to the weight of the inorganic binder.
7. The housing according to claim 6, wherein the additives comprise an intercalating agent, which is intercalated in the layered double hydroxide.
8. The housing according to claim 7, wherein the intercalated layered double hydroxide is intercalated with a compound comprising a carbon backbone and a hydroxide group.
9. The housing according to any one of claim 8, comprising 1.0 to 30 wt% sodium gluconate relative to the sum of sodium gluconate and the layered double hydroxide.
10. The housing according to claim 1, wherein the endothermic particles are present in a range from 50 wt% to 95 wt% based upon the total weight of the endothermic particles and the inorganic binder.
11. The housing according to any one of the preceding claims, wherein the amount of inorganic binder present is in the range of 2.0 wt% to 50 wt% of the total weight of the composite.
12. The housing according to any one of the preceding claims, wherein the endothermic particles comprise a coating of the inorganic binder.
13. The housing according to any one of the preceding claims wherein the sum of endothermic particles and the inorganic binder comprises at least 80 wt% of the composite.
14. The housing according to any one of the preceding claims, wherein the inorganic binder comprises at least 70 wt% of the layered double hydroxide.
15. The housing according to any one of the preceding claims, wherein the porosity of the composite is in the range of 3 v/v% to 70 v/v%.
16. The housing according to any one of the preceding claims, wherein the composite has an endotherm of greater than 600 J/g
17. The housing according to any one of the preceding claims comprising: to 95 wt% endothermic particles; to 30 wt% inorganic binder; 0 to 8 wt% additives; and 0 to 25 wt% filler materials.
18. The housing according to any one of the preceding claims, wherein the composite has a weight gain of less than 5.0 wt% when exposed to an atmosphere of 95% relative humidity for 24 hours.
19. The housing according to any one of the preceding claims, wherein the composite has a modulus of rupture of greater than 6.0 MPa.
20. The housing according to any one of the preceding claims, comprising an elongated tube with a wall thickness of between 0.2 and 2.0 mm.
21. A process of manufacturing an energy storage device housing according to any one of the preceding claims comprising the steps of: a forming a paste comprising the inorganic endothermic particles, inorganic binder and a solvent; b shaping the paste to form a green shaped article; and c drying the green shaped article to form the energy storage device housing
22. The process according to claim 21, wherein the shaping of the paste or slurry is performed via calendaring, injecting, casting, coating, extruding, rolling or pressing.
23. An extruded elongated tube comprising the inorganic composite as defined in any one of claims 1 to 20, produced by the process according to any one of claims 21 or 22.
24. The inorganic composite as defined in any one of claims 1 to 20.
25. The inorganic composite of claim 24, wherein an inorganic composite precursor thereof is extrudable into the extruded elongated tube of claim 23.