WO2020168391A1

WO2020168391A1 - Inert current collector

Info

Publication number: WO2020168391A1
Application number: PCT/AU2020/050154
Authority: WO
Inventors: Thomas Ellis
Original assignee: Gelion Technologies Pty Ltd
Priority date: 2019-02-22
Filing date: 2020-02-21
Publication date: 2020-08-27
Also published as: TW202105812A; AU2020224696A1

Abstract

The present specification relates to a battery, comprising an anode, a cathode, an electrolyte disposed between the anode and the cathode, a halogen, and a metal in contact with the anode, wherein the cathode comprises a collector, and wherein the collector comprises an alloy coated with a passivating layer and the passivating layer is in contact with the halogen.

Description

INERT CURRENT COLLECTOR

Cross-reference to Related Applications

[0001] The present application claims priority to Australian provisional application

AU2019900572, 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 cells separated by a permeable membrane through which a zinc bromide/bromine electrolyte is circulated. During the charging step, zinc is electroplated on the carbon anode, and Br₂ is evolved at the carbon cathode. A molecular complexing agent dissolved in the electrolyte, such as N-ethyl-N-methylpyrrolidiniumbromide (MEPBr), is used to reduce the reactivity and vapour pressure of the elemental Br₂ by complexing the majority of the Br₂ 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 stacks 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 Br₂ 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] Batteries having non-metallic electrodes, such as carbon-based electrodes, typically employ a current collector to improve conductivity between the electrode and the external circuit. The collector is a conductive component which provides electrical contact between the electrode and the external circuit.

[0006] Many existing battery types, such as lithium batteries, employ metallic current collectors, e.g. a metal plate. However, bromine and other halogens are highly corrosive to many materials including metals, making them unsuitable for use as collectors in zinc-bromine, and other metal- halogen, batteries. Existing zinc-bromine batteries, and other batteries having a halogen as one of the redox species typically utilise electrodes comprising carbon impregnated plastics, as carbon impregnated plastic is capable of withstanding the corrosive action of bromine. Other existing halogen batteries utilise electrodes comprising a titanium mesh coated with mixed metal oxide. Existing bromine-resistant electrodes have a number of disadvantages including poor conductivity (both electrical and thermal), large size, poor mechanical strength, difficulty to manufacture, poor ductility, and poor stability to organic solvents.

[0007] The present invention relates to a current collector which is at least partially resistant to corrosion by halogens and suitable for use in a halogen battery. The collector of the present invention may overcome one or more of the disadvantages or existing halogen-resistant collectors.

Summary of Invention

[0008] In a first aspect of the invention there is provided a battery, comprising an anode, a cathode, an electrolyte disposed between the anode and the cathode, a halogen, and a metal in contact with the anode, wherein the cathode comprises a collector, and wherein the collector comprises an alloy coated with a passivating layer and the passivating layer is in contact with the halogen.

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

[00010] During discharge the halogen may be reduced at the cathode and the metal may be oxidised at the anode. [00011] In a second aspect of the invention there is provided a discharged battery, comprising an anode, a cathode, an electrolyte disposed between the anode and the cathode, a halide, and a metal cation in contact with the anode, wherein the cathode comprises a collector, and wherein the collector comprises an alloy coated with a passivating layer and the passivating layer is in contact with the halide.

[00012] The following options may be used in conjunction with the second aspect, either individually or in any suitable combination.

[00013] During charging the halide may be oxidised at the cathode and the metal cation may be reduced at the anode.

[00014] The following options may be used in conjunction with the first or the second aspect, either individually or in any suitable combination.

[00015] The metal of the alloy may not be in contact with the halogen or the halide. The passivating layer may be formed from one or more elements of the alloy. The passivating layer may comprise an oxide of one or more elements from the alloy.

[00016] The electrolyte may be a non-aqueous electrolyte. The electrolyte may contain less than 1 wt.% water. The electrolyte may be a gel electrolyte.

[00017] The collector may comprise less than 5 wt.% titanium or aluminium.

[00018] The alloy may be a nickel based alloy. The nickel based alloy may comprise about 50- 65 wt.% combined Ni and Co and about 25-50 wt.% Cu. The nickel based alloy may comprise about 40-80 wt.% combined Ni and Co, about 10-35 wt.% Cr, and about 1-25 wt.% Fe. The nickel based alloy may comprise about 35-80 wt.% combined Ni and Co, about 1-30 wt.% Cr, and about 5-30 wt.% Mo. The nickel based alloy may be a Hastelloy® alloy, an Inconel® alloy, or a Monel® alloy. The nickel based alloy may be Hastelloy® C-276.

[00019] The alloy may be a stainless steel. The stainless steel may comprise about 60-80 wt.% Fe, about 10-15 wt.% Ni., and about 15-20 wt.% Cr. The stainless steel may be SAE grade 316L stainless steel. [00020] The halogen may be selected from the group consisting of fluorine, chlorine, bromine, and iodine or the halide may be selected from the group consisting of fluoride, chloride, bromide, and iodide. The halogen may be bromine or the halide may be bromide.

[00021] The metal may be selected from the group consisting of Zn, Mg, Li, K, Na, Ca, Fe, Ni, and Al. The metal may be Zn.

[00022] In a third aspect of the invention there is provided a method of producing a battery, the method comprising providing an anode, a cathode, and an electrolyte disposed between the anode and the cathode, wherein the cathode comprises a collector, wherein the collector comprises an alloy coated with a passivating layer, and placing a halogen in contact with the passivating layer and placing a metal in contact with the anode.

[00023] In a fourth aspect of the invention there is provided a method of storing electrical energy, the method comprising providing a battery comprising an anode, a cathode, an electrolyte disposed between the anode and the cathode, a halide in contact with the cathode, and a metal cation in contact with the anode; wherein the collector comprises an alloy coated with a passivating layer and the halide is in contact with the passivating layer, and applying a voltage between the anode and the cathode such that the halide is oxidised and the metal cation is reduced.

[00024] The following options may be used in conjunction with the third or the fourth aspect, either individually or in any suitable combination.

[00025] The metal of the alloy may not be in contact with the halogen or the halide. The passivating layer may be formed from one or more elements of the alloy. The passivating layer may comprise an oxide of one or more elements from the alloy.

[00026] The electrolyte may be a non-aqueous electrolyte. The electrolyte may contain less than 1 wt.% water. The electrolyte may be a gel electrolyte.

[00027] The collector may comprise less than 5 wt.% titanium or aluminium.

[00028] The alloy may be a nickel based alloy. The nickel based alloy may comprise about 50- 65 wt.% combined Ni and Co and about 25-50 wt.% Cu. The nickel based alloy may comprise about 40-80 wt.% combined Ni and Co, about 10-35 wt.% Cr, and about 1-25 wt.% Fe. The nickel based alloy may comprise about 35-80 wt.% combined Ni and Co, about 1-30 wt.% Cr, and about 5-30 wt.% Mo. The nickel based alloy may be a Hastelloy® alloy, an Inconel® alloy, or a Monel® alloy. The nickel based alloy may be Hastelloy® C-276.

[00029] The alloy may be a stainless steel. The stainless steel may comprise about 60-80 wt.% Fe, about 10-15 wt.% Ni., and about 15-20 wt.% Cr. The stainless steel may be SAE grade 316L stainless steel.

[00030] The halogen may be selected from the group consisting of fluorine, chlorine, bromine, and iodine. The halogen may be bromine.

[00031] The metal may be selected from the group consisting of Zn, Mg, Li, K, Na, Ca, Fe, Ni, and Al. The metal may be Zn.

Brief Description of Drawings

[00032] Figure 1. Schematic of corrosion test cell Assembly A (PTFE test cell).

[00033] Figure 2. Schematic of electrochemical cell Assembly B (CR2032 test cell).

[00034] Figure 3a. Cyclic voltammogram at 50 mV/s of stainless steel 316L electrode in 1M zinc bromide aqueous solutions. Figure 3b. The electrode foil appearance after cycling shows clear pitting through the electrode.

[00035] Figure 4a.: Cyclic voltammogram at 50 mV/s of stainless steel 316L electrode in saturated acetonitrile zinc bromide aqueous solution demonstrating stability of several cycles. Figure 4b. The electrode foil appearance after cycling shows no pitting or signs of corrosion after cycling.

[00036] Figure 5. Cyclic voltammogram at 10 mV/s using Assembly B with a saturated zinc bromide in DMSO electrolyte for Hastelloy C-276 collector.

[00037] Figure 6. Cyclic voltammogram at 10 mV/s using Assembly B with a saturated zinc bromide in DMSO electrolyte for niobium collector. [00038] Figure 7. Cyclic voltammogram at 10 mV/s using Assembly B with a saturated zinc bromide in DMSO electrolyte for stainless steel 316L collector.

[00039] Figure 8. Cyclic voltammogram at 10 mV/s using Assembly B with a saturated zinc bromide in DMSO electrolyte for tantalum collector.

[00040] Figure 9. Cyclic voltammogram at 10 mV/s using Assembly B with a saturated zinc bromide in DMSO electrolyte for titanium collector.

[00041] Figure 10. Discharge capacity vs cycle number at a C-rate of 2C for a cell with a 3 M zinc bromide propylene carbonate electrolyte.

[00042] Figure 11. Discharge capacity vs cycle number at a C-rate of 4C for a cell with a 2 M zinc bromide dimethyl sulfoxide electrolyte.

Definitions

[00043] As used in this application, the singular form“a”,“an” and“the” include plural references unless the context clearly dictates otherwise.

[00044] As used herein, the term“comprising” means“including.” Variations of the word “comprising”, such as“comprise” and“comprises,” have correspondingly varied meanings.

[00045] 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.

[00046] 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.

[00047] A“semipermeable barrier” refers to a material which is typically electrically non- conductive and is situated between the anode and the cathode of an electrochemical cell. The semipermeable barrier 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“semipermeable barrier” may also include providing a controlled space between the anode and cathode to ensure an evenly distributed electro-chemical potential, and to provide a resistive barrier to dendrites and other uneven deposits of the oxidant and/or reductant species.

[00048] 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.

[00049] 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.

[00050] 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.

[00051] For the purposes of description, all documents referred to herein are hereby

incorporated by reference in their entirety unless otherwise stated.

Description of Embodiments

[00052] The present invention relates to a metallic current collector (also referred to as a “collector”) that is resistant to corrosion by halogens and suitable for use in a halogen battery, such as a zinc-bromine battery. The inventors have surprisingly found that certain alloys form a passivating layer that is sufficiently resistant to bromine (and other halogens) to prevent the halogen from accessing the metal of the alloy, imparting corrosion resistance. However, the passivating layer is also sufficiently thin so that the collector is highly conductive. Without wishing to be bound by theory, it is believed that when the passivating layer is very thin, electrons are able to tunnel through the layer.

[00053] The use of alloys coated with a passivating layer in a halogen battery provides a number of advantages such as:

• smaller collector size as alloys can be shaped into a number of forms such as foils

• ease of manufacture as a result of improved ductility and weldability

• improved electrical and thermal conductivity relative to carbon plastic electrodes

• decreased cost

• improved mechanical strength

• improved stability to organic solvents, compared to carbon plastic electrodes

[00054] 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, such as activated carbon.

[00055] The battery comprises an oxidant and reductant, which, in the operation of the battery, react with one another 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, CI₂, Br₂ 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 is 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.

[00056] 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 Bn. 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 oxidised 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.

[00057] 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, Bn, I2, 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.

[00058] It is typically necessary to confine the oxidant, i.e. the halogen to the cathode side of the battery in order to prevent self-discharge. This may be achieved, for example, by including a semipermeable barrier in the battery. A“semipermeable barrier” refers to a material which is typically electrically non-conductive and is situated between the anode and the cathode of an electrochemical cell. The semipermeable barrier 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“semipermeable barrier” may also include providing a controlled space between the anode and cathode to ensure an evenly distributed electro-chemical potential, and to provide a resistive barrier to dendrites and other uneven deposits of the oxidant and/or reductant species. Suitable semipermeable barriers include micro-porous lead-acid battery membranes, polyolefin membranes, or ion- exchange membranes.

[00059] The battery of the invention comprises an electrolyte. The electrolyte may be a solution or may be a gel. The electrolyte contains dissolved ions which neutralise the charges formed at the cathode and anode. For example, the dissolved ions may be lithium ions and perchlorate ions. The electrolyte may contain water. The electrolyte may also contain less than about 50 wt.% water, or less than about 40, 30, 20, 10, 5, 2.5, 1, 0.5, 0.2, 0.1, or about 0.05% wt.% water. The electrolyte may contain no water. The electrolyte may contain a polar organic solvent such as acetonitrile, propylene carbonate or dimethyl sulfoxide (DMSO). The electrolyte may be a gelated ionic liquid film, such as those described in the publication WO 2015/117189, incorporated herein by cross-reference.

[00060] In the battery of the invention, the cathode comprises a collector. The collector is typically connected to the wires of an external circuit. The collector and the cathode are typically in extensive physical contact to enable good conductivity between the cathode and the external circuit. The cathode may be disposed on a surface of the collector. The cathode may be coated or cast on a surface of the collector. For example, the cathode may comprise a cathode material such as binder -held activated carbon powder which is cast on a collector. The anode may also comprise a collector.

[00061] The battery of the invention comprises a collector which comprises an alloy. The alloy is coated with a passivating layer. The passivating layer is a layer of material which is formed on the surface of the alloy as a result of chemical reactions of the alloy. The passivating layer may form spontaneously as a result of chemical reactions of the elements of the alloy with oxygen and water in the atmosphere, or alternatively, the passivating layer may be formed as a result of a chemical treatment, for example with nitric acid. In both cases, the passivating layer is formed from one or more elements which are comprised in the alloy and is commonly an oxide of one or more elements which are comprised in the alloy. As the alloy is coated with the passivating layer, the metal of the alloy is not in contact with the oxidant of the battery. Instead, the passivating layer is in contact with the oxidant, i.e. the halogen, and forms a substantially impervious barrier to the oxidant. [00062] Suitable alloys for use in the collector of the invention include nickel-based alloys. Nickel-based alloys are alloys in which nickel is the element that is present in the largest wt.% proportion. The skilled person will understand that the proportion of nickel present in an alloy may also include cobalt. Nickel-based alloys may also contain other elements such as copper, chromium, iron, and molybdenum. Nickel based alloys may also contain further elements including tungsten, cobalt, silicon, manganese, carbon, aluminium, titanium, niobium, vanadium, and iron.

[00063] One group of nickel-based alloys which are suitable for use in the collector of the invention are nickel-based alloys which comprise about 50-65 wt.% Ni and about 25-50 wt.% Cu. These alloys are commercially available under the trade name Monel® and are referred to herein as‘Monels’. Monel alloys may typically contain about 63-73 wt.% Ni, 28-34 wt.% Cu, 0.5-2.5 wt.% Fe, 0.1-2.0 wt.% Mn, and 0.1-0.5 wt.% Si. Alternatively, Monel alloys may contain about 52-57 wt.% Ni, 43-48 wt.% Cu, 0.5-2.5 wt.% Fe, 0.1-2.0 wt.% Mn, and 0.1-0.5 wt.% Si. Monels may also contain about 0.05-3.2 wt.% Al and about 0.3-0.9 wt.% Ti. The compositions of several exemplary Monels are set out in the table below.

[00065] Another group of nickel-based alloys which are suitable for use in the collector of the invention are nickel-based alloys which comprise about 40-80 wt.% Ni, about 10-35 wt.% Cr, and about 1-25 wt.% Fe. These alloys are commercially available under the trade name

Inconel® and are referred to herein as Tnconelsk Inconel alloys may typically contain about 44- 80 wt.% Ni, 14-30 wt.% Cr, 1-25 wt.% Fe, 0-10 wt.% Mo, 0-5.5 wt.% Nb and Ta, 0-15 wt.% Co, 0-1 wt.% Mn, 0-0.5 wt.% Cu, 0-1.5 wt.% Al, 0-3.0 wt.% Ti, 0-0.5 wt.% Si, 0-0.15 wt.% C, 0-0.01 wt.% S, 0-0.02 wt.% P, and 0-0.01 wt.% B. The compositions of several exemplary Inconels are set out in the table below.

[00067] Another group of nickel-based alloys which are suitable for use in the collector of the invention are nickel-based alloys which comprise about 35-80 wt.% combined Ni, about 1-30 wt.% Cr, and about 5-30 wt.% Mo. These alloys are commercially available under the trade name Hastelloy® and are referred to herein as‘Hastelloysk Hastelloy alloys may typically contain about 39-78 wt.% Ni, 1.5-30 wt.% Cr, 5.5-28.5 wt.% Mo, 0-3.0 wt.% Co, 0-3.0 wt.% W, 0-15 wt.% Fe, 0-1.0 wt.% Si, 0-3.0 wt.% Mn, and 0-1.0 wt.% C. The compositions of several exemplary Hastelloy s are set out in the table below. A particularly preferable Hastelloy for use in the collector of a battery of the invention is Hastelloy® C-276.

[00069] Alloys which are suitable for use in the collector of the invention include stainless steels. Stainless steels are alloys where iron is the element that is present in the largest wt.% proportion, which also contain between about 0.002 and 2.14 wt.% carbon, and a minimum of about 11 wt.% chromium. Stainless steels may also contain other elements such as molybdenum, nickel and/or copper. Stainless steels suitable for use in the collector of the invention may typically contain about 67-72 wt.% Fe, 16-18 wt.% Cr, 10-12 wt.% Ni, and 2-3 wt.% Mo. These alloys are commercially available under the name SAE 316L stainless steel. The composition of 316L stainless steel is set out in the table below.

[00071] The inventors have surprisingly found that certain alloys coated with a passivating layer have been found to be particularly preferable for use in the metal-halogen battery of the invention. The collector of the battery of the invention may preferably comprise Hastelloy® C- 276 or stainless steel 316L. The collector of the battery of the invention may preferably comprise Hastelloy® C-276. The collector of the battery of the invention may preferably comprise stainless steel 316L.

[00072] The collector may comprise less than 5 wt.% titanium or aluminium. That is, the collector may comprise less than 5 wt.% titanium and less than 5 wt.% aluminium.

[00073] Also described herein is a method of producing a battery, the method comprising providing an anode, a cathode, and an electrolyte disposed between the anode and the cathode, wherein the cathode comprises a collector, wherein the collector comprises an alloy coated with a passivating layer, placing a halogen in contact with the passivating layer and placing a metal in contact with the anode. Typically, the cathode, anode, and collector are assembled. Optionally a separator is placed between the cathode and the anode. The electrolyte is then added. The electrolyte may contain the halogen or halide and/or the metal or metal cation, for example the oxidant or the reductant may be dissolved in the electrolyte.

[00074] Also disclosed is a method of storing electrical energy comprising providing a battery of the invention as described above, which is in its discharged state (i.e. contains a halide and a metal cation), and applying to the battery an electric current such that the halide is oxidised and the metal cation is reduced. The battery of the invention has a charged state wherein the oxidant is a molecular halogen e.g. Cl₂, Br₂, I₂, etc. and the reductant is a metal, typically electroplated on the anode. 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 halide anion e.g. Cl-, Br-, G, etc. (the reduced state of the halogen), and the reductant is a metal cation, e.g. Zn²⁺, Mg²⁺, etc. (the oxidised state of the metal). When the battery of the invention is provided in its discharged state, a voltage may be applied between the anode and the cathode, such that the halide to be oxidised and the metal cation to be reduced, thereby storing electrical energy.

Examples

Corrosion Test Cell

[00075] Assembly A: Sample is mounted to a PTFE holder with an O-ring seal to make contact with electrolyte (Figure 1). The reference and counter electrode are immersed in the electrolyte for electrochemical scans. Electrolyte is degassed and protected by flow of nitrogen.

[00076] Assembly B: Collectors are cut to a round circles approximately 19 mm in diameter and assembled in a typical coin cell construction (CR2032). The collectors are placed in the positive lid and sealed in the edges to ensure that the casing does not interfere with the current response (Figure 2). The cell also contains an electrolyte- soaked glass fiber filter paper separating a zinc counter electrode with a wave spring pressing the electrode to the separator.

Cyclic Voltammetry

Water v. organic solvent

[00077] A cyclic voltammogram at 50 mV/s of the test cell was performed using Assembly A with a 316L stainless steel collector, with electrolyte containing an aqueous solution of 1M ZnBr₂ (Figures 3 a and 3b), and with electrolyte containing a saturated acetonitrile solution of ZnBr₂ (Figured 4a and 4b).

[00078] In Figures 3a and 3b, the increasing current in oxidation is indicative of the electrode being corroded by pitting into the current collector as the surface area of electrode increases. There is also no evident reductive peak for bromine as it is being consumed by corroding the surface. [00079] In Figures 4a and 4b, the resulting cyclic voltammogram is unchanged after several cycles indicating that the electrode is not being corroded. Inspection of the electrode also confirms no pitting or corrosion.

Performance of various collectors

[00080] Figures 5-9 show the cyclic voltammogram at 10 mV/s using Assembly B using a saturated zinc bromide in DMSO electrolyte for various metal collectors which show no pitting corrosion signal. (Figure 5 - Hastelloy C-276, Figure 6 - niobium, Figure 7 - stainless steel 316L, Figure 8 - tantalum, Figure 9 - titanium).

Electrochemical Cell Assembly

[00081] Anode preparation: PvDF-HFP (4 wt%) was dissolved in NMP (76wt%) with stirring at 60 °C for several hours. Activated carbon (20 wt%) was added and the suspension stirred for a few more hours at 60 °C. The suspension was then k-bar (100 mm) coated on a 316L stainless steel foil (27 mm thick) at 60 °C heating, resulting in a ~55 mm thick layer on the foil.

[00082] Cathode preparation: PvDF-HFP (4 wt%) was dissolved in NMP (71 wt%) with stirring at 60 °C for several hours. Activated carbon (25 wt%) was added and the suspension stirred for a few more hours at 60 °C. The suspension was then k-bar (200 mm) coated on 316L stainless steel foil (27 mm thick) at 60 °C heating, resulting in a ~100 mm thick layer on the foil.

[00083] The anode and cathode were separated by a glass fibre filter paper (260 mm thick) in a 316L stainless steel casing with a stainless-steel spring to press the electrodes. The cell was filled with electrolyte: 3 M zinc bromide in propylene carbonate (PC) or 2 M zinc bromide in dimethyl sulfoxide. Cell assembly was conducted under nitrogen flow gas. The discharge capacity of the cell was measured over a number of cycles (see Figures 10 and 11).

Claims

1. A battery, comprising

an anode,

a cathode,

an electrolyte disposed between the anode and the cathode,

a halogen, and

a metal in contact with the anode,

wherein the cathode comprises a collector, and

wherein the collector comprises an alloy coated with a passivating layer and the passivating layer is in contact with the halogen.

2. The battery of claim 1, wherein during discharge the halogen is reduced at the cathode and the metal is oxidised at the anode.

3. A discharged battery, comprising

an anode,

a cathode,

an electrolyte disposed between the anode and the cathode,

a halide, and

a metal cation in contact with the anode,

wherein the cathode comprises a collector, and

wherein the collector comprises an alloy coated with a passivating layer and the passivating layer is in contact with the halide.

4. The battery of claim 3, wherein during charging the halide is oxidised at the cathode and the metal cation is reduced at the anode.

5. The battery of any one of claims 1 to 4, wherein the metal of the alloy is not in contact with the halogen or the halide.

6. The battery of any one of claims 1 to 5, wherein the passivating layer is formed from one or more elements of the alloy.

7. The battery of any one of claims 1 to 6, wherein the passivating layer comprises an oxide of one or more elements from the alloy.

8. The battery of any one of claims 1 to 7, wherein the electrolyte is a non-aqueous electrolyte.

9. The battery of any one of claims 1 to 8, wherein the electrolyte contains less than 1 wt.% water.

10. The battery of any one of claims 1 to 9, wherein the electrolyte is a gel electrolyte.

11. The battery of any one of claims 1 to 10, wherein the collector comprises less than 5 wt.% titanium or aluminium.

12. The battery of any one of claims 1 to 11, wherein the alloy is a nickel based alloy.

13. The battery of claim 12, wherein the nickel based alloy comprises about 50-65 wt.% combined Ni and Co and about 25-50 wt.% Cu.

14. The battery of claim 12, wherein the nickel based alloy comprises about 40-80 wt.% combined Ni and Co, about 10-35 wt.% Cr, and about 1-25 wt.% Fe.

15. The battery of claim 12, wherein the nickel based alloy comprises about 35-80 wt.% combined Ni and Co, about 1-30 wt.% Cr, and about 5-30 wt.% Mo.

16. The battery of any one of claims 12 to 15, wherein the nickel based alloy is a Hastelloy® alloy, an Inconel® alloy, or a Monel® alloy.

17. The battery of any one of claims 12 to 16, wherein the nickel based alloy is Hastelloy® C- 276.

18. The battery of any one of claims 1 to 11, wherein the alloy is a stainless steel.

19. The battery of claim 18, wherein the stainless steel comprises about 60-80 wt.% Fe, about 10-15 wt.% Ni., and about 15-20 wt.% Cr.

20. The battery of claim 18 or claim 19, wherein the stainless steel is SAE grade 316L stainless steel.

21. The battery of any one of claims 1 to 20, wherein the halogen is selected from the group consisting of fluorine, chlorine, bromine, and iodine or wherein the halide is selected from the group consisting of fluoride, chloride, bromide and iodide.

22. The battery of any one of claims 1 to 21, wherein the halogen is bromine or wherein the halide is bromide.

23. The battery of any one of claims 1 to 22, wherein the metal is selected from the group consisting of Zn, Mg, Li, K, Na, Ca, Fe, Ni, and Al.

24. The battery of any one of claims 1 to 23, wherein the metal is Zn.

25. A method of producing a battery, the method comprising

providing an anode, a cathode, and an electrolyte disposed between the anode and the cathode, wherein the cathode comprises a collector,

wherein the collector comprises an alloy coated with a passivating layer,

placing a halogen in contact with the passivating layer and placing a metal in contact with the anode.

26. A method of storing electrical energy, the method comprising

providing a battery comprising an anode, a cathode, an electrolyte disposed between the anode and the cathode, a halide in contact with the cathode, and a metal cation in contact with the anode;

wherein the collector comprises an alloy coated with a passivating layer and the halide is in contact with the passivating layer, and

applying a voltage between the anode and the cathode such that the halide is oxidised and the metal cation is reduced.