GB2605021A

GB2605021A - Ionically conductive inorganic platelets and the production thereof

Info

Publication number: GB2605021A
Application number: GB2203631.3A
Authority: GB
Inventors: Brown Martyn; Freeman Craig
Original assignee: Thermal Ceramics UK Ltd
Current assignee: Thermal Ceramics UK Ltd
Priority date: 2021-03-17
Filing date: 2022-03-16
Publication date: 2022-09-21
Anticipated expiration: 2042-03-16
Also published as: GB202103716D0; GB202203631D0; DE102022202604A1; GB2605021B

Abstract

A plurality of ionically conductive inorganic platelets have ionic conductivity of at least 10-6 S/cm at room temperature; average thickness between 50 nm and 100 μm; and an aspect ratio of each of the minimum and maximum transverse dimension to thickness in the range 10:1 to 25,000:1. The minimum and maximum transverse dimension may be at least 40 μm. The platelets may be a glass ceramic. The surface area to thickness ratio of the platelets may be at least 1600. A composite electrolyte film of thickness between 5 and 500 μm may include a polymer and the ionically conductive platelets, which may include a lithium zirconium silicate glass. The platelets may be aligned parallel to the surface of the film and there may be at least two layers of orientated platelets. The average thickness of the platelets may be at least 50% of the average thickness of the film. The platelets may be formed by feeding raw material into a vessel; heating to form a molten mass; feeding the molten mass into a rotating cup (5, Figure 1); ejecting the molten mass into a quenching chamber (13, Figure 1); and optionally segregating to obtain a target platelet size.

Description

lonically conductive inorganic platelets and the production thereof

Field of the Invention

The present invention relates to ionically conductive inorganic platelets, composite films comprising thereof; inorganic membranes made therefrom; and the production of said platelets, membranes films.

Background

The development of solid lithium-ion conductors has attracted considerable attention in recent years as the evolution of battery technology progresses towards higher energy density solutions. Inorganic conductors have emerged as particularly promising candidates due to their excellent conductivity and wide electrochemical stability window.

An example of a particularly preferred compound according to the invention having a garnet-like structure is Li7La2r2012 (LLZO). The high lithium ion conductivity, good thermal and chemical stability in respect of reactions with possible electrodes, environmental compatibility, availability of the starting materials. However, further improvements are required to lower manufacturing costs and simplify production to make Li7La3Zr2012a more attractive solid electrolyte which is particularly suitable for rechargeable lithium ion batteries.

The ionic conductivity of these garnet-like materials is enhanced in the cubic crystalline form. The cubic crystalline structure is thermodynamically stable at relative high temperatures (e.g. > 600°C), whilst the tetragonal crystalline structure is stable at room temperature. Whilst the utility of these garnet-like materials in energy storage devices and the like is not questioned, the adoption of these materials has been at least partially slowed by the complex and expensive processing routes required to produce them.

Current production methods include; (i) A sol-gel process wherein a solution (either aqueous or organic, typically acidic) is made using soluble salts of the desired elements. The prepared sol is then processed to give the desired form (e.g. powder, fibre, sintered pellet) and crystallised at elevated temperatures -typically >1000 °C -to achieve the preferred cubic crystalline phase. (ii) A mixed oxide method where the desired quantities of oxide raw materials or precursors are milled together before a firing step to crystallise the powder into the desired cubic form. The milling and firing steps are often repeated to achieve a homogeneous crystalline phase in the powder. Both methods of production are costly, either in terms of raw materials or processing cost due to the multiple step, batch synthesis.

Other methods such as nebulized spray pyrolysis, electrospinning and thin film processing either suffer from difficulties in scalability or low ionic conductivity.

US2019/0173130 discloses the production of Nb doped LLZO through direct quenching or solidification to form an intermediate amorphous composition, which goes through a comminution process prior to being shaped into sintered beads at 1150°C.

W02019150083 discloses a melt formed lithium zirconium silicate based composition which provides good conductivity whilst being produced using readily scalable technology.

US10,147,968 discloses a standalone lithium ion-conductive solid electrolyte comprising a lithium ion conducting glass sheet, which sacrificed ionic conductivity for large scale manufacturability. However, the requirements for obtaining a glass sheet with sufficient quality imposed significant limitations to the glass sheet compositions which could be made.

Despite these advances, there is still a need for improvements in the properties of ionically conductive inorganic materials and the production thereof

Summary of the Invention

In a first aspect of the present invention, there is provided a composite film comprising: a. a binder; and b. a plurality of ionically conductive inorganic platelets, said platelets having an average thickness of less than 100 pm, an aspect ratio of each of the minimum transverse dimension to thickness and the maximum transverse dimension to thickness of 10:1 to 25,000:1, wherein said film has an average thickness of between 5 pm and 500 pm.

The minimum thickness of the platelets will be dictated by manufacturing methods. Platelet thickness of greater than 10 nm or greater than 30 nm or greater than 50 nm may be obtainable using current production techniques.

The binder may be an organic or inorganic binder. The organic binder may be a polymer. The inorganic binder may be a solvent soluble inorganic binder. A solvent soluble inorganic binder may be used to form a membrane, with the solvent being removed after the formation of the membrane (e.g. by drying or sintering). In some embodiments, the inorganic binder is a water soluble binder. The water soluble binder may be a water glass (e.g. sodium, potassium or lithium silicate). In a preferred embodiment, the water soluble inorganic binder is lithium silicate. The use of the water soluble binder may be a means to densify the membrane under lower temperatures and shorter sintering times.

Solid platelet multi-component composite films may be used in secondary battery, where the composite material prevents the formation and growth of dendrites of metals on electrodes.

Particularly, when the platelets are melt formed, the composite film may be readily made in a large commercial scale. Melt formed platelet production for use in an intermediate or component within a solid electrolyte does not require the same stringent product or process specifications and, as such, enables a greater diversity of melt formed compositions to be produced.

Further the production of platelets enables better control of the morphological form as the maximum distance from a central axis to the nearest surface point can be more readily controlled compared to a large scale production method for particle and fibre formation.

In some embodiments, the platelets are substantially orientated with the maximum traverse dimension aligned substantially parallel to the surface of the film. Given the ability to form platelets with sub-micron thickness, the composites may comprise multiple layers of platelets. The multiple layers of platelets provide enhanced mechanical properties in terms of the film strength and the resistance of the film to dendrite penetration. As opposed to particle or fibre composites, the orientated platelets are able to provide a more comprehensive barrier to dendrite penetration.

The film may comprise an average of at least two or at least three or at least four layers of platelets. The number of layers within the film may be determined by examining a cross-section of the film and counting the number of layers in a line traversing the film, normal to the direction of the platelet layers.

In other embodiments, the platelets are aligned in the same plane. Improved conductivity and/or mechanical properties may be achieved using platelets aligned in a composite film.

In alternative embodiments, the thickness of the platelets may be at least 40% or at least 50% of at least 60% of the film thickness. A composite film with fewer platelets is able to reduce interfacial resistance and thereby increase ionic conductivity.

Suitable polymers include, but are not limited to, polyvinylidene fluoride (PVDF) , poly (vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) ) , Polyphenylene sulphide (PPS), polymethyl methacrylate (PMMA) , polyacrylonitrile (PAN) , polyimide (PI) , polyvinyl pyrrolidone (PVP) , polyethylene oxide (PEO) , polyvinyl alcohol (PVA), polylactic acid (PLA), polysaccharides (for example carboxymethyl cellulose (CMC)), styrene-butadiene rubber (SBR) and derivative and combinations thereof.

Depending upon the end use application, the film may be less than 400 pm or less than 300 pm or less than 200 pm or less than 100 pm or less than 50 pm or less than 30 pm or less than 20 pm or less than 10 pm thick. The minimum thickness of the film may be dictated by the thickness of the platelets. The film thickness may be at least 150% or at least 200% or at least 300% or at least 400% thicker than the mean platelet thickness.

In some embodiments, the platelets comprise an average maximum thickness of less than 90 pm or less than 50 pm or less than 20 pm or less than 10 pm or less than 5.0 pm or less than 4.0 pm or less than 3.0 pm or less than 2.0 pm or less than 1.0 pm or less than 0.8 pm or less than 0.6 pm. The minimum average thickness of the platelets may be at least 200nm or at least 300nm or at least 400nm or at least 500nm or at least 600nm or at least 700nm or at least 800nm.

In some embodiment, 80% of the platelets are within 40% or 30% or 20% of the average thickness of a population of platelets produced.

The platelets may have an aspect ratio of each of the minimum and maximum transverse dimension to thickness of 100:1 to 20,000:1 or 110:1 to 20,000:1 or 140:1 to 20,000:1 or 150:1 to 20,000:1 or 200:1 to 10,000:1 or 200:1 to 5,000:1 or 300:1 to 2,000:1 or 400:1 to 1000:1. The higher the aspect ratio the larger the surface area of the platelet per unit volume of material. This is advantageous where the platelet's role is to resist dendrite growth and penetration across the electrolyte. A high surface area to thickness ratio enables the potential for a reduced level of platelets to be used, whilst still meeting functional requirements. In some embodiment, the ratio of the minimum to the maximum transverse dimension is in the range of 1:1.1 to 1:1000 or 1:2: 1:500 or 1:3 to 1:10.

In some embodiments, the surface area to thickness ratio is at least 1600 (e.g, platelet with dimension of 40 pm x 40 pm x 1 pm) .or at least 2000 or at least 2500 or at least 3000 or at least 3500 or at least 4000 or at least 4500 or at least 5000 or at least 6000 or at least 7000 or at least 8000 or at least 9000 or at least 10,000 or at least 12,000 or at least 14,000 or at least 16,000 or at least 18,00001 at least 20,000. (e.g, platelet with dimension of 50 pm x 40 pm x 0.1 pm).

In some embodiments, the platelets comprise a minimum and maximum transverse dimension of at least 8 pm or at least 10 pm or at least 20 pm or at least 30 pm or at least 40 pm or at least 44 pm or at least 50 pm or at least 60 pm or at least 70 pm or at least 80 pm.

In some embodiments, the platelets comprise a maximum transverse dimension of the platelets is at least 8 pm or at least 10 pm or at least 20 pm or at least 30 pm or at least 40 pm or at least 45 pm or at least 50 pm or at least 58 pm at least 60 pm or at least 70 pm or at least 80 pm.

The film may comprise in the range of 2.0 wt% to 95 wt% platelets or in the range of 3.0 wt% to 80 wt% platelets or in the range of 5.0 wt% to 60 wt% platelets or comprises in the range of 10.0 wt% to 50 wt% platelets or in the range of 20.0 wt% to 40 wt% platelets. In some embodiments, the film comprises less than 20 wt% or less than 10 wt% platelets. In some embodiments the film comprises at least 60 wt% or at least 70 wt% or at least 80 wt% platelets or platelets and other ionically conductive shaped articles. The proportion of platelets in the composite film will be determined by the mechanical and ionic conductivity The platelets may be formed through any known method. In some embodiments the platelets are melt formed. In some embodiments, "melt formed" refers to a composition that has been obtained from a molten mass of glass that forms a glass or glass ceramic or ceramic composition obtained from the molten mass of glass. Molten may refer to the mass of glass being raised sufficiently above the softening point of the glass to lower the viscosity of the glass sufficiently to enable platelets to be formed. It will be understood that a melt formed composition is a composition directly derived from a molten mass (i.e. not via a precursor glass material which is further processed (e.g. ion exchange) to obtain the composition.) In one embodiment, the ionic conductive platelets are amorphous. The formation of amorphous, glassy, vitreous or non-crystalline ionic conductive platelets are generally more conducive to large scale production techniques, as solid-state transformation reactions to obtain desired crystalline forms may be dispensed with. However, in some embodiments, the platelets may be crystalline, semi-crystalline or glass-ceramic structures.

The platelets may have an amorphous content between 20 wt% to 99 wt% or between 30 wt% to 85 wt% or between 40 wt% to 80 wt% or between 50 wt% to 78wrk. In some embodiments, the amorphous content is at least 60 wt% or at least 70 wt% or at least 80 wt% or at least 90 wt%. In some embodiments, the platelets comprise a minor crystalline component. The minor crystalline component is preferably a target crystalline component, which may be transferred to a major crystalline component of the platelets after further process, such as heat treatment.

The ionic conductive platelets may be derived metal sulphides glass, metal oxide glass, metal phosphate glass (e.g. LiTi2(PO4)3), metal borate glass and/or metal silicate glass. The metals may include metals corresponding to metal ion battery chemistries and include magnesium, sodium, aluminium or lithium. The inorganic platelet may comprise any suitable composition, with the mechanical resistance of the platelets to dendrites being the primary consideration.

In some embodiments, the sulfur-based glass is of a type Li2S-YS; Li2S-YSn-YOn and combinations thereof, wherein Y is selected from the group consisting of Ge, Si, As, B, or P, and n=2, 3/2 or 5/2, and the glass is chemically and electrochemically compatible in contact with lithium metal. Suitable glass may comprise Li2S and/or Li20 as a glass modifier and one or more of a glass former selected from the group consisting of P2S5, P205, SiS2, Si02, B2S3 and B203. In some embodiments, the glass may be devoid of phosphorous.

In some embodiments, the predominant glass former is Si02 (i.e. largest glass forming component is 8i02). In some embodiments, the predominant glass former is SiS2.

The precise chemical composition may be determined through a balance of desirable end use properties such as ionic conductivity, manufacturability and mechanical properties of the platelets. To assist in the manufacturability of the platelets, the melting temperature of the glass melt is preferably less than 1600°C or less than 1500°C or less than 1450°C or less than 1400°C or less than 1350°C or less than 1300°C.

The ionic conductive platelets may be derived metal oxide glass In some embodiments, the oxide based glass has a composition of: MvM1v"M2xSiyOr where M is selected from the group consisting of Li, Na, K, Al, and Mg M1 is selected from the group consisting of alkaline metals, alkaline earth metals, Ti, Mn, Fe, Zr, Ce, La, Ta, Nb, V and combinations thereof; M2 is selected from the group consisting of B, Al, Ga, Ge or combinations thereof: v, y and z are greater than 0; w and/or x is greater than 0; y x.

In another embodiment, the platelet may have the formulation: 1_7÷w-3.-rMlwM2.G3_,vZrz_y_,M3yM4r012, where o L is in each case independently a monovalent cation, o G is in each case independently a trivalent cation, o M1 = a divalent dopant, o M2 = trivalent dopant o M3 = tetravalent dopant o M4 = pentavalent dopant o w, x, y, z are each in the range of 0 to <1.0 o 0 can be partly or completely replaced by divalent or trivalent anions such as N3-.

A preferred embodiment of the above formula is Li7La3Zr2012 (LLZO).

Other suitable glass or glass ceramic or ceramic platelet compositions may be found in W02019/150083, which is herein incorporated by reference.

In some embodiments, the platelets may: * be combined with one or more other shaped articles (e.g. fibre and particles); * comprise one or more compositions and/or * comprise one or more crystalline structures.

The ability of the process of the present disclosure to produce platelets which may not require additional size reduction enables the benefits of the multi-layered platelet structure to be delivered to the composite film.

The platelets have an ion conductivity (grain or total) at room temperature or 30°C or 50°C or 80°C of at least 1.0 x 106s cm-lor 5.0 x 10-6S cm-lor 6.0 x 106 S cm-lor 7.0 x 10-6 S cm' or 8.0 x 106 S cm-lor 9.0 x 106 S cm-1 or 1.0 x 10-5 S cm-lor 1.2 x 10-5 S cm-1 or 1.4 x 10-5 S cmt or or 1.5 x 10-5S cm-1 or 2.0 x 10-5S cm-1 or 3.0 x 10-5 S cm-1 or 4.0 x 10-5S cm-lor 5 x 10-5S cm-1, or lx 10-4S cm-1 or 5.0 x 10-45 cm-1 or 1.0 x1033 cm-1.

Grain conductivity (og) of a material relates to the ionic conductivity through a single grain or crystallite and is dependent on multiple factors, including but not limited to the composition, crystallinity and temperature.

In a second aspect of the present invention, there is provided a process for the production of ionically conductive platelets comprising the steps of: A. Providing raw materials in the appropriate stoichiometric amounts to obtain said platelets; B. Feeding the raw material into a melting vessel; C. Optionally providing a dopant to the melting vessel; D. Melting the raw material to form a molten mass; E. Feeding the molten mass into a rotating cup; and F. Ejecting the molten mass from the rotating cup into an optional quenching chamber comprising a cooling medium to produce platelets.

In some embodiments, no further heat treatment step(s) are required to transform the platelets to the desired morphological form after the quenching step.

In some embodiments, the platelets are exposed to heat treatment step(s) to transform the platelets in the desired morphological form.

While the use of a quenching chamber is optional, in most embodiments the quenching chamber provides the ability for the molten platelets to cool at the controlled rate to thereby enable the morphology of the resultant platelets to be controlled.

The raw material is preferably melted to a temperature sufficient to melt the raw materials to above the melting temperature of the target composition and crystalline/amorphous form thereof The melting vessel may operate above 8000C or at least 900'C or at least 1000-C or at least 11000 or at least 12000 or at least 1300)0 or at least 14000. The maximum operating temperature may be limited by the temperature at which the composition decomposes.

A cooling medium is preferably used to quench the molten mass. The cooling medium may be a fluid (gas or liquid) stream. The cooling medium is preferably inert, such as nitrogen or a noble gas. Although in some embodiments, the cooling medium may be air.

It will be understood that a quenching chamber is any space (enclosed or open) which comprises a cooling medium that comes into contact with the molten mass exiting the rotating cup.

The average quenching rate may be at least 50t per second or at least 1000 per second or at least 200'C per second or at least 400t per second or at least 600t per second or at least 800t per second or at least 1000'C per second or at least 1500t per second or at least 20000 per second between the time the molten mass contacts the cooling medium and the solidification of the molten mass or when the platelets cool to less than 2000.

In one embodiment, the average temperature differential between the molten mass and cooling medium while the molten mass is in contact with the cooling medium is at least 200t or at least 300t or at least 400t or at least 500'C or at least 600t or at least 700t.

The molten mass is preferably formed into platelets of dimensions which require little or no further processing to reduce its size for end-use application (e.g. in an electrolyte system in a battery), then there is not the propensity of the crystalline phase to change from the preferred form during size reduction operations, such as milling or grinding. However, in some embodiments, the platelets undergo further size reduction through grinding, milling and the like.

Quenching is dependent upon a rapid decrease in temperature across the molten mass to result in solidification without enabling the atomic structure time to reorder into a more thermodynamically stable structure (e.g. stable crystal polymorph) at the quenched temperature. It will be appreciated that a number of factors will influence the quenching process which enables this effect to be achieved including, but not limited to: * shape of the molten material; * temperature of the molten material and the cooling medium used to quench it; * the surface area to volume ratio of the molten material * maximum distance between a central axis and a surface of the molten mass; * the heat capacity and conductivity of the molten mass and the cooling medium; * distance from a central axis to the surface of the molten mass; and * the volume of cooling medium and its movement relative to the molten mass Due to variations in the dimensions of the shaped mass, to obtain the required level of crystallinity or amorphous form, the shaped mass may need to be separated on the basis of size or shape to separate out the shaped mass with the target morphology structure. Separation techniques may include sieving, air classification or the like. Through the platelets having a small cross-sectional dimension, the quenching process can be more effectively achieved compared to the quenching of particles with varying minimum dimensions.

In other embodiments, the shaping process in the rotating cup occurs at a high temperature (e.g. greater than 900t or greater than 1000C or greater than 1200t or greater than 1300t or greater than 1400t), with the platelets still in a molten form. Higher shaping temperatures are favourable to thinner platelet formation.

Film formation To produce the film from the platelets the following additional steps may be taken: G. Optionally, segregating the platelets to obtain a target platelet size, H. Mixing the platelets with a binder (e.g. polymer) and optional solvent to form a slurry; and Casting or extruding the slurry to form a film.

Size reduction operations may be performed, however the degree of size reduction operations would be expected to be minimal compared to the formation of other particles, given the ability to control the thickness of the platelets.

In some embodiments, the slurry flows through a progressively reducing effective diameter of a channel thereby orientating the platelets with the largest dimension parallel with the direction of flow. To facilitate the flow regime, particularly at high solids loading content, the slurry may also contain a solvent, which is removed (e.g. evaporation) from the film upon formation. The binder may be miscible or immiscible in the solvent.

Membrane formation A membrane may be formed from the platelets, which have been preferably orientated using the same method described in relation to the formation of the film. The methodology is analogous, with the solvent, rather than the polymer, being used as the medium to orientate the platelets.

They membrane may be between about 5 pm and 500 pm The process for forming a membrane may further include the steps of A. Forming the platelets into a layer, B. Heat treating the layer to densify the layer; and C. Maintaining the heat treatment for sufficient time to achieve a targeted morphology.

The membrane may also be formed under pressure to assist in the densificafion process and control the resultant morphology.

Heat treatment conditions may vary with the composition and morphology of the membrane. Guidance as to suitable heat treatment or sintering conditions may be found in Table 2.1 of Ramakumar et al, "Lithium garnets: Synthesis, structure, Li* conductivity, Li + dynamics and applications"; Progress in Material Science 88 (2017) 325-411, which is incorporated herein by reference.

In a third aspect of the present invention, there is provided a plurality of ionically conductive inorganic platelets comprising an ionic conductivity of at least 10-6 S/cm at room temperature, said platelets having an average thickness of between 50 nm and 500 pm, an aspect ratio of each of the minimum and maximum transverse dimension to thickness of 10:1 to 25,000:1. The average thickness of the platelets may be no more than 50 pm or no more than 25 pm or no more than 10 pm or no more than 5.0 pm or no more than 1.0 pm or no more than 0.9 pm or no more than 0.8 pm or no more than 0.7 pm.

The average thickness of the platelets may be at least 30% or at least 40% or at least 50% or at least 60% or at least 70% or at least 80% or at least 90% of the average thickness of the film.

The plurality of platelets may be used in the formation of inorganic composite electrolyte films or other shaped articles. Alternatively, the platelets may be used as an intermediate in the formation of a solid inorganic electrolyte membrane or layer thereof.

The inorganic platelets may be characterised as indicated in previous aspects of the present invention.

In one embodiment, the platelets may be sintered to form a membrane.

In a fourth aspect of the present invention, there is provided platelets produced according to the second aspect of the present invention.

Unless otherwise indicated, reference to a dimension are a reference to an average dimension. The average dimensions of the platelets are determined via SEM imaging techniques, with averages determined from at least 10 representative platelets within a population.

Reference to ionically conductive inorganic platelets encompasses not only lithium ion conductive platelets, but other metal ion conductive platelets. It will be appreciated that the inventive concept may be applied to other metal ion battery chemistries including magnesium, aluminium or sodium ion batteries. As such, the inventive concept extends to all metal ion electrochemical devices comprising the associated metal ion conducting inorganic platelets.

Forthe purpose of the invention, garnet-like and garnet-like composition encompasses garnet-like crystalline phases and amorphous phases capable of transforming into a garnet-like crystalline phase.

Brief Description of the Figure

Figure 1 is a schematic diagram of the apparatus used to produce the quenched platelets according to a process of the present disclosure.

Figure 2 is a schematic diagram of a composite film with multiple layers of platelets under the scope of the present invention.

Figure 3 is a schematic diagram of a composite film comprising fibres of the prior art. Figure 4 is a schematic diagram of a composite film comprising particles of the prior art. Figures 5 to 7 are a SEM of LZS platelets for use in the formation of the film of Figure 2.

Detailed Description of a preferred embodiment Forming the melt The raw materials are preferably provided in stoichiometric oxide form. Due to the volatility of some components, such as lithium, excess amounts may be required to achieve the desired stoichiometric quantities in the final product.

Hydroxide, hydrate and carbonate forms may also be used, as the gaseous reaction products are generally non-toxic. Nitrates, sulphates and other salts are less preferred due to the formation of toxic gases and the requirement to provide a washing step to remove impurities from the garnet-like final product.

Any suitable melting vessel may be used which is able to melt the raw materials to form a molten mass which can then be drawn out at a controlled rate through a discharge opening to enable the material to be shaped and quenched. A nozzle may be used to control the flow rate exiting the melting vessel. Electrical furnaces, such as an arc fumace may be used. The temperature of the molten mass may be determined by the temperature required to produce the desired shaped platelets.

The melting step may be conducted on a batch, semi-batch or continuous basis, heating the raw materials up to above the melting point of the raw material components and that of the stoichiometric composition being targeted. Operating under continuous conditions requires a plug like flow regime to ensure that the raw material is exposed to a minimum residence time to avoid variations in the molten material exiting the vessel. The inlet of the furnace is preferably protected from the ingress of contaminants. An inert gas to blanket the exposed melt may also be used.

The molten material may be blanketed in a controlled atmosphere such as air, hydrogen, helium or other gases prior to shaping and/or quenching. The purpose of the controlled atmosphere may include blocking chemical reaction or controlling surface tension.

Shaped material formation In general, the shaping process requires a sufficient temperature to be maintained to form the required shape and dimensions from the molten mass. As such, the shaping step is usually conducted at a similar temperature to that of the molten mass leaving the melting vessel (e.g. less than 200°C or less than 100°C difference). As a result, the shaping device is typically located within 1m or within 0.5m of the melting vessel outlet. In some embodiments, the molten mass is heated and/or insulated from heat loss after leaving the melting vessel and up to and during the formation of the platelets.

Platelets W01988008412 (incorporated herein by reference) discloses an apparatus and a method of producing platelets from a molten material through feeding a stream of molten material in a downwards direction into a rotating cup. Details of the apparatus and operating conditions to form the platelets are provided in W02004/056716, EP0289240 and US8796556, which are incorporated herein by reference Platelet thickness down to and less than the micron level is obtainable in such processes, depending upon the nature of the molten material and the process conditions used. As such, a range of materials can be manufactured without recourse to further grading, crushing or grinding operations.

The rotating cup is preferably heated and/or insulated to maintain a temperature which enables the existing molten mass to be made into thinner platelets.

For the purposes of the current application, the mean thickness of the platelets is preferably in the range of 40 nm to 50 pm or 100 nm to 30 pm or 200 nm to 10 pm or 0.5 pm to 5 pm. Greater platelet thickness may be required when the mechanical properties of the platelet are important, while thinner platelet thickness may be required in the formation of thin films.

A limitation of the method in the abovementioned disclosures in the production of the disclosed invention is that the thickness of the platelets was dependent upon the molten mass having sufficiently low viscosity as it contacted the rotating cup walls to form sufficiently thin sheets or ribbons that were the precursor to the solidified platelets of the required thickness. The temperature of the molten mass in the rotating cup is typically above 1000°C (e.g. about 1100°C to about 1400°C or even higher) to achieve platelets at the required thickness.

The formation of glassy platelets may require rapid quenching therefore the thin sheets of molten mass are required to be quenched after exiting the rotating cup. The platelet formation process can facilitate the quenching process by reducing the thickness of the molten material such that exposure of the exiting sheet/ribbon to a cooling medium can more effectively reduce the temperature of the molten material to form and stabilise the glassy structure.

Quenching It will be appreciated that not all platelets for use in composite films require to be quenched to obtain the required crystalline or glassy form. This section is relevant for those platelets in which quenching is required to obtain the desired crystalline or amorphous form.

Prior to or during quenching, the molten material is preferably shaped into sufficiently small enough dimensions to enable rapid cooling throughout the molten material to generate a predominately cubic crystalline structure in the final product. It will be appreciated that the required dimensions of the shaped material will be dependent upon the heat transfer properties (including the temperature, heat capacity and conductivity) of the cooling medium as well as the shaped material. Routine experimentation may be required to optimise the quenching and material shaping processes to obtain the desired level of crystalline or amorphous structure.

With reference to Figure 1 (prior art device), the molten mass leaving the centrifuge or rotating cup 3 at 7 is located within the gap and prevented from touching the sides of the annular plates 9 and 11 by the cooling medium flow. The cooling medium flow continues to quench the glass until it reaches a solid state, and due to friction upon the molten mass, continues to pull in a radial direction, thus preventing the molten mass from rolling or rucking over, keeping the solidifying mass flat and breaking it into small platelets. The platelets are collected in the cyclone vacuum chamber 13 and exit via connection 15 to a precipitator cyclone and filter section (not shown).

The size (loosely described as the diameter of platelet) and the thickness of platelet can be varied through a considerable range by adjusting the flow of glass into the cup 3 adjusting the speed of rotation of the cup 3, adjusting the distance between the annular extraction plates 9 and 11 and varying the vacuum pull or velocity through the gap 19 between the annular extraction plates for any given gap by varying the amount of cooling medium flow through the extraction connection 15.

In a preferred embodiment, the injection ports (not shown) are integrated into the plates 9 and 11, which injects a stream of a cooling fluid through the gap 19. The injection ports may be placed at the entrance to the quenching chamber 21. An air curtain or the like may be used to reduce the amount of hotter gases being drawn into the quenching chamber in addition to the gases from the injection port.

In some embodiments, the rotating cup space encompassing the outlet of the melting vessel; the rotating cup and quenching chamber is filled with an inert gas. The plates 9 and 11 may have internal cooling channels, such that the gases entering the chamber at 21 are cooled as they travel along the length of the plates. In other embodiments, a mist of a liquid (preferably an inert liquid) is sprayed between the plates to further quench the platelets. In a preferred embodiment, the thinness of the platelets is such that the temperature differential between the solidifying platelets and the gas flowing into the quenching chamber 13 is sufficient for the temperature of the platelets to be cooled at sufficient rate to reach the desired proportion of cubic crystalline phase in the resultant platelets.

The cooling medium is preferably diverted to a recycle path and passed through a chiller unit to reduce the temperature down and recirculated back through the injection ports to between plates 9 and 11.

In one embodiment, the molten material preferably flows through a quenching chamber. The quenching chamber comprises: (A) a first inlet for receiving the molten mass from the rotating cup; (B) a second inlet for receiving a cooling medium steam; and (C) an outlet for the outputting the quenched glass ceramic material from the quenching chamber.

The cooling medium may contact the molten mass in a co-current or counter-current flow pattern.

The flow configuration of the cooling fluid is preferably such that the venturi effect is utilised to transport and quench the platelets. In some embodiments, the quenching chamber comprises a vacuum chamber, preferably a cyclone vacuum chamber.

Quenching may be accomplished using inert gases, such as nitrogen and noble gases. Nitrogen is commonly used at greater than atmospheric pressure ranging up to 20 bar absolute. Helium is also used because its thermal capacity is greater than nitrogen.

Alternatively, argon can be used; however, its density requires significantly more energy to move, and its thermal capacity is less than the alternatives. The gases are preferably compressed gases. Alternatively, the cooling medium may be a liquid, including water or liquid nitrogen. The use of inert gases reduces the likelihood that the quenching process contributes to the formation of impurities, which may affect the functionality of the final product. Air may also be used if the quality of the final product is not detrimentally affected for the desired end-use application.

According to various embodiments, the fluid stream can have a temperature ranging from about room temperature to about -200° C., from about 10° C. to about -100° C., from about 0° C. to about -60° C., or from about -10° C. to about -50° C., including all ranges and subranges therebetween. The velocity of the compressed fluid stream may range for example, from about 0.5 m/sec to about 2000 m/sec, such as from about 1 m/sec to about 1000 m/sec, from about 2 m/sec to about 100 m/sec, from about 5 m/sec to about 20 m/sec, or from about 5 m/sec to about 15 m/sec, including all ranges and subranges therebetween. It is within the ability of one skilled in the art to select the stream velocity appropriate for the desired operation and result.

The glass ceramic can thus be rapidly cooled to a temperature below its solidification point, e.g., a temperature less than about 600° C., such as less than about 575° C., less than about 550° C., less than about 525° C., or less than about 500° C. In certain embodiments, the glass ceramic can be rapidly cooled to a temperature ranging from about 200° C. to about 600° C., or from about 250°C. to about 500° C., or from about 300° C. to about 400° C., including all ranges and subranges therebetween.

According to various embodiments, the term "rapid cooling", "quenching" and variations thereof is used to denote cooling of the glass ceramic to at least its solidification temperature (and preferably less than 200°C or less than 150°C) within a period of time sufficient to form and stabilise the desired cubic crystalline structure. According to various embodiments, the time period may be less than about 10 seconds, for instance, less than about 5.0 seconds, less than about 4.0 seconds, less than about 2.0 seconds, or less than about 1.0 seconds, although longer or shorter time periods are possible and intended to fall within the scope of the disclosure. In other embodiments, the rapid cooling may occur within the time period from about 0.1 to about 0.9 seconds.

In some embodiments, the molten mass is quenched through contacting the molten mass with a liquid. The liquid is preferably inert (e.g. ionic liquid or liquid nitrogen). The characteristics of the liquid is preferably such that, in addition to quenching, the characteristics and/or temperature of the liquid is selected to alter one or more of a. the surface area of the platelets; b. the surface porosity of the platelets; and/or c. the presence of functional groups on the platelets.

Film formation and platelet alignment The processing of the mixture may comprise melting the binder and producing a flow regime which aligns the platelets substantially on the same plane. Preferably, the platelets are aligned in the same orientation (e.g. the length dimension of the platelets are aligned in the same direction). Methods of flow induced alignment of platelets are known in the art and details of such method may be found in reference texts, such as Flow Induced Alignment in Composite Materials edited by T.D.Papathanasiou and D.C.Guell, Woodhead Publishing Limited, Cambridge England (1997).

In some embodiments, a composite is formed by forming a slurry comprising the platelets and a binder dissolved or dispersed in a solvent. Flow induced alignment of the platelets are achieved prior to the solvent being evaporated to leave behind a binder-aligned platelet composite. The polymer may be miscible or immiscible in the solvent. The use of a solvent may assist in forming a film with a higher inorganic content (e.g. greater than 50 wt% or greater than 60 wt% or greater than 70 wt% or greater than 80 wt% platelets or platelets and other shaped articles) In other embodiments, a solvent is not required. In some embodiments, platelet alignment may be obtained with the use of a fugitive solvent to form a slurry, via the techniques previous described. After then solvent is removed (e.g.via heating), an aligned layer of platelets in formed, which may be sintered to form an ionically conductive membrane.

Flow induced alignment may be achieved through progressively reducing the effective diameter of a channel in which the slurry flows which results in the platelets orientating with the largest dimension parallel with the direction of flow.

Example 1 (partially theoretical) The shaping and quenching steps in this example are theoretical, with the actual experiment using air to impinge upon the molten stream, simultaneously quenching and forming spherical particles. The person skilled in the art will appreciate that the theoretical modification will result in the formation of platelets of a doped lithium lanthanum zirconium oxide (Al-LLZO) with a major amorphous phase and a minor cubic crystalline phase.

Stoichiometric qualities of A1203 (dopant), La203 and Zr02 were combined with 20% stoichiometric excess of Li2CO3to form a powdered mixture which was added to the melt rig. A small amount of Mo dopant was provisioned to be added from the molybdenum electrodes used in the melt rig. The quantity of Mo added was calculated from levels of Mo added to previous batches operated at similar operating conditions.

The melt rig comprises a cylindrical water-cooled stainless-steel vessel having an internal diameter of 340 mm and an internal height of 160mm. The melt rig comprised of two molybdenum electrodes which were submerged in the powdered mixture with the electrode tips being approximately 5 mm apart. An alumina plate was positioned at the bottom of the rig, with an alumina rod covering a 14 mm orifice which functioned as a discharge opening.

The mixture was manually fed into the vessel from an opening at the top. An insulating layer covered the majority of the opening, with an exhaust fan used to remove gases generated. The mixture was initially heated using an oxyacetylene torch to melt a small pool, at which point the electrodes were powered to form a current between them. The power was increased slowly over 30-45 minutes and the electrodes were moved further apart to build a larger melt pool within the furnace with the temperature of the melt pool being approximately >1250°C -1500°C. Batch process conditions were used, with the total residence time of the melt pool, once formed, not exceeding 1 hour.

When the melt pool was sufficiently large, the alumina rod was removed from the plate instantly releasing the melt pool through the 12 mm orifice to form a molten stream.

The molten stream is feed into a rotating cup apparatus as illustrated in Figure 1. The following ranges and conditions may be adopted, or at least some of them, in order to produce very thin platelets according to the disclosure: o mass flow between 0.2 and 2.5 kilos per minute o glass temperature at control nozzle of from 1200 to 1450°C.

o glass temperature of the rotating cup 5 of from 1220 to 1350°C.

o distance between the melt tank control nozzle and entry to the rotating cup 5 of from 75 to 500 mm o rotating cup 5 diameter of from 28 to 48 mm OD o rotating cup 5 depth of from 15 to 60 mm o rotation speed of the rotating cup 5 from 5,000 to 14,000 RPM o rotating cup 5 externally insulated as per example 2 and/or heated.

o distance between edge of spinner 7 and entry to annular venturi of from 10 to 75 mm o gap between plates 19 forming annular venturi of from 2 to 12 mm o air pressure within system of from 180 to 580 mm water gauge Platelets entered a quenching chamber 13 (annular venturi) which cooled the platelets to about 160°C in less than one second. Therefore, the cooling rate of the molten mass was at least 1000°C per second.

The platelets travelled along a quenching chamber 13 before being collected on a steel mesh in a collection bin.

Effect of particle size on crystal/amorphous morphology Quantitative phase analysis was performed on size fraction of Al doped LLZO powders with differing amounts of Al dopant.

Rietveld quantitative amorphous content analysis was performed with reference to: De La Torre et S., J. Appl. Cryst., (2001) 34 196-202; and Chapter 5 -Quantitative phase analysis in Practical Powder Diffraction Pattern Analysis using TOPAS. P. E. Dinnebier, A. Leinewber, J. S. 0. Evans LaB6 used as internal standard for spiking. Masses of sample and LaB6 were recorded (next slide) and powders were mixed by hand grinding for 10 minutes. Particle size used for Brindley correction in refinement is 45 pm.

LaB6 MAC = 237.405 cm2g-1; LaB6 LAC = 1116.067 cm-1 Li7La2r2012 MAC = 205.267 cm2 g-1; Li7La3Zr2012LAC = 1040.262 cm-1 Brindley correction and LAC values applied in refinement Absolute weight fractions of known materials can then be calculated by: Wk(absolute) Wk(sample) Wk(standard) Wk(standard-re f) Weight fraction of unknown or amorphous material comes from: W(amorphous) = 1 -1Wk(abso lute) The morphological composition of particles with two different dopant levels is provided in table 1. It may be deduced that the smaller size fractions possessed a higher amorphous content. Further, it would be expected that the quenching of doped LLZO platelets with a thickness of less than 1.0 pm would obtain platelets with an even higher proportion of amorphous content.

Comparative Example (samples 0960 and 1421) Example 1 was repeated under the same conditions but without the addition of the A1203 dopant. The XRD from the resultant particles produced indicated that a major amorphous phase was still produced, but the amount of the tetragonal phase was about twice that of the cubic phase. This highlights the effect of the dopants in stabilising the cubic phase in preference to the less ionically conductive tetragonal phase. The results also appear to indicate that the amorphous content is not dependent upon particle size for undoped samples of LLZO.

Sample Composition Size Table 1 Cubic Tetragonal Crystalline Amorp.

0960 LLZO 180-355 pm 15.3 30.7 46.0 54.0 1421 LLZO <180 pm 15.3 30.7 46.1 53.9 0906 Alo 25 LLZO 350+ pm 26.2 12.5 49.3 50.9 1252 Alp 25 LLZO 40-180 pm 13.2 5.9 23.4 76.6 0976 Alp so LLZO 500+ pm 29.3 12.9 50.2 49.8 0981 Alo 50 LLZO 40-180 pm 13.8 6.1 28.8 71.2 The resultant film, produced via an extrusion process in which the diameter of the feed channel progressively narrowed to align platelets parallel with the surface of the film, as indicated in Figure 2. The film (Figure 2) may have an average of two platelet layers or more, from an average of at least 3 cross sections through the film (A, B and C). The alignment of the platelets with the film also ensures that the platelets will be aligned parallel with electrodes when configured within a battery. This configuration will provide a greater barrier to dendrite formations with dendrites more likely to encounter greater resistance in platelet composites compared to fibre composites (Figure 3) and particle composites (Figure 4).

Example 2

The bulk material is made via a melt formation process used in refractory fibre production. A raw material feed containing oxides or oxide precursors (e.g. carbonates) of the requisite elements were mixed thoroughly in a powder mixing system. The resultant flake composition comprised 5.82 wt% Li20, 23.99 wt% Zr02 and 70.19 wt% 8i02. The powder mixture is then fed into a melting furnace and the temperature is raised above 1300 °C to obtain a flowing melt pool. Using a small aperture, in the region of 5-15 mm, the molten stream is then dropped from the furnace onto an incident air stream. The high-pressure air stream is used to disperse the molten stream into particulate matter. The form of the particulate matter is varied in the process with limited control over ratios of platelet: fibre: grain.

The desired particulate form may be isolated using various techniques. In the case of platelet extraction a series of air classification techniques are employed with varying rotor speeds and suction. Material collected after the air classification process is then screened to remove any coarse grain material that could have been carried through. The screening process employs ceramic breaker balls to avoid the formation of clumps of fibre -bundling up the desired platelet material.

Following the screening process, typically employing multiple size aperture screens to ensure the collection of only the desired material, the resulting batch of material is then analysed using optical and electron microscopy. The use of microscopy enables the elimination of fibre and grain particulate matter to be monitored. If fibre and/or grain content is considered too high, further air classification and/or screening techniques may need to be performed to ensure the homogeneity of the sample.

With reference to Figures 5 to 7, there are SEM images of ionically conductive platelets. The maximum dimension in the platelet in Figure 6 is over 59 pm with the estimated thickness of the platelet being no more than 0.40 pm, resulting in a maximum aspect ratio of about 148. The minimum transverse dimension (measured at right angles to the maximum transverse dimension) is about 44 pm, resulting in a minimum aspect ratio of 110. The corresponding minimum surface area to thickness ratio is 4,840 (44x44/0.4).

As illustrated in Figure 7, the thickness of the platelets has been measured down to a thickness of at least 0.073 pm (73 nm). An estimation of the aspect ratio of each of the minimum and maximum transverse dimension to thickness is at least 200 and it would be much higher aspect ratios (e.g. at least 300 or at least 400 or at least 500) would be expected to be achieved through the teaching of this disclosure.

For the avoidance of doubt it should be noted that in the present specification the term "comprise" in relation to a composition is taken to have the meaning of include, contain, or embrace, and to permit other platelets to be present. The terms "comprises" and "comprising" are to be understood in like manner. It should also be noted that no claim is made to any composition in which the sum of the components exceeds 100%.

Many variants of the housing of the present disclosure will be apparent to the person skilled in the art and are intended to be encompassed by this disclosure.

Claims

Claims A plurality of ionically conductive inorganic platelets comprising an ionic conductivity of at least 1 0-6 S/cm at room temperature, said platelets having an average thickness of between 50 nm and 100 pm, and an aspect ratio of each of the minimum and maximum transverse dimension to thickness is in the range 10:1 to 25,000:1.
2 The inorganic platelets of claim 1, wherein the aspect ratio of each of the minimum and maximum transverse dimension to thickness is in the range 110:1 to 20,000:1
3. The inorganic plates of claim 1, wherein the aspect ratio of each of the minimum and maximum transverse dimension to thickness is in the range 140:1 to 20,000:1
4. The inorganic platelets according to any one of the preceding claims, wherein the platelets comprise an average thickness of between 50 nm and 1.0 pm.
5. The inorganic platelets according to any one of the preceding claims, comprising a minimum and maximum transverse dimension of at least 40 pm.
6. The inorganic platelets according to any one of the preceding claims, wherein the maximum transverse dimension of the platelets is at least 45 pm.
7. The inorganic platelets according to any one of the preceding claims, wherein the amorphous content is at least 50 wt%.
8. The inorganic platelets according to any one of the preceding claims, wherein the inorganic platelets are glass ceramic.
9. The inorganic platelets according to any one of the preceding claims, wherein the surface area to thickness ratio of the platelets is at least 1,600.
10. A composite electrolyte film comprising: a. a polymer; and b. a plurality of ionically conductive inorganic platelets according to any one of the preceding claims, wherein said film has an average thickness of between 5 pm and 500 pm.
11. The film according to claim 10, wherein the platelets are substantially orientated with the maximum transverse dimension aligned parallel to the surface of the film.
12. The film according to claim 10 or 11, comprising at least two layers of substantially orientated platelets.
13. The film according to any one of claims 10 or 12, wherein the average thickness of the platelets is at least 50% of the average thickness of the film.
14. The film according to any one of claims 10 to 13, wherein the film comprises in the range of 2.0 wt% to 95 wt% platelets.
15. The film according to any one of claims 10 to 14, wherein the platelets have a composition according to the formula: L7,3x-7M1w1M2.G3_,,,,Zrz_y_zM3yM4z012, where o L is in each case independently a monovalent cation, o G is in each case independently a trivalent cation, o M1 = a divalent dopant, o M2= trivalent dopant o M3= tetravalent dopant o M4= pentavalent dopant o w, x, y, z are each in the range of 0 to <2.0 o 0 can be partly or completely replaced by divalent or trivalent anions such as N3-
16. The film according to any one of claims 10 to 15, wherein the platelets comprise a lithium zirconium silicate based glass.
17. A process for production of the ionically conductive inorganic platelets as defined in any one of the preceding claims comprising the steps of A. Providing a raw material for the ionically conductive inorganic platelets; B. Feeding the raw material into a melting vessel; C. Optionally, providing a dopant to the melting vessel; D. Heating the raw material to form a molten mass; E. Feeding the molten mass into a rotating cup; and F. Ejecting the molten mass from the rotating cup into a quenching chamber comprising a cooling medium to produce platelets; and G. Optionally, segregating the platelets to obtain a target platelet size; wherein the cooling rate of the molten mass is controlled to produce platelets of a target morphology.
18. The process according to claims 17, wherein the average cooling rate is at least 500°C per second between the time the molten mass contacts the cooling medium and the solidification of the molten mass.
19. The process according to claim 17 or 18, wherein the average temperature differential between the molten mass and cooling medium while the molten mass is in contact with the cooling medium is at least 500t.
20. The process according to any one of claims 17 to 19, wherein the combination of the cooling rate and the dimensions of the platelet are sufficient to form amorphous platelets with an amorphous content of at least 50 wt%.
21. The process according to any one of claims 17 to 20, wherein the quenching chamber comprises a zone where a cooling medium comes into contact with the molten mass.
22. A process for the production of a film comprising the steps of: A. Mixing the platelets according to any one of claims 1 to 9 or produced according to any one of claims 17 to 21 with a polymer and/or a solvent to form a slurry; B. Casting or extruding the slurry to form a film; and C. Removing the solvent, when present.
23. The process according to claim 22, wherein the slurry flows through a progressively reducing effective diameter of a channel to thereby orientate the platelets with the largest dimension parallel with the direction of flow.
24. The process according to claims 22 or 23, wherein the solvent, when used, is evaporated upon formation of the film.
25. The process according to claim 24, wherein a solvent is evaporated to leave a film comprising a layer of orientated platelets which is then sintered to form an inorganic membrane