Open vessel for high temperature applications

Abstract

The present invention relates to an open vessel for containing cathode active materials with a capacity in the range of 0.01 to 2000 litres composed of a composite comprising an aggregate phase comprising refractory particles; and a binder phase comprising binder refractory particles and an aluminosilicate phase. The binder refractory particles are embedded within the aluminosilicate phase; and wherein the sum of the refractory particles + aluminosilicate phase + binder refractory particles is at least 70 wt% of the total weight of the composite composition.

Description

[0001] Open vessel for high temperature applications

[0002] FIELD

[0003] The present invention relates to open vessels, such as saggars, for holding and processing cathode active materials for lithium batteries; a method for producing said open vessels and the use of said open vessels for calcining cathode active materials.

[0004] BACKGROUND

[0005] Lithium batteries have been widely used as energy storage devices for mobile communications devices, hybrid electric vehicles, and household appliances, due to relatively high energy density and excellent output characteristics.

[0006] Core materials of lithium batteries may be classified as an anode, a cathode, an electrolyte, or a separator. Examples of cathode materials include LiCoO2or nickel manganese cobalt (NMC)-series cathode active material or the like is used. Such a cathode active material may be produced, by providing a raw material including a compound and a transition metal compound to a saggar, a firing vessel, and firing the raw material at a temperature ranging from 400°C to 1100°C depending on the type of the raw material, to produce a cathode active material such as a lithium composite oxide or the like.

[0007] The interaction between the cathode active materials and the refractory vessels (e.g. saggar) can result in the formation of newly formed lithium based phases which results in differing thermal expansion coefficients within the top layer of the refractory vessel in contact with the cathode material. The resultant vessels are more prone to crack formation and the penetration of these lithium-based phases further into the vessel, further compromising the vessel’s mechanical integrity and conductive properties. The corroded vessels result in a higher energy consumption, longer processing times and a shorter service life.

[0008] WO2017 / 198506 address this problem through providing a two component vessel comprising a ceramic matrix base with an insert made from a monolithic matrix material. The monolithic matrix material is reported to be resistant to corrosion and thermal shock. However, there is still scope to provide vessels with improved corrosive resistance to prolong the working life of the vessels. Hence, there is a need for an open refractory vessel for processing cathode active materials for lithium batteries or similar corrosive materials, which has an improved service life and operational performance.

[0009] Summary of the invention

[0010] In a first aspect of the present invention, there is provided an open vessel for processing cathode active materials at temperatures above 600°C, with a capacity in the range of 0.01 to 2000 litres composed of a composite comprising: an aggregate phase comprising or consisting of:

[0011] • refractory particles having a particle size distribution with a median particle size D5o value of greater than or equal to 100 pm with a Feret diameter of greater than 50 pm using image analysis software; a binder phase comprising:

[0012] • an aluminosilicate phase; and

[0013] • binder refractory particles having a particle size distribution with a median particle size D5o value in the range of > 0 pm to 30 pm with a Feret diameter of no more than 50 pm using image analysis software, said refractory particles and binder refractory particles being selected from the list consisting of metal carbides, metal nitrides, silicon carbide, boron carbide, boron nitride, graphite and oxides of aluminium, zirconium, silicon, chromium, yttrium, hafnium, tungsten and titanium and combinations thereof, wherein a microstructure of a cut plane of the composite comprises, in % surface area, 1.0 to 40 % binder refractory particles, relative to the total surface area of the composite, said binder refractory particles are embedded within the aluminosilicate phase; and wherein the sum of the refractory particles + aluminosilicate phase + binder refractory particles is at least 70 wt% of the total weight of the composite composition.

[0014] The median particle size (D5o) of the refractory particles and the binder refractory particles and the surface area of binder refractory particles may be determined from an image of a cut plane observed at a magnification of 2000 times or 3000 times for the refractory binder particles and a magnification of 100 times with a microscope (optical or scanning electron). Preferably at least 50 particles or more preferably at least 100 particles are analysed to determine the particle size distribution, including the median particle size or the surface area covered thereby. The analysis is preferably carried out by image analysis software, such as Imaged™ software.

[0015] The Feret diameter (or maximum Feret diameter) is the Feret diameter with the maximum length as determined by the Imaged software or in accordance with ISO9276-6:2008. Unless otherwise indicated reference to the Feret diameter is reference to the maximum Feret diameter.

[0016] Energy dispersive X-ray spectroscopy (EDS) analysis combined with the use of image analysis software (e.g. Imaged™) may be used to determine the surface area % portions of each of the components (phases and particles). A magnification of x100 to x200 magnification may be used to determine the % surface area of the aggregate phase and components therein. A magnification of x1000 to x3000 magnification may be used to determine the % surface area of the binder phase and components therein. The % wt proportion of each of the components, including the refractory particles in the aggregate phase may be determined by XRD Rietveld analysis. Alternatively, the % wt proportion may be determined using EDS analysis; the % surface area and density data, using the assumption that the % surface area of the cut plane is equal to the % volume of the binder refractory particles within the composite.

[0017] In an alternative aspect of the present invention, there is provided a composite comprising:

[0018] 20 to 80 wt% of an aggregate phase comprising or consisting of:

[0019] • refractory particles comprising a particle size distribution with a median particle size D5o value of greater than or equal to 100 pm; and

[0020] 20 to 80 wt% of a binder phase comprising:

[0021] • 20 to 99 wt% of an aluminosilicate phase; and

[0022] 1.0 to 80 wt% binder refractory particles comprising a particle size distribution with a median particle size D5o value in the range of >0 pm to 50 pm, wherein binder refractory particles are embedded within the aluminosilicate phase; and wherein the sum of the refractory particles + aluminosilicate phase + binder refractory particles is at least 70 wt% of the total weight of the composite composition.

[0023] In some embodiments, the sum of the aggregate phase and the binder phase is equal 100 wt%. Therefore, the wt% of binder phase = 100 - %wt aggregate phase.

[0024] The composite may comprise a portion of other refractory materials (excluding the refractory particles and the binder refractory particles of the designated particle size distributions) such as carbides and nitrides and oxides of zirconium, silicon, tungsten, titanium, hafnium and yttrium. These other refractory materials preferably form part of the aggregate phase or the binder phase.

[0025] In some embodiments, the refractory materials may partially substitute one or both of the refractory particles and binder refractory particles. In some embodiments, the sum of the refractory particles + aluminosilicate phase + binder refractory particles may be 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.

[0026] The composition and structure of the open vessel provides a beneficial balance between corrosive resistance (including oxidation resistance), thermal shock and mechanical strength (including impact strength) when processing cathode active materials for lithium batteries. The presence of refractory materials such as AI2O3particles slows corrosion whilst maintaining mechanical strength. Unexpectedly, the addition of refractory materials, such as AI2O3particles within the composite does not detrimentally affect thermal shock performance.

[0027] While not wanting to be bound by theory, it is thought that the refractory binder or clay component particles nucleate crystalline alumino-silicates phases, such as mullite, during the firing of the raw material mixture. The dispersal of binder refractory particles into the raw materials, such as clay, enable the formation of a binder phase comprising the binder refractory particles and a network of small aluminosilicate grains. The network of small aluminosilicate grains comprise micropores (e.g. <10pm) and grain boundaries where glassy phases may concentrate. The resultant microstructure of small pores promotes good thermal shock characteristics, while the grain boundaries and fine binder refractory particles promotes good impact strength, with the binder refractory particles also contributing to the corrosion resistance of the binder

[0028] The sum of the aggregate phase +binder phase is preferably at least 70 wt% or at least 80 wt% or at least 85 wt% of the total weight of the composite. The wt% ratio of the aggregate phase to the binder phase may be in the range of 0.2:1 to 5:1 or 0.4:1 to 4:1 or 0.5:1 to 2:1 or 0.8:1 to 1.5:1. Ratios within these ranges possess a beneficial proportion of aggregate and binder to provide a composite with excellent mechanical, thermal shock and corrosive resistant properties.

[0029] Additives

[0030] The composite may further comprise additives including impregnates used to improve corrosion resistance properties of the composite; and oxidation inhibitors or precursors thereof which are used to inhibit the oxidation of non-oxide materials, such as silicon carbide and graphite. Suitable impregnates include, but are not limited to, phosphates, phosphoric acid, colloidal silica, colloidal alumina, colloidal titania, colloidal zirconia, boron, borax and / or boric acid. Suitable oxidation inhibitors include, but are not limited to, steel, metal forms of zirconium, silicon, tungsten, chromium, boron, zinc, molybdenum, titanium, aluminium iron, bronze and magnesium; borides including zirconium boride, calcium boride and titanium boride; ferrosilicon (FeSi), carbides including boron carbide and aluminium carbide, or a combination of any thereof. Additives may make up between >0 or 1.0 to 15 wt% or between 2.0 and 10 wt% of the total weight of the composite material.

[0031] Aggregate phase

[0032] The aggregate phase provides both mechanical strength and corrosive resistance in cooperation with the binder phase.

[0033] In one embodiment, the refractory particles of the aggregate phase are selected from the list consisting of metal carbides, metal nitrides, silicon carbide, boron carbide, boron nitride and oxides of aluminium, zirconium, chromium, yttrium, hafnium, silicon, tungsten and titanium and combinations thereof. In one embodiment, the refractory particles comprise one or both or SiC and alumina. SiC particles provide excellent thermal shock resistance, while alumina particles provide excellent corrosive resistance. The refractory particles may comprise refractory oxides, such as Cr2O3, AI2O3, ZrO2, TiO2, HfO2, Y2O3and combination thereof. In one embodiment, the refractory particles comprise alumina. Examples of commercially available crystalline alumina include, but are not limited to tabular alumina, calcined alumina and white fused alumina. The refractory particles are preferably crystalline or at least partially crystalline. Other particles which may be able to provide a substitute for the good thermal shock properties of SiC include partly stabilised ZrO2, B4C and Si3N4.

[0034] In one embodiment the composite comprises, relative to the total weight of the composite:

[0035] 20 to 80 wt% aggregate phase;

[0036] 20 to 80 wt% binder phase; and optionally

[0037] 0 to 15 wt% additives.

[0038] In one embodiment the composite comprises, relative to the total weight of the composite:

[0039] 10 to 60 wt% or 15 to 38 wt% SiC in the aggregate phase; 3 to 40 wt% or 5 to 20 wt% refractory oxide particles in the aggregate phase;

[0040] 1 to 40 wt% or 2 to 30 wt% binder refractory particles in the binder phase;

[0041] 8 to 30 wt% or 1o to 25 wt% aluminosilicate phase; and

[0042] 0 to 15 wt% additives. The additives may include oxidation inhibitors and impregnates.

[0043] In one embodiment, the composite comprises refractory particles with a D5o value greater than 120 pm or greater than 150 pm or greater than 175 pm or greater than 200 pm or greater than 225 pm or greater than 250 pm. The refractory particles may comprise a D5o value no more than 800 pm or no more than 600 pm or no more than 500 pm or no more than 400 pm or no more than 300 pm. The refractory particles are sufficiently large to maintain mechanical strength of the composite, whilst improving the composite’s corrosion resistance. Too large a D5o value may result in a deterioration in the mechanical properties of the resultant composite. Whilst too small a D5o value may result in a deterioration in the corrosive resistance properties of the composite. In some embodiments, less than 10% of the refractory particles has a Feret diameter of more than 500 pm and / or less than 5% of the refractory particles has a Feret diameter of more than 700 pm.

[0044] The cross-sectional (i.e. cut plane) surface area of the aggregate phase may be in the range of 20 to 80% of the total surface area of the composite. In some embodiments, the aggregate phase may be at least 25 % or at least 30 % or at least 35 % or at least 40 % of the total surface area of the cut plane of the composite. The cut plane surface area of the aggregate phase may be no more than 75 % or no more than 70 % or no more than 65 % or no more than 60 % or no more than 55 % or no more than 50 % of the total surface area of the cut plane of the composite.

[0045] In one embodiment, the cut plane of the composite comprises, in % surface area, relative to the total surface area of the composite:

[0046] 10 to 50 % (or 20 to 45%) SiC in the aggregate phase; and

[0047] 3 to 40% (or 5 to 20%) other refractory particles (excluding SiC e.g. alumina) in the aggregate phase.

[0048] In another embodiment, the composite comprises an aggregate phase comprising:

[0049] 10 to 90 wt% SiC particles;

[0050] 10 to 90 wt% of other refractory particles, excluding SiC. The composite may comprise an aggregate phase with between 1 wt% and 40 wt% of refractory oxide (e.g. AI2O3) particles. The aggregate phase refractory or refractory oxide particles may make up at least 5 wt% or 10 wt% or 15 wt% or 20 wt% of the total weight of the composite. The aggregate phase refractory or refractory oxide particles may make up no more than 40 wt% or no more than 30 wt% or no more than 20 wt% of the total weight of the composite. Too much refractory or refractory oxide particles may detrimentally affect the mechanical and thermal shock resistant properties of the composite.

[0051] In some embodiments, the aggregate comprises silicon carbide (SiC). SiC comprises good thermal shock resistant properties. However, the corrosive resistant properties of SiC may be less suitable for some applications. As such, there are advantages to combine SiC with other refractory particles to provide a composite with the required thermal shock and corrosive resistant properties. In some embodiments, the surface area ratio of SiC to other refractory particles in the aggregate phase is in the range of 1 :0.1 to 1:5 or 1 :0.2 to 1 :3 or 1 :0.3 to 1:2 or 1:0.4 to 1 :1.5.

[0052] The composite may comprise a binder phase of between 20 wt% and 80 wt% of the total weight of the composite. In one embodiment, the binder phase may be derived from clay and fine alumina particles.

[0053] The composite may comprise between 8 wt% and 55 wt% aluminosilicate phase or between 12 wt% and 45 wt% aluminosilicate phase or between 13 wt% and 42 wt% aluminosilicate phase or between 14 wt% and 38 wt% aluminosilicate phase or between 15 wt% and 35 wt% aluminosilicate phase. A higher aluminosilicate phase content may result in lower corrosive resistance and a reduction in mechanical strength while a lower aluminosilicate phase content may result an increase in porosity and a decrease in mechanical properties, due to a decrease in the bonding quality between the aluminosilicate phase and (i) the alumina particles in the binder phase; or (ii) the aggregate particles.

[0054] In some embodiments, the apparent porosity of the composite is no more than 26% or no more than 25% or no more than 22% or no more than 21% or no more than 20% or no more than 19% or no more than 18% or no more than 17% or no more than 16% or no more than 15%. The apparent porosity is preferably at least 14% or at least 14.5% or at least 15%. Lower apparent porosity is associated with improved mechanical and corrosive resistant properties of the composite. However, too low an apparent porosity may negatively affect the thermal shock properties of the composite. The bulk density of the composite may be in the range of 2.10 to 2.90 g / cc or in the range of 2.20 to 2.80 g / cc.

[0055] The composite may comprise, relative to the total weight of the composite, at least 15 wt% or at least 20 wt% or at least 25 wt% or at least 30 wt% or at least 35 wt% or at least 40 wt % or at least 45 wt% SiC particles. The composite may comprise no more than 58 wt% or no more than 55 wt% or no more than 52 wt% or no more than 50 wt% or no more than 48 wt% SiC particles or no more than 46 wt% or no more than 44 wt% SiC particles or no more than 42 wt% or no more than 40 wt% SiC particles or no more than 39 wt% or no more than 38 wt% or no more than 37 wt% SiC particles or no more than 36 wt% SiC particles. SiC particles outside these ranges may detrimentally affect the balance between corrosion resistance and mechanical properties of the composite. Unexpectedly, the thermal shock properties of the composite may be maintained with relatively low amounts of SiC particles, whilst the inclusion of refractory particles, such as alumina improves the oxidative corrosion resistance of the composite.

[0056] In embodiments, containing SiC particles and other refractory particles in the aggregate phase, the SiC particles may have similar or the same particle size characteristics as the other refractory particles. For example, both the AI2O3particles and the SiC particles may have a D5o value greater than 100 pm or greater than 150 pm or greater than 175 pm or greater than 200 pm or greater than 225 pm or greater than 250 pm. The D5o value of the AI2O3particles is preferably at no more than 800 pm or no more than 600 pm or no more than 500 pm or no more than 400 pm or no more than 300 pm or no more than 280 pm. In some embodiments the D5o value of the refractory particles (other than SiC) is within 100 pm of the D5o value of the SiC particles.

[0057] In other embodiments, the more corrosive resistant refractory particles have a greater D5o compared to the less corrosive resistant refractory particles. For example, in composite’s comprising AI2O3and SiC refractory particles, the D5o of AI2O3particles is greater (e.g. by at least 10 pm or at least 20 pm or at least 40 pm or at least 60 pm) than the D5o of the SiC refractory particles.

[0058] The AI2O3or other refractory particles may be seen as least a partial substitute for the SiC particles in the composite matrix, with the AI2O3or other refractory particles enhancing corrosive resistance and the SiC particles enhancing thermal shock resistance and thermal conductivity of the composite.

[0059] Binder phase The binder phase may comprise 20 to 99 wt% of an aluminosilicate phase; and 1.0 to 80 wt% binder refractory particles relative to the total weight of the binder phase.

[0060] The binder phase is used to bond together the aggregate phase to form a low porosity composite matrix. The binder phase encompasses (i.e. surrounds) the refractory particles of the aggregate phase. In some embodiments, the binder phase is a continuous phase and the aggregate phase is a discontinuous phase within the composite.

[0061] The binder phase may comprise the aluminosilicate phase (e.g. mullite), binder refractory particles; crystalline silica phases and an amorphous phase. The quantification of these components may be determined by XRD analysis in addition to image and EDS analysis.

[0062] The composite may comprise a binder phase of at least 20 wt% or at least 25 wt% or at least 30 wt% or at least 35 wt% or at least 40 wt% of the total weight of the composite. Too little a binder phase content may result in inhomogeneous bonding with the aggregate phase and an increase in porosity, and consequently a decrease in strength. The composite may comprise a binder phase of no more than 75 wt% or no more than 70 wt% or no more than 65 wt% or no more than 60 wt% or no more than 55 wt% or no more than 50 wt% or no more than 45 wt% of the total weight of the composite. Too high a binder content may compromise the mechanical performance of the composite.

[0063] In some embodiments, the weight ratio or the surface area ratio between the aluminosilicate phase to the binder refractory particles is in the range of 1:1 to 20:1 or 1 :2 to 1:10. In one embodiment, the binder refractory particles comprise between 2 and 15% (or 3 to 12%) of the total surface area of the composite. Having a greater proportion of the aluminosilicate phase to the binder refractory particles enables the aluminosilicate phase to be sufficient large to encompass and embed the binder refractory particles therein, whilst reducing the void space between aggregate particles.

[0064] In some embodiments, the aluminosilicate phase comprises a polycrystalline phase (e.g. mullite) comprising an average grain / particle size (Feret diameter) of no more than 50 pm or no more than 40 pm or no more than 30 pm or no more than 20 pm or no more than 10 pm or no more than 5 pm or no more than 1 pm. The average grain size may range from detectable or at least 100 A or at least 500 A or at least 1.0 pm. The grains may be needle like in share, with an aspect ratio of at least 2:1 and typically up to 50: 1.

[0065] The average crystallite size (a sub component of the grain) may be determined via the Scherrer equation using HighScore Plus™ software available from Malvern Panalytical. The average crystallite size may be influenced by the amount and size of the binder refractory particles or the raw materials from which the mullite crystals are derived.

[0066] Binder refractory particles

[0067] In some embodiments, a microstructure of a cut plane of the composite comprises, in % surface area, at least 2% or at least 2.5% or at least 3.0% or at least 3.5% or at least 4.0% or at least 4.5% or at least 5.0% binder refractory particles, relative to the total surface area of the composite, having a particle size distribution with a median particle size D5o value in the range of > 0 pm to 30 pm. Typically, the cut plane of the composite comprises no more than 30% or no more than 20% or no more than 15% of the surface area of binder refractory particles, relative to the total surface area of the composite.

[0068] The binder refractory particles may include the same refractory particle composition of the refractory particles in the aggregate phase, with the difference between the particles being that the binder refractory particles are embedded within the aluminosilicate phase and the binder refractory particles are typically much finer in particle size compared to the refractory particles in the aggregate phase.

[0069] The binder refractory particles, and any refractory particles or material, with a Feret diameter of less than 50 pm or less than 45 pm or less than 40 pm or less than 30 pm are embedded within the aluminosilicate phase. The binder refractory particles are typically evenly or homogeneously distributed throughout the aluminosilicate phase (i.e. the binder refractory particle is typically not concentrated towards the periphery of the binder phase at the interface with the refractory particles of the aggregate phase).

[0070] The binder refractory particles may be added to improve the corrosive resistance of the composite as well as improving the mechanical and thermal shock resistant properties of the binder phase. The binder refractory particles may include oxide and / or non-oxides. In one embodiment, the binder refractory particles are refractory oxides, which may be derived from the corresponding oxides in the raw material or from metallic precursors of the refractory oxides which convert to the oxide form during the calcination / firing step.

[0071] The binder refractory oxide particles may be oxide derived from refractory metals or the refractory oxide particles may be selected from the group consisting of Cr2O3, AI2O3, ZrO2, TiO2, HfO2, Y2O3and combination thereof. In one embodiment, the refractory oxide particles comprise one or both of AI2O3and ZrO2. In one embodiment, the refractory oxide particles comprise partially stabilised zirconia, which possess enhanced thermal shock resistance. The refractory oxide particles may be selected depending upon the cathode material being processed in the open vessel and of thermal expansion compatibility with the aluminosilicate component of the binder phase.

[0072] In one embodiment, the cut plane of the composite, in % surface area of the total surface area of binder refractory particles, comprises:

[0073] 0 to 100 % alumina particles with a D5o value of at least 3.0 pm; and

[0074] 0 to 100 % of one or more of ZrO2, TiO2, HfO2, Y2O3, SiC particles with a D5o value greater than 0.1 pm.

[0075] In some embodiments, the alumina particles represent at least 30% or at least 40 % or at least 50% of the % surface are of the binder refractory particles.

[0076] In other embodiments, the binder refractory particles comprise non-oxide particles, such as carbides and nitrides. In some embodiments, the non-oxide particles comprise one or both of graphite and SiC.

[0077] The binder refractory particles (e.g. alumina particles) preferably comprise a particle size distribution, with at least some particles (e.g. at least 5%) having a Feret diameter of greater than 3.0 pm or greater than 4.0 pm or greater than 5.0 pm or greater than 6.0 pm or greater than 7.0 pm or greater than 8.0 pm or greater than 9.0 pm or at least 10.0 pm or at least 11.0 pm. Larger particles sizes have a greater resistance to corrosion. Whilst some binder refractory particles (e.g. alumina particles) may be smaller due to their potential participation in the reaction with silica to form mullite, the raw material sizing and composition is preferably formulated to ensure that there is sufficient larger binder refractory particles to enhance the corrosive properties of the binder phase. Preferably, at least 3 % or at least 5 % or at least 6 % or at least 7 % or at least 10 % or at least 15 % or at least 20 % or at least 25 % or at least 30 % or at least 40 % or at least 50 % or at least 60 % of the surface area of the binder refractory particles embedded in the binder phase have a particle size with a Feret diameter of greater than 5.0 pm or greater than 6.0 pm or greater than 7.0 pm or greater than 8.0 pm and preferably comprise a Feret diameter of no more than 50 pm or no more than 40 pm or no more than 30 pm or no more than 20 pm. Preferably, the largest of the binder refractory particles are less than the average binder width and preferably no more than 70% or no more than 50% of the average binder width. Within this particle size range, the binder refractory particles enhance corrosive resistance, whilst not adversely affect porosity of the composite.

[0078] In one embodiment, the composite comprises a binder phase having binder refractory particles with a D5o value less than 30 pm or less than 25 pm or less than 20 pm or less than 15 pm. The D5o value of the binder refractory particles is preferably at least 0.1 pm at least 0.2 pm or at least 0.5 pm or at least 1.0 pm at least 2.0 pm or at least 2.5 pm or at least 3.0 pm or at least 3.5 pm or at least 4.0 pm or at least 5.0 pm or at least 6.0 pm or at least 8.0 pm or at least 10 pm. In some embodiments, the average Feret diameter of the binder refractory particles is at least 3.0 pm or at least 4.0 pm or at least 5.0 pm or at least 6.0 pm or at least 7.0 pm or at least 8.0 pm. In some embodiments, the D value of the binder refractory particles is preferably at least 1 .0 pm or at least 2.0 pm or at least 3.0 pm or at least 4.0 pm or at least 5.0 pm. Too small a particle size may result in lower corrosive resistance and / or mechanical properties. The minimum size of the binder refractory particles may be dependent upon their reactivity to components within the aluminosilicate phase precursor. As such, reactive grades of binder refractory particles may have preferred higher DR5o compared to non-reactive grades.

[0079] The average cross-sectional surface area of the particles (as measured by imaged™) in a cut plane is preferably at least 15 pm2or at least 20 pm2or at least 25 pm2, for particles measured under x2000 magnification and with a Feret diameter of at least 2 pm.

[0080] In one embodiment, the D5o of alumina particles may be greater than 2.0 or greater than 2.5 pm or greater than 3.0 pm or greater than 4.0 pm or greater than 5.0 pm or greater than 6.0 pm or greater 7.0 pm than or greater than 8.0 pm, whilst the D5o of other binder refractory particles such as Cr2O3ZrO2, TiO2, HfO2and Y2O3and SiC may be less than 5.0 pm or less than 4 5 pm. The D5o value of Cr2O3ZrO2, TiO2, HfO2and Y2O3and SiC may be at least 0.2 pm or at least 0.5 pm or at least 1.0 pm. Too small a D5o value may be detrimental to the corrosive resistance of the binder phase. In another embodiment, the D5o of alumina particles is at least 1.0 pm or at least 2.0 pm greater than the D5o of Cr2O3ZrO2, TiO2, HfO2and Y2O3

[0081] The population of binder refractory particles in the binder phase are preferably crystalline, such as corundum (AI2O3). Examples of commercially available crystalline alumina include, but are not limited to tabular alumina, calcined alumina, white fused alumina and brown fused alumina.

[0082] The aluminium oxide particles may be derived from any reactive grade of alumina, such as calcined alumina or alumina with a fine particle size (e.g. less than 30pm or less than 20 pm or less than 10 pm or less than 5 pm). A reactive form of AI2O3, (e.g. reactive aluminas available from Almatis), such that the AI2O3particles can partially react with silica to form an aluminosilicate binder phase. The binder phase is typically formed during a firing process with the non-stoichiometric amounts of silica and alumina in the raw materials such that there is an excess proportion of alumina to promote the formation of an aluminosilicate phase, such as mullite. As a result of providing a stoichiometric excess of alumina, at least part of the alumina in the raw materials are maintained or are converted into fine AI2O3particles.

[0083] In some embodiments, the AI2O3particles in the binder phase are an unreacted portion of AI2O3particles in the raw material. The size of the population of AI2O3particles in the raw materials may be controlled to enable at least some of the AI2O3particles to react with excess silica in the raw material (e.g. silica from clay). If the AI2O3particles in the raw material are too big to adequately react with silica (e.g. D5o > 2.0 or >3.0 or >4.0 pm and / or Dio > 1.0 pm), then not a sufficient amount of the excessive silica may react (depending upon the firing temperature), thereby potentially weakening the corrosive resistance of the composite. If the AI2O3particles in the raw material are too small (e.g. D5o < 2.0 pm or <1.0 pm or < 0.5 pm or less than 0.2 pm or < 0.1 pm), then their ability to provide adequate corrosion resistance may diminish. The more corrosive resistant AI2O3particles function to slow down the ingress of, for example, the cathode active material and the corrosive products thereof. The raw material may have a population of reactive alumina particles of sufficient size and quality to react with excess silica whilst also having another population of larger alumina particles as precursors to the embedded alumina particles within the aluminosilicate binder phase.

[0084] The composition may comprise between 0.5 wt% and 40 wt% of binder refractory particles from the binder phase. The composite may comprise at least 1.0 wt% or at least 2.0 wt% or at least 3.0 w% or at least 4.0 w% or at least 5.0 wt% or at least 6.0 wt% or at least 7.0 wt% or at least 10 wt% or at least 15 wt% or at least 20 wt% or at least 25 wt% binder refractory particles (e.g. AI2O3particles) from the binder phase. Generally, the more binder refractory particles in the binder phase, the greater the corrosive resistance of the binder phase and increasing the relative size of the binder phase contributes to lowering porosity of the composite, which contributes to improved mechanical properties. The presence of the fine binder refractory particles within the binder phase is also thought to inhibit the propagation of cracks, thereby improving thermal shock resistance of the composite. Typically, binder refractory particles from the binder phase of the composite comprises no more than 40 wt% or no more than 35 wt% or no more than 30 wt% or no more than 20 wt % of the total weight of the composite. Too much binder refractory particles or too large the binder refractory particles may detrimentally affect the thermal shock resistant properties of the composite. In one embodiment, the combined AI2O3particles from the aggregate and binder phases may make up between 5 wt% and 60 wt% of the total weight of the composite. In some embodiments, the total AI2O3particle content is at least 10 wt% or at least 15 wt% or at least 20 wt% or at least 25 wt% or at least 30 wt% of the total weight of the composite. In some embodiments, the total AI2O3particle content is no more than 50 wt% or no more than 40 wt% or no more than 30 wt% or no more than 25 wt% or no more than 20 wt% of the total weight of the composite.

[0085] In a further embodiment, the composite comprises 5 to 40 wt% alumina particles in the aggregate phase and 2 to 45 wt% alumina particles in the binder phase.

[0086] In one embodiment of the first aspect of the present invention, the composite comprises (as determined XRD Rietveld analysis):

[0087] 20 to 60 wt% SiC particles;

[0088] 25 to 70 wt% of an aluminosilicate phase; and

[0089] 5.0 to 70wt% (or to 50 wt%) AI2O3particles (or other refractory or binder refractory particles) derived from one or both of the binder and aggregate phases.

[0090] In one embodiment of the first aspect of the present invention, the composite comprises (as determined XRD Rietveld analysis):

[0091] 20 to 40 wt% SiC particles;

[0092] 25 to 70 wt% of an aluminosilicate phase; and

[0093] 10.0 to 50 wt% AI2O3particles.

[0094] In one embodiment, the composite comprises:

[0095] 10 to 50 wt% wt% SiC and 2.0 to 50 wt% (or 5.0 to 40 wt%) of AI2O3particles (or other refractory particles) from the aggregate phase; and

[0096] 2.0 to 50 wt% (or 5.0 to 40 wt%) of AI2O3particles (or binder refractory particles) from the binder phase.

[0097] The combination of both populations of particles in the aggregate and binder phases may provide enhanced corrosion resistance through the matrix. The binder phase fill spaces between the larger refractory particles, such as AI2O3particles and SiC particles reducing the porosity of the composite, thereby improving the composite’s thermal shock resistance and mechanical strength. The composite may comprise refractory particles with a D5o greater than the average width of the binder phase. In some embodiments, the average width of the binder phase is less than 100 pm or less than 80 pm or less than 70 pm. An average binder phase of at least 30 pm or at least 40 pm is preferably to assist in the reduction in porosity and to provide sufficient thermal shock resistance. The proportion and size of the larger refractory particles is such that the binder phase tends to form relatively narrow passageways therebetween.

[0098] The portion of the binder phase and the refractory particles of the aggregate phase may be adjusted depending upon the corrosive resistant requirements of the composite and the thermal cycling profile that the apparatus is exposed to. A tendency for open vessels to fail due to thermal shock may result in decreasing the amount of corrosive resistant aggregate refractory particles (e.g. AI2O3particles), whilst a tendency for open vessels or molten metal apparatus to fail due to excessive corrosion may result in an increase in corrosive resistant particles in one or both of the aggregate and binder phase. A balance between failures due to predominantly thermal shock or predominantly corrosion is an indicator of the right balance of AI2O3, (or other refractory oxides and non-oxide constituents) particles in the composite. This balance will be specific to the application and readily optimised by the skilled artisan using the teachings of the present disclosure.

[0099] One or both of the refractory particles and binder refractory particles may have a roundness value of between 0.4 and 1.0 and preferably at least 0.5 or at least 0.55 or at least 0.59. One of both of the refractory particles and binder refractory particles may have an aspect ratio between 1.0 and 2.5 and preferably less than 2.0 or less than 1.8. In general, the lower the aspect ratio and roundness of the particles the lower the surface area per unit volume and the more corrosion resistant the particles are.

[0100] The aluminosilicate phase

[0101] The aluminosilicate phase is preferably crystalline in part or in totality. Whilst the aluminosilicate phase may comprise mullite other crystalline and non-crystalline forms may also exist (with or without mullite). In some embodiments, the aluminosilicate phase comprises mullite as the major aluminosilicate crystalline phase as identified using XRD analysis.

[0102] The firing conditions and proportions of mullite precursors in the raw materials, including fine reactive alumina particles to react with any excess silica, may be controlled to promote the formation of mullite. The composite composition may comprise between 8 wt% and 55 wt% of aluminosilicate phase from the binder phase. The aluminosilicate phase may make up at least 10 wt% or at least 13 wt% or at least 15 wt% or at least 20 wt% or at least 25 wt% or or at least 30 wt % of the total weight of the composite (as measured by XRD Rietveld analysis). The aluminosilicate phase may make up no more than 50 wt% or no more than 45 wt% or no more than 40 wt% or no more than 30 wt% or no more than 15 wt% of the total weight of the composite (as measured by XRD Rietveld analysis).

[0103] In a second aspect, there is provided an open vessel comprising the composite of the first aspect.

[0104] In a third aspect of the present invention, there is provided a composite (e.g. a used article, such as an open vessel) comprising a surface layer and a base layer, said base layer comprising a composition according to any one of the preceding claims and wherein the surface layer comprises binder refractory particles from the aggregate phase (e.g. AI2O3or titania or zirconia) comprising a largest transverse dimension greater than 60 pm or greater than 80 pm or greater than 100 pm. The largest transverse dimension is taken to be the Feret length (i.e. the largest distance between parallel tangents of the particle. The used composite may have been corroded via the conditions stated in the “the corrosion test” as later described herein.

[0105] It has been found that binder refractory particles are able to better withstand the corrosive nature of the cathode active materials, relative to other components within the base layer.

[0106] The surface layer may comprise corrosion products derived from components in the base layer reacting with the cathode active material, such as one or more compounds of lithium aluminosilicates, such as spodumene, lithium silicate and lithium aluminate.

[0107] The composite may have been used in the formation of battery materials with the cathode active material partially corroding the open vessel. The action of the corrosive material on the composite may selectively corrode the aluminosilicate phase and the SiC particles (or other non-oxide particles), leaving a higher proportion of binder refractory particles.

[0108] In some embodiments, the surface layer may comprise a lower content of metallic components (e.g. zirconium, silicon, tungsten, titanium and / or aluminium) compared to the base layer. The reduction in the metallic component in the surface layer may be reflective of the metallic components functioning to protect the SiC particles from oxidation through preferentially consuming oxygen.

[0109] The composite may be such that the ratio (%wt / %wt) of AI2O3particles (or other binder refractory particles) to SiC particles in the surface layer is greater than ratio (%wt / %wt) of AI2O3particles (or other binder refractory particles) to SiC particles in the base layer. The difference in the ratio may be at least 10% or at least 20% or at least 30% or at least 40% or at least 50%.

[0110] In a fourth aspect of the present invention, there is provided a method of producing a composite according to the first aspect comprising: a. Mixing together refractory particles (preferably comprising SiC) comprising a DRSO greater than 100 pm; binder refractory particles comprising a DR5o greater than 0 pm (or greater than 0.1 pm) and less than 50 pm (or less than 30 pm); and one or more compounds comprising SiO2and AI2O3;b. Packing or pressing the mixture into a mould c. Firing the mixture at sufficient temperature for sufficient time to convert the one of more compounds comprising SiO2and AI2O3into the crystalline aluminosilicate phase and wherein the binder refractory particles (e.g. AI2O3) are embedded therein.

[0111] The skilled addressee would be able to readily determine the portion of raw material components (e.g. through density and %wt) required to produce the composite of the first aspect of the invention, which is partially defined in terms of relative surface area of the components.

[0112] The raw material preferably comprises the refractory particles and binder refractory particles comprising AI2O3particles, each of the required particle size distribution.

[0113] The crystalline aluminosilicate phase may be mullite, sillimanite, andalusite and / or kyanite. The one or more compounds comprising SiO2and AI2O3may comprise clay or other suitable source of SiO2and AI2O3as known to those skilled in the art.

[0114] In an alternative aspect, there is provided a method of producing an open vessel comprising:

[0115] • Mixing together:

[0116] 25 to 75 wt% refractory particles refractory particles having a particle size distribution with a median particle size DR5o value of greater than or equal to 100 pm as measured in accordance with ISO 13320:2009; said refractory particles comprising at least 15 wt% silicon carbide;

[0117] 2 to 45 wt% binder refractory particles comprising a DR5o greater than 6 pm and less than 30 pm; as measured in accordance with ISO 13320:2009; and one or more compounds comprising SiO2and AI2O3, sufficient to produce 10 to 50 wt% of a mullite phase;

[0118] • Packing the mixture into a mould;

[0119] • Firing the mixture at sufficient temperature for sufficient time to convert the one of more compounds comprising SiO2and AI2O3into the mullite phase and wherein the binder refractory particles are embedded therein to form a binder phase; said binder phase bonding the refractory particles together.

[0120] The firing conditions and raw materials are preferably selected to create binder refractory particles with a D5o or at least 2.0 pm or at least 2.5 pm or at least 3.0 pm or at least 3.5 pm or at least 4.0 pm or at least 4.5 pm.

[0121] To promote a high proportion of mullite formation, additional components may be added to the clay to ensure that the stoichiometric ratios of the available SiO2and AI2O3match that the stoichiometric ratio in the target crystalline aluminosilicate phase. For example, if mullite is the target phase, then the amount of available SiO2and AI2O3may be adjusted to about 2 moles SiO2to 3 moles AI2O3. To promote additional AI2O3particles in the binder phase, an excess stoichiometric amount of AI2O3formulated above that required for the target aluminosilicate phase. Reactive forms of SiO2and AI2O3are preferably added to adjust the stoichiometric ratio. To increase the reactiveness of the SiO2and AI2O3components, their particle size distribution preferably has a DR5o less than 2.0 pm or less than 1.0 pm.

[0122] In some embodiments, the ratio and characteristics of the raw materials and processing conditions are such to avoid the formation of residual SiO2phases, such as quartz or cristobalite as these phases have a mismatch in the coefficient of thermal expansion compared to aluminosilicate phases, such as mullite or aluminium phases, such as corundum. However, SiO2phase levels of up to 15 or 20 wt% have been found to be corrosion resistant, whilst maintaining good thermal shock resistance in the composites, with the SiO2phases being found to have good corrosion resistance against the active cathode materials tested thereon. In other embodiments, quartz and cristobalite phases comprise greater than 0 or greater than 2.0 or greater than 4.0 wt% and total no more than 20 wt% or no more than 15 wt% or no more than 10 wt% of no more than 5 wt% of the total weight of the composite.

[0123] In some embodiments, the particle sizing of the binder refractory AI2O3particles combined with the firing conditions are such that the majority (i.e. > 50 wt% ) of the binder refractory particles remain unreacted, even in the presence of excess stoichiometric SiO2. In some embodiment, at least 70 wt% or at least 80 wt% or at least 90 wt% of the fine AI2O3particles remain unreacted during the firing process. In some embodiments, the binder refractory particles comprise a DR5o of greater than 6 pm or greater than 8 pm or greater than 10 pm, with the larger particles size distribution resulting in a greater proportion of particles remaining after the firing process to produce embedded binder refractory particles within the aluminosilicate phase.

[0124] The binder refractory AI2O3particles may comprise tabular alumina, calcined alumina, white fused alumina and bauxite. The AI2O3particles preferably comprises at least 95 wt% AI2O3.

[0125] In a fifth aspect of the present invention, there is provided a method for manufacturing a cathode active material for a lithium battery comprising operations of: a. Loading a raw material into a saggar comprising the composite according to the first aspect and inserting the raw material in a firing furnace and then firing; and b. Recovering the raw material in the saggar after the firing, and cooling and pulverizing to prepare a cathode active material for a lithium battery.

[0126] The raw material may be calcined / fired in an oxygen rich atmosphere.

[0127] In a sixth aspect of the present invention, there is provided a composite for use in contact with cathode active materials as defined in the first aspect of the present invention.

[0128] In a sixth aspect of the present invention, there is provided a use of the composite according to the first aspect of the present invention for the firing / calcining of a cathode active material for a lithium battery.

[0129] Open Vessel structure

[0130] The open vessel structure may be monolithic or layered. In some embodiments the vessel is monolithic. In layered structures the composite of the present invention preferably forms a layer accounting for at least 20 wt% or 30 wt% or 40wt% or 50 wt% or 60 wt% or 70 wt% or 80 wt% of 90 wt% or 100 wt% of the total weight of the open vessel. The composite preferably forms part of the inner surface of the open vessel.

[0131] In some embodiments, the open vessel comprises a base layer and a top layer. The top layer preferably comprises the composition of the first aspect of the present invention. The top layer may function as a liner or an insert which is placed into the concave portion of the base vessel. Within this embodiment, the inner surface of the top layer will be in contact with the cathode active material. The insert or lining may be a single use or reusable. The service life of the top layer will dictate the top layer’s specific composition, thickness and form.

[0132] In other embodiments, the base and the top layer may form an integral part of the structure in which the top layer is more securely bonded to the base. Within these embodiments, the vessel is designed to be useable and replaceable, rather than just the top layer. As known to those skilled in the art, the vessel may be impregnated or coated with a refractory component. Impregnated and / or coated vessels may have enhanced corrosive resistance.

[0133] Vessels

[0134] In one embodiment, the open vessel, which is a saggar or a crucible, although other open vessels for containing cathode active materials, precursors and derivatives thereof (e.g. waste components) at high temperatures (e.g. > 600°C). The volume of the open vessel (measured to the rim) may vary between 0.01 to 2000 litres. In some embodiments, the volume of the open vessel is in the range of 0.1 to 25 litres.

[0135] The open vessel may be in the shape of an open rectangular prism and have minimum dimensions of 100 mm width by 100 mm length by 40 mm height. In some embodiments, the open vessel may have a minimum volume of at least 0.4 litres or at least 0.6 litres or at least 1.0 litres. Typically, the vessel is no more than 2000 litres or no more than 1000 litres or no more than 500 litres or no more than 25 litres in capacity.

[0136] In one embodiment of the present invention, vessels have an average wall thickness in the range of from 2 to 15 mm, preferably from 4 to 15 mm and even more preferably, from 6 to 12 mm.

[0137] In one embodiment of the present invention, the vessels have an angle between each wall and the basis of 90°. In a preferred embodiment, the vessels have bent walls, and the angle between each wall and the basis is in the range of from 91 to 100°. In a preferred embodiment of the present invention, the vessels may contain 100 ml up to 25 litres of particulate material, preferred are 2 litres to 20 litres, and even more preferred are 3 litres to 15 litres.

[0138] Smaller open vessels according to the present invention are possible, but they are economically disadvantageous. In state-of-the-art open vessels the heat transfer may be disadvantageous in a way that the residence time in heating and / or cooling zones is unfavourably long or in way that pronounced temperature profiles in the powder to be thermally treated are observed that are in disfavour of a homogeneous product. If heat treatment is performed in the disclosed open vessels, heat transfer is facilitated and accelerated. That leads to improved homogeneity of the heat-treated material. The vessels are advantageous for any solid-state reaction producing oxide materials from a precursor. By using the disclosed open vessels, the exchange of precursor materials is easy, and heating and cooling before and after the thermal treatment may be performed at much faster a rate compared to conventional open vessels.

[0139] Cathode Active Materials and processing thereof

[0140] Examples of cathode active materials for lithium ion batteries include LiCoO2, LiNiCh, LiMnO2, mixed transition metal oxides with a layered structure, also referred to as lithiated layered oxides, having the general formula Li(i+z)[NiaCObMnc](i-z)O2+e wherein z is 0 to 0.3; a, b and c may be same or different and are selected from 0.0 to 0.8 wherein a + b + c = 1 ; and -0.1 < e < 0.1 , lithiated spinels ("NMO"), for example manganese- containing spinels like LiMn2O4and spinels of general formula Li(i+t)M(2-t) O<4-d) wherein d is 0 to 0.4, t is 0 to 0.4 and M is a combination of Mn and at least one further metal selected from the group consisting of Co and Ni, and lithiated nickel-cobalt aluminum oxides ("NCA"), the latter being materials of general formula Li(i+g)[NihCOAIj](1-g)O2. Typical values for g, h, i, and j are: g from 0.0 to 0.1 , h from 0.80 to 0.85, i = 0.15 to 0.20, and j = 0.02 to 0.03. In a preferred embodiment the cathode active material is selected from lithiated layered oxides, lithiated spinels and lithiated nickel-cobalt aluminum oxides.

[0141] In one embodiment of the present invention, cathode active material is selected from LiCoCL coated layered nickel-cobalt-magnesium oxides, doped or non-doped, for example LiCoCL coated LiNi0.9Co0.09Mg0.01O2. Each thermal treatment step useful in making LiCoO2coated layered nickel-cobalt-magnesium oxides may be performed in the vessels.

[0142] In another embodiment, the cathode active material comprises nickel, manganese and cobalt, such as NMC 111 , NMC 532, NMC 622 and NMC 811. NMC 811 , due to its low cobalt content, is attractive of cost reasons, although the reactivity of this material is also more challenging than other cathode active materials.

[0143] The firing process starts off from a mixture of at least two particulate materials, of which at least one is an oxide or hydroxide or carbonate. For example, one of the particulate materials is a lithium salt, preferably lithium oxide or lithium hydroxide or preferably lithium carbonate, Li2CO3, and one of the particulate materials is a so-called precursor, for example a hydroxide or oxide or oxyhydroxide or carbonate of a transition metal selected from Ni, Mn and Co, or a mixed hydroxide or oxide or oxyhydroxide or carbonate of at least two transition metals selected from at least two out of Ni, Mn and Co. In a preferred embodiment, one of the particulate materials is lithium carbonate and the other is a mixed oxyhydroxide of Ni, Co and Mn or of Ni, Co and Al.

[0144] The molar ratio of lithium to metals other than lithium may be selected within certain ranges, in case of lithiated spinels it is lithium: transition metal 1:2. In case of NCA it is from 1:1 up to 1.02:1 , in case of lithiated layered oxides it is from 1 :1 up to 1.86:1 .

[0145] Lithium salt and precursor are mixed thoroughly and the resulting mixture is provided. The mixture provided is transferred into at least one of the vessels of the present invention. The vessel together with the mixture is then moved through an appliance in which said mixture is subjected to a heat treatment, thereby reacting the particulate materials with each other. The reaction is a solid-state reaction. In one embodiment of the present invention the heat treatment is performed at a temperature in the range of from 600 to 1,000 °C. Preferably, the temperature is ramped up, for example to a first heat treatment temperature in the range of from 600 to 650°C, then to a second heat treatment temperature in the range of from 700 to 750°C, and then to a third heat treatment temperature in the range of from 850 to 900°C. In one embodiment, the mixture is maintained at each heat treatment temperature for a period of 1 to 10 hours, preferably 3 to 8 hours.

[0146] Particle size distribution

[0147] For clarity, reference to larger particles is reference to particles from the aggregate phase and reference to finer particles to particles from the binder phase of the composite. It would be understood that particles of the same composition (e.g. alumina) may be present in both the aggregate and binder phases.

[0148] The presence of different particle populations may be detected by different modal peaks. On a particle size distribution graph the one or more modes from the binder refractory particles of the binder phase should be distinguishable from the one or more modes from the refractory particles from the aggregate phase. The modal peak(s) of refractory particles from the aggregate phase and modal peak(s) of the binder refractory particles of the binder phase are preferably separate by a size of at least 50 pm or at least 80 pm or at least 100 pm or at least 120 pm or at least 150 pm. Reference to D5o is reference to the median particle size, unless otherwise specified. D5o is determined in accordance with ISO 13320:2009 for raw materials particles and using SEM imaging in combination with Imaged™ processing software for particles with the composite. For all particle size distributions, the D90value may be no more than 3 or 4 or 5 times the D50value. The D value may be greater than 5% or 10% or 20% or 25% or 35% of the D5o value. D , D5o and D90values are provided on a weight basis.

[0149] Reference to AI2O3is to be construed as reference to one or both of the refractory particles of the aggregate phase and binder refractory particles of the binder phase, depending upon context.

[0150] Reference to the PSD distribution of particles within the composite relate to the diameter determined using the Feret method.

[0151] It is understood that the PSD of the raw materials used for the aggregate phase may overlap with the binder refractory particles used for the binder phase. For the calculation of the PSD of the binder refractory particles of the binder phase, binder refractory particles are taken to be the particles which are embedded within the aluminosilicate phase. The binder refractory particles may also include binder refractory particles derived from the PSD of the refractory particles of the raw material of the aggregate phase. To avoid difficulties in differentiating the aggregate refractory particle size distribution from the binder refractory particle size distribution, all particles (binder refractory, refractory material and refractory) with a Feret diameter of greater than 50 pm or will be deemed to be refractory particles from the aggregate phase, whilst all particles with a Feret diameter of no more than 50 pm will be deemed to be binder refractory particles from the binder phase.

[0152] As an alternative to defining the aggregate phase by reference to the D59of the refractory particles, the aggregate phase may also be defined as comprising at least 50 wt% of particles comprising a Feret diameter of greater than or equal to 100 pm.

[0153] The proportion of raw materials added to form the aggregate phase should is substantially the same as the portion of aggregate material in the composite.

[0154] Unless otherwise indicated reference to the % surface area of the cut plane is reference to the % surface area relative to the total surface area of the cut plane of the composite.

[0155] Brief Descriptions of the Figures

[0156] Figure 1 is a particle size distribution (PSD) of the SiC particles of the aggregate phase.

[0157] Figure 2 is a PSD of the alumina particles of the aggregate phase.

[0158] Figure 3 is a PSD of tabular alumina particles of the binder phase. Figure 4 is a PSD of calcined alumina particles of the binder phase.

[0159] Figure 5 is an SEM image (x200 magnification) of the composite of Example 1 with grid lines used to measure binder width between aggregate particles.

[0160] Figure 6 is an SEM image of cross-sectional area of comparative example 1 (CE-1) of the present invention.

[0161] Figure 7 is an EDS scan for Mg of a section of the cross-sectional area of Figure 1.

[0162] Figure 8 is a SEM image (x100 magnification) of the composite microstructure of Example 1 the present invention.

[0163] Figure 9a is a SEM image (x3,000 magnification) of the composite microstructure of Example 1.

[0164] Figure 9b is a SEM image (x25,000 magnification) of the binder microstructure of Example 1.

[0165] Figure 9c is a SEM image (x10,000 magnification) of the binder microstructure of Example 8.

[0166] Figure 10 is a SEM image of the composite of Figure 8, which has been partially corroded.

[0167] Figures 11, 12 and 13 are EDS scan images aluminium, oxygen and silicon respectively of part of the SEM image of Figure 10.

[0168] Figures 14, 15 and 16 are EDS scan images silicon, aluminium and oxygen respectively of Example 1.

[0169] Details Description of a Preferred Embodiment

[0170] The present invention relates to open vessels, and in particular saggars, for firing cathode active materials. In general, a lithium battery positive electrode active material is manufactured by firing a raw material in a high-temperature firing furnace, and in this case, the raw material is loaded into the saggar and inserted in the firing furnace.

[0171] The service life of saggars is typically less than 30 cycles in which the saggars are systematically loaded with cathode active material and fired to a temperature of up to about 1000°C for several hours prior to the saggar being cooled and unloaded and the next cycle started. The service life of the saggar is typically limited to the corrosion resistance of the saggar materials, with the cathode active material reacting and penetrating into the saggar walls eventually resulting in crack initiation, propagation and mechanical failure. The open vessels are typically produced via the steps of:

[0172] • Mixing the raw materials to form a homogenous mixture;

[0173] • Optionally drying or vacuum treating the mixture. Said optional steps may be performed to remove some percentage of water before firing. An optional drying step may be performed at a temperature in the range of from 10° C. to 300° C., preferably 80° C. to 200° C. Combined drying in ambient atmosphere and subsequently in an oven is preferred.

[0174] • Shaping the mixture into the form of the open vessel. This may be achieved through vacuum filling; packing or pressing into moulds as known to those skilled in the art;

[0175] • Firing the mixture above 900°C for sufficient time (e.g. greater than 2 hrs) to form the resultant binder phase.

[0176] An alternative method comprises:

[0177] • Mixing the raw materials to form a homogeneous mixture

[0178] • Moisturizing with >3 wt% moisture

[0179] • Shaping the mixture into the form of open vessel. This may be done through filling the homogeneous mixture into a mould and pressing uniaxially

[0180] • Firing the pressed open vessels >900 °C.

[0181] The firing temperature may be in the range of from 900 to 1,500° C; or 1000 to 1,450° C; or 1,100 to 1 ,400° C. The firing temperature may be dependent upon the raw materials use and, in particular, the silica and alumina containing compounds and the conditions under which these components convert to an aluminosilicate phase, such as mullite and reduce residual levels of SiO2. In some embodiments, the firing temperature is no more than 1450 °C or no more than 1400°C or no more than 1350°C. High firing temperatures may result in the formation of degradation gases, such as those from the oxidation of SiC. The formation of gases may result in an increase in porosity and the decrease in mechanical properties.

[0182] Examples:

[0183] Sample plates (50 mm x 50 mm x 15 mm) were prepared from formulations as indicated in Tables 4 to 6, with the mixtures pressed and fired at a temperature above 1050°C for about 1 hour. The crystalline phase present determined by XRD analysis, with the results presented in Tables 10a & 10b. The examples were all pressed under isostatic conditions, with Examples 1 and 2 also pressed under uniaxial conditions.

[0184] Raw materials

[0185] Table 1 Clay composition (dry basis)

[0186] The clay had a loss of ignition (LOI) value of 11.23 wt%.

[0187] The material from commercial saggars were also assessed as comparative examples (CE- 1 , CE-2 and CE-3). CE-3 is the composition of a coating applied to a saggar with the composition of CE-2. The results for CE-3 (Table 4) relate to a saggar with a base of CE-2 composition and a coating with CE-3 composition. Semi-quantitative XRD analysis revealed the approximate crystalline composition of the comparative examples in Table 2.

[0188] Table 2 Comparative Example Composition (% wt)

[0189] Test methodology:

[0190] Particle Size Distribution (PSD)

[0191] Reference to the median particle size D5o is reference to the median particle size determined in accordance with ISO 13320:2009 in respect to the raw materials and using optical / SEM images in combination with Imaged™ software (manufactured by National Institute of Health, NIH) as described in relation to the methodology for determining PSD for composites below.

[0192] The median value using the Imaged™ is the value where half the particles have a smaller Feret diameter and half have a larger Feret diameter. The Feret diameter is the longest distance between any two points along the selection boundary, also known as “maximum caliper”. In contrast the median value using ISO 13320:2009 is based upon 50% of the volume of the particles being less than the median. Thus, the composite PSD may be biased towards lower D5o compared to the raw materials. The results of Table 3a and 3b are generally consistent with the two different PSD methodology being used. T1

[0193] Raw materials

[0194] The PSD of the raw materials were determined according to a laser diffraction method which was ISO 13320:2009 and JIS8825-1 compliant, using a Shimadzu Laser Diffraction Size Analyzer SALD-2300. Figures 1 to 4 illustrate the PSD for Alumina (aggregate), SiC (aggregate), tabular alumina (binder) and calcined alumina (binder), respectively. Multiple PSDs were conducted for each raw material. The particle size distribution of the raw materials is denoted by DR , DR5O, DR90to differentiate from the particle size distribution of the composite which is denoted by D , D5o, D90.

[0195] Composite

[0196] The PSD distribution, including the median particle size D59of the particles within the composite was measured as follows.

[0197] Sample preparation

[0198] • Sample of the size 10mmx10mm cross sections were cut from composites.

[0199] • Samples were cold mounted by epoxy resin and polyamide hardener at the middle in cup mold under vacuum 0.1-0.15 bar and cured for 12h.

[0200] • Sample surface was grounded with the help of series of diamond grinding pad from 400 pm to 20 pm on polishing machine. Final polishing was done with 9, 6, 3 and 1 pm diamond paste on a polishing machine to create a cut plane with a mirror finish surface.

[0201] • Polished surfaces of the cut plane were analyzed by scanning electron microscope.

[0202] SEM-EDX imaging process

[0203] • Microstructures of polished samples were collected from Scanning Electron Microscopy (Manufacturer: Zeiss, Model: EV015), EHT 20 kV, working distance 30-9.5 mm used for the micrographs collection.

[0204] • Microstructures of polished samples were collected at different magnification, in the range of x30-x25,000.

[0205] • Figures 9b and 9c were chemically etched by 5 wt% HF solution for 60 seconds before the SEM image was taken. EDX spectra were collected during viewing through SEM using OXFORD EDS detector (Manufacturer: Oxford Instruments) using EHT 20 kV.

[0206] PSD analysis

[0207] • Imaged™ (manufactured by National Institute of Health, NIH) software was used for the PSD and phase size measurement.

[0208] • EDS analysis was used to identify the composition of the particles.

[0209] • PSD measured from SEM images (Magnification in the range of X30-X200 for refractory aggregates; X2000 for fine populations of particles in the binder; X200- X500 magnification for binder width). At a magnification of X2000, the minimum particle sized threshold was about 2 pm. For particle sizes less than about 2 pm, their presence may be determined by XRD, when crystalline, with the D , D5o and Dg0assumed to be in the range of >0 to 2 pm, if there is no detection by SEM techniques at x2000 magnification. EDS should be able to confirm that the particles are within the binder phase. Alternatively, higher magnification may be used to lower the particle size threshold.

[0210] • The median values (D5o) Feret diameter of the particles (at least 100 target particles) were calculated, with all particle types (e.g. aggregate or binder fine particles) measured within a designated area until a minimum of a least 30 particles of a designated type was measured.

[0211] • Feret diameter, roundness and Aspect ratios are determined by the Imaged™ software package.

[0212] Binder width measurement

[0213] • SEM image of magnification x200 was used for binder width measurement;

[0214] • An SEM image of approximately 13 mm by 9mm had a grid lines of 109 by 109 pm (Figure 5). The aggregate particles were numbered 1 to 88, with the width of the binder phase between adjacent aggregate particles measured along the horizonal grid lines H1 to H9 and the vertical gridlines V1 to V13 using Imaged™ software. The average binder width was then determined from the 181 binder width measurements.

[0215] A minimum image area of 10,000 pm2should be used to determine the binder width measurement.

[0216] Surface area fraction measurement • SEM image of magnification x2000 was used for the measurement of binder refractory particles, with a

[0217] • SEM image of magnification x100 was used for the measurement of the aggregate phase.

[0218] • Area fraction of total binder phase (which includes binder + embedded refractory binder particles) and embedded binder refractory particles population were measured by Imaged™

[0219] • The surface area percentage of embedded refractory binder particles with respect to total binder phase was calculated based on relative areas as indicated in the expression below:

[0220] The composite consists of the aggregate phase and the binder phase. XRD Rietveld analysis in combination with EDS analysis and surface area fraction measurement may be used to determine the wt% of the composite components.

[0221] The image size of at least 5,000,000 pm2under a magnification of x100 should be used to assess the surface area of the different components. To obtain the % surface area of the binder refractory particles, the surface area of at least 10,000 pm2at x2000 magnification should be used to determine the proportion of binder refractory particles within the binder phase.

[0222] Apparent porosity and bulk density were determined in accordance with ASTM C20 standard procedures.

[0223] Transverse Bending (or Flexural) Strength (TBS) was determined in accordance with ASTM C1161-13 standard procedures.

[0224] Impact strength was determined in accordance with ISO 179-2.

[0225] Young’s modulus was determined in accordance with ASTM D790.

[0226] The co-efficient of thermal expansion was determined in accordance with ASTM E228-17 standard procedures.

[0227] XRD analysis: 2-3 grams of fired samples were crushed and passed through 30 mesh sieve, with further particle size reduction done on Agate-Pestle. XRD patterns (source Cu) were collected by using powder samples with the following parameters: 20: 10°to 90°; scan rate: 2°per minute; step size: 0.05. Qualitative and guantitative analysis of phases were performed by HighScore Plus™ software (quantitative analysis by Rietveld refinement method).

[0228] Thermal shock resistance was determined in accordance with ASTM C1171-16 standard procedures. For the thermal shock testing, samples were heated from room temperature to 1000°C in a furnace, where the temperature was maintained for 10 minutes, before the samples were removed from the furnace and kept for 10 minutes at ambient temperature (i.e. air quenched). This completed a single cycle of the thermal shock test. The heatingcooling cycles were repeated for 30 cycles, with TBS determined thereafter as a measure of mechanical strength retention (compared to the initial TBS) after a prolonged period of cyclic thermal shock like that experienced by a in operation.

[0229] The corrosion test

[0230] Cathode powder (1 g of Li-Ni-Mn-Co oxide (NMC811)) on each sample and heat treated at 900 °C. Every cycle treated powder was removed and replace with fresh cathode powder. Each heat treatment cycle increased the sample from room temperature to 900°C in 290 minutes, with the sample maintained at this temperature for 12 hrs to enable the cathode powder to penetrate into the sample. The furnace was turned off and the sample cooled to room temperature in about 7 hours. The treated powder was removed, replenished and the cycle repeated.

[0231] After, completing 30 and 50 thermal shock cycles while exposed to the corrosive effects of a cathode active material (corrosion cycles), we measured the corrosion depth by stereomicrographs, and further detailed study by SEM-EDX and XRD. Stereo-images showed very clear corroded zones of the samples which were recorded in Table 4 and 5.

[0232] Experimental results

[0233] Tables 3a & 3b provide the particle size distribution data for the raw material and composite product respectively, unless otherwise indicated. The differences in the D5o measurements between the tabular alumina in the raw material (DR5o) and the composite product (D5O) is indicative of the tabular alumina reacting with the clay and other raw materials during the firing step. The presence of crystalline silica in the final products suggests that an excess of silica in the clay (mullite comprises 28 wt% silica) may be responsible for reacting with the tabular alumina to form mullite, thereby reducing the particle size distribution of alumina in the process. The differences in the other raw material PSD may be at least partially accounted for by the different measurement techniques used. The Imaged® software could only detect particle sizes down to about 2 pm at a magnification of x2000, which may bias some results. Table 3a Raw material: particle size distribution

[0234] Table 3b Example 1 and 5: particle size distribution The aspect ratio of the particle’s fitted ellipse, i.e., [Major Axis][Minor Axis]

[0235] The Roundness is equal to 4 x [Area]TT x [Major axis]2

[0236] Table 3c: Example 1 : phase proportions

[0237] Table 3c provides the surface area proportions of the aggregate phase. The binder and void surface area space is calculated by difference. Due to the microporosity within the binder phase and between the aggregate phase and binder phase, it is not effective to accurately determine the relative surface area of the binder phase. However, the binder phase (excluding the binder refractory particles) for Example 1 may be determined by the XRD data (Table 11a) as can the total of the aluminosilicate phase (mullite) and refractory particles and binder refractory particles (SiC + AI2O3).

[0238] Table 3d Example 1: binder proportions

[0239] The % surface area of binder refractory particles suggests a decrease compared to the raw materials added, even when accounting for the % wt conversion. This is consistent with the observation that the binder refractory particles were reacting and converting to the mullite phase.

[0240] Tables 3d are the PSD results from a further sample analysis from Example 1 (focusing in of the binder phase), with the proportion and particle size distribution of binder refractory particles analysed under a x2000 magnification. The results are consistent with the results in Table 3b & 3c. The results confirm a reduction in refractory binder particles with most of the surface area from the refractory binder phase accounted for by particles with a Feret diameter of > 5 pm.

[0241] Alumina particles in the aggregate and the binder phases

[0242] Tables 4 to 10b demonstrate that the composites of the present invention possess good mechanical and corrosive resistant properties compared to CE-1 to CE-3. The XRD results (Table 11a & 11b), in combination with a mass balance of the raw materials, indicates that the clay has largely converted or was comprised of mullite, quartz and cristobalite and other minor crystalline and amorphous phases not detected by the XRD analysis. The XRD results were consistent with the composition reported in Tables 4, 6, 7 and 9, given the margins of errors of each data set and the proportion of amorphous material derived by the XRD analysis. The proportion of amorphous material was found to be less than 10 wt% in all samples. Composites with low amorphous material content (e.g. less than 10 wt% or less than 8 wt%) are generally preferred as amorphous material has typically lower corrosion resistance compared to crystalline materials. The use of Isostatic pressing resulted in superior corrosive resistance compared to uniaxial pressing (Examples 1&2). This is expected to be attributable to the decrease in porosity achieved with isostatic pressing, with a more open composite structure more susceptible to chemical attack. Unless otherwise indicated in the results, examples have been isostatically pressed.

[0243] It was noted that in Examples 3 & 4, the lower clay content resulted in difficulties for the clay to adequately bond to the aggregate particles of SiC and white fused alumina. The reduced TBS in Example 3 is likely to be a result on poor coverage of the aggregate particles surfaces with the binder phase. As Example 4 still achieved good TBS results, it is likely that improvements to the mixing process may avoid a decrease in mechanical properties at lower binder levels. However, the results indicate that clay levels at 25 wt% or lower may adversely affect the mechanical properties, unless additional steps are taken to facilitate surface coverage of the aggregate particles. However, the lower corrosion resistance of Example 4 as indicated by the relatively poor reaction depth after 30 thermal shock cycles, suggest that the presence of a sufficient amount of binder phase is required to obtain good corrosion resistance.

[0244] While not wanting to be bound by theory, it is thought that at last part of the deficiencies in the performance of the comparative examples is related to the presence of magnesium containing compounds (spinel and cordierite), which result in a reaction with the cathode material (e.g. Lithium-Nickel-Manganese-Cobalt oxide) which results in the formation of MgO via the following reactions pathways:

[0245] Li O+MgAl O (spire\)—>-2Li.AlO2+MgO

[0246] Li2O+2M gO .2Al2(h.5Si(h (cordierite ^LiAlO^+LinSiO +LiAlSiOii+MgO

[0247] The resultant MgO (periclase) has a higher coefficient of thermal expansion of 14x10-6 / °C which will generate a strong thermal expansion mismatch leading to crack formation and propagation.

[0248] In contrast, alumina particles in both the aggregate and binder phase provide good corrosive resistance. Further, the fine alumina particles in the binder phase also assists in improving mechanical properties, with a larger binder phase decreasing porosity and thereby improving the thermal shock resistance of the composite. The fine alumina particles not only improve corrosive resistance of the binder phase, but the fine alumina particles inhibit crack propagation, thereby maintaining the mechanical integrity of the binder phase. In addition to low porosity and a more mechanical and corrosive resistance binder phase, the composite of the present invention preferably avoids the formation of phases with large mismatches in the co-efficient of thermal expansion which lower thermal shock performance.

[0249] The average binder width (Example 1) was calculated to be an average of 62.6 pm from 181 measurements (Figure 5). The average binder width value is about a quarter of the median D5o size of the alumina and SiC particles in the aggregate phase. The relatively narrow width of the binder phase increases the corrosive resistance of the composite as the binder refractory particles create a corrosion resistance defence within the binder phase (e.g. particles 120 in the binder phase 110 of Figure 9) whilst further enhancing the mechanical properties of the composite.

[0250] Figures 6 illustrates the SEM image of the corroded test sample of CE-1 with a top corroded zone 2 and a bottom non-corroded zone 4. An EDS image (Figure 7) of the Mg distribution indicates that the body of corroded zone 6 has been depleted of Mg with a Mg rich phase (MgO) forming at the surface region of the sample 8. Visual inspection of the corroded samples confirms that there is surface crack formation. It is thought that the high thermal coefficient mismatch between MgO and neighbouring phases initiate crack formation. Visual cracking was observed on both CE-1 and CE-2 samples. The composite structure of Example 1 of the present invention is illustrated in Figure 8, in which it may be observed that the composite 10 comprises relatively large particles of white fused alumina 20 and silicon carbide 30 bound together within a binder 40. The proportion and flow characteristics of the binder 40, in addition to the pressing techniques, contributes to the void level of the composite. As indicated in the Tables, the void level or porosity of the composites of the present invention are significantly lower that the comparative examples, contributing to the improved mechanical properties of the composite of the present invention.

[0251] With reference to Figure 9a, with higher magnification (x3000), binder is sandwiched between silicon carbide particles 100. The binder comprises a continuous aluminosilicate phase 110, with EDS and XRD analysis confirming the presence of a mullite phase. Embedded within the aluminosilicate phase are smaller particles of tabular alumina 120. Table 4

[0252] Formulations (dry basis)

[0253] (* pressed under uniaxial conditions)

[0254] 5 Figure 9b is a further magnified image (x25,000) of the binder phase of Example 1 , in which sub-micron mullite grains average needle length 0.25 pm average needle width 0.04 pm; determined from a 50 grain sample size using Imaged™ software) 150 may be observed with refractory binder particles 160 embedded therein. Figure 9c illustrates the binder phase of Example 8, with alumina particles 160 embedded in a mullite phase 150 0 (grain size: average needle length 0.37 pm average needle width 0.04 pm; determined from a 50 grain sample size using Imaged™ software).

[0255] The concentration and size of the alumina particles 160 combine to provide a corrosive resistant barrier to better resist corrosive attack, than the mullite phase alone. XRD analysis also revealed the presence of quartz and cristobalite, indicating that, under the 5 firing conditions used, there was not complete conversion of silica and alumina to mullite or other aluminosilicate phases. Due to the presence of alkaline earth metal cations and alkali metal cations, it is likely that the binder also comprises a glassy aluminosilicate component. To further improve corrosive resistance, the proportion of the binder phase comprising glass is preferably minimised (e.g. less than 20 wt% or less than 10 wt%). The crystalline phase components of the binder phase may be maximised (e.g. at least 60 wt% or at least 70 wt% or at least 80 wt% or at least 90 wt%) to improve corrosive resistance.

[0256] As illustrated in Figures 10 to 12, after exposure to cathode powder (Lithium-Nickel- Manganese-Cobalt oxide) and thermal cycling as defined in the corrosion test, the saggar could be divided into an uncorroded zone 200, in which there no reaction between the cathode powder and the composite; a mildly corroded zone 210 and a corroded zone 220 stemming from the surface of the saggar in contact with the cathode powder. As indicated in Figure 5, the uncorroded zone 200 comprises large SiC grains 230; a large grain of white fused alumina 240, each encompassed by a binder phase 250.

[0257] Table 5 presents the XRD results in the saggar at the corroded, mildly corroded and uncorroded zones 220, 210, 200. The XRD results supports the visual observations, with the alumina phase (corundum) being the dominant crystalline phase in the corroded zone, confirming the corrosion resistance of this binder refractory particles to the cathode powder. In comparison, SiC is the dominant crystalline phase in the uncorroded base zone. The mullite phase appears to have been totally corroded and converted into an amorphous phase or transformed into the lithium silicate phases or the approximately 5 wt % of lithium aluminosilicate phases. The crystalline silica phases appeared to possess good corrosion resistance (quartz in particular) and their presence did not appear to adversely affect the thermal shock resistance of the composite (Table 5).

[0258] Table 5

[0259] As illustrated in Figures 11-13, the large alumina grains 640 are present not only in the uncorroded zone 200, but in the corroded zone 220, indicating that the alumina grains are more resistance to chemical attack than SiC grains. Some brighter smaller gains corresponding to the corroded 220 and mildly corroded zones 210 are also indicators of residual small grains of tabular alumina 620 within the binder phase 250. Table 6

[0260] Formulations (dry basis)

[0261] As highlighted in Figure 12, the SiC grains 730 have been largely oxidised in the corroded zone 220, with SiC grains going through the process of oxidation in the mildly corroded zone 210. The combination of SiC and alumina aggregate larger grains enables the composite to inhibit the good thermal shock characteristics of the SiC grains 730 as well as the good corrosion resistance properties of the larger alumina grains 640. Importantly, additional corrosive resistance is provided to the binder phase through the presence of the finer tabular alumina particles 620, which delay the chemical attack zone from reaching the larger SiC grains 730. The finer tabular alumina particles are also thought to suppress crack propagation further inhibiting the mechanism of both mechanical and chemical deterioration. By comparing Figures 11-13, areas of silica 750 within the binders phase may be also detected.

[0262] Effect of refractory particles

[0263] The effects of the refractory particles of the aggregate phase were assessed with the results provided in Table 6. From a comparation of Examples 8 & 10, SiC grains provide better mechanical performance compared to alumina, although both are superior to the mechanical performance exhibited by the comparative examples. The absence of SiC particles was also correlated with a greater decrease in TBS after 30 Thermal Shock Cycles (Examples 10, 13), confirming the ability of SiC particles to better withstand long periods exposed to cyclic thermal shocks, such as experienced in saggars and molten metal processing. The absence of larger alumina particles in the aggregate phase (Examples 7 & 8) appeared to have contributed to a lower corrosive resistance compared to formulations containing such particles (Examples 1 & 2), as indicated in the reaction depth data of Tables 4 to 6.

[0264] Effect of binder refractory particles in the binder phase

[0265] As indicated in Table 7, examples CE-4 to CE-8, which contained no fine alumina, had poor TBS values which were sufficiently poor to not warrant further extensive corrosive testing. Comparative Example 5 (CE-5) was tested for corrosion resistance after 30 Corrosion Cycles, with the relatively poor result of a penetration depth of 1955 pm being over twice the penetration depth of Example 1, which had a similar composition except for the absence of fine alumina particles.

[0266] The proportion of fine particles (alumina and SiC) embedded within the binder phase in Example 1 was determined to be 9.4 wt% relative to the total weight of the binder phase, with about 7 wt% attributable to embedded alumina particles. The proportion of alumina particles greater than 6 pm in diameter (Feret diameter) was 61%. The proportion and size of the alumina particles contribute to the superior corrosive resistance properties of the binder phase.

[0267] The effect of the size of the binder refractory particles may be shown through a comparison of Example 1 (tabular alumina DR5o - 11.1 pm) and Example 5 (calcined alumina DR5o - 6.3 pm). Whilst the smaller binder refractory particles of Example 5 may have contributed to slightly improved mechanical properties (Young’s modulus and TBS), the larger binder refractory particles of Example 1 appear to have contributed to improved shock resistance and corrosion resistance, with the larger particles in Example 1 resulting in less than half the corrosion depth compared to the use of the finer particles of Example 5. A comparison between Example 5 and CE-5 indicates that whilst the corrosion resistance levels are comparable, the absence of fine alumina particles results in inferior mechanical and thermal shock properties in CE-5. With the binder refractory particles of Example 1 comprising a D5o of 6.6 pm, 6.8 pm (and average particle size of 7.5 pm, 8.4 pm) for the alumina particles in the binder phase compared to a DR5o of 11.1 pm (average 8.1 pm) in the raw material, the alumina particles in the binder phase in Example 5 had a D5oOf 2.5 pm, with an average of 3.1 pm (measured at x3000 magnification) compared to a DR5O of 6.3 pm (average 5.3 pm) in the raw material (Table 3a). Thus, the binder refractory particles significantly decrease in size during the firing process. The apparent lack of reduction in average particle size (in contrast to the median particle size decrease) in Example 1 is likely to be derived from the methodology for the particle size distribution in the composite in which particles had a threshold value to about 2 pm. In some embodiments, to obtain a good combination of corrosion resistance and thermal shock resistance, the raw material particle diameters of the binder refractory materials, should be such that the D5o of the binder refractory particles in the binder is preferably at least 2.5 pm or at least 3.0 pm or at least 3.5 pm or at least 4.0 pm.

[0268] As can be observed in Examples 14 to 18 (Table 9), the composition of the binder refractory particles may also have an impact upon the mechanical and thermal shock characteristics of the composite, with fine TiO2(D5o - 0.42 pm) particles exhibiting superior results. Although, the relatively small D5o of TiO2may not be effective in enhancing corrosion resistance of the binder phase. Thus, in some embodiments, a combination of different binder refractory particles may be used to optimise the mechanical, thermal shock and corrosive resistance properties of the composite for a specific application. The presence of TiO2may be detected through a combination of XRD analysis and EDS analysis.

[0269] The average crystallite size of mullite was measured for Examples 5, 7 to 9 and CE-5 with the results all being between the range of 475 to 575 A, with no correlation between the amount of tabular alumina (binder refractory particles) and the crystallite size. Additional experimentation had indicated that the clay was the predominant source of nucleation sites and that the effect of the binder refractory particles on crystallite size would have been more pronounced if different mullite precursor raw materials were used. The small crystallite size enables the mullite phase to form an effective bonding agent and assisted in reducing porosity levels of the composite.

[0270] Figures 14-16 highlight the EDS images of silicon, aluminium and oxygen concentrations. Large SiC particles 800 and bonded together with a binder phase 805. The binder phase comprises a plurality of alumina particles 820 all less than 50 pm is diameter. The binder phase also included small particles of SiC 810 and areas of SiO2830. The small crystallite size of the mullite phase makes the majority of the binder phase 805 enable the binder phase to contain these particles 810, 820, 830 embedded therein without significant porosity being formed.

[0271] In comparison, examples 7 to 10 (Table 6), demonstrate that an increase in fine alumina particles correlates to an increase in mechanical properties. An increase in corrosion resistance between Ex 7 and 8 correlates with an increase in tabular alumina in the binder phase. A binder refractory particle content of 40 wt% in Ex 9, resulted in a deterioration in thermal shock performance, as indicated by a TBS retention of 74% compared to a TBS retention of 98% of Ex 8 (30 wt% binder refractory particles), although the TBS value was still acceptable. This suggests that binder refractory particles levels above 50 wt% may be detrimental to the composite’s thermal shock performance.

[0272] Table 7

[0273] Formulations (dry basis)

[0274] The absence of SiC in Examples 10 and 13 corresponded to relatively poor corrosion resistance as indicated by the reaction depth after 30 Corrosion Cycles. Surface cracking had developed on both of these samples after 15 Corrosion Cycles, indicating the importance of SiC and thermal shock performance in the mechanism underlying corrosion resistance. It is noted that the cathode powder used for examples 1 & 2 was different to the batch used for Examples 7 & 8 and, as such, batch to batch variation may have contributed to the improved corrosion test results for Examples 1 & 2, compared to Examples 7 & 8. Retesting of Examples 1 & 2, with the newer batch resulted in a 6% increase in penetration depths. The results were normalised accordingly.

[0275] Effect of type of binder refractory particles

[0276] As indicated in Table 8 (composite properties including selective standard deviation values), the composites of the present invention provide a stronger more corrosive resistant material. Whilst the coefficient of thermal expansion of Examples 1 & 2 is higher compared to the comparative example (CE-1), no signs of cracking were observed and the examples exhibited good thermal shock resistance as measured by the TBS retention after 30 thermal shock cycles. Table 8

[0277] The effect of binder refractory particles was investigated in Examples 14 to 18 (Table 9), with the type of binder refractory particles varied. The results indicate that a variety of binder refractory particles can provide good mechanical properties, even after 30 thermal shock cycles. The TiO2was particularly favourably for contributing to improved mechanical properties. This may be at least partially attributable to TiO2small particle size distribution, with a median particle size D50 of 0.42 pm. The small particles appear to have contributed to a lower apparent porosity, which correlates with improved mechanical properties. TiO2may be regarded as a non-reactive binder refractory particle in comparison with alumina, which may be prone to react with silica in the clay, particularly at lower particles sizes. The selection of the elemental type and size of binder refractory particles may be dependent upon the balance between mechanical and corrosive performance for a specific cathode active material or derivative thereof being handled. The improved corrosion resistance is attributable to the composite of the present invention with the SEM and XRD analysis of the partially corroded samples indicating that the binder refractory particles are inhibiting the penetration of the cathode powder and reactants thereof. Table 9

[0278] Formulations (dry basis)

[0279] As indicated from Table 10, the substitution of graphite from a portion of the SiC in the aggregate or the binder phase results in a decrease in mechanical properties. However, this is more than offset by the increase in mechanical properties contributed by the present of alumina in the binder phase, with the TBS values (E-19 to E-22) all being greater than the comparative example (CE-5) which does not contain alumina in the binder phase or graphite. Graphite may be added to improve one or more of the conductivity, wettability and machinability of the apparatus.

[0280] 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 ingredients 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%.

[0281] Table 10

[0282] Formulations (dry basis)

[0283] Table 11a Table 11b

Claims

Claims1 . An open vessel for processing cathode active materials at temperatures above 600°C, with a capacity in the range of 0.01 to 2000 litres composed of a composite comprising: an aggregate phase comprising or consisting of:• refractory particles having a particle size distribution with a median particle size D5o value of greater than or equal to 100 pm with a Feret diameter of greater than 50 pm using image analysis software; a binder phase comprising:• an aluminosilicate phase; and• binder refractory particles having a particle size distribution with a median particle size D50value in the range of > 0 pm to 30 pm with a Feret diameter of no more than 50 pm using image analysis software, said refractory particles and binder refractory particles being selected from the list consisting of metal carbides, metal nitrides, silicon carbide, boron carbide, boron nitride, graphite and oxides of aluminium, zirconium, silicon, chromium, yttrium, hafnium, tungsten and titanium and combinations thereof, wherein a microstructure of a cut plane of the composite comprises, in % surface area, 1.0 to 40 % binder refractory particles, relative to the total surface area of the composite, said binder refractory particles are embedded within the aluminosilicate phase; and wherein the sum of the refractory particles + aluminosilicate phase + binder refractory particles is at least 70 wt% of the total weight of the composite composition.

2. The open vessel of claim 1 , wherein the median particle size D5o of the binder refractory particles and the surface area of binder refractory particles is determined from an image of the cut plane observed with a microscope at a magnification of 2000 to 3000 times for the refractory binder particles using image analysis software.

3. The open vessel of claim 1 , wherein the cut plane of the composite, in % surface area, comprises 20% silicon carbide refractory particles relative to the total surface area of the aggregate phase, wherein the surface area of refractory particles is determined from an image of the cut plane observed with a microscope at a magnification of 100 times for the refractory particles using image analysis software.

4. The open vessel of any one of the preceding claims, wherein the binder refractory particles are selected from the group consisting of AI2O3, ZrO2, TiO2, HfO2, Y2O3, SiC and combinations thereof.

5. The open vessel according to any one of the preceding claims, wherein the binder phase comprises binder refractory particles with a median particle D5o value of at least 2.0 pm as measured using image analysis software.

6. The open vessel according to any one of the preceding claims, wherein the binder phase comprises binder refractory particles with a median particle D5o value of at least 4.0 pm as measured using image analysis software.

7. The open vessel according to any one of the preceding claims, wherein the cut plane of the composite, in % surface area of the total surface area of binder refractory particles, comprises:0 to 100 % alumina particles with a D5o value at least 3.0 pm; and0 to 100 % of one or more of ZrO2, TiO2, HfO2, Y2O3, SiC particles with a D5o value greater than 0.1 pm.

8. The open vessel according to any one of the preceding claims, wherein the cut plane of the composite, in % surface area, comprises:10 to 45% SiC in the aggregate phase; and5 to 40% refractory particles (excluding SiC) in the aggregate phase.

9. The open vessel according to any one of the preceding claims, wherein the microstructure of a cut plane of the composite comprises, in % surface area, 2.0 to 20 % binder refractory particles with a Feret diameter of at least 2.0 pm, relative to the total surface area of the composite.

10. The open vessel according to any one of the preceding claims, wherein the cut plane of the composite, in % surface area, comprises 4.0 to 15 % of binder refractory particles.

11. The open vessel according to any one of the preceding claims, wherein the cut plane of the composite, in % surface area relative to the total surface area of binder refractory particles, comprises at least 3.0 % of the binder refractory particles with a Feret diameter of between 5 pm and 50 pm, determined using image analysis software.

12. The open vessel according to any one of the preceding claims, wherein the cut plane of the composite, in % surface area relative to the total surface area of binder refractory particles, comprises at least 3.0 % of alumina particles with a Feret diameter of between 5 pm and 50 pm, using image analysis software.

13. The open vessel according to any one of the preceding claims, wherein the binder refractory particles have an average surface area of at least 15 pm2using Imaged® software at a magnification of x2000 for particles with a Feret diameter of at least 2 pm.

14. The open vessel according to any one of the preceding claims, wherein the aggregate phase comprises refractory particles having a particle size distribution with a median particle size D5o value in the range of 120 pm to 500 pm and the binder refractory particles having a particle size distribution with a median particle size D5o value in range of 2.0 to 30 pm.

15. The open vessel according to any one of the preceding claims, wherein the aggregate phase comprises or consists of refractory particles of silicon carbide and AI2O3.

16. The open vessel according to any one of the preceding claims, wherein the binder refractory particles comprise TiO2with a particle size distribution with a D5o in the range of 0.1 pm to 15 pm.

17. The open vessel according to any one of the preceding claims, wherein the composite composes, relative to the total weight of the composite:25 to 75 wt% refractory particles in the aggregate phase;13 to 30 wt% of a crystalline aluminosilicate phase; and the cut plane of the composite, in % surface area relative to the total surface area of the composite, comprises:1 .0 to 25 % binder refractory particles.

18. The open vessel according to any one of the preceding claims, wherein the composite comprises:10 to 50 wt% SiC in the aggregate phase;2.0 to 40 wt% alumina in the aggregate phase; and the cut plane of the composite, in % surface area of binder refractory particles relative to the total surface area of the composite, comprises:2.0 to 20 % alumina particles.

19. The open vessel according to any one of the preceding claims, wherein the composite comprises an aggregate phase comprising:10 to 90 wt% SiC particles;10 to 90 wt% of other refractory particles, excluding SiC.

20. The open vessel according to claim 19, wherein the other refractory particles comprise or consist of alumina.

21. The open vessel according to any one of the preceding claims, further comprising 0 to 20 wt% quartz and cristobalite as determined by XRD Rietveld analysis.

22. The open vessel according to any one of the preceding claims, wherein the aluminosilicate phase comprises polycrystalline mullite with a crystallite size of no more than 10 pm.

23. The open vessel according to any one of the preceding claims, comprising in the range of at least 20 wt% and no more than 39 wt% SiC as determined by XRD Rietveld analysis.

24. The open vessel according to any one of the preceding claims, wherein a crystalline aluminosilicate phase comprises at least 10 wt% and no more than 25 wt% of the total weight of the composite as determined by XRD Rietveld analysis.

25. The open vessel according to any one of claims of the preceding claims, comprising a composite wherein the average binder phase thickness is in the range of 30 to 100 pm.

26. A open vessel comprising a surface layer and a base layer, said base layer comprising a composite as defined in any one of claims 1 to 25 and wherein the surface layer comprises refractory particles with a Feret diameter of greater than 60 pm.

27. The open vessel according to claim 26, wherein a surface area ratio (% / %) of AI2O3particles to SiC particles in the surface layer is greater than surface area ratio (% / %) of AI2O3particles to SiC particles in the base layer.

28. The open vessel according to claim 26 or 27, wherein the surface layer comprises lithium aluminate, lithium aluminosilicate or lithium silicate species, as determined by XRD Rietveld analysis.

29. A method of producing an open vessel comprising:• Mixing together:25 to 75 wt% refractory particles refractory particles having a particle size distribution with a median particle size DR5o value of greater than or equal to 100m as measured in accordance with ISO 13320:2009; said refractory particles comprising at least 15 wt% silicon carbide;2 to 45 wt% binder refractory particles comprising a DR5o greater than 6 pm and less than 30 pm; as measured in accordance with ISO 13320:2009; and one or more compounds comprising SiO2and AI2O3, sufficient to produce 10 to 50 wt% of a mullite phase;• Packing the mixture into a mould;• Firing the mixture at sufficient temperature for sufficient time to convert the one of more compounds comprising SiO2and AI2O3into the mullite phase and wherein the binder refractory particles are embedded therein to form a binder phase; said binder phase bonding the refractory particles together to thereby form a composite.

30. The method according to claim 29, wherein the firing temperature is no more than 1450°C.

31. The method according to claim 29 or 30, wherein the one or more compounds comprising SiO2and AI2O3comprise clay.

32. The method according to any one of claims 29 to 31 , wherein the binder refractory particles comprise a DR5o greater than 8 pm.

33. The method according to any one of claims 29 to 32, wherein the binder refractory particles or one or more compounds comprising SiO2and AI2O3function as nucleation sites to achieve an average mullite crystallite size of less than 10 pm.

34. The method according to any one of claims 29 to 33, wherein the refractory particles further comprise one or both of AI2O3and ZrO2particles.

35. The method according to any one of claims 29 to 34, wherein the open vessel is defined in accordance with any one of claims 1 to 25.

36. An open vessel obtained or obtainable by the method according to any one of claims 29 to 35.

37. A method for manufacturing a cathode active material for a lithium battery comprising operations of:• Loading a raw material into an open vessel as defined in any one of claims 1 to 25 and inserting the raw material in a firing furnace and then firing; and• Recovering the raw material in the open vessel after the firing, and cooling and pulverizing to prepare a cathode active material for a lithium battery.

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