Composite material

Abstract

A method of preparing a composite material, the method comprising mixing a carbonaceous polymer with an metal or metalloid acetate templating agent; and carbonising at a temperature of at least about 500°C. The composite material comprises a rod morphology with a core derived from the templating agent and a shell derived from the carbonaceous polymer.

Description

[0001] Composite Material

[0002] Field

[0003] The present disclosure relates to a composite material and a method for its manufacture. The present disclosure relates more particularly, but not necessarily exclusively, to a composite material which may be used in battery electrodes, for example in a sodium ion battery.

[0004] Background

[0005] Sodium ion batteries (NIBs) have demonstrated potential as a cost-effective successor to lithium-ion batteries (LIBs) for large-scale, low-cost electrical energy storage applications and short distance mobility.

[0006] Like LIBs, NIBs include two components: a negative electrode, known as the anode, where electrons are released, and a positive electrode, called the cathode, which accepts these electrons. While LIB technology uses natural graphite as the standard anode material, in the case of NIBs, hard carbons (non-graphitisable disordered carbon materials with larger interlayer spacing, pores and defects) have been found to be effective anodes.

[0007] However, one of the limitations of hard carbons is their drop in performance at higher charging rates: capacities lower than 50 mAh g-1for charging rates above 2 hours. Anode materials with high reversible capacities are thus the target to enable fast-charging high energy density NIBs.

[0008] In this context, the cost of for the carbon anode is normally taken as that of synthetic graphite, which is relatively expensive compared to other carbon sources. Therefore, to make this technology competitive, it is desirable to reduce manufacturing costs.

[0009] It would be desirable to provide an anode that has improved or alternative electrochemical performance, and / or to obviate, mitigate and / or ameliorate one or more deficiencies in known anode, whether identified herein or otherwise.

[0010] Alternatively or additionally, it would be desirable to provide an improved or alternative method of manufacture. Summary

[0011] According to a first aspect, there is provided a method of preparing a composite material, the method comprising: mixing a carbonaceous polymer with an acetate templating agent; and carbonising at a temperature of at least about 500°C.

[0012] According to a second aspect, there is provided a composite material comprising: a carbon phase; and a metal or metalloid phase (e.g. a metal oxide phase) derived from an acetate as templating agent; wherein the weight ratio of the carbon phase to the metal or metalloid phase is from about 1 :1 to about 5:1 , based on the weights of the carbon phase relative to the weight of the metal or metalloid phase; and wherein the phases collectively have a rod morphology; wherein the rods have a length of at most about 100 pm.

[0013] According to a third aspect, there is provided a composite material of the second aspect prepared by the method of the first aspect.

[0014] According to a fourth aspect, there is provided an electrode (e.g. anode) material for a rechargeable electrochemical cell, the electrode material comprising a composite material according to the second or third aspects.

[0015] According to a fifth aspect, there is provided a kit of parts for assembling a sodium ion battery, the kit comprising the electrode material according to the fourth aspect and an electrolyte (optionally comprising a solution of NaPFe and a solvent mixture of ethylene carbonate, dimethyl carbonate and fluoroethylene carbonate).

[0016] According to a sixth aspect, there is provided a sodium ion battery comprising the electrode material according to the fourth aspect.

[0017] According to a seventh aspect, there is provided use of the electrode material according to the fourth aspect in a sodium ion battery.

[0018] According to an eighth aspect, there is provided use of an acetate precursor serving as templating agent in the manufacture of a composite material comprising a carbon phase derived from a carbonaceous polymer. Description of the Figures

[0019] Figure 1 shows a) and b) SEM and c) TEM images of a material prepared by the autogenic carbonisation of PET and tin(IV) acetate (SnAc) at 700°C and pressure of at least 30 bar.

[0020] Figure 2 shows XRD patterns of a composite material (PETSnAc) and Sn, SnO2 and graphite reference diffractograms.

[0021] Figure 3 shows specific capacity versus cycle number d) with and e) without FEC additive of current rates between 137.8 and 2756 mA g-1, corresponding to cycle rates between 0.1 C and 2 C based on a theoretical capacity of 1378 mAh g-1. 5 cycles at each current rate (i.e. 0.1 C, 0.2C, 0.5C, 1 C and 2C) were performed up to 2C and then current rates were brought back to 0.1 C following the same staircase protocol (i.e. 2C, 1C, 0.5C, 0.2C, 0.1 C) of 5 cycles per current density. C-rate testing was followed by 247 cycles of charge / discharge at 0.1 C.

[0022] Figure 4 shows a top view of the electrodes after 5 charge / discharge galvanostatic cycles vs Na Metal in 1 M NaPFe in EC:DMC. The three images f), g) and h) are from the same material at different magnifications. Arrows are identifying cracks formed during charge / discharge and expansion / contraction caused by Na-Sn alloying.

[0023] Figure 5 shows a FIB-SEM cross-section of a cycled electrode after 200 cycles with inset of: electrode interfacial contrast showing regions of solid electrolyte interface formation and void spaces within anode material.

[0024] Definitions

[0025] Unless otherwise defined herein, terms have their usual meaning, e.g. as defined in the IUPAC Compendium of Chemical Terminology (2019), version 3.0.1 , informally known as the "Gold Book".

[0026] The following definitions apply for terms used herein.

[0027] The term “at least one” is synonymous with “one or more”, i.e. one, two, three, four, five, six, or more.

[0028] As used herein, the term “about” or “approximately” generally encompasses or refers to a range of values that one skilled in the art would consider equivalent to the recited values (i.e. having substantially the same function or result and / or achieving those in the same way). Where the term “about” is used in relation to a numerical value, it can represent (in increasing order of preference) a 10%, 5%, 2%, 1 % or 0% deviation from that value. Unless otherwise indicated, the term “substantially”, as applied to characteristics, generally encompasses slight deviations in that characteristic which the skilled person would nonetheless consider equivalent (e.g. having substantially the same function or result and / or achieving the function / result and / or substantially in the same way).

[0029] The term “polymer” as used herein may refer to a molecule comprising two or more (such as three or more, four or more, five or more, six or more, seven or more, eight or more, nine or more, or ten or more) monomer units. A polymer may comprise many monomer units, such as 100 or more monomer units (which may be denoted using subscripts, e.g. “n”). The term “monomer” or “repeating unit” is one of the art. For the avoidance of any doubt, monomers are molecules that can be bonded to other molecules to form a polymer comprising units of the monomer.

[0030] The term “carbonaceous polymer” refers to a polymer that comprises carbon in its polymeric backbone. Examples of carbonaceous polymer include thermoplastic materials such as polyethylene terephthalate, polyethylene and polypropylene. Carbonaceous polymers may be described as “organic polymers”. Carbonaceous polymers are distinguished from inorganic polymers, such as polysiloxanes and the like, which do not comprise a carbon polymeric backbone.

[0031] The phrase “derived from a carbonaceous polymer” refers to materials that may be formed from the carbonaceous polymer. For example, carbonising a carbonaceous polymer causes the polymer to break down into a carbon material. Thus, carbon may be derived from the carbonaceous polymer during a carbonisation process.

[0032] The term “metal” is a term of art and has an accepted meaning in the field of battery technology and composite materials comprising the electrodes therein. It may be understood as referring to a chemical element which may be found in the left-hand side of the periodic table (e.g. left of the metalloids below), with elements to the left of each of: boron; silicon; germanium; antimony and astatine being classified as metals, with the exception of hydrogen. The metals of the periodic table include the alkali metals, alkaline earths, transition metals, lanthanides, and actinides.

[0033] The term “metalloid” refers to a chemical element which has a preponderance of properties in between, or that are a mixture of, those of metals and nonmetals. Commonly recognised metalloids are boron, silicon, germanium, arsenic, antimony, tellurium and selenium.

[0034] The term “carbonising” refers to the process of converting or being converted into carbon (i.e. breaking down or decomposing into elemental carbon / an allotrope thereof), typically by heating and / or heating above thermal decomposition in non-oxidative conditions. A carbonaceous polymer may, for example, be heated beyond its decomposition temperature, causing the polymer to break down to form a substantially carbonaceous material (comprising carbon and limited other elements, preferably consisting essentially of carbon). In the present disclosure, the “carbonising” process preferably takes place in the substantial absence oxygen (preferably in an atmosphere of at most 0.5 ppm oxygen), such that material cannot oxidise during said carbonising / heating. This means that the material substantially changes into elemental carbon rather than oxidising into carbon dioxide and the like.

[0035] The term “composite material” refers to a material formed by the combination of two or more distinct phases. The term “phase” (e.g. the “metal phase”) refers to a part which is substantially uniform in chemical composition and morphology and which may be different in chemical composition and morphology to another phase (e.g. the “carbon phase”).

[0036] The term “morphology” of the composite material refers to characteristics of its shape, size, and structure. In the context of the present disclosure, the composite material can be described as having a rod or rod-like morphology (which alternatively may be described as “needles” or “needle-like”). The composite material morphology may be described as having phases which comprise “rod-shaped” structures. The term “rod” is used in its typical sense, referring to a solid elongate / tubular structure.

[0037] Thus, as used herein, the term rod morphology (and needle morphology) may be used to describe a composite material having a plurality of solid elongate / tubular structures comprising the bulk composite material.

[0038] The morphology of the composite material may be derived from visual inspection of scanning electron microscopy (SEM) and / or transmission electron microscopy (TEM) images to identify the shape, size and structures comprising the composite material. For example, visual inspection of the TEM and / or SEM images may reveal that the composite material comprises elongate-shaped structures (e.g. solid tubes) resembling rods or needles, thus meaning that the composite material has a rod morphology (or needle morphology). The length of a rod is the length of the elongate structure and can again be derived from visual inspection of SEM and / or TEM.

[0039] The term “templating agent” refers to an initial reagent, material or compound (e.g. an acetate, such as tin acetate) used in the carbonisation process to form the composite material. The morphology of the composite material is influenced by the templating agent. On heating (i.e. when carbonising), the templating agent decomposes into nanoparticles (e.g. tin acetate decomposes into nanoparticles of tin and tin oxide). These nanoparticles agglomerate (i.e. join together or grow) into a rod-like (or needlelike) shape. This may be thought of as a ‘core’, comprising the agglomerated nanoparticles.

[0040] During the carbonisation process, the core becomes surrounded by carbon derived from the carbonaceous polymer, as it breaks down, which is deposited around the core of the composite material as a ‘shell’. Thus, the nanoparticles behave as a template (or scaffold) on which the carbonaceous shell grows. The resultant structure / shape may then be described overall with reference to a core-shell rod morphology, with a metal phase (e.g. agglomerated tin and tin oxide nanoparticles, derived from the decomposed tin acetate template) in the centre, surrounded by a carbon phase shell. The size of structures e.g. rods or nanoparticles may be determined by visual inspection e.g. TEM or SEM images. Here the size will be determined from a mean size from a collection of 50 randomly selected and measured structures. For example, in the context of measuring the size of rods, you may take an SEM image of a particle sample, measure the size of 50 random rods visible in the sample (and / or 50 rods spread over 2 or more SEM images, as needed), add the measurements together and then divide by 50.

[0041] Nanoparticles in the context of the present disclosure refer to particles having a particle size diameter of from about 1 nm to about 100 nm. In the context of the present disclosure, they can be measured by, for example, visual inspection as described above.

[0042] Autoclaving refers to a process in which substances are heated under high pressures (e.g. at least about 40 bar, such as at least about 50 bar, for example from about 50 bar to about 60 bar) in airtight vessel, typically an airtight steel vessel. The pressure may be self-generated, meaning that the autoclave or reactor is not pressured initially. The term “autogenic pressure” refers to pressure which is generated internally, in which an autoclave is sealed and heated.

[0043] Carbon nanotubes are cylindrical molecules consisting of a hexagonal arrangement of sp2 hybridized carbon atoms, which may comprise a single rolled up sheet of graphene (single-walled carbon nanotubes, SWCNTs) or multiple rolled up sheets of graphene (multi-walled carbon nanotubes, MWCNTs).

[0044] The term “conductive additive” is one of the art. It refers to an additive (typically carbon based) which form a percolating network for electron transport in the electrode layer which improves electrode conductivity.

[0045] The term “voids” is used to refer to vacant space or gaps that exist within the composite material. The composite material of the present disclosure may have a rod morphology. Voids may form when said composite material is packed, pressed or condensed because the rod morphology does not pack efficiently and / or tightly. Thus, voids may form between the rods.

[0046] As used herein, when the particle size of the carbonaceous polymer is described as being “mm in size”, this means that the polymer has been shredded to about 9 mm (major dimension), e.g. up to about 5 mm in size, optionally up to around 1 mm in size. Generally speaking, smaller sizing is preferred.

[0047] Where the term “at least” is applied to ratios, this should be interpreted as referring to the fact that the first number in the ratio is the number shown or is larger than the number shown, and / or the second number in the ratio is the number shown or is correspondingly smaller than the number shown. For example, a carbonaceous polymer and the acetate templating agent being mixed in a weight ratio of at least about 1 : 4 means that a ratio described as such may have values such as 2:4, 1 :3, 2:2, etc.

[0048] Various amounts discussed herein are expressed in terms of weight ratios. For the avoidance of doubt, wherein amounts of components in a composition are described in wt. or weight %, this means the weight percentage of the specified component in relation to the whole composition referred to, unless otherwise stated.

[0049] When the carbonaceous polymer is “substantially free of pigments, dyes, and / or titanium oxide”, this means that there is less than 1 wt% of said pigments, dyes and / or titanium oxide (total). Generally speaking, less pigment, dye and / or titanium oxide content is preferred, such as less than 0.5 wt%, preferably less than 0.25 wt%, preferably less than 0.1 wt% and preferably 0 wt%.

[0050] Detailed Description

[0051] According to a first aspect, there is provided a method of preparing a composite material, the method comprising: mixing a carbonaceous polymer with an acetate templating agent; and carbonising at a temperature of at least about 500°C.

[0052] Without wishing to be bound by theory, it is understood that, during carbonising, the acetate templating agent thermally decomposes (in view of the elevated temperature) into nanoparticles which agglomerate to form a ‘core’. For example, in instances where the templating agent is tin acetate, this decomposes into nanoparticles of tin and tin oxide. During carbonising, the core becomes surrounded by a carbon phase formed from carbonisation of the carbonaceous polymer, forming a ‘shell’ of carbon surrounding the core. Thus, in the method of the first aspect, the nanoparticles / core material derived from the acetate templating agent behave as a scaffold on which the carbon phase (derived from the carbonaceous polymer) grows.

[0053] The resultant structure may have a rod or needle-like shape (morphology), comprising said core and shell, which is templated by the decomposing templating agent.

[0054] The composite materials produced by this methodology have particular utility in the production of battery electrodes. Suitably, the carbonaceous polymer can be derived from plastic waste (such as from shredded plastic PET bottles). In this way, the composite materials of the first aspect have utility in the manufacture of cheaper and more sustainable battery electrodes and thereby represent a more competitive option than traditional electrodes based on, for example, hard carbons derived from mixed feedstocks including fossil-fuel derivatives. Moreover, as described more fully below, the composite materials of the present disclosure unexpectedly have improved and / or comparative electrochemical performance as compared with traditional materials.

[0055] The rods may suitably have a length of at most about 100 pm, such as at most about 90 pm; such as at most about 80 pm.

[0056] The rods may suitably have a length of at least about 20 pm, such as at least about 40 pm.

[0057] The rods may suitably have a length from about 20 pm to 90 pm, optionally from about 40 pm to 80 pm.

[0058] The length of the rods may suitably be determined by visual inspection of the SEM images.

[0059] As described above, the rods may suitably each comprise a core and a shell; optionally wherein the core is derived from the acetate templating agent (e.g. wherein the core is formed during said carbonising) and / or wherein the shell is derived from the carbonaceous polymer (e.g. wherein the shell is formed during said carbonising).

[0060] In the method of the first aspect, the carbonaceous polymer and the acetate templating agent are mixed. For example, in the method of the first aspect, the carbonaceous polymer and the acetate templating agent may be mixed in a weight ratio of at least about 1 : 4, such as at least about 1 : 3, for example at least about 1 : 2, the weight ratio being based on the weights carbonaceous polymer relative to the weight of the acetate templating agent.

[0061] In the method of the first aspect, the carbonaceous polymer and the acetate templating agent may be mixed in a weight ratio of at most about 4: 1 , such as at most about 3: 1 , for example at most about 2: 1 , the weight ratio being based on the weights carbonaceous polymer relative to the weight of the templating agent.

[0062] In the method of the first aspect, the carbonaceous polymer and the acetate templating agent may be mixed in a weight ratio from about 1 : 4 to about 4: 1 ; such as from about 1 : 3 to 3: 1 , for example from about 1 : 2 to 2: 1 , such as from about 2: 3 to 3: 2, for example from about 9: 1 1 to 1 1 : 9; optionally about 1 : 1 , the weight ratio being based on the weights carbonaceous polymer relative to the weight of the acetate templating agent.

[0063] The method of the first aspect uses a carbonaceous polymer. The carbonaceous polymer may comprise a polyester.

[0064] The carbonaceous polymer may comprise aromatic residues, optionally teroterephthalate and / or naphthalate residues (e.g. aliphatic teroterephthalate and / or naphthalate), optionally wherein the carbonaceous polymer comprises polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN) or polytrimethylene terephthalate (PTT), or mixtures thereof.

[0065] Suitably the carbonaceous polymer comprises polyethylene terephthalate (PET).

[0066] The carbonaceous polymer may comprise a polyamide, optionally nylon; and / or wherein the carbonaceous polymer comprises polystyrene.

[0067] Suitably the carbonaceous polymer may be derived from plastic bottles (e.g. PET bottles) and / or is in the form of pieces, for example pieces that are mm in size. For example, advantageously, the method of the first aspect may be a method which makes use of plastic waste.

[0068] The carbonaceous polymer is suitably substantially free of pigments, dyes, and / or titanium oxide.

[0069] In the method of the first aspect a carbonaceous polymer and an acetate templating agent are mixed.

[0070] The acetate templating agent in the method of the first aspect may be:

[0071] (i) a metal acetate templating agent; and / or

[0072] (ii) a metalloid acetate templating agent.

[0073] The templating agent may be selenium acetate, tin acetate or silicon acetate, or a combination thereof.

[0074] Suitably, the templating agent is tin acetate.

[0075] Suitably, in the method of the first aspect, when carbonising, the tin acetate templating agent decomposes into nanoparticles of tin and tin oxide. These nanoparticles agglomerate into a rod core. The resultant shape may then be described overall with reference to a core-shell rod morphology, with agglomerated tin and tin oxide nanoparticles, derived from the decomposed tin acetate template in the centre, surrounded by a carbon phase shell.

[0076] Thus, the composite material prepared by the method of the first aspect may be a material formed by the combination of a tin phase (derived from a tin acetate templating agent) and a carbon phase (derived from a carbonaceous polymer, suitably PET).

[0077] The method of the first aspect involves carbonising at a temperature of at least about 500°C, such as at least about 600°C, such as at least about 650°C, such as at least about 700°C.

[0078] For example, carbonising may be at a temperature of at most about 1300°C, such as at most about 1200°C, such as at most about 1100°C. For example, carbonising may be at a temperature of from about 600°C to about 1300°C, for example about 650°C to 1200°C, such as about 700°C to about 1100°C.

[0079] Suitably, carbonising is performed by autoclaving.

[0080] Carbonising may occur at autogenic pressure, optionally at least about 10 atm; optionally at least about 20 atm, for example at least about 25 atm. For example, carbonising may occur at autogenic pressure at most about 150 atm, optionally at most about 120 atm, for example at most about 100 atm optionally at most about 90 atm, for example at most about 80 atm. Suitably, carbonising may occur at autogenic pressure at from about 10 atm to about 150 atm, optionally from about 20 atm to about 120 atm, optionally from about 25 atm to about 100 atm.

[0081] Carbonising may occur in an inert atmosphere, such as an atmosphere comprising a noble gas selected from helium, neon, argon, xenon, radon, krypton; nitrogen and / or carbon dioxide. Suitably carbonising occurs in an argon atmosphere.

[0082] For example, carbonising may occur in an atmosphere comprising at most about 0.5 ppm oxygen.

[0083] For example, carbonising may occur in an atmosphere comprising at most about 0.5 ppm water.

[0084] The method of the first aspect may further comprising mixing a conductive additive (optionally a carbon additive) with the carbonaceous polymer and the acetate templating agent prior to carbonising, optionally wherein the carbon additive is graphite, graphene, carbon nanotubes (CNTs) or a mixture thereof.

[0085] The carbon additive is, suitably, carbon nanotubes (CNTs), for example multi-walled carbon nanotubes (MWCNTs) or single-walled carbon nanotubes (SWCNTs).

[0086] The conductive additive, optionally carbon additive, and the carbonaceous polymer may be mixed in a weight ratio of: at most about 5: 100, optionally about 4: 100, such as about 2: 100; and / or at least about 0.05: 100, optionally at least about 0.1 : 100, optionally at least about 0.5: 100; and / or from about 0.05: 100 to about 5: 100, such as about 0.1 : 100 to about 4: 100, such as about 0.5: 100 to about 2: 100, the weight ratio being based on the weights of the conductive additive relative to the combined weight of the carbonaceous polymer and the acetate templating agent.

[0087] The weight ratio of the carbon additive (when present) to the combined weight of the carbonaceous polymer and the acetate templating agent may be about 1 :100. According to a second aspect, there is provided a composite material comprising a carbon phase; and a metal or metalloid phase derived from an acetate templating agent; wherein the weight ratio of the carbon phase to the metal or metalloid phase is from about 1 :1 to about 5:1 , based on the weights of the carbon phase relative to the weight of the metal or metalloid phase; and wherein the phases collectively have a rod morphology; wherein the rods have a length of at most about 100 pm.

[0088] The composite material of the second aspect may be prepared by the method of the first aspect. Therefore, features described in relation to the composite material prepared by the method of the first aspect apply equally to the second aspect, and vice versa.

[0089] The weight ratio of the carbon phase to the metal or metalloid phase is suitably: at most about 4: 1 ; optionally at most about 3: 1 ; and / or at least about 1.5: 1 ; optionally at least about 2: 1 ; and / or from about 1.5: 1 to about 4: 1 ; optionally about 2:1 to about 4:1 , optionally at least about 2:1 to about 3:1 . the weight ratio being based on the weights of the carbon phase relative to the weight of the metal or metalloid phase.

[0090] The composite material may comprise at least about 50 wt%, such as at least about 60 wt%, for example at least about 65 wt%, of the carbon phase, wherein the wt% is based on the total weight of the composite material.

[0091] The composite material may comprise at most about 90 wt%, such as at most about 80 wt%, for example at most about 75%, of the carbon phase, wherein the wt% is based on the total weight of the composite material.

[0092] The composite material may comprise from about 50 wt% to about 90 wt%, such as from about 60 wt% to 80 wt%; for example from about 65 wt% to about 75% of the carbon phase, wherein the wt% is based on the total weight of the composite material.

[0093] The composite material may comprise at least about 10 wt%, such as at least about 20 wt%, for example at least about 25 wt%, of the metal or metalloid phase, wherein the wt% is based on the total weight of the composite material. The composite material may comprise at most about 50 wt%, such as at most about 40 wt%, for example at most about 35%, of the metal or metalloid phase, wherein the wt% is based on the total weight of the composite material.

[0094] The composite material may comprise from about 10 wt% to about 50 wt%, such as from about 20 wt% to 40 wt%; for example from about 25 wt% to about 35% of the metal or metalloid phase, wherein the wt% is based on the total weight of the composite material.

[0095] The composite material may comprise 70 wt% of the carbon phase and about 30 wt% of the metal or metalloid phase, wherein the wt% is based on the total weight of the composite material.

[0096] The composite material may comprise a metal phase, such as a nickel, zinc, copper or tin phase. Suitably the metal phase is a tin phase.

[0097] The tin phase may be derived from tin acetate (e.g. formed from heating tin acetate, e.g. in a carbonation step).

[0098] The composite material may comprise a metalloid phase, such as a silicon phase, selenium or antimony phase.

[0099] The metal or metalloid phase suitably comprises (a) metal or metalloid; and (b) metal oxide or metalloid oxide.

[0100] For example, the metal or metalloid phase may be a tin phase and may comprise (a) tin; and (b) tin oxide.

[0101] The composite material may comprise XRD peaks with the following characteristic peaks at 20 at from about 26 to 28°; and / or from about 31 to 33°; and / or from about 32 to 34°; and / or from about 43 to 45°; and / or from about 44 to 46°; and / or from about 52 to 54°.

[0102] The composite material may comprise XRD peaks with characteristic peaks of carbon at 20 at from about 26 to 28°; and / or from about 31 to 33°. The composite material may comprise XRD peaks with characteristic peaks of tin and tin oxide at from about 31 to 33°; and / or from about 32 to 34°; and / or from about 43 to 45°; and / or from about 44 to 46°; and / or from about 52 to 54°.

[0103] The composite material may comprise XRD peaks with the following characteristic peaks at 20 from about 26 and 28° and from about 31 to 33°; from about 32 to 34°; and from about 43 to 45°; and from about 44 to 46°; and from about 52 to 54°. The composite material may comprise XRD peaks with the following characteristic peaks at 20 at about 27°; and / or about 32°; and / or about 33°; and / or about 44°; and / or about 44°; and / or about 53°.

[0104] The composite material may comprise XRD peaks with the following characteristic peaks at 20 at about 27°; and about 32°; and about 33°; and about 44°; and about 44°; and about 53°.

[0105] Suitably, the XRD peaks are measured using a PANalytical X’Pert Pro MPD equipment for crystal structure determination of powders, films and solid samples, employing a Cu Anode (Ka = 1.5406 A) and X’Celerator detector. X’Pert High Score and ICDD PDF4+ Database were employed to determine the crystalline phases present.

[0106] The XRD pattern obtained for the composite material is suitably compared to reference diffractograms for the metal phase (e.g. the metal and metal oxide phrase) and / or graphite to determine the characteristic peaks.

[0107] The weight ratio of said (a) metal or metalloid; and (b) metal oxide or metalloid oxide is suitably: at most about 1 :10; optionally at most about 1 : 9; optionally at most about 1 : 8; and / or at least about 1 :2; optionally at least about 1 : 3; optionally at least about 1 : 5; and / or from about 1 : 2 to about 1 : 10, optionally from about 1 : 3 to about 1 : 9; for example from about 1 : 5 to about 1 : 8, such as about 1 : 7, the weight ratio being based on the weights of said (a) metal or metalloid relative to the weight of the (b) metal oxide or metalloid oxide.

[0108] The carbon phase is suitably a substantially amorphous carbon phase.

[0109] The composite material according to the second aspect comprises a rod morphology. Suitably the rod morphology comprises rods having a length of at most about 90 pm, such as at most about 80 pm.

[0110] The rod morphology suitably comprises rods having a length of at least about 20 pm, such as at least about 40 pm.

[0111] The rod morphology suitably comprises rods having a length of from about 20 pm to about 90 pm, optionally from about 40 pm to about 80 pm.

[0112] The rod morphology may comprise rods each comprising a core comprising the metal or metalloid phase; optionally wherein the metal or metalloid phase comprises nanoparticles (optionally agglomerated nanoparticles) of at most about 15 nm in size, such as at most about 12 nm in size.

[0113] The metal or metalloid phase may comprise nanoparticles of at least about 1 nm in size, such as at least about 2 nm in size. The metal or metalloid phase may comprise nanoparticles of from about 1 nm to about 15 nm in size, such as from about 2 nm to about 10 nm in size.

[0114] The rods may each comprise a metal or metalloid phase core surrounded by a carbon shell, optionally a substantially amorphous carbon shell.

[0115] The metal or metalloid phase core may be formed from agglomerated nanoparticles.

[0116] The carbon shell may have a thickness of at most about 20 nm, such as about 15 nm.

[0117] The carbon shell may have a thickness of at least about 5 nm, such as about 10 nm.

[0118] The carbon shell may have a thickness of from about 5 nm to about 20 nm, such as about 10 nm to about 15 nm.

[0119] The carbon phase is suitably derived from a carbonaceous polymer (e.g. by carbonisation thereof).

[0120] The carbon phase may be derived from a carbonaceous polymer comprising polyester.

[0121] The carbon phase may be derived from a carbonaceous polymer comprising aromatic residues, optionally teroterephthalate and / or naphthalate residues (e.g. aliphatic teroterephthalate and / or naphthalate), optionally wherein the carbonaceous polymer comprises polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN) or polytrimethylene terephthalate (PTT), or mixtures thereof.

[0122] The carbon phase is suitably derived from a carbonaceous polymer comprising polyethylene terephthalate (PET).

[0123] The carbon phase may be derived from a carbonaceous polymer comprising a polyamide, optionally nylon; and / or wherein the carbonaceous polymer comprises polystyrene.

[0124] The composite material may further comprise carbon nanotubes (CNTs), optionally multi-walled carbon nanotubes (MWCNTs) or single-walled carbon nanotubes (SWCNTs).

[0125] The composite material may comprise voids between the rods.

[0126] According to a third aspect, there is provided a composite material of the second aspect prepared by the method according the first aspect. The composite material of the second aspect may be obtained or obtainable by a method according to the first aspect. According to a fourth aspect, there is provided an electrode (e.g. anode) material for a rechargeable electrochemical cell, the electrode material comprising a composite material according to the second aspect. The electrode material suitably comprises a composite material prepared by the first aspect.

[0127] The manufacturing costs of the electrode (e.g. anode) may be reduced by up to 70% compared to comparable electrodes.

[0128] The electrode material may further comprise a carboxymethyl cellulose binder.

[0129] During manufacture of the electrode, voids may form when the composite material of the second aspect is coated, together with a polymeric binder, onto a substrate (e.g. current collector). Due to the morphology of the composite material, the coating does not allow for tight packing. The voids within the composite material may be beneficial to prevent the volumetric expansion the metal or metalloid phase during charge / discharge.

[0130] The electrode material may comprise the composite material and the carboxymethyl cellulose binder in a weight ratio of from about 20: 1 to about 1 : 1 , such as about 15: 1 to about 3: 1 , for example about 12: 1 to about 5: 1 , optionally about 9:1 .

[0131] The electrode material of the third aspect may be for a sodium ion battery.

[0132] The electrode material may comprise an alloy of sodium and tin, optionally Nai5Sn4.

[0133] The electrode material may have a capacity of at least about 100 mAhg1, such as at least about 200 mAhg-1, for example at least about 400 mAhg-1

[0134] The electrode material may have a power density of at least about 80 Wh / 36Ah, such as at least about 90 Wh / 36Ah.

[0135] The electrode material may have capacity which decreases by about 5% or less after 100 cycles.

[0136] According to a fifth aspect, there is provided a kit of parts for assembling a sodium ion battery, the kit comprising the electrode material according to the third aspect and an electrolyte (optionally comprising a solution of NaPFe and a solvent mixture of ethylene carbonate, dimethyl carbonate and fluoroethylene carbonate).

[0137] According to a sixth aspect, there is provided a sodium ion battery comprising the electrode material according to the fourth aspect. The sodium ion battery suitably comprises an electrolyte comprising a solution of NaPFe and a solvent mixture of ethylene carbonate, dimethyl carbonate and fluoroethylene carbonate.

[0138] According to a seventh aspect, there is provided use of the electrode material according to the fourth aspect in a sodium ion battery.

[0139] According to an eighth aspect, there is provided use of an acetate templating agent in the manufacture of a composite material comprising a carbon phase derived from a carbonaceous polymer.

[0140] Features described above in relation to one of the foregoing aspects apply equally, mutatis mutandis, to the other aspects. For example, features described above in relation to the method of preparing a composite material of the first aspect of the invention apply equally to the composite material according to the second aspect, mutatis mutandis.

[0141] Examples

[0142] Composite Material Preparation

[0143] 50 mg of shredded PET bottles, 50 mg of Sn(CH3COO)2(Sigma Aldrich) and 1 mg of MWCNTs (Sigma Aldrich) are introduced into a 100ml vol Swagelok reactor and sealed inside an Ar glovebox (<0.5 ppm O2, <0.5 ppm H2O) employing silver goop for the threads. The reactor is then taken to 700°C at 10°C / min and maintained at that temperature for 2h, after which the reactor is let to reach room temperature naturally. The produced materials are then morphologically characterised through scanning electron microscopy (SEM) and transmission electron microscopy (TEM) using a FEI Inspect F SEM operated at 10 kV and a JEOL 2100Plus TEM at 200 kV operating voltage, respectively. Images were then processed and the observed features measured using the open-source programme Image J. To corroborate the composition of the material, X-ray diffraction patterns of samples were recorded using a . Diffractograms were then compared to the reference patterns of , obtained through the High Score database license..

[0144] Morphology

[0145] Morphological characterisation was carried out by using an FEI Inspect F SEM operated at 10 kV and TEM, using a JEOL 2100Plus TEM at 200 kV operating voltage.

[0146] The FEI Inspect F is a high vacuum FEG source SEM with EDS and WDS analysis. The JEM-21 OOPIus is a multipurpose transmission electron microscope. Both are commercially available.

[0147] The prepared material is a C-Sn composite, having 70%C and 30%Sn / SnO2 (ratio of Sn:SnO2 of 1 :7).

[0148] Figure 1 shows SEM and TEM images of the prepared composite material. As can been seen from Figure 1 , the material has needle-like rods of about 40-80 pm in length; nanoparticles (2-10 nm) of the Sn-phase are protected with an amorphous carbon layer (shell) of about 10-15 nm in thickness.

[0149] Figure 2 shows the XRD patterns of the prepared composite material (PETSnAc) and Sn, SnO2 and graphite reference diffractograms.

[0150] Electrochemical Characterization

[0151] Electrodes were made using an 90:10 weight ratio of active material and carboxymethyl cellulose binder (CMC) (Mw ~ 250 000, Sigma Aldrich), respectively. A 250 pm layer of the slurry was then coated onto a carbon-coated aluminium foil (18 pm conductive coating, MTI corporation) through blade casting (doctor blade coater). Once dried at room temperature for 24 h, 13 mm disks were cut and dried at 100 °C for 2 h under vacuum. The electrolyte preparation and coin cell assembly were conducted in an argon-filled glovebox (MBraun GmbH Labstar glovebox workstation) with H2O < 0.5 ppm and O2 < 0.5 ppm levels. CR2032 coin cells were assembled using sodium metal counter electrode disks (less than 0.5 mm thick, rolled, and cut from a sodium ingot, 99.8% metals basis, Alfa Aesar), the coated hard carbon as working electrodes, and a glass fiber separator (Whatman GF / B glass microfiber, 18 mm diameter) saturated with electrolyte (150 pL) which was a 1 M solution of NaPFe in a 50:50 ethylene carbonate: dimethyl carbonate solvent mixture.

[0152] Galvanostatic cycling tests were performed on a Basytec system in the potential range of 0.001-2.5 V versus Na+ / Na and using sodiation / desodiation current rates between 137.8 and 2756 mA g-1, corresponding to cycle rates between 0.1 C and 2 C based on a theoretical capacity of 1378 mAh g-1. The results are shown in Figure 3.

[0153] Figure 4 shows a top view of the electrodes after 5 charge / discharge galvanostatic cycles vs Na Metal in 1 M NaPFe in EC:DMC.

[0154] Figure 5 shows a FIB-SEM cross-section of a cycled electrode after 200 cycles with inset of: electrode interfacial contrast showing regions of solid electrolyte interface formation and void spaces within anode material.

[0155] This work was supported by the Engineering and Physical Sciences Research Council [grant numbers EP / R51 1547 / 1 and EP / S018204 / 2]; and the Faraday Institution [grant number EP / T012404 / 1].

[0156] Aspects of the present invention are set out in the following numbered clauses.

[0157] Clause 1 . A method of preparing a composite material, the method comprising: mixing a carbonaceous polymer with an acetate templating agent; and carbonising at a temperature of at least about 500°C.

[0158] Clause 2. The method according to clause 1 , wherein the composite material comprises a rod morphology.

[0159] Clause 3. The method according to clause 2, wherein the rods have a length of: at most about 100 pm, such as at most about 90 pm; such as at most about 80 pm; and / or at least about 20 pm, such as at least about 40 pm; and / or from about 20 pm to 90 pm, optionally from about 40 pm to 80 pm.

[0160] Clause 4. The method according to clause 2 or clause 3, wherein the rods each comprise a core and a shell; optionally wherein the core is derived from the acetate templating agent (e.g. wherein the core is formed during said carbonising) and / or wherein the shell is derived from the carbonaceous polymer (e.g. wherein the shell is formed during said carbonising).

[0161] Clause 5. The method according to any preceding clause, wherein the carbonaceous polymer and the acetate templating agent are mixed in a weight ratio of at least about 1 : 4, such as at least about 1 : 3, for example at least about 1 : 2; and / or at most about 4: 1 , such as at most about 3: 1 , for example at most about 2: 1 ; and / or from about 1 : 4 to about 4: 1 ; such as from about 1 : 3 to 3: 1 , for example from about 1 : 2 to 2: 1 , such as from about 2: 3 to 3: 2, for example from about 9: 11 to 11 : 9; optionally about 1 : 1 ; the weight ratio being based on the weights carbonaceous polymer relative to the weight of the templating agent.

[0162] Clause 6. The method according to any preceding clause, wherein the carbonaceous polymer comprises a polyester.

[0163] Clause 7. The method according to any preceding clause, wherein the carbonaceous polymer comprises aromatic residues, optionally teroterephthalate and / or naphthalate residues (e.g. aliphatic teroterephthalate and / or naphthalate), optionally wherein the carbonaceous polymer comprises polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN) or polytrimethylene terephthalate (PTT), or mixtures thereof. Clause 8. The method according to clause 7, wherein the carbonaceous polymer comprises polyethylene terephthalate (PET).

[0164] Clause 9. The method according to any preceding clause, wherein the carbonaceous polymer comprises a polyamide, optionally nylon; and / or wherein the carbonaceous polymer comprises polystyrene.

[0165] Clause 10. The method according to any preceding clause, wherein the carbonaceous polymer is derived from plastic bottles (e.g. PET bottles) and / or is in the form of pieces (optionally wherein the pieces are mm in size).

[0166] Clause 11 . The method according to any preceding clause, wherein the carbonaceous polymer is substantially free of pigments, dyes, and / or titanium oxide.

[0167] Clause 12. The method according to any preceding clause, wherein the acetate templating agent is:

[0168] (i) a metal acetate templating agent; and / or

[0169] (ii) a metalloid acetate templating agent.

[0170] Clause 13. The method according to any preceding clause, wherein the templating agent is selenium acetate, tin acetate or silicon acetate, or a combination thereof.

[0171] Clause 14. The method according to any preceding clause, wherein the templating agent is tin acetate.

[0172] Clause 15. The method according to any preceding clause, wherein carbonising is at a temperature of at least about 600°C, such as at least about 650°C, such as at least about 700°C.

[0173] Clause 16. The method according to any preceding clause, wherein carbonising is at a temperature of at most about 1300°C, such as at most about 1200°C, such as at most about 1100°C.

[0174] Clause 17. The method according to any preceding clause, wherein carbonising is at a temperature of from about 600°C to about 1300°C, for example about 650°C to 1200°C, such as about 700°C to about 1100°C.

[0175] Clause 18. The method according to any preceding clause, wherein carbonising is performed by autoclaving.

[0176] Clause 19. The method according to any preceding clause, wherein carbonising occurs at autogenic pressure, optionally: at least about 10 atm; optionally at least about 20 atm, for example at least about 25 atm; and / or at most about 150 atm, optionally at most about 120 atm, for example at most about 100 atm optionally at most about 90 atm, for example at most about 80 atm; and / or from about 10 atm to about 150 atm, optionally from about 20 atm to about 120 atm, optionally from about 25 atm to about 100 atm

[0177] Clause 20. The method according to any preceding clause, wherein carbonising occurs in an inert atmosphere, such as an atmosphere comprising a noble gas selected from helium, neon, argon, xenon, radon, krypton; nitrogen and / or carbon dioxide; optionally wherein carbonising occurs in an argon atmosphere.

[0178] Clause 21 . The method according to any preceding clause, wherein carbonising occurs in an atmosphere comprising at most about 0.5 ppm oxygen.

[0179] Clause 22. The method according to any preceding clause, wherein carbonising occurs in an atmosphere comprising at most about 0.5 ppm water.

[0180] Clause 23. The method according to any preceding clause, further comprising mixing a conductive additive (optionally a carbon additive) with the carbonaceous polymer and the acetate templating agent prior to carbonising, optionally wherein the carbon additive is graphite, graphene, carbon nanotubes (CNTs) or a mixture thereof.

[0181] Clause 24. The method according to clause 23, wherein the carbon additive is carbon nanotubes (CNTs).

[0182] Clause 25. The method according to clause 24, wherein the carbon nanotubes (CNTs) are multiwalled carbon nanotubes (MWCNTs) or single-walled carbon nanotubes (SWCNTs).

[0183] Clause 26. The method according to any one of clauses 23 to 25, wherein the conductive additive, optionally carbon additive, and the carbonaceous polymer are mixed in a weight ratio of: at most about 5: 100, optionally about 4: 100, such as about 2: 100; and / or at least about 0.05: 100, optionally at least about 0.1 : 100, optionally at least about 0.5: 100; and / or from about 0.05: 100 to about 5: 100, such as about 0.1 : 100 to about 4: 100, such as about 0.5: 100 to about 2: 100, the weight ratio being based on the weights of the conductive additive relative to the combined weight of the carbonaceous polymer and the acetate templating agent. Clause 27. The method according to any one of clauses 23 to 25, wherein the weight ratio of the carbon additive to the combined weight of the carbonaceous polymer and the acetate templating agent is about 1 :100.

[0184] Clause 28. A composite material obtained or obtainable by the method of any one of clauses 1 to 27.

[0185] Clause 29. A composite material comprising a carbon phase; and a metal or metalloid phase (e.g. a metal oxide phase) derived from an acetate as templating agent; wherein the weight ratio of the carbon phase to the metal or metalloid phase is from about 1 :1 to about 5:1 , based on the weights of the carbon phase relative to the weight of the metal or metalloid phase; and wherein the phases collectively have a rod morphology; wherein the rods have a length of at most about 100 pm.

[0186] Clause 30. The composite material according to clause 29, wherein the weight ratio of the carbon phase to the metal or metalloid phase is: at most about 4: 1 ; optionally at most about 3: 1 ; and / or at least about 1.5: 1 ; optionally at least about 2: 1 ; and / or from about 1 .5: 1 to about 4: 1 ; optionally about 2:1 to about 4:1 , optionally at least about 2:1 to about 3:1 . the weight ratio being based on the weights of the carbon phase relative to the weight of the metal or metalloid phase.

[0187] Clause 31 . The composite material according to clause 30, wherein the composite material comprises: at least about 50 wt%, such as at least about 60 wt%, for example at least about 65 wt%, of the carbon phase; and / or at most about 90 wt%, such as at most about 80 wt%, for example at most about 75%, of the carbon phase; and / or from about 50 wt% to about 90 wt%, such as from about 60 wt% to 80 wt%; for example from about 65 wt% to about 75% of the carbon phase; and / or at least about 10 wt%, such as at least about 20 wt%, for example at least about 25 wt%, of the metal or metalloid phase; and / or at most about 50 wt%, such as at most about 40 wt%, for example at most about 35%, of the metal or metalloid phase; and / or from about 10 wt% to about 50 wt%, such as from about 20 wt% to 40 wt%; for example from about 25 wt% to about 35% of the metal or metalloid phase; optionally wherein the composite material comprises 70 wt% of the carbon phase and about 30 wt% of the metal or metalloid phase, wherein the wt% is based on the total weight of the composite material.

[0188] Clause 32. The composite material according to any one of clauses 29 to 31 comprising a metal phase, such as a nickel, zinc, copper, selenium or tin phase.

[0189] Clause 33. The composite material according to clause 32, wherein the metal phase is a tin phase.

[0190] Clause 34. The composite material according to clause 32 or 33, wherein the tin phase is derived from tin acetate (e.g. formed from heating tin acetate, e.g. in a carbonation step).

[0191] Clause 35. The composite material according to any one of clauses 29 to 34 comprising a metalloid phase, such as a silicon phase.

[0192] Clause 36. The composite material according to any one of clauses 29 to 35, wherein the metal or metalloid phase comprises (a) metal or metalloid; and (b) metal oxide or metalloid oxide.

[0193] Clause 37. The composite material according to clause 36, wherein the metal or metalloid phase is a tin phase and comprises (a) tin; and (b) tin oxide.

[0194] Clause 38. The composite material according to any one of clauses 29 to 37, wherein the composite material comprises XRD peaks with the following characteristic peaks at 20 at from about 26 to 28°; from about 31 to 33°; from about 32 to 34°; from about 43 to 45°; from about 44 to 46°; and / or from about 52 to 54°; or optionally wherein the composite material comprises XRD peaks with the following characteristic peaks at 20 at from about 26 to 28°; from about 31 to 33°; from about 32 to 34°; from about 43 to 45°; from about 44 to 46°; and from about 52 to 54°; such as wherein the composite material comprises XRD peaks with the following characteristic peaks at 20 at about 27°; and / or about 32°; and / or about 33°; and / or about 44°; and / or about 44°; and / or about 53°; or optionally wherein the composite material comprises XRD peaks with the following characteristic peaks at 20 at about 27°; about 32°; about 33°; about 44°; about 44° and about 53°.

[0195] Clause 39. The composite material according to any one of clauses 29 to 38, wherein the weight ratio of said (a) metal or metalloid; and (b) metal oxide or metalloid oxide is: at most about 1 :10; optionally at most about 1 : 9; optionally at most about 1 : 8; and / or at least about 1 :2; optionally at least about 1 : 3; optionally at least about 1 : 5; and / or from about 1 : 2 to about 1 : 10, optionally from about 1 : 3 to about 1 : 9; for example from about 1 : 5 to about 1 : 8, such as about 1 : 7.

[0196] Clause 40. The composite material according to any one of clauses 29 to 39, wherein the carbon phase is a substantially amorphous carbon phase.

[0197] Clause 41 . The composite material according to any one of clauses 29 to 40, wherein the rod morphology comprises rods having a length of at most about 90 pm, such as at most about 80 pm.

[0198] Clause 42. The composite material according to any one of clauses 29 to 41 , wherein the rod morphology comprises rods having a length of at least about 20 pm, such as at least about 40 pm.

[0199] Clause 43. The composite material according to any one of clauses 29 to 42, wherein the rod morphology comprises rods having a length of from about 20 pm to about 90 pm, optionally from about 40 pm to about 80 pm.

[0200] Clause 44. The composite material according to any one of clauses 29 to 43, wherein the rod morphology comprises rods each comprising a core comprising the metal or metalloid phase; optionally wherein the metal or metalloid phase comprises nanoparticles (optionally agglomerated nanoparticles) of at most about 15 nm in size, such as at most about 12 nm in size.

[0201] Clause 45. The composite material according to any one of clauses 29 to 44, wherein the metal or metalloid phase comprises nanoparticles of at least about 1 nm in size, such as at least about 2 nm in size.

[0202] Clause 46. The composite material according to any one of clauses 29 to 45, wherein the metal or metalloid phase comprises nanoparticles of from about 1 nm to about 15 nm in size, such as from about 2 nm to about 10 nm in size.

[0203] Clause 47. The composite material according to any one of clauses 29 to 46, wherein the rod morphology comprises rods each comprise a metal or metalloid phase core surrounded by a carbon shell, optionally a substantially amorphous carbon shell. Clause 48. The composite material according to clause 47, wherein the metal or metalloid phase core is formed from agglomerated nanoparticles.

[0204] Clause 49. The composite material according to clauses 47 or 48, wherein the shell has a thickness of at most about 20 nm, such as about 15 nm.

[0205] Clause 50. The composite material according to any one of clauses 47 to 49, wherein the shell has a thickness of at least about 5 nm, such as about 10 nm.

[0206] Clause 51 . The composite material according to any one of clauses 47 to 50, wherein the shell has a thickness of from about 5 nm to about 20 nm, such as about 10 nm to about 15 nm.

[0207] Clause 52. The composite material according to any one of clauses 29 to 51 , wherein the carbon phase is derived from a carbonaceous polymer (e.g. by carbonisation thereof).

[0208] Clause 53. The composite material according to clause 52, wherein the carbon phase is derived from a carbonaceous polymer comprising polyester.

[0209] Clause 54. The composite material according to clause 53, wherein the carbon is derived from a carbonaceous polymer comprising aromatic residues, optionally teroterephthalate and / or naphthalate residues (e.g. aliphatic teroterephthalate and / or naphthalate), optionally wherein the carbonaceous polymer comprises polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN) or polytrimethylene terephthalate (PTT), or mixtures thereof.

[0210] Clause 55. The composite material according to clause 54, wherein the carbon phase is derived from a carbonaceous polymer comprising polyethylene terephthalate (PET).

[0211] Clause 56. The composite material according to clause 52, wherein the carbon phase is derived from a carbonaceous polymer comprising a polyamide, optionally nylon; and / or wherein the carbonaceous polymer comprises polystyrene.

[0212] Clause 57. The composite material according to any one of clauses 29 to 56, further comprising carbon nanotubes (CNTs), optionally multi-walled carbon nanotubes (MWCNTs).

[0213] Clause 58. The composite material according to any one of clauses 29 to 57 comprises voids between the rods.

[0214] Clause 59. The composite material according any one of clauses 29 to 58, wherein the composite material is prepared by the method according to any one of clauses 1 to 27. Clause 60. The composite material of any one of clauses 29 to 58 obtained or obtainable by a method according to any one of clauses 1 to 27.

[0215] Clause 61 . An electrode (e.g. anode) material for a rechargeable electrochemical cell, the electrode material comprising a composite material according to any one of clauses 28 to 60.

[0216] Clause 62. The electrode material according to clause 61 further comprising a carboxymethyl cellulose binder.

[0217] Clause 63. The electrode material according to clause 62, comprising the composite material and the carboxymethyl cellulose binder in a weight ratio of from about 20: 1 to about 1 : 1 , such as about 15: 1 to about 3: 1 , for example about 12: 1 to about 5: 1 , optionally about 9:1.

[0218] Clause 64. The electrode material according to any one of clauses 61 to 63, which is for a sodium ion battery.

[0219] Clause 65. The electrode material according to clause 64, wherein the electrode material comprises an alloy of sodium and tin, optionally Nai5Sn4.

[0220] Clause 66. The electrode material according to any one of clauses 61 to 65, wherein the electrode material has a capacity of at least about 100 mAhg1, such as at least about 200 mAhg- 1 , for example at least about 400 mAhg1

[0221] Clause 67. The electrode material according to any one of clauses 61 to 66, wherein the electrode material has a power density of at least about 80 Wh / 36Ah, such as at least about 90 Wh / 36Ah.

[0222] Clause 68. The electrode material according to any one of clauses 61 to 67, wherein the electrode material has a capacity which decreases by about 5% or less after 100 cycles.

[0223] Clause 69. A kit of parts for assembling a sodium ion battery, the kit comprising the electrode material according to any one of clauses 61 to 68 and an electrolyte (optionally comprising a solution of NaPFe and a solvent mixture of ethylene carbonate, dimethyl carbonate and fluoroethylene carbonate).

[0224] Clause 70. A sodium ion battery comprising the electrode material according to any one of clauses 61 to 68. Clause 71 . The sodium ion battery according to clause 70, comprising an electrolyte comprising a solution of NaPFe and a solvent mixture of ethylene carbonate, dimethyl carbonate and fluoroethylene carbonate.

[0225] Clause 72. Use of the electrode material according to any one of clauses 61 to 68 in a sodium ion battery.

[0226] Clause 73. Use of a precursor serving as acetate templating agent in the manufacture of a composite material comprising a carbon phase derived from a carbonaceous polymer.

[0227] Any listing or discussion of an apparently prior-published document in this specification should not necessarily be taken as an acknowledgement that the document is part of the state of the art or common general knowledge. All references disclosed herein are to be considered to be incorporated herein by reference.

[0228] Those skilled in the art will recognise or be able to ascertain using no more than routine experimentation many equivalents to the specific embodiments described herein. The scope of the present embodiments described herein is not intended to be limited to the above description, but rather is as set forth in the appended clauses. Those of ordinary skill in the art will appreciate that various changes and modifications to this description may be made without departing from the spirit or scope of the present disclosure, as defined in the following clauses.

Claims

Claims1 . A method of preparing a composite material, the method comprising: mixing a carbonaceous polymer with an acetate templating agent; and carbonising at a temperature of at least about 500°C.

2. The method according to claim 1 , wherein the composite material comprises a rod morphology, optionally wherein the rods have a length of at most about 100 pm, such as at most about 90 pm; such as at most about 80 pm.

3. The method according to claim 2, wherein the rods each comprise a core and a shell; optionally wherein the core is derived from the acetate templating agent (e.g. wherein the core is formed during said carbonising) and / or wherein the shell is derived from the carbonaceous polymer (e.g. wherein the shell is formed during said carbonising).

4. The method according to any preceding claim, wherein the carbonaceous polymer and the acetate templating agent are mixed in a weight ratio of at least about 1 : 4, such as at least about 1 : 3, for example at least about 1 : 2, the weight ratio being based on the weights carbonaceous polymer relative to the weight of the templating agent.

5. The method according to any preceding claim, wherein the carbonaceous polymer comprises a polyester, optionally wherein the carbonaceous polymer comprises polyethylene terephthalate (PET) and / or optionally wherein the carbonaceous polymer is substantially free of pigments, dyes, and / or titanium oxide.

6. The method according to any preceding claim, wherein the acetate templating agent is:(i) a metal acetate templating agent, optionally tin acetate; and / or(ii) a metalloid acetate templating agent.

7. The method according to any preceding claim, wherein carbonising is at a temperature of from about 600°C to about 1300°C, for example about 650°C to 1200°C, such as about 700°C to about 1100°C; and wherein carbonising occurs at autogenic pressure, optionally: at most about 150 atm, optionally at most about 120 atm , for example at most about 100 atm optionally at most about 90 atm, for example at most about 80 atm.

8. The method according to any preceding claim, further comprising mixing a conductive additive with the carbonaceous polymer and the acetate templating agent prior to carbonising, whereinthe carbon additive is carbon nanotubes (CNTs), such as multi-walled carbon nanotubes (MWCNTs) or single-walled carbon nanotubes (SWCNTs). wherein the conductive additive and the carbonaceous polymer are mixed in a weight ratio of: at least about 0.05: 100, optionally at least about 0.1 : 100, optionally at least about 0.5: 100; the weight ratio being based on the weights of the conductive additive relative to the combined weight of the carbonaceous polymer and the acetate templating agent.

9. A composite material comprising a carbon phase; and a metal or metalloid phase derived from an acetate templating agent; wherein the weight ratio of the carbon phase to the metal or metalloid phase is from about 1 :1 to about 5:1 , based on the weights of the carbon phase relative to the weight of the templating agent; and wherein the phases collectively have a rod morphology; wherein the rods have a length of at most about 100 pm.

10. The composite material according to claim 9, wherein the weight ratio of the carbon phase to the metal or metalloid phase is from about 1 .5: 1 to about 4: 1 ; optionally about 2:1 to about 4:1 , optionally at least about 2:1 to about 3:1 , the weight ratio being based on the weights of the carbon phase relative to the weight of the metal or metalloid phase.11 . The composite material according to claim 9 or 10, wherein the composite material comprises: from about 50 wt% to about 90 wt%, such as from about 60 wt% to 80 wt%; for example from about 65 wt% to about 75% of the carbon phase; and from about 10 wt% to about 50 wt%, such as from about 20 wt% to 40 wt%; for example from about 25 wt% to about 35% of the metal or metalloid phase; optionally wherein the composite material comprises 70 wt% of the carbon phase and about 30 wt% of the metal or metalloid phase, wherein the wt% is based on the total weight of the composite material.

12. The composite material according to any one of claims 9 to 11 wherein the metal or metalloid phase comprises (a) metal or metalloid; and (b) metal oxide or metalloid oxide, optionally wherein the metal or metalloid phase is a tin phase and comprises (a) tin; and (b) tin oxide,13. The composite material according to any one of claims 9 to 12 optionally wherein wherein the comprise material comprises XRD peaks with the following characteristic peaks at 20 at from about 26 to 28°; and from about 31 to 33°; and from about 32 to 34°; and from about 43 to 45°; and from about 44 to 46°; and / from about 52 to 54°.

14. The composite material according to any one of claims 9 to 13, wherein the rod morphology comprises rods having a length of from about 20 pm to about 90 pm, optionally from about 40 pm to about 80 pm; and / or wherein the rod morphology comprises rods each comprising a core comprising the metal or metalloid phase; wherein the metal or metalloid phase comprises agglomerated nanoparticles of at most about 15 nm in size, such as at most about 12 nm in size.

15. The composite material according to any one of claims 9 to 14 wherein the metal or metalloid phase comprises nanoparticles of from about 1 nm to about 15 nm in size, such as from about 2 nm to about 10 nm in size; and wherein the rods each comprise a metal or metalloid phase core surrounded by a substantially amorphous carbon shell; and wherein the metal or metalloid phase core is formed from agglomerated nanoparticles; and wherein the shell has a thickness of from about 5 nm to about 20 nm, such as about 10 nm to about 15 nm.

16. The composite material according to any one of claims 9 to 15, wherein the carbon phase is derived from a carbonaceous polymer comprising polyester, optionally wherein the carbon phase is derived from a carbonaceous polymer comprising polyethylene terephthalate (PET).

17. The composite material according to any one of claims 9 to 16, further comprising carbon nanotubes (CNTs), optionally multi-walled carbon nanotubes (MWCNTs).

18. The composite material according to any one of claims 9 to 17 comprising voids between the rods.

19. The composite material according any one of claims 9 to 18, wherein the composite material is prepared by the method according to any one of claims 1 to 8.

20. An electrode (e.g. anode) material for a rechargeable electrochemical cell, the electrode material comprising a composite material according to any one of claims 9 to 19.

21. The electrode material according to claim 20 further comprising a carboxymethyl cellulose binder.

22. A kit of parts for assembling a sodium ion battery, the kit comprising the electrode material according to claims 20 or 21 and an electrolyte (optionally comprising a solution of NaPFe and a solvent mixture of ethylene carbonate and dimethyl carbonate).

23. A sodium ion battery comprising the electrode material according to claim 20 or 21 , optionally comprising an electrolyte comprising a solution of NaPFe and a solvent mixture of ethylene carbonate, dimethyl carbonate and fluoroethylene carbonate.

24. Use of the electrode material according to claim 20 or 21 in a sodium ion battery.

25. Use of an acetate templating agent in the manufacture of a composite material comprising a carbon phase derived from a carbonaceous polymer.

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