Electrochemical cell

Abstract

The invention relates to an electrochemical cell comprising: a positive electrode in contact with a positive electrode electrolyte; a negative electrode in contact with a negative electrode electrolyte; and a separating element which separates the positive electrode electrolyte from the negative electrode electrolyte. An apparatus comprising electrochemical cell is also disclosed.

Description

[0001] ELECTROCHEMICAL CELL

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to an electrochemical cell that exhibits stable cycling performance. Further, the invention provides an apparatus comprising such an electrochemical cell. Inventive methods and uses are also disclosed.

[0004] BACKGROUND OF THE INVENTION

[0005] Recent developments in rechargeable battery technology have been mainly directed to lithium-ion and sodium-ion batteries. Lithium-ion and sodium-ion batteries are reusable secondary batteries that comprise an anode (negative electrode), a cathode (positive electrode) and an electrolyte material, both are capable of storing energy, and they both charge and discharge via a similar reaction mechanism. When a sodium-ion (or lithium-ion) battery is charging, Na+(or Li+) ions de-intercalate from the cathode and insert into the anode. Meanwhile charge balancing electrons pass from the cathode through the external circuit containing the charger and into the anode of the battery. During discharge the same process occurs but in the opposite direction.

[0006] A sodium-ion (or lithium-ion) cell comprises an active material layer coated on a current collector foil to form a cathode, and a similar arrangement exists for a corresponding anode. The cathode and anode are physically separated by a separator which allows for a flow of ions within a liquid electrolyte medium, which is present uniformly within the cell and wets the entire cathode, anode and separator. During charging, Na+(or Li+) ions shuttle from the cathode active material and are inserted in the anode active material (electrons flow through the external circuit) and the reverse process occurs during discharging (sodium (or lithium) ions are extracted from the anode active material and are inserted into the cathode active material with the electrons flowing through the external circuit, doing the useful work).

[0007] For any rechargeable battery, the energy density is represented by its specific energy which for its component cells, is a function of the delivered voltage (V) and the specific capacity (mAh / g) of each cell. For completeness, specific capacity is the electrochemical capacity of the cell divided by its mass (units of mAh / g or Ah / kg). Thus, the specific energy (in units such as Wh / kg - here, kg is the mass of the cell) is simply a product of the delivered V of the cell and the specific capacity (Ah / kg) of the cell. In the case of conventional lithium-ion batteries, for example those which use cells that comprise a lithium nickel cobalt aluminium oxide (NCA) or a lithium nickel manganese cobalt oxide (NMC) cathode material and a carbon or silicon anode, the current practically-achievable specific energy is around 300 - 350 Wh / kgceii, typically delivering a nominal cell voltage of around 3.7 V. However, most consumer-driven battery applications such as passenger electric vehicles contain battery systems with many (often hundreds) of individual cells. Consequently, the resultant commercial product or ‘battery pack’ will also include many non-cell components such as power electronics and cell-to-cell wiring to manage the smooth functioning of the battery pack. Thus, once the weights of non-cell components are taken into account, the specific energies of a lithium-ion battery pack typically do not exceed 250 Wh / kgpaCk when using today’s advanced lithium-ion cells. That said, prototype next-generation lithium-ion technology, using lithium metal anode-based cells, could, in theory, achieve upper specific energy limits of 400 - 700 Wh / kgceii (up to 500 Wh / kgpaCk). See High-energy battery technologies: The Faraday Institution (2020). Available online: https: / / faraday.ac.uk / wp- content / uploads / 2020 / 01 / High-Energy-battery-technologies-FINAL.pdf (accessed November 6, 2023)).

[0008] In the case of conventional sodium-ion batteries, for example those which use cells that comprise a sodium metal oxide cathode and a hard carbon anode, the current practically- achievable cell specific energy is limit around 160 - 220 Wh / kgceii, typically delivering a nominal cell voltage of between 2.8 - 3.6 V depending on the cell chemistry used. However, as above, once the weights of non-cell components are taken into account, the specific energies of a sodium-ion battery pack typically will not exceed 125 - 150 Wh / kgpaCk when using today’s advanced sodium-ion cells.

[0009] Hydrocarbon-based fuels such as petrol, diesel and aviation fuel (kerosine) on the other hand, have extremely high energy densities represented by specific energies of approximately 12,000 Wh / kg. Thus, even next-generation lithium-ion technology is still far short of the specific energies that are obtained from hydrocarbon-based fuels.

[0010] To enable successful battery-powered transcontinental air and ship travel, it is predicted that a minimum specific energy requirement of from 700-1200 Wh / kgpaCk is required (see Bills et al., ACS Energy Lett., 2020, 5, 663-668). Therefore, prototype next-generation lithium-ion technology will still struggle to enable successful battery-powered transcontinental air and ship travel. As a result of these high energy requirements, it is clear that a different type of battery technology is required to compete with hydrocarbon-based fuels for use in applications such as air or water travel.

[0011] The first practical rechargeable battery ever invented was the Voltaic Pile by Alessandro Volta in the 19th century which used zinc metal anodes and copper metal cathodes in water-based electrolytes such as brine and led to other similar batteries such as the Daniell Cell. In this regard, and for the purposes of this disclosure, a battery (or an electrochemical cell) that uses both a metallic active anode (negative) region and a metallic active cathode (positive) region is termed an ‘All Metal Battery (AMB)’ (or an ‘All Metal Cell (AMC))’. The Voltaic Pile, Daniell Cell or Edison’s Zn / / Ni battery (as versions of prior art AMCs) were unable to achieve energy densities that could compete with the current practically achievable specific energies of lithium- or sodium-ion batteries due to the low operating voltage of a water-based electrolyte. For instance, the reported specific energy of improved versions of Edison’s Zn / / Ni AMC (Zn as the anode and Ni as the cathode, as described in US patent 684,204 in 1901) is only around 50 - 60 Wh / kg, as reported in section 31.1 in: Linden and Reddy, Handbook of Batteries, McGraw-Hill, Third Edition, 2001.

[0012] An aim of the present invention, therefore, is to provide an electrochemical cell, particularly an AMB or an AMC, which is designed to facilitate higher specific energies and voltages than the Voltaic Pile as invented by Alessandro Volta in the 19th century. A further aim is to provide an electrochemical cell which is capable of stable cycling. Additionally, a further aim is to increase the practical specific energy delivered by an electrochemical cell (i.e. , to increase the weight fraction of active materials to the total cell weight, such that the practical specific energy will be more closely aligned with the theoretical specific energy).

[0013] SUMMARY OF THE INVENTION

[0014] The present invention achieves these aims by providing: an electrochemical cell comprising: a positive electrode in contact with a positive electrode electrolyte; a negative electrode in contact with a negative electrode electrolyte; a separating element which separates the positive electrode electrolyte from the negative electrode electrolyte; each of the positive and negative electrodes including a metallic active region; the metallic active region of the negative electrode comprising a first metallic element M1 ; the metallic active region of the positive electrode comprising a second metallic element M2; optionally the first metallic element M1 having a different standard electrode potential to the second metallic element M2; and optionally in which each of the positive and negative electrode electrolytes are selected from the group consisting of a non-aqueous electrolyte, a solid electrolyte, and combinations thereof.

[0015] In one preferred embodiment, at least one of the positive electrode electrolyte and the negative electrode electrolyte includes a solid electrolyte. In another preferred embodiment, at least one of the positive electrode electrolyte and the negative electrode electrolyte includes a nonaqueous electrolyte which preferably comprises one or more glyme-based solvents.

[0016] The term “negative electrode” as used herein refers to an electrode which comprises metallic element M1. M1 has a lower standard potential value than metallic element M2 (with reference to the standard electrode potentials as discussed herein). The term “negative electrode” may be used interchangeably with the term “anode electrode”.

[0017] The term “positive electrode” as used herein refers to an electrode which comprises metallic element M2. M2 has a higher standard potential value than metallic element M1 (with reference to the standard electrode potentials as discussed herein). The term “positive electrode” may be used interchangeably with the term “cathode electrode”.

[0018] By providing an electrochemical cell which comprises the above configuration it has been surprisingly found that such an electrochemical cell (e.g., an AMC) of the present invention shows a higher specific energy and voltage window compared to the 19thand 20thcentury versions of AMCs. More particularly, it is the use of a non-aqueous electrolyte and / or a solid electrolyte compared to the use of a water-based (i.e. , an aqueous) electrolyte in an AMC which provides such unexpected performance benefits in terms of specific energy and operating voltage window.

[0019] Preferably, the electrochemical cell as disclosed herein is an “All Metal Cell (AMC)” which is an electrochemical cell that uses both a metallic active anode (negative) region and a metallic active cathode (positive) region.

[0020] The present invention also provides an “All Metal Battery (AMB)” which comprises two or more electrochemical cells as defined herein. An “All Metal Battery (AMB)” is a battery in which all of the two or more electrochemical cells use both a metallic active anode (negative) region and a metallic active cathode (positive) region.

[0021] It will however be appreciated that an AMC or AMB as described herein could also be used in conjunction with one or more metal-ion cells, such as one or more sodium-ion cells. Indeed, an example energy storage device may comprise one or more electrochemical cells as defined herein as well as one or more sodium-ion cells.

[0022] As used herein term “non-aqueous electrolyte” refers to any suitable non water-based electrolyte that is capable of transporting ions (e.g., ions of M1 and / or M2). The non-aqueous electrolyte is ideally in a liquid state when in use. The non-aqueous electrolyte is also chemically compatible with the further components of the cells (e.g., the positive electrode, negative electrode, and separating element), and will therefore otherwise allow the electrochemical cell to function as intended.

[0023] As described above, the term “non-aqueous electrolyte” means that such an electrolyte is typically substantially free of water. However, to the extent that the non-aqueous electrolyte contains water, it contains an amount that was previously assumed to have no, or no substantial impact in terms of specific energy and operating voltage window of the electrochemical cell. Such water may occur for example as an impurity or an additive in the non-aqueous electrolyte.

[0024] In one embodiment, the non-aqueous electrolyte may contain water in an amount of no greater than about 500 ppm. Ideally, in a preferred embodiment, the non-aqueous electrolyte may contain water in an amount of no greater than about 100 ppm. Most preferably, in a very preferred embodiment, the non-aqueous electrolyte is substantially free of water.

[0025] In one embodiment, the positive electrode electrolyte is the same as the negative electrode electrolyte. Preferably, the chemical structure of the positive electrode electrolyte is the same as the chemical structure of the negative electrode electrolyte when the electrochemical cell is assembled. Therefore, the same electrolyte in terms of chemical structure may be used for both the positive electrode and the negative electrode.

[0026] Alternatively, the state of the positive electrode electrolyte is the same as the state of the negative electrode electrolyte when the electrochemical cell is in use. By ‘state’ it is meant ‘state of matter’. Thus, the electrolyte could be in either a solid state, a liquid state, or a combination thereof. A liquid state in this regard is meant to also encompass a gel state. Thus, in one embodiment, the same electrolyte in terms of state of matter is used for both the positive electrode and the negative electrode. That is, both the positive and negative electrode electrolytes may each utilise a liquid state (e.g., a non-aqueous electrolyte) when the electrochemical cell is in use. Alternatively, both the positive and negative electrode electrolytes may each utilise a solid state (e.g., a solid electrolyte) when the electrochemical cell is in use.

[0027] In one embodiment, the chemical structure and the state of matter of the positive electrode electrolyte is the same as the chemical structure and the state of matter of the negative electrode electrolyte.

[0028] Preferably, the positive electrode electrolyte is different from the negative electrode electrolyte.

[0029] In one embodiment, the chemical structure of the positive electrode electrolyte is different to the chemical structure of the negative electrode electrolyte. Therefore, a different electrolyte in terms of chemical structure maybe used for each of the positive electrode and the negative electrode.

[0030] Preferably, the state of the positive electrode electrolyte is different to the state of the negative electrode electrolyte when the electrochemical cell is in use. As set out above, by ‘state’ it is meant ‘state of matter’. Thus, the electrolyte could be in either a solid state, a liquid state, or a combination thereof. A liquid state in this regard encompasses a gel state.

[0031] Thus, in one embodiment, a different electrolyte in terms of state of matter is used for both the positive electrode and the negative electrode. Preferably, the positive electrode electrolyte may comprise a liquid state (e.g., a non-aqueous electrolyte) when the electrochemical cell is in use and the negative electrode electrolyte may comprise a solid state (e.g., a solid electrolyte) when the electrochemical cell is in use.

[0032] In a highly preferred embodiment, the chemical structure and the state of matter of the positive electrode electrolyte is different to the chemical structure and the state of matter of the negative electrode electrolyte.

[0033] As used herein, the term “metallic active region” is intended to refer to a region of an electrode (which could be the whole of the electrode, or at least a part of the electrode) that comprises an effective amount of either the first metallic element, M1 , or the second metallic element, M2. Preferably, the metallic active region is a region of the electrode that consists essentially of either the first metallic element, M1 , or the second metallic element, M2.

[0034] An ‘effective amount’ in this context means that the fi rst M1 and / or second M2 metallic element will permit charging and discharging of the electrochemical cell in use. In particular, such an amount will be effective to enable the occurrence of plating and stripping of a metal or metalloid atom.

[0035] In one embodiment, during charging of the electrochemical cell, plating occurs at the first metallic element M1 (which is ideally Na, at the negative electrode), and stripping occurs at the second metallic element M2 (which is ideally Sn, at the positive electrode). Then during discharging of the electrochemical cell, stripping occurs at the first metallic element M1 (which is ideally Na, at the negative electrode), and plating occurs at the second metallic element M2 (which is ideally Sn, at the positive electrode).

[0036] As used herein, the term “metallic” refers to a metal or metalloid.

[0037] As will be appreciated, metals and metalloids can be found in the Periodic Table in any of Group 1 (i.e., the alkali metals), Group 2 (i.e., the alkaline earth metals), Groups 3-12 (i.e., the transition metals, including the lanthanides and the actinides), Group 13, Group 14 (excluding carbon), and Group 15 (excluding nitrogen and phosphorous).

[0038] Preferably, the metallic active region of the negative electrode comprises at least 70% by weight of the first metallic element, M1. Further preferably, the metallic active region of the negative electrode comprises at least 75%, optionally at least 80%, by weight of the first metallic element, M1 . In one embodiment, the metallic active region of the negative electrode comprises at least 85%, optionally at least 90%, by weight of the first metallic element, M1.

[0039] In a further embodiment, the metallic active region of the negative electrode consists essentially of the entire weight of the first metallic element, M1. In one embodiment, the entire negative electrode consists essentially of the entire weight of the first metallic element, M1.

[0040] Preferably, the metallic active region of the positive electrode comprises at least 70% by weight of the second metallic element, M2. Further preferably, the metallic active region of the positive electrode comprises at least 75%, optionally at least 80%, by weight of the second metallic element, M2. In one embodiment, the metallic active region of the positive electrode comprises at least 85%, optionally at least 90%, by weight of the second metallic element, M2.

[0041] In a further embodiment, the metallic active region of the positive electrode consists essentially of the entire weight of the second metallic element, M2. In one embodiment, the entire positive electrode consists essentially of the entire weight of the second metallic element, M2.

[0042] In a particularly preferred embodiment, the metallic active region of the negative electrode comprises at least 70% by weight of the first metallic element, M1 , and the metallic active region of the positive electrode comprises at least 70% by weight of the second metallic element, M2.

[0043] Ideally, the metallic active region of each of the positive and negative electrodes is selected from the group consisting of a metallic body, a metallic sheet or layer, a metallic foam, a metallic sponge, a metallic element deposited onto a substrate, particles of metallic element optionally incorporated in a binder, and combinations thereof.

[0044] Preferably, the metallic active region of each of the positive and negative electrodes is selected from the group consisting of a metallic sheet or layer, and particles of metallic element optionally incorporated in a binder.

[0045] Preferably, the metallic active region of the negative electrode comprises a metallic body (i.e. , a body of metallic element), which is ideally a metallic sheet or layer when assembled in the electrochemical cell. In particular, it is preferable for the metallic active region of the negative electrode to comprise metallic sodium. Therefore, the metallic sodium may initially comprise a lump of sodium metal which is compressed to form a sheet of metallic sodium. This will typically have a constant cross-sectional thickness.

[0046] Highly preferably, the metallic active region of the negative electrode is a metallic active layer of the negative electrode.

[0047] Preferably, the metallic active region (preferably as a layer) of the negative electrode has a thickness of less than 500 pm. Further preferably, the metallic active region of the negative electrode has a thickness of between 50 pm and 450 pm, optionally between 100 pm and 300 pm. Ideally, the metallic active region of the negative electrode has a thickness of between 150 pm and 250 pm. Highly preferably, the negative electrode comprises a metallic active region which comprises a layer of the first metallic element, M1 , disposed on a surface of a suitable substrate (e.g., a current collecting element). Typically, M1 is disposed on one side of a current collecting element as a single layer of the first metallic element, M 1. Therefore, together with the current collecting element, the metallic active region (typically provided as a single layer or sheet of M1) represents the entirety of the negative electrode. Ideally, the negative electrode may be prepared by cutting a metal foil sheet to an appropriate size, and then contacting the metal foil sheet with the single sheet of M 1.

[0048] Alternatively, the negative electrode may be formed by providing a region (preferably a layer) of M1 on to a surface of a suitable substrate (e.g., a current collecting element). The region may be providing using a deposition technique selected from the group consisting of magnetron sputtering, physical vapour deposition, plasma deposition, electroplating and chemical vapour deposition. Further alternatively, the metallic active region of the negative electrode may comprise particles of metallic element, which are optionally incorporated in a binder, and further optionally one or more conductive additives as described below for the metallic active region of the positive electrode.

[0049] Preferably, the metallic active region of the positive electrode comprises particles of metallic element, which are optionally incorporated in a binder.

[0050] Highly preferably, the metallic active region of the positive electrode is a metallic active layer of the positive electrode.

[0051] Preferably, the metallic active region (preferably as a layer) of the positive electrode has a thickness of less than 500 pm. Further preferably, the metallic active region of the positive electrode has a thickness of between 50 pm and 450 pm, optionally between 100 pm and 400 pm. Ideally, the metallic active region of the positive electrode has a thickness of between 150 pm and 350 pm.

[0052] Highly preferably, the positive electrode comprises a metallic active region which comprises a layer of the second metallic element, M2, disposed on a surface of a suitable substrate (e.g., a current collecting element). Typically, M2 is disposed on one side of a current collecting element as a single layer of the second metallic element, M2. Therefore, together with the current collecting element, the metallic active region (typically provided as a layer comprising particles of M2) represents the entirety of the positive electrode. In one embodiment, the metallic active region of the positive electrode comprises a metallic active material (A), one or more optional polymeric binders (B), and one or more optional conductive additives (C). Such a mixture is typically mixed with an aqueous or non-aqueous solvent (such as water or N-methyl Pyrrolidone (NMP)) and then disposed as a layer on a surface of a suitable substrate (e.g., a current collecting element) via techniques such as doctor blade or slot die methods.

[0053] Preferably, the one or more optional polymeric binders are selected from polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), and carboxymethylcellulose (CMC). Highly preferably, the polymer binder comprises carboxymethylcellulose (CMC).

[0054] Preferably, the one or more optional conductive additives (C) may include one or more of carbon black, carbon nanotubes, graphene, acetylene black, and carbon nanofiber. Highly preferably, the one or more conductive additives includes carbon black, such as TIMCAL Super C65.

[0055] Typically, A:B:C are present in a weight ratio of from (30 to 98) : (1 to 69) : (1 to 69), and ideally in a weight ratio of from (85 to 98) : (1 to 10) : (1 to 10). When the polymer binder preferably comprises carboxymethylcellulose (CMC), A:B:C are preferably in a weight ratio of about 85:10:5 or alternatively, 90:10:10.

[0056] Alternatively, the positive electrode may be formed by providing a region (preferably a layer) of M2 on to a surface of a suitable substrate (e.g., a current collecting element). The region may be providing using a deposition technique selected from the group consisting of magnetron sputtering, physical vapour deposition, electroplating, plasma deposition, and chemical vapour deposition. Further alternatively, the metallic active region of the positive electrode may comprise a metallic body, which is ideally a sheet or layer of metallic element when assembled in the electrochemical cell.

[0057] Preferably, a current collecting element is formed from aluminium or aluminium alloy (e.g., an alloy of aluminium and one or more of Mg, Mn, Cr, Zn, Si, Fe, and Ni). Preferably, the negative electrode current collector comprises an aluminium current collector. Highly preferably, both the positive electrode current collector and the negative electrode current collector comprise an aluminium current collector. Alternatively, copper, magnesium, carbon and tin may also be used as current collector materials. Furthermore, the negative electrode current collector could be in the form of a thin foil, or in the form of porous mesh-type foils. In one embodiment, the negative and / or positive electrode current collector may also include one or more carbon-containing layers formed on one or more surfaces of the current collector. Such layers can comprise amorphous carbon (e.g., a carbon black, such as TIMCAL Super C65), ideally having a thickness from about 10 Angstrom to about 1000 pm.

[0058] In one embodiment, the positive electrode (and / or the negative electrode) are substantially free of one or more components selected from the group consisting of conductive additives, binding agents, and current collecting elements. Preferably, the negative electrode is substantially free of conductive additives and / or binding agents.

[0059] As described above, term “metallic” refers to a metal or metalloid.

[0060] The first metallic element, M1 is different to the second metallic element, M2.

[0061] The electrochemical cell of the present invention is a non-symmetrical electrochemical cell (i.e., an asymmetric electrochemical cell). This is because the positive electrode includes a metallic active region that comprises an active material which is different to the active material of the metallic active region of the negative electrode.

[0062] The first metallic element, M1 , and the second metallic element, M2, are selected such that the first metallic element M1 has a lower standard electrode potential to the standard electrode potential of the second metallic element M2.

[0063] For absolute clarity, the definition of the ‘standard electrode potential’ as used herein is synonymous with the definition that is used in the field of electrochemistry which would be known to the skilled person at the filing date of this application. Please see chapter 13 in R. Huggins, Advanced batteries: materials science aspects, Springer, 2008.

[0064] In particular, it is the value of the standard electromotive force of a cell in which molecular hydrogen under standard pressure is oxidized to solvated protons, that is, it is a measure of the H2 / H+ reaction (commonly known as the Standard Hydrogen Electrode or S.H.E.). In traditional electrochemistry, this value is taken as 0 V in aqueous solution, and all other redox couples are compared to this value: the compiled data results in the commonly-known ‘table of standard electrode potentials’ for different redox couples. Please see Table B.1 in Linden and Reddy, Handbook of Batteries, McGraw-Hill, Third Edition, 2001 In this disclosure, by reference to the aforementioned table, the first metallic element, M1 , should be at a different (i.e. , lower) standard potential than the second metallic element, M2.

[0065] The first metallic element, M1 , has a lesser (i.e., more negative) standard electrode potential than the second metallic element, M2. This is so that when the electrochemical cell in use, the electrochemical cell delivers an output voltage.

[0066] Preferably, the difference between the standard electrode potential of the first metallic element, M1 , and the second metallic element, M2 is greater than 1.2V, optionally greater than 1.5V, optionally greater than 1.75V, preferably greater than 2V or, most preferably, greater than 2.25V.

[0067] Preferably, the first metallic element first metallic element, M1 , and the second metallic element, M2 are selected such that the electrochemical cell may deliver an output voltage of greater than 1 ,2V while in use.

[0068] In one embodiment, the output voltage of the electrochemical cell in use may be greater than 1.2V, optionally greater than 1.5V or optionally greater than 1.75V. In a preferred embodiment, the output voltage of the electrochemical cell in use may be greater than 2V or, most preferably, greater than 2.25V.

[0069] In one embodiment, the electrochemical cell, delivers, in use, an output voltage of from about 1.2V to about 4.5V.

[0070] Based on data disclosed herein (e.g., the disclosure of Table 1 in experiment s), M1 and M2 may be paired as follows:

[0071] In one embodiment, M1 comprises, preferably consists essentially of, Na and M2 comprises, preferably consists essentially of, Sn.

[0072] In one embodiment, M1 comprises, preferably consists essentially of, Na and M2 comprises, preferably consists essentially of, Zn.

[0073] In one embodiment, M1 comprises, preferably consists essentially of, Na and M2 comprises, preferably consists essentially of, Cu. In one embodiment, M1 comprises, preferably consists essentially of, Na and M2 comprises, preferably consists essentially of, Fe.

[0074] In one embodiment, M1 comprises, preferably consists essentially of, Ca and M2 comprises, preferably consists essentially of, Zn.

[0075] In one embodiment, M1 comprises, preferably consists essentially of, Ca and M2 comprises, preferably consists essentially of, Cu.

[0076] In one embodiment, M1 comprises, preferably consists essentially of, Ca and M2 comprises, preferably consists essentially of, Fe.

[0077] In one embodiment, M1 comprises, preferably consists essentially of, Li and M2 comprises, preferably consists essentially of, Cu.

[0078] In one embodiment, M1 comprises, preferably consists essentially of, Li and M2 comprises, preferably consists essentially of, Fe.

[0079] In one embodiment, M1 comprises, preferably consists essentially of, Al and M2 comprises, preferably consists essentially of, Zn.

[0080] In one embodiment, M1 comprises, preferably consists essentially of, Al and M2 comprises, preferably consists essentially of, Cu.

[0081] In one embodiment, M1 comprises, preferably consists essentially of, Al and M2 comprises, preferably consists essentially of, Fe.

[0082] In one embodiment, M1 comprises, preferably consists essentially of, Mg and M2 comprises, preferably consists essentially of, Zn.

[0083] In one embodiment, M1 comprises, preferably consists essentially of, Mg and M2 comprises, preferably consists essentially of, Fe.

[0084] In one embodiment, M1 comprises, preferably consists essentially of, Mg and M2 comprises, preferably consists essentially of, Cu. Preferably, M1 comprises (preferably consists essentially of) a metal selected from the group consisting of aluminium, zinc, calcium, lithium, magnesium, potassium, sodium, and combinations thereof. Ideally, M1 is a metal selected from the group consisting of aluminium, calcium, lithium, magnesium, and sodium.

[0085] Highly preferably, M1 comprises, preferably consists essentially of, sodium.

[0086] Preferably, the second metallic element, M2 comprises (preferably consists essentially of) a metal selected from the group consisting of copper, lead, iron, tin, zinc, and combinations thereof. Ideally, M2 comprises (preferably consists essentially of) a metal selected from the group consisting of copper, iron, tin, and zinc.

[0087] Highly preferably, M2 comprises, preferably consists essentially of, tin.

[0088] According to the present invention, the negative electrode is in contact with the negative electrode electrolyte. By being ‘in contact’ in this regard it is meant that the negative electrode is in direct or indirect contact with the negative electrode electrolyte such that M1 ions can transfer from the negative electrode electrolyte and plate as M1 atoms on the metallic active region of the negative electrode during charging, and that M1 atoms on the metallic active region of the negative electrode can transfer to the negative electrode electrolyte as M1 ions during discharging.

[0089] Preferably, the negative electrode is in direct contact with the negative electrode electrolyte. That is, the metallic active region of the negative electrode is in direct physical contact with the negative electrode electrolyte during charging and / or discharging of the electrochemical cell.

[0090] According to the present invention, the positive electrode is in contact with the positive electrode electrolyte. By being ‘in contact’ in this regard it is meant that the positive electrode is in direct or indirect contact with the positive electrode electrolyte such that M2 atoms can transfer from the metallic active region of the positive electrode to the positive electrode electrolyte as M2 ions during charging, and that M2 ions can transfer from the positive electrode electrolyte and as plate as M2 atoms on the metallic active region of the positive electrode during discharging. Preferably, the positive electrode is in direct contact with the positive electrode electrolyte. That is, the metallic active region of the positive electrode is in direct physical contact with the positive electrode electrolyte during charging and / or discharging of the electrochemical cell.

[0091] According to the present invention, the electrochemical cell includes one or more separating elements. Ideally, at least one of the one or more separating elements separate the positive electrode electrolyte from the negative electrode electrolyte. In one embodiment, all of the one or more separating elements separate the positive electrode electrolyte from the negative electrode electrolyte.

[0092] Preferably, the electrochemical cell of the present invention includes a negative electrode compartment comprising a negative electrode which is disposed in contact with a negative electrode electrolyte (preferably a solid electrolyte). Preferably, the electrochemical cell of the present invention includes a positive electrode compartment comprising a positive electrode which is disposed in contact with a positive electrode electrolyte (preferably a liquid nonaqueous electrolyte). Preferably, between the negative electrode compartment and the positive electrode compartment are one or more separating elements.

[0093] Preferably, at least one of the one or more separating elements includes a polymeric separating element. Preferably, the polymeric separating element is formed from polyolefinic materials, further preferably of polypropylene.

[0094] Preferably, at least one of the one or more separating elements includes a thickness of from about 5 to about 25 pm. Preferably, all of the one or more separating elements includes a thickness of from about 5 to about 25 pm.

[0095] Preferably, the electrochemical cell includes two or more separating elements. Ideally, at least one of the two or more separating elements separate the positive electrode electrolyte from the negative electrode electrolyte. In one embodiment, all of the two or more separating elements separate the positive electrode electrolyte from the negative electrode electrolyte.

[0096] Preferably, between the negative electrode compartment and the positive electrode compartment are two or more separating elements.

[0097] Preferably, at least one of the two or more separating elements includes a polymeric separating element. Alternatively, at least one of the two or more separating elements includes a glass fibre separating element. Preferably, at least one of the two or more separating elements includes a polymeric separating element and at least one of the two or more separating elements includes a glass fibre separating element.

[0098] Alternatively, in a further preferable embodiment, the electrochemical cell includes a separating element and further includes a free-standing polymeric substrate. The separating element and the negative electrode of the electrochemical cell are located in contact with opposite sides of the free-standing polymeric substrate. The term “free-standing” means not attached to, or fixed to anything else. Thus, whilst the free-standing polymeric substrate may contact and weakly adhere to components of the electrochemical cell (e.g., the separating element or the negative electrode, for example) it remains independent. Also whilst the freestanding substrate is in use, it remains independent.

[0099] Ideally, the free-standing polymeric substrate comprises an interconnected network of pores. Therefore, as the free-standing polymeric substrate ideally comprises an interconnected network of pores the free-standing polymeric substrate therefore comprises porosity. As such, the free-standing polymeric substrate maybe defined as a free-standing porous polymeric substrate. Most preferably, the free-standing porous substrate will comprise ‘bulk region’ porosity as well as ‘surface region’ porosity to provide improved electrochemical performance.

[0100] A ‘bulk region’ as defined herein is a region that substantially extends across the thickness (in the height direction, when lying flat) of the free-standing polymeric substrate between opposite sides. A ‘surface region’ as defined herein is a region that is a surface of one or more sides (in the height direction, when lying flat) of the free-standing polymeric substrate.

[0101] The free-standing polymeric substrate may have a porosity of from about 5 to about 95%, or about 10 to about 95%, or about 20 to about 90%, or about 30 to about 80%. The porosity corresponds to a value obtained by subtracting the volume expressed from the weight and density of each ingredient in the free-standing polymeric substrate, from the volume calculated from the thickness (height), width, and length of the free-standing polymeric substrate.

[0102] Preferably, the free-standing polymeric substrate is a film, which is ideally flexible. Highly preferably, the free-standing polymeric substrate is an interfacial film positioned between the separating element and the negative electrode of the electrochemical cell. According to an embodiment of the present invention, the free-standing polymeric substrate has a cross-sectional thickness (in the height direction, when lying flat) from about 1 pm to about 40 pm.

[0103] Preferably, the free-standing polymeric substrate comprises one or more polymers. That is, one or more polymeric components. The one or more polymers may be selected from the group consisting of polyvinylidene fluoride (PVDF), polyethylene oxide (PEO), and combinations thereof. Preferably, the free-standing polymeric substrate comprises polyvinylidene fluoride (PVDF).

[0104] According to an embodiment of the present invention, the free-standing polymeric substrate may comprise one or more polymers and one or more stabilising additives. Preferably, the one or more stabilising additives are selected from the group consisting of carbon black, nanozeolites, or a combination thereof. Examples of carbon black include a C65 powder. Examples of nano zeolite include a 5 A nanozeolite powder, the ‘Nano H-ZSM-5 P-9T material provided by ACSMaterial (which is a class of nanosized crystalline aluminosilicates with the molar ratio of SiO2:AI2O3 being 91 :1) - here 5 A is the pore size of the nanozeolite.

[0105] When a stabilising additive is incorporated in the free-standing polymeric substrate, it is convenient to express the total amount of the polymeric component relative to the amount of one or more stabilising additives, as a weight ratio. Preferably, the weight ratio of the one or more polymers to the one or more stabilising additives is in the range 1 :1 to 10:1 , further preferably 2:1 to 9:1 , and particularly preferably 3:1 to 5:1. A ratio in the range 4:1 is especially preferred.

[0106] According to an embodiment of the present invention, the positive electrode electrolyte and the negative electrode electrolyte are selected from the group consisting of a non-aqueous electrolyte, a solid electrolyte, and combinations thereof.

[0107] Preferably, one of the positive electrode electrolyte and negative electrode electrolyte includes a non-aqueous electrolyte, and the other of the positive electrode electrolyte and negative electrode electrolyte includes a solid electrolyte.

[0108] In a preferred embodiment, one of the positive electrode electrolyte and the negative electrode electrolyte includes a solid electrolyte. That is, preferably at least one of the positive electrode electrolyte and the negative electrode electrolyte includes a solid electrolyte. Preferably, the other of the positive electrode electrolyte and the negative electrode electrolyte includes a non-aqueous electrolyte. That is, one of the positive electrode electrolyte and the negative electrode electrolyte includes a solid electrolyte, and the other of the positive electrode electrolyte and the negative electrode electrolyte includes a non-aqueous electrolyte.

[0109] Preferably, the positive electrode electrolyte includes the non-aqueous electrolyte and the negative electrode electrolyte includes the solid electrolyte.

[0110] In another preferred embodiment, one of the positive electrode electrolyte and the negative electrode electrolyte includes a non-aqueous electrolyte which preferably comprises one or more glyme-based solvents. That is, preferably at least one of the positive electrode electrolyte and the negative electrode electrolyte includes a non-aqueous electrolyte which preferably comprises one or more glyme-based solvents.

[0111] Preferably, the other of the positive electrode electrolyte and the negative electrode electrolyte includes a solid electrolyte. That is, one of the positive electrode electrolyte and the negative electrode electrolyte includes a non-aqueous electrolyte which preferably comprises one or more glyme-based solvents and the other of the positive electrode electrolyte and the negative electrode electrolyte includes a solid electrolyte.

[0112] Preferably, the positive electrode electrolyte includes the non-aqueous electrolyte which preferably comprises one or more glyme-based solvents, and the negative electrode electrolyte includes the solid electrolyte.

[0113] Highly preferably, the positive electrode electrolyte includes a non-aqueous electrolyte, and the negative electrode electrolyte includes a solid electrolyte. Alternatively, the negative electrode electrolyte includes a non-aqueous electrolyte, and the positive electrode electrolyte includes a solid electrolyte.

[0114] As set out above, “non-aqueous electrolyte” refers any suitable non water-based electrolyte that is capable of transporting ions and is ideally in a liquid state in use. Preferably, the positive electrode electrolyte includes a non-aqueous electrolyte.

[0115] Preferably, the non-aqueous electrolyte is an essentially non-aqueous liquid electrolyte (at ambient temperature, 25 °C, atmospheric pressure) which typically includes one or more organic solvents and / or one or more ionic liquids (i.e., a salt in a liquid state at ambient conditions).

[0116] Preferably, the non-aqueous electrolyte comprises one or more organic solvents, optionally two or more organic solvents. Highly preferably, the non-aqueous electrolyte comprises one or more glyme-based solvents, optionally two or more glyme-based solvents.

[0117] The one or more glyme-based solvents (or optional two or more glyme-based solvents) may be saturated non-cyclic polyethers preferably containing no other functional groups. Glymes are also known as glycol diethers. Suitable glyme-based solvents may be selected from: ethylene glycol dimethyl ether (monoglyme CH3-O-CH2CH2-O-CH3); diethylene glycol dimethyl ether (diglyme CH3-O-(CH2-CH2-O)2-CH3); triethylene glycol dimethyl ether (triglyme, CH3-O-(CH2CH2-O)3-CH3); tetraethylene glycol dimethyl ether (tetraglyme, CH3- O-(CH2CH2-O)4-CH3); ethylene glycol diethyl ether (ethyl glyme, CH3CH2-O-CH2CH2-O- CH2CH3); diethylene glycol diethyl ether (ethyl diglyme, CH3CH2-O-(CH2CH2-O)2- CH2CH3); ethylene glycol dibutyl ether (butyl glyme, CH3CH2CH2CH2-O-CH2CH2-O- CH2CH2CH2CH3); diethylene glycol dibutyl ether (butyl diglyme, CH3CH2CH2CH2-O- (CH2CH2-O)2-CH2 CH2CH2CH3); polyethylene glycol) dimethyl ether (polyglyme, CH3-O- (CH2CH2 -O)n-CH3); and dipropylene glycol dimethyl ether (proglyme, CH3-O- (CH2CH2CH2-O)2-CH3).

[0118] Highly suitable glyme-based solvents may be selected from ethylene glycol dimethyl ether (monoglyme), diethylene glycol dimethyl ether (diglyme), triethylene glycol dimethyl ether (triglyme) and tetraethylene glycol dimethyl ether (tetraglyme). Ethylene glycol dimethyl ether (monoglyme), diethylene glycol dimethyl ether (diglyme) and tetraethylene glycol dimethyl ether (tetraglyme) are especially preferred glyme-based solvents.

[0119] The non-aqueous electrolyte may comprise, or optionally consist essentially of, monoglyme. Alternatively, the non-aqueous electrolyte may comprise, or optionally consist essentially of, diglyme. Further alternatively, the non-aqueous electrolyte may comprise, or optionally consist essentially of, tetraglyme.

[0120] Preferably, in one embodiment, the non-aqueous electrolyte comprises, or optionally consists essentially of, monoglyme. Preferably, in an alternative embodiment, the non-aqueous electrolyte comprises, or optionally consists essentially of, a mixture of diglyme and tetraglyme. When a mixture of glyme-based compounds is used, it is convenient to express the amount of each of the one or more glyme-based solvents in terms of a weight ratio. For example, as discussed above, a glyme-based solvent might contain a mixture of diglyme and tetraglyme, and this would ideally be in the weight ratio 1 to 20: 1 to 20 wt / wt, further preferably in the weight ratio 1 to 10 : 1 to 10 wt / wt, also preferably 1 to 5 : 1 to 5 wt / wt, and most preferably in the weight ratio 1 :1 wt / wt.

[0121] Advantageous electrolyte compositions of the present invention may include one or more glyme-based solvents in an amount of at least about 60% of the total solvent composition (that is, at least 60 wt% of the total solvent weight), preferably at least about 70%, further preferably at least about 90%, by weight of the non-aqueous electrolyte. Further advantageous electrolyte compositions of the present invention may include one or more glyme-based solvents which account for substantially 100% by weight of the non-aqueous electrolyte’s total solvent composition. That is, the non-aqueous electrolyte may consist essentially of one or more glyme-based solvents, optionally two or more glyme-based solvents.

[0122] The non-aqueous electrolyte may comprise one or more metallic-containing salts. These may be described as one or more metallic-ion containing salts. As described above, term “metallic” refers to a metal or metalloid. Therefore, the non-aqueous electrolyte may include one or more metal-containing salts and / or metalloid-containing salts.

[0123] In one embodiment, the non-aqueous electrolyte may include one or more salts of the first metallic element M1 and / or one or more salts of the second metallic element M2. Preferably, the non-aqueous electrolyte comprises one or more salts of the second metallic element M2.

[0124] In one embodiment, the non-aqueous electrolyte comprises one or more salts of metallic elements selected from the group consisting of aluminium, zinc, calcium, lithium, magnesium, potassium, sodium, copper, lead, iron, tin, zinc, and combinations thereof.

[0125] As set out above, M1 may be selected from the group consisting of aluminium, zinc, calcium, lithium, magnesium, potassium, sodium, and combinations thereof. Similarly, M2 may be selected from the ground consisting of copper, lead, iron, tin, zinc, and combinations thereof.

[0126] Preferably, the non-aqueous electrolyte comprises one or more salts of metallic elements selected from the group consisting of sodium, tin, and combinations thereof. The one or more metallic-containing salts (preferably one or more salts of the first and / or second metallic element, M1 , M2) ideally comprise one or more weakly coordinating anions. The term “weakly coordinating anion” or “WCA” is well known to those skilled in the art and is used to refer to anions which comprise several (more than one) elements, which may contain halogen atoms and / or oxygen atoms, and which share a single negative charge. This means that the negative charge is spread out over the anion and makes the coordinating ability of the anion comparatively weak, for example relative to the coordinating ability of an anion which has a concentrated negative charge or one with multiple negative charges.

[0127] Highly preferably, the one or more metallic-containing salts (preferably one or more salts of the first and / or second metallic elements, M1 and / or M2) are metal or metalloid salts of one or more fluoro sulfonyl-containing compounds. Preferred fluoro sulfonyl-containing compounds (i.e., weakly coordinating anions) includes trifluoromethanesulfonate (triflate), bis(trifluoromethylsulfonyl)imide (TFSI) and / or bis(fluorosulfonyl)imide (FSI).

[0128] Most preferred fluoro sulfonyl-containing compounds include triflate and / or bis(fluorosulfonyl)imide.

[0129] Alternatively, the one or more metallic-containing salts (preferably one or more salts of the first and / or second metallic elements, M1 and / or M2) are metal or metalloid salts of one or more phosphate-containing compounds (such as hexafluorophosphate-containing compounds) or borate-containing compounds (such as tetrafluoroborate-containing compounds).

[0130] For example, preferred alternative salts may be salts of the formula M1mM2nXx, in which:

[0131] M1 is one or metals;

[0132] M2 is one or more metals and / or non-metals; and

[0133] X is a group that comprises or consists of one or more halogens, preferably selected from fluorine, chlorine, bromine and iodine, further preferably fluorine.

[0134] The amount, m, of the one or more metals, M1 , is n=1 . Ideally, the one or more metals are selected from sodium and tin.

[0135] The amount, n, of the one or more metals and / or non-metals, M2, is preferably n=1 to 3, further preferably m=1 to 2, and particularly preferably m=1. Ideally, the one or more metals and / or non-metals, M, is preferably selected from aluminium, boron, gallium, indium, iridium, platinum, scandium, Yttrium, lanthanum, antimony, arsenic and phosphorus. Particularly preferably, M is selected from aluminium, boron, gallium, phosphorus and arsenic. The amount x of halogen X is preferably x=1 to 16, further preferably x=1 to 8, more preferably x=4 or 6.

[0136] The most preferred salts of the general formula M1M2mXx, are one of more selected from sodium tetrafluoroborate (NaBF4), sodium hexafluorophosphate (NaPF6), and tin tetrafluoroborate (SnB2F8).

[0137] When M2 = tin, preferred one or more salts of the second metallic element M2 include tin tri fl ate.

[0138] In one embodiment, the non-aqueous electrolyte may comprise two or more metallic- containing salts. In particular, the non-aqueous electrolyte may include one or more salts of the first metallic element M1 and one or more salts of the second metallic element M2.

[0139] In one embodiment, the non-aqueous electrolyte comprises two or more salts of metallic elements selected from the group consisting of aluminium, zinc, calcium, lithium, magnesium, potassium, sodium, copper, lead, iron, tin, zinc, and combinations thereof. Preferably, the non-aqueous electrolyte comprises salts of sodium and tin.

[0140] Preferably, one (e.g., M1 or M2) of the two or more (e.g., M1 and M2) metallic-containing salts are metal or metalloid salts of one or more fluoro sulfonyl-containing compounds. Most preferably, all (e.g., M1 and M2) of the two or more (e.g., M1 and M2) metallic-containing salts are metal or metalloid salts of one or more fluoro sulfonyl-containing compounds. Most preferred fluoro sulfonyl-containing compounds include triflate and / or bis(fluorosulfonyl)imide.

[0141] When M1 = sodium and M2 = tin, preferred two or more metallic-containing salts include sodium triflate and tin triflate. Alternatively, preferred two or more metallic-containing salts include sodium bis(trifluoromethanesulfonyl)imide also known as NaTFSI (C2FeNNaO4S2) and tin triflate.

[0142] It is convenient to express the amount of the one or more metallic-containing salts in terms of its concentration (particularly molality) of the components in the non-aqueous electrolyte; that is, the total number of moles of the one or more metallic-containing salt (i.e., solute), per kilogram of the non-aqueous electrolyte’s solvent (i.e., the weight of the organic solvent or ionic liquid, including any electrolyte additives (if applicable)) - i.e., mol / kg. Preferably, the molality of each of the one or more metallic-containing salts is in the range 0.1 mol / kg to 5 mol / kg, and further preferably in the range 0.1 mol / kg to < 4.0 mol / kg.

[0143] Preferably, particularly when the component is tin triflate, the molality is in the range 0.5 mol / kg to < 2.5 mol / kg, more preferably 0.1 mol / kg to < 0.5 mol / kg, and most preferably 0.1 mol / kg to < 0.3 mol / kg.

[0144] Preferably, particularly when the component is sodium NaTFSI, the molality is in the range 2 mol / kg to 5 mol / kg, and further preferably in the range 2 mol / kg to < 4.0 mol / kg.

[0145] Preferably, particularly when the component is sodium triflate, the molality is in the range 0.1 mol / kg to 2 mol / kg, and further preferably in the range 0.5 mol / kg to < 1.5 mol / kg.

[0146] The total molality of all of the sodium-containing salts is preferably in the range 0.1 mol / kg to 10 mol / kg, and more preferably in the range 0.1 mol / kg to 6 mol / kg, and most preferably in the range 0.1 mol / kg to < 5 mol / kg.

[0147] In one embodiment, the non-aqueous electrolyte comprises tin triflate in the range of 0.5 mol / kg to < 2.5 mol / kg, preferably in a mixture of diglyme and tetraglyme, ideally in the weight ratio 1 : 1 wt / wt.

[0148] In an alternative embodiment, the non-aqueous electrolyte comprises tin triflate in the range of 0.5 mol / kg to < 2.5 mol / kg and NaTFSI in the range of 2 mol / kg to 5 mol / kg, ideally in monoglyme.

[0149] In a further alternative embodiment, the non-aqueous electrolyte comprises tin triflate in the range of 0.5 mol / kg to < 2.5 mol / kg and sodium triflate in the range of 0.1 mol / kg to 2 mol / kg, preferably in a mixture of diglyme and tetraglyme, ideally in the weight ratio 1 :1 wt / wt.

[0150] Preferably, the concentration of the one or more salts of the first metallic element M1 is from about 0.05 mmol / kg to about 10 mol / kg in the non-aqueous electrolyte, and preferably the concentration of the one or more salts of the second metallic element M2 in the non-aqueous electrolyte is from about 0.05 mmol / kg to about 10 mol / kg. For the avoidance of doubt, throughout this disclosure, whenever and wherever the concentration of metallic salt is mentioned, the units used are mmol or mol of the salt per kilogram of the solvent (the solvent here includes the entire solvent system, including any electrolyte additives). Further preferably, the concentration of the one or more salts of the first metallic element M1 is from about 0.1 mol / kg to about 7 mol / kg in the non-aqueous electrolyte, and further preferably the concentration of the one or more salts of the second metallic element M2 in the non-aqueous electrolyte is from about 0.075 mol / kg to about 5 mol / kg.

[0151] Highly preferably, the concentration of the one or more salts of the first metallic element M1 is from about 0.15 mol / kg to about 5 mol / kg in the non-aqueous electrolyte, and highly preferably the concentration of the one or more salts of the second metallic element M2 in the nonaqueous electrolyte is from about 0.1 mol / kg to about 3 mol / kg.

[0152] In one embodiment, the concentration of M1 ions in the non-aqueous electrolyte is at least about 250 mmol per kg of total electrolyte weight. Preferably, the concentration of M1 ions in the non-aqueous electrolyte is at least about 500 mmol per kg of total electrolyte weight. More preferably, the concentration of M1 ions in the non-aqueous electrolyte is at least about 700 mmol per kg of total electrolyte weight. For the avoidance of doubt, in this case (for the concentration of the M1 ions), the units used are mmol of the M1 ions per kilogram of the total electrolyte weight (here, the total electrolyte weight includes the weights of all metallic salts, all solvents and also all electrolyte additives, if any).

[0153] The term “solid electrolyte” as used herein refers to any suitable solid electrolyte that is capable of transporting ions. ‘Solid’ means it is in a solid state at ambient temperature (i.e. , 25 °C at atmospheric pressure), and it ideally remains in a solid state over the operating temperature range of the electrochemical cell, which for certain applications could be up to 45 or 60 °C at atmospheric pressure.

[0154] Preferably, the negative electrode electrolyte includes a solid electrolyte. Preferably, the solid electrolyte is selected from the group consisting of ceramics, sulfides, chalcogenides, halides, and combinations thereof.

[0155] More preferably, the solid electrolyte comprises one or more ceramic electrolytes. Ideally, the one or more ceramic electrolytes are doped with one or more of lithium, sodium or potassium.

[0156] Highly preferably, the one or more ceramic electrolytes includes one or more of oxides such as Na Beta Alumina, and super-ionic conductors (NASICONS) such as the poly anions, for example NZSP (NasZr2Si2POi2) Highly preferably, the sulfides I chalcogenides solid electrolytes include Na3MS4 or Na2.88Sb0.88W0.12S4. Highly preferably, the halides include Na3YCI6.

[0157] In a preferable embodiment, the one or more electrolytes of the electrochemical cell of the present invention comprise sodium beta alumina or NZSP.

[0158] Preferably the solid electrolyte has a thickness of from 50pm to 1.5mm. Further preferably, the solid electrolyte has a thickness of from 100pm to 1.25mm, optionally from 250pm to 1 .0mm. Most preferably, the solid electrolyte has a thickness of from 500pm to 950pm, such as 750pm.

[0159] Preferably, the electrochemical cell of the present invention will retain at least 50% of its first- cycle specific discharge capacity after 50 cycles at room temperature (i.e., a capacity retention of at least 50% after 50 cycles at room temperature).

[0160] Further preferably, the electrochemical cell of the present invention will retain at least 60%, optionally at least 70%, of its first-cycle specific discharge capacity after 50 cycles at room temperature. More preferably, the electrochemical cell of the present invention will retain at least 80% of its first-cycle specific discharge capacity after 50 cycles at room temperature, and ideally at least 90% of its first-cycle specific discharge capacity after 50 cycles at room temperature.

[0161] In one embodiment, the electrochemical of the present invention will retain at least 50% of its first-cycle specific discharge capacity after 100 cycles at room temperature. Preferably, the electrochemical cell of the present invention will retain at least 60%, optionally at least 70%, of its first-cycle specific discharge capacity after 100 cycles at room temperature. More preferably, the electrochemical cell of the present invention will retain at least 80% of its first- cycle specific discharge capacity after 100 cycles at room temperature, and ideally at least 90% of its first-cycle specific discharge capacity after 100 cycles at room temperature.

[0162] The present invention also provides in another aspect an energy storage device comprising two or more electrochemical cells as described herein. An energy storage device may include a battery (particularly a secondary battery), a battery pack, a battery module, or other similar energy storage device.

[0163] The present invention also provides in another aspect an apparatus or system comprising an electrochemical cell as defined herein and / or an energy storage device as described herein. A typical apparatus may include stationary or a mobile apparatus.

[0164] A typical system may include a power source system, such as a renewable energy power source system (e.g., a photovoltaic power source system or a wind power source system) which comprises an electrochemical cell as defined herein and / or an energy storage device as described herein.

[0165] A further apparatus may include a transportation device (such as vehicle, aircraft, or ship).

[0166] An apparatus may include vehicles (particularly electric vehicles), cars (particularly electric cars) and other personal transport vehicles, electric long- and short-haul buses, trucks and lorries, ships (for transporting passengers or freight or both), aeroplanes (for transporting passengers or freight or both), submarines, specialised defence vehicles, and extra-terrestrial exploration vehicles (such as manned or unmanned satellites, probes, and vehicles).

[0167] An apparatus may include any machine that is propelled along or in an environment selected from the group consisting of land, water, air, space and extraterrestrial atmosphere. The machine could be self-propelled (e.g. car, ship, or aeroplane) or it may have the ability to move without the benefit of a propulsion system (e.g. a satellite).

[0168] A further apparatus may include a flying machine. That is, any apparatus which propels itself through the air or space.

[0169] The present invention also provides in another aspect a method of operating an electrochemical cell, comprising the step of charging and / or discharging the electrochemical cell as described herein.

[0170] In one embodiment, the method comprises the step of discharging the electrochemical cell at a discharge C-rate of about C / >0.5, and more preferably about C / >1. For the avoidance of any doubt, the discharge C-rate is the discharge current divided by the theoretical current drawn under which the cell would deliver its nominal rated capacity in the specified period of hours. Therefore, a discharge C-rate of C / >0.5 (<2C) means that a discharge current will discharge the entire cell in 30 minutes or more. Similarly, a discharge C-rate of C / >1 (<1C) means that a discharge current will discharge the entire cell in 1 or more hours. In one embodiment, the step of discharging the electrochemical cell is at a discharge C-rate of from C / >0.5 to C / <200, further preferably from C / >0.5 to C / <100, further preferably from C / >0.5 to C / <50, further preferably from C / >0.75 to C / <20, and ideally from C / >1 to C / <10.

[0171] The present invention also provides in another aspect, the use, in an electrochemical cell, of an electrolyte as defined herein such as those selected from the group consisting of a nonaqueous electrolyte, a solid electrolyte, and combinations thereof. The electrochemical cell is defined as disclosed herein. In particular, the present invention may comprise:

[0172] The use, in an electrochemical cell, of an electrolyte, in which the electrochemical cell comprises: a positive electrode in contact with a positive electrode electrolyte; a negative electrode in contact with a negative electrode electrolyte; a separating element which separates the positive electrode electrolyte from the negative electrode electrolyte; each of the positive and negative electrodes including a metallic active region; the metallic active region of the negative electrode comprising a first metallic element M1 and the metallic active region of the positive electrode comprising a second metallic element M2; and optionally the first metallic element M1 having a different standard electrode potential to the second metallic element M2.

[0173] In one embodiment, the electrolyte is selected from the group consisting of a non-aqueous electrolyte, a solid electrolyte, and combinations thereof.

[0174] In one preferred embodiment, the use is of a solid electrolyte. Ideally, such solid electrolyte is used in at least one of the positive electrode electrolyte and the negative electrode electrolyte of an electrochemical cell.

[0175] In another preferred embodiment, the use is of a non-aqueous electrolyte which preferably comprises one or more glyme-based solvents. Ideally, such non-aqueous electrolyte is used in at least one of the positive electrode electrolyte and the negative electrode electrolyte of an electrochemical cell.

[0176] The electrochemical cell and / or electrolyte may be further defined as disclosed herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0177] The present invention will now be described with reference to the following figures in which:

[0178] FIGURE 1A shows a plot of cell voltage vs capacity (mAh / gSn) of a Sn / Sn AMC, cycling according to 1 mAh / cm2areal capacity, not according to the present invention;

[0179] FIGURE 2 shows a plot of cell voltage vs capacity (mAh / gSn) of a Na / Sn AMC, according to the present invention (i.e. , AMC 9);

[0180] FIGURE 3 shows a plot of cell voltage vs capacity (mAh / gSn) of a further Na I Sn AMC, according to the present invention (i.e., AMC 11);

[0181] FIGURE 4A shows a plot of cell voltage vs capacity (mAh / gSn) of a further Na I Sn AMC, according to the present invention (i.e., AMC 13);

[0182] FIGURE 4B shows a plot of discharge capacity (mAh / gSn) vs cycling number of AMC 13; and

[0183] FIGURE 5 shows a cross-sectional diagram of an example electrochemical cell according to the present invention.

[0184] DETAILED DESCRIPTION

[0185] Figure 5 illustrates a cross-sectional diagram of an example electrochemical cell 10 according to the present invention.

[0186] The electrochemical cell 10 includes a positive (cathode) electrode 12 and a negative (anode) electrode 14. The positive electrode 12 has a metallic active layer 16 situated on a positive current collector 18 and the negative electrode 14 has a metallic active layer 20 situated on a negative current collector 22. The metallic active layers 16, 20 are disposed in a face-to-face arrangement with a separator 24 there between.

[0187] In some embodiments (not shown), the positive current collector 18 and the negative current collector 22 may be absent from the electrochemical cell 10. The metallic active layer 20 of the negative electrode 14 comprises a first metallic element, M1 , and the metallic active layer 16 of the positive electrode 12 comprises a second metallic element, M2.

[0188] The electrochemical cell 10 further includes a non-aqueous liquid electrolyte 26 and a solid electrolyte 28. The non-aqueous liquid electrolyte 26 is in contact with the metallic active layer 16 of the positive electrode 12 and not in contact with the metallic active layer 20 of the negative electrode 14 as the separator 24 acts to keep the non-aqueous liquid electrolyte 26 in place.

[0189] The solid electrolyte 28 is in contact with the metallic active layer 20 of the negative electrode 14 and not in contact with the metallic active layer 16 of the positive electrode 12 as the separator 24 acts to keep the solid electrolyte 28 in place.

[0190] As the separator acts to prevent the non-aqueous liquid electrolyte 26 from mixing with the solid electrolyte 28 the separator 24 therefore divides the electrochemical cell 10 into a positive electrode compartment (including the positive electrode 12 and the non-aqueous liquid electrolyte 26) and a negative electrode compartment (including the negative electrode 14 and the solid electrolyte 28).

[0191] Of course, the separator 24 is not solely limited to one element or device as shown in Figure 5. For instance, the separator 24 may comprise two or more different sheets or films which are positioned between the positive electrode 16 and negative electrode 14 as described with reference to the specific examples below.

[0192] EXAMPLES

[0193] The electrochemical cells (All Metal Cells; AMCs) of the present application were prepared using the following general procedure:

[0194] General procedure for non-aqueous liquid electrolyte preparation

[0195] The non-aqueous liquid electrolyte compositions were prepared as follows.

[0196] Appropriate amounts of solvents for a desired solvent system were mixed together in a glass vial in the desired weight ratio. To dry the solvent-mix, activated 4 A molecular sieves were added and the solvent mix was allowed to dry at last for 18 h. In a separate glass bottle with a magnetic pellet, the required weights of one or more desired metal salts were added followed by the required quantity of the required solvent mix. The salts and solvent mix were magnetically stirred at least for 18 h, whereupon the resultant electrolyte was ready for use.

[0197] The liquid electrolyte compositions used in this disclosure were:

[0198] AHL 1 : 0.25 m Sn(SOsCF3)2 (Tin Triflate) in (Tetragylme: Diglyme = 1 :1 wt / wt).

[0199] AEL 2: 0.2 m Sn Triflate + 4 m NaFSI in Monoglyme.

[0200] AEL 3a: 0.25 m Sn Triflate + 1 m Na Triflate in (Tetragylme: Diglyme = 1 :1 wt / wt).

[0201] In this regard, the weight % is with respect to the total solvent system weight (solvents and additives) and does not include the salt weight.

[0202] In some examples (as indicated below), a ceramic solid electrolyte was also used. This solid electrolyte is sodium beta alumina (in the ” phase, with the nominal composition of “Na1.7Li0.3AI10.7O17” as stated by the chemical supplier), purchased commercially, with a thickness of 750 pm. In this disclosure, this ceramic solid electrolyte is simply called ‘Na Beta Alumina’.

[0203] General procedure for metal electrode preparation

[0204] Sodium metal electrodes were made as follows: inside an argon-filled glove box, a lump of sodium metal was first hand-rolled to achieve consistent thickness. Then, a 2.2 cm x 2.2 cm Al based current collector was placed on it and with a sharp knife, the sodium metal was cut around the Al foil, to result in the final electrode.

[0205] Tin metal electrodes were made as follows, using a traditional slurry casting method. Commercially-available micrometre-sized Tin particles were mixed with 10 wt% carbon black conductive additives (such as C65 conductive additives) and either 5 wt% or 10 wt% of sodium salt of carboxymethyl cellulose (CMC) as the binder in water solvent, and then slurry cast onto an Al based current collector via the doctor blade technique. The final electrode composition of Sn used in this work was approximately 85 wt% Sn, 10 wt% carbon additives and 5 wt% CMC binder, or in some examples, 90 wt% Sn, 10 wt% carbon additives and 10 wt% CMC binder. General procedure for Cell Fabrication

[0206] For comparative symmetrical cells with Sn metal cathodes and anodes:

[0207] Outside the glove box, one or more 25 pm polypropylene (PP) separators were placed inbetween two Sn electrodes secured with Kapton tape. The electrode stack was then placed inside a pouch material and placed for drying under dynamic vacuum. Subsequently, this pouch was brought into the glove box and appropriate amount (-100 mg) of liquid electrolyte was added. Finally, the pouch cell was sealed inside the glove box. The sealed pouch cell was brought out of the glove box, placed between clamps to achieve a desired pressure and internal resistance, incubated for 9-24 h at 30 °C, then placed for cycling.

[0208] For asymmetric M1 / / M2 All Metal Cells (AMCs):

[0209] Outside a glove box, ‘half’ electrode stacks were firstly fabricated with the following configurations (as specified for different experiments):

[0210] Sn Cathode (as prepared above) | 25 pm polypropylene separator or

[0211] Sn Cathode (as prepared above) | 6-7 pm 5A Nanozeolite free standing film | 25 pm polypropylene separator or

[0212] Sn Cathode (as prepared above) | 25 pm polypropylene separator | 260pm GF / A glass fibre separator

[0213] This ‘half electrode stack’ was placed for drying in dynamic vacuum at a suitable temperature (such as 60 °C), before being brought into the glove box.

[0214] Once inside the glove box, Na Beta Alumina solid electrolyte was placed on the other side of the PP or GF / A separators, and then, the Na metal electrode was added. An appropriate amount of the liquid electrolyte composition (such as 200 - 225 mg) was then added to the separators on the Sn cathode side. Finally, the pouch cell was sealed inside the glove box. The sealed pouch cell was brought out of the glove box, placed between clamps to achieve a desired pressure and internal resistance, incubated for 9-24 h at 30 °C, then placed for cycling.

[0215] The 25 pm polypropylene separator used was bought commercially from Shenzhen Senior Technology Material of grade SD425202, although any other similar polyolefinic separator could also be used. The 260pm GF / A glass fibre separator was the grade Whatman 1820- 047 bought from Whatman®.

[0216] The 6-7 pm 5A Nanozeolite free standing film was prepared by the technique described in GB patent application number GB2403292.2 (it is film FC 2 in that application). It was prepared as follows:

[0217] The Nanozeolite free standing film was prepared via a slurry casting and delamination technique. It involved first making a mixture of a hydrophobic polymer (such as PVDF) with solvent (such as NMP, although other suitable solvents can be used here as well, such as acetonitrile), followed by adding a stabilizing additive to the mixture (such as 5 A nanozeolite powder), slurry casting this on a flat glass plate, soaking this casted polymer film (in the wet state) into a water bath, followed by delamination (peeling off the layer), and then finally placing the film for drying at room temperature in ambient air.

[0218] Cell Testing

[0219] The cells were tested using Constant Current (Galvanostatic) Cycling techniques. Generally speaking, the cells were first charged via the constant current (CC) mode to a pre-defined maximum voltage limit. Afterwards, the cell was made to undergo a constant voltage (CV) step at that maximum voltage limit, to either a pre-defined time or this CV step was made to last until the current dropped to a pre-defined value, as indicated in the examples. The discharge process was conducted at CC-mode to the lower cut-off voltage.

[0220] In some examples, cells were only subjected to CC charge, to either a pre-defined voltage value, or to a specified time for CC charging (that is, to a specific capacity value) - the cell was made to stop charging as soon as it reached either of the end condition. The discharge process was as usual in CC mode, to a pre-defined lower cut-off voltage value.

[0221] In comparative symmetrical cells, the cycling was conducted in purely CC mode: the cells were made to cycle between -1 V to +1 V, or to a pre-defined time (capacity) value, for each- half cycle. In this way, Sn plating occurred during one half-cycle on one electrode, whilst Sn stripping occurred on the other electrode, during this half-cycle - the process was reversed in the next half-cycle.

[0222] A commercial battery cycler from Neware (China) or Biologic (France) was used. During charging of AMCs including Na Beta Alumina solid electrolyte and a glyme-based nonaqueous liquid electrolyte, M2 atoms stripped from the cathode and entered into the liquid electrolyte composition as M2 ions, whilst simultaneously Na+ions travelled from the liquid electrolyte composition, through the Na Beta Alumina solid electrolyte and then plated on the Na metal anode. During discharge, Na was stripped from the Na metal and travelled through the Na Beta Alumina solid electrolyte as Na+ions, before entering the liquid electrolyte composition as Na+ions. Meanwhile, the M2 ions in the liquid electrolyte composition then plated back onto the cathode electrode as M2 metal.

[0223] Comparative Experiment 1 - Cycling of a symmetrical AMC

[0224] A Sn / / Sn symmetrical AMC pouch cell was fabricated, to study whether Sn plating / stripping could occur reliably, as follows:

[0225] Cell # AMC 2: Sn metal | 25 pm PP separator filled with AHL 1 | Sn metal

[0226] AHL 1 (as stated above) = 0.25 m Sn Triflate in Tetraglyme: Diglyme = 1 :1 wt / wt.

[0227] The cell was made to cycle at different areal capacities, in different cycles.

[0228] Figure 1 shows the cycling of Cycles 3 - 6 of AMC 2, with a reversible areal capacity of 1 mAh / cm2. It was observed in the cycling curves that the polarization actually decreased with each cycle number.

[0229] The cycling curves of Figure 1 confirmed reliable and efficient Sn plating / stripping from the Sn metal electrodes in AHL 1 liquid electrolyte. In particular, this is because the polarization was very low in each cycle (and polarization actually decreased with each cycle). Further, the system showed its expected full Sn plating / stripping with each half-cycle. One can see in Figure 1 , that for each half-cycle, the voltage did not significantly increase.

[0230] Experiment 2 - Cycling of asymmetric AMCs

[0231] The following asymmetric AMCs according to the present invention (that is, full cells with M1 anode and a separate M2 cathode) were fabricated as follows. Na / / Sn asymmetric AMC - improved capacity.

[0232] For the case of a Na / / Sn asymmetric AMC, it was realized that Sn2+in the electrolyte reacts with Na metal. Therefore, an ionically conducting barrier between Na metal, and the Sn2+containing liquid electrolyte ‘compartment’ or ‘half-cell’ was utilised in this example. This was achieved by using a ceramic solid electrolyte (Na Beta Alumina) which was placed in physical contact with the Na metal electrode. Please refer to the ‘general cell construction’ section for further information.

[0233] For the case of a Na / / Sn asymmetric AMC, it was also realized that low capacities can arise when there was insufficient Na+in the non-aqueous liquid electrolyte ‘to complete the internal circuit’: as such, during charging, Sn2+strips from the Sn electrode, and to complete the internal circuit, either Sn2+needs to ‘reach’ the Na metal anode, or Na+needs to ‘reach’ the Na metal anode.

[0234] Hence, the second key insight was that for Na / / Sn AMC to work, there needs to be sufficient Na+in the electrolyte - this can either be achieved via:

[0235] Option (a): little electrolyte quantity (but with sufficient Na+present by virtue of high concentration of the Na salt in the liquid electrolyte), or

[0236] Option (b): standard concentration (such as 1 m) of Na+salt present in the liquid electrolyte, but higher quantities of liquid electrolyte presence.

[0237] Both of the above approaches were tried:

[0238] Cell # AMC 9:

[0239] Configuration:

[0240] Na metal | Na Beta Alumina | (25 pm PP separator | 6-7 5A Nanozeolite Molecular Sieve filled with 57 mg of AEL 1) | Sn metal.

[0241] Electrolyte: AEL 2 = 4 m NaFSI + 0.2 m Sn Triflate in Monoglyme.

[0242] Hence, this approach is equivalent to Option (a) above. Result:

[0243] The actual areal capacity of the Sn electrode was 1 .5 mAh / cm2 (assuming Sn shows its full theoretical capacity of 450 mAh / gsn). However, from the previous results which the inventor acquired and whose results were qualitatively summarized in the previous page, it is now clear that not all of this will be the ‘accessible’ capacity - that will be dictated by the amount of Na+in the electrolyte.

[0244] In AMC 9 cell, 57 mg of AEL 2 was added. This equates to 0.12 mmol of Na+, which equates to an areal capacity of 0.666 mAh / cm2- to be clear, this is the areal capacity of Na+present just in the electrolyte, which could also be termed as the ‘accessible capacity’ of AMC 9.

[0245] Figure 2 shows two cycles of AMC 9. It was designed to be cycled at ±C / 10 to result in 150 mAh / gsn (assuming it lasts 10 h), with a resultant areal capacity of 0.233 mAh / cm2. As can be seen from Figure 2, AMC 9 delivered 95.7 mAh / gsn in the first cycle, although the cycling was not stable, as the second cycle only delivered 17.1 mAh / gsn.

[0246] Na / / Sn asymmetric AMC - improved cycling stability

[0247] It was hypothesized that the poor cycling stability of AMC 9 was due to influence of the FSI' anion on the Sn plating / stripping since the Sn / / Sn symmetrical AMC 2 showed reversible and stable cycling when the counter ion was the triflate anion (SO3CF3)' moiety.

[0248] Hence, attempts were made to use just the triflate anion in the electrolyte.

[0249] Cell # AMC 11 :

[0250] Configuration:

[0251] Na metal | Na Beta Alumina | (1 Layer of Whatman GF / A glass fiber separator + 25 pm PP separator filled with 220 mg of AEL 3a) | Sn metal.

[0252] Electrolyte: AEL 3a = 1 m Na Triflate + 0.25 m Sn Triflate in Tetraglyme: Diglyme = 1 :1 wt / wt.

[0253] Hence, this approach is equivalent to Option b) above.

[0254] Result: The actual areal capacity of the Sn electrode was 1.365 mAh / cm2(assuming Sn shows its full theoretical capacity of 450 mAh / gsn).

[0255] In AMC 11 cell, 220 mg of AEL 3a was added. This equates to 0.172 mmol of Na+, which equates to an areal capacity of 0.955 mAh / cm2- of Na+present just in the electrolyte, which could also be termed as the ‘accessible capacity’ of AMC 11.

[0256] Figure 3 shows three cycles of AMC 11. It was designed to be cycled at ±C / 10 to result in 120 mAh / gsn (assuming it lasts 10 h), with a resultant areal capacity of 0.364 mAh / cm2. As can be seen from Figure 3, the cell could now deliver a relatively stable capacity around 93 mAh / gsn in the first three cycles, confirming relatively stable reversible cycling, proving the concept. 93 mAh / gsn is equivalent to 20 % of the total Sn electrode’s capacity.

[0257] Another experiment was undertaken, this time, with the target of demonstrating further cycling stability of the Na / / Sn AMC. With this in mind, AMC 13 was fabricated in an identical manner to AMC 11 , but cycled differently, as shown below:

[0258] Cell # AMC 13:

[0259] Configuration:

[0260] Na metal | Na Beta Alumina | (1 Layer of Whatman GF / A glass fiber separator + 25 pm PP separator filled with 220 mg of AEL 3a) | Sn metal.

[0261] Electrolyte: AEL 3a = 1 m Na Triflate + 0.25 m Sn Triflate in Tetraglyme: Diglyme = 1 :1 wt / wt.

[0262] Hence, this approach is equivalent to Option b) above.

[0263] Result:

[0264] The actual areal capacity of the Sn electrode was 1.365 mAh / cm2(assuming Sn shows its full theoretical capacity of 450 mAh / gsn).

[0265] In AMC 13 cell, 220 mg of AEL 3a was added. This equates to 0.172 mmol of Na+, which equates to an areal capacity of 0.955 mAh / cm2- the areal capacity of Na+ present just in the electrolyte, which could also be termed as the ‘accessible capacity’ of AMC 11. AMC 13 was designed to be cycled at ±1C to result in nominal 27 mAh / gsn (assuming it lasts 1 h) which is effectively 6 % of the full capacity of Sn. The cell was subjected to 1 h 15 min of constant current charging or 3.4 V (whichever occurred first), and 1 h 20 min of constant current discharge or to 1 .8 V, whichever occurred first.

[0266] Figure 4a shows cycling profiles of cycles 1 , 2, 10, 50 and 75, whilst Figure 4b shows the capacity and the Round Trip Energy Efficiency (RTEE) vs cycle life plot for AMC 13.

[0267] As can be seen from Figures 4a and 4b, AMC 13 could now deliver stable capacity of around 30-31 mAh / gsn over 80 cycles (the capacity actually increased with cycle number), confirming the stable reversible cycling. This is equivalent to ~6.8 % of the total Sn electrode’s capacity.

[0268] As shown, the cell also displayed an RTEE of around 80 - 86 % throughout its cycle life.

[0269] When modelled to a 20 Ah cell, the expected cell energy density of AMC 13 equates to 49 Wh / kg at that scale.

[0270] With a particular reference to lead-acid batteries, which typically deliver no higher than 40 Wh / kg at comparable scales and with an RTEE around 75 %, it can be seen that the Na / / Sn AMC, even when operated at 6-7% of its rated capacity, can deliver higher specific energy and RTEE values than the ubiquitous lead-acid batteries.

[0271] Conclusions

[0272] AMC 11 was reversibly cycled at 20 % of its theoretical capacity (90mAh / gsn). In contrast, the first lithium cell reported by Whittingham in 1976 cycled at a mere 4% of its theoretical capacity. Indeed, translating the performance of AMC 11 into a scaled-up cell still operating at 20% of theoretical capacity would deliver a cell with an energy density of 137Wh / kg. This is already significantly higher than that of a lead acid battery (40-60 Wh / kg).

[0273] Assuming that productive AMC development continues in the coming years, the inventors anticipate that AMCs will soon exhibit energy densities that greatly exceed even those of the most advance lithium-ion cells available today.

[0274] Furthermore, AMC 13 demonstrated that AMCs are able to exhibit stable and reversible cycling over 80 cycles. Therefore, future AMCs would additionally maintain their high energy densities for many cycles. Experiment 3 - Modelled data

[0275] Table 1 below lists preferable M1 / / M2 pairings, alongside modelled electrochemical data for resulting cells (AMCs). In the modelling, realistic cell performance in terms of energy density (for example, the Wh / kgceii) has been predicted. The cell voltage is as per the standard electrode potentials in large-format pouch cells (cell capacity in excess of 290 Ah).

[0276] The results of the modelling have been captured in the following key metrics: the modelled (and realistic) Wh / kgceii, the calculated weights of M1 and M2, and the estimated price per kWh ($ / kWh) of stored energy. The cost includes only the weights of metal anodes and metal cathodes (both electrodes are just used as metal foils). The costing analyses was conducted in February 2024 and reflects the market price of the metals, during this time period. Table 1 From Table 1 , it can be seen that the inventors expect such AMCs to either result in similar or higher Wh / kgceii than the current best state-of-the-art next-generation Li-ion cells. Furthermore, all AMCs are expected to be extremely low cost.

Claims

CLAIMS1. An electrochemical cell (10) comprising: a positive electrode (12) in contact with a positive electrode electrolyte (26); a negative electrode (14) in contact with a negative electrode electrolyte (28); a separating element (24) which separates the positive electrode electrolyte (26) from the negative electrode electrolyte (28); each of the positive and negative electrodes (12, 14) including a metallic active region (16, 20); the metallic active region (20) of the negative electrode (14) comprising a first metallic element M1 and the metallic active region (16) of the positive electrode (12) comprising a second metallic element M2; the first metallic element M1 having a different standard electrode potential to the second metallic element M2; and in which at least one of the positive electrode electrolyte (26) and the negative electrode electrolyte (28) includes a solid electrolyte.

2. The electrochemical cell according to claim 1 , in which the other of the positive electrode electrolyte (26) and the negative electrode electrolyte (28) includes a nonaqueous electrolyte.

3. The electrochemical cell according to claim 2, in which the positive electrode electrolyte (26) includes the non-aqueous electrolyte, and the negative electrode electrolyte (28) includes the solid electrolyte.

4. The electrochemical cell according to any one of claims 2 to 3, in which the nonaqueous electrolyte comprises one or more glyme-based solvents.

5. The electrochemical cell according to any one of claims 1 to 4, in which the solid electrolyte comprises a ceramic electrolyte.

6. The electrochemical cell according to claim 5, in which the ceramic electrolyte is doped with one or more of lithium, sodium or potassium.

7. An electrochemical cell (10) comprising: a positive electrode (12) in contact with a positive electrode electrolyte (26);a negative electrode (14) in contact with a negative electrode electrolyte (28); a separating element (24) which separates the positive electrode electrolyte (26) from the negative electrode electrolyte (28); each of the positive and negative electrodes (12, 14) including a metallic active region (16, 20); the metallic active region (20) of the negative electrode (14) comprising a first metallic element M1 and the metallic active region (16) of the positive electrode (12) comprising a second metallic element M2; the first metallic element M1 having a different standard electrode potential to the second metallic element M2; and in which at least one of the positive electrode electrolyte (26) and the negative electrode electrolyte (28) includes a non-aqueous electrolyte which comprises one or more glyme-based solvents.

8. The electrochemical cell according to any one of claims 2 to 4 or claim 7, in which the non-aqueous electrolyte comprises one or more metallic-containing salts.

9. The electrochemical cell according to claim 8, in which the non-aqueous electrolyte comprises one or more salts of metallic elements selected from the group consisting of aluminium, zinc, calcium, lithium, magnesium, potassium, sodium, copper, lead, iron, tin, zinc, and combinations thereof.

10. The electrochemical cell according to any one of claims 8 to 9, in which each of the one or more metallic-containing salts are present in a concentration from about 0.1 mol / kg to about 5 mol / kg.11 . The electrochemical cell according to any one of claims 7 to 10, in which the other of the positive electrode electrolyte (26) and negative electrode electrolyte (28) includes a solid electrolyte.

12. The electrochemical cell according to claim 11 , in which the positive electrode electrolyte (26) includes the non-aqueous electrolyte, and the negative electrode electrolyte (28) includes the solid electrolyte.

13. The electrochemical cell according to any one of claims 11 to 12, in which the solid electrolyte comprises a ceramic electrolyte.

14. The electrochemical cell according to claim 13, in which the ceramic electrolyte is doped with one or more of lithium, sodium or potassium.

15. The electrochemical cell according to any one of claims 1 to 14, in which the metallic active region (20) of the negative electrode (14) comprises at least 70% by weight of M1 and the metallic active region (16) of the positive electrode (12) comprises at least 70% by weight of M2.

16. The electrochemical cell according to any one of claims 1 to 15, in which the metallic active region (16, 20) is selected from the group consisting of a metallic body, a metallic sheet or layer, a metallic foam, a metallic sponge, a metallic element deposited onto a substrate, particles of metallic element optionally incorporated in a binder, and combinations thereof.

17. The electrochemical cell according to any one of claims 1 to 16, in which M1 is selected from the group consisting of aluminium, zinc, calcium, lithium, magnesium, potassium, sodium, and combinations thereof.

18. The electrochemical cell according to claim 17, in which M1 comprises sodium.

19. The electrochemical cell according to any one of claims 1 to 18, in which M2 is selected from the group consisting of copper, lead, iron, tin, zinc, and combinations thereof.

20. The electrochemical cell according to claim 19, in which M2 comprises tin.21 . The electrochemical cell according to any one of claims 1 to 20, in which the positive electrode (12) and / or the negative electrode (14) are substantially free of one or more components selected from the group consisting of conductive additives, binding agents, and current collecting elements.

22. The electrochemical cell according to any one of claims 1 to 21 , which delivers, in use, an output voltage of greater than 1 ,2V, preferably greater than 2.25V.

23. An energy storage device comprising two or more electrochemical cells according to any one of claims 1 to 22.

24. An apparatus comprising the electrochemical cell according to any one of claims 1 to 22 or the energy storage device according to claim 23.

25. A method of operating an electrochemical cell, comprising the step of charging and / or discharging the electrochemical cell according to any one of claims 1 to 22.

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