Electrolyte composition

Abstract

The present invention relates to one or more sodium-containing salts; and a solvent system comprising a first component comprising one or more glyme-based solvents and a second component comprising an additive; The present invention further relates to an anode-free sodium cell comprising said non-aqueous electrolyte composition.

Description

[Technical field]

[0001] The present invention relates to a novel non-aqueous electrolyte composition, an anode-free sodium cell comprising said novel non-aqueous electrolyte composition, and an energy storage device including said anode-free sodium cell. The present invention further relates to a sodium-ion cell comprising said novel non-aqueous electrolyte composition. [Background technology]

[0002] Sodium-ion batteries are similar in many ways to the lithium-ion batteries commonly used today; they are both reusable secondary batteries that contain an anode (negative electrode), a cathode (positive electrode) and electrolyte materials, they both can store energy, and they both charge and discharge via similar reaction mechanisms. When a sodium-ion (or lithium-ion) battery is charged, Na + (or Li + ) ions are deintercalated from the cathode and inserted into the anode, while charge-balancing electrons pass from the cathode through an external circuit containing the charger to the battery's anode. During discharge, the same process occurs in the reverse direction.

[0003] Lithium-ion battery technology has attracted much attention in recent years, providing the preferred portable battery for most electronic devices in use today. However, lithium is not a cheap metal to supply and is considered too expensive for large-scale applications. In contrast, sodium is much more abundant than lithium, and some researchers predict that this could provide a cheaper and more durable method of energy storage in the future, especially for large-scale applications such as energy storage in power grids.

[0004] A sodium-ion cell comprises a layer of active material coated onto a current collector foil to form the cathode, and a similar arrangement exists for the corresponding anode. The cathode and anode are physically separated by a separator that allows the flow of ions in a liquid electrolyte medium that is uniformly present within the cell and wets the cathode, anode, and separator throughout. During charging, Na + Ions are shuttled from the cathode active material and inserted into the anode active material (electrons flow through the external circuit), and during discharge the reverse process occurs (sodium ions are extracted from the anode active material and inserted into the cathode active material, and electrons flow through the external circuit to perform useful work).

[0005] In contrast, in the case of a "sodium cell", the anode consists of sodium metal (either as a separate Na metal foil / sheet or as a sodium metal foil / sheet laminated onto another current collector foil / sheet), and the cathode, separator and electrolyte are the same as those used in the sodium-ion cell above. Thus, in the case of a "sodium cell", Na plating / stripping occurs on the Na metal foil during each charge / discharge cycle (the cathode behaves the same as in a sodium-ion cell).

[0006] However, as will be appreciated, the use of sodium metal as an anode may not be the most ideal candidate, especially from the perspective of battery production. Furthermore, the plating and stripping process at the anode is rarely fully reversible, and dendritic growth occurs, resulting in premature failure. Furthermore, sodium metal reacts violently with water, and such a reaction may cause an explosion during the manufacturing process. Therefore, the use of sodium metal as the anode in a sodium battery requires the use of an inert atmosphere, which is expected to significantly increase the cost of battery production.

[0007] Sodium-ion cells currently cannot compete with lithium-ion cells in terms of gravimetric energy density. However, sodium cells (using sodium metal as the anode as described above) can have higher energy density than existing commercially available lithium-ion cells. However, they are more expensive to manufacture for the reasons described above. Thus, there remains a need to devise room temperature rechargeable sodium-containing cells that are cheap and easy to manufacture, yet can achieve a specific energy density equal to or greater than that of existing commercially available lithium-ion cells.

[0008] WO 2018 / 151674 describes an "anode-free sodium cell," also known as an in-situ sodium plating cell. The working principle of the anode-free sodium cell is to remove sodium metal cations (Na + a) "Sodium-ion cell": The working principle of a sodium-ion cell is the extraction / insertion of sodium metal cations (Na) at the cathode active material and the plating / stripping of sodium metal (Na) at the anode current collector. + ) extraction / insertion and sodium metal cation (Na + ) in the cathode active material; b) "sodium cell", the working principle of the sodium cell is to extract / insert sodium metal cations (Na + ) and plating / stripping of sodium metal (Na) at a sodium metal anode;

[0009] More specifically, WO 2018 / 151674 demonstrates an "anode-free sodium cell" that uses an anode current collector that was "pristine" before the anode-free sodium cell's first charge cycle; 1M NaBF4 in tetraglyme as the electrolyte; and rhombohedral Na2Fe2(CN)6 as the cathode active material. After the first cycle, this anode-free sodium cell was capable of delivering a capacity of about 90 mAh / g at an average discharge voltage of 3.22 V. Cycling of such a cell was extremely stable, showing a capacity retention of about 76% of its initial value after 60 cycles.

[0010] US Patent Application Publication No. 2020 / 0058222 also describes an "anode-free sodium cell." In this disclosure, the anode-free sodium cell was demonstrated using an anode current collector that includes one or more carbon nucleation layers prior to the first charge cycle of the anode-free sodium cell; 1M NaPF6 as the electrolyte; and pre-sodiated FeS2 as the cathode active material. Such pre-sodiation is an expensive and difficult process to implement, making the commercial usefulness of this disclosure questionable.

[0011] One of the more noteworthy areas is the development of electrolyte compositions that are particularly suitable for anode-free sodium cells. Although the design of appropriate electrolyte compositions has received less attention than the active materials (electrodes), their importance should not be overlooked, since they are primarily critical in determining the battery life and the practical performance that a cell can achieve, e.g., capacity, rate capability, safety, etc.

[0012] However, for a suitable electrolyte composition to be present, a number of attributes must be met, including: · Chemical stability - there must be no significant adverse reactions during operation of the cell, including reactions with the electrolyte itself or with the separator, electrodes, current collectors, or packaging materials used; · Electrochemical stability - there must be a wide electrochemical stability window, i.e. a large gap between the high and low onset potentials for degradation by oxidation or reduction; Thermal stability - the electrolyte composition must not decompose or chemically decompose during normal cell operation and at operating temperatures; Physical properties - the electrolyte composition must be liquid, so its melting and boiling points must be well outside the range of the cell's internal operating temperatures; ·Na + High ionic conductivity and low electronic conductivity are required to maintain cell operation by transport and to minimize cell self-discharge, respectively; Low toxicity; are based on sustainable chemistry, i.e., they use abundant elements and are produced via environmentally friendly synthesis (energy, pollution, etc.); and Cost-efficient production. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] International Publication No. 2018 / 151674 [Patent Document 2] US Patent Application Publication No. 2020 / 0058222 Summary of the Invention [Problem to be solved by the invention]

[0014] It is therefore an object of the present invention to provide improved sodium ion conducting electrolyte compositions, i.e., electrolyte compositions that are specifically designed for use in anode-free sodium cells. The electrolyte compositions of the present invention will be cost effective and exhibit superior electrochemical performance, especially in anode-free sodium cells. The electrolyte compositions of the present invention may also find utility in sodium ion cells. [Means for solving the problem]

[0015] The present invention relates to one or more sodium-containing salts; and A first component comprising one or more glyme solvents and: · a sulfur-containing compound in an amount of about 10% by weight or less of the solvent system; a boron-containing compound in an amount of about 20% by weight or less of the solvent system; · a nitrile-containing compound in an amount of about 10% or less of the solvent system; a phosphorus-containing compound in an amount of about 10% by weight or less of the solvent system; a surfactant in an amount of about 20% or less by weight of the solvent system; a second component comprising (or, optionally, consisting essentially of) one or more additives selected from: These objectives are achieved by providing a non-aqueous electrolyte composition comprising: DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] For the avoidance of doubt, if one or more additives contain a combination of compounds as described above, the amounts of such compounds are applied as described above.For example, TEL66X is not according to the present invention because it contains sulfur-containing compounds in an amount of 15% by weight of the solvent system. That is, it does not meet the requirement of "sulfur-containing compounds in an amount of about 10% by weight or less of the solvent system."

[0017] Preferably, the second component is: a sulfur-containing compound in an amount of about 5% by weight or less, preferably about 3% by weight or less, and highly preferably about 2.5% by weight or less of the solvent system; a boron-containing compound in an amount of about 15% or less, preferably about 8.5% or less, and highly preferably about 5% or less by weight of the solvent system; a nitrile-containing compound in an amount of about 10% or less, preferably about 5% or less by weight of the solvent system; a phosphorus-containing compound in an amount of about 10% or less by weight of the solvent system, preferably about 5% or less by weight; a surfactant in an amount of 20% or less by weight of the solvent system, preferably in an amount of about 10% or less by weight of the solvent system, preferably about 8.5% or less by weight; and optionally the total amount of the one or more additives selected from:

[0018] Optionally, the total amount of one or more additives does not exceed about 30% by weight of the solvent system. In one aspect, the present invention provides a method for producing a method for manufacturing a semiconductor device comprising: One or more sodium-containing salts; and a solvent system comprising a first component comprising one or more glyme-based solvents and a second component as defined herein; The present invention provides a non-aqueous electrolyte composition comprising:

[0019] The second component can comprise, or consist essentially of, one or more additives selected from sulfur-containing compounds, boron-containing compounds, nitrile-containing compounds, phosphorus-containing compounds, and surfactants.

[0020] Preferably, the second compound can comprise or consist essentially of one or more additives selected from sulfur-containing compounds in an amount of >0 to ≦10% by weight of the solvent system. The sulfur-containing compound may be present in an amount of >0.1 to ≦10% by weight of the solvent system, preferably ≧0.2 to ≦9% by weight of the solvent system, even more preferably ≧0.3 to ≦5% by weight, very preferably ≧0.4 to ≦4% by weight, more preferably 0.5% to ≦2.5% by weight, and ideally 0.5% to ≦2% by weight.

[0021] More preferably, the second component can comprise or consist essentially of one or more additives selected from boron-containing compounds in an amount of >0 to ≦20% by weight of the solvent system. The boron-containing compound may be present in an amount of >0 to ≦15% by weight of the solvent system, preferably >0.4 to ≦9% by weight of the solvent system, and more preferably >1 to ≦8.5% by weight of the solvent system.

[0022] Alternatively, the second component can comprise or consist essentially of one or more additives selected from nitrile-containing compounds in an amount >0 to ≦20% by weight of the solvent system. The nitrile-containing compound may be present in an amount of >0.1 to ≦15% by weight of the solvent system, preferably ≧0.2 to ≦9% by weight of the solvent system, more preferably ≧0.3 to ≦5% by weight, most preferably ≧0.4 to ≦4% by weight, and ideally 0.5% to ≦3% by weight.

[0023] Alternatively, the second component can comprise or consist essentially of one or more additives selected from phosphorus-containing compounds in an amount >0 to ≦20% by weight of the solvent system. The phosphorus-containing compound may be present in an amount of >0.1 to ≦15% by weight of the solvent system, preferably ≧0.2 to ≦9% by weight of the solvent system, more preferably ≧0.3 to ≦5% by weight, most preferably ≧0.4 to ≦4% by weight, and ideally 0.5% to ≦4% by weight.

[0024] Alternatively, the second component may comprise or consist essentially of one or more additives selected from surfactants in an amount >0 to ≦20% by weight of the solvent system. The surfactant may be present in an amount of >0.1 to ≦15% by weight of the solvent system, preferably ≧0.1 to ≦9% by weight of the solvent system, and more preferably ≧0.5 to ≦7.5% by weight of the solvent system.

[0025] The second component may comprise or consist essentially of two or more additives. Preferably, the second component can comprise or consist essentially of two or more additives including a boron-containing compound and a surfactant, i.e., one or more boron-containing compounds can be mixed with one or more surfactants to provide a mixture of two or more additives as the second component of the solvent system.

[0026] The second component can include two or more additives including a boron-containing compound in an amount >0-<20% by weight of the solvent system and a surfactant in an amount >0-<20% by weight of the solvent system. In this embodiment, the total amount of the two or more additives preferably does not exceed about 20% by weight based on the weight of the solvent system.

[0027] The second component can include two or more additives including a boron-containing compound in an amount of ≧0.5 to <20% by weight of the solvent system and a surfactant in an amount of ≧0.5 to <15% by weight of the solvent system. Optionally, the total amount of the two or more additives does not exceed about 20% by weight, based on the weight of the solvent system.

[0028] The second component can include two or more additives including a boron-containing compound in an amount of ≧0.5 to <10% by weight of the solvent system and a surfactant in an amount of ≧0.5 to <10% by weight of the solvent system. Optionally, the total amount of the two or more additives does not exceed about 10% by weight, based on the weight of the solvent system.

[0029] The second component may include two or more additives including a boron-containing compound in an amount of ≧0.5 to <5% by weight of the solvent system and a surfactant in an amount of >0.5 to <5% by weight of the solvent system. Optionally, the total amount of the two or more additives does not exceed about 5% by weight, based on the weight of the solvent system.

[0030] The second component can include two or more additives including a boron-containing compound in an amount of about 2% by weight of the solvent system and a surfactant in an amount of about 1% by weight of the solvent system. Optionally, in this embodiment, the total amount of the two or more additives does not exceed about 3% by weight based on the weight of the solvent system.

[0031] Alternatively, the second component can comprise or consist essentially of two or more additives, including sulfur-containing compounds and surfactants, i.e., one or more sulfur-containing compounds can be mixed with one or more surfactants to provide a mixture of two or more additives as the second component of the solvent system.

[0032] Additionally, the second component can include or consist essentially of two or more additives, including a sulfur-containing additive and a boron-containing additive, i.e., one or more sulfur-containing compounds can be mixed with one or more boron-containing compounds to provide a mixture of two or more additives as the second component of the solvent system.

[0033] The second component may comprise or consist essentially of three or more additives. Preferably, the second component is sulfur-containing compounds; boron-containing compounds; and Surfactants; The composition may comprise or consist essentially of three or more additives including:

[0034] That is, one or more sulfur-containing compounds can be mixed with one or more boron-containing compounds and one or more surfactants to provide a mixture of three or more additives. The second component is a sulfur-containing compound in an amount of >0 to <10% by weight of the solvent system; a boron-containing compound in an amount of >0 to <20% by weight of the solvent system, and A surfactant in an amount of >0 to <20% by weight of the solvent system; The additives may include three or more additives, including

[0035] The second component is a sulfur-containing compound in an amount of >0 to <10% by weight of the solvent system; a boron-containing compound in an amount of >0 to <10% by weight of the solvent system, and A surfactant in an amount of >0 to <10% by weight of the solvent system; The additives may include three or more additives, including

[0036] The second component is a sulfur-containing compound in an amount of ≧0.5 to <10% by weight of the solvent system; a boron-containing compound in an amount of ≥ 0.5 to < 10% by weight of the solvent system, and a surfactant in an amount of ≧0.5 to <10% by weight of the solvent system; The additives may include three or more additives, including

[0037] Optionally, the total amount of the three or more additives does not exceed about 20% by weight, based on the weight of the solvent system. The second component is a sulfur-containing compound in an amount of >0 to <5% by weight of the solvent system; a boron-containing compound in an amount of >0 to <5% by weight of the solvent system, and a surfactant in an amount of >0 to <5% by weight of the solvent system; The additives may include three or more additives, including

[0038] Alternatively, the second component is a sulfur-containing compound in an amount of ≧0.5 to <5% by weight of the solvent system; a boron-containing compound in an amount of ≥ 0.5 to < 5% by weight of the solvent system, and a surfactant in an amount of >0 to <5% by weight of the solvent system; The additives may include three or more additives, including

[0039] The total amount of the three or more additives preferably does not exceed about 10% by weight, based on the weight of the solvent system. More preferably, the total amount of the three or more additives does not exceed about 5% by weight, based on the weight of the solvent system.

[0040] The second component is a sulfur-containing compound in an amount of about 2% by weight of the solvent system; a boron-containing compound in an amount of about 1% by weight of the solvent system, and a surfactant in an amount of about 1% by weight of the solvent system; The additives may include three or more additives, including

[0041] The total amount of the three or more additives can be about 4% by weight based on the weight of the solvent system. The second component is a sulfur-containing compound in an amount of about 0.5% by weight of the solvent system; a boron-containing compound in an amount of about 2% by weight of the solvent system, and a surfactant in an amount of about 1% by weight of the solvent system; The additives may include three or more additives, including

[0042] The total amount of the three or more additives can be about 3.5% by weight based on the weight of the solvent system. The second component is Sulfur-containing compounds in an amount of >0 to ≦2.5% by weight of the solvent system; a boron-containing compound in an amount of >0 to ≦15% by weight of the solvent system, and A surfactant in an amount of >0 to ≦2.5% by weight of the solvent system; The additives may include three or more additives, including

[0043] Optionally, the total amount of the three or more additives does not exceed about 20% by weight, based on the weight of the solvent system. The second component is Sulfur-containing compounds in an amount of >0 to ≦2.5% by weight of the solvent system; a boron-containing compound in an amount of >0 to ≦2.5% by weight of the solvent system, and A surfactant in an amount of >0 to ≦15% by weight of the solvent system; The additives may include three or more additives, including

[0044] Optionally, the total amount of the three or more additives does not exceed about 20% by weight, based on the weight of the solvent system. Alternatively, the second component is Nitrile-containing compounds; boron-containing compounds; and Surfactants; The composition may comprise or consist essentially of three or more additives including:

[0045] That is, one or more nitrile-containing compounds can be mixed with one or more boron-containing compounds and one or more surfactants to provide a mixture of three or more additives. The second component is a nitrile-containing compound in an amount of >0 to <5% by weight of the solvent system; a boron-containing compound in an amount of >0 to <5% by weight of the solvent system, and a surfactant in an amount of >0 to <5% by weight of the solvent system; The additives may include three or more additives, including

[0046] Optionally, the total amount of the three or more additives does not exceed about 5% by weight, based on the weight of the solvent system. The second component is sulfur-containing compounds; Nitrile-containing compounds; boron-containing compounds; and Surfactants; The composition may comprise or consist essentially of four or more additives including:

[0047] That is, one or more sulfur-containing compounds can be mixed with one or more nitrile-containing compounds, one or more boron-containing compounds, and one or more surfactants to provide a mixture of four or more additives.

[0048] The second component is a sulfur-containing compound in an amount of >0 to <5% by weight of the solvent system; a nitrile-containing compound in an amount of >0 to <5% by weight of the solvent system; a boron-containing compound in an amount of >0 to <5% by weight of the solvent system, and a surfactant in an amount of >0 to <5% by weight of the solvent system; The additive may include four or more additives, including

[0049] Optionally, the total amount of the four or more additives does not exceed about 20% by weight, based on the weight of the solvent system. Optionally, the total amount of the four or more additives does not exceed about 10% by weight, based on the weight of the solvent system.

[0050] Optionally, the total amount of the four or more additives does not exceed about 5% by weight based on the weight of the solvent system. In another aspect, the present invention provides a method for producing a method for manufacturing a semiconductor device comprising: One or more sodium-containing salts; and a solvent system consisting essentially of a first component consisting essentially of one or more glyme-based solvents and a second component as defined herein; The present invention provides a non-aqueous electrolyte composition consisting essentially of:

[0051] The one or more sodium-containing salts of the present invention can be defined as described herein. The one or more sodium-containing salts (a) preferably contain one or more weakly coordinating anions. The term "weakly coordinating anions" or "WCA" is well known to those skilled in the art and is used to refer to anions that contain several (more than one) elements that may contain halogen atoms and / or oxygen atoms and share a single negative charge. This means that the negative charge is spread throughout the anion, making the coordination ability of the anion relatively weak, for example, compared to the coordination ability of anions with a high concentration of negative charges or anions with multiple negative charges.

[0052] Preferably, the sodium containing salt has the formula NaM m X x one or more compounds of the formula NaXO4; one or more sodium salts of fluorosulfonyl-containing compounds; one or more sodium salts of fluorosulfonate-containing compounds; one or more sodium salts of oxalatoborate compounds; one or more sodium salts of difluorooxalatoborate compounds; and the tetrakis[3,5-bis(trifluoromethyl)phenylborate anion (B[3,5-(CF3)2C6H3] - 4), Tris(pentafluorophenyl)borate anion (B(C6F5) - 4), and tetrakiscarboxy(trifluoromethyl)aluminate anion (Al[OC(CF3)3] - 4).

[0053] Highly preferably, the one or more sodium containing salts have the formula NaM m X xwherein M is one or more metals and / or non-metals and X is a group containing or consisting of one or more halogens; one or more sodium salts of fluorosulfonyl-containing compounds; one or more sodium salts of fluorosulfonate-containing compounds; one or more sodium salts of oxalatoborate compounds; and one or more sodium salts of difluorooxalatoborate compounds.

[0054] Preferred formula NaM m X x In one or more sodium-containing salts of the formula (I), M is one or more metals and / or nonmetals and X is a group comprising or consisting of one or more halogens, preferably selected from fluorine, chlorine, bromine and iodine, more preferably fluorine. The amount x of halogens X is preferably x=1-16, more preferably x=4 or 6. The amount m of one or more metals and / or nonmetals M is preferably m=1-3, more preferably m=1-2, especially preferably m=1. Ideally, the one or more metals and / or nonmetals M are preferably selected from aluminum, boron, gallium, indium, iridium, platinum, scandium, yttrium, lanthanum, antimony, arsenic and phosphorus. Especially preferably, M is selected from aluminum, boron, gallium, phosphorus and arsenic. The general formula NaM n X x The most preferred sodium-containing salt is one or more selected from sodium tetrafluoroborate (NaBF4) and sodium hexafluorophosphate (NaPF6).

[0055] In the preferred sodium compound(s) of formula NaXO4, the element X is preferably one or more halogens selected from fluorine, chlorine, bromine and iodine. Chlorine is especially preferred, and the most preferred sodium-containing salt of formula NaXO4 is NaClO4. Preferred sodium salts of the one or more fluorosulfonyl-containing compounds include sodium bis(fluorosulfonyl)imide, also known as NaFSI (NaN(SO2F)2), and sodium bis(trifluoromethanesulfonyl)imide, also known as NaTFSI (C2F6NNaO4S2). Preferred sodium salts of the one or more fluorosulfonate-containing compounds include sodium triflate or sodium trifluoromethanesulfonate, also known as NaOTf (CF3NaSO3). Preferred sodium salts of the one or more oxalate-borate compounds include sodium bis(oxalate), also known as borate NaBOB or NaB(C2O4)2; and sodium difluoro(oxalato)borate, also known as NaDFOB.

[0056] Highly preferably, the one or more sodium-containing salts are selected from sodium tetrafluoroborate (NaBF4), sodium hexafluorophosphate (NaPF6), sodium trifluoromethanesulfonate (CF3NaSO3), sodium bis(fluorosulfonyl)imide (Na(SO2F)2N), sodium bis(trifluoromethanesulfonyl)imide (C2F6NNaO4S2), sodium bis(oxalate) (NaB(C2O4)2), and sodium difluoro(oxalato)borate. Most preferably, the one or more sodium-containing salts are sodium tetrafluoroborate (NaBF4).

[0057] The amount of the one or more sodium-containing salts is conveniently expressed as the molar concentration of the components in the solvent system, i.e., the total number of moles of the one or more sodium-containing salts (i.e., solutes) per kilogram (combined weight of the first component and the second component) of the solvent system, i.e., mol / kg.

[0058] The molality of each sodium-containing salt individually is preferably in the range of 0.1 mol / kg to 5 mol / kg, more preferably in the range of 0.1 mol / kg to ≦2.5 mol / kg. Highly preferably, especially when the component is NaBF4, the molality is 0.1 mol / kg to ≦2.5 mol / kg, most preferably about 1.5 mol / kg. The total molality of all sodium-containing salts is preferably in the range of 0.1 mol / kg to 10 mol / kg, more preferably in the range of 0.1 mol / kg to 6 mol / kg, most preferably in the range of 0.1 mol / kg to ≦4 mol / kg.

[0059] One or more glyme solvents of the present invention can be defined as described herein. The one or more glyme solvents present in the first solvent component can be saturated acyclic polyethers that preferably contain no other functional groups. Glymes are also known as glycol diethers. Suitable glyme solvents include 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-CH2CH2CH2CH3);Poly(ethylene glycol) dimethyl ether (Polyglyme, CH3-O-(CH2CH2-O) n-CH3); and dipropylene glycol dimethyl ether (Proglyme, CH3-O-(CH2CH2CH2-O)2-CH3).

[0060] Very suitable glyme solvents can be selected from ethylene glycol dimethyl ether (monoglyme), diethylene glycol dimethyl ether (diglyme), triethylene glycol dimethyl ether (triglyme) and tetraethylene glycol dimethyl ether (tetraglyme). Diethylene glycol dimethyl ether (diglyme) and tetraethylene glycol dimethyl ether (tetraglyme) are particularly preferred glyme solvents.

[0061] Preferred non-aqueous electrolyte compositions of the present invention comprise a solvent system that includes a first component consisting essentially of diglyme and / or tetraglyme. Alternatively, the non-aqueous electrolyte compositions of the present invention include a solvent system that includes a first component consisting essentially of diglyme and / or tetraglyme in combination with one or more additional glyme-based compounds.

[0062] When mixtures of glyme compounds are used, it is convenient to express the amount of each of one or more glyme solvents in terms of weight ratios. For example, as noted above, a highly preferred glyme solvent may contain a mixture of diglyme and tetraglyme, ideally in a weight ratio of 1-20:1-20 wt / wt, more preferably 1-10:1-10 wt / wt, also preferably 1-5:1-5 wt / wt, and most preferably 1:1 wt / wt.

[0063] Highly advantageous electrolyte compositions of the present invention include one or more glyme-based solvents in an amount of at least about 40% by weight of the glyme-based solvent (i.e., the first component of the solvent system), preferably at least about 50% by weight, and more preferably at least about 60% by weight.

[0064] For the avoidance of doubt, the phrase "weight of the solvent system" as used herein means the weight of a first component of the solvent system combined with the weight of a second component of the solvent system. Highly preferably, diglyme and tetraglyme are used as the glyme solvent in a 50% by weight combination, i.e.: diglyme is present in an amount of about 50% by weight of the first component of the solvent system; and The tetraglyme is present in an amount of about 50% by weight of the first component of the solvent system.

[0065] Thus, the total amount of diglyme and tetraglyme is preferably about 100% by weight of the first component of the solvent system. As noted above, the non-aqueous electrolyte composition according to the present invention can include one or more surfactants. The one or more surfactants of the present invention can be defined as described herein.

[0066] The total amount of one or more surfactants used in the electrolyte composition of the present invention can be >0.2 to ≦20% by weight of the solvent system, based on the total weight of the electrolyte solvent system used in the electrolyte composition, preferably ≧0.2 to ≦10% by weight of the solvent system, more preferably ≧0.2 to ≦4% by weight, very preferably ≧0.5 to ≦3% by weight, and ideally 0.5 to ≦2.5% by weight.

[0067] The amount of one or more surfactants used in the second component of the electrolyte composition of the present invention can be >0% by weight of the solvent system, ideally >0.2% by weight of the solvent system, and preferably >0.5% by weight, based on the total weight of the electrolyte solvent system used in the electrolyte composition.

[0068] In a preferred embodiment, the one or more surfactant additives used in the second component of the present invention are preferably selected to improve the ability of the electrolyte composition to wet the separator (especially polyolefin separators) and / or the electrodes of the battery. This is advantageous in promoting longer battery cycle life. Furthermore, it is known in the literature that surfactants can result in non-dendritic metal plating / stripping (and also inhibit corrosion) by surface adsorption on various substrates. The preferred one or more surfactant additives are selected from anionic surfactants, cationic surfactants, nonionic (hydrophilic) surfactants, and amphoteric (zwitterionic) surfactants, with anionic surfactants and nonionic (hydrophilic) surfactants being particularly preferred. Such surfactant additives are ideally one or more selected from the following:

[0069] 1) Anionic (negatively charged) surfactants. Suitable examples include carboxylates, such as alkyl carboxylates (e.g., fatty acid salts), carboxylate fluorosurfactants; sulfates, such as alkyl sulfates (e.g., sodium lauryl sulfate), alkyl ether sulfates (e.g., sodium laureth sulfate); sulfonates, such as docusate (e.g., sodium dioctyl sulfosuccinate) and alkyl benzene sulfonates; and phosphate esters, such as alkyl aryl ether phosphates and alkyl ether phosphates (e.g., trioctyl phosphate);

[0070] 2) Zwitterionic (amphoteric) surfactants, which can be anionic, cationic or nonionic depending on the pH of the solution in which they are found. Examples include RN + H2CH2COO - , R.N. + (CH3)2CH2CH2SO3 - , phospholipids (such as phosphatidylcholine (lecithin));

[0071] 3) Positively charged cationic surfactants, e.g., RN+ H3Cl - , R.N. + (CH3)3Cl - , diotadecyldimethylammonium chloride, cetylpyridinium chloride, benzalkonium chloride, hexadecyltrimethylammonium chloride (CTAC), and hexadecyltrimethylammonium bromide (CTAB); and

[0072] 4) Nonionic surfactants: These are uncharged and examples include polyol esters (e.g., glycols, glycerol esters, sorbitan and sorbitan derivatives, such as fatty acid esters of sorbitan (Span®) and its ethoxylated derivatives (Tween®)), polyoxyethylene esters, and poloxamer including block copolymers, such as poloxamer 84, poloxamer 105, poloxamer 123, poloxamer 124, poloxamer 188, poloxamer 237, poloxamer 338, poloxamer 407 and poloxamer F127.

[0073] Most preferably, the surfactant of the non-aqueous electrolyte composition of the present invention contains one or more nonionic block copolymer-containing surfactants and / or anionic phosphate ester-containing surfactants. Highly suitable examples include poloxamers and / or alkyl ether phosphates (e.g., trioctyl phosphate) as described above.

[0074] As described above, the non-aqueous electrolyte composition according to the present invention can include one or more sulfur-containing compounds. The one or more sulfur-containing compounds of the present invention can be defined as described herein.

[0075] The sulfur-containing compounds used in the second solvent component of the present invention are preferably selected to enable the formation of a stable cathode-electrolyte interface (CEI) on the cathode and / or a stable solid-electrolyte interface (SEI) on the anode, which provides advantages such as improved first cycle coulombic efficiency (FCE=first cycle coulombic efficiency) and improved cycle life. Alternatively, such additives may decompose significantly and preferentially on the first cycle, which may result in a lower first cycle efficiency, but thereafter improved cycle stability.

[0076] Suitable sulfur-containing compounds can include cyclic and / or acyclic sulfur-containing compounds. Preferably, the sulfur-containing compound is a sulfone, sulfate, or sulfonate.

[0077] In other words, a sulfur-containing compound can have a sulfonyl functional group attached to two carbon atoms (sulfone), a sulfonyl functional group attached to two oxygen atoms (sulfate), or a sulfonyl functional group attached to one carbon atom and one oxygen atom in a cyclic or acyclic structure (sulfonate). When the sulfonate is cyclic, the compound is sometimes called a sultone.

[0078] As used herein, the term "sulfone" means that a central hexavalent sulfur atom is double bonded to each of two oxygen atoms and has single bonds to each of two carbon atoms.

[0079] As used herein, the term "sulfate" means that a central hexavalent sulfur atom is double bonded to two of the oxygen atoms and has single bonds to two other oxygen atoms, which are each further single bonded to a carbon atom.

[0080] As used herein, the term "sulfonate" means a central hexavalent sulfur atom doubly bonded to two of the oxygen atoms, single bonded to one carbon atom, and single bonded to another oxygen atom, which is in turn single bonded to a carbon atom, and when connected in a ring with the other carbon atom bonded to the sulfur atom, it becomes a sultone.

[0081] The general formula for such compounds is RY(S=O)2Y'R' [In formula: Y and Y' are independently selected from C or O (i.e., they can be the same or different from each other); When Y and Y' are the same, R and R' can be independently selected from any linear or branched, substituted or unsubstituted C1-C6 alkyl group; linear or branched, substituted or unsubstituted C1-C6 alkenyl group; linear or branched, substituted or unsubstituted C1-C6 alkoxy group (i.e., they can be the same or different from each other); or R and R' can, independently or together, form a substituted or unsubstituted C3-C6-cycloalkyl-containing group, a phenyl-containing group, or a heterocycle-containing group; and When Y and Y' are different from each other, R' can be independently selected from any linear or branched, substituted or unsubstituted C1-C6 alkyl group; linear or branched, substituted or unsubstituted C1-C6 alkenyl group; linear or branched, substituted or unsubstituted C1-C6 alkoxy group; or R and R' can independently or together form a substituted or unsubstituted C3-C6-cycloalkyl-, cycloalkenyl-, phenyl-, or heterocyclic-containing group.

[0082] In some embodiments, the general formula of such compounds is R-SO2-R', where R and R' can be independently selected from any linear or branched, substituted or unsubstituted C1-C6 alkyl group; linear or branched, substituted or unsubstituted C1-C6 alkenyl group; linear or branched, substituted or unsubstituted C1-C6 alkoxy group (i.e., they can be the same or different from each other); or R and R' can, independently or together, form a substituted or unsubstituted C3-C6-cycloalkyl-containing group, a phenyl-containing group, or a heterocycle-containing group.

[0083] Preferably, the general formula of such compounds is RO(S=O)2OR', where R and R' can be independently selected from any linear or branched, substituted or unsubstituted C1-C6 alkyl group; linear or branched, substituted or unsubstituted C1-C6 alkenyl group; linear or branched, substituted or unsubstituted C1-C6 alkoxy group (i.e., they can be the same or different from each other); or R and R' can independently or together form a substituted or unsubstituted C3-C6-cycloalkyl-containing group, a phenyl-containing group, or a heterocycle-containing group.

[0084] Highly preferably, the sulfur-containing compound is selected from cyclic sulfates (e.g. 1,3-propanediol cyclic sulfate (PCS), also known as 1,3,2-dioxathiane 2,2-dioxide (DTD or (CH2)3SO4)); 1,5,2,4-dioxadithiane 2,2,4,4-tetraoxide; or 1,3,2-dioxathiolane 2,2-dioxide. 1,3-propanediol cyclic sulfate (PCS) is particularly preferred.

[0085] Suitable examples of cyclic sulfones include sulfolane ((CH2)4SO2), 3-methylsulfolane ((CH3)CH(CH2)3SO2), and trimethylsulfone ((CH2)3SO2). Suitable examples of acyclic sulfones include methylphenylsulfone ((CH3)(CH5)SO2).

[0086] Suitable examples of sultones include 1-propene 1,3-sultone ((CH)2CH2SO3), and 1,3-propane sultone (CH2)3SO3. The total amount of one or more sulfur-containing compounds used in the electrolyte composition of the present invention can be >0.5 to ≦10% by weight of the solvent system, based on the total weight of the electrolyte solvent system used in the electrolyte composition, preferably ≧0.6 to ≦6% by weight of the solvent system, more preferably ≧0.6 to ≦4% by weight, most preferably ≧0.6 to ≦3% by weight, and ideally 0.6 to ≦2.5% by weight.

[0087] The amount of one or more sulfur-containing compounds used in the second component of the electrolyte composition of the present invention can be >0% by weight of the solvent system, ideally >0.2% by weight of the solvent system, and preferably >0.5% by weight, based on the total weight of the electrolyte solvent system used in the electrolyte composition.

[0088] As described above, the non-aqueous electrolyte composition according to the present invention contains one or more boron-containing compounds. The one or more boron-containing compounds of the present invention can be defined as described herein.

[0089] The boron-containing compound used in the second solvent component of the present invention is preferably selected to enable the formation of a stable cathode-electrolyte interface (CEI) on the cathode and / or a stable solid-electrolyte interface (SEI) on the anode, which provides advantages such as improved first cycle coulombic efficiency and / or improved cycle life.

[0090] Suitable boron-containing compounds can include cyclic and / or acyclic boron-containing compounds. Preferably, the one or more boron-containing compounds is a borate or a boroxine.

[0091] In other words, the one or more boron-containing compounds can have a central boron atom attached to three oxygen atoms, each of which is further single-bonded to a carbon or silicon atom (a borate). Alternatively, the one or more boron-containing compounds can include a six-membered heterocyclic ring structure composed of three boron and oxygen atoms linked together by alternating shared single bonds. Each boron atom is further single-bonded to an outer carbon atom or oxygen of the heterocyclic ring structure.

[0092] As used herein, the term "borate" means a central trivalent boron atom single-bonded to three oxygen atoms, each of which is in turn single-bonded to a carbon or silicon atom.

[0093] As used herein, the term "boroxine" refers to a six-membered heterocyclic compound composed of alternating single-bonded trivalent boron atoms and divalent oxygen atoms, with each boron atom further single-bonded to an oxygen or carbon atom outside the heterocyclic ring structure.

[0094] The general formula of the borate compound is B(OYR)3, where Y and R can be the same or different in each individual attachment situation. More specifically, it can be written as follows: B(OYR)(OY'R')(OY''R'') [In formula: Y, Y' and Y'' are independently selected from C or Si (i.e., they can be the same or different from one another); and R, R' and R'' may be independently selected from hydrogen; any linear or branched, substituted or unsubstituted C1-C6 alkyl group; linear or branched, substituted or unsubstituted C1-C6 alkenyl group; linear or branched, substituted or unsubstituted C1-C6 alkoxy group; or substituted or unsubstituted C3-C6-cycloalkyl-, phenyl-, or heterocycle-containing group.

[0095] More preferably, the boron-containing compound is selected from non-cyclic borates. Suitable examples include tris(trimethylsilyl)borate (TMSB); Tris(2,2,2-trifluoroethyl) borate; Trimethyl borate; and Triethyl borate; Examples include:

[0096] Tris(trimethylsilyl)borate (TMSB) is a particularly preferred example. The general formula of the boroxine compounds is B3(YR)3O3, where Y and R can be the same or different in each individual attachment situation. More specifically, it can be written as follows: B a (YR) b (O) c [In formula: Y is independently selected from C or O (i.e., they can be the same or different from each other); and R may be the same or different in each individual attachment situation and may be independently selected from hydrogen; any linear or branched, substituted or unsubstituted C1-C6 alkyl group; linear or branched, substituted or unsubstituted C1-C6 alkenyl group; linear or branched, substituted or unsubstituted C1-C6 alkoxy group; or substituted or unsubstituted C3-C6-cycloalkyl-, phenyl-, or heterocyclic-containing group; and · a=b=c, where a, b, and c are each 3].

[0097] A good example is: Trimethoxyboroxine; and Trimethylboroxine; Examples include:

[0098] The amount of one or more boron-containing compounds used in the second component of the electrolyte composition of the present invention can be >0% by weight of the solvent system, ideally >0.2% by weight of the solvent system, and preferably >0.5% by weight, based on the total weight of the electrolyte solvent system used in the electrolyte composition.

[0099] As described above, the nonaqueous electrolyte composition according to the present invention contains one or more nitrile-containing compounds. The one or more nitrile-containing compounds of the present invention can be defined as described herein.

[0100] The nitrile-containing compounds used in the second solvent component of the present invention are preferably selected to enable the formation of a stable cathode-electrolyte interface (CEI) on the cathode and / or a stable solid-electrolyte interface (SEI) on the anode, which provides advantages such as improved first cycle coulombic efficiency and / or improved cycle life.

[0101] Suitable examples include adiponitrile, glutaronitrile, acetonitrile and 1,3,6-hexanetricarbonitrile, with 1,3,6-hexanetricarbonitrile being a particularly preferred example.

[0102] The amount of one or more nitrile-containing compounds used in the second component of the electrolyte composition of the present invention can be >0% by weight of the solvent system, ideally >0.2% by weight of the solvent system, and preferably >0.5% by weight, based on the total weight of the electrolyte solvent system used in the electrolyte composition.

[0103] As described above, the non-aqueous electrolyte composition according to the present invention can include one or more phosphorus-containing compounds. The one or more phosphorus-containing compounds of the present invention can be defined as described herein.

[0104] The phosphorus-containing compound used in the second solvent component of the present invention is preferably selected to enable the formation of a stable cathode-electrolyte interface (CEI) on the cathode and / or a stable solid-electrolyte interface (SEI) on the anode, which provides advantages such as improved first cycle coulombic efficiency and / or improved cycle life.

[0105] Preferably, the phosphorus-containing compound is a phosphite or phosphate-containing compound. Suitable examples include tris(trimethylsilyl)phosphite (TMSP) or tri(trimethylsilyl)phosphate.

[0106] The amount of one or more phosphorus-containing compounds used in the second component of the electrolyte composition of the present invention can be >0% by weight of the solvent system, ideally >0.2% by weight of the solvent system, and preferably >0.5% by weight, based on the total weight of the electrolyte solvent system used in the electrolyte composition.

[0107] The non-aqueous electrolyte composition according to the present invention may further comprise one or more additional compounds which may or may not be a solvent. Examples of such additional compounds include flame retardant compounds (e.g., polyalkyl phosphate-containing compounds, preferably non-fluorinated polyalkyl phosphate-containing compounds), diluents (e.g., hydrofluoroether-containing compounds, preferably hydrofluoroalkyl ether-containing compounds), glycol ether acetates, ionic liquids, and any solvent that can act as an inert diluent to help reduce the viscosity of the electrolyte (e.g., hydrofluoroalkyl ethers, preferably 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE or TTE)).

[0108] Electrolyte compositions according to the present invention may also optionally include one or more performance additives, typically in an amount of <15 wt%, preferably <10 wt%, and more preferably 0.1 wt% to <5 wt%, based on the total weight of the solvent system used in the electrolyte composition. Such performance additives preferably act at the electrolyte-electrode interface rather than in the bulk of the electrolyte.

[0109] Suitable performance additives include polymerizable additives for promoting overcharge protection, such as biphenyl, diphenylamine, dimethoxydiphenylsilane (DDS), 3-chloroanisole (3CA), N-phenylmaleimide, xylene (methyl substituted benzene), and cyclohexylbenzene; additives for promoting overcharge protection based on a redox shuttle mechanism, such as 2,5-di-tert-butyl-1,4 dimethoxybenzene (DDB), 4-tert-butyl-1,2-dimethoxybenzene (TDB), 1,4 bis(trimethylsilyl)-2,5-dimethoxybenzene (BTMSDB), and 1,4-bis(2-methoxyethoxy)-2,5 di-tert-butylbenzene; additives to impart further flame retardant properties to the electrolyte, such as dimethylmethylphosphonate (DMMP), ethoxy-pentafluoro-cyclotriphosphazene (N3P3F5OCH2CH3, EFPN), tri(2,2,2-trifluoroethyl)phosphite and / or tri(2,2,2-trifluoroethyl)phosphate (TFEP), methyl nonafluorobutyl ether (MFE) and silane-Al2O3 nanoparticles; additives to promote better high temperature cycling, such as succinic anhydride; and additives to scavenge unwanted inert decomposition products (e.g., HF, water or CO2) in-situ, such as zeolites.

[0110] The non-aqueous electrolyte composition of the present invention is particularly useful in anode-free sodium cells, also known as in-situ sodium plating cells, which can be used in energy storage devices, such as batteries, rechargeable batteries, electrochemical devices, and electrochromic devices.

[0111] Thus, in one aspect, the present invention provides an anode-free sodium cell comprising the non-aqueous electrolyte composition defined herein. More specifically, in one aspect, the present invention provides an anode-free sodium cell comprising: a cathode comprising a sodium-containing active material; Anode current collector; a separator positioned between the cathode and the anode current collector; and a non-aqueous electrolyte composition as defined herein; The present invention provides an anode-free sodium cell comprising:

[0112] The present invention also provides, in another aspect, the use of a non-aqueous electrolyte composition as defined herein in an anode-free sodium cell. The present invention also provides, in another aspect, a method of operating an anode-free sodium cell as defined herein.

[0113] Preferably, the anode-free sodium cell has a charge cutoff voltage of 4.0 V or greater. The invention also provides, in another aspect, an apparatus comprising one or more anode-free sodium cells as defined herein. For example, a typical apparatus can include a device such as a battery pack that can be used in either stationary or mobile applications.

[0114] As used herein, an "anode-free sodium cell" refers to a cell whose operating principle is the transport of sodium metal cations (Na 2 O 3 ) from the cathode active material. + (anode current collector) and deposition and plating / removal and stripping of sodium metal (Na) on the anode current collector.

[0115] During the first charge cycle of an anode-free sodium cell, a sodium metal anode is formed in situ on the anode current collector when sodium metal cations are reduced and deposited as sodium metal on the anode current collector.

[0116] When an anode-free sodium cell is fully discharged, the anode current collector contains only trace amounts of sodium metal, or substantially less sodium metal than in a fully charged cell, and most of the sodium metal is oxidized to form sodium metal cations, which are present in the electrolyte and / or stored in the cathode.

[0117] When an anode-free sodium cell is fully charged, the anode current collector includes a layer of sodium in electrical contact with the anode current collector, with a correspondingly lower amount of sodium in the cathode. The layer of sodium in electrical contact with the anode current collector may be across the entire surface of the anode current collector, or may be deposited on some areas of the anode current collector. However, if sodium is deposited, it is preferred that any such layer of sodium be uniform and homogeneous.

[0118] The anode-free cells disclosed herein can include a separator positioned between the cathode and the anode current collector. The electrolyte non-aqueous electrolyte composition according to the present invention has been found to be particularly useful when used in an anode-free cell that includes a polyolefin separator.

[0119] The cathode typically comprises a sodium-containing active material disposed on one or more surfaces of a (cathode) current collector. The cathode and anode current collectors can each independently be fabricated from any suitable conductive material. For example, the cathode current collector, the anode current collector, or both the cathode and anode current collectors can be formed from a metal such as nickel, aluminum, titanium, copper, gold, silver, platinum, an aluminum alloy, stainless steel, or any other metal substrate (similar to current collectors currently commonly used in sodium-ion batteries).

[0120] The cathode current collector, the anode current collector, or both the cathode current collector and the anode current collector can be formed of aluminum or an aluminum alloy (e.g., an alloy of aluminum with one or more of Mg, Mn, Cr, Zn, Si, Fe, and Ni). Highly preferably, both the cathode current collector and the anode current collector comprise an aluminum current collector. Alternatively, copper, magnesium, carbon paper / foil / substrate, and tin can also be used as current collector materials.

[0121] The cathode and anode current collectors can be formed into any suitable shape that is compatible with the overall design of the electrochemical cell. For example, the cathode and anode current collectors can each independently be formed as a foil, a plate, a mesh, a net, a lath, a punched metal or an embossment, or a combination of these shapes (e.g., a mesh-like plate). If desired, irregularities can be formed on one or more surfaces of the cathode and / or anode current collectors, for example, by etching one or more surfaces of the current collectors.

[0122] Highly preferably, the anode current collector is formed from aluminum or an aluminum alloy and comprises a foil or mesh form. Preferably, the anode current collector also includes one or more nucleation layers formed on one or more surfaces of the anode current collector prior to the first charge cycle of the anode-free sodium cell. Highly preferably, such one or more nucleation layers comprise one or more carbon-containing nucleation layers.

[0123] When an anode current collector is formed having one or more nucleation layers on one or more surfaces of the anode current collector, during the first charge cycle of the anode-free sodium cell, metal cations are reduced and precipitated as sodium metal onto the one or more nucleation layers.

[0124] As used herein, the term "nucleation layer" means any coating or layer disposed on one or more surfaces of a "pristine" anode current collector prior to the first charge cycle of an anode-free sodium cell. The use of a nucleation layer allows for more uniform and homogeneous deposition of sodium metal compared to a current collector not having such a nucleation layer.

[0125] A particularly preferred nucleation layer is any coating or layer that provides a reduction in the "nucleation overpotential" of sodium metal plating. As sodium metal is deposited onto the anode current collector via constant current (galvanostatic) cycling, the sodium plating potential initially drops (to a more negative value below 0 V vs. Na / Na+) and then rises to a higher potential value (but still below 0 V vs. Na / Na+) during steady state conditions at the same constant current value.

[0126] Thus, the "nucleation overpotential" for sodium deposition is defined herein as the difference between the most negative potential and the steady-state plating potential. Thus, one skilled in the art can easily measure the nucleation overpotential for sodium deposition using an anode current collector that includes one or more nucleation layers formed on its surface and compare it to the nucleation overpotential for sodium deposition using a "pristine" anode current collector to determine the preferred nucleation layer described herein. This can be done in a half-cell or a three-electrode cell constructed using well-known general knowledge.

[0127] As noted above, the one or more nucleation layers advantageously enable precipitation of sodium metal atoms and atomic clusters at and across the surface of the anode current collector, thereby promoting more uniform plating while minimizing parasitic reactions.

[0128] The one or more nucleation layers may be formed over the majority (or even 100%) of one or more surfaces of the anode current collector, or may be formed as partial coatings by design (e.g., one or more nucleation layers formed over some areas of such surfaces - these areas being homogenous and uniform within their extent).

[0129] The one or more nucleation layers preferably comprise one or more layers of anode active material (e.g., a thin layer such as 0.1 μm to 1000 μm), which may or may not be mixed with any type of conductive additive such as carbon black (to increase the electronic conductivity of the anode active material) and / or a binder material that is compatible with water or an organic solvent.

[0130] Highly preferably, the one or more nucleation layers comprise one or more carbon-containing nucleation layers, highly preferably one or more carbon-containing nucleation layers having a thickness of from about 10 Angstroms to about 1000 μm.

[0131] Suitable carbon-containing nucleation layers may include carbon black, carbon nanotubes, carbon nanofibers, graphite / graphene, hard carbon, glassy carbon, soft carbon, activated carbon (e.g., fibrous), or combinations thereof. In some cases, the carbon-containing nucleation layer may include amorphous carbon (e.g., carbon black such as TIMCAL® Super C65). Techniques such as doctor blade coating, slot die coating, ultrasonic spray deposition, screen printing, physical vapor deposition (PVD), and chemical vapor deposition (CVD) may also be used to prepare such carbon-containing nucleation layers.

[0132] Such one or more carbon-containing nucleation layers may further include one or more binders and / or conductive additives. Examples of the one or more binders include polymers such as PAA, PVDF, PEO, PTFE, SBR (styrene butadiene rubber), acrylic emulsion polymers, cellulose polymers (e.g., CMC), copolymers thereof, and blends thereof.

[0133] In some embodiments, the nucleation layer (preferably a carbon-containing nucleation layer) is present at a concentration of 2 mg / cm on the surface of the anode current collector. 2 areal loadings (based on the weight of the active material (e.g., C65), excluding, for example, optional binders and / or additives) of less than 1.75 mg / cm 2 Less than 1.5 mg / cm 2 Less than 1.25 mg / cm 2 Less than 1 mg / cm 2 Less than 900 μg / cm 2 Less than 800 μg / cm 2 Less than 700 μg / cm 2 Less than 600 μg / cm 2 Less than 500 μg / cm 2 Less than 400 μg / cm 2 Less than 300 μg / cm 2 Less than 200 μg / cm 2 Less than 100 μg / cm 2 Less than or equal to 50 μg / cm 2 less than).

[0134] In some embodiments, the nucleation layer (preferably a carbon-containing nucleation layer) is at least 20 μg / cm on the surface of the first metal current collector. 2 area loading (e.g., at least 50 μg / cm 2 , at least 100 μg / cm 2 , at least 200 μg / cm 2 , at least 300 μg / cm 2 , at least 400 μg / cm 2 , at least 500 μg / cm 2 , at least 600 μg / cm 2 , at least 700 μg / cm 2, at least 800 μg / cm 2 , at least 900 μg / cm 2 , at least 1 mg / cm 2 , at least 1.25 mg / cm 2 , at least 1.5 mg / cm 2 , or at least 1.75 mg / cm 2 ) can exist.

[0135] In some embodiments, the nucleation layer (preferably a carbon-containing nucleation layer) can be present on the surface of the first metal current collector at an areal loading ranging from any of the minimum values ​​above to any of the maximum values ​​above. For example, the nucleation layer can be present on the surface of the first metal current collector at an areal loading of 20 μg / cm 2 ~2mg / cm 2 , 50μg / cm 2 ~2mg / cm 2 , 100μg / cm 2 ~2mg / cm 2 , 200μg / cm 2 ~2mg / cm 2 , 400μg / cm 2 ~2mg / cm 2 , 20μg / cm 2 ~1mg / cm 2 , 50μg / cm 2 ~1mg / cm 2 , 100μg / cm 2 ~1mg / cm 2 , 200μg / cm 2 ~1mg / cm 2 , or 400 μg / cm 2 ~1mg / cm 2 The catalyst may be present at an areal loading of 0.1 to 1000 nm.

[0136] Nucleation is a surface process. Thus, the nucleation layer (preferably, a carbon-containing nucleation layer) can be, in principle, a single atomic layer with a thickness that provides an interface (surface) for sodium nucleation. In some embodiments described herein, the nucleation layer (preferably, a carbon-containing nucleation layer) can have a thickness of 1000 angstroms or less (e.g., 500 angstroms or less, 100 angstroms or less, 50 angstroms or less, 30 angstroms or less, 25 angstroms or less, 20 angstroms or less, or 10 angstroms or less).

[0137] Alternatively, the anode current collector also includes two or more nucleation layers formed on one or more surfaces of the anode current collector prior to the first charge cycle of the anode-free sodium cell, hi one embodiment, such two or more nucleation layers are preferably two or more carbon-containing nucleation layers.

[0138] Alternatively, the anode current collector disclosed herein does not include one or more nucleation layers on one or more surfaces of the anode current collector prior to the first charge cycle of the anode-free sodium cell, and thus the anode current collector is "pristine" prior to the first charge cycle of the anode-free sodium cell.

[0139] As used herein, the phrase "pristine" means that the current collector is in an "as-prepared" state prior to the first charge cycle of the anode-free sodium cell. In other words, the anode current collector is substantially pure material from its source of formation, free of impurities (e.g., surface oxide layers, etc.). Thus, the anode current collector is not coated with one or more nucleation layers (as described above), conventional active materials, binders, etc.

[0140] After charge and discharge cycling, the anode current collector in a fully Na-stripped state can be identical to the "pristine" state, or can incorporate one or more layers that substantially contain sodium-containing materials, which can also include inorganic-rich and / or organic-rich materials, for example, from the electrolyte composition and its decomposition products.

[0141] Based on the disclosure herein, it is believed that an anode-free sodium cell according to the present invention can be formed using any type of sodium-containing active material to function as the cathode.

[0142] Examples of these include sodium transition metal oxides, polyanionic compounds (including fluorinated polyanionic compounds), Prussian blue compounds (and analogues thereof, e.g., Prussian white or Berlin green), materials that store sodium via conversion reactions, sodium transition metal fluorides, oxyfluorides, phosphates, sulfates and silicates (and fluorinated versions thereof). A preferred example is sodium transition metal oxide.

[0143] Preferred sodium transition metal oxides are of the general formula: A 1±δ M 1 V M 2 W M 3 X M 4 Y M 5 Z O 2-c [In formula: A is one or more alkali metals selected from sodium, potassium and lithium; M 1 comprises one or more redox active metals having an oxidation state of +2, preferably selected from the group consisting of nickel, copper, cobalt and manganese; M 2 contains metals with oxidation states greater than 0 and less than or equal to +4; M3 contains a metal in the oxidation state +2; M 4 contains metals with oxidation states greater than 0 and less than or equal to +4; M 5 contains a metal in the oxidation state +3; 0≦δ≦1; V is >0; W is ≧0; X is ≧0; Y is ≧0; At least one of W and Y is >0; Z is ≧0; C is in the range 0≦c<2; V, W, X, Y, Z and C are selected to maintain electrochemical neutrality].

[0144] Ideally, metal M 2 contains one or more transition metals, preferably selected from manganese, titanium and zirconium; M 3 is preferably one or more selected from magnesium, calcium, copper, tin, zinc and cobalt; M 4 comprises one or more transition metals preferably selected from manganese, titanium and zirconium; and M 5 is preferably one or more selected from aluminum, iron, cobalt, tin, molybdenum, chromium, vanadium, scandium and yttrium.

[0145] Particularly preferred sodium-containing active materials are nickelate-based materials. Sodium-containing active materials having any crystalline structure can be used, but the structure is preferably O3 or P2 or a derivative thereof, and strictly speaking, the sodium-containing active material may have a heterogeneous structure, i.e., a mixture of phases, consisting of several different crystalline forms. For example, the sodium-containing active material may contain a compound having the above general formula in a mixture of O3 and P2 phases. The ratio of O3 phase:P2 phase is preferably 1-99:99-1.

[0146] The cathodes disclosed herein can also include a binder. The binder improves the bonding properties of the sodium-containing active material particles to each other and to the current collector. The binder can be a non-aqueous binder, an aqueous binder, or a combination thereof.

[0147] Non-aqueous binders that may be described herein include, but are not limited to, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, and polyimide.

[0148] The water-based binders that can be described herein include, but are not limited to, rubber-based binders or polymer resin binders. The rubber-based binders can be selected from styrene-butadiene rubber, acrylated styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, and combinations thereof.

[0149] The polymeric resin binder may be selected from ethylene propylene copolymers, epichlorohydrin, polyphosphazenes, polyacrylonitrile, polystyrene, ethylene propylene diene copolymers, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resins, acrylic resins, phenolic resins, epoxy resins, polyvinyl alcohol, and combinations thereof.

[0150] Cellulosic compounds may be used as binders (or in combination with other materials). Examples of suitable cellulosic materials include, but are not limited to, one or more of carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, or alkali metal salts thereof. The alkali metal can be Na, K, or Li. Such cellulosic compounds can be included in an amount of about 0.1 parts by weight to about 20 parts by weight based on 100 parts by weight of active material. A particular cellulosic binder that may be described herein is the sodium salt of carboxymethylcellulose.

[0151] The anode-free cells disclosed herein can include a separator positioned between the cathode and the anode current collector. The electrolyte compositions according to the present invention have been found to be particularly useful when used in anode-free cells that include a polyolefin separator.

[0152] In another aspect, the present invention also provides a sodium cell comprising a non-aqueous electrolyte composition as defined herein. More particularly, the present invention provides a sodium-ion cell comprising a negative electrode, a positive electrode, and a non-aqueous electrolyte composition as defined herein. Such a sodium-ion cell can be used in energy storage devices, such as batteries, rechargeable batteries, electrochemical devices, and electrochromic devices.

[0153] Ideally, the non-aqueous electrolyte compositions defined herein are used in sodium-ion cells that utilize a carbon-containing material as the negative (anode) electrode active material. Most preferably, the non-aqueous electrolyte compositions of the present invention are used with a non-graphitizable carbon-containing anode, preferably a hard carbon anode. [Brief description of the drawings]

[0154] The invention will now be described with reference to the following figures: [Figure 1a]FIG. 1a shows a plot of cathode discharge capacity (mAh / g) versus cycle number to illustrate the cycling stability within the 3.70 to 1.0 V window of a cell using a control electrolyte composition (sample TEL66i). [Figure 1b] FIG. 1b shows a plot of coulombic efficiency % versus cycle number to illustrate the cycling performance of a cell using a control electrolyte composition (sample TEL66i). [Figure 2a] FIG. 2a shows a plot of cathode discharge capacity (mAh / g) versus cycle number to illustrate the cycling stability of cells using the electrolyte compositions of the present invention (samples TEL66j, TEL66k, TEL66L, TEL66m, and TEL66n) compared to the cycling stability of a cell using a control electrolyte composition (sample TEL66i). [Figure 2b] FIG. 2b shows a plot of coulombic efficiency % versus cycle number to illustrate the cycling performance of cells using the electrolyte compositions of the present invention (samples TEL66j, TEL66k, TEL66L, TEL66m, and TEL66n) compared to the cycling performance of a cell using a control electrolyte composition (sample TEL66i). [Figure 2c] FIG. 2c shows a plot of full cell voltage (V) versus cathode discharge capacity (mAh / g) for the fifth cycle (i.e., voltage-capacity cycling curve) of a cell using an electrolyte composition of the invention (sample TEL66n) compared to a cell using a control electrolyte composition (sample TEL66i). [Figure 3a] FIG. 3a shows a plot of cathode discharge capacity (mAh / g) versus cycle number to illustrate the cycling stability of a cell using sample TEL66R compared to that of a cell using sample TEL66o. [Figure 3b] FIG. 3b shows a plot of coulombic efficiency % versus cycle number to illustrate the cycling performance of a cell using sample TEL66R compared to the cycling performance of a cell using sample TEL66o. [Figure 4a]FIG. 4a shows a plot of cathode discharge capacity (mAh / g) versus cycle number to illustrate the cycling stability of cells using electrolyte compositions of the present invention (samples TEL66P, ​​TEL66Q, TEL66P, ​​TEL66h, TEL66Q, TEL66S, and TEL66T). [Figure 4b] FIG. 4b shows a plot of coulombic efficiency % versus cycle number to illustrate the cycling performance of cells using electrolyte compositions of the present invention (samples TEL66P, ​​TEL66Q, TEL66P, ​​TEL66h, TEL66Q, TEL66S, and TEL66T). [Figure 5a] FIG. 5a shows a plot of cathode discharge capacity (mAh / g) versus cycle number to illustrate the cycling stability of a cell using an electrolyte composition of the present invention (sample TEL66d). [Figure 5b] FIG. 5b shows a plot of cathode discharge capacity (mAh / g) versus cycle number to illustrate the cycling performance of a cell using an electrolyte composition of the present invention (sample TEL66d). [Figure 6a] FIG. 6a shows a plot of cathode discharge capacity (mAh / g) versus cycle number to illustrate the cycling stability of cells using the electrolyte compositions of the invention (samples TEL85b, TEL66U, TEL85g, TEL85h, TEL85i, and TEL66V) compared to the cycling stability of a cell using a control electrolyte composition (sample TEL66i). [Figure 6b] FIG. 6b shows a plot of coulombic efficiency % versus cycle number to illustrate the cycling performance of cells using the electrolyte compositions of the present invention (samples TEL85b, TEL66U, TEL85g, TEL85h, TEL85i, and TEL66V) compared to the cycling performance of a cell using a control electrolyte composition (sample TEL66i). [Figure 7a]FIG. 7a shows a plot of cathode discharge capacity (mAh / g) versus cycle number to illustrate the cycling stability of cells (INFC73, INFC74, INFC75, INFC82, INFC83, INFC76, INFC96, and INFC97), each using an electrolyte composition of the invention (sample TEL66P) but each constructed with a different type of anode current collector. [Figure 7b] FIG. 7b shows a plot of % coulombic efficiency versus cycle number to illustrate the cycling performance of cells (INFC73, INFC74, INFC75, INFC82, INFC83, INFC76, INFC96, and INFC97), each using an electrolyte composition of the present invention (sample TEL66P), but each constructed with a different type of anode current collector. [Figure 8a] FIG. 8a shows a plot of cathode discharge capacity (mAh / g) versus cycle number to illustrate the cycling stability of cells using electrolyte compositions of the present invention (samples TEL66W, TEL66X, TEL66Y, TEL66Z, TEL85, and TEL85a). [Figure 8b] FIG. 8b shows a plot of coulombic efficiency % versus cycle number to illustrate the cycling performance of cells using electrolyte compositions of the present invention (samples TEL66W, TEL66X, TEL66Y, TEL66Z, TEL85, and TEL85a). [Figure 9a] FIG. 9a shows a plot of cathode discharge capacity (mAh / g) versus cycle number to illustrate the cycling stability of cells using electrolyte compositions of the present invention (samples TEL66d, TEL85e, TEL85f, and TEL66P). [Figure 9b] FIG. 9b shows a plot of coulombic efficiency % versus cycle number to illustrate the cycling performance of cells using electrolyte compositions of the present invention (samples TEL66d, TEL85e, TEL85f, and TEL66P). EXAMPLES

[0155] The electrolyte compositions of the present invention are particularly useful as electrolyte compositions for use in anode-free sodium cells. The anode-free sodium cells can be prepared as described below.

[0156] The cathode is formed from a first current collector with positive electrode active material disposed on a surface of the first current collector. The positive electrode active material is a sodium-containing active material, which may or may not be mixed with any type of conductive additive, such as carbon black (to enhance the electronic conductivity of the positive electrode active material) and / or binder material (water or organic solvent). The positive electrode active material is then coated onto an aluminum (or other metal) current collector using conventional electrode processing techniques, such as those described in International Publication WO2020 / 240209 A1.

[0157] The anode is formed from another (second) current collector (similar to the current collectors currently commonly used in sodium-ion batteries) that is simply a thin metal substrate (e.g., a sheet of foil) made from copper, aluminum, stainless steel, or any other metal substrate.

[0158] As shown in the Examples, in one embodiment, the anode current collector does not include a nucleation layer on one or more surfaces of the anode current collector prior to the first charge cycle of the anode-free sodium cell, and thus the anode current collector is pristine prior to the first charge cycle of the anode-free sodium cell.

[0159] Also as shown in the Examples, in other embodiments, the anode current collector includes one or more nucleation layers formed on one or more surfaces of the anode current collector prior to the first charge cycle of the anode-free sodium cell.

[0160] Positive electrode (cathode electrode) The anode-free sodium cell was prepared using a mixed phase O3 / P2 oxide cathode active material, O3 / P2-A, prepared as described in International Application No. PCT / GB2019 / 051022 (published as International Publication WO2019 / 197812 A1) and U.S. Pat. No. 1,055,0007. 1±δ M 1 V M 2 W M 3 X M 4 Y M 5 Z O 2-c It was made using.

[0161] The particle size d50 of the positive electrode active material was 10±2 μm, as measured using a laser diffraction method with a Malvern Mastersizer® 2000 and ethanol as a dispersant, and the tap density of the positive electrode active material was >0.96 g / mL.

[0162] The positive (cathode) electrode was then prepared by solution casting a slurry of active material, conductive carbon, binder and solvent. The conductive carbon used was C65 (Imerys). PVdF copolymer (e.g., W#7500 from Kureha Chemicals) was used as the binder, and N-methylpyrrolidone (NMP) was used as the solvent. The slurry was then cast onto a carbon-coated aluminum foil and dried at about 80°C. The electrode film contained the following components in weight percent: 89% active material, 5% C65 carbon, and 6% V7500 binder. Alternatively, the electrode film contained the following components in weight percent, as described in "Cell Assembly" below: 92% active material, 4% C65 carbon, and 4% W#7500 binder.

[0163] Preparation of electrolyte The electrolyte compositions under investigation were prepared using the following general procedure: an appropriate amount of a first component (e.g., a solvent for a desired solvent system) and an appropriate amount of a second component (e.g., an additive selected from sulfur-containing compounds / boron-containing compounds / nitrile-containing compounds / phosphorus-containing compounds / surfactants) were weighed in an argon-filled glove box and added to a brown or clear glass or metal bottle.

[0164] To completely dry the formed solvent system, 4 Å molecular sieves (Sigma-Aldrich®) were added and the solvent mixture was left to dry for at least 24 hours. The solvent mixture was then transferred, still in the glove box, to another brown or clear glass bottle containing a magnetic stir bar. Then, in the argon-filled glove box, an accurate amount of one or more sodium-containing salts was weighed and slowly added to the solvent mixture with continuous stirring. The electrolyte mixture was stirred on a magnetic stir plate until the sodium-containing salt(s) was visually determined to have dissolved (stirring time is typically at least 10 minutes, e.g., 2 hours or 48 hours). The electrolyte composition was then removed from the stir plate and stored and used in the argon-filled glove box.

[0165] The exact composition of each electrolyte composition investigated is detailed in Table 1 below:

[0166] [Table 1]

[0167] [Table 2]

[0168] Abbreviations used: VC = vinylene carbonate, FEC = fluoroethylene carbonate, PCS = 1,3-propanediol cyclic sulfate, P123 = poloxamer (Pluronic®) P123, TMSB = tris(trimethylsilyl) borate, TOC = trioctyl phosphate, TMSP = tris(trimethylsilyl) phosphite; HTC = 1,3,6-hexanetricarbonitrile; TMB = trimethoxyboroxine; PST = 1-propene 1,3 sultone; SUL = sulfolane Tetraglyme = tetraethylene glycol dimethyl ether, diglyme = diethylene glycol dimethyl ether, NaBF4 = sodium tetrafluoroborate It should be noted that in Table 1 above, the wt% of the various solvents and / or additives are listed with respect to the total solvent weight (these do not take into account the weight (one or more) of the sodium-containing salts). Additionally, the salt concentrations in Table 1 are listed in molality, m (moles of solute per kg of solvent, mol / kg). Cell Assembly The anode-free sodium cells described throughout the examples were fabricated as pouch cells. The cathode contained mixed phase O3 / P2 layered oxide sodium ion active material mixed with C65 carbon black conductive additive and polyvinylidene fluoride (PVDF) binder (e.g., in a weight ratio of 89:05:06 or 92:04:04) on a carbon-coated Al foil.

[0169] The anode was aluminum foil with or without a thin surface carbon coating. Thus, in embodiments where the anode was prepared without a coating of active material disposed on a current collector, the anode was simply aluminum foil.

[0170] Alternatively, in embodiments where the anode was prepared by disposing a nucleation layer on the surface of a current collector, the anode was a "bare En'Safe 92" substrate sourced from ARMOR (an En'Safe® series product from ARMOR) that was aluminum foil coated with a thin (approximately 1 μm) carbon primer layer; or an aluminum foil current collector that was coated with a carbon black (C65):PVDF (=90:10 wt / wt) layer at the indicated GSM using a doctor blade technique.

[0171] After the cathode and anode were coated, they were stamped to the desired dimensions. The separator used was a typical polyolefin separator commonly used in any type of rechargeable lithium-ion or sodium-ion battery, such as Celgard® 2500. The cathode / separator / anode assembly was placed in a pouch inside a glove box and filled with a volume of the above liquid electrolyte typical for lithium-ion or sodium-ion cells containing said type of polyolefin separator. These pouch cells were then sealed inside the glove box and removed for cell testing. Throughout this disclosure, pouch cells of two different nominal capacities are used (depending on the dimensions of the electrode stack): most of the default results are for pouch cells with a nominal capacity of 6 mAh, and where noted, some results are also for larger scale 0.1 Ah anode-free pouch cells.

[0172] Cell Test The cells are tested using a constant current (galvanostatic) cycling technique as follows: the cells are cycled at a given current density between preset voltage limits defined in the examples, with an upper cut-off voltage that may or may not include a constant voltage step. Commercially available battery cyclers from MTI Inc. (Richmond, CA, USA) or Maccor (Tulsa, Oklahoma, USA) were used. The cells were cycled at 30°C.

[0173] [Table 3]

[0174] [Table 4]

[0175] [Table 5]

[0176] [Table 6]

[0177] [Table 7]

[0178] [Table 8]

[0179] [Table 9]

[0180] Example 1 Performance of an anode-free sodium cell using 1.5m NaBF4 (TEL66i) in 1:1 wt / wt tetraglyme:diglyme.

[0181] Cycling performance was investigated using TEL66i with anode current collectors without a nucleation layer (INFC59) and with a nucleation layer (INFC53; INFC58). In particular, INFC53; INFC58 both used carbon-containing nucleation layers; that is, INFC53 used an "En'safe 92 Foil" current collector and INFC58 used an 11.3 GSM C65 layer on Al foil.

[0182] 1a and 1b show the Na plating-stripping process of three cells over 50 to 110 cycles when subjected to cycling from 3.7 to 1.0 V at a rate of ±C / 5.

[0183] The results shown in Figure 1a indicate that INFC53 and INFC58 provide higher capacity than INFC59 under the same cycling conditions within the window of 3.7–1.0 V. Specifically, the delivered capacity at cycle 50 of INFC53 was 65 mAh / g, while the delivered capacity at cycle 50 of INFC59 was 0 mAh / g.

[0184] From the results shown in Figure 1b, it was observed that for both INFC53 and INFC58, stable coulombic efficiency close to 100% was achieved throughout the cycles (e.g., the coulombic efficiency was about 99% for INFC53 and about 98% for INFC58 at the cycle 50 mark), indicating very stable Na plating and stripping. As is evident from Figure 1b, the coulombic efficiency of INFC59 was shown to be low.

[0185] Example 2 Lower voltage Performance at lower voltages of anode-free sodium cells using 1.5M NaBF4 in 1:1 wt / wt tetraglyme:diglyme with no additive or one additive as shown in Table 2.

[0186] The cycling performance was investigated at low voltages (i.e., 3.7 to 1.0 V) using TEL66L or TEL66n with the "En'safe 92 Foil" anode. Figures 2a and 2b show the Na plating-stripping process of two cells (INFC65; INFC69) when subjected to cycling from 3.7 to 1.0 V at a rate of +C / 5, -1C.

[0187] From the results shown in Figure 2a, it was found that INFC65 and INFC69 provided similar cathode discharge capacity within the window of 3.7 to 1.0 V compared to the cathode discharge capacity of cell INFC53, which used the control electrolyte composition (TEL66i) as seen in Figure 1a. Cells INFC53, INFC65, and INFC69 each used the "En'Safe 92 Foil" anode current collector.

[0188] Specifically, the delivered capacity at cycle 30 for INFC65 and INFC69 was 72.9 mAh / g and 76 mAh / g, respectively, while the delivered capacity at cycle 30 for INFC53 was 73.9 mAh / g, as shown in Figure 1a. Such similar capacities were observed despite cells INFC65 and INFC69 being discharged at a faster rate of -1C (1 h discharge) compared to cell INFC53 being discharged at a slower rate of -C / 5 (5 h discharge).

[0189] It is known that as the C-rate of the cell discharge increases, the delivered capacity is expected to decrease. Thus, the results for INFC65 and INFC69 led to the conclusion that improved electrochemical performance is observed with the addition of a boron-containing additive (i.e., TMSB). It also shows improved capacity for INFC69 compared to INFC65, which can be attributed to the use of a higher amount of TMSB (i.e., 1 wt% vs. 2 wt%).

[0190] From the results shown in Figure 2b, it was also observed that stable coulombic efficiencies close to 100% were achieved throughout the cycle for both INFC65 and INFC69, indicating very stable Na plating and stripping, which was comparable or slightly improved compared to the coulombic efficiency of INFC53 shown in Figure 1b.

[0191] However, a further advantage of the use of the additive according to the invention was seen at higher voltages, as described below.

[0192] Higher voltage Performance at higher voltages of anode-free sodium cells using 1.5 m NaBF4 in 1:1 wt / wt tetraglyme:diglyme with no additive or one additive as shown in Table 2. The voltage profile was increased from a 3.7-1.0 V window to a 4.0-1.0 V window.

[0193] 2a and 2b show the Na plating-stripping process of five cells (i.e., INFC62; INFC64; INFC67; INFC61; and INFC60) using an electrolyte composition according to the present invention when cycled from 4.0 to 1.0 V.

[0194] Results are also shown for two cells not according to the invention (ie, INFC57; and INFC63) when cycled from 4.0 to 1.0 V. The results shown in FIG. 2a show that INFC62; INFC64; INFC67; INFC61; and INFC60 provide higher capacity within the 4.0-1.0 V window compared to INFC57 and INFC63, which either do not use an additive (INFC57) or use an additive other than that of the present invention (INFC63), respectively.

[0195] The cells containing the borate-containing additive (INFC62; INFC64; and INFC67) showed higher capacity performance compared to the cells containing the sulfur-containing additive (INFC60) or the surfactant (INFC61). The cell containing the sulfur-containing additive (INFC60) also showed higher capacity performance compared to the cell containing the surfactant (INFC61).

[0196] Specifically, the delivery capacities at cycle 20 of INFC62; INFC64; INFC67; INFC61; and INFC60 were 95 mAh / g, 92.2 mAh / g, 88.9 mAh / g, 29.2 mAh / g, and 45.4 mAh / g, respectively.

[0197] Compared to INFC62; INFC64; INFC67; INFC61; and INFC60, respectively, the cycling performance of INFC57 and INFC63 was extremely poor from 4 to 1 V, with both cells essentially failing after 5 cycles.

[0198] FIG. 2b also provides an indication of how the additives of the present invention affect performance. It can be seen that the first cycle efficiencies (FCE) of the cells whose electrolyte compositions contained either a borate-containing additive or a surfactant-containing additive were all significantly higher than the control samples: specifically, the FCEs of INFC62, INFC64, INFC67 and INFC61 were 87.2%, 91.3%, 91% and 70.9%, all of which were higher than either INFC57, which contained no additive (64%), or INFC63, which contained an additive not according to the present invention, i.e., the FEC additive (29.8%).

[0199] Although the FCE of INFC60 containing a sulfur-containing additive (i.e., PCS) was very low (9.7%), the subsequent increase in capacity and stable cycling point, see FIG. 2a, indicates a difference in the mechanism of PCS as a film-forming additive.

[0200] Apparently, when the electrolyte contains 2 wt% PCS as the only additive, the decomposition of PCS initially leads to a lower FCE, but then the decomposition products appropriately modify the anode current collector substrate, subsequently resulting in more stable sodium plating / stripping in the next cycle. Thus, this data indicates differences in the mechanisms of the tested additives, results that were not previously expected. Moreover, this can explain the higher capacity observed for the PCS-based electrolyte.

[0201] Figure 2c further illustrates the cycling performance of anode-free sodium cells using the electrolyte composition of the present invention. More specifically, Figure 2c illustrates a plot of full cell voltage (V) versus cathode discharge capacity (mAh / g) (i.e., voltage-capacity cycling curve) for the fifth cycle of a cell using the electrolyte composition of the present invention (sample TEL66n) compared to a cell using a control electrolyte composition (sample TEL66i). Specifically, cells INFC69 and INFC67 using TEL66n were compared to cells INFC53 and INFC57 using TEL66i.

[0202] When cells INFC53 and INFC69 were cycled within the 3.7 to 1 V window (i.e., lower voltage), cell INFC69 was found to deliver substantially the same capacity as cell INFC53. In comparison, when cells INFC57 and INFC67 were cycled within the 4.0 to 1 V window (i.e., higher voltage), cell INFC67 delivered significantly more capacity than cell INFC57.

[0203] More specifically, subjecting cell INFC57 to cycling to higher voltages gradually led to more electrolyte oxidation, and after two more cycles, INFC57 was unable to charge to completion to 4V. FIG. 2c further shows that in the fifth cycle of cell INFC57, a cell voltage of 3.2V was achieved after a 7 hour charge cycle at a C-rate of C / 5. One skilled in the art would understand that a higher cell voltage (e.g., 4V) should have been achieved by / before the 5th hour under these conditions. Instead, this data suggests that continued electrolyte oxidation during cycling rendered the control electrolyte unusable at higher voltages.

[0204] Advantageously, in the case of cell INFC67, which used the electrolyte composition of the present invention (sample TEL66n), the cell was able to charge to about 4 V on cycle 5. Thus, this data demonstrates Applicants' understanding that TMSB can impart surprising oxidative stability to glyme-based electrolytes, particularly when used in anode-free sodium-ion cells.

[0205] Example 3 The higher voltage performance of an anode-free sodium cell using 1.5 m NaBF4 in 1:1 wt / wt tetraglyme:diglyme with two additives was tested with the cell having a voltage profile from 4.0 to 1.0 V. More specifically, this experiment confirms the surprising synergistic effect of using an electrolyte composition of the invention with two additives after establishing the behavior of the electrolyte composition of the invention with one additive in previous experiments.

[0206] 3a and 3b show the Na plating-stripping process of four cells (INFC72, INFC92, FPC220215 and FPC220218) using two different types of additives according to the present invention (i.e., a combination of a boron-containing additive (TMSB) and a surfactant (P-123)) (sample TEL66R).

[0207] 3a and 3b also show the Na plating-stripping process of cell INFC68 using one additive according to the present invention (i.e., the boron-containing additive (TMSB)) in combination with an additive not according to the present invention (i.e., the carbonate-containing additive (VC)) (sample TEL66o).

[0208] The results shown in FIG. 3a show that INFC72, INFC92, and FPC220218 each deliver higher capacity in the 4.0-1.0 V window than INFC68 using one additive according to the present invention in combination with an additive not according to the present invention. Specifically, the delivered capacities at cycle 4 for INFC72, INFC92, FPC220218, and INFC68 were 101 mAh / g, 104.1 mAh / g, 109.6 mAh / g, and 46.5 mAh / g, respectively. This indicates that additive selection is important to performance and that different combinations of additives result in different electrochemical performance, which is unpredictable.

[0209] Therefore, the non-aqueous electrolyte composition according to the present invention is preferably substantially free of one or more carbonate-based compounds such as vinylene carbonate. Additionally, cells INFC72, INFC92, and FPC220218 exhibited greater or similar capacity performance compared to cells INFC62, INFC64, and INFC67 using the boron-containing additive (TMSB) alone, or cell INFC61 using the surfactant (P123) alone, respectively.

[0210] Specifically, the delivered capacities at cycle 20 of INFC72, INFC92 and FPC220218 were 92.3 mAh / g, 92.5 mAh / g and 102.3 mAh / g, respectively, whereas the delivered capacities at cycle 20 of INFC62, INFC64, INFC67, INFC61 and INFC60 were 95 mAh / g, 92.2 mAh / g, 88.9 mAh / g, 29.2 mAh / g and 45.4 mAh / g, respectively.

[0211] This synergistic performance is highly unexpected and demonstrates once again that different combinations of additives result in different electrochemical performance, which cannot be predicted. From the results shown in Figure 3b, it was observed that for each of INFC72, INFC92, and FPC220218, a stable coulombic efficiency close to 100% was achieved throughout the cycles (approximately 92–96% at cycle 20), indicating very stable Na plating and stripping. In contrast, for cell INFC68, a coulombic efficiency of 36.9% was observed at cycle 4.

[0212] Also, as verified by cell cycling of FPC220215 with sample TEL66R, good cycling was observed even under different cycling conditions in different voltage windows (e.g., stable cycling was observed from 3.7 to 1 V, and the capacity retention at 110 cycles was 78.4%).

[0213] Example 4 Lower Voltage Performance at lower voltages of anode-free sodium cells using 1.5 m NaBF in 1:1 wt / wt tetraglyme:diglyme with three additives as shown in Table 2. The cells were tested over a voltage profile from 3.7 to 1.0 V.

[0214] 4a and 4b show the Na plating-stripping process of cell FPC220213 using three different types of additives according to the present invention (i.e., boron-containing additive (TMSB) in combination with both sulfur-containing additive (PCS) and surfactant (P-123)) (i.e., sample TEL66P).

[0215] Results for a cell (FPC220214) using two additives according to the invention (i.e., a boron-containing additive (TMSB) and a surfactant (P123)) in combination with an additive not according to the invention (i.e., a carbonate-containing additive (FEC)) are also shown in Figures 4a and 4b. This is sample TEL66Q.

[0216] The results shown in Figure 4a indicate that FPC220213 delivers higher capacity than FPC220214 under the same cycling conditions within the window of 3.7 to 1.0 V. Specifically, the delivered capacities at cycle 110 for FPC220213 and FPC220214 were 76.9 mAh / g and 66.9 mAh / g, respectively.

[0217] Higher voltage Performance at higher voltages of anode-free sodium cells using 1.5 m NaBF4 in 1:1 wt / wt tetraglyme:diglyme with additives as shown in Table 2. The voltage profile was increased from a 3.7-1.0 V window to a 4.0-1.0 V window.

[0218] 4a and 4b show the Na plating-stripping process of cell FPC220216 using sample 66P in the 4.0-1.0 V window in comparison with cell FPC220217 using sample TEL66Q also in the 4.0-1.0 V window.

[0219] The results shown in Figure 4a and Figure 4b indicate that FPC220216 delivers higher capacity than FPC220217 under the same cycling conditions within the 4.0-1.0 V window: after cycle 20, the former delivered a specific capacity of 103.3 mAh / g, while the latter's specific capacity was only 79.7 mAh / g.

[0220] FPC220216 with TEL66P also showed greater capacity performance compared to cells using only boron-containing additives (INFC62; INFC64; and INFC67), only sulfur-containing additives (INFC60), or only surfactants (INFC61), as described above in Example 2 (see FIG. 2a).

[0221] Specifically, the delivered capacities at cycle 20 for INFC60, INFC61, INFC62, INFC64 and INFC67 were 45.3 mAh / g, 29.2 mAh / g, 95 mAh / g, 92.2 mAh / g and 88.9 mAh / g, respectively. These capacity values ​​are lower, and in some cases significantly lower, than the specific capacity (103.3 mAh / g) seen in cell FPC220216 after cycle 20, demonstrating the surprising beneficial effect of using TEL66P.

[0222] Anode-free cells utilizing a glyme-based electrolyte containing three additives according to the invention also outperformed anode-free cells utilizing a glyme-based electrolyte containing three additives, one of which was not according to the invention.

[0223] Focusing on anode-free cells of similar capacity (~6 mAh) in Figures 4a and 4b, it can be seen that the cycling stability of INFC70 (TEL66P), INFC78 (TEL66S) and INFC79 (TEL66T) is better than that of INFC45 (TEL66h) and INFC71 (TEL66Q).

[0224] Specifically, the 20th cycle discharge capabilities of the various cells were as follows: INFC70(TEL66P)=90.8mAh / g INFC78(TEL66S)=93.1mAh / g INFC79(TEL66T)=90.2mAh / g INFC45(TEL66h)=0.02mAh / g INFC71(TEL66Q)=83.1mAh / g Therefore, the non-aqueous electrolyte composition according to the present invention is preferably substantially free of one or more carbonate-based compounds such as fluoroethylene carbonate.

[0225] Example 5 High voltage; Effect of three additives; Long cycle time The long-term cycling performance was investigated for anode-free sodium cells (INFC16, INFC17, INFC19, and INFC20) using an electrolyte composition (sample TEL66d) containing 1.5 m NaBF4 in 1:1 wt / wt tetraglyme:diglyme with a mixture of 2 wt % PCS, 1 wt % P123, and 1 wt % TMSB from 4.0 V to 1 V for 200 cycles.

[0226] INFC16, INFC17, INFC19 and INFC20 were all cycled from 4.0 to 1.0 V with TEL66d, with slight differences in cycling rates: · INFC16 and INFC17: first 2 cycles at ±C / 10, followed by +C / 5, -1C for 200 cycles. · INFC19: +C / 10, -1C for the first 2 cycles, then +C / 5, -1C for 200 cycles. · INFC20: +C / 10, -1C at 3~1V for the first 5 cycles, then +C / 10, -1C for 2 cycles, and finally +C / 5, -1C for 200 cycles.

[0227] As can be seen from Figure 5a, all four cells showed good capacity retention after 200 cycles at +C / 5, -1C: the capacity retention of each cell relative to the first cycle at +C / 5, -1C was INFC16 (50.4%), INFC17 (49.9%), INFC19 (33.3%) and INFC20 (31.9%).

[0228] As shown in Figure 5b, the stable coulombic efficiency of all cells was around 100% throughout the cycle life at +C / 5, -1C: as an example, the coulombic efficiency at the 200th cycle at +C / 5, -1C for each cell was INFC16 (98.5%), INFC17 (100.5%; the efficiency at the 199th cycle was 97.6%), INFC19 (95.2%; the efficiency at the 199th cycle was 101.5%) and INFC20 (97.2%).

[0229] These coulombic efficiency values ​​after 200 cycles are significantly greater than those obtained for cell INFC57, which was cycled with the control electrolyte composition (sample TEL66i). Indeed, as shown in FIG. 2a for cell INFC57, the coulombic efficiency at cycle 5 (+C / 5, 3rd cycle at −1C) was only 16.99% (see FIG. 2c for the corresponding cycling profile for this cell).

[0230] As noted above in Example 2, Applicants believe that the low coulombic efficiency values ​​of cells cycled with the control electrolyte composition (sample TEL66i) are due to poor oxidative stability when cycled at high voltages. However, as demonstrated in this extended cycling experiment, such poor oxidative stability is not observed in anode-free sodium cells cycled with sample TEL66d at higher voltages.

[0231] Example 6 Cycling performance was investigated at rates of +C / 5, -1C from 4 to 1 V for anode-free sodium cells using electrolyte compositions containing 1.5m NaBF4 in 1:1 wt / wt tetraglyme:diglyme with an additive not used in any of the above experiments. Such compositions are specified in Table 2, Experiments 6A to 6F.

[0232] 6a / 6b show plots of cathode discharge capacity (mAh / g) / % coulombic efficiency versus cycle number for cells using electrolyte compositions of the invention (samples TEL85b, TEL66U, TEL85g, TEL85h, TEL85i, and TEL66V) compared to a cell using a control electrolyte composition (sample TEL66i). Taking each sample in turn:

[0233] TEL85b (containing boroxine): Cell INFC93 was cycled with TEL85b and the cycling performance was shown to be significantly more stable than cell INFC57 cycled with the control electrolyte composition TEL66i. Surprisingly, although the FCE of INFC93 was lower than that of INFC57, the subsequent coulombic efficiency was about 100%, significantly higher than that of INFC57 (e.g., the coulombic efficiency of the fifth cycle of INFC93 was 97.1%, compared to only 16.99% for INFC57).

[0234] TEL66U (containing phosphite) Cell INFC100 was cycled with TEL66U and showed lower cycling performance than cell INFC93 cycled with TEL85b, but significantly better than cell INFC57 cycled with the control electrolyte composition TEL66i: for example, the capacity at cycle 5 of INFC100 was 41.2 mAh / g, significantly higher than the 21.4 mAh / g delivered by INFC57.

[0235] TEL 85g (containing sultone) Cell INFC105 was cycled with TEL85g and showed better cycling performance than cell INFC57, which was cycled with the control electrolyte composition TEL66i: for example, the capacity of INFC105 at cycle 5 was 72.6 mAh / g, significantly higher than the 21.4 mAh / g delivered by INFC57.

[0236] TEL85h (contains sulfolane) Cell INFC106 was cycled with TEL85h and cycle performance was very similar to cell INFC105 cycled with TEL85g, but with improved cycling stability measurements (92.1 mAh / g capacity at cycle 5 for INFC106 vs. 72.6 mAh / g for INFC105) followed by similar FCE (77.3% for INFC106 vs. 80.7% for INFC105) and stable coulombic efficiency (97.2% coulombic efficiency at cycle 5 for INFC106 vs. only 51.8% for INFC105). Cell INFC106 performed much better than cell INFC57 cycled with the control electrolyte composition TEL66i.

[0237] TEL85i and TEL66V (containing nitrile) Cells INFC107 and INFC81 were cycled with the nitrile-containing additive 1,3,6-hexanetricarbonitrile. Specifically, cell INFC107 was cycled with TEL85i and cell INFC81 was cycled with TEL66V.

[0238] The cycling performance of INFC107 with TEL85i was shown to be better than that of the cell INFC57 cycled with the control electrolyte composition TEL66i: for example, the capacity of INFC107 at cycle 5 was 73.2 mAh / g, significantly higher than the 21.4 mAh / g delivered by INFC57.

[0239] Similarly, the cycling performance of INFC81 with TEL66v was shown to be better than that of the cell INFC57 cycled with the control electrolyte composition TEL66i; for example, the cycle 5 capacity of INFC81 was 53.3 mAh / g, significantly higher than the 21.4 mAh / g delivered by INFC57.

[0240] Example 7 In this experiment, the cycling performance of anode-free sodium cells constructed with various types of anode current collector / substrates is examined when using an electrolyte composition according to the present invention (TEL66P). Such cells were cycled at +C / 5, -1C from 3.7 to 1.0 V, and the experimental results are shown in Table 2 as Experiments 7A to 7H.

[0241] 7a and 7b show plots of cathode discharge capacity (mAh / g) / % coulombic efficiency versus cycle number to illustrate the cycling stability of cells INFC73, INFC74, INFC75, INFC82, INFC83, INFC76, INFC96, and INFC97, each of which uses an electrolyte composition of the present invention (sample TEL66P), but each is constructed with a different type of anode current collector / substrate.

[0242] Pristine current collector Three different types of pristine anode current collectors were investigated: ·INFC73 used pristine aluminum foil as the substrate; INFC74 used pristine copper mesh foil (Microgrid® Cu25 obtained from Dexmet Corporation); and · INFC75 used pristine aluminum mesh foil (Microgrid® Al25 obtained from Dexmet Corporation).

[0243] From the results shown in FIG. 7a, it is clear that INFC73 exhibited the least favorable cycling performance, i.e., very unstable cycling characteristic of an unreliable sodium plating / stripping process.

[0244] INFC75 performed significantly better than INFC73 in all measurements: INFC75 showed more stable cycling (40 mAh / g at cycle 80, i.e., 74.2% capacity retention vs. first cycle) and high and stable coulombic efficiency (e.g., coulombic efficiency at cycle 80 was 101.6%).

[0245] INFC74 gave even better measurements than INFC75: INFC74 showed higher capacity and better capacity retention after 80 cycles compared to INFC75 (58.6 mAh / g and 85.5%, respectively), along with a similarly high and stable coulombic efficiency (the coulombic efficiency of INFC75 at cycle 80 was 99.3%).

[0246] This experiment shows that when using an electrolyte composition according to the present invention, a variety of anode current collectors can be used in anode-free sodium cells.

[0247] Current collector including a nucleation layer Five different types of anode current collectors containing one or more carbon-containing nucleation layers were investigated, as shown in Table 3: · INFC82, INFC83 and INFC76 each used one carbon-containing nucleation layer on aluminum foil; · INFC97 used one carbon-containing nucleation layer on an aluminum mesh; · INFC96 used two carbon-containing nucleation layers on an aluminum foil (i.e., Applicant applied one carbon (C65) nucleation layer to an En'Safe 92 current collector composed of an aluminum foil which itself contained one carbon nucleation layer).

[0248] Carbon-containing nucleation layer was prepared by mixing carbon black (C65) as active material with PVDF binder (C65:PVDF at 90:10 weight ratio). NMP solvent was then added and mixed to obtain a slurry. The slurry was then applied onto aluminum foil / aluminum mesh / En'Safe 92 current collector foil with a doctor blade as shown. The GSM (loading of C65 only) for each cell substrate is shown in Figure 7a and Figure 7b.

[0249] The cycling performance of cells using these coated substrates, specifically INFC82, INFC83, INFC76, INFC96 and INFC97, is compared in Table 3 below:

[0250] [Table 10]

[0251] As can be seen from the results in Table 3, cells cycled with TEL66P showed good cycling performance with a variety of different types of current collectors containing one or more carbon-containing nucleation layers in a variety of coating GSMs.

[0252] For cells INFC82, 83 and 76 using current collectors fabricated from aluminum foil, the initial capacity and FCE decreased but the cycling stability increased as the GSM of one or more carbon nucleation layers increased.

[0253] INFC96, using a 0.7 GSM C65 coating on En'Safe 92 foil, also showed very good performance measurements in terms of delivered capacity, FCE and cycling stability.

[0254] It is also seen that one or more carbon-containing nucleation layers (C65) on the Al mesh improves cycling performance, as shown by the performance of INFC97 versus that of INFC75: INFC75 delivered 56.3 mAh / g in the first cycle (FCE=61.4%), which is significantly lower than the capacity delivered by INFC97.

[0255] Example 8 Effect of higher weight percent additive Performance at higher voltages of anode-free sodium cells using 1.5 m NaBF in 1:1 wt / wt tetraglyme:diglyme with higher wt % of the three additives as shown in Table 2. The cells were tested with a voltage profile from 4.0 to 1.0 V.

[0256] 8a / 8b show plots of cathode discharge capacity (mAh / g) / % coulombic efficiency versus cycle number for cells using electrolyte compositions of the present invention (samples TEL66W, TEL66Y, TEL66Z, TEL85, and TEL85a).

[0257] Higher weight percent sulfur content (PCS) Cell INFC84 was cycled with 7 wt % PCS and cell INFC85 was cycled with 15 wt % PCS.

[0258] As shown in Figures 8a and 8b, the performance at such high wt% PCS was extremely poor, with both cells failing rapidly after a few cycles. Particularly notable is cell INFC85, which showed no reversible capacity, indicating the negative effect on performance when the electrolyte composition contained 15 wt % PCS.

[0259] Higher weight percent boron content (TMSB) Cell INFC91 was cycled with 8.5 wt % TMSB and cell INFC90 was cycled with 15 wt % TMSB.

[0260] As shown in Figures 8a and 8b, both INFC91 and INFC90 delivered high first discharge capacities (106.2 mAh / g and 105.2 mAh / g, respectively) with high FCE values ​​(91.1% and 90.3%, respectively) and had adequate cycling stability after 50 cycles (capacity retention after 30 cycles was 80.5% and 80.6%, respectively).

[0261] Higher weight percent surfactant (P123) Cell INFC88 was cycled with 7.5 wt % P123 and cell INFC89 was cycled with 15 wt % P123.

[0262] As shown in Figures 8a and 8b, cell INFC88 delivered a first cycle capacity of 100.6 mAh / g with an FCE of 76.1%. With increasing the amount of P123 to 15 wt%, cell INFC89 showed a reduced first cycle capacity of 68.9 mAh / g with an FCE of 49.2%.

[0263] conclusion Compared to cell INFC57 using the control electrolyte composition (TEL66i), the following performance advantages in terms of higher discharge capacity and coulombic efficiency (shown in brackets) at the 5th cycle were observed under comparable conditions: INFC57: 21.4mAh / g (16.99%) INFC91: 102.7mAh / g (97.2%) INFC90: 101.6mAh / g (97.3%) INFC88: 95.9mAh / g (97.3%) INFC89: 71.1mAh.g (50.8%) Thus, good cycling performance of the anode-free sodium cell can still be observed at higher wt % additive.

[0264] Example 9 Effect of alternative voltage windows Higher voltage performance of anode-free sodium cells using 1.5m NaBF4 in 1:1 wt / wt tetraglyme:diglyme with higher wt% of the three additives as shown in Table 2. The cells were tested with the voltage profile shown in Table 2 and described below.

[0265] 9a / 9b show plots of cathode discharge capacity (mAh / g) / % coulombic efficiency versus cycle number for cells using electrolyte compositions of the present invention (samples TEL66d, TEL85e, TEL85f, and TEL66P).

[0266] 4.05~1V Using either TEL66d (cell INFC101), TEL85e (INFC102) or TEL85f (INFC103), the cells were cycled over a wider voltage window from 4.05 to 1 V. Data from the 10th cycle are shown below: INFC101: 89.7mAh / h (Coulombic efficiency = 101.6%; capacity retention = approximately 100%) INFC102: 89.4mAh / g (Coulombic efficiency = 95.6%; capacity retention = approximately 100%) INFC103: 100mAh / h (Coulombic efficiency = 95.5%; capacity retention = 95.2%) Capacity retention is calculated for the first cycle of each cell.

[0267] As can be seen from this data and in Figures 9a and 9b, these cells exhibited good cycling stability and performance under these conditions.

[0268] 4~2.5V Cell FPC220245 was cycled with TEL66P over a window from 4 to 2.5 V. Data from the 10th cycle is shown below (compared to the 1st cycle): FPC220245: 84.6mAh / g (Coulombic efficiency = 98.9%; capacity retention = 94%) Capacity retention is calculated for the first cycle of each cell.

[0269] These examples demonstrate that anode-free sodium cells using the electrolyte compositions of the present invention can exhibit good cycling performance with stable cycling over different voltage windows, demonstrating versatility.

Claims

1. One or more sodium-containing salts selected from sodium tetrafluoroborate (NaBF4), sodium hexafluorophosphate (NaPF6), sodium trifluoromethanesulfonate (CF3NaSO3), sodium bis(fluorosulfonyl)imide (Na(SO2F)2N), sodium bis(trifluoromethanesulfonyl)imide (C2F6NNaO4S2), sodium bis(oxalate) (NaB(C2O4)2), and sodium difluoro(oxalato)borate; and A first component comprising one or more glyme-based solvents and a sulfur-containing compound in an amount of about 10% or less by weight of the solvent system selected from sulfone-containing compounds, sulfate-containing compounds, and sulfonate-containing compounds; a nitrile-containing compound in an amount of about 10% by weight or less of the solvent system; a phosphorus-containing compound in an amount of about 10% or less by weight of the solvent system; a surfactant in an amount up to about 20% by weight of the solvent system; a second component comprising one or more additives selected from the group consisting of: wherein the total amount of the one or more additives does not exceed about 20 wt % based on the weight of the solvent system.

2. One or more sodium-containing salts selected from sodium tetrafluoroborate (NaBF4), sodium hexafluorophosphate (NaPF6), sodium trifluoromethanesulfonate (CF3NaSO3), sodium bis(fluorosulfonyl)imide (Na(SO2F)2N), sodium bis(trifluoromethanesulfonyl)imide (C2F6NNaO4S2), sodium bis(oxalate) (NaB(C2O4)2), and sodium difluoro(oxalato)borate; and A first component comprising diglyme and the following: a sulfur-containing compound in an amount of about 10% or less by weight of the solvent system selected from sulfone-containing compounds, sulfate-containing compounds, and sulfonate-containing compounds; a boron-containing compound in an amount of about 20% or less by weight of the solvent system; a nitrile-containing compound in an amount of about 10% by weight or less of the solvent system; a phosphorus-containing compound in an amount of about 10% or less by weight of the solvent system; a surfactant in an amount up to about 20% by weight of the solvent system; a second component comprising one or more additives selected from the group consisting of: wherein the total amount of the one or more additives does not exceed about 20 wt % based on the weight of the solvent system.

3. 3. The non-aqueous electrolyte composition of claim 1 or 2, wherein the second component comprises two or more additives including a boron-containing compound in an amount of >0 to <20% by weight of the solvent system and a surfactant in an amount of >0 to <20% by weight of the solvent system, the total amount of the two or more additives not exceeding about 20% by weight based on the weight of the solvent system.

4. 3. The non-aqueous electrolyte composition of claim 1 or 2, wherein the second component comprises three or more additives including a sulfur-containing compound in an amount of >0 to <10 wt % of the solvent system, a boron-containing compound in an amount of >0 to <20 wt % of the solvent system, and a surfactant in an amount of >0 to <20 wt % of the solvent system, wherein the total amount of the three or more additives does not exceed about 20 wt % based on the weight of the solvent system.

5. 3. The nonaqueous electrolyte composition according to claim 1, wherein the sulfur-containing compound is selected from sulfolane, 3-methylsulfolane, trimethylsulfone, methylphenylsulfone, 1,3-propanediol cyclic sulfate (PCS), 1,5,2,4-dioxadithiane 2,2,4,4-tetraoxide, 1,3,2-dioxathiolane 2,2-dioxide, 1-propene 1,3-sultone, and 1,3-propane sultone.

6. 3. The non-aqueous electrolyte composition according to claim 1, wherein the sulfur-containing compound includes 1,3-propanediol cyclic sulfate (PCS).

7. The non-aqueous electrolyte composition of claim 2 , wherein the boron-containing compound is selected from borate-containing compounds and boroxine-containing compounds.

8. 8. The non-aqueous electrolyte composition of claim 7, wherein the boron-containing compound is selected from tris(trimethylsilyl)borate (TMSB), tris(2,2,2-trifluoroethyl)borate, trimethylborate, triethylborate, trimethoxyboroxine, and trimethylboroxine.

9. 3. The non-aqueous electrolyte composition according to claim 1, wherein the nitrile-containing compound includes 1,3,6-hexanetricarbonitrile.

10. 3. The non-aqueous electrolyte composition according to claim 1, wherein the phosphorus-containing compound comprises tris(trimethylsilyl)phosphite (TMSP).

11. 3. The non-aqueous electrolyte composition according to claim 1, wherein the surfactant is selected from an anionic surfactant, a cationic surfactant, a nonionic (hydrophilic) surfactant, and an amphoteric (zwitterionic) surfactant.

12. 12. The non-aqueous electrolyte composition of claim 11, wherein the surfactant comprises at least one non-ionic block copolymer surfactant.

13. The non-aqueous electrolyte composition of claim 1, wherein a first component of the solvent system comprises diglyme.

14. The non-aqueous electrolyte composition of claim 13, wherein the first component further comprises tetraglyme, preferably comprising tetraglyme and diglyme in a 1:1 weight ratio.

15. a cathode comprising one or more sodium-containing active materials; Anode current collector; a separator positioned between the cathode and the anode current collector; and The nonaqueous electrolyte composition according to any one of claims 1 to 2; 1. An anode-free sodium cell comprising:

16. 16. The anode-free sodium cell of claim 15, wherein the anode current collector includes one or more carbon-containing nucleation layers formed on a surface of the anode current collector prior to the first charge cycle of the anode-free sodium cell.

17. 16. The anode-free sodium cell of claim 15, wherein the one or more sodium-containing active materials are selected from sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds (including analogs thereof).

18. 16. An apparatus comprising one or more anode-free sodium cells according to claim 15.

19. 16. A method of operating the anode-free sodium cell of claim 15.

20. 20. The method of claim 19, wherein the anode-free sodium cell has a charge cutoff voltage of 4.0 V or greater.

21. Use of the non-aqueous electrolyte composition according to any one of claims 1 to 2 in an anode-free sodium cell.

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