WO2020186307A1

WO2020186307A1 - Carbon gel electrode

Info

Publication number: WO2020186307A1
Application number: PCT/AU2020/050263
Authority: WO
Inventors: Thomas Maschmeyer; Nathan Coad; Kirsty EVANS; Martin Schneider; Michael Horgan
Original assignee: Gelion Technologies Pty Ltd
Priority date: 2019-03-19
Filing date: 2020-03-19
Publication date: 2020-09-24
Also published as: TW202046547A; AU2020243832A1

Abstract

CARBON GEL ELECTRODE The present invention relates to a battery, comprising an anode, a cathode, and at least one electrolyte disposed between the anode and the cathode, wherein the at least one electrolyte comprises a gelating agent and a composition of carbon particles.

Description

CARBON GEL ELECTRODE

Cross-reference to related applications

[0001] The present application claims priority to AU 2019900911, the entire disclosure of which is incorporated herein by cross-reference.

Field

[0002] The present invention relates to energy storage and generation, in particular batteries.

Background

[0003] Flow batteries have long been considered to be the most suitable storage technology for utility applications due to their potential long life, deep discharge characteristics and potential low manufacturing cost. Flow batteries differ from other battery technologies in that the electrolyte is pumped over the electrodes, which remain electrochemically inert, storing charge through a change in oxidation state (e.g. vanadium redox) or through an electrodeposition such as the zinc- bromine battery. Of these, the zinc-bromine battery (ZBB) offers a solution to most of the problems that have challenged flow battery systems and is considered a highly prospective technology.

[0004] A zinc -bromine flow battery consists of two half cells separated by a permeable membrane through which an aqueous zinc bromide/bromine electrolyte is circulated. During the charging step, zinc is electroplated on the anode, and Bn is evolved at the cathode. A molecular complexing agent dissolved in the electrolyte, such as A- c t h y 1 - A- in c t h y 1 p y rro 1 i d i n i u in b ro in i dc (MEPBr), is used to reduce the reactivity and vapour pressure of the elemental Bn by complexing the majority of the Bn to MEPBr, forming a so-called polybromide complex (MEPBr_n). This reduces the self-discharge of the battery and improves the safety of the system. This complex is removed from the electrodes via the flowing electrolyte and is stored in an external reservoir. On discharge, the complex is returned to the battery stacks by the operation of a valve or a third pump. Zinc is oxidized to zinc ions on the anodes; the Bn is released from the complex and subsequently reduced to Br ions on the cathodes. Such system may also be operated with various metals and halides other than zinc and bromine. [0005] While operational and economic for some applications, existing zinc -bromine battery technology currently only operates at 15% of the theoretically achievable (based on ZnBn solubility) specific energy due to sub-optimal electrode design, poor fluid dynamics and the inefficient two-phase fluid, gravity- separated complexing of Bn. This limits the battery to non transport and low specific energy and energy density applications. Many of the disadvantages with current zinc -bromine battery technology relate to problems with efficiently storing and/or transporting Zn²⁺ and Bn/Br in the electrolyte solution. For example, current battery systems are limited in their specific energy output by the complexing capacity of bromine sequestering agents (BSAs) in the electrolyte. A further problem with zinc -bromine batteries is stratification and the formation of zinc dendrites during charging, which can reach through to the cathode and cause self-discharge.

[0006] 3D electrodes having a large surface area have been used in conjunction with a conventional liquid electrolyte in zinc-bromine batteries, in an attempt to improve performance. One example of such a 3D electrode is carbon felt. However, carbon felt is not a suitable material for commercial manufacture of batteries because of its high cost.

[0007] Disclosed herein is an improved electrolyte for use in zinc -bromine, or other metal- halogen batteries that overcomes one or more of the disadvantages discussed above such as poor energy efficiency, inefficient storage and transport of Bn, stratification and formation of zinc dendrites, and high cost.

Summary of Invention

[0008] In a fist aspect of the invention, there is provided a battery, comprising an anode, a cathode, and at least one electrolyte disposed between the anode and the cathode, wherein the at least one electrolyte comprises a gelating agent and a composition of carbon particles.

[0009] The following options may be used in conjunction with the first aspect, either individually or in any suitable combination.

[00010] The battery may further comprise a halogen in contact with the cathode, and a metal in contact with the anode, wherein during discharge the halogen is reduced at the cathode and the metal is oxidised at the anode. The battery may further comprise a halide in contact with the cathode, and a metal cation in contact with the anode, wherein during charging the halide is oxidised at the cathode and the metal cation is reduced at the anode. The halogen may be bromine. The halide may be bromide. The metal may be zinc.

[00011] The at least one electrolyte may be a gel. The at least one electrolyte may be an aqueous electrolyte.

[00012] The gelating agent may comprise silica particles, zeolite particles, aluminium silicate particles, clay particles, or a mixture thereof. The gelating agent may comprise silica particles.

[00013] The battery may further comprise a separator.

[00014] The at least one electrolyte may comprise a gelating agent which is silica particles in an amount of 1 to 15 % w/v. The at least one electrolyte may comprise a gelating agent which is silica particles in an amount of about 3 to 5 % w/v.

[00015] The at least one electrolyte may comprise the composition of carbon particles in an amount of 1 to 40 % w/v. The at least one electrolyte may comprise the composition of carbon particles in an amount of about 5 to 20 % w/v.

[00016] The composition of carbon particles may comprise one or more types of carbon particles selected from the group consisting of graphite, graphene, vitreous carbon, activated (porous) carbon, carbon nanotubes, expanded graphite, carbon fibre, glassy carbon, shredded carbon felt, carbon black, and carbon foam. The composition of carbon particles may comprise one or more types of carbon particles selected from the group consisting of activated (porous) carbon, expanded graphite, shredded carbon felt, and carbon black. The composition of carbon particles may comprise one type of carbon particles selected from the group consisting of activated (porous) carbon, expanded graphite, shredded carbon felt, and carbon black. The composition of carbon particles may comprise one type of carbon particles which are activated (porous) carbon particles. The composition of carbon particles may comprise one type of carbon particles which are expanded graphite particles. The composition of carbon particles may comprise one type of carbon particles which are shredded carbon felt particles. The composition of carbon particles may comprise one type of carbon particles which are carbon black particles. The composition of carbon particles may comprise two or more types of carbon particles selected from the group consisting of graphite, graphene, vitreous carbon, activated (porous) carbon, carbon nanotubes, expanded graphite, carbon fibre, glassy carbon, shredded carbon felt, carbon black, and carbon foam. The composition of carbon particles may comprise graphite and carbon black. The composition of carbon particles may comprise graphite or expanded graphite, carbon black, and activated carbon. The composition of carbon particles may comprise graphite, carbon black, activated carbon, and carbon fibre.

[00017] The electrolyte may further comprise a halogen sequestering agent, wherein the halogen sequestering agent (HSA) is an organic compound comprising a moiety capable of sequestering the halogen. The moiety capable of sequestering the halogen may be a quaternary ammonium group, a phosphonium group, or a sulfonium group. The moiety capable of sequestering the halogen may be a quaternary ammonium group.

[00018] The electrolyte may further comprise at least one additive selected from the group consisting of polyethyleneglycol. The electrolyte may further comprise at least one electrolyte salt selected from KC1, KBr, LiCl, LiBr, NaCl, NaBr, NH₄C1, NH₄Br, LiC104, PbCl₂, PbBr₂, and PbO.

[00019] When in use, the battery may be in a vertical configuration.

[00020] In a second aspect of the invention, there is provided a method of producing a battery, the method comprising providing a cell casing comprising an anode and a cathode, providing a separator between the anode and the cathode, preparing an anolyte by dissolving a metal halide salt, electrolyte salt, HSA and additives, preparing a catholyte by mixing silica and carbon particles in to the anolyte by high shear mixing, filling the cathode cavity with the catholyte, and filling the anode cavity with the anolyte.

[00021] In one embodiment of the invention, there is provided a battery, comprising an anode, a cathode, wherein a halogen is in contact with the cathode and a metal is in contact with the anode, and at least one electrolyte disposed between the anode and the cathode, wherein the at least one electrolyte comprises silica particles and a composition of carbon particles.

Brief Description of Drawings

[00022] Figure 1. Exemplary horizontal cell configurations (Figure 1A - horizontal

configurations with anode up; Figure IB - horizontal configurations with cathode up). [00023] Figure 2: Comparison of energy efficiency (%) of base electrolyte solution with and without the addition of silica for horizontal cell.

[00024] Figure 3: Comparison of energy efficiency (%) of carbon felt and carbon gel comprising a single type of carbon for horizontal cell.

[00025] Figure 4: Energy efficiency (%) of blended carbon silica types. Carbon felt is used as a comparison for horizontal cell.

[00026] Figure 5. Exemplary vertical cell configuration.

[00027] Figure 6. Comparison of energy efficiency (%) of electrolyte, silica, and carbon gel compositions for vertical cell.

[00028] Figure 7. Comparison of energy efficiency (%) of electrolyte, silica, carbon felt and carbon gel compositions for vertical cell.

[00029] Figure 8. Comparison of reduction in energy efficiency (%) after 12 h pause for electrolyte, silica, carbon felt and carbon gel compositions for vertical cell.

[00030] Figure 9. Anode of vertical cell after cycling with base electrolyte only on cathode side. Clear line across the middle of the electrode indicates stratification of bromine-containing electrolyte at the bottom of the cell. Mobility of bromine through liquid electrolyte enabled crossover to Zn side causing corrosion on the Zn deposit.

[00031] Figure 10. Anode of vertical cell after cycling with silica gel electrolyte (Si and base electrolyte) on cathode side. Stratification of electrolyte is clearly visible (area w/o coating on top of electrode). Crossover of bromine to the anode was clearly reduced.

[00032] Figure 11. Anode of vertical cell after cycling with carbon felt on cathode side. Carbon felt shows clear signs of stratification (area w/o coating on top of electrode; line through middle of plating). Slight signs of corrosion at bottom of electrode indicate crossover of bromine to anode. [00033] Figure 12. Anode of vertical cell after cycling with silica carbon mix gel 1 (Si, activated carbon and base electrolyte) on cathode side. Even plating quality is evident.

[00034] Figure 13. Anode of vertical cell after cycling with silica carbon gel 2 (Si, expanded graphite and base electrolyte) on cathode side. Even plating quality is evident.

[00035] Figure 14. Anode of vertical cell after cycling with silica carbon gel 3 (Si, carbon black and base electrolyte) on cathode side. Even plating quality is evident.

[00036] Figure 15. Anode of vertical cell after cycling with shredded carbon felt fibre gel (Si, shreded carbon felt and base electrolyte) on cathode side. Even plating quality is evident, but line through middle of Zn plating indicates slight stratification.

[00037] Figure 16. Anode of vertical cell after cycling with silica carbon mix gel (Si, activated carbon, expanded graphite, carbon black, and base electrolyte) on cathode side. Excellent plating quality is evident.

[00038] Figure 17. Comparison of energy efficiency (%) after 12 h pause of electrolyte, silica, 10% activated carbon gel and 20% activated carbon gel for vertical cell.

[00039] Figure 18. Comparison of recoverable charge (%) after 12 h pause of electrolyte, silica, 10% activated carbon gel and 20% activated carbon gel for vertical cell.

[00040] Figure 19. Comparison of reduction in recoverable charge (%) after 12 h pause for electrolyte, silica, 10% activated carbon gel and 20% activated carbon gel for vertical cell.

Definitions

[00041] As used in this application, the singular form“a”,“an” and“the” include plural references unless the context clearly dictates otherwise.

[00042] As used herein, the term“comprising” means“including.” Variations of the word “comprising”, such as“comprise” and“comprises,” have correspondingly varied meanings. [00043] It will be understood that use the term“about” herein in reference to a recited numerical value includes the recited numerical value and numerical values within plus or minus ten per cent of the recited value.

[00044] It will be understood that use of the term“between” herein when referring to a range of numerical values encompasses the numerical values at each endpoint of the range. For example, a temperature of between 80 °C and 150 °C is inclusive of a temperature of 80 °C and a temperature 150 °C.

[00045] As used herein, % w/v means g/mL x 100. For example, 1 g in 100 mL is equal to 1 % w/v. As used herein, the volume referred to in“% w/v” refers to the volume of base electrolyte prior to addition of gelating agent or carbon particles.

[00046] The“oxidant” refers to the element which is reduced during discharge of the battery. The “reductant” refers to the element which is oxidised during the discharge of the battery. This terminology may be applied to each element regardless of whether the battery is charging or discharging. Accordingly, during charging the“oxidant” is oxidised and the“reductant” is reduced. For example, in a metal-halogen battery, the halogen species may be referred to as the oxidant and the metal species may be referred to as the reductant.

[00047] The“anode” refers to the electrode at which the reductant is oxidised during discharge of the battery. The“cathode” refers to the electrode at which the oxidant is reduced during discharge of the battery. This terminology may be applied to each electrode regardless of whether the battery is charging or discharging. Accordingly, during charging, the oxidant is oxidised at the cathode and the reductant is reduced at the anode. For example, the halogen is reduced and oxidised at the cathode, and the metal is oxidised and reduced at the anode.

[00048] References to the“anode side” or“cathode side” of the battery refer to the electrolyte between the anode and the separator, and the electrolyte between the cathode and the separator, respectively.

[00049] Any description of prior art documents herein, or statements herein derived from or based on those documents, is not an admission that the documents or derived statements are part of the common general knowledge of the relevant art. [00050] For the purposes of description, all documents referred to herein are hereby incorporated by reference in their entirety unless otherwise stated.

Description of Embodiments

[00051] The present specification relates to a gel electrolyte for a battery, comprising carbon particles dispersed in a gel, such as a silica gel. The battery is of a type that generates electrical energy by the oxidation of a metal and the reduction of a halogen (henceforth a halogen battery). During battery discharge, the reductant, which often comprises elemental metal, is oxidised at the anode to produce metal cations. At the cathode, the halogen species, typically a molecular halogen, is reduced to halide ions.

[00052] For example, the oxidation reaction of a divalent metal at the anode during battery discharge may be represented by the forward direction of Equation 1 :

M(_s) M²⁺ + 2e ...Equation 1

The reduction reaction at the cathode during battery discharge may be represented by the forward direction of Equation 2:

...Equation 2

[00053] During charging of the battery, an electrical current is applied such that the reverse of Equations 1 and 2 take place.

[00054] Effective management of the halogen, such as bromine, is important for battery performance. Ideally, the halogen should be confined to the cathode side of the battery and the concentration of the halogen should be uniform throughout the cathode and cathode-side electrolyte. Surprisingly, the inventors have found that a gel electrolyte, comprising carbon particles dispersed in a gel, such as a silica gel, provides effective halogen management and superior battery performance, compared to other 3D electrode materials such as carbon felt in conjunction with a liquid electrolyte. It is believed that suspension of carbon particles in a gel, such a silica gel, leads to the formation of percolation pathways, enabling the entire mass of the electrolyte to effectively function as a 3 -dimensional electrode, with redox reactions occurring on the surface of the carbon particles. Superior performance of batteries of the invention may include one or more of the following advantages: • Improvement of cathode performance due to uniform halide distribution on the cathode electrode surface and reduced stratification.

• Improvement of zinc plating quality and suppression of zinc dendrites.

• Improvement in energy efficiency due to decreased halogen transport.

• Reduction of diffusion of halogen, improving cell performance by reduction of self discharge.

• Reduction of cell resistance, by reducing the non-conductive cell gap, reducing the energy loss associated with transport distances of the active species.

• Operation of the cell in multiple orientations.

Other advantages include reduced cost, the ability to tune the electrical and mechanical properties of the gel, for example to increase ease of handling and production, and improved safety due to reduced impact and risk of cell leakage.

The anode and cathode

[00055] The battery of the invention comprises an anode and a cathode. The anode is the electrode at which the oxidation reaction takes place during discharge. The cathode is the electrode at which the reduction reaction takes place during discharge. An electrode is an electrical conductor used to make contact with a non-metallic part of a circuit. The anode and cathode may comprise any suitable material, typically an inert conductor. Suitable anode materials include carbon-filled polymers, carbon fibre felts, metals (including zinc), alloys, conductive organic polymers, conductive metallo-organic polymers, and binder-held carbon powders. Suitable cathode materials include inert metals such as platinum, carbon fibre felts, halogen resistant metals, conductive oxides, carbon-filled polymers, and binder-held carbon powders. The anode and the cathode may each comprise a collector which is typically a conductive plate or mesh which is connected to the wires of an external circuit.

The redox species

[00056] The battery comprises an oxidant and reductant, which, in the operation of the battery, react in spatially separated half-reactions to generate electrical energy. This is known as discharge. The“oxidant” refers to the element which is reduced during discharge of the battery. The “reductant” refers to the element which is oxidised during the discharge of the battery. In the battery of the invention, the oxidant is a halogen, that is, one of fluorine, chlorine, bromine or iodine. Specifically, the oxidant is molecular halogen (i.e. F₂, Cb, Bn or I₂). The reductant is a metal, which may be selected from the group consisting of Zn, Mg, Ca, K, Na, Al, Fe, and Ni. Specifically, the reductant may be an elemental metal (e.g. elemental Zn, Mg, Ca, K, Na, Al, Fe, or Ni). The halogen is in contact with the cathode, where it is reduced during discharge and the metal is in contact with the anode, where it is oxidised during discharge. In alternative embodiments, the battery of the invention may contain a redox couple comprising a metal ion in two different oxidation states, such as Fe²⁺/Fe³⁺ or Mh²⁺/Mhq₂· In this case, the higher oxidation state metal ion is the oxidant (e.g. Fe³⁺), and the lower oxidation state metal ion is the reductant, (e.g. Fe²⁺).

[00057] The discharged battery of the invention comprises a halide that is derived from the halogen. That is, during the discharge of the battery the molecular halogen (i.e. F₂, CI₂, Br₂ or I₂) is reduced to the corresponding halide (i.e. F , CT, Br or G). For example, Br₂ is reduced to Br during discharge of the battery, thus the Br is derived from Br₂. The halogen from which the halide is derived may also be referred to as the halogen of the halide. The discharged battery of the invention also comprises a cation derived from the metal. That is, during discharge of the battery the elemental metal (e.g. elemental Zn Mg, Ca, K, Na, Al, Fe, or Ni) is reduced to the corresponding metal cation (e.g. Zn²⁺, Mg²⁺, Ca²⁺, K⁺, Na⁺, Al³⁺, Fe²⁺, or Ni³⁺). For example, Zn metal is oxidised to Zn²⁺ during discharge of the battery, thus the Zn²⁺ is derived from Zn metal.

[00058] Thus, the battery of the invention has a charged state wherein the oxidant is a halogen species which is a molecular halogen e.g. CI₂, Br₂, h, etc. and the reductant is a metal species which is a metal. In the charged state, when the anode and cathode are connected in an electrical circuit, electrical energy is generated by the reduction of the oxidant and the oxidation of the reductant. The battery of the invention also has a discharged state wherein the oxidant is a halogen species which is a halide anion e.g. CT, Br , G, etc. (the reduced state of the halogen), and the reductant is a metal species which is a metal cation, e.g. Zn²⁺, Mg²⁺, etc. (the oxidised state of the metal). Preferable combinations of oxidant and reductant which may be used with the battery of the invention are zinc and bromine, magnesium and bromine, or sodium and chlorine. In the battery of the invention, the oxidant is preferably a molecular bromine, and the reductant is preferably zinc metal. The separator

[00059] The battery of the invention may comprise a separator, which is a semipermeable barrier disposed between the cathode and the anode. A“semipermeable barrier” refers to a material which is typically electrically non-conductive and allows electrolyte ions to move between the anode and the cathode sides of the battery to balance charge, but reduces the diffusion of the oxidant and reductant between the two sides of the battery. Other roles of the separator may also include providing a controlled space between the anode and cathode to ensure an evenly distributed electro-chemical potential, and to provide a physical barrier to dendrites and other uneven deposits of the oxidant and/or reductant species.

The electrolyte

[00060] The battery of the invention comprises an electrolyte disposed between the anode and the cathode. The electrolyte contains a dissolved electrolyte salt which provide ionic neutrality for the charges formed at the cathode and anode during charging and discharging. For example, the dissolved electrolyte salt may be KC1, KBr, LiCl, LiBr, NaCl, NaBr, NH4CI, NFBBr, L1CIO4, PbCb, PbBn, or PbO. The salt may be KC1.

[00061] The electrolyte may contain water. The electrolyte may contain no water. The battery of the invention may comprise two different electrolytes: a catholyte disposed between the cathode and the separator, and an anolyte disposed between the anode and the separator. At least the catholyte is the“carbon gel” of the invention. In one embodiment, the battery of the invention comprises the carbon gel as the catholyte only. In an alternative embodiment, the battery of the invention comprises the carbon gel as both the catholyte and the anolyte.

[00062] The electrolyte also comprises the redox species. The electrolyte comprises a salt of the metal redox species. For example, an acetate, nitrate, sulfate, triflate permanganate, oxide, hydroxide, dichromate, perchlorate, or halide salt salt of Zn²⁺, Mg²⁺, Ca²⁺, K⁺, Na⁺, Al³⁺, Fe²⁺, or Ni³⁺. The electrolyte may comprise one, two, three, four or more salts of the metal redox species. For example, the electrolyte may comprise zinc bromide, zinc chloride, or a mixture of zinc bromide and zinc chloride. The electrolyte, specifically the catholyte, comprises the halogen redox species. For example, the catholyte may comprise bromine, chlorine or iodine. [00063] The electrolyte may also comprise additives. Additives may serve, for example to stabilise the carbon gel and/or to disperse the carbon particles. Examples of additives are polymers, including cationic, anionic, and neutral polymers. A wide range of polymers maybe used to stabilise a gel. One example of a polymer additive is polyethylene glycol (PEG). PEG may be used in an amount of between 1 to 5 % w/v, or 2 to 4, or 4% w/v. The PEG may have a molecular weight of 1000 to 10,000, or 2000-8000, or 6000 gmol ¹. Alternatively, the electrolyte may contain no additives.

[00064] The electrolyte comprises a gel in which is dispersed a composition of carbon particles. This is referred to as the“carbon gel”. The gel may be an aqueous gel. A gelating agent is a compound which forms a gel when mixed with a solvent. The gelating agent may comprise silica particles. The silica particles may be porous silica, including mesoporous silica or microporous amorphous silica, semi-crystalline or crystalline silica (such as an all-silica zeolite). The silica particles are preferably fumed silica. The diameter of the silica particles may be about 0.01 to 100 pm, it may be about 0.01 to 10, 0.01 to 25, 0.01 to 50, 0.01 to 75, 0.1 to 10, 0.1 to 25, 0.1 to 50, 0.1 to 75, 0.1 to 100, 1 to 25, 1 to 50, 1 to 75, 1 to 100, 10 to 25, 10 to 50, 10 to 75, 10 to 100, 25 to 50, 50 to 75, 75 to 100, 0.01 to 50, or about 50 to 100 pm. Preferably the particle size of the silica is about 0.2 to 30 pm. The electrolyte may comprise silica particles in an amount of about 1 to 15 % w/v of the electrolyte composition, or about 1 to 3, 1 to 5, 1 to 7, 2 to 5, 5 to 7, 1 to 5, 5 to 10, or about 10 to 15 % w/v. The electrolyte may comprise silica particles in an amount of about 1 % w/v, or about 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or about 15 % w/v. Preferably the electrolyte comprises silica particles in an amount of about 3 % w/v of the electrolyte composition. Preferably the electrolyte comprises silica particles in an amount of about 5 % w/v of the electrolyte composition. The silica acts as a thickening agent, and causes the aqueous electrolyte to form a gel. The use of a gel electrolyte reduces halide stratification, which in turn allows for more even charge distribution across the electrode.

[00065] Alternatively or additionally, the gelating agent may comprise aluminium silicate particles. Alternatively or additionally, the gelating agent may comprise particles of a zeolite. The aluminium silicate may be a zeolite. The aluminium silicate may be a solid or layered (e.g. a clay), or a porous aluminosilicate, including mesoporous aluminosilicate or microporous amorphous, semi-crystalline or crystalline aluminosilicate (such as found in zeolites). For example, suitable aluminosilicates include MCM41, ZSM-5, and USY. [00066] The carbon gel comprises a composition of carbon particles. The composition of carbon particles may contain one type of carbon particle, or it may contain two, three, four, five, six, seven, eight, nine, ten, or more types of carbon particles. The carbon particles may comprise one or more types of carbon particle selected from the group consisting of graphite, graphene, vitreous carbon, activated (porous) carbon, carbon nanotubes, expanded graphite, carbon fibre, glassy carbon, carbon black, carbon foam. The total amount of carbon particles in the electrolyte may be about 1 to 40 % w/v of the electrolyte composition, or about 1 to 5, 5 to 10, 10 to 20, 10 to 30, 10 to 40, 20 to 30, 30 to 40, 5 to 20, or about 3 to 20 % w/v. The total amount of carbon particles in the electrolyte may be about 1, 2, 3, 4, 5, 6, 7, 7.5, 8, 9, or 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 30, or 40 % w/v.

[00067] Where the electrolyte comprises one type of carbon particle, it may be present in an amount of about 3 to 40 % w/v, or about 3 to 20 % w/v, or about 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,

13, 14, 15, 16, 17, 18, 19, 20, 30 or 40 % w/v. Preferably where the electrolyte comprises one type of carbon particle, it is present in an amount of about 5 to 10, or in an amount of about 5 to 20, or in an amount of about 5 to 40 % w/v of the electrolyte composition.

[00068] Where the electrolyte comprises two types of carbon particle, each may be present in an amount of about 2 to 10 % w/v, or about 5 to 10 % w/v, or about 2, 2.5, 3, 3.5, or 4, 5, 6, 7, 8, 9, or 10 % w/v. Preferably where the electrolyte comprises two types of carbon particle, each is present in an amount of about 3 % w/v (giving a total amount of carbon particles of 6 % w/v of the electrolyte composition).

[00069] Where the electrolyte comprises three types of carbon particle, each may be present in an amount of about 1 to 5 % w/v, or about 1, 1.5, 2, 2.5, 3, 4 or 5 % w/v. Preferably where the electrolyte comprises three types of carbon particle, each is present in an amount of about 3.3 % w/v (giving a total amount of carbon particles of 10 % w/v of the electrolyte composition).

[00070] Where the electrolyte comprises four types of carbon particle, each is present in an amount of about 1 to 3 % w/v of the electrolyte composition, or about 1, 1.5, 2, 2.5, or 3 % w/v. Preferably, where the electrolyte comprises four types of carbon particle, each is present in an amount of about 2 % w/v of the electrolyte composition (giving a total amount of carbon particles of 8 % w/v of the electrolyte composition). [00071] Exemplary two carbon compositions include graphite and carbon black, carbon black and carbon nanotubes, graphite and carbon fibre, activated carbon and expanded graphite, activated carbon and carbon black, and activated carbon and graphite. Exemplary three carbon compositions include graphite, activated carbon, and carbon nanotubes, activated carbon, carbon black and expanded graphite, and graphene, expanded graphite, and carbon black. Exemplary four carbon compositions include graphite, carbon black, activated carbon, and carbon fibre, and graphene, carbon nanotubes, activated carbon, and carbon black. The carbon particles, being conductive, reduce the cell resistance by reducing the non-conductive cell gap, reducing the energy loss associated with transport distances of the active species.

Halogen sequestering agent

[00072] The electrolyte may further comprise a halogen sequestering agent (HSA). The HSA is an organic compound comprising a moiety capable of sequestering the halogen redox species. The moiety capable of sequestering the halogen may be a quaternary ammonium group, a phosphonium group, or a sulfonium group. Preferably the moiety capable of sequestering the halogen is a quaternary ammonium group. The HSA may be an ionic liquid comprising a quaternary ammonium group. For example, the HSA may comprise (a) one or more anions selected from the group consisting of bromide, chloride, iodide,

bis(trifluoromethylsulfonyl)imide, bis(fluorosulfonyl)imide, acetate, propionate, pentanoate, hexanoate, hexafluorophosphate, and tris(pentafluoro)trifluorophosphate; and (b) one or more cations selected from the group consisting of 1-butylpyridinium, 1-octylpyridinium, l-(2- hydroxyethyl)pyridinium, l-ethyl-3-methylimidazolium, l-butyl-3-methylimidazolium, 1- pentyl-3-methylimidazolium,l-hexyl-3-methylimidazolium, l-(2-methoxyethyl)-3- methylimidazolium, 1 - ( 1 -methoxymethyl) - 3 -methylimidazolium, 1 -methyl- 3 -octylimidazolium, 1 -methyl- 1 -ethylpyrolidinium, 1 -methyl- 1 -butylpyrrolidinium, 1 -methyl- 1 -hexylpyrolidinium,

1 -(2-methoxyethyl)- 1 -methylpyrrolidinium, 1 -( 1 -methoxymethyl)- 1 -methylpyrrolidinium, tetrabutylphosphonium, tributyloctylphosphonium, tributyl(2-methoxyethyl)phosphonium, tributyl-tert-butylphosphonium, tributyl( 1 -methoxymethyl)phosphonium, tetraethylammonium, tetrabutylammonium, tributyloctylammonium, tributyl(2-methoxyethyl)ammonium, tributyl(l- methoxymethyl)ammonium, and tributyl-tert-butylammonium. For example, the HSA may be 1- methylethypyrrolidinium bromide. Battery according to the invention and method of assembly

[00073] The battery according to the invention comprises an anode and a cathode as described above, which are separated by an electrolyte disposed between the anode and the cathode. The battery may also comprise a separator disposed between the anode and the cathode. A current collector may be in contact with the anode and with the cathode, to connect the cell to an external circuit. An exemplary schematic of the battery of the invention is depicted in Figure 1. Electrolyte 1 (the anolyte) and Electrolyte 2 (the catholyte) as depicted in Figure 1 may be the same or may be different.

[00074] When in use, that is, when being charged or discharged, the battery according to the invention may be in a horizontal configuration or in a vertical configuration. In use, the battery according to the invention may be in a horizontal configuration. Alternatively, in use, the battery according to the invention may be in a vertical configuration. In a horizontal configuration, the surfaces of the electrodes that are in contact with electrolyte are substantially parallel to the ground. In the horizontal configuration, the anode may be positioned above the cathode.

Alternatively, in the horizontal configuration, the anode may be positioned above the cathode (see Figures 1A and IB). In a vertical configuration, the surfaces of the electrodes that are in contact with electrolyte are substantially perpendicular to the ground. Batteries in a vertical configuration are particularly prone to stratification, which leads to uneven metal plating and the formation of dendrites. A battery according to the invention comprising the carbon gel electrolyte may have improved performance in a vertical orientation due to reduced

stratification.

[00075] The battery may be assembled in a charged state, comprising elemental metal and molecular halogen. Alternatively, the battery may be prepared in a discharged state comprising metal halide dissolved in the electrolyte. During charging, the metal ions will be reduced to elemental metal at the anode and the halide will be oxidised to molecular halogen at the cathode, resulting in the catholyte comprising dissolved molecular halogen.

[00076] The battery according to the invention may be prepared by (i) providing a cell casing comprising an anode and a cathode, and optionally current collectors (ii) providing a separator between the anode and the cathode (iii) preparing the anolyte by dissolving the metal halide salt, electrolyte salt, HSA and additives (iv) preparing the catholyte by mixing silica and carbon particles in to the anolyte by high shear mixing (v) filling the cathode cavity with the catholyte (vi) filling the anode cavity with the anolyte. Alternatively, the catholyte solution comprising the carbon gel may be filled into both the anode cavity and the cathode cavity.

Examples

Horizontal Battery Configuration

[00077] A base electrolyte solution was prepared containing ZnB n (2.5 M), ZnCh (0.5 M), KC1 (1.5 M), 1-methylethypyrrolidinium bromide (1 M) and polyethyleneglycol (MW6000, 0.94 % w/v).

[00078] Relevant parameters of the carbons used in the below examples (for both horizontal and vertical battery configurations) are as follows. The activated carbon used is activated carbon having dso of 10-15 pm. The carbon black used is carbon black having DBP absorption of 360 cm³/100 g (9g method), BET surface area of 800 m²/g, and primary particle radius of 39.5 nm. The expanded graphite used is expanded graphite having dso of between 20 and 75 pm, and powder density of 120 g/L. The graphite used is graphite having particle size < 44 pm.

[00079] Where noted, fumed silica (3 % w/v, 0.02-30 pm particle size) is mixed into the base electrolyte solution through high shear mixing.

[00080] Where noted, carbon particles of various types were mixed into the base electrolyte solution, through high shear mixing. For carbon compositions comprising a single type of carbon, 7.5 % w/v of that carbon type was added. Where the carbon composition contains two types of carbon, 3 % w/v of each carbon was added (total of 6 % w/v). Where the carbon composition contains four types of carbon, 2 % w/v of each carbon was added (total of 8 % w/v carbon).

A cell according to Figure 1 was prepared. The cell is composed of two carbon plastic electrodes, and a polymeric plastic membrane. The cathode cavity was filled with carbon gel electrolyte, and the anode cavity was filled with the base electrolyte. The cell was then sealed and cycled at a current density of 10 mA/cm². The energy efficiency (%) is reported as a function of cycle number in Figures 2 to 4. Energy efficiency is calculated as follows: E_h = E_n · E_c

Energy efficiency = Voltaic efficiency x Coulombic efficiency

[00081] The input/output current and voltage for each cell was measured during cycling. The discharge to charge ratio was calculated from these measurements and used to determine the voltaic and coulombic efficiencies.

[00082] The following electrolyte compositions were tested.

* Comparative example

[00083] In both Figure 3 and Figure 4, a mixture of carbon and silica results in a higher energy efficiency (compare, e.g. 9 and 12 in Figure 4).

Comparative Examples

[00084] Carbon felt was used in replacement of both the silica and carbon, and the carbon only. The base electrolyte solution was used, with the electrolyte being soaked into the felt prior to cell assembly.

[00085] In an additional comparative study, cells were prepared with no carbon additive and tested with and without silica addition (Figure 2). Vertical Battery Configuration

[00086] A base electrolyte solution was prepared containing ZnBn (2.5 M), ZnCE (0.5 M), KC1 (1.5 M), 1-methylethypyrrolidinium bromide (1 M) and polyethyleneglycol (MW6000, 0.94 % w/v).

[00087] Where noted, fumed silica (0.02-30 mih particle size) is mixed into the base electrolyte solution through high shear mixing. Where noted, carbon particles of various types were mixed into the base electrolyte solution, through high shear mixing.

[00088] A cell according to Figure 5 was prepared. The cell is composed of two carbon plastic electrodes, and a polymeric plastic membrane. The cathode cavity was filled with carbon gel electrolyte, and the anode cavity was filled with the base electrolyte. The cell was then sealed and cycled at 0.25 C for 4 h. Each cell was then cycled with a 12 h pausing test. Cells were run in for three cycles, then energy efficiency measurements were taken for five cycles, followed by a 12 hour pause, then one further cycle. The 12 h pause between testing induces stratification in the electrolyte. The energy efficiency (%) is reported in Figures 6 and 7. Energy efficiency values are an average of the five runs post-run-in over four cells (total of 20 values), and an average over four cells for the one cycle after 12 h pause (total of four values). Energy efficiency is calculated as above for the horizontal cell configuration.

[00089] The following electrolyte compositions were tested.

00090] *Carbon felt shredded to fine particles in a food processor.

[00091] In addition to the above, it was observed that carbon blacks (CB) provide the most consistently efficient performing gels (standard deviation < 0.3%). However these may be less stable at high C-rate for extended testing, and as shown in Figures 6 and 7 may be somewhat prone to ambient discharge during long standing between cycling (12 h pausing test). Expanded graphite (Silica carbon gel 2) and activated carbons (Silica carbon gel 1) show good stability for longer cycling (longer than the measurements above) but lower efficiencies. Equivalent blends of these materials performed well during pausing and extended cycling.

[00092] The performance of the vertical cells is also shown in tabular form below. Figure 8 depicts the % decrease in energy efficiency after 12 h pause for the vertical cells.

[00093] The anodes of the above vertical cells were examined after cycling, and are depicted in Figures 9 to 16. Stratification of bromine on the cathode side is evident as a horizontal line across the anode, with sparse zinc plating above the line. Corrosion of the zinc plating is also evident in some cells, e.g. Figure 1, due to mobility of bromine causing crossover to the anode side. Anodes from cells with the carbon gel of the invention as catholyte show good to excellent plating quality.

[00094] It was also found that increasing the activated carbon content of the silica carbon gel (such as in silica carbon gel 4, compared to silica carbon gel 1) greatly improves energy efficiency (+15%) and recoverable charge (+13%). The comparison between silica carbon gel 1 and silica carbon gel 4 is shown in Figures 17 to 19.

[00095] A common issue with silica gel is the drop in charge capacity over time. The self discharge of silica carbon gel with 10% w/v activated carbon content is more stable in the long term than either liquid electrolyte only or silica gel electrolyte. By increasing the content of activated carbon to 20% w/v the recoverable charge is greatly improved. Also observed is a reduction in stratification in vertical configuration, which is further improved with increase in activated carbon content.

[00096] By combining the stability of activated carbon with other carbons that display low resistance and high charge capacity, these properties can be tuned to produce a novel 3- dimensional electrode (gel) with high energy efficiencies and long life-time and stability.

Claims

1. A battery, comprising

an anode,

a cathode, and

at least one electrolyte disposed between the anode and the cathode,

wherein the at least one electrolyte comprises a gelating agent and a composition of carbon particles.

2. The battery of claim 1, further comprising a halogen in contact with the cathode, and a metal in contact with the anode, wherein during discharge the halogen is reduced at the cathode and the metal is oxidised at the anode.

3. The battery of claim 1, further comprising a halide in contact with the cathode, and a metal cation in contact with the anode, wherein during charging the halide is oxidised at the cathode and the metal cation is reduced at the anode.

4. The battery of claim 2, wherein the halogen is bromine.

5. The battery of claim 3, wherein the halide is bromide.

6. The battery of any one of claims 2 to 5, wherein the metal is zinc.

7. The battery of any one of claims 1 to 6, wherein the at least one electrolyte is a gel.

8. The battery of any one of claims 1 to 7, wherein the at least one electrolyte is an aqueous electrolyte.

9. The battery of any one of claims 1 to 8, wherein the gelating agent comprises silica particles, zeolite particles, aluminium silicate particles, clay particles, or a mixture thereof.

10. The battery of any one of claims 1 to 9, wherein the gelating agent comprises silica particles.

11. The battery of any one of claims 1 to 10, further comprising a separator.

12. The battery of any one of claims 1 to 11, wherein the at least one electrolyte comprises a gelating agent which is silica particles in an amount of 1 to 15 % w/v.

13. The battery of any one of claims 1 to 12, wherein the at least one electrolyte comprises a gelating agent which is silica particles in an amount of about 3 to 5 % w/v.

14. The battery of any one of claims 1 to 13, wherein the at least one electrolyte comprises the composition of carbon particles in an amount of 1 to 40 % w/v.

15. The battery of any one of claims 1 to 14, wherein the at least one electrolyte comprises the composition of carbon particles in an amount of about 5 to 20 % w/v.

16. The battery of any one of claims 1 to 15, wherein the composition of carbon particles comprises one or more types of carbon particles selected from the group consisting of graphite, graphene, vitreous carbon, activated (porous) carbon, carbon nanotubes, expanded graphite, carbon fibre, glassy carbon, shredded carbon felt, carbon black, and carbon foam.

17. The battery of any one of claims 1 to 16, wherein the composition of carbon particles comprises one or more types of carbon particles selected from the group consisting of activated (porous) carbon, expanded graphite, shredded carbon felt, and carbon black.

18. The battery of any one of claims 1 to 16, wherein the composition of carbon particles comprises two or more types of carbon particles selected from the group consisting of graphite, graphene, vitreous carbon, activated (porous) carbon, carbon nanotubes, expanded graphite, carbon fibre, glassy carbon, shredded carbon felt, carbon black, and carbon foam.

19. The battery of any one of claims 1 to 18, wherein the composition of carbon particles comprises graphite and carbon black.

20. The battery of any one of claims 1 to 19, wherein the composition of carbon particles comprises graphite or expanded graphite, carbon black, and activated carbon.

21. The battery of any one of claims 1 to 20, wherein the composition of carbon particles comprises graphite, carbon black, activated carbon, and carbon fibre.

22. The battery of any one of claims 1 to 21, wherein the electrolyte further comprises a halogen sequestering agent, wherein the halogen sequestering agent (HSA) is an organic compound comprising a moiety capable of sequestering the halogen.

23. The battery of claim 22, wherein the moiety capable of sequestering the halogen is a quaternary ammonium group, a phosphonium group, or a sulfonium group.

24. The battery of claim 22 or claim 23, wherein the moiety capable of sequestering the halogen is a quaternary ammonium group.

25. The battery of any one of claims 1 to 24, wherein the electrolyte further comprises at least one additive selected from the group consisting of poly ethyleneglycol.

26. The battery of any one of claims 1 to 25, wherein the electrolyte further comprises at least one electrolyte salt selected from KC1, KBr, LiCl, LiBr, NaCl, NaBr, NH4CI, NtBBr, L1CIO4, PbCk, PbBr₂, and PbO.

27. The battery of any one of claims 1 to 26, wherein, when in use, the battery is in a vertical configuration.

28. A method of producing a battery, the method comprising:

(i) providing a cell casing comprising an anode and a cathode,

(ii) providing a separator between the anode and the cathode,

(iii) preparing an anolyte by dissolving a metal halide salt, electrolyte salt, HSA and additives,

(iv) preparing a catholyte by mixing silica and carbon particles into the anolyte by high shear mixing,

(v) filling the cathode cavity with the catholyte, and

(vi) filling the anode cavity with the anolyte.