GB2563451A - A lithium sulphur-cell - Google Patents

A lithium sulphur-cell Download PDF

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Publication number
GB2563451A
GB2563451A GB1709670.2A GB201709670A GB2563451A GB 2563451 A GB2563451 A GB 2563451A GB 201709670 A GB201709670 A GB 201709670A GB 2563451 A GB2563451 A GB 2563451A
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United Kingdom
Prior art keywords
current collector
cathode
electroactive sulphur
cathode portion
cell
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
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GB1709670.2A
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GB201709670D0 (en
Inventor
Kovacik Peter
Purkayastha Rajlakshmi
Minton Geraint
Urrutia Lisset
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Oxis Energy Ltd
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Oxis Energy Ltd
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Priority to GB1709670.2A priority Critical patent/GB2563451A/en
Publication of GB201709670D0 publication Critical patent/GB201709670D0/en
Priority to PCT/GB2018/051629 priority patent/WO2018229489A1/en
Publication of GB2563451A publication Critical patent/GB2563451A/en
Withdrawn legal-status Critical Current

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/381—Alkaline or alkaline earth metals elements
    • H01M4/382—Lithium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/64—Carriers or collectors
    • H01M4/70—Carriers or collectors characterised by shape or form
    • H01M4/72—Grids
    • H01M4/74—Meshes or woven material; Expanded metal
    • H01M4/742—Meshes or woven material; Expanded metal perforated material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/64—Carriers or collectors
    • H01M4/70—Carriers or collectors characterised by shape or form
    • H01M4/72—Grids
    • H01M4/74—Meshes or woven material; Expanded metal
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/64—Carriers or collectors
    • H01M4/70—Carriers or collectors characterised by shape or form
    • H01M4/72—Grids
    • H01M4/74—Meshes or woven material; Expanded metal
    • H01M4/747—Woven material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/002—Inorganic electrolyte
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Secondary Cells (AREA)
  • Battery Electrode And Active Subsutance (AREA)
  • Cell Electrode Carriers And Collectors (AREA)

Abstract

A cathode 14 for a lithium sulfur cell 10 comprises a first cathode portion 14a comprising an electroactive sulphur material 16a deposited on a first current collector 18; and a second cathode portion 14b comprising an electroactive sulphur material 16b deposited on a second current collector 20, wherein the second current collector is provided with flow channels, such that, when the first cathode portion and second cathode portion are positioned in an overlapping configuration, the flow channels in the second current collector provide fluid communication through the second current collector between electroactive sulphur material deposited on the second current collector and electroactive sulphur material deposited on the first current collector. The second current collector may be a perforated sheet of metal foil or a mesh or web of conductive fibre material. The first current collector may also be provided with flow channels. The second electrode portion may comprise electroactive sulphur material deposited on both of the faces of the second current collector. The electroactive sulphur material deposited on the first current collector may be perforated to provide fluid communication between the surface of the electroactive sulphur material and the first current collector.

Description

[0001] The present invention relates to a lithium-sulphur cell. The present invention also relates to a method of assembling a lithium-sulphur cell.
BACKGROUND [0002] A lithium-sulphur cell may comprise an anode (negative electrode) formed from lithium metal or a lithium metal alloy, and a cathode (positive electrode) formed from elemental sulphur or other electroactive sulphur material. The sulphur or other electroactive sulphur material may be mixed with an electrically conductive material, such as carbon, to improve its electrical conductivity. Typically, the carbon and sulphur are ground and then mixed with solvent and, optionally, binder to form a slurry. The slurry may then be applied to a current collector and then dried to remove the solvent. The resulting structure may be calendared to form a composite structure, which may be cut into the desired shape to form a cathode. A separator may be placed on the cathode and a lithium anode placed on the separator. Electrolyte may be introduced into the cell to wet the cathode and separator.
DESCRIPTION [0003] Before particular examples of the present invention are described, it is to be understood that the present disclosure is not limited to the particular cell, method or material disclosed herein. It is also to be understood that the terminology used herein is used for describing particular examples only and is not intended to be limiting, as the scope of protection will be defined by the claims and equivalents thereof.
[0004] In describing and claiming the cell and method of the present invention, the following terminology will be used: the singular forms a, an, and the include plural forms unless the context clearly dictates otherwise. Thus, for example, reference to an anode includes reference to one or more of such elements.
[0005] According to one aspect, there is provided a cathode for a lithium sulphur cell, said cathode comprising a first cathode portion comprising an electroactive sulphur material deposited on a first current collector, and a second cathode portion comprising an electroactive sulphur deposited on a second current collector, wherein the second current collector is provided with flow channels, such that, when the first cathode portion and second cathode portion are positioned in an overlapping configuration, the flow channels in the second current collector provide fluid communication through the second current collector between electroactive sulphur material deposited on the second current collector and electroactive sulphur material deposited on the first current collector. According to a further aspect, there is provided a lithium sulphur cell comprising a cathode as described herein. The lithium sulphur cell may further comprise a lithium anode and an electrolyte. The electrolyte may be present between the lithium anode and the second cathode portion, as well as between the second cathode portion and the first cathode portion. Thus, both the electroactive sulphur material on the first current collector and electroactive sulphur material on the second current collector may be in contact with the electrolyte. In some embodiments, a porous separator soaked with the electrolyte is disposed between electroactive sulphur deposited on the second current collector and the anode.
[0006] High loadings of an electroactive sulphur-containing material may be required to increase the discharge capacity and/or energy density of a lithium sulphur cell. However, it has now been found that, when high loadings of electroactive sulphur material are employed, utilisation of electroactive sulphur material may decrease. This may be because not all the electroactive sulphur material employed is accessible for reaction, for example, if the layer of electroactive sulphur material on the cathode exceeds a threshold value.
[0007] In the present disclosure, a cathode comprising a first cathode portion and a second cathode portion is employed. Each cathode portion comprises an electroactive sulphur material deposited on a current collector. The current collector of the second electrode portion (the second current collector) is provided with flow channels, such that, when the first cathode portion and second cathode portion are positioned in an overlapping configuration, flow channels in the second current collector provide fluid communication through the second current collector between electroactive sulphur material deposited on the second current collector and electroactive sulphur material of the first cathode portion. In this way, electrolyte in the cell can reach the electroactive sulphur material deposited on both the first cathode portion and the second cathode portion. This can lead to improved utilisation of the electroactive sulphur material. For example, the thickness of the layer of electroactive sulphur material on the first cathode portion and/or the second cathode portion may be kept below a certain threshold. This may make the electroactive sulphur material on the first cathode portion and/or the second cathode portion more accessible for reaction.
[0008] In some embodiments, the second current collector may be a perforated sheet of metal foil. The perforations provide flow channels for electrolyte to flow through the second cathode portion and contact the electroactive sulphur material of the first cathode portion. The perforations may be made by any suitable method, for example, by piercing the second current collector. Other suitable methods include punching, photo etching, and chemical etching. Where a metal foil is used, the metal foil may be formed of a pure metal or an alloy. Examples of suitable metals include aluminium, nickel and copper. In some embodiments, the second current collector is a mesh or web of conductive material. The second current collector may be a porous material permeable to the electrolyte, such as carbon fibre mat. [0009] The first current collector may or may not be provided with flow channels. In one embodiment, the first current collector comprises a sheet that is impermeable to the flow of electrolyte. The first current collector may comprise a sheet of metal, for example, a sheet of metal foil. Where a metal foil is used, the metal foil may be formed of a pure metal or an alloy. Examples of suitable metals include aluminium, nickel and copper.
[0010] In another embodiment, the first current collector comprises flow channels and is permeable to the flow of electrolyte. The first current collector may comprise a perforated sheet of metal foil. The perforations provide flow channels for electrolyte to flow through the first cathode portion and contact the electroactive sulphur material of other cathode portions in the cell. The perforations may be made by any suitable method, for example, by piercing the first current collector. Other suitable methods include punching, photo etching, and chemical etching. Where a metal foil is used, the metal foil may be formed of a pure metal or an alloy. Examples of suitable metals include aluminium, nickel and copper. In some embodiments, the first current collector is a mesh or web of conductive material.
[0011] The first current collector may be a porous material permeable to the electrolyte, such as carbon fibre mat.
[0012] In some embodiments, the first cathode portion comprises a mixture comprising the electroactive sulphur material and an electrically conductive material deposited on the first current collector. The second cathode portion may also comprise a mixture comprising the electroactive sulphur material and an electrically conductive material deposited on the second current collector. In some embodiments, the cell may comprise at least one further cathode portion. The at least one further cathode portion may comprise a mixture comprising the electroactive sulphur material and an electrically conductive material deposited on a further current collector. The further current collector may be impermeable or may comprise flow channels (e.g. perforations) as discussed above.
[0013] The electroactive sulphur material may comprise elemental sulphur, sulphur-based organic compounds, sulphur-based inorganic compounds and sulphur-containing polymers. Preferably, elemental sulphur is used.
[0014] The solid electroconductive material may be any suitable conductive material. Preferably, this solid electroconductive material may be formed of carbon. Examples include carbon black, carbon fibre, graphene and carbon nanotubes. Other suitable materials include metal (e.g. flakes, filings and powders) and conductive polymers. Preferably, carbon black is employed.
[0015] The mixture of electroactive sulphur material and electroconductive material may be applied to the current collector in the form of a slurry in a solvent (e.g. water or an organic solvent). The solvent may then be removed and the resulting structure calendared to form a composite structure, which may be cut into the desired shape to form a cathode.
[0016] The ratio of surface capacity of the first cathode portion to the surface capacity of the second cathode portion may be 30 : 1 to 1 : 15, preferably 7 : 1 to 1 : 3, more preferably 3 : 1 to 1 : 1.
[0017] Each layer of electroactive sulphur material deposited on each current collector may be 1 to 1000 pm thick, preferably 20 to 150 pm thick, more preferably 40 to 100 pm thick.
[0018] The second cathode portion may comprise electroactive sulphur material deposited on one face of the second current collector. Alternatively, the second cathode portion may comprise electroactive sulphur material deposited on both faces of the second current collector. Where the electroactive sulphur material is deposited on both faces of the second current collector, the electroactive sulphur material on both faces of the second current collector be accessible by electrolyte by the flow channels in the second current collector. By depositing electroactive sulphur material on both sides of the cathode, and allowing access to the electroactive sulphur material by the electrolyte, even higher loadings of electroactive sulphur material may be achieved while maintaining desirable levels of sulphur utilisation.
[0019] In some embodiments, electroactive sulphur material may be deposited on both faces of the first cathode portion. Thus coated, the first cathode portion may be provided with two (or more) second cathode portions, a second cathode portion for each face of the first cathode portion. Thus, each face of the first cathode portion may be associated with its respective second cathode portion and anode. In one embodiment, the first current collector of the first cathode portion may be devoid of flow channels, such that electrolyte is prevented from flowing from one face of the first current collector to the other. A series of anodes and cathode portions may be arranged to provide a stack of cells. The stack of cells may be sealed in a cell housing, for example, a cell pouch.
[0020] In some embodiments, the first current collector and the second current collectors are each provided with a contact tab, such that the contact tabs can be placed in contact with one another to place the first electrode portion in electrical communication with the second electrode portion.
[0021] The anode comprises a lithium metal or lithium metal alloy. Preferably, the anode comprises a foil formed of lithium metal or lithium metal alloy. Examples of lithium alloy include lithium aluminium alloy, lithium magnesium alloy and lithium boron alloy. Preferably, a lithium metal foil is used.
[0022] Any suitable electrolyte may be employed in the cell. In some embodiments, the electrolyte comprises an organic solvent or an ionic liquid. Suitable organic solvents for use in the electrolyte are tetrahydrofurane, 2-methyltetrahydrofurane, dimethylcarbonate, diethylcarbonate, ethylmethylcarbonate, methylpropylcarbonate, methylpropylpropionate, ethylpropylpropionate, methyl acetate, acetonitrile, dimethyl acetamide, dimethoxyethane, 1, 3-dioxolane, diglyme (2-methoxyethyl ether), 2-ethoxyethyl ether, triglyme, tetraglyme, polyethylene glycol dimethyl ether, diethylene glycol dibutyl ether, ethylene carbonate, propylene carbonate, butyrolactone, , hexamethyl phosphoamide, pyridine, dimethyl sulfoxide, tributyl phosphate, trimethyl phosphate, and N, N, N, N-tetraethyl sulfamide. In some embodiments, the organic solvent may comprise a sulfone, for example, sulfolane. In some embodiments, the organic solvent may comprise a fluorinated ether, such as 1,1,2,2tetra-fluoroethyl 2,2,3,3-tetrafluoropropyl ether.
[0023] In one example, the organic solvent comprises an ether. In one example, the organic solvent comprises tetraethylene glycol dimethyl ether (TEGDME). In another example, the organic solvent comprises TEGDME, dimethoxyethane and, optionally, 1, 3dioxolane. In one example, TEGDME may form at least 40 v/v%, preferably at least 50% v/v of the organic solvent of the electrolyte. In one example, dimethoxyethane may form at least 20 v/v%, preferably at least 30% v/v of the organic solvent of the electrolyte. In one example, the organic solvent contains TEGDME, dimethoxyethane and 1, 3-dioxolane in a v/v ratio of 50:30:20.
[0024] The organic solvent of the electrolyte may have a viscosity of less than 20cP, preferably less than 10cP, more preferably less than 7cP at 25 degrees C. Where mixtures of organic solvents are employed in the electrolyte, the mixtures may have a viscosity of less than 20cP, preferably less than 10cP, more preferably less than 7cP at 25 degrees C. In one embodiment, the electrolyte may have a viscosity of less than 20cP, preferably less than 10cP, more preferably less than 7cP at 25 degrees C.
[0025] The electrolyte comprises a lithium salt dissolved in the organic solvent. Suitable lithium salts include lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium tetrafluoroborate, lithium nitrate, lithium perchlorate, lithium trifluoromethanesulfonimide, lithium trifluoromethanesulphonate, lithium bis(fluorosulfonyl)imide, lithium bis(perfluoroethanesulfonyl) imide, lithium bis(oxalate) borate, lithium bid(difluoro oxalate)borate, lithium bis(fluoromalonato)-borate, lithium tetracyanoborate, lithium dicyanotriazolate, lithium dicyano-trifluoromethyl-imidazole and lithium dicyanopentafluoroethyl-imidazole. Preferably the lithium salt is lithium trifluoromethanesulphonate (also known as lithium triflate). Combinations of salts may be employed. For example, lithium triflate may be used in combination with lithium nitrate. The lithium salt may be present in the electrolyte at a concentration of 0.1 to 5M, preferably, 0.5 to 3M, for example, 1M.
[0026] The electrolyte may also comprise lithium polysulphides. For example, lithium polysulphides may be added to the electrolyte before the cell is discharged. The concentration of lithium polysulphide dissolved in the electrolyte may be between 0.1% and 20% weight % (preferred concentration 1.5%). Examples of suitable lithium polysulphides include Li2Sn where n = at least 5, for example, 6 to 15, for example, 8-12 (e.g. 8) Lithium polysulphides may help to buffer the electrolyte, increase capacity of the cell or act as a source of sulphur to compensate for any loss of sulphur through the formation of nonconducting species.
[0027] A separator may be placed between the second cathode portion and anode. Electrolyte may then be introduced into the assembled cell to wet the cathode and separator. Alternatively, the electrolyte may be applied to the separator, for example, by coating or spraying before the lithium anode is placed on the separator. A separator may also be placed between the first cathode portion and the second cathode portion. Optionally separators may also be placed between the second cathode portion and any further cathode portion and, optionally, between subsequent cathode portions.
[0028] Where a separator is present in the cell of the present invention, the separator may comprise any suitable porous substrate that allows ions to move between the electrodes of the cell. The separator should be positioned between the electrodes to prevent direct contact between the electrodes. An additional separator can be positioned between the first and the second cathode to improve access of the electrolyte to the surface of the first cathode. The porosity of the substrate should be at least 30%, preferably at least 50%, for example, above 60%. Suitable separators include a mesh formed of a polymeric material. Suitable polymers include polypropylene, nylon and polyethylene. Non-woven polypropylene is particularly preferred. It is possible for a multi-layered separator to be employed.
[0029] These and other aspects of the cathode of the present disclosure will now be described in further detail, by way of example, with reference to Figure 1.
[0030] Figure 1 is a schematic cross-sectional view of a lithium sulphur cell according to one example of the present disclosure. The cell 10 comprises an anode 12 and a cathode
14. The cathode 14 comprises a first cathode portion 14a and a second cathode portion
14b. The first cathode portion 14a comprises an active layer 16a comprising a mixture of an electroactive sulphur material (e.g. elemental sulphur) and an electrically conductive material (e.g. carbon black) deposited on a first current collector 18. The second cathode portion 14b comprises an active layer 16b comprising mixture of an electroactive sulphur material (e.g. elemental sulphur) and an electrically conductive material (e.g. carbon black) deposited on a second current collector 20. The first 18 and second 20 current collectors are formed from sheets of foil (e.g. aluminium foil). The second current collector 20 and the active layer 16b are perforated to provide flow channels through the second cathode portion. This allows electrolyte in the cell to flow through the second cathode portion and contact the active layer 16a of the first cathode portion.
[0031] The anode 12 may be formed of lithium metal foil or lithium metal alloy foil.
[0032] A separator 22 may be positioned between the second cathode portion 14b and the anode 12. The separator may be soaked with electrolyte.
[0033] Figure 2 is a schematic exploded three-dimensional view of the cell 10 of Figure 1. As can be seen from the Figure, the first current collector 18 and the second current collector 20 may be provided with respective contact tabs 17a and 17b. These contact tabs may be coupled together (not shown) to provide electrical communication between the first cathode portion 14a and second cathode portion 14b. The contact tabs 17a and 17b may be coupled to the contact tab 13 of the anode 12 via an electrical circuit during discharge, or to a source of electricity during charging (not shown).
[0034] Figures 3a to 3c show alternative cell configurations.
[0035] In Figure 3a, the cell 100 comprises a lithium anode 112 and a cathodes 114. The cathodes 114 comprise first cathode portions 114a and second cathode portions 114b. The first cathode portions 114a each comprises an active layer 116a comprising a mixture of an electroactive sulphur material (e.g. elemental sulphur) and an electrically conductive material (e.g. carbon black) deposited on a first current collector 118. Both sides of each first current collector 118 are coated with an active layer, allowing the cathode portion 114a to be paired with further anodes (not shown).
[0036] The second cathode portions 114b each comprise an active layer 116b comprising a mixture of an electroactive sulphur material (e.g. elemental sulphur) and an electrically conductive material (e.g. carbon black) deposited on a second current collector 120. The second current collector 120 and the active layer 116b are perforated to provide flow channels through the second cathode portion. This allows electrolyte in the cell to flow through the second cathode portion and contact the active layer 116a of the first cathode portions 114a.
[0037] Separators 122 may be positioned between the second cathode portions 114b and the anode 112. The separators may be soaked with electrolyte.
[0038] The cell of Figure 3b is substantially the same as the cell of Figure 3a except that the first cathode portions 114a are also perforated.
[0039] The cell of Figure 3c is substantially the same as the cell of Figure 3a except that separators 122 are also included between the first and second cathode portions.
Examples [0040] Experiments were performed in a cell (2Q/2Q# cell) comprising a lithium foil anode and first and second cathode portions comprising elemental sulphur and carbon black deposited on an aluminium foil current collector (see Figure 1). Each cathode portion had a capacity of 2Q (1.2 mg of sulphur/cm2), where 1Q = 1 mAh/cm2. The perforations of the front (second) cathode portion were made using a needle roller.
[0041] As a comparison (4Q cell), the first and second cathode portions were replaced with a cathode portion having a capacity of 4Q (2.4 mg of sulphur/cm2). Both cells contained the same amount of sulfur.
[0042] All cells were -cycled three times at 0.2C charge/0.2C discharge and reached similar discharge capacities prior to cycling at higher C rates (0.5-5C). The two-cathode portion cell (2Q/2Q# cell) exhibits significantly better performance at higher C rates, both in terms of discharge capacity and average voltage (thus also energy density). The improvement may be attributed to an enhanced interaction area between the electrolyte and the cathode surface, a more uniform deposition/extraction of S and U2S within the cathode pores, and/or a shorter collection path for electrons due to a double current collector. Following the C-rate sweep, all cells were cycled at 0.2C/0.2C and returned to discharge capacities similar to their original values, indicating that the differences in power performance were not due to side mechanisms, e.g. degradation.
[0043] Figures 4 and 5 show the capacity loss and average voltage drop, respectively of the comparative (4Q) cell and the two-cathode-portion cell (2Q/Q#) of the present disclosure. It can be seen that both capacity drop and average voltage drop is greater for the comparative cell at charge rates of 0.5, 1,2 and 5C, respectively.

Claims (17)

Claims
1. A cathode for a lithium sulphur cell, said cathode comprising a first cathode portion comprising an electroactive sulphur material deposited on a first current collector, and a second cathode portion comprising an electroactive sulphur deposited on a second current collector, wherein the second current collector is provided with flow channels, such that, when the first cathode portion and second cathode portion are positioned in an overlapping configuration, the flow channels in the second current collector provide fluid communication through the second current collector between electroactive sulphur material deposited on the second current collector and electroactive sulphur material deposited on the first current collector.
2. A cathode as claimed in claim 1, wherein the second current collector is a perforated sheet of metal foil.
3. A cathode as claimed in claim 1, wherein both the first current collector and the second current collector are provided with flow channels.
4. A cathode as claimed in claim 1, wherein the second current collector is a mesh or web of conductive fibre material.
5. A cathode as claimed in any one of the preceding claims, wherein the first cathode portion comprises a mixture comprising the electroactive sulphur material and an electrically conductive material deposited on the first current collector, and wherein the second cathode portion comprises a mixture comprising the electroactive sulphur material and an electrically conductive material deposited on the second current collector.
6. A cathode as claimed in any one of the preceding claims, wherein the second cathode portion comprises electroactive sulphur material deposited on one face of the second current collector.
7. A cathode as claimed in any one of claims 1 to 5, wherein the second electrode portion comprises electroactive sulphur material deposited on both faces of the second current collector.
8. A cathode as claimed in any one of the preceding claims, wherein the first current collector and the second current collectors are each provided with a contact tab, such that the contact tabs can be placed in contact with one another to place the first cathode portion in electrical communication with the second cathode portion.
9. A cathode as claimed in any one of the preceding claim, wherein the electroactive sulphur material is elemental sulphur.
10. A cathode as claimed in any one of the preceding claim, wherein the electroactive sulphur material deposited on the first current collector is perforated to provide fluid communication between the surface of the electroactive sulphur material and the first current collector.
11. A cathode as claimed in any one of the preceding claims, wherein the first current collector is unperforated.
12. The electroactive sulphur loading on the cathodes may be 1 to 60 mg(s)/cm2, preferably 2 to 30 mg(s)/cm2, more preferably 3 to 9 mg(s)/cm2.
13. A lithium sulphur cell comprising a cathode as claimed in any one of claims 1 to 12.
14. A cell as claimed in claim 13, which further comprises a lithium anode and an electrolyte disposed between the lithium anode and the electroactive sulphur deposited on the second electrode portion.
15. A cell as claimed in claim 14, wherein electroactive sulphur material on the first current collector and electroactive sulphur material on the second current collector are in contact with the electrolyte.
16. A cell as claimed in any one of claims 13 to 15, which comprises a porous separator that is soaked with the electrolyte disposed between electroactive sulphur deposited on the second current collector and the anode.
17. A cell as claimed in any one of claims 13 to 15, wherein a separator is placed between the first cathode portion and the second cathode portion.
GB1709670.2A 2017-06-16 2017-06-16 A lithium sulphur-cell Withdrawn GB2563451A (en)

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