Non-aqueous electrolyte composition

Abstract

The present invention relates to a non-aqueous electrolyte composition having a solvent system including a first component including a first organic carbonate-based solvent and a second organic carbonate-based solvent, and a second component including one or more performance additives including tris(trimethylsilyl)borate (TMSB). Devices, methods, and uses including the electrolyte composition are also disclosed.

Description

[Technical field]

[0001] The present invention relates to a novel non-aqueous electrolyte composition, a sodium-ion cell comprising said novel non-aqueous electrolyte composition, and an energy storage device, such as a battery, a rechargeable battery, an electrochemical device, and an electrochromic device, that includes said non-aqueous electrolyte composition. Methods and applications that include said novel electrolyte composition are also disclosed. [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 charging a sodium-ion (or lithium-ion) battery, 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] One area that requires more attention is the development of suitable electrolyte compositions, particularly for use in sodium-ion cells. Although the design of suitable electrolyte compositions has received less attention than the active materials (electrodes), their importance should not be overlooked, as they are key to determining primarily the battery life and the practical performance that the cell can achieve, e.g., capacity, rate capability, safety, etc. However, a suitable electrolyte composition must satisfy many attributes, including: Chemical stability - during operation of the cell there must be no reaction of the electrolyte with 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 upper and lower onset potentials for oxidative or reductive decomposition; 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; High ionic conductivity and low electronic conductivity are respectively + Necessary to maintain cell operation through transportation and to minimize cell self-discharge; 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 effective production.

[0004] In lithium-ion cells, the most common electrolyte compositions contain LiPF6 or LiBF4 dissolved in an organic carbonate-based solvent; electrolyte compositions containing 1M LiPF6 in a mixture of EC (ethylene carbonate) / DMC (dimethyl carbonate) or a mixture of EC (ethylene carbonate) / EMC (ethyl methyl carbonate) are considered the "standard" Li-ion cell electrolyte by most researchers.

[0005] For sodium-ion cells, the sodium analogue NaPF6 can be used instead of LiPF6, but a much more cost-effective alternative is NaBF4; the latter also has the advantage of improved thermal stability compared to NaPF6. Unfortunately, however, NaBF4 has very low solubility in organic carbonate-based electrolyte solvents, and as a result, the ionic conductivity of the resulting electrolyte composition is generally too low for practical applications. Thus, the low solubility of NaBF4-containing electrolyte compositions in conventional organic carbonate-based solvents results in inferior electrochemical performance compared to comparable cells using NaPF6.

[0006] Additionally, while some materials used in lithium systems can be carried over to their sodium counterparts, this is by no means always possible. This is in part because the atomic radius of sodium is larger than that of lithium. Thus, a solvent system that is suitable for a lithium-ion battery may not be suitable for a sodium-ion battery, or vice versa. A notable example of this difference is the incompatibility of propylene carbonate (PC) solvent in lithium-ion batteries with graphite anodes (the anodes currently most commonly used in commercial lithium-ion systems). Due to this incompatibility, commercial lithium-ion batteries typically use EC / DMC or EC / EMC solvent systems, as described above. In contrast, sodium-ion systems tolerate electrolyte solvents that include PC well.

[0007] It is clearly desirable to find an optimal electrolyte composition to enhance the performance of sodium-ion batteries. One strategy to enhance the performance of sodium-ion batteries is to dope the electrolyte composition's solvent system with a performance additive to promote or even impart one or more desirable properties of the electrolyte composition. However, sodium-ion cells are dependent on how the electrolyte composition interacts with the components of the sodium-ion cell (e.g., separator, positive and negative electrodes, etc.). This interaction is based on a mosaic of the electrolyte composition's physical properties and cannot be predicted. Among other things, as noted above, the electrolyte composition needs to have high ionic conductivity and low electronic conductivity to sustain cell operation by transport of Na+. However, such high ionic conductivity and low electronic conductivity must be balanced with the ability to maintain chemical and electrochemical stability, at least to allow the sodium-ion cell to be charged and discharged over many cycles.

[0008] Due to the differences in the chemistry of lithium and sodium ions resulting from the atomic radius of sodium being larger than that of lithium as mentioned above and the different electrode active materials used (graphite and hard carbon anodes in lithium-ion and sodium-ion cells, respectively), additives that are efficient for use in lithium-ion cells are not necessarily efficient for use in sodium-ion cells. This is very clearly shown in Hijazi et al., Batteries & Supercaps, 2021, 4, 1-17.

[0009] Furthermore, most of the existing research on additives for use in electrolyte compositions containing one or more sodium-containing salts has been done in sodium metal half cells, not in sodium ion full cells, where problems from the positive electrode can be observed. For example, Chen et al., Chem. Commun., 2015, 51, 9809-9812, investigated sodium-difluoro(oxalato)borate (NaDFOB) as an additive in one or more organic carbonate-based solvents, but the experimental data was generated using a sodium metal half cell. Comparisons between sodium metal half cells and sodium ion full cells can be misleading due to several factors, including:

[0010] First, sodium metal half-cells typically do not operate under the same voltage conditions as sodium-ion full cells.

[0011] In a sodium metal half-cell, the experimenter pairs the electrode material they wish to study (called the "working electrode" or WE) with a Na metal counter electrode (CE), which acts as the anode (and reference electrode) and is used with the electrolyte they wish to evaluate. The WE can be operated at low potentials vs. Na (e.g., operating between 0V and 2V vs. Na / Na+) or at high potentials vs. Na (e.g., operating between 2.5V and 4.5V vs. Na / Na+). In the former case, the WE becomes the anode when used in a "full cell" (i.e., a Na-ion cell as conventionally understood), while in the latter the WE becomes the cathode of the full cell.

[0012] For example, if an experimenter is studying a low potential WE in a half cell (e.g., operating between 0V and 2V vs. Na / Na+), the performance of the WE-electrolyte combination is evaluated only at these low potentials, and not at higher potentials (i.e., 2.5V to 4.5V vs. Na / Na+). For electrolyte compositions, this is highly relevant because in a sodium-ion full cell, the electrolyte composition undergoes not only low potentials (which it did in the half-cell experiments above), but also high potentials (which it undergoes in the full cell when paired with a high potential cathode). Thus, even if an electrolyte composition can show excellent performance for a low potential WE in a sodium half cell, the experimenter does not know whether that electrolyte composition can be utilized in a Na-ion “full cell” when paired with a conventional cathode.

[0013] This problem is well known in the battery literature. See, for example, Ponrouch et al., Energy Environ.Sci, 2012, 5, 8572-8583, which illustrates how the electrochemical stability window of different salt-solvent combinations changes when used in sodium-ion batteries: in particular, from its FIG. 8a it is clear that the "NaTFSI-PC" electrolyte composition can be used as an electrolyte composition from 0 to 3.5 V vs. Na / Na+, but is not suitable for testing above 3.5 V vs. Na / Na+. This particular electrolyte composition is therefore only suitable for testing anodes in half cells, but not for testing Na-ion full cells where the cathode is operated at potentials >3.5 V vs. Na / Na+.

[0014] Second, the analytical error of a sodium metal half-cell is not the same as the analytical error of a sodium ion full-cell. A doctoral dissertation titled "ENERGY STORAGE USING SODIUM-ION BATTERIES" published in 2015 by Ashish Rudola highlights two artifacts that the Na metal counter electrode (which is the anode used in the half-cell) can cause when studying the performance of WEs. In a sodium metal half-cell, the cycling profile of a WE can have artifacts during the cycle, such as a "voltage step" caused by enhanced polarization of the sodium metal counter electrode (and this voltage step is not caused by the WE that the experimenter is evaluating). Furthermore, the high polarization of the sodium metal counter electrode reduces the high rate performance of the WE that the experimenter is trying to evaluate, which obviously causes analytical errors.

[0015] Third, electrolyte compositions tested in sodium metal half cells may not decompose in the same way as electrolyte compositions tested in sodium ion full cells. As explained in chapter 6 of the book "Na-ion Batteries" (Monconduit, L., Croguennec, L. (eds) (2020). Na-ion Batteries. ISTE Ltd, London and Wiley, New York), surface species can form spontaneously on sodium metal electrodes due to the decomposition of the electrolyte when in contact with the highly reactive sodium metal. As pointed out there, this problem is more pronounced in Na half-cells than in Li half-cells ("Higher reactivity of sodium metal compared to lithium metal anodes in contact with aprotic carbonate-based electrolytes commonly used in batteries"). Obviously, if the surface of the Na metal counterelectrode is covered with surface species that only occur in half-cells and not in full-cells (because sodium metal is absent in full-cells), this surface layer will affect the results and conclusions from half-cell experiments and may not be translatable to full-cells.

[0016] Therefore, due at least to the factors noted above, conclusions from studies conducted with electrolyte compositions tested in sodium metal half cells are not directly transferable to full cells. WO 2020 / 240209A1 relates to a non-aqueous electrolyte composition having a first solvent component comprising one or more organic carbonate-based solvents; and a second component comprising one or more surfactants in an amount of >0.5 to ≦10% based on the weight of the solvent system. With regard to the application of additives, WO 2020 / 240209A1 undoubtedly relates to the use of surfactants as additives. It mentions the use of tris(trimethylsilyl)borate (TMSB) in experiment 17, but WO 2020 / 240209A1 does not indicate that TMSB can be used with two or more carbonate-based solvents.

[0017] The doctoral dissertation by Du Kang entitled "STUDIES OF ANODES AND THEIR INTERACTIONS WITH ELECTROLYTES IN SODIUM-ION BATTERIES" is related to the anode material and its interaction with the electrolyte in sodium-ion batteries. With regard to the application of the additive, the paper mentions the use of TMSB in sodium metal half cells but not in sodium-ion full cells. Furthermore, TMSB is a 1M NaBF in tetraglyme. 4 Therefore, this doctoral dissertation does not demonstrate that TMSB can be used with more than one carbonate solvent.

[0018] In summary, neither WO 2020 / 240209A1 nor the doctoral dissertation by Du Kang teaches or suggests the use of TMSB as a performance additive in two or more carbonate-based solvents in sodium-ion full cell electrolyte compositions. Moreover, neither of these documents provides an indication that such electrolyte compositions possess the mosaic of physical properties necessary to promote high sodium-ion full cell performance. [Prior art documents] [Patent documents]

[0019] [Patent Document 1] International Publication No. 2020 / 240209A1 [Non-patent literature]

[0020] [Non-Patent Document 1] Hijazi et al., Batteries & Supercaps, 2021, 4, 1-17 [Non-Patent Document 2] Chen et al., Chem. Commun., 2015, 51, 9809-9812 [Non-Patent Document 3] Ponrouch et al., Energy Environ.Sci, 2012, 5, 8572-8583 [Non-Patent Document 4] "ENERGY STORAGE USING SODIUM-ION BATTERIES" PhD thesis published by Ashish Rudola in 2015 [Non-Patent Document 5] Chapter 6 of the book "Na-ion Batteries" (Monconduit, L., Croguennec, L. (eds) (2020). Na-ion Batteries. ISTE Ltd, London and Wiley, New York) [Non-Patent Document 6] A doctoral thesis entitled "STUDIES OF ANODES AND THEIR INTERACTIONS WITH ELECTROLYTES IN SODIUM-ION BATTERIES" by Du Kang Summary of the Invention [Problem to be solved by the invention]

[0021] It is therefore an object of the present invention to provide improved sodium ion conducting electrolyte compositions (i.e., electrolyte compositions designed for use in sodium ion secondary cells) that use a sodium-containing salt in a solvent system that includes two or more carbonate-based solvents. The electrolyte compositions of the present invention are particularly useful in sodium ion cells that employ anode electrodes that include non-graphitic carbon-containing materials, such as hard carbon-containing materials, or anodes that include sodium insertion materials, or conversion and / or alloying anode materials. The electrolyte compositions of the present invention exhibit excellent electrochemical performance in sodium ion cells, most preferably sodium ion full cells. [Means for solving the problem]

[0022] The present invention relates to a) one or more sodium-containing salts; and b) a solvent system comprising: i. a first component comprising a first organic carbonate based solvent and a second organic carbonate based solvent, optionally wherein the second organic carbonate based solvent is different from the first organic carbonate based solvent; and ii. a second component comprising one or more performance additives including tris(trimethylsilyl)borate (TMSB) in an amount >0 to ≦10% by weight of the solvent system; These objectives are achieved by providing a non-aqueous electrolyte composition comprising: DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Advantageously, TMSB used in the second solvent component of the solvent system enables 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 benefits such as improved long-term cycling stability and improved discharge capacity retention and / or energy retention, which is particularly surprising in solvent systems that include two or more carbonate-based solvents.

[0024] The amount of TMSB used in the second component of the solvent system according to the present invention is typically >0.5 to ≦10% by weight of the solvent system, 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 of the solvent system.

[0025] The amount of TMSB used in the second component of the electrolyte composition of the present invention is >0 wt.% based on the weight of the solvent system, preferably >0.2 wt.% based on the weight of the solvent system, and highly preferably ≧0.5 wt.% based on the weight of the solvent system.

[0026] For the avoidance of doubt, the phrase "weight of the solvent system" as used herein means the total weight of the solvent system (i.e. excluding the weight (s) of the one or more sodium-containing salts).

[0027] The second component of the solvent system can include or consist essentially of two or more performance additives. The two or more performance additives can be present as the second component of the solvent system in an amount of >0 to ≦10% by weight of the solvent system. The two or more performance additives can include tris(trimethylsilyl)borate (TMSB) in an amount of >0 to ≦10% by weight of the solvent system, and a surfactant or a sulfur-containing compound.

[0028] Preferably, the two or more performance additives as the second component of the solvent system can include a mixture of TMSB and a surfactant. That is, TMSB can be mixed with one or more surfactants to provide a mixture of two or more performance additives. The addition of a surfactant to the electrolyte composition of the present invention can further improve the performance of the electrolyte due to the unexpected synergistic effect between TMSB and one or more surfactants in a solvent system including two or more carbonate-based solvents.

[0029] The two or more performance additives as the second component of the solvent system can include a mixture of TMSB in an amount >0 to ≦10% by weight of the solvent system and a surfactant in an amount >0 to ≦10% by weight of the solvent system. Optionally, the total amount of the two or more performance additives as the second component of the solvent system does not exceed about 10 wt.% by weight of the solvent system.

[0030] Preferably, the two or more performance additives as the second component of the solvent system can include a mixture of TMSB in an amount >0-≦5% by weight of the solvent system and a surfactant in an amount >0-5% by weight of the solvent system. In this embodiment, the total amount of the two or more performance additives as the second component of the solvent system can be no more than about 10% by weight of the solvent system.

[0031] More preferably, the two or more performance additives as the second component of the solvent system can comprise a mixture of TMSB in an amount >0 to ≦2.5% by weight of the solvent system and a surfactant in an amount >0 to 2.5% by weight of the solvent system. In this embodiment, the total amount of the two or more performance additives as the second component of the solvent system can be no more than about 5 wt.% by weight of the solvent system.

[0032] One example of the two or more performance additives as the second component of the solvent system can include a mixture of TMSB 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.

[0033] Alternatively, the two or more performance additives as the second component of the solvent system can include a mixture of TMSB and a sulfur-containing compound. That is, TMSB can be mixed with one or more sulfur-containing compounds to provide a mixture of two or more performance additives. The addition of a sulfur-containing compound to the electrolyte composition of the present invention can further improve the performance of the electrolyte due to an unexpected synergistic effect between TMSB and one or more sulfur-containing compounds in a solvent system including two or more carbonate-based solvents.

[0034] The two or more performance additives as the second component of the solvent system can include a mixture of TMSB in an amount >0 to ≦10% by weight of the solvent system and a sulfur-containing compound in an amount >0 to ≦10% by weight of the solvent system. Optionally, the total amount of the two or more performance additives as the second component of the solvent system does not exceed about 10 wt.% by weight of the solvent system.

[0035] Preferably, the two or more performance additives as the second component of the solvent system can include a mixture of TMSB in an amount >0 to ≦5% by weight of the solvent system and a sulfur-containing compound in an amount >0 to ≦5% by weight of the solvent system. In this embodiment, the total amount of the two or more performance additives as the second component of the solvent system can be no more than about 10 wt.% by weight of the solvent system.

[0036] More preferably, the two or more performance additives as the second component of the solvent system can include a mixture of TMSB in an amount >0 to ≦2.5% by weight of the solvent system and a sulfur-containing compound in an amount >0 to ≦2.5% by weight of the solvent system. In this embodiment, the total amount of the two or more performance additives as the second component of the solvent system can be no more than about 5 wt.% by weight of the solvent system.

[0037] One example of the two or more performance additives as the second component of the solvent system can include a mixture of TMSB in an amount of about 1% by weight of the solvent system and a sulfur-containing compound in an amount of about 1 or 2% by weight of the solvent system.

[0038] The second component of the solvent system can comprise or consist essentially of three or more performance additives. The three or more performance additives can be present as the second component of the solvent system in an amount of >0 to ≦20% by weight of the solvent system. Preferably, the three or more performance additives can be present as the second component of the solvent system in an amount of >0 to ≦10% by weight of the solvent system.

[0039] The triple or more performance additive as the second component of the solvent system can include a mixture of TMSB, a sulfur-containing compound, and a surfactant. The triple or more performance additive can include TMSB, a surfactant, and a sulfur-containing compound in an amount of >0 to ≦10% based on the weight of the solvent system. That is, TMSB can be mixed with one or more sulfur-containing compounds and one or more surfactants to provide a triple or more performance additive mixture.

[0040] The addition of sulfur-containing compounds and surfactants to the electrolyte compositions of the present invention can further improve the performance of the electrolyte due to an unexpected synergistic effect between TMSB, one or more sulfur-containing compounds, and the surfactants in a solvent system that includes two or more carbonate-based solvents.

[0041] The three or more performance additives as the second component of the solvent system can include a mixture of TMSB in an amount >0 to ≦10% by weight of the solvent system, a sulfur-containing compound in an amount >0 to ≦10% by weight of the solvent system, and a surfactant in an amount >0 to ≦10% by weight of the solvent system. Optionally, the total amount of the three or more performance additives as the second component of the solvent system does not exceed about 20% by weight of the solvent system.

[0042] Preferably, the three or more performance additives as the second component of the solvent system can include a mixture of TMSB in an amount >0 to ≦2.5% by weight of the solvent system, a sulfur-containing compound in an amount >0 to ≦2.5% by weight of the solvent system, and a surfactant in an amount >0 to ≦2.5% by weight of the solvent system.

[0043] Highly preferably, the three or more performance additives as the second component of the solvent system can include a mixture of TMSB in an amount >0.5 to ≦2.5% by weight of the solvent system, a sulfur-containing compound in an amount >0.5 to ≦2.5% by weight of the solvent system, and a surfactant in an amount >0.5 to ≦2.5% by weight of the solvent system. Optionally, the total amount of the three or more performance additives as the second component of the solvent system does not exceed about 5 wt.% by weight of the solvent system.

[0044] Most preferably, the three or more performance additives as the second component of the solvent system can include TMSB in an amount of about 1% by weight of the solvent system, a sulfur-containing compound in an amount of about 1-2% by weight of the solvent system, and a surfactant in an amount of about 1% by weight of the solvent system.

[0045] One highly preferred example of the three or more performance additives as the second component of the solvent system can include TMSB in an amount of about 1% by weight of the solvent system, a sulfur-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.

[0046] Another highly preferred example of the three or more performance additives as the second component of the solvent system can include TMSB in an amount of about 1% by weight of the solvent system, a sulfur-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.

[0047] 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, which 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 compared to, for example, the coordination ability of anions with concentrated negative charges or anions with multiple negative charges.

[0048] One or more sodium-containing salts may be represented by 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 one or more compounds containing a tetrahedral anion, such as 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); can be selected from.

[0049] 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.

[0050] Preferred one or more of the formula NaM m X x In the sodium-containing salts of the formula (I), M is one or more metals and / or nonmetals, and X is a group containing or consisting of one or more halogens, the halogens being preferably selected from fluorine, chlorine, bromine and iodine, more preferably fluorine. The amount x of halogen 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).

[0051] In one or more of the preferred sodium compounds of formula NaXO4, the element X is one or more halogens, preferably selected from fluorine, chlorine, bromine and iodine. Chlorine is especially preferred, and the most preferred sodium-containing salt of formula NaXO4 is NaClO4.

[0052] Preferred sodium salts of one or more fluorosulfonyl-containing compounds include sodium bis(fluorosulfonyl)imide, also known as NaFSI (Na N(SO2F)2), and sodium bis(trifluoromethanesulfonyl)imide, also known as NaTFSI (C2F6NNaO4S2). Preferred sodium salts of one or more fluorosulfonate-containing compounds include sodium triflate or sodium trifluoromethanesulfonate, also known as NaOTf(CF3NaSO3). Preferred sodium salts of 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.

[0053] Highly preferably, the one or more sodium-containing salts are selected from sodium hexafluorophosphate (NaPF6), sodium bis(fluorosulfonyl)imide (NaFSI), and sodium bis(trifluoromethanesulfonyl)imide (NaTFSI). Most preferably, the one or more sodium-containing salts include sodium hexafluorophosphate (NaPF6).

[0054] Highly preferably, the electrolyte composition of the present invention can include two or more sodium-containing salts. The addition of two or more sodium-containing salts to the electrolyte composition of the present invention can further improve the performance of the electrolyte due to unexpected synergistic effects. Advantages such as significantly reduced total charging time may be observed in addition to greater cycle stability and / or greater discharge capacity.

[0055] Most preferably, the two or more sodium-containing salts can include a mixture of sodium hexafluorophosphate (NaPF6) in combination with sodium bis(fluorosulfonyl)imide (NaFSI) and / or sodium bis(trifluoromethanesulfonyl)imide (NaTFSI). Specific examples include a mixture of sodium hexafluorophosphate (NaPF6) and sodium bis(fluorosulfonyl)imide (NaFSI) or a mixture of sodium hexafluorophosphate (NaPF6) and sodium bis(trifluoromethanesulfonyl)imide, also known as NaTFSI (C2F6NNaO4S2).

[0056] It is convenient to express the amount of the one or more sodium-containing salts 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., the solutes) per kilogram of solvent system (combined weight of the first component and the second component), i.e., in mol / kg.

[0057] 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 0.3 mol / kg to 5 mol / kg, even more preferably in the range of 0.1 mol / kg to ≦2.5 mol / kg, and most preferably in the range of 0.3 mol / kg to ≦2.5 mol / kg. Highly preferably, especially when the component is NaPF6, the molality is in the range of 0.1 mol / kg to ≦2.5 mol / kg, ideally in the range of 0.3 mol / kg to ≦2.5 mol / kg, and most preferably about 1 mol / kg.

[0058] 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 0.3 mol / kg to 10 mol / kg, more preferably in the range of 0.3 mol / kg to 6 mol / kg, and most preferably in the range of 0.3 mol / kg to ≦4 mol / kg. Highly preferably, when the component is a mixture of NaPF6 and NaFSI or a mixture of NaPF6 and NaTFSI, the total molality is in the range of 0.1 mol / kg to ≦2.5 mol / kg, ideally in the range of 0.3 mol / kg to ≦2.5 mol / kg, and most preferably about 1.5 mol / kg.

[0059] The non-aqueous electrolyte composition of the present invention includes a first component including a first organic carbonate-based solvent and a second organic carbonate-based solvent. The second organic carbonate-based solvent is different from the first organic carbonate-based solvent. Typically, the second organic carbonate-based solvent has a different chemical structure from the first organic carbonate-based solvent. Thus, the non-aqueous electrolyte composition of the present invention includes a first component including two or more carbonate-based solvents.

[0060] The second organic carbonate-based solvent includes one carbonate-based solvent, but as described below, the second organic carbonate-based solvent can also include one or more additional (third) organic carbonate-based solvents. That is, the second organic carbonate-based solvent can be a mixture of organic carbonate-based solvents. Thus, the non-aqueous electrolyte composition of the present invention can include a first component that includes three or more carbonate-based solvents.

[0061] The first and second organic carbonate solvents can be cyclic or acyclic compounds characterized by the fact that they contain a carbonate ester group, i.e., a carbonyl group R1O(C=O)OR2, which is adjacently arranged with one or two alkoxy groups. The R1 and R2 groups can be hydrogen; or C1-C 20 or a cyclic or acyclic, branched or unbranched, substituted or unsubstituted alkyl group of the formula:20 or a cyclic or acyclic, branched or unbranched, substituted or unsubstituted alkenyl group of the formula: 20 branched or unbranched, substituted or unsubstituted cycloalkyl-, phenyl-, or heterocycle-containing groups;

[0062] Highly suitable primary and secondary carbonate solvents include C3-C 10 Cycloalkyl organic carbonates include, for example, propylene carbonate (C4H6O3) and ethylene carbonate (C3H4O3). Propylene carbonate (PC) (C4H6O3) shows particularly good compatibility with electrode materials, and the high solubility of this material, wide liquidus range, and high boiling point also make this solvent advantageous for use in metal-ion batteries, especially sodium-ion batteries. Other highly suitable organic carbonate-based solvents include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylene carbonate (EC), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC), and vinylene carbonate (VC).

[0063] Ethylene carbonate (EC), diethyl carbonate (DEC), and propylene carbonate (PC) are preferred as the first and second organic carbonate-based solvents. However, it is particularly preferred that the first organic carbonate-based solvent comprises propylene carbonate and the second organic carbonate-based solvent is selected from ethylene carbonate (EC) and diethyl carbonate (DEC).

[0064] Advantageous electrolyte compositions of the present invention may include propylene carbonate as the first organic carbonate solvent in an amount of at least 20%, preferably at least 25%, by weight of the solvent system.

[0065] In a preferred embodiment, the first component comprises a majority of propylene carbonate (PC). Preferably, the first organic carbonate-based solvent comprises propylene carbonate (PC) in an amount of >55% to <100% by weight of the solvent system, and the second organic carbonate-based solvent comprises diethyl carbonate (DEC) in an amount of >0 to <45% by weight of the solvent system. Ideally, in this embodiment, propylene carbonate (PC) is present in an amount of about 76% by weight of the solvent system, and diethyl carbonate (DEC) is present in an amount of about 20% by weight of the solvent system. Alternatively, in this embodiment, propylene carbonate (PC) is present in an amount of about 56% by weight of the solvent system, and diethyl carbonate (DEC) is present in an amount of about 40% by weight of the solvent system.

[0066] In another preferred embodiment, the first organic carbonate solvent comprises propylene carbonate (PC) and the second organic carbonate solvent comprises a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC). Thus, when the first component comprises a mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and propylene carbonate (PC), this is ideally in a weight ratio range of 1-4:1-10:1-10 wt / wt, more ideally in a weight ratio of 1-2:1-5:1-2 wt / wt, and most preferably in a weight ratio of 1:2:1 wt / wt.

[0067] As noted above, the second component of the solvent system 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.

[0068] The amount of surfactant used in the second component of the solvent system of the present invention can be >0.2 to ≦10% by weight of the solvent system, preferably ≧0.2 to ≦4% by weight, highly preferably ≧0.5 to ≦3% by weight, and ideally 1% to ≦2.5% by weight based on the weight of the solvent system.

[0069] The amount of surfactant used in the second component of the electrolyte composition of the present invention can be >0 wt.% based on the weight of the solvent system, preferably >0.2 wt.% based on the weight of the solvent system, and highly preferably ≧0.5 wt.% based on the weight of the solvent system.

[0070] The one or more surfactants used in the second component of the solvent system according to the present invention are performance additives that are preferably selected to enhance the ability of the electrolyte composition to wet the separator (especially a polyolefin separator) and / or the electrodes of a battery, which advantageously promotes longer battery cycle life.

[0071] Preferred one or more surfactant additives are selected from anionic surfactants, cationic surfactants, non-ionic (hydrophilic) surfactants, and amphoteric (zwitterionic) surfactants, with anionic surfactants and non-ionic (hydrophilic) surfactants being particularly preferred. Such surfactant additives are ideally one or more selected from the following: 1) Anionic (negatively charged) surfactants. Suitable examples include carboxylates (e.g., alkyl carboxylates (e.g., fatty acid salts)), carboxylate fluorosurfactants; sulfates (e.g., alkyl sulfates (e.g., sodium lauryl sulfate), alkyl ether sulfates (e.g., sodium laureth sulfate); sulfonates (e.g., docusate (e.g., sodium dioctyl sulfosuccinate) and alkyl benzene sulfonates); and phosphates (e.g., alkyl aryl ether phosphates and alkyl ether phosphates (e.g., trioctyl phosphate)); 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)); 3) Positively charged cationic surfactants, e.g., RN + H3Cl - , R.N. + (CH3)3Cl - , didecyldimethylammonium chloride (DDAC), cetylpyridinium chloride, benzalkonium chloride, hexadecyltrimethylammonium chloride (CTAC), and hexadecyltrimethylammonium bromide (CTAB); and 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 (spans) and its ethoxylated derivatives (tweens)), 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.

[0072] Most preferably, the one or more surfactants used in the second component of the solvent system according to the present invention comprise one or more non-ionic block copolymer-containing surfactants. A very suitable example is poloxamer. A very specific example is poloxamer 123 (P123).

[0073] As mentioned above, the second component of the solvent system 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.

[0074] The amount of sulfur-containing compound used in the second component of the solvent system of the present invention can be >0.2 to ≦10% by weight of the solvent system, preferably ≧0.2 to ≦4% by weight, highly preferably ≧0.5 to ≦3% by weight, and ideally 1% to ≦2.5% by weight based on the weight of the solvent system.

[0075] The amount of sulfur-containing compound used in the second component of the electrolyte composition of the present invention can be >0 wt.% based on the weight of the solvent system, preferably >0.2 wt.% based on the weight of the solvent system, and highly preferably ≧0.5 wt.% based on the weight of the solvent system.

[0076] The one or more sulfur-containing compounds used in the second component of the solvent system according to the present invention are performance additives, 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 benefits such as improved cycle life.

[0077] Suitable sulfur-containing compounds can include cyclic and / or acyclic sulfur-containing compounds. Preferably, the sulfur-containing compound is a sulfone-containing compound, a sulfate-containing compound, or a sulfonate-containing compound.

[0078] In other words, a sulfur-containing compound can have a sulfonyl functional group attached to two carbon atoms (sulfone), two oxygen atoms (sulfate), or one carbon atom and one oxygen atom (sulfonate) in a cyclic or acyclic structure. When the sulfonate is cyclic, the compound is sometimes called a sultone.

[0079] 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.

[0080] As used herein, the term "sulfate" means a central hexavalent sulfur atom that is double bonded to two oxygen atoms and has single bonds to two other oxygen atoms, which are in turn each single bonded to a carbon atom.

[0081] As used herein, the term "sulfonate" means a central hexavalent sulfur atom doubly bonded to two oxygen atoms, a single bond to one carbon atom, and a single bond to another oxygen atom, which is in turn single bonded to a carbon atom which, when joined in a ring with the other carbon atom bonded to the sulfur atom, becomes a sultone.

[0082] The general formula for such compounds is RY(S=O)2Y'R', where: 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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).

[0087] Suitable examples of sultones include 1-propene 1,3-sultone ((CH)2CH2SO3), and 1,3-propane sultone (CH2)3SO3. Most preferably, the sulfur-containing compound is 1,3-propanediol cyclic sulfate (PCS).

[0088] The electrolyte composition according to the present invention may further comprise one or more additional compounds which may or may not be solvents. 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 help reduce the viscosity of the electrolyte by acting as an inert diluent (e.g., hydrofluoroalkyl ethers, preferably 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE or TTE)).

[0089] The electrolyte composition according to the invention can also optionally include one or more additional performance additives, typically in an amount of <15% by weight, preferably <10% by weight, and more preferably 0.1% to <5% by weight, 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, such as, for example, tris(trimethylsilyl)phosphite, or tris(trimethylsilyl)phosphate.

[0090] Suitable other performance additives include polymerizable additives for promoting overcharge protection, such as biphenyl, diphenylamine, dimethoxydiphenylsilane (DDS), 3-chloroanisole (3CA), N-phenylmaleimide, xylene (methyl substituted benzenes) 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 that impart additional flame retardancy 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 for promoting better high temperature cycling, such as succinic anhydride; and additives for rendering unwanted inert decomposition products (e.g., HF, water or CO2) in-situ, such as zeolites.

[0091] In one embodiment, the electrolyte compositions of the present invention do not include an inert diluent (eg, a hydrofluoroalkyl ether, preferably 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE or TTE)).

[0092] In one embodiment, the electrolyte composition of the present invention does not include 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE or TTE) in an amount of 20% based on the weight of the solvent system.

[0093] The electrolyte compositions of the present invention are particularly useful in sodium-ion cells, most preferably sodium-ion full cells (not sodium metal half cells). Thus, in a further aspect, the present invention provides a sodium-ion cell comprising a negative electrode, a positive electrode, and an electrolyte composition as defined herein.

[0094] The sodium-ion cell disclosed herein can also include an anode (negative) electrode including an anode current collector, and / or a cathode (positive) electrode including a cathode current collector. 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). Preferably, the anode current collector includes an aluminum current collector. Highly preferably, both the cathode current collector and the anode current collector include an aluminum current collector. Alternatively, copper, magnesium, carbon paper / foil / substrate, and tin may also be used as current collector materials.

[0095] Preferably, the anode (negative) current collector also includes one or more carbon-containing layers formed on one or more surfaces of the anode current collector prior to the first charge cycle of the sodium-ion cell. Such layers can ideally comprise amorphous carbon (e.g., carbon black such as TIMCAL Super C65) having a thickness of about 10 Angstroms to about 1000 μm.

[0096] Alternatively, the anode (negative) current collector disclosed herein does not include one or more carbon-containing layers on one or more surfaces of the anode current collector prior to the first charge cycle of the sodium-ion cell. Thus, the anode current collector is "pristine" prior to the first charge cycle of the sodium-ion cell. When used herein with respect to the current collector, the phrase "pristine" means that the current collector is in an "as-made" state prior to the first charge cycle of the sodium-ion cell. In other words, the anode current collector is substantially pure material from its source of formation, absent impurities (e.g., surface oxide layers, etc.). Thus, the anode current collector is not coated with one or more carbon-containing layers (as described above), conventional active materials, binders, or the like.

[0097] The sodium-ion cells disclosed herein can also include a separator located between the cathode current collector and the anode current collector. A polyolefin separator is preferred.

[0098] The anode (negative) electrode of the sodium-ion cell according to the invention preferably further comprises a polymer binder. Typically, the polymer binder is selected from polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC). Preferably, the polymer binder comprises carboxymethyl cellulose (CMC). Highly preferably, the polymer binder comprises a mixture of styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC).

[0099] The anode (negative) electrode of a sodium-ion cell according to the invention ideally comprises an active negative electrode material (A), one or more polymeric binders (B), and one or more conductive additives (C). Such a mixture is typically mixed with an aqueous or non-aqueous solvent (e.g., water or N-methylpyrrolidone (NMP)) and then disposed as a layer or film on one or more surfaces of the anode current collector using techniques such as doctor blading or slot die techniques.

[0100] A:B:C are typically present in a weight ratio of (80-98):(1-19):(1-19), ideally (90-98):(1-9):(1-9). When the polymer binder comprises polyvinylidene fluoride (PVDF), A:B:C are preferably present in a weight ratio of about 88:9:3. When the polymer binder comprises preferably carboxymethylcellulose (CMC), most preferably a mixture of styrene-butadiene rubber (SBR) and carboxymethylcellulose (CMC), A:B:C are preferably present in a weight ratio of about 95:3.5:1.5.

[0101] The one or more conductive additives (C) can include one or more of carbon black, carbon nanotubes, graphene, acetylene black, and carbon nanofibers. Preferably, the one or more conductive additives include carbon black, such as TIMCAL Super C65.

[0102] The anode (negative) electrode of the sodium-ion cell according to the present invention preferably further comprises a negative electrode active material. For example, the negative electrode comprising the negative electrode active material can be one or more of graphite materials, soft carbon, hard carbon, carbon fiber, mesocarbon microbeads, silicon-based materials, tin-based materials, P-based materials, Sb-based materials, SnSb-based materials, other types of materials that store charge by conversion and / or alloying type reaction (e.g., simple / binary / ternary oxides of Fe, Cu, Ni, Mn, etc.), and materials that store charge by conventional intercalation type reaction, such as lithium titanium oxide, various types of sodium titanate, titania, etc.; and any combination of one or more of these materials, such as carbon / Sb, carbon / P, carbon / Fe2O3. The combination can be either a mixture produced by physical blending (e.g., carbon and Sb blended together by physical or chemical mixing methods such as ball milling or spray drying), or via in-situ reaction (e.g., via suitable synthetic routes such as solvothermal / hydrothermal, sol-gel, solution-based, reflux, co-precipitation, or solid-state reactions, with or without a subsequent heating / pyrolysis step), the latter of which may also result in doped materials (e.g., carbon doped with Sb or P or Sn) and / or substituted materials (e.g., substitution of Fe2O3 with a small amount of TiO2). The anode electrode of the sodium-ion cell according to the present invention preferably includes a negative active material comprising hard carbon.

[0103] The electrolyte compositions of the present invention are particularly useful in sodium-ion cells that employ anode electrodes that include anode active materials that include non-graphitic carbon-containing materials, such as hard carbon, or anodes that include sodium insertion materials, or conversion and / or alloying anode materials.

[0104] The cathode (positive) electrode of the sodium-ion cell according to the present invention preferably further comprises a polymer binder. Typically, the polymer binder is selected from polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC). Preferably, the polymer binder comprises polyvinylidene fluoride (PVDF).

[0105] A cathode (positive) electrode of a sodium-ion cell according to the invention ideally comprises a positive electrode active material (A), one or more polymeric binders (B), and one or more conductive additives (C). Such a mixture is typically mixed with an aqueous or non-aqueous solvent (e.g., water or N-methylpyrrolidone (NMP)) and then disposed as a layer or film on one or more surfaces of an anode current collector using techniques such as doctor blading or slot die techniques.

[0106] A:B:C are typically present in a weight ratio of (80-98):(1-19):(1-19). When the polymer binder comprises polyvinylidene fluoride (PVDF), A:B:C are preferably present in a weight ratio of about 89:5:6, or 92:4:4.

[0107] The one or more conductive additives (C) can include one or more of carbon black, carbon nanotubes, graphene, acetylene black, and carbon nanofibers. Preferably, the one or more conductive additives include carbon black, such as TIMCAL Super C65.

[0108] The cathode (positive) electrode of the sodium-ion cell according to the invention preferably further comprises a sodium-containing positive active material adapted to allow insertion / extraction of sodium ions during charge / discharge. Examples of these include sodium transition metal oxides, polyanion compounds (including fluorinated polyanion compounds), Prussian Blue Analogue (PBA) compounds (such as Prussian White or Berlin Green), materials that store sodium via conversion reactions, sodium transition metal fluorides, oxyfluorides, phosphates, sulfates, and silicates (and their fluorinated versions). A preferred example is sodium transition metal oxide.

[0109] 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; M 3 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].

[0110] Ideally, metal M 2 comprises 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.

[0111] Particularly preferred cathode active materials for use in sodium-ion cells 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 cathode electrode active material can also have a heterogeneous structure, i.e., composed of several different crystalline forms, comprising a mixture of phases. For example, the cathode active material comprises 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.

[0112] The present invention also provides in another aspect the use of a non-aqueous electrolyte composition as defined herein in a sodium-ion cell. The sodium-ion cells of the present invention can be used in energy storage devices, such as batteries, rechargeable batteries, electrochemical devices, and electrochromic devices.

[0113] The present invention also provides, in another aspect, an apparatus comprising one or more sodium-ion cells as disclosed herein. Exemplary apparatus can include devices such as battery packs that can be used in either stationary or mobile applications.

[0114] The present invention also provides, in another aspect, a method for producing the non-aqueous electrolyte composition defined herein. In an alternative view, a) one or more sodium-containing salts; and b) a solvent system comprising: i) a first component comprising one or more organic carbonate based solvents; and ii) a second component comprising one or more performance additives including tris(trimethylsilyl)borate (TMSB) in an amount >0 to ≦10% based on the weight of the solvent system; and optionally not including 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE) in an amount of 20% based on the weight of the solvent system.

[0115] In another alternative aspect, there is provided a sodium-ion cell, preferably a sodium-ion full cell (not a sodium metal half-cell), comprising a non-aqueous electrolyte composition according to the above alternative aspect. [Brief description of the drawings]

[0116] The invention will now be described with reference to the following figures: [Figure 1] FIG. 1 shows a plot of discharge energy retention (%) versus cycle number to demonstrate the long-term cycling stability of a cell using an electrolyte composition of the present invention (sample TEL24d) and compares it to the cycling performance of a cell using a control electrolyte composition (sample TEL24b). [Figure 2A] FIG. 2A shows a plot of discharge energy retention (%) versus cycle number to demonstrate the long-term cycling stability of a cell using an electrolyte composition of the present invention (sample TEL67a) and compares it to the cycling performance of a cell using a control electrolyte composition (sample TEL67). [Figure 2B] FIG. 2B shows the plot of FIG. 2A, but with a different (expanded) scale on the y-axis (discharge energy retention (%)). [Figure 3A] FIG. 3A shows a plot of discharge energy retention (%) versus cycle number to demonstrate the long-term cycling stability of a cell using an electrolyte composition of the present invention (sample TEL67a) and compares it to the cycling performance of a cell using a control electrolyte composition (sample TEL67). [Figure 3B] FIG. 3B shows the plot of FIG. 3A, but with a different (expanded) scale on the y-axis (discharge energy retention (%)). [Figure 4] FIG. 4 shows a plot of percent discharge capacity retention versus cycle number to demonstrate the long-term cycling stability of a cell using an electrolyte composition of the present invention (sample TEL67a) and compares it to the cycling performance of a cell using a control electrolyte composition (sample TEL67). [Diagram 5] FIG. 5 shows a plot of cathode discharge capacity (mAh / g) versus cycle number to demonstrate the long-term cycling stability of cells using electrolyte compositions of the invention containing a mixture of sodium-containing salts (samples TEL87b and TEL90) and compares it to the cycling performance of a cell using an electrolyte composition of the invention containing only one sodium-containing salt (sample TEL67a). [Figure 6] FIG. 6 shows a plot of voltage (V) versus state of charge (SOC) or depth of discharge (DOD) to illustrate the reduced total charge time of cells using electrolyte compositions of the invention containing a mixture of sodium-containing salts (samples TEL87b and TEL90) compared to a cell using an electrolyte composition of the invention containing only one sodium-containing salt (sample TEL67a). EXAMPLES

[0117] The electrolyte compositions under investigation were prepared using the following general procedure: the appropriate amount of the first component (e.g., a solvent for the desired solvent system) and then the second component (e.g., a precise amount of one or more performance additives) were weighed into an argon-filled glove box and added to an amber or clear glass bottle.

[0118] To completely dry the formed solvent, 4 Å molecular sieves (Sigma-Aldrich) were added and the solvent mixture was left to dry for at least 24 hours. The solvent system was then ready for use and stored in an argon-filled glove box. An appropriate amount of metal-containing salt (one or more) was then added to a separate bottle (clear or amber glass bottle or container made from alternative materials such as polypropylene, PTFE, stainless steel, etc.) to which the required amount of solvent mixture was added.

[0119] The electrolyte was then stirred via a magnetic pellet or mechanical stirrer for any period between 5 minutes and 100 hours, or the salt(s) were allowed to dissolve naturally in the electrolyte by simply leaving the bottle / container undisturbed or a method accelerated by mechanically shaking the bottle / container.

[0120] The exact composition of each electrolyte composition investigated is detailed in Table 1 below:

[0121] [Table 1]

[0122] For the avoidance of doubt, the concentrations expressed above as "m" (molality) relate to the total number of moles of metal-containing salt per kg or 1000 g of solvent system.

[0123] Abbreviations used: EC = ethylene carbonate, DEC = diethyl carbonate, PC = propylene carbonate, PCS = 1,3-propanediol cyclic sulfate, P123 = poloxamer (Pluronic®) P123, TMSB = tris(trimethylsilyl) borate, NaTFSI = sodium bis(trifluoromethylsulfonyl)imide, NaFSI = sodium bis(fluorosulfonyl)imide Please note that in Table 1 above, the wt % of the various solvents and / or performance additives are referenced to the total solvent system weight (these do not take into account the weight (s) of one or more sodium-containing salts). Cell Configuration General procedure for fabricating hard carbon Na-ion cells Sodium ion cells were fabricated using a mixed phase O3 / P2 oxide cathode, a hard carbon anode, and electrolyte (as appropriate). Aluminum tabs were attached to each electrode and the cell was placed in a polymer-coated aluminum pouch.

[0124] The positive (cathode) electrodes were prepared by solution casting a slurry of active material, conductive carbon, binder, and solvent using a doctor blade technique. 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 under vacuum at about 120°C. The electrode films contained the following components, expressed in weight percent, for FPC200725, FPC200818, FPC200728, and FPC200729 cells: 89% active material, 5% C65 carbon, and 6% W#7500 binder. Alternatively, in all other cells, the following electrode formulation was used in the cathode: 92% active material, 4% C65 carbon, and 4% PVdF binder.

[0125] The hard carbon negative (anode) electrode was prepared by solution casting a slurry of hard carbon active material (Kuranode type 1 supplied by Kureha), conductive carbon, binder and solvent by doctor blade technique. The conductive carbon used was C65 (Imerys). Sodium carboxymethylcellulose (CMC) (Aqualon from Ashland) was used. TM A mixture of styrene butadiene rubber (SBR) (BM-451B from Zeon Europe Gmbh) and styrene butadiene rubber (SBR) (BM-451B from Zeon Europe Gmbh) was used as the binder, and water was used as the solvent. The slurry was then cast onto a carbon-coated aluminum foil and dried under vacuum at about 120 °C. The electrode films contained the following components expressed in weight percent for FPC200725, FPC200818, FPC200728, and FPC200729 cells: 88% active material, 3% C65 carbon, and 9% PVdF binder. Alternatively, for all other cells, the following electrode formulation was used for the anode: 95% active material, 1.5% C65 carbon, and 3.5% CMC-SBR binder mixture.

[0126] After the cathode and anode were coated, they were stamped to the desired dimensions. The coating weights of the cathode and anode are referred to as GSM values ​​(grams per square meter). "C / A" refers to the mass ratio of the cathode active material to the anode active material in each coating.

[0127] 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 with two Al-based connection tabs that served as terminals in a glove box and filled with a volume of the above liquid electrolyte typical for lithium-ion or sodium-ion cells containing such types of polyolefin separators. These pouch cells were then sealed in the glove box and removed for cell testing.

[0128] Cell Test The cells were tested using a constant current (galvanostatic) cycling technique. Generally speaking, the cells were first charged in constant current (CC) mode up to a predefined maximum voltage limit. The cells were then subjected to a constant voltage (CV) step at that maximum voltage limit for a predefined time, or the CV step was continued until the current dropped to a predefined value as shown in the examples. In some examples, the cells were subjected to a series of different CC modes up to different voltage values, and then to a CV step only at the maximum voltage value. The discharge process was performed in either CC mode up to a lower cutoff voltage, or in constant power (CP) mode as shown.

[0129] Commercial battery cyclers from MTI Inc. (Richmond, CA, USA) or Maccor (Tulsa, OK, USA) were used. During charging, alkali ions are inserted into the carbon-containing anode material. During discharging, alkali ions are desorbed and reinserted into the cathode active material.

[0130] All cells were cycled at charge rates such as ±1C (which can also be expressed as ±C / 1), ±C / 5, or ±C / 10 (or other rates, e.g., ±C / 50 as noted in each experiment). Discharge rates of C / 5, C / 10, 1C, and 2C were also examined for rate capability testing. All cells were rested for at least 4-24 hours before cycling. Table 2 provides a summary of the conditions for each experiment. In some embodiments, cells were charged according to a dynamic protocol, which is described in the specific examples.

[0131] [Table 2]

[0132] [Table 3]

[0133] Experiment 1 - Cycling performance of cells using electrolyte compositions containing a solvent system of EC:DEC:PC=1:2:1 wt / wt with and without TMSB additive. Experiment 1 compares the cycling performance of two identical Na-ion 100 mAh pouch cells (two cathode / anode electrode pairs stacked in parallel within a single pouch cell) with an anode coat weight of 61 GSM (grams per square meter). Experiment 1A A hard carbon sodium ion cell was prepared using the general method described above, and a test pouch cell (FPC200725) was prepared using electrolyte composition TEL24b (not according to the invention). The cycling performance of the test cell was then investigated by cycling as follows: The FPC200725 was cycled between 4.05 and 1V at ±1C, with the CV step at 4.05V lasting for 20 minutes or stopped when the current dropped to a value equivalent to below C / 10 (whichever came first). Thus, the longest time this cell spent at 4.05V was 20 minutes after each charge cycle. Test 1B A hard carbon sodium ion cell was prepared using the general method described above, and a test pouch cell (FPC200818) was prepared using electrolyte composition TEL24d (according to the present invention). The cycling performance of the test cell was then investigated by cycling as follows: FPC200818 was cycled between 4.05 and 1V at ±1C with a CV (constant voltage) step at 4.05V lasting 1 hour (60 minutes). Thus, the longest time this cell spent at 4.05V was 60 minutes after each charge cycle. analysis The cycling stability over 1000 cycles is shown in Figure 1, which compares the discharge energy retention versus cycle number for cells FPC200725 and FPC200818.

[0134] It can be seen that cell FPC200725, which used the control electrolyte composition (sample TEL24b), retained 83.2% of its initial energy after 1000 cycles, while cell FPC200818, which used the electrolyte composition of the present invention (sample TEL24d), retained 88% of its initial delivered energy after 1000 cycles.

[0135] Additionally, cell FPC200818 was subjected to more severe conditions (i.e., higher voltage conditions where electrolyte oxidation may occur) than cell FPC200725, since cell FPC200818 was maintained at 4.05 V under CV conditions for 60 minutes after each charge cycle, compared to cell FPC200725, which was maintained at 4.05 V under CV conditions for 20 minutes after each charge cycle.

[0136] Those skilled in the art will appreciate that longer CV steps may increase cell capacity, but at the expense of reduced energy retention. Surprisingly, however, cell FPC200818 exhibited improved energy retention after 1000 cycles compared to cell FPC200725.

[0137] Specifically, cell FPC200818 achieved a capacity of 98.82 mAh / g on the first cycle and 92.19 mAh / g after 1000 cycles (hence the capacity retention over 1000 cycles was 93.3%), which corresponds to a discharge energy retention of 88%, as shown in Figure 1.

[0138] On the other hand, cell FPC200725 achieved a capacity of 97.62mAh / g on the initial cycle and 87.18mAh / g after 1000 cycles (hence the capacity retention over 1000 cycles was 89.3%), which corresponds to a discharge energy retention of 83.2%, as shown in Figure 1.

[0139] Thus, the stability and cycling performance in terms of discharge capacity (and energy retention) in sodium ion cells is improved by using the electrolyte composition according to the present invention. Experiment 2 - Cycling performance of cells using electrolyte compositions containing a PC based carbonate ester solvent system with and without TMSB additive and using an anode with a 61 GSM coat weight.

[0140] In experiment 2, the same type of Na-ion pouch cell used in experiment 1 (100 mAh pouch cell with similar C / A, 61 GSM coat weight hard carbon anode) was used with a similar cycling protocol as shown below:

[0141] Experiment 2A A sodium ion cell with a hard carbon anode and an O3 / P2 layered oxide cathode was prepared using the general method described above, and a test pouch cell (FPC200728) was prepared using electrolyte composition TEL67 (not according to the invention). The cycling performance of the test cell was then investigated by cycling as follows: FPC200728 was cycled between 4.05 and 1V at ±1C.

[0142] Experiment 2B A sodium ion cell with a hard carbon anode and an O3 / P2 layered oxide cathode was prepared using the general method described above, and a test pouch cell (FPC200729) was prepared with electrolyte composition TEL67a (according to the present invention). The cycling performance of the test cell was then investigated by cycling as follows: FPC200729 was cycled between 4.05 and 1V at ±1C.

[0143] analysis Cycling stability is shown in Figures 2A and 2B, which show a comparison of the discharge energy retention over 2000 cycles for cell FPC200728 and over 4050 cycles for cell FPC200729.

[0144] It can be seen that cell FPC200728, which used the control electrolyte composition (sample TEL67), retained 74.6% of its initial energy after 2000 cycles, while cell FPC200729, which used the electrolyte composition of the present invention (sample TEL67a), retained 73.1% of its initial achieved energy after 4050 cycles.

[0145] Specifically, cell FPC200728 achieved a capacity of 97.56 mAh / g on the first cycle and 78.12 mAh / g after 2000 cycles (hence, 80% capacity retention after 2000 cycles), which corresponds to a discharge energy retention of 74.6%, as shown in Figures 2A and 2B.

[0146] On the other hand, cell FPC200729 achieved a capacity of 98.37 mAh / g on the first cycle and 78.83 mAh / g after 4050 cycles (hence, the capacity retention after 4000 cycles was 80.13%), which corresponds to a discharge energy retention of 73.1%, as shown in Figures 2A and 2B.

[0147] Thus, the stability and cycling performance in terms of discharge capacity (and energy retention) in sodium ion cells is improved by using the electrolyte composition according to the present invention. Experiment 3 - Cycling performance of cells using electrolyte compositions containing a PC-based carbonate ester solvent system with and without TMSB additive and using a 121 GSM coated heavy anode.

[0148] In experiment 3, we discuss the results of cycling a 150 mAh Na-ion pouch cell using a hard carbon anode with a C / A of approximately 1.5–1.6 and a 121 GSM coat weight between 4.05 and 1.8 V at ±C / 3 with either TEL67 or TEL67a (see Table 2).

[0149] Experiments 3A and 3B Sodium ion cells with hard carbon anodes and O3 / P2 layered oxide cathodes were prepared using the general method described above, and test pouch cells FPC220205 and FPC220206 were prepared using electrolyte composition TEL67 (not according to the invention). The cycling performance of the test cells was then investigated by cycling as follows: FPC220205 and FPC220206 were cycled between 4.05 and 1.8 V at ±C / 3.

[0150] Experiments 3C, 3D and 3E Sodium ion cells with hard carbon anodes and O3 / P2 layered oxide cathodes were prepared using the general method described above, and test pouch cells FPC211008, FPC211009, and FPC211011 were prepared using electrolyte composition TEL67a (in accordance with the present invention). The cycling performance of the test cells was then investigated by cycling as follows: FPC211008, FPC211009, and FPC211011 were cycled between 4.05 and 1.8 V at ±C / 3.

[0151] analysis Cycling stability is shown in Figures 3A and 3B, which show a comparison of the discharge energy retention over 791 cycles of cell FPC220205 and 793 cycles of cell FPC220206 with the discharge energy retention over 1214 cycles of cell FPC211008, the discharge energy retention over 1227 cycles of cell FPC211009, and the discharge energy retention over 1200 cycles of cell FPC211011.

[0152] It can be seen that when the control electrolyte composition (sample TEL67) was used, cell FPC220205 had an energy retention of 86.1% after 791 cycles and cell FPC220206 had an energy retention of 87.5% after 793 cycles.

[0153] On the other hand, when the electrolyte composition of the present invention (sample TEL67a) was used, cell FPC211008 had an energy retention of 90.5% after 1214 cycles, cell FPC211009 had an energy retention of 89.7% after 1227 cycles, and cell FPC211011 had an energy retention of 91.2% after 1200 cycles.

[0154] in particular: FPC220205 achieved a capacity of 97.25 mAh / g on the first cycle and 86.4 mAh / g after 791 cycles (hence, a capacity retention of 88.8%), which corresponds to a discharge energy retention of 86.1%.

[0155] FPC220206 achieved a capacity of 96.9 mAh / g on the first cycle and 87.39 mAh / g after 793 cycles (hence a capacity retention of 90.2%), which corresponds to a discharge energy retention of 87.5%.

[0156] FPC211008 achieved a capacity of 96.79 mAh / g on the first cycle and 89.33 mAh / g after 1214 cycles (hence a capacity retention of 92.3%), which corresponds to a discharge energy retention of 90.5%.

[0157] FPC211009 achieved a capacity of 96.28mAh / g on the first cycle and 88.02mAh / g after 1227 cycles (hence a capacity retention of 91.4%), which corresponds to a discharge energy retention of 89.7%.

[0158] FPC211011 achieved a capacity of 96.89 mAh / g on the first cycle and 90.05 mAh / g after 1200 cycles (hence a capacity retention of 92.94%), which corresponds to a discharge energy retention of 91.2%.

[0159] Thus, the stability and cycling performance in terms of discharge capacity retention (and energy retention) in sodium ion cells is improved by using the electrolyte composition according to the present invention. Experiment 4 - Cycling performance of a 32 Ah Na-ion pouch cell using a 121 GSM coated heavy anode with an electrolyte composition containing a PC-based carbonate ester solvent system with and without TMSB additive.

[0160] In experiment 4, a 32 Ah Na-ion pouch cell using a hard carbon anode with a C / A of approximately 1.6 and a 121 GSM coat weight was cycled with either TEL67 or TEL67a as follows (see Table 2):

[0161] Experiments 4A and 4B Sodium ion cells with hard carbon anodes and O3 / P2 layered oxide cathodes were prepared using the general method described above, and test pouch cells U016 and U018 were prepared using electrolyte composition TEL67 (not according to the present invention). The cycling performance of the test cells was then investigated by cycling as follows: U016 and U018 were cycled with CC charging between 4.05 and 2 V and CV at 4.05 V, followed by CP discharge at 35 W (corresponding to approximately 2 h of discharge).

[0162] Experiments 4C and 4D Sodium ion cells with hard carbon anode and O3 / P2 layered oxide cathode were prepared using the general method described above, and test pouch cells U007 and U008 were prepared using electrolyte composition TEL67a (according to the present invention). The cycling performance of the test cells was then investigated by cycling as follows: U007 and U008 were cycled with CC charging between 4.05 and 1.8 V and CV at 4.05 V, followed by CP discharge at 35 W (corresponding to approximately 2 h of discharge).

[0163] analysis The cycling stability is shown in Figure 4, which shows the discharge capacity retention over 800 cycles for cell U016 and over 1254 cycles for cell U018 compared to the discharge capacity retention over 2570 cycles for cell U007 and over 2468 cycles for cell U008.

[0164] It can be seen that when the control electrolyte composition (sample TEL67) was used, cell U016 had 82.6% capacity retention after 800 cycles and cell U018 had 82.3% capacity retention after 1254 cycles.

[0165] On the other hand, when the electrolyte composition of the present invention (sample TEL67a) was used, cell U007 had a capacity retention of 85% after 2570 cycles, and cell U008 had a capacity retention of 84.1% after 2468 cycles.

[0166] in particular: U016 achieved a capacity of 86.09 mAh / g on the first cycle and 71.1 mAh / g after 800 cycles (hence, a capacity retention of 82.6%).

[0167] U018 achieved a capacity of 88.66 mAh / g on the first cycle and 72.97 mAh / g after 1254 cycles (hence, a capacity retention of 82.3%). U007 achieved a capacity of 90.64 mAh / g on the first cycle and 77.09 mAh / g after 2570 cycles (hence, 85% capacity retention).

[0168] U008 achieved a capacity of 92.96 mAh / g on the first cycle and 78.21 mAh / g after 2468 cycles (hence, a capacity retention of 84.1%). Thus, the stability and cycling performance in terms of discharge capacity retention in sodium ion cells are improved by using the electrolyte composition according to the present invention. Experiment 5 - Cycling performance of Na-ion cells using electrolyte compositions containing a PC-based carbonate ester solvent system with TMSB additive and investigating the effect of fast charging.

[0169] In experiment 5, we discuss the results of cycling a 100 mAh Na-ion pouch cell between 4.15 and 1.8 V with either TEL67a, TEL87b or TEL90 using different charging protocols as shown below (see Table 2).

[0170] Experiments 5A and 5B A sodium ion cell with a hard carbon anode and an O3 / P2 layered oxide cathode was prepared using the general method described above, and a test pouch cell FPC220504 was prepared using electrolyte composition TEL87b (according to the present invention), and a test pouch cell FPC220505 was prepared using electrolyte composition TEL90 (according to the present invention). The cycle performance of the test cells was then investigated by cycling as follows: CC charging at +8C to 3.5V, then +4C to 3.8V, then +2C to 4V, then +1C to 4.15V. CV charge to C / 10 at 4.15V or 5 minutes, whichever comes first. CC discharge to 1.8V.

[0171] Experiment 5C A sodium ion cell with hard carbon anode and O3 / P2 layered oxide cathode was prepared using the general method described above, and a test pouch cell FPC220710 was prepared with electrolyte composition TEL67a (according to the present invention). The cycling performance of the test cell was then investigated by cycling as follows: the cell was cycled between 4.15 and 1.8 V at ±1 C, with a CV step at 4.15 V (CV to C / 10 or 10 min, whichever occurs first).

[0172] analysis The cycling stability is shown in Figure 5, which shows the cathode discharge capacity over 500 cycles for three cells.

[0173] It can be seen that the cells (FPC220504, FPC220505) cycled with an electrolyte composition of the invention containing a mixture of sodium-containing salts (samples TEL87b and TEL90, respectively) exhibited higher discharge capacity as well as better capacity retention after 500 cycles compared to the cell (FPC220710) cycled with an electrolyte composition of the invention containing only one sodium-containing salt (sample TEL67a).

[0174] in particular: FPC220504 achieved a capacity of 107.2 mAh / g on the first cycle and 91.66 mAh / g after 500 cycles (hence, 85.5% capacity retention), which corresponds to a discharge energy retention of 81%. FPC220505 achieved a capacity of 106.1 mAh / g on the first cycle and 88.96 mAh / g after 500 cycles (hence, a capacity retention of 83.8%), which corresponds to a discharge energy retention of 80.8%.

[0175] FPC220710 achieved a capacity of 103.98mAh / g on the first cycle and 86.46mAh / g after 500 cycles (hence a capacity retention of 83.15%), which corresponds to a discharge energy retention of 80.3%.

[0176] Thus, it is clearly seen that the electrolyte composition of the present invention is compatible with various types / mixtures of sodium-containing salts. Furthermore, better cycling stability and higher discharge capacity for the TEL87b and TEL90 cells were obtained, along with a significant reduction in total charge time. This is illustrated in Figure 6, which shows the cycling profile of the cells during cycle 2. The x-axis is the state of charge (SOC) or depth of discharge (DOD): those skilled in the art will recognize these metrics as plots of normalized energy (vs. energy achieved at 1.8V, which is 100% DOD for this particular experiment) versus cell voltage. Also shown in Figure 6 is the total CC+CV charge time for the cells. From this figure, it is clear that FPC220504 and FPC220505 not only provide higher initial discharge capacity and better capacity and energy retention after 500 cycles, but achieve this while cutting the total charge time in half: The total charge time for cycle 2 of FPC220504 using TEL87b was 32.7 minutes. The total charge time for cycle 2 of FPC220505 using TEL90 was 31.8 minutes. The total charge time for cycle 2 of FPC220710 using TEL67a was 68.5 minutes.

[0177] Furthermore, it can be seen that FPC220504 and FPC220505 can be charged to about 92.5% of energy (SOC) within only 17 minutes, while FPC220710 can be charged to 92.5% SOC after about 54 minutes. As can be seen, fast charging shortens the time to charge a cell quickly, so the industrial applicability is immense.

[0178] From Experiment 5, it is clear that the electrolyte composition of the present invention is compatible with various types / mixtures of sodium-containing salts, and further reduces the total charging time significantly.

[0179] conclusion From the above experiments, it is clear that the electrolyte compositions of the present invention comprising a combination of two or more organic carbonate-based solvents (i.e., mixtures) and TMSB achieve at least a longer cycle life when cycled in a sodium-ion cell than their counterparts that do not contain TMSB. Also, when the electrolyte compositions of the present invention further include two or more sodium-containing salts, a significant reduction in the total charge time in the sodium-ion cell may also occur.

Claims

1. a) one or more sodium-containing salts; and b) a solvent system comprising: i. a first component comprising a first organic carbonate based solvent and a second organic carbonate based solvent, the second organic carbonate based solvent being different from the first organic carbonate based solvent; and ii. a second component comprising two or more performance additives including tris(trimethylsilyl)borate (TMSB) in an amount of >0 to ≦10% based on the weight of the solvent system and a sulfur-containing compound in an amount of >1 to ≦10% based on the weight of the solvent system; Including, the first and second organic carbonate solvents are selected from ethylene carbonate (EC), diethyl carbonate (DEC), and propylene carbonate (PC); Nonaqueous electrolyte composition.

2. 2. The non-aqueous electrolyte composition of claim 1, wherein the first organic carbonate solvent comprises propylene carbonate and the second organic carbonate solvent is selected from ethylene carbonate (EC) and diethyl carbonate (DEC).

3. 2. The non-aqueous electrolyte composition of claim 1, wherein the first organic carbonate based solvent comprises propylene carbonate (PC) in an amount of >55% to <100% based on the weight of the solvent system, and the second organic carbonate based solvent comprises diethyl carbonate (DEC) in an amount of >0 to <45% based on the weight of the solvent system.

4. 2. The non-aqueous electrolyte composition of claim 1, wherein the first organic carbonate solvent comprises propylene carbonate (PC) and the second organic carbonate solvent comprises a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC).

5. 2. The non-aqueous electrolyte composition of claim 1, wherein the second component comprises three or more performance additives including tris(trimethylsilyl)borate (TMSB) in an amount of 1% based on the weight of the solvent system, a surfactant in an amount of 1% based on the weight of the solvent system, and a sulfur-containing compound in an amount of 2% based on the weight of the solvent system.

6. 10. The non-aqueous electrolyte composition of claim 1, wherein the second component further comprises one or more surfactants in an amount of >0.2 to ≦10% based on the weight of the solvent system.

7. 7. The non-aqueous electrolyte composition of claim 6, wherein the surfactant comprises at least one non-ionic block copolymer surfactant, preferably selected from one or more poloxamers.

8. 2. The non-aqueous electrolyte composition of claim 1, wherein the sulfur-containing compound comprises 1,3-propanediol cyclic sulfate (PCS).

9. The one or more sodium-containing salts are sodium hexafluorophosphate (NaPF ６ 2. The non-aqueous electrolyte composition of claim 1, wherein the anionic surfactant is selected from the group consisting of sodium bis(fluorosulfonyl)imide (NaFSI), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), and sodium bis(fluorosulfonyl)imide (NaTFSI).

10. One or more sodium-containing salts are sodium hexafluorophosphate (NaPF ６ The non-aqueous electrolyte composition according to claim 9 .

11. The non-aqueous electrolyte composition according to claim 1 , further comprising two or more sodium-containing salts.

12. The two or more sodium-containing salts are sodium hexafluorophosphate (NaPF ６ 12. The non-aqueous electrolyte composition of claim 11, comprising a mixture of 1,2-difluoromethanesulfonyl-2-imide (NaFSI) and / or 1,2-difluoromethanesulfonyl-2-imide (NaTFSI).

13. A composition comprising: a) two or more sodium-containing salts; and b) a solvent system comprising: i. a first component comprising a first organic carbonate based solvent and a second organic carbonate based solvent, the second organic carbonate based solvent being different from the first organic carbonate based solvent; and ii. a second component comprising one or more performance additives including tris(trimethylsilyl)borate (TMSB) in an amount of >0 to ≦10% based on the weight of the solvent system; A non-aqueous electrolyte composition comprising:

14. A sodium ion cell comprising the nonaqueous electrolyte composition according to any one of claims 1 to 13.

15. Use of the non-aqueous electrolyte composition according to any one of claims 1 to 13 in a sodium ion cell.

16. 15. An apparatus comprising the sodium-ion cell of claim 14.

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