WO2025123086A1

WO2025123086A1 - Composite organic electrode materials, organic electrochemical devices and preparation methods thereof

Info

Publication number: WO2025123086A1
Application number: PCT/AU2024/051341
Authority: WO
Inventors: Shizhang Qiao; Xin Xu
Original assignee: University of Adelaide
Current assignee: Adelaide University
Priority date: 2023-12-12
Filing date: 2024-12-12
Publication date: 2025-06-19
Anticipated expiration: 2026-06-12

Abstract

The present disclosure provides a composite electrode material comprising submicrometer particles of an oxocarbon salt (eg a monocyclic oxocarbon alkali metal salt having a formula of M_m(CO)_n (wherein M = Li, Na or K; 2 ≤ m ≤6; n= 4, 5 or 6), and a functionalised carbon-based material (eg graphene oxide). The composite electrode material may be suitable for use in an electrochemical device under ultra-low temperature conditions.

Description

COMPOSITE ORGANIC ELECTRODE MATERIALS, ORGANIC ELECTROCHEMICAL DEVICES AND PREPARATION METHODS THEREOF

PRIORITY DOCUMENT

[0001] The present application claims priority from Australian Provisional Patent Application No. 2023904029 titled “COMPOSITE ORGANIC ELECTRODE MATERIALS, ORGANIC ELECTROCHEMICAL DEVICES AND PREPARATION METHODS THEREOF” and fded on 12 December 2023, the content of which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

[0002] The present disclosure relates generally to electrochemical devices. In a particular form, the present disclosure relates to an organic electrochemical device comprising a composite organic electrode material prepared from an oxocarbon salt.

BACKGROUND

[0003] Building rechargeable batteries for use at high-latitude/altitude regions and in deep- sea/defense/aerospace explorations presents unique challenges due to the extreme environmental conditions under which the batteries need to operate. These applications require reliable energy storage systems capable of functioning efficiently in ultra-low-temperature (for example < -40 °C) environments. Conventional batteries often struggle to maintain their performance under such extreme conditions.

[0004] Organic batteries have emerged as a promising alternative to conventional batteries in ultra-low- temperature applications. Organic batteries have some distinct advantages such as natural abundance and low cost of electrode materials, and especially fast kinetics associated with their flexible molecular structures and surface-controlled reactions, which bypass the solid-state diffusion limitations for the inorganic hosts.^{1 7} Organic electrode materials (OEMs) have been applied in various energy storage devices due to their universal properties. Examples of such devices are nonaqueous Li-ion, Na-ion, K-ion, dual-ion batteries, multivalent-metal batteries, aqueous batteries, all-solid-state batteries, and redox flow batteries. OEMs can deliver remarkable performance in rechargeable batteries under extreme conditions such as wide temperature ranges (-70 °C to 150 °C), wide pH ranges, and in the presence of O2. Various types of organic biomass have been used to prepare electrode materials for energy storage devices. For example, supercapacitors have been fabricated using cotton, bacterial cellulose (cellulose nanofibers), silk, lignin, starch, sucrose, chitosan, bamboo, basswood, gelatin, peanut shells, chitin, and sisal leaves. [0005] However, OEMs may suffer from issues such as low electronic conductivity, low redox stability, and rapid capacity attenuation. The battery performance for OEMs is determined by the redox-active functional groups. Generally, the reduction of unsaturated bonds such as C=C, C=N, and C=O in organic molecules form radical intermediates and produce a negative charge on N or O atoms, and an unpaired electron on C atoms.^{8 9} These organic intermediates are unstable and can dissolve in the electrolyte which eventually results in capacity loss, and thus leads to unsatisfactory cycling stability.^{10 11} Over the past decades, various strategies have been proposed to prevent the dissolution and formation of metastable active organic materials.¹² For example, designing functional separators, polymerizing redox-active compounds, and tailoring electrolytes^{13 14}, which enhance the stability of organic electrodes.

[0006] There is a need for new or improved organic electrode materials that can alleviate or overcome one or more technical problem and can be used under ultra-low temperature conditions. Alternatively, or in addition, there is a need for an alternative to known organic electrode materials that can alleviate or overcome one or more technical problem and can be used under ultra-low temperature conditions.

SUMMARY

[0007] According to a first aspect, there is provided a composite electrode material comprising submicrometer particles of an oxocarbon salt and a functionalised carbon-based material.

[0008] In some embodiments of the first aspect, the functionalised carbon-based material is loaded over the particles of the oxocarbon salt.

[0009] In some embodiments of the first aspect, the particles of the oxocarbon salt are crystalline particles.

[0010] In some embodiments of the first aspect, the functionalised carbon-based material comprises, or is, graphene oxide.

[0011] In some embodiments of the first aspect, the composite electrode material is a composite organic electrode material, which comprises submicrometer particles of the oxocarbon salt and graphene oxide, wherein the oxocarbon salt is derived from a natural source.

[0012] In some embodiments of the first aspect, the oxocarbon salt comprises or is a monocyclic oxocarbon salt. In some further embodiments, the oxocarbon salt comprises or is a monocyclic oxocarbon metal salt. In some further embodiments, the oxocarbon salt comprises or is a monocyclic oxocarbon alkali metal salt, for example, sodium salt, lithium salt and/or potassium salt. In even further embodiments, the oxocarbon salt comprises or is a monocyclic oxocarbon alkali metal salt having a formula of M_m(C0)_n (wherein M = Li, Na or K; 2 < m < 6; n= 4, 5 or 6). In even further embodiments, the oxocarbon salt comprises or is a monocyclic oxocarbon alkali metal salt having a formula of M2(C0)_n (wherein M = Li, Na or K; n = 4, 5 or 6). In even further embodiments, the oxocarbon salt comprises or is a monocyclic oxocarbon alkali metal salt having a formula of M_m(C0)6 (wherein M = Li, Na or K; 2 < m < 4, for example, m is 2, 2.5, 3, 3.5, or 4). In a preferred embodiment, the oxocarbon salt comprises or is a sodium rhodizonate (i.e. NazCeOe).

[0013] In some embodiments of the first aspect, the longest dimension of the submicrometer particles is about 5 nm to about 800 nm, for example about 100 nm to about 800 nm. In some further embodiments, the longest dimension of the submicrometer particles is about 200 nm to about 600 nm. In even further embodiments, the longest dimension of the submicrometer particles is about 400 nm to about 500 nm.

[0014] In some embodiments of the first aspect, the crystalline submicrometer particles of the oxocarbon salt comprise or have a rod-like morphology, a sphere-like morphology, a diamond-like morphology and/or an irregular morphology. In some further embodiments, the crystalline submicrometer particles of the oxocarbon salt comprise a diamond-like morphology. In even further embodiments, the crystalline submicrometer particles of the oxocarbon salt have a diamond-like morphology.

[0015] In some embodiments of the first aspect, the functionalised carbon-based material is graphene oxide which comprises or is a single layer graphene oxide. In some further embodiments, the single layer graphene oxide has a thickness of about 0.7 nm to about 1.2 nm.

[0016] In some embodiments of the first aspect, the graphene oxide has a water solubility of > about 5 mg/ml at room temperature. In some further embodiments, the graphene oxide has a water solubility of > about 8 mg/ml at room temperature. In some further embodiments, the graphene oxide has a water solubility of > about 10 mg/ml at room temperature.

[0017] In some embodiments of the first aspect, the oxocarbon salt and the functionalised carbon-based material are present in a weight ratio of about 12:1 to about 2:1. In some further embodiments, the oxocarbon salt and the functionalised carbon-based material are present in a weight ratio of about 10:1 to about 3:1, for example about 8:1 to about 4:1. In even further embodiments, the oxocarbon salt and the functionalised carbon-based material are present in a weight ratio of about 5:1. In even further embodiments, when the composite electrode material consists of submicrometer particles of the monocyclic oxocarbon alkali metal salt (for example, NazCeOe) and graphene oxide, the oxocarbon salt and the graphene oxide are in a weight ratio of about 5:1. [0018] In some embodiments of the first aspect, the composite electrode material further comprises a functional material, such as an aerogel. In some further embodiments, the functional material is selected from sodium alginate, chitosan and agarose.

[0019] In some embodiments of the first aspect, the composite electrode material displays a decreased contact angle and increased interfacial wettability compared to those of the individual oxocarbon salt.

[0020] In some embodiments of the first aspect, an electrode prepared from the composite electrode material exhibits a capacity of about 110 mAh g ¹ to about 125 mAh g ¹ (for example, 119 mAh g ') at -50 °C in half-cell configurations.

[0021] In some embodiments of the first aspect, the composite electrode material is used in an electrochemical device under ultra-low temperature conditions. In some further embodiments, the composite electrode material is used in an electrochemical device at a temperature of < about -30 °C. In some further embodiments, the composite electrode material is used in an electrochemical device at a temperature of < about -40 °C. In ever further embodiments, the composite electrode material is used in an electrochemical device at a temperature of < about -50 °C. In even further embodiments, the composite electrode material is used in an electrochemical device at a temperature of < about -70 °C.

[0022] According to a second aspect, there is provided a method for preparing a composite electrode material, the method comprising:

(i) forming a first composition comprising an oxocarbon salt, water and, optionally, an antisolvent,

(ii) forming a second composition comprising a functionalised carbon-based material, water and, optionally, an antisolvent,

(iii) combining the first composition and the second composition to obtain a third composition, and

(iv) introducing an amount of an antisolvent into the third composition under conditions to allow formation of a precipitate comprising submicrometer particles of the oxocarbon salt and the functionalised carbon-based material.

[0023] In some embodiments of the second aspect, the method for preparing a composite electrode material comprises:

(i) introducing an oxocarbon salt into a first mixture comprising water and an antisolvent to obtain the first composition, (ii) introducing a functionalised carbon-based material into a second mixture comprising water and an antisolvent to obtain the second composition,

[0024] In some embodiments of the second aspect, the composite electrode material is a composite electrode material according to the first aspect. In some further embodiments, the method further comprises

(v) subjecting the precipitate to conditions that allow or improve crystallisation of the oxocarbon salt if a crystalline state is desired for the precipitate obtained from (iv) and the latter dose not achieve the crystalline state.

[0025] In some embodiments of the second aspect, the antisolvents used in steps (i), (ii) and (iv) are the same. In some embodiments, each of the antisolvents used in steps (i), (ii) and (iv) is selected from an alcohol, an ether, a ketone and a combination thereof. In some further embodiments, the alcohol is selected from methanol, ethanol, n-propanol, iso-propanol, iso-butanol, and a combination thereof. In some further embodiments, the alcohols used in steps (i), (ii) and (iv) are the same. In even further embodiments, each of the alcohols used in steps (i), (ii) and (iv) is ethanol.

[0026] In some embodiments of the second aspect, water and the antisolvent comprised in each of the first and second compositions or in each of the first and second mixtures are in a volume ratio of > about 1:1. In some further embodiments, water and the antisolvent comprised in each of the first and second compositions or in each of the first and second mixtures are in a volume ratio of > about 1.5:1. In even further embodiments, water and the antisolvent comprised in each of the first and second compositions or in each of the first and second mixtures are in a volume ratio of > about 2:1. In even further embodiments, the first mixture is the same as the second mixture.

[0027] In some embodiments of the second aspect, each of the first and second mixtures consist of water and ethanol. In some further embodiments, each of the first and second mixtures consist of water and ethanol in a volume ratio of about 2:1.

[0028] In some embodiments of the second aspect, the amount of the antisolvent added to the third composition and the total amount of water in the first and second compositions are in a volume ratio of about 6:1 to about 9:1. In some further embodiments, the amount of the antisolvent added to the third composition and the total amount of water in the first and second compositions are in a volume ratio of about 7.5:1.

[0029] In some embodiments of the second aspect, the oxocarbon salt and the functionalised carbonbased material are used in a weight ratio of about 12:1 to about 2:1. In some further embodiments, the oxocarbon salt and the functionalised carbon-based material are used in a weight ratio of about 10:1 to about 3:1, for example about 8:1 to about 4:1. In even further embodiments, the oxocarbon salt and the functionalised carbon-based material are used in a weight ratio of about 5:1. In even further embodiments, when the composite electrode material consists of submicrometer particles of a monocyclic oxocarbon alkali metal salt (for example, NazCeCk) and graphene oxide, the monocyclic oxocarbon alkali metal salt and the graphene oxide are used in a weight ratio of about 5:1.

[0030] In some embodiments of the second aspect, the step (iv) of introducing an amount of an antisolvent into the third composition under conditions to allow formation of a precipitate comprising submicrometer particles of the oxocarbon salt and the functionalised carbon-based material is carried out at a temperature between about 0 °C to about 70 °C, for example at about 20 °C or at about 30 °C. In some further embodiments, in step (iv), the antisolvent is added into the third composition. In even further embodiments, in step (iv), the antisolvent is added at one time into the third composition. In even further embodiments, the step (iv) is carried out with stirring or agitation, for example under sonication.

[0031] According to a third aspect, there is provided an electrochemical device comprising a composite electrode material according to the first aspect or obtained according to the method of the second aspect.

[0032] According to a fourth aspect, there is provided a use of a composite electrode material according to the first aspect or obtained according to the method of the second aspect in preparing an electrochemical device.

[0033] According to a fifth aspect, there is provided a use of a composite electrode material according to the first aspect or obtained according to the method of the second aspect in an electrochemical device.

[0034] In some embodiments of the third, fourth or fifth aspect, the electrochemical device is operable at a temperature of < about -30 °C. In some further embodiments, the electrochemical device is operable at a temperature of < about -40 °C. In some further embodiments, the electrochemical device is operable at a temperature of < about -50 °C. In even further embodiments, the electrochemical device is operable at a temperature of < about -60 °C. In even further embodiments, the electrochemical device is operable at a temperature of < about -70 °C. [0035] In some embodiments of the third, fourth or fifth aspect, the electrochemical device is selected from a battery, a cell, a photovoltaic device, and a capacitor. In some further embodiments, the electrochemical device is a secondary battery. In even further embodiments, the electrochemical device is an ion secondary battery.

[0036] In some embodiments of the third, fourth or fifth aspect, the electrochemical device comprises the composite electrode material as anode material. In some further embodiments, the electrochemical device comprises MnFe-Prussian blue analogue (PBA) as cathode material. In some further embodiments, the MnFe-Prussian blue analogue (PBA) is Na2MnFe(CN)6. In even further embodiments, the anode material is a composite electrode material which consists of crystalline submicrometer particles of NazCeOr, and graphene oxide. In even further embodiments, the electrochemical device comprises NaPF₍₎ in diethylene glycol dimethyl ether (DGM) as electrolyte.

[0037] In some embodiments of the third, fourth or fifth aspect, the electrochemical device comprises the composite electrode material as cathode material. In some further embodiments, the composite electrode material comprises reduced state sodium terephthalate (Na4TP) as anode material. In some further embodiments, the cathode material is a composite electrode material which consists of crystalline submicrometer particles of NazCeOr, and graphene oxide. In even further embodiments, the electrochemical device comprises NaPF₍₎ in diethylene glycol dimethyl ether as electrolyte.

[0038] In some embodiments of the third, fourth or fifth aspect, the electrochemical device delivers cycling stability over 7000 cycles at about -40 °C. In some further embodiments, the electrochemical device maintains a discharge capacity of about 95 mAh g ¹ to 110 mAh g ¹ (for example, 101 mAh g ') over 7000 cycles at a high current density of 300 mA g ¹ and about -40 °C.

[0039] In some embodiments of the third, fourth or fifth aspect, the electrochemical device exhibits a capacity of about 130 mAh g ¹ to about 140 mAh g ¹ (for example, 136 mAh g ') over 300 cycles at a current density of 100 mA g ¹ and about -30 °C.

[0040] In some embodiments of the third, fourth or fifth aspect, the electrochemical device is a pouch full-cell, and the pouch full cell powers four light-emitting diodes (LEDs, 2.0 V) continuously for over 1.5 hours at -50 °C.

BRIEF DESCRIPTION OF THE FIGURES

[0041] Embodiments of the present disclosure will be discussed with reference to the accompanying figures wherein: [0042] Figure 1 shows solid-liquid-solid conversion reaction in disodium rhodizonate (DSR): (a) Operando Raman spectra of submicrometer disodium rhodizonate (sub-DSR) and corresponding dischargecharge profile; (b) Operando Raman 3D projection contour plot for Na||sub-DSR/graphene oxide (GO) cell;

(c) Raman spectra of sub-DSR/GO electrode at different discharge and charge states and corresponding discharge-charge profile.

[0043] Figure 2 shows cell performance is enhanced via GO incorporation: (a) Galvanostatic voltage profile for the 5^th cycle of Na||DSR at 500 mA g '; (b) Molecular structures of DSR (NazCeOe) and NtuCeOr,. accompanying with photographs of diethylene glycol dimethyl ether (DGM) solutions immersed with purchased DSR and synthesized Na4C6O6; (c) Cycling performance of Na||DSR at 300 mA g ¹ and 30 °C;

(d) scanning electron microscope (SEM) image of sub-DSR; (e) SEM image of sub-DSR/GO composites; (f) Cycling performance of Na||sub-DSR/GO at 300 mA g ¹ and 30 °C.

[0044] Figure 3 shows kinetic investigations of cells: (a) cyclic voltammetry (CV) curves of sub-DSR; (b) CV curves of sub-DSR/GO electrodes at various temperatures; (c) Arrhenius plot for peak cathodic current of C2 of sub-DSR and sub-DSR/GO.

[0045] Figure 4 shows analysis of molecular structure: (a) operando Fourier-transform infrared spectroscopy (FTIR) contour map of sub-DSR electrode for sodium-ion storage; (b) operando FTIR contour map of sub-DSR/GO electrode for sodium-ion storage; (c) FTIR spectra of prepared (I) sub-DSR and (II) sub-DSR/GO powder and the selected operando spectra corresponding to pristine, fully discharged (1.0 V) and charged (3.2 V) states for the initial two cycles; synchrotron X-ray absorption spectroscopy of (d) O and (e) C K-edge for sub-DSR and sub-DSR/GO powder.

[0046] Figure 5 shows ultralow-temperature sodium storage properties: electrochemical properties of Na||sub-DSR/GO half-cell (a) cycling performance at a current density of 50 mA g ¹ and -50 °C and (b) corresponding discharge-charge profiles for different cycles; sodium storage performance for sub- DSR/GO||PBA full cells: (c) long-term cycling performance at -40 °C, current density of 100 mA g ¹, and 300 mA g ¹ (the inset), (d) cycling performance at an ultra-low temperature of -50 °C and a current density of 50 mA g ¹ with a sudden temperature change to RT, then dropping to -40 °C due to the power cut of the thermal chamber, (e) corresponding discharge-charge profiles for different cycles at -50 °C, and (f) comparison of cycling performance of this work and previously reported lithium and sodium-ion batteries at ultra-low temperatures. (Note: cells without marking temperature are measured at -40 °C).

[0047] Figure 6 shows pouch full cell performance at -50 °C: (a) digital image of single sub- DSR/GO||PBA pouch full cell; (b) discharge-charge profiles for single sub-DSR/GO||PBA pouch cell for different cycles; (c) long-term cycling performance for sub-DSR/GO||PBA pouch cell at current density 20 mA g ¹ and -50 °C (The mass loading for a single pouch cell is ca. 18.5 mg); and (d) two pouch full cells arranged in series power four green LEDs.

[0048] Figure 7 shows Raman spectra for (I) DSR powder and (II) sub-DSR/GO electrode.

[0049] Figure 8 shows X-ray diffraction (XRD) patterns of purchased DSR and synthesized Na4C6C>6 powder.

[0050] Figure 9 shows SEM images of sub-DSR in diamond-like shape with different sizes, synthesized using different precursor solution volumes (a) 90 ml and (b) 60 ml and PLO/EtOH in volume ratio of 2:1.

[0051] Figure 10 shows optical images of separators obtained from (a) sub-DSR and (b) sub-DSR/GO half-cell configured with 1 M NaPE₍₎-DGM electrolyte after three cycles at a fully discharged state of 1.0 V.

[0052] Figure 11 shows cycling performance of sub-DSR and sub-DSR/GO at a current density of 1000 mA g ¹ and a temperature of 30 °C.

[0053] Figure 12 shows the first discharge-charge profiles of (a) sub-DSR and (b) sub-DSR/GO at 30 °C and 1000 mA g '.

[0054] Figure 13 shows rate capability of sub-DSR/GO at 30 °C.

[0055] Figure 14 shows in-situ electrochemical impedance spectroscopy (EIS) plots of Na||sub-DSR for the 1^st cycle (a) and the 2^nd cycle (b). The discharge-charge range between 1.0 ~ 3.2 V at 100 mA g ¹ and room temperature (RT).

[0056] Figure 15 shows in-situ EIS plots of Na||sub-DSR/GO for the 1^st cycle (a) and the 2^nd cycle (b). The discharge-charge range between 1.0 ~ 3.2 V at 100 mA g ¹ and RT.

[0057] Figure 16 shows contact angle measurement on (a) sub-DSR, and (b) sub-DSR/GO electrode.

[0058] Figure 17 shows EIS for a) sub-DSR and b) sub-DSR/GO at varying temperatures.

[0059] Figure 18 shows FTIR spectra of (I) sub-DSR and (II) sub-DSR/GO powder.

[0060] Figure 19 shows synchrotron X-ray absorption spectroscopy of Na K-edge for sub-DSR and sub- DSR/GO powders. [0061] Figure 20 shows synchrotron X-ray absorption spectroscopy of C K-edge for graphene oxide.

[0062] Figure 21 shows cycling performance of sub-DSR and sub-DSR/GO half-cell at current density of 200 mA g ¹ and -30 °C.

[0063] Figure 22 shows discharge-charge profile of Na||sub-DSR/GO at current density 100 mA g ¹ and -30 °C.

[0064] Figure 23 shows rate capability of Na||sub-DSR/GO at -30 °C.

[0065] Figure 24 shows CV curves of Na||sub-DSR/GO at different scan rate and -30 °C.

[0066] Figure 25 shows continuous cycling measurements after a 4200 cycling test of sub- DSR/GO||PBA at -40 °C and current density of 300 mA g ¹. The interrupted test is due to the laboratory relocation and retesting the cell after a half month.

[0067] Figure 26 shows rate capability at current density ranging from 50 to 1000 mA g ¹ at -40 °C.

[0068] Figure 27 shows (a) temperature-dependent rate performance of sub-DSR/GO||PBA at current density of 100 mA g (b) corresponding EIS at different temperatures.

[0069] Figure 28 shows (a) cycling performance of Na4TP||sub-DSR/GO full organic cell at current density of 100 mA g ¹ and -30 °C. The specific capacity is based on the mass of sub-DSR/GO. (b) corresponding discharge-charge profiles for different cycles.

[0070] Figure 29 shows digital images of (a) two sub-DSR/GO||PBA pouch full cells in series and (b) tested in a thermal chamber at -50 °C.

DESCRIPTION OF EMBODIMENTS

[0071] The term “electrochemical device” used herein refers to a device that can convert chemical energy into electrical energy through an electrochemical reaction, such as a battery, a cell, a capacitor and a photovoltaic device. The battery may be a secondary battery, for example an ion secondary battery. A secondary battery is a type of electrical battery which can be charged, discharged into a load, and recharged many times, as opposed to a disposable or primary battery, which is supplied fully charged and discarded after use. Ion batteries are rechargeable batteries in which ions (particularly metal ions) move from the negative electrode to the positive electrode and then come back during the charging and discharging processes. [0072] The term “electrode material” used herein refers to an active material for a cathode or an anode of an electrochemical device. The term “cathode material” used herein refers to an active material for the cathode of an electrochemical device. The term “anode material” used herein refers to an active material for the anode of an electrochemical device.

[0073] The term “organic electrode material” used herein refers to an electrode material that may be derived from biomass. Many organic electrode materials can be synthesised from biomass using greenchemistry techniques that have negligible impact on the environment. For example, the organic electrode dilithium rhodizonate (LizCeOe) can be prepared from the natural sugar myo-inositol, which exists in corn plants in the hexaphosphate form.

[0074] The term “oxocarbon salt” used herein refers to salt compounds in which all, or nearly all, of the carbon atoms bear ketonic oxygen functions or their hydrated equivalents. An example of the oxocarbon salts is monocyclic oxocarbon salts. Further explanation is made hereinafter.

[0075] The term “ultra-low temperature” used herein refers to a temperature < about -30 °C, for example, < about -40 °C, < about -50 °C, < about -60 °C, or < about -70 °C.

[0076] The term “submicrometer” used herein refers to a size less than 1000 nanometers, for example, 5 nanometers to less thanlOOO nanometers, or 10 nanometers to 800 nanometers.

[0077] The term “functionalised carbon-based material” used herein refers to a carbon-based material that has functional groups. The functional groups may be chosen to increase the hydrophilicity of the carbon material which, in turn, may render the carbon-based material more suitable for use in an aqueous environment. For example, the functional groups may contain oxygen. The oxygen functional groups include, but are not limited to, hydroxyl, ketone, lactone, carboxyl, quinone and/or epoxy.

[0078] The present disclosure arises from the inventors’ finding that graphene oxide in a composite electrode material (for example, a composite organic monocyclic oxocarbon salt) effectively anchors unstable intermediate organic species and enables fast conversion reaction kinetics on the electrode during cycling with ultra-long-term stability. The n-conjugation interactions of graphene oxide effectively delocalise energy density of the unpaired electrons on C atoms of the electrode material (such as NazCeCT). and thereby significantly decreased side reactions on C atoms with clear C=C band for the composite electrode. The intermediates interact with n-electron clouds of graphene oxide forming a charge transfer complex through 71-71 interaction, which enables the redox reactivity to be tuned and side reactions of the electrode to be suppressed during the carbonyl redox process (C=0<->C-0 ). It has also been found that a smaller particle size with increased contact area accelerated the charge transfer and shortened metal ion (for example, alkali metal ion) diffusion pathways, which in turn improved the electrochemical performance of the composite electrode material. The composite electrode material comprising graphene oxide showed a decreased contact angle with increased interfacial wettability. The 71-71 interactions and increased interfacial wettability between an oxocarbon salt (for example, a monocyclic oxocarbon salt) and graphene oxide significantly boosted overall kinetics and advantageously affected the activation energy of the electrode, which led to a stable resistance at an ultra-low temperature with more efficient carbonyl redox reactions.

[0079] Accordingly, the present disclosure provides a composite electrode material comprising submicrometer particles of an oxocarbon salt and a functionalised carbon-based material.

[0080] Organic electrode materials have been extensively investigated for rechargeable batteries due to their low cost, abundance, environmental benignity, and high sustainability. Therefore, in a particular form, the composite electrode material may be a composite organic electrode material based on an oxocarbon salt and graphene oxide, wherein the oxocarbon salt is derived from a natural source. The carbonyl groups are known to act as redox active sites in oxocarbon salts.

[0081] Among oxocarbon salts, consideration may be given to monocyclic oxocarbon salts, especially monocyclic oxocarbon metal salts. The monocyclic oxocarbon metal salts include, but are not limited to, alkali metal salts, for example, sodium salt, lithium salt and/or potassium salt. The monocyclic oxocarbon alkali metal salt in a crystalline state may possess a layer structure and conjugate property ideal for the insertion/extraction of an alkali metal ion. If needed, a mixture of monocyclic oxocarbon metal salts might be used, for example a mixture of NazCsOs and NazCTCk.

[0082] For the purpose of illustration, the monocyclic oxocarbon alkali metal salt may have a formula of M_m(C0)_n (M = Li, Na or K; 2 < m <6; n= 4, 5 or 6). The “m” may be 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5 or 6. In an embodiment, the monocyclic oxocarbon alkali metal salt has a formula of M_m(C0)6 (M = Li, Na or K; 2 < m <4, for example, m is 2, 2.5, 3, 3.5, or 4). In another embodiment, the monocyclic oxocarbon alkali metal salt has a formula of M2(C0)_n (M = Li, Na or K; n = 4, 5 or 6). When n=4, it can be called a squarate salt or a salt of squaric acid. When n=5, it can be called a croconate salt or a salt of croconic acid. When n=6, it can be called a rhodiaonate salt or a salt of rhodizonic acid. Their molecular structures are shown below:

(i) squarate (ii) croconate (iii) rhodiaonate

[0083] Both croconic acid and rhodizonic acid are now known to be products of microbiological oxidation of myoinositol (hexa-hydroxycyclohexanc), a compound which is widely distributed in plants. M₂(CO)₅/M₂(CO)6 salts can insert two or four metal ions reversibly, while M₂(CO)4 might show less electrochemical activity. Taking Na₂(CO)s and Na₂(CO)6 as an example, the sodiation/de-sodiation mechanism are shown below.

[0084] It has been demonstrated that disodium rhodizonate (Na₂C&06) can deliver good rechargeable capacity. Given the high theoretical specific capacity 501 mAh g ¹ and earth abundance of disodium rhodizonate, it may be preferably selected for sodium ion batteries (SIBs). It has been reported that dilithium rhodizonate (LiTTCD exhibited a theoretical capacity of 590 mAh g ¹ based on a four-electron redox chemistry in lithium ion batteries.

[0085] The monocyclic oxocarbon alkali metal salt mentioned above can be prepared through one -pot proton exchange reactions with different metal ions (M=Li, Na, K) and frameworks (n=4, 5, 6) and may be used in rechargeable Li, Na, and K-ion batteries. The monocyclic oxocarbon alkali metal salt mentioned above may also be commercially available, for example from Sigma Aldrich.

[0086] The functionalised carbon-based material can be any suitable material. It is recommended that the functionalised carbon-based material to be used has functional groups (for example oxygen functional groups which include, but are not limited to, hydroxyl, ketone, lactone, carboxyl, quinone and/or epoxy) and n-electron clouds so as to anchor unstable intermediate organic species. In some situations, the functionalised carbon-based material is soluble in water. One suitable material is graphene oxide (GO). GO has various oxygen functional groups attached to the graphene lattice in random locations. Examples of the oxygen functional groups include epoxide C-Q-C, carbonyl C=O, hydroxyl C-OH, and carboxyl OH-C=O. The functional groups present on GO are polar, making it very hydrophilic and water-soluble. Without intending to be bound by theory, the present inventors propose that graphene oxide in the composite electrode material (for example, a composite organic monocyclic oxocarbon salt) can effectively anchor unstable intermediate organic species (for example, Na4C6O6) and enable fast conversion reaction kinetics on the electrode during cycling with ultra-long-term stability. The n-conjugation interactions of graphene oxide may also effectively delocalise energy density of the unpaired electrons on C atoms of the electrode material (such as NazCeOe). and thereby significantly decrease side reactions on C atom for the composite electrode.

[0087] The graphene oxide to be used herein may be in the form of powder, which is beneficial for better solubility. A dispersion of graphene oxide in water/ethylene glycol/dimethylformamide (DMF) or a dispersion of graphene oxide in water could be used. Graphene oxide is commercially available, for example from Hangzhou Gaoxi Technology Co., Ltd., China. The graphene oxide may also be prepared by a method known in the art, for example by Hummer's method or a modified Hummer's method, from pure graphite powder. For the purpose of the present disclosure, it may be preferable to use a single layer graphene oxide. The single layer graphene oxide may have a single layer thickness of about 0.70 to about 1.20 nm, for example about 0.75 nm, about 0.8 nm, about 0.85 nm, about 0.9 nm, about 0.95 nm, about 1.0 nm, about 1.05 nm, about 1.10 nm, about 1.15 nm, about 1.20 nm. Advantageously, the graphene oxide used herein has a water solubility of > about 5 mg/ml, > about 8 mg/ml, or even > about 10 mg/ml, at room temperature.

[0088] When used for the composite electrode material disclosed herein, it may be desirable for the oxocarbon salt to be in a crystalline state. There is no limitation on the morphology of the oxocarbon salt crystal within the composite electrode material. The oxocarbon salt crystal within the composite electrode material may comprise or have a rod-like morphology, a diamond-like morphology, a sphere-like morphology and/or an irregular morphology. In an embodiment, the crystalline submicrometer particles of the oxocarbon salt comprise or have a diamond-like morphology. [0089] Preferably, the submicrometer particles of the oxocarbon salt substantially comprise or consist of crystalline submicrometer particles. The present inventors propose that a smaller particle size with increased contact area accelerates the charge transfer and shortens metal ion (for example, alkali metal ion) diffusion pathways, which in turn can help improve the electrochemical performance of the composite electrode material. The size of the oxocarbon salt can be controlled by adjusting the precipitation conditions, such as the concentration of raw materials and the volume ratio of water to antisolvent (eg alcohol solvent) used in the precipitation. The submicrometer particles may have the longest dimension of about 5 nm to less than about 1000 nm, for example about 5 nm to about 800 nm. In some circumstances, the longest dimension of the crystalline submicrometer particles is about 200 nm to about 600 nm, or about 400 nm to about 500 nm, for example about 400 nm, 450 nm, or 500 nm.

[0090] In the case of NazCTCT in diamond-like morphology, it can be synthesised using a molecular selfassembly technique and a solvent exchange process. When a mixture of an alcohol and water (for example, water and ethanol) is used, NazCTCT can be transferred from water to the alcohol to induce self-assembly through intermolecular stacking interactions. The size of NazCTCk can be controlled by adjusting the concentration of raw materials and the volume ratio of water to the alcohol.

[0091] The weight ratio between the oxocarbon salt and the functionalised carbon-based material (for example, graphene oxide) within the composite electrode material may be chosen in order to stabilise the electrode during cycling. In some embodiments of the composite electrode material disclosed herein, the functionalised carbon-based material is loaded over the submicrometer particles of the oxocarbon salt. In choosing the weight ratio, considerations may be given to, for example, the conductivity of the composite electrode material, the sufficiency of active material (i.e. the oxocarbon salt), and structural integrity during electrode preparation. In some circumstances, if there is too much functionalised carbon-based material like graphene oxide, the conductivity of the electrode material will disadvantageously decline. Furthermore, when the functionalised carbon-based material is graphene oxide, a high content of graphene oxide will decrease the sufficiency of active material (for example, NazCTCT). and easily cause cracking during electrode preparation. If the content of graphene oxide is too low, an inadequate coverage over the submicrometer particles of the oxocarbon salt ('NazCTCD will occur and thus a stable resistance at an ultralow temperature may not be achieved. It may be possible for the oxocarbon salt and the graphene oxide to be present within the composite electrode material in a weight ratio of about 12: 1 to about 2:1, such as 12:1, 11:1, 10:1, 9:1, 8:1, 7:1, 6:1, 5:1, 4:1, 3:1, and 2:1. In some circumstances, the weight ratio between the submicrometer particles of the oxocarbon salt and the graphene oxide is about 10:1 to about 3:1, or about 8:1 to about 4:1, for example 5:1. When the composite electrode material consists of submicrometer particles of a monocyclic oxocarbon alkali metal salt (for example, NazCTOe) and graphene oxide, the oxocarbon salt and the graphene oxide can be in a weight ratio of about 5:1. [0092] In some circumstances, the composite electrode material further comprises a functional material, such as an aerogel, which might contain various functional groups such as hydroxyl, amino, and carboxyl. Aerogels include, but are not limited to, sodium alginate, chitosan and agarose.

[0093] In some embodiments, the composite electrode material comprising the oxocarbon salt and the graphene oxide displays a decreased contact angle and increased interfacial wettability compared to those of the oxocarbon salt. The contact angle can be measured through Sessile drop analysis. For example, the liquid used to measure the contact angle is the electrolyte used in the Examples, that is, IM NaPF₍₎ in diethylene glycol dimethyl ether (DGM)). Alternatively, or in addition, an electrode prepared from the composite electrode material exhibits a remarkable capacity of 119 mAh g ¹ at -50 °C in half-cell configurations.

[0094] Also disclosed herein is a method for preparing a composite electrode material, the method comprising:

[0095] In some embodiments, the method for preparing a composite electrode material comprises:

(i) introducing an oxocarbon salt into a first mixture comprising water and an antisolvent to obtain the first composition,

(ii) introducing a functionalised carbon-based material into a second mixture comprising water and an antisolvent to obtain the second composition,

(iii) combining the first composition and the second composition to obtain a third composition, and (iv) introducing an amount of an antisolvent into the third composition under conditions to allow formation of a precipitate comprising submicrometer particles of the oxocarbon salt and the functionalised carbon-based material.

[0096] It would be appreciated that the method can be used to prepare a composite electrode material as described hereinabove.

[0097] The antisolvents used in steps (i), (ii) and (iv) may be the same or may be different. In some embodiments, it is preferable for the antisolvents used in steps (i), (ii) and (iv) to be the same. In selecting the antisolvents used in the method, considerations may be given to solubility of the oxocarbon salt in each of the antisolvents and miscibility between water and each of the antisolvents. It is proposed by the inventors that the oxocarbon salt be much less soluble or insoluble in each of the antisolvents compared to in water, and each of the antisolvents be miscible water. There is no particular limitation on the antisolvents that may be used. Antisolvents other than those mentioned herein can be considered for the present disclosure. The antisolvent that may be used for the method includes, but is not limited to, an alcohol, an ether (such as diethyl ether) and/or a ketone (such as acetone). For the purpose of illustration, each of the antisolvents used in steps (i), (ii) and (iv) is an alcohol, such as methanol, ethanol, n-propanol, iso-propanol, and/or iso-butanol. When the ratio between the total amount of water and the total amount of the antisolvent (such as an alcohol) in the third composition is set, the size of the particles within the precipitate may be adjusted through varying the concentration of the oxocarbon salt based on the total amount of water and the antisolvent in the third composition. When the concentration of the oxocarbon salt based on the total amount of water and the antisolvent in the third composition is set, the morphology (for example, a rodlike morphology and a diamond-like morphology) of the particles within the precipitate may be adjusted through varying the ratio between the total amount of water and the total amount of the antisolvent (such as an alcohol) in the third composition.

[0098] In some embodiments, a first mixture consisting of water and an antisolvent is used in step (i) and/or a second mixture consisting of water and an antisolvent is used in step (ii). For example, each of the first and second mixtures consists of water and an alcohol such as ethanol.

[0099] For each of the first and second compositions in step (i) and step (ii) or for each of the first and second mixtures in step (i) and step (ii), water and the antisolvent comprised therein may be in a volume ratio of about 1:1,

about 1.5:1, for example, 2:1, 3:1 and 4:1. The content and the amount of the water component within the first composition or the first mixture of step (i) are selected to ensure that the first composition or the first mixture is capable of fully dissolving the oxocarbon salt. The content and the amount of the water component within each of the first composition or the first mixture of step (i) and the second composition or the second mixture of step (ii) are selected to ensure that the oxocarbon salt is completely dissolved in the third composition which is obtained through combing the first composition and the second composition. There is no particular limitation on the upper limits of the water and antisolvent ratios in the mixtures. It is possible to use water without antisolvent in step (i) and/or step (ii). In some embodiments, the first composition or the first mixture comprises water and the antisolvent at the same volume ratio as the second composition or the second mixture does. The first mixture can be the same as the second mixture. In a specific embodiment that ethanol is used as the antisolvent in step (i) and step (ii), the water and the ethanol may be in a volume ratio of about 2:1. In a specific embodiment that each of the first and second mixtures used in step (i) and step (ii) consists of water and ethanol, the water and the ethanol may be in a volume ratio of about 2:1.

[0100] The oxocarbon salt may be dissolved within the first composition (i.e. step (i)) and the graphene oxide may be dispersed within the second composition (i.e. step (ii)). For example, the oxocarbon salt is dissolved into the first mixture (i.e. step (i)) and the graphene oxide is dispersed into the second mixture (i.e. step (ii)). The first composition and/or the second composition may be formed with the aid of stirring or agitation. The oxocarbon salt and the graphene oxide can be introduced into the mixtures under stirring or agitation, for example for about 10 to 20 minutes under sonication. Step (i) and/or step (ii) can be carried out without extra heating, for example at ambient temperature. For step (i), the amount and the composition of the first mixture are selected to dissolve the oxocarbon salt. For step (ii), the amount and the composition of the second mixture are selected to disperse graphene oxide. For the method disclosed herein, the total amount and/or the composition of the first composition or the first mixture used in step (i) and the second composition or the second mixture used in step (ii) is/are chosen to (1) allow complete dissolution of the oxocarbon salt in the third composition which is obtained through combing the first composition and the second composition; and (2) provide a certain concentration for the oxocarbon salt based on the total amount of the first mixture and the second mixture in order to subsequently achieve a desirable size of the particles within the precipitate and/or a desirable morphology of the particles within the precipitate. In some embodiments, based on the total weight of the first mixture and the second mixture, the weight percentage of the oxocarbon salt introduced in step (i) amounts to > about 60% by weight, > about 65% by weight, > about 66% by weight, or > about 67% by weight. For example, when each of the first mixture and the second mixture comprises water and an alcohol (such as ethanol), the oxocarbon salt introduced in step (i) amounts to > about 60% by weight (e.g. > about 65% by weight, > about 66% by weight, or > about 67% by weight) based on the total weight of the first mixture and the second mixture.

[0101] As discussed above, the oxocarbon salt and the functionalised carbon-based material (such as graphene oxide) are used in a weight ratio of about 12:1 to about 2:1, about 9:1 to about 3:1 or 8:1 to about 4:1. As an example, when the composite electrode material consists of submicrometer particles of a monocyclic oxocarbon alkali metal salt (for example, NazCTCk) and graphene oxide, the weight ratio between the monocyclic oxocarbon alkali metal salt and the graphene oxide may be about 5:1. [0102] After the first composition comprising the oxocarbon salt and the second composition comprising the functionalised carbon-based material (such as graphene oxide) are combined to obtain a third composition, an amount of an antisolvent is introduced to the third composition under conditions to allow formation of a precipitate in step (iv). This is an antisolvent precipitation process, which may be controlled to adjust the particle size of the precipitate. If a smaller particle size of the precipitate is needed, conditions can be chosen to favour very rapid particle formation and little or no particle growth. It is proposed by the inventors that the amount of the antisolvent introduced into the third composition significantly exceed the total amount of water in the first and second compositions. The amount of the antisolvent introduced into the third composition and the total amount of water in the first and second compositions can be in a volume ratio of about 6:1 to about 9:1, for example about 6.5:1, about 7:1, about 7.5:1, about 8:1 and about 8.5:1. Step (iv) introducing an amount of an antisolvent into the third composition under conditions to allow formation of the precipitate can be done with the aid of a water bath and/or under agitation, for example under sonication. The conditions may include a temperature between about 0 °C to about 70 °C, for example at about 20 °C, about 25 °C, or about 30 °C. For example, in step (iv), the amount of the antisolvent (such as an alcohol) can be added into the third composition. In an embodiment, in step (iv), the amount of the antisolvent (such as an alcohol) can be added at one time into the third composition, which may lead the particles within the precipitate to comprise or have a diamond-like morphology. Alternatively, in step (iv), the third composition can be added to the amount of an antisolvent, which may lead the particles within the precipitate to comprise or have a rod-like morphology and/or an irregular morphology. The salt will start to precipitate (and preferably crystallize) owing to their poor solubility in the water/alcohol mixture and then self-assemble into particles (preferably crystalline particles) and the functionalised carbon-based material (such as graphene oxide) will be loaded over the particles (preferably crystalline particles) of the oxocarbon salt.

[0103] After a precipitate is formed, any method known in the art can be used to collect and dry the precipitate. For example, the precipitate is collected via centrifugation and dried in a vacuum oven.

[0104] The method may include other steps. For example, it may also include subjecting the precipitate to conditions that allow or improve crystallisation of the oxocarbon salt if a crystalline state is desired for the precipitate obtained from (iv) and the latter does not achieve the crystalline state. For this purpose, a hydrothermal treatment can be employed, for example at about 180 °C.

[0105] If desirable, the composite electrode disclosed herein may be prepared by an antisolvent precipitation and solvothermal method. In some embodiments, only water without an antisolvent is used in step (i) and/or step (ii). For example, to prepare a composite electrode comprising crystalline particles of NazCeCT in a rod-like morphology and graphene oxide, an aqueous solution of NazCeOr, wherein the graphene oxide is dispersed is prepared, then the solution is added dropwise to a large amount of an alcohol such as absolute ethanol (for example at a volume ratio of 1:5). The mixture is allowed to stand for a period with subsequent hydrothermal treatment, for example at about 180 °C.

[0106] The present disclosure further provides an electrochemical device comprising the composite electrode disclosed herein or obtained through the method disclosed herein. The electrochemical device may be a cell or a battery such as an ion battery.

[0107] The electrochemical device may be suitable for use at ultra-low temperature conditions. For instance, the electrochemical device operable at a temperature of < about -30 °C, < about -40 °C, < about - 50 °C, < about -60 °C, or < about -70 °C. This makes it possible to withstand harsh conditions, for example, ultra-low temperature conditions in the deep ocean.

[0108] An electrochemical device comprising the composite electrode material disclosed herein can be designed and assembled according to the state of the art. In selecting a cathode material, consideration might be given to the following factors: (1) high electronic and ionic conductivity that ensure fast electron and ionic transport in electrode materials to achieve an outstanding rate performance, (2) high sodium storage capacity enables high reversible specific capacity, (3) high redox potential to realize a high operating voltage, (4) superior structural stability during the charge/discharge process to obtain a long cycle life, (5) high thermal and chemical stability to ensure high safety, (6) good compatibility with electrolyte to reduce the side reaction at the electrode/electrolyte interface and thus improve the Coulombic efficiency, and (7) low cost and environmental friendliness. The composite electrode material may be used as anode material or cathode material.

[0109] For sodium ion batteries wherein the composite electrode material is used as anode material, the electrochemical device may comprise Prussian blue analogues (PBAs), such as MnFe-Prussian blue analogue (PBA) as cathode material. The PBAs have the general formula A P[R(CN)6] i-y ii'IFO where A is an insertion ion, often potassium or sodium, P and R are transition metals and y is the number of [R(CN)6] vacancies. An example of the PBAs that may be used is Na2MnFe(CN)6. In some embodiments, the composite electrode material consists of crystalline submicrometer particles of NazCTCT and graphene oxide.

[0110] For sodium ion batteries wherein the composite electrode material is used as cathode material, the anode material may include, but is not limited to, reduced state (Na4TP) of sodium terephthalate, sodium metal, alloying sodium metal, and graphite. In some embodiments, the composite electrode material consists of crystalline submicrometer particles of NazCeCT and graphene oxide.

[0111] For sodium ion batteries, it is possible to use NaPF₍₎ or NaCICF as sodium salt and a suitable organic solvent that will not freeze at subzero temperatures or ultra-low temperatures to form an electrolyte. The organic solvent includes, but is not limited to, dimethoxyethane (DME), diethylene glycol dimethyl ether (DGM), and carbonates such as propylene carbonate or a ternary solvent mixture of ethylene carbonate, propylene carbonate and ethyl methyl carbonate. Examples of the electrolyte are NaPF₍₎ in dimethoxyethane (DME), NaPF₍₎ in diethylene glycol dimethyl ether (DGM), and NaC104 in a mixture of antifreeze modified ethylene carbonate/dimethyl carbonate (EC/DMC, 1:1 by volume).

[0112] In fabricating the electrochemical device, other components such as a separator, a binder, a conductive agent, and a current collector may be employed. A separator serves to provide a barrier with no electrical conductivity between the negative electrode (anode) and the positive electrode (cathode) while allowing ion transport from one electrode to the other electrode. The separator is expected to retain chemical stability in the electrolyte while also having a high affinity for the electrolyte. It is also desirable for the separator to have good mechanical stability. Non-limiting examples of separators include glass fibre separators, ceramic separators, polyolefin separators (e.g. polyolefin porous membrane), nonwoven separators, and porous polymer separators. A specific example is polypropylene -polyethylenepolypropylene membrane, which is commercially available under Celgard®.

[0113] When powdered materials are used for the electrodes, a binder may be added to the electrodes to bring various components together and provide consistent mixing of electrode components so as to allow the electrodes to conduct the requisite amount of electrons and guarantee electronic contact during cycling of the electrochemical device. Non-limiting examples of the binder include polytetrafluoroethylene (PTFE), poly vinylidene fluoride (PVDF), and carboxymethyl cellulose (CMC).

[0114] The primary role of a conductive material is to enhance conductivity of the electrodes. In some circumstances, the conductive agent used can be identical to that used for the composite electrode material. Non-limiting examples of the conductive agent include carbon black, Ketjen black, graphene, conductive nano carbon fiber (VGCF), carbon nanotubes (CNTs), and multi-walled carbon nanotubes (MWCNTs). In some embodiments, a conductive agent may be introduced into the solid positive electrode in addition to the conductive material combined with the functional carbohydrate.

[0115] A current collector is a bridging component that collects electrical current generated at the electrodes and connects with external circuits. It can have a great influence on the capacity, rate capability and long-term stability of the electrochemical device. Non-limiting examples of the current collector include aluminium (Al) foil, copper (Cu) foil, carbon-coated aluminium, carbon-coated titanium (Ti) foil, and carbon-based materials.

[0116] As an example, for fabrication of an electrode from the composite electrode material disclosed herein, the sub-DSR/GO composite, carbon black (> 99%, Alfa Aesar), and poly(vinylidene fluoride) (PVDF, Sigma) can be mixed (for example, at a mass ratio of 70:20:10) in anhydrous N-methyl-2- pyrrolidone (NMP, Sigma, 99.5%). The mixture is ball-milled and then applied onto an aluminium foil. The combination is subjected to drying (for example, under vacuum at 80 °C). The mass loading of the sub- DSR/GO composite can be 0.7-1.0 mg cm ².

[0117] In some embodiments, the electrochemical device may deliver cycling stability over 7000 cycles at about -40 °C. In particular, the electrochemical device may maintain a discharge capacity of 101 mAh g ¹ over 7000 cycles at a high current density of 300 mA g ¹ and about -40 °C. Alternatively or in addition, the electrochemical device may exhibit a capacity of 136 mAh g ¹ over 300 cycles at a current density of 100 mA g ¹ and about -30 °C. Alternatively or in addition, in the situation that the electrochemical device is a pouch full-cell, and the pouch full cell powers four light -emitting diodes (LEDs, 2.0 V) continuously for over 1.5 hours at -50 °C.

[0118] It would be appreciated from the above description that the present disclosure also provides use of the composite electrode material in preparing an electrochemical device as well as use of the composite electrode material according to the fist aspect or obtained according to the second aspect in an electrochemical device.

EXAMPLES

[0119] PREPARATION OF MATERIALS

[0120] Synthesis of submicrometer disodium rhodizonate (sub-DSR, Na^CsOs)

[0121] DSR in diamond-shaped morphologies with different sizes were synthesized using molecular self-assembly techniques and employing solvent exchange processes. The organic compound was transferred from water (H2O) to ethanol (EtOH) to induce self-assembly through intermolecular stacking interactions. The size of DSR were controlled by manipulating the concentration of raw materials and the volume ratio of H2O to EtOH solvent. To produce diamond-shaped sub-DSR, DSR (40 mg, sigma, purity: 97%) was dissolved in a mixture of H2O and EtOH (2:1, 60 ml total) with stirring for 10 minutes. Subsequently, 300 ml of EtOH was added to the solution with sonication in a water bath of about 20 °C for 12 minutes. The experiment was conducted at ambient temperature without extra heating. The resulting reddish-purple precipitate was collected via centrifugation and further dried overnight in a vacuum oven at 60 °C. [0122] Synthesis of sub-DSR /graphene oxide (sub-DSR/GO) composite

[0123] For preparation of the sub-DSR/GO composite, the same method was followed with the addition of a single layer GO (8 mg, GaoxiTech, lOmg/ml) during the sonication step. Na4C6O6 was prepared based on previous report by annealing DSR at 400 °C for 3 hours under Ar atmosphere. ²⁹

[0124] A solvent mixture consisting of 60 ml of water/ethanol (2/1) was initially prepared. 40 mg DSR was introduced into 30 ml of the solvent mixture to obtain a DSR composition, and single layer GO (8 mg, GaoxiTech, 10 mg/ml aqueous dispersion) was added to another 30 ml of the solvent mixture to obtain a GO composition. The GO composition underwent a 10-minute sonication process to achieve uniform dispersion. Subsequently, the DSR composition and the GO composition were combined to obtain a DSR/GO composition and stirred for an additional 10 minutes. Following this, the DSR/GO composition was subjected to sonication in a water bath at ambient temperature for a duration of 12 minutes while simultaneously adding 300 ml of ethanol (EtOH) at one time. A precipitate formed and was collected via centrifugation and dried overnight in a vacuum-oven at 60 °C.

[0125] Synthesis ofNa₂MnFe(CN)₆ (PBA )

[0126] PBA was synthesized via a facile co-precipitation method. Specifically, Na4Fe(CN)6 (1.52 g) and NaCl (15 g) were dissolved in de-ionized (DI) water (100 ml). Separately, MnCl (0.63 g) was dissolved in another 50 ml of DI water. The MnCh solution was then added dropwise into the Na4Fe(CN)6 solution under stirring. The resulting suspension was aged for 2 hours, followed by separation through centrifugation. The obtained precipitate was washed three times with DI water and dried under vacuum at 120 °C for 10 hours. The resulting sample was finely ground into a powder for further use.

[0127] Synthesis of sodium terephthalate (Na₂TP)³⁰

[0128] NazTP was synthesized using a modified method based on a previously reported procedure. Terephthalic acid (1.73 g) was added to a hot solution (50 °C) of sodium hydroxide (1.38 g) in DI water (5 ml). Subsequently, another 15 ml of DI water was added to obtain a clear solution. The mixture was stirred for 30 minutes, followed by the addition of ethanol (80 ml, EtOH) with continuous stirring for another 6 hours at 70 °C. The resulting precipitated crystals were collected and dried under vacuum at 150 °C for 1 hour. The counter electrode, Na4TP, was prepared by fully discharging Na TP in the presence of Na foil.

[0129] Preparation of the electrolyte

[0130] All chemicals used for preparation of the electrolyte were purchased from Sigma Aldrich. The diethylene glycol dimethyl ether (DGM, anhydrous, 99.5%) was subjected to further drying using activated 4 A molecular sieves over 12 hours prior to use. The sodium hexafluorophosphate (NaPFe, 98%) was purchased and used without further treatment. In a typical procedure, NaPF₍₎ (1.68 g) was dissolved in 10 ml DGM at room temperature (RT). The electrolyte was left stirring overnight and ready to be used for testings. All the procedures were conducted in an Ar-filled glove box (H2CK 0.5 ppm and O < 0.5 ppm).

[0131] CHARACTERISATION METHODS

[0132] The sample morphology was analysed by FEI Quanta 450 FEG scanning electron microscope (SEM). X-ray diffraction (XRD) patterns of the sample powders were obtained using a Bruker D8 ADVANCE ECO X-ray diffractometer operating at 40 kV and 25 mA using Cu-Ka radiation (1=0.15418 nm). Ex-situ synchrotron soft X-ray spectroscopy (XAS) measurements were conducted at Australian Synchrotron (ANSTO), Melbourne. The acquired data was processed and analysed using Igor Pro software. To eliminate soluble species on the electrode surface, all samples for ex-situ testing were thoroughly rinsed with DGM solvent.

[0133] Operando Raman spectroscopy

[0134] Raman spectroscopy was conducted using a confocal Raman microscope (Renishaw, InVia™) with 50X objective, and signals were recorded using a 532 nm laser over the range of 100-1800 cm¹. The laser power was maintained at 0.1 % and an 1800 line/mm diffraction grating was utilized.

[0135] Operando Fourier-transform infrared spectroscopy (FTIR)

[0136] Operando FTIR measurements were conducted on a Nicolet 6700. The spectra were collected in transmission mode with 64 scans at a resolution of 4 cm ¹ in the range of 4000-1200 cm '. Spectra were collected operando with a series of consecutive scans every 2.5 minutes during galvanostatic cycling under current density of 50 mA g ^-1. The automatic baseline correction and atmospheric compensation were performed on OMNIC software.

[0137] ELECTROCHEMICAL PERFORMANCE

[0138] The electrochemical performance was evaluated using 2032 type coin cells. To fabricate an electrode, the synthesized sub-DSR/GO composite, carbon black (> 99%, Alfa Aesar), and poly(vinylidene fluoride) (PVDF, Sigma) were mixed in a mass ratio of 70:20:10 in anhydrous N-methyl-2-pyrrolidone (NMP, Sigma, 99.5%). The mixture was ball-milled at 400 rpm over 4 hours and then applied onto a 1.2 cm diameter aluminium foil. After drying under vacuum at 80 °C for 12 hours, the mass loading of sub- DSR/GO was 0.7-1.0 mg cm². The sub-DSR control electrode and Na4TP counter electrode were prepared through the same procedure. For the PBA counter electrode, PBA powder, carbon black, and polytetrafluoroethylene (PTFE) binder (6% aqueous solution, Sigma-Aldrich) were mixed in a mass ratio of 70:20:10. The mixture was grounded in an agate mortar with a few drops of ethanol and then rolled into a free-standing film. After drying under vacuum at 80 °C for 12 hours, the sample was cut into small pieces and pasted onto a stainless-steel mesh. In half cells, fresh sodium metal and Whatman glass fiber were used as the anode and separator, respectively. For full cells, PBA or NazTP was employed as the counter electrode. All coin cells were assembled within an argon-filled glovebox. Galvanostatic cycling tests were conducted using a Land CT2001 A and Newware battery testing system at different rates and temperatures. A thermal test chamber (GWS-MT3065 and HSLIF Husheng) was utilized for variable temperature tests. Prior to starting the low-temperature electrochemical tests, cells were all kept at the low temperature for 5 hours. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) data were collected using an electrochemical workstation (BioLogic and CHI 760E). EIS tests were performed in the frequency range from 1 MHz to 0.01 Hz with an amplitude of 5 mV.

[0139] Determination of diffusion coefficient and activation energy

[0140] The activation energy of the electrode can be calculated based on thermally activated process.³¹ ~Eq

I_p = A_o e RT (eq. SI) where Ao is a constant, R is the gas constant, T is the temperature in Kelvin, and E_a represents the activation energy. The peak current (I_p) were obtained from CV profiles at different temperatures.

[0141] RESULTS AND DISCUSSION

[ 0142 ] Solid-liquid-solid conversion

[0143] The redox reaction of DSR organic electrode occurs between Na⁺ and carbonyl groups.¹⁵ Na||sub- DSR half-cells were assembled with Na foil anode, sub-DSR organic cathode, and 1 M NaPF₍₎ electrolyte. The reaction process of organic-Na ion batteries is monitored at room temperature (RT) via operando Raman spectroscopy which offers high sensitivity in detecting transient species. The Raman spectrum of sub-DSR powder has multiple features in the range of 100-1800 cm ¹ (Figure 7). Figure la demonstrates the time-dependent evolution of Raman spectra for sub-DSR (300-500 nm). After initial discharging to 1.7 V, all peaks vanished, indicating the formation of soluble species that are unstable and readily dissolves in ether-based electrolytes.¹⁶ The dissolution of the intermediate products leads to the loss of active materials and absence of Raman activity for sub-DSR electrode at RT in subsequent cycles. To mitigate dissolution and fully utilize the capacity of the materials, sub-DSR was hybridized with GO. As shown in Figure lb, the operando Raman 3D projection contour plot of the sub-DSR/GO composite electrode demonstrates a reversible molecule structural change with obvious Raman features during cycling, indicating a highly reversible electrochemical process. Notably, there were no Raman activities at the discharging plateau of 1.7 V (Figure 1c), corresponding to the formation of Na^eOe intermediates.^{17 20} The disappearance of Raman peaks suggests the intermediate product Na^eOe on the surface of the electrode is soluble in electrolytes, while both the discharging and charging end-products remain in solid phase with distinct Raman activity. This reveals a solid-liquid-solid conversion reaction of DSR electrodes and provides valuable insights into its electrochemical behaviour.

[0144] Electrochemical stability

[0145] Figure 2a shows the discharge-charge curve of bulk DSR with distinct discharge plateau at 1.7 V, corresponding to the intermediate product, Na^eOe. It can be synthesized according to previous reports (Figure 8). Upon being immersed in the DGM electrolyte, Na 'eOr, yields a yellow solution after, while the solution of pristine DSR ('NazCeOr,) remains clear, as demonstrated in Figure 2b. This agrees well with our Raman results that the intermediate product at 1.7 V is soluble, involving a solution-mediated reaction. The dissolution of active materials adversely affects the cycling performance of bulk DSR with a rapid capacity loss at 30 °C due to the depletion of active materials, as shown in Figure 2c. To address this challenge, a molecular self-assembly method was employed to fabricate sub-DSR particles, as shown in Figure 2d. By modifying the initial volume of the solvent mixture of H₂O/EtOH, particles of varying sizes were synthesized (Figure 9). The charge storage of DSR relies on the surface redox centres of carbonyl groups. A small particle size with increased contact area accelerates the charge transfer and shortens the Na⁺ diffusion pathways, improving the electrochemical performance of DSR. To enhance the cycling performance of the electrode, GO with n-conjugated structure is introduced to tune the molecular structure stability of sub-DSR. The SEM image of sub-DSR/GO composite is presented in Figure 2e. Upon hybridization, sub-DSR/GO exhibits significantly improved capacity, reaching 333.7 mAh g ¹ (based on the total mass of the sub-DSR and GO) compared to 211.8 mAh g ¹ of sub-DSR at a current density of 300 mA g ¹ for the initial cycle. Furthermore, the sub-DSR/GO composite can maintain 98 % of its capacity over 100 cycles, as shown in Figure 2f. Optical images of the separators from sub-DSR and sub-DSR/GO batteries obtained after 3 cycles are displayed in Figure 10. GO in the composite electrode effectively anchors the unstable intermediate organic species on the electrode during cycling with much cleaner separator comparing to that of sub-DSR. As a result, the sub-DSR/GO composite electrode demonstrates remarkable stability, exhibiting negligible capacity lose over 500 cycles at a high current density of 1000 mA g ¹ (Figure 11). Figure 12 shows the initial discharge-charge curves of sub-DSR and sub-DSR/GO at a high current density of 1000 mA g '. Notably, sub-DSR/GO exhibits a high initial capacity of 317 mAh g ', indicating the occurrence of three -electron redox reaction (the theoretical capacity of a four-electron redox reaction is 501 mAh g ¹). More electrochemical tests of sub-DSR and sub-DSR/GO at RT are demonstrated in Figures 13-15. Here, the n-conjugated effect and abundant functional groups of GO contribute to a strong adsorption to soluble species produced during carbonyl redox process (C=0<->C-0 ). [0146] Interfacial and liquid-phase conversion kinetics

[0147] The sodiation process of DSR proceeds via a solid-liquid-solid phase transition. The discharge and charge end-products, corresponding to NaTTO, and NazCeOr, respectively, exists as a solid phase, while intermediate product Na^eOe easily dissolves in the ether-based electrolyte. To prevent the dissolution of Na4C&06, the adsorption and conversion of the soluble intermediate species are two key strategies. To study the impact of GO incorporation on reaction kinetics of solution-mediated process, cyclic voltammetry (CV) measurements were performed on sub-DSR and sub-DSR/GO electrodes at various temperatures ranging from -20 °C to 25 °C, using a scan rate of 0.2 mV s'¹. The study focuses on the characterization of the solution-mediated redox reaction, namely C2, which correspond to the reduction peak at around 1.7 V, as marked in Figures 3a-3b. According to the Arrhenius relationship (eq. SI), the activation energy (Ea) associated with the reduction processes of C2 for both sub-DSR and sub-DSR/GO electrodes was determined from the slope of the peak current (Ip) versus the inverse of temperature (1/T) plot, as illustrated in Figure 3c. The calculated Ea values for Cl, C2 and C3 are presented in Table 1. Notably, the incorporation of GO leads to a reduction in Ea for C2 redox process, with the energy barrier being lowered impressively by -25%. This facilitates the liquid-solid conversion process of C2. The inset of Figure 16 demonstrates the corresponding sessile drop contact angle tests of sub-DSR and sub-DSR/GO, respectively. Following the hybridization with GO, the composite electrode shows an obviously decreased contact angle with increased interfacial wettability. The enhanced wettability of organic electrodes plays a crucial role in decreasing the resistance of the battery caused by declined transport properties of the electrolyte and stagnant charge transfer at low temperatures. Figure 17 demonstrates the EIS measurements for sub-DSR and sub-DSR/GO electrodes across a temperature range from 25 °C to -40 °C. At -30 °C, the sub-DSR electrode exhibits a lower R_ct compared to the sub-DSR/GO composite, as illustrated in Figure 17a. However, as the temperature decreases below -30 °C, the R_ct of sub-DSR undergoes a significant increase. Conversely, the R_ct of sub-DSR/GO experiences only a marginal increase from 25 °C to -40 °C (Figure 17b). This further verifies that the hybridization strategy of sub-DSR with GO predominantly influences the activation energy of the electrode, leading to a relatively stable resistance at ultra-low temperatures with more efficient surface reactions. The enhanced reaction kinetics and lowered Ea of C2 process promote the conversion of the unstable intermediate phase. Consequently, the dissolution is well regulated, which enables excellent stability of the electrode at ultra-low temperatures. [0148] Table 1. The fitted results of activation energy for sub-DSR and sub-DSR/GO corresponding to different cathodic peaks.

Electrode Activation energy (Ea, kJ mol )

Cl C2 C3 sub-DSR 5.56 7.02 2.12 sub-DSR/GO 5.00 5.24 4.87

[0149] Tuneable redox reactivity and stability of radical intermediates

[0150] Molecular and atomic structural analyses were conducted using operando FTIR spectroscopy and ex-situ synchrotron XAS. The operando FTIR contour maps depict the molecular behaviour of sub-DSR and sub-DSR/GO electrode during the initial two cycles. The sharp peaks observed at approximately 1450 cm ¹ and 1350 cm ¹ correspond to the vibration of C=O and C-0 stretching, respectively.^{19, 21 22} By virtue of the incorporation of GO, the position of C=O stretching of the composite, as shown in Figure 18, shifts to a lower wavenumber associated with the electronic interaction of 1-71 stacking between sub-DSR and GO.^{23 24} Figure 3a demonstrates an operando FTIR contour map of sub-DSR electrode, exhibiting a continuous molecular structure evolution over cycling. The composite electrode shows a distinct molecular structure transformation boundary between C=O and C-0 (Figure 3b). The continuous changes observed in sub-DSR indicate the occurrence of intermediate side reactions. Selected spectra from operando tests, representing the pristine, fully discharged (1.0 V), and charged (3.2 V) states of the electrodes during the initial two cycles, are displayed in Figure 3c. The intensity of C=O bands gradually decreases during the discharging process, while the intensity of C-0 bands has increased. This trend is reversed during the charging process for both electrodes. The reversible intensity changes in the C=O vibrations confirm the high reversibility of the redox reactions involving enolate and quinonoid carbonyl groups for the initial two cycles. Notably, a broad peak at around 1550 cm'¹, which can be assigned to the vibration of the C=C bond occurs upon the discharging process of sub-DSR/GO electrode,²² while it is absent in sub-DSR electrode. After the initial sodiation, the organic molecules form radical intermediates with an unpaired electron located on the C atom of C-0 . This active C atom is susceptible to attack by molecules in the electrolyte. Here, the 71-conjugation interactions of GO can effectively delocalize the energy density of the unpaired electrons on C atom, and thereby significantly decrease side reactions on C atom with clear C=C band for the composite electrode. The limited reversibility observed in sub-DSR is primarily caused by side reactions with the electrolyte. The 71-conjugation effect of GO facilitates the rapid electron transfer between molecules and improves the tolerance of the organic electrode to ether-based electrolyte. Furthermore, synchrotron soft XAS of sub-DSR and sub-DSR/GO powders are demonstrated in Figures 3d-3e and Figure 19, along with the C K-edge of GO (Figure 20). The XAS K-edge of O and Na is similar for both electrodes. While the results of C K-edge at 287.3 eV, which represents Cls-7t*(C=C-O),^{25 26} show an obvious change after the hybridization of GO with decreasing intensity. It confirms a decreased electron cloud density associated with the C atom of C-O-. Here, the conjugation of GO effectively tune the redox reactivity and stability of DSR.

[0151] Electrochemical properties at ultra-low temperatures

[0152] In exploration of the low-temperature properties of the organic electrodes, the Na storage performance of half cells coupling with Na metal were evaluated at -30 °C first, as demonstrated in Figures 21-24. The composite electrode delivers an impressively high capacity of 318 mAh g ¹ at a current density of 100 mA g ¹ for the initial cycle. At an ultra-low temperature of -50 °C, the Na||sub-DSR/GO half-cell can achieve a high capacity of 130 mAh g ¹ at 50 mA g ¹ (Figure 5a). This is among the best ultra-low temperature performance for non-aqueous batteries. The corresponding galvanostatic discharge-charge curves presented in Figure 5b demonstrate stable capacity output with three distinct and flat discharge plateaus at around 2.2 V, 2.1 V, and 1.8 V throughout cycling. The sub-DSR/GO holds great potential for ultra-low temperature applications. However, Na metal anode is unable to achieve a long cycling performance at ultralow temperatures due to sluggish Na⁺ diffusion and dendrite formation.^{27 28} Therefore, a full-cell configuration comprises sub-DSR/GO anode coupling with a MnFe-Prussian blue analogue (PB A) cathode was proposed, which exhibits extraordinary long-term cycling life and is fail-safe. Excessive PBA was used to satisfy the redox of the organic electrode. Figure 5c shows the cycling performance of sub-DSR/GO||PBA full-cell at -40 °C, delivering a high initial capacity of 192 mAh g ¹ (based on the mass of sub-DSR/GO) at a current density of 100 mA g ¹ and maintains 138 mAh g ¹ over 1000 cycles. In addition, the full-cell remains at capacity of 101 mAh g ¹ at a high current density of 300 mA g ¹ over 7000 cycles (Figure 5c (inset) and Figure 25). That’s the best cycling performance ever reported at ultralow temperatures. The rate capability of sub-DSR/GO||PBA at -40 °C is demonstrated in Figure 26, where the full-cell operates even at a high current density of 1000 mA g ¹ exhibiting fast kinetics. Furthermore, when the temperature is further decreased to -50 °C, the initial cycle still achieves a discharge capacity of 108 mAh g '. More importantly, sub-DSR/GO||PBA full cells exhibit a strong temperature tolerance, as evidenced by a restored capacity after a sudden increasing temperature from -50 °C to RT and subsequently decreasing to -40 °C (Figure 5d). The corresponding discharge-charge curves of the full-cell for different cycles at -50 °C are presented in Figure 5e, demonstrating clear voltage plateaus with an average discharge voltage of 1.25 V.

[0153] The sub-DSR/GO||PBA full-cell exhibits the superior cycling electrochemical performance among reported non-aqueous batteries at ultra-low temperatures, as demonstrated in Figure 5f (Table 2). Figure 27a also demonstrated the temperature-dependent rate performance of the sub-DSR/GO||PBA full cells. And corresponding EIS at differing temperatures is shown in Figure 27b. Notably, the full-cell, after hybridizing with GO, maintains a stable charge transfer resistance even as the temperature decreases to -40 °C. This result is attributed to the GO-enhanced interfacial and solution-mediated reaction kinetics. Furthermore, apart from coupling with high-voltage cathode PBA, an all-organic Na-ion full-cell utilizing a pre-cycled sodium terephthalate anode (Na4TP) was assembled. The cell exhibits a capacity of 136 mAh g ¹ at a current density of 100 mA g ¹ and -30 °C, over 300 cycles (Figure 28). This is a good example of a sustainable battery composed solely of C, O, and Na atoms. The exceptional low-temperature tolerance of DSR renders it a promising candidate for large-scale applications.

[0154] Table 2. Comparison of the ultra-low temperature ( -40 °C and bellow) properties of different non-aqueous batteries.

[0155] Pouch cell properties at -50 °C

[0156] To demonstrate the feasibility of practical application of sub-DSR/GO electrode in extreme cold conditions, a pouch full-cell in coupling with PBA cathode was assembled. Figure 6a shows a digital image of a single pouch full cell, exhibiting an open circuit voltage of 2.1 V in its fully charged state. The discharge-charge curve of the pouch cell, recorded at a temperature of -50 °C and current density 20 mA g ', is displayed in Figure 6b, revealing an average discharge voltage of 1.1 V. The long-term cycling performance of the pouch cell is presented as Figure 6c. After 300 cycles, the capacity maintains 77 mAh g ¹ with no apparent capacity fading. To highlight the potential of the sub-DSR/GO||PBA system in practical applications, two pouch cells in series, as shown in Figure 6d, Figure 29 and supporting video are demonstrated to power continuously four green LEDs (with a voltage requirement of 2.0 V) for a duration over 1.5 hours, underscoring the high potential of the sub-DSR/GO||PBA system. Further optimization of the mass balance between the cathode and anode to enhance the energy density and cycling performance of full cells could be made. This work represents a significant advancement in the search for reliable and high-performance battery systems suitable for extreme cold environments.

[0157] It will be understood that the terms “comprise” and “include” and any of their derivatives (e.g. comprises, comprising, includes, including) as used in this specification is to be taken to be inclusive of features to which the term refers, and is not meant to exclude the presence of any additional features unless otherwise stated or implied.

[0158] The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement of any form of suggestion that such prior art forms part of the common general knowledge.

[0159] It will be appreciated by those skilled in the art that the disclosure is not restricted in its use to the particular application or applications described. Neither is the present disclosure restricted in its preferred embodiment with regard to the particular elements and/or features described or depicted herein. It will be appreciated that the disclosure is not limited to the embodiment or embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the scope as set forth and defined by the following claims.

[0160] In some cases, a single embodiment may, for succinctness and/or to assist in understanding the scope of the disclosure, combine multiple features. It is to be understood that in such a case, these multiple features may be provided separately (in separate embodiments), or in any other suitable combination. Alternatively, where separate features are described in separate embodiments, these separate features may be combined into a single embodiment unless otherwise stated or implied. This also applies to the claims which can be recombined in any combination. That is a claim may be amended to include a feature defined in any other claim. Further a phrase referring to “at least one of’ a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover: a, b, c, a-b, a-c, b-c, and a-b-c. REFERENCES

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Claims

1. A composite electrode material comprising submicrometer particles of an oxocarbon salt and a functionalised carbon-based material.

2. The composite electrode material according to claim 1, wherein the composite electrode material is a composite organic electrode material comprising submicrometer particles of the oxocarbon salt and the functionalised carbon-based material, wherein the oxocarbon salt is derived from a natural source.

3. The composite electrode material according to claim 1 or 2, wherein the functionalised carbonbased material is loaded over the submicrometer particles of the oxocarbon salt.

4. The composite electrode material according to any one of claims 1 to 3, wherein the functionalised carbon-based material comprises or is graphene oxide.

5. The composite electrode material according to any one of claims 1 to 4, wherein the oxocarbon salt comprises or is a monocyclic oxocarbon alkali metal salt.

6. The composite electrode material according to any one of claims 1 to 5, wherein the oxocarbon salt comprises or is a monocyclic oxocarbon alkali metal salt having a formula of M_m(CO)_n (wherein M = Li, Na or K; 2 < m <6; n= 4, 5 or 6).

7. The composite electrode material according to any one of claims 1 to 6, wherein the oxocarbon salt comprises or is a sodium rhodizonate (NazCeOf,).

8. The composite electrode material according to any one of claims 1 to 7, wherein the submicrometer particles of the oxocarbon salt comprise a diamond-like morphology.

9. The composite electrode material according to any one of claims 1 to 8, wherein the functionalised carbon-based material is a graphene oxide that has a water solubility of > about 5 mg/ml at room temperature.

10. The composite electrode material according to any one of claims 1 to 9, wherein the oxocarbon salt and the functionalised carbon-based material are present in a weight ratio of about 12:1 to about 2:1.

11. The composite electrode material according to any one of claims 1 to 10, wherein the composite electrode material consists of submicrometer particles of a monocyclic oxocarbon alkali metal salt (for example, NazCeOe) and graphene oxide in a weight ratio of about 5:1.

12. The composite electrode material according to any one of claims 1 to 11, wherein the composite electrode material is used in an electrochemical device at a temperature of < about -30 °C.

13. The composite electrode material according to any one of claims 1 to 12, wherein the composite electrode material is for use in an electrochemical device at a temperature of < about -50 °C.

14. A method for preparing a composite electrode material, the method comprising:

15. The method according to claim 14, wherein the method comprises:

16. The method according to claim 14, wherein the composite electrode material is a composite electrode material according to any one of claims 1 to 13.

17. The method according to claim 14 or 15, wherein each of the antisolvents used in steps (i), (ii) and (iv) is selected from an alcohol, an ether, a ketone and a combination thereof.

18. An electrochemical device comprising a composite electrode material according to any one of claims 1 to 13 or obtained according to the method of any one of claims 14 to 17.

19. Use of a composite electrode material according to any one of claims 1 to 13 or obtained according to the method of any one of claims 14 to 17 in preparing an electrochemical device.

20. Use of a composite electrode material according to any one of claims 1 to 13 or obtained according to the method of any one of claims 14 to 17 in an electrochemical device.