This invention relates to novel electrolytes for use in lithium-sulfur batteries (LSBs) and to lithium-sulfur batteries that employ electrolytes of the invention.
The lithium-sulfur battery (LSB) is one of the most promising technologies for next-generation power systems because of its high theoretical gravimetric energy density of 2500 Wh/kg,1-2 which is up to 5 times higher than the theoretical value of state-of-the-art (SOA) commercial lithium-ion battery (LIB) cells.34 The higher energy density LSB enables more energy for an equivalent battery pack, or a lighter pack with equivalent energy delivered. LSBs rely on a non-insertion charge-discharge mechanism which proceeds through a series of lithium polysulfide (LiPS) intermediates. Sulfur is advantageous for battery cathode applications because it is a low-cost and earth-abundant material with an extremely high theoretical capacity of 1675 mAh/g.5 Future LSB cells are estimated to deliver a practical gravimetric energy density of 400 to 600 Wh/kg,6 which is still two- to three-fold higher than SOA LIB cells. However, despite its promise, several fundamental challenges limit commercial practical applications of LSBs. These obstacles include poor electrical conductivity of sulfur, dissolution of lithium polysulfides (LiPSs) in the electrolyte, large volume increase (80%) of the sulfur cathode after full lithiation to Li2S, polysulfide shuttling between the cathode and anode, as well as dendrite formation and electrolyte decomposition at the lithium metal anode interface.
The standard state SOA Li—S electrolyte is one cause of chronically low cycle life in Li—S batteries. The dissolution of LiPS intermediates into the electrolyte and subsequent diffusion to the anode results in a polysulfide shuttle reaction. This reaction is parasitic, reducing efficiency, consuming electrolyte and lithium, resulting in an insulating product layer on the anode surface which inhibits Li transport and is therefore detrimental to cycle life performance. Lithium trifluoromethane sulfonyl imide (LiTFSI) used in standard LSB electrolytes is a weakly bound salt with a calculated ionic association energy, ΔGion association, of −58 KJ/mol Li+.7 This weak ionic interaction between Li+ and the TFSI− salt anion leaves the Li+ cation more available to coordinate with polysulfide dianions (Sx2−), thus promoting formation of large clustered aggregates of Li2S4 which inhibit the kinetics of lithium polysulfide conversion reactions.7 Low temperature operation conditions also place unique performance challenges on LSBs.
Published work describes the use of fluorinated co-solvents (e.g., fluorinated-carbonates,8-9 fluorinated-ethers,10 and fluorinated-esters,10-14) to demonstrate low temperature performance of LIBs. Specifically, fluorinated ester co-solvents such as 2,2,2-trifluoroethyl butyrate (TFEB)13 and 2,2,2-trifluoroethyl propionate (TFEP)14 have been incorporated into multicomponent carbonate electrolytes to achieve enhanced LIB performance down to −60° C. for TFEB and −40° C. for TFEP. In another example, a fluorinated ether cosolvent, monoglycol bis(tetrafluoroethyl) ether, was added to ethyl carbonate (EC) to achieve favorable LIB cell performance down to −50° C. Fluorinated ether cosolvents have also been used in LSBs electrolytes to mitigate polysulfide dissolution at room temperature conditions. For example, several fluorinated ethers including bis(2,2,2-trifluoroethyl) ether (BTFE),15-16 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE),17-19 and ethyl-1,1,2,2-tetrafluoroethyl ether (TTFE),20 have shown improvements in capacity retention, coulombic efficiency, and self-discharge performance in LSB cells compared to the baseline 1,3-dioxolane/dimethoxyethane (DOL/DME) electrolyte.21-22
In addition, to the choice of salt and solvent system, a range of additives can be utilized to control polysulfide dissolution. The solubility of lithium polysulfide will be affected by the concentration of polysulfide ions already present in the electrolyte by the common ion effect. If the concentration of the polysulfide in the electrolyte is significantly larger than the solubility of polysulfide, the electrolyte will have reduced polysulfide dissolution from the cathode. Therefore, when a LiPS pre-dissolved electrolyte is used, the solubility of lithium polysulfide will naturally be reduced significantly.
Therefore, a need exists to overcome or minimize the above-referenced problems.
In one embodiment, the invention is directed towards an electrolyte that includes a lithium (Li) salt, a fluorinated solvent, a 1,3-dioxaolane (DOL) solvent, a 1,2-dimethyoxyethane (DME) solvent, a lithium polysulfide (LiPS), and a lithium nitrate (LiNO3).
In another embodiment, the invention is directed to a lithium-sulfur electrochemical device that includes a cathode, an anode, a separator between the cathode and the anode, and at least one of a liquid electrolyte and a polymer gel electrolyte, wherein the electrolyte includes a lithium (Li) salt, a fluorinated solvent, a 1,3-dioxaolane (DOL) solvent, a 1,2-dimethyoxyethane (DME) solvent, a lithium polysulfide (LiPS), and a lithium nitrate (LiNO3).
This invention has many advantages, such as mitigating generation of lithium polysulfides. Furthermore, this invention improves the operation of lithium sulfur batteries at low temperature conditions. These advantages enhance the cycle life performance of lithium sulfur batteries.
The foregoing will be apparent from the following more particular description of example embodiments, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating embodiments.
The invention generally is directed to electrolytes and rechargeable lithium-ion sulfur batteries that employ the electrolytes of the invention.
In one embodiment, the invention is directed to a fluid that includes a lithium (Li) salt, a fluorinated solvent, 1,3-dioxolane (DOL) solvent, 1,2-dimethoxyethane (DME) solvent, lithium polysulfide (LiPS), and lithium nitrate (LiNO3).
In another embodiment, the invention is directed to an lithium-sulfur (Li—S) electrochemical device, such as an electrochemical cell or battery, such as a rechargeable battery, that includes a cathode, an anode, a separator between the cathode and the anode, and at least one of a liquid electrolyte and a polymer gel electrolyte in fluid communication with the cathode, the anode, and the separator, wherein the electrolyte includes a Li salt, a fluorinated solvent, 1,3-dioxolane (DOL) solvent, 1,2-dimethoxyethane (DME) solvent, lithium polysulfide (LiPS), and lithium nitrate (LiNO3).
In one embodiment of the invention, the Li salt includes at least one member of the group consisting of lithium trifluoromethane sulfonate (LiCF3SO3), lithium trifluorosulfonyl methane (LiTFSM), lithium trifluoroacetate (LiTFA), and lithium bis(fluorosulfonyl)imide (LiFSI).
In a specific embodiment, the Li salt includes at least one member of the group consisting of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), and lithium trifluoromethanesulfonate (LiTf), lithium nonafluoro-1-butane sulfonate (Li(CF3(CF2)3)SO3), lithium acetate (LiCH3SO2), lithium bis(trifluoromethanesulfonyl)imide (Li(CF3SO2)2N), lithium (fluorosulfonyl)-(trifluoromethanesulfonyl)imide (Li(FSO2)(CF3SO2)N), lithium bis(pentafluoroethanesulfonyl)imide (Li(CF3CF2SO2)2N), lithium bis(nonafluorobutanesulfonyl)imide (Li(C4F9SO2)2N), lithium tris(trifluoromethanesulfonyl) methide (Li(CF3SO2)3C, LiBF4, LiBF3(C2F5), LiB(C2O4)2, LiB(C6F5)4, LiPF3(C2F5)3, LiClO4, LiPF6, LiAsF6, LiSbF6, LiTaF6, and LiNbF6. In one such embodiment the Li salt is a blend that further includes at least one member of the group consisting of lithium trifluoromethane sulfonate (LiCF3SO3), lithium trifluorosulfonyl methane (LiTFSM), lithium trifluoroacetate (LiTFA), and lithium bis(fluorosulfonyl)imide (LiFSI).
In an embodiment of the electrochemical cell of the invention, the fluorinated solvent includes at least one member of the group consisting of 2,2,2-trifluoroethyl butyrate, 2,2,2-trifluoroethyl propionate, bis(2,2,2-trifluoroethyl) ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether, ethyl-1,1,2,2-tetrafluoroethyl ether, 2,2,2-trifluoroethyl 1,1,2,2-tetrafluoroethyl ether, ethyl 1,1,2,2-tetrafluoroethyl ether, propyl 1,1,2,2-tetrafluoroethyl ether, fluoromethyl 1,1,1,3,3,3-hexafluoroisopropyl ether, ethyl 1,1,2,3,3,3-hexafluoropropyl ether, hexafluoroisopropyl methyl ether, methyl 1,1,2,2-tetrafluoroethyl ether, 1,1,2,3,3,3-hexafluoropropyl methyl ether, 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether, ethyl 1,1,1,2,2,3,4,5,5,5-decafluoro-3-methoxy-4-(trifluoromethyl)pentane, difluoromethyl 2,2,3,3-tetrafluoropropyl ether, methyl nonafluorobutyl ether, ethyl nonafluorobutyl ether, 1H,1H,5H-octafluoropentyl 1,1,2,2-tetrafluoroethyl ether, 1,1,1,3,3,3-hexafluoro-2-methoxypropane, 1,1,1,3,3,3-hexafluoro-2-(fluoromethoxy)propane, bis(2,2,2-trifluoroethoxy)methane, bis((1,1,1,3,3,3-hexafluoropropan-2-yl)oxy)methane, 2,2,2-trifluoroethyl acetate, 1,1,1,3,3,3-hexafluoropropan-2-yl acetate, methyl (2,2,2-trifluoroethyl) carbonate, 1,1,1,3,3,3-hexafluoropropan-2-yl methyl carbonate, tris(2,2,2-trifluoroethyl) phosphate, tris(1,1,1,3,3,3-hexafluoropropan-2-yl) phosphate, tris(2,2,2-trifluoroethyl) phosphite, and bis(2,2,2-trifluoroethyl) sulfite.
In one embodiment, the lithium polysulfide of the invention has the chemical formula: Li2Sx, wherein x is in a range of from 1 to 8.
In an embodiment of the invention, the lithium polysulfide of the invention has a concentration of 0 M to 8 M.
In a specific embodiment of the invention, the Li salt of the invention has a concentration of 0.01 M to 10 M.
In another embodiment of the invention, the lithium nitrate of the invention has a concentration of 0.01 M to 10 M.
In still another embodiment of the invention, the fluorinated solvent of the invention is 0% to 100% by volume of the electrolyte.
In one embodiment of the invention, the electrochemical cell is a lithium-sulfur battery.
In an embodiment of the invention, the anode of the electrochemical cell is selected from the group consisting of a silicon anode, a graphitic anode, a lithium metal anode, and a lithium alloy metal anode.
In yet another embodiment of the invention, at least one of the anode, the cathode, and the separator of the electrochemical cell of the invention is coated with an MXene-polymer composite material that includes a MXene component and a polymer component. In one such embodiment, the MXene polymer composite material is at least one of a multilayer film and a blend of MXene and polymer components of the MXene polymer composite material. In another embodiment, the MXene-polymer composite material is a multilayer film. In still another embodiment, the MXene-polymer composite material is a blend of the MXene and polymer components of the MXene polymer composite material.
In some embodiments, the electrochemical cells of the invention employ electrolytes comprising strongly bound Li salts dissolved in fluorinated ether-based cosolvents that enable low temperature performance. These electrolytes employ strongly bound Li salts7, 23 dissolved in a multi-component solvent blend which includes a low-viscosity and low-freezing point fluorinated ether15-20, 24-28 cosolvent blended with DOL and DME. This invention also encompasses the combination of these electrolytes paired with a Li anode protected with an artificial solid electrolyte interface (ASEI) to eliminate long chain polysulfide reactions.
In another aspect of this invention, pre-determined quantities of lithium polysulfide (LiPS) additive are dissolved in the electrolytes described above in addition to the Li-salt. Pre-dissolving LiPS in the electrolyte reduces the polysulfide dissolution at the cathode. The pre-dissolved LiPS in the electrolyte serves as a common ion (Sx−) and shifts the polysulfide dissolution reaction equilibrium towards polysulfide reduction into Li2S. This common ion effect prevents the polysulfide dissolution by decreasing the solubility of polysulfides.
The electrolytes described in this invention include the standard LiTFSI salt as well as additional range of strongly bound Li salts, including but not limited to Lithium trifluoromethane sulfonate (LiCF3SO3), Lithium trifluorosulfonyl methane (LiTFSM) and Lithium trifluoroacetate (LiTFA). The electrolytes encompassed in this invention are comprised of solvent blends which incorporate fluorinated cosolvents and may also incorporate pre-dissolved polysulfide additives. Co-solvents include, but are not limited to fluorinated ester co-solvents such as 2,2,2-trifluoroethyl butyrate (TFEB)13 and 2,2,2-trifluoroethyl propionate (TFEP)14, fluorinated ethers including bis(2,2,2-trifluoroethyl) ether (BTFE),15-16 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE),17-19 and ethyl-1,1,2,2-tetrafluoroethyl ether (TTFE).20,21-22
Electrolytes described in this invention have salt concentrations between 0.01 M and 10 M, including both dilute and high concentration, “salt-in-solvent” type electrolytes. In this invention, heat may be utilized to produce supersaturated electrolyte blends with very high salt concentrations. Choice of salt and solvent combinations can be tailored by those skilled in the art for specific applications, such as high rate, low temperature, or reduced flammability. The co-solvent may comprise between 0-100% of the solvent volume to achieve the desired characteristics.
In another aspect of the innovation, LiPS is pre-dissolved in the electrolyte to stop the polysulfides formed at the cathode from dissolving into the electrolyte. LiPS included in this invention include Li2Sx (x=1-8). Pre-dissolved polysulfides included in this invention can be incorporated at concentrations between 0 M and 8 M.
In another aspect of this invention, the electrolytes may be combined with an artificial solid electrolyte interphase (ASEI) on the lithium metal anode. When combined with the an ASEI-protected Li metal anode, the disclosed electrolytes have demonstrated excellent chemical and electrochemical compatibility, low overpotential for the sulfur redox reaction and reduced polysulfide dissolution by providing a stable SEI. The anode used in this invention can also comprise a graphitic anode, silicon anode, or other anodes capable of storing Li ions in rechargeable batteries.
The teachings of all patents, published applications and references cited herein are incorporated by reference in their entirety.
While example embodiments have been particularly shown and described, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the embodiments encompassed by the appended claims.
1a. Electrolyte Preparation and Coin Cell Assembly. Fluorinated cosolvents were blended with 1:1 volume ratio dioxolane (DOL):dimethoxyethane (DME) at a 1:9 volume ratio of cosolvent to DOL:DME. Separate salts (LiTFA, LiTFSM, LiTFSI, LiCF3SO3) were dissolved in each solvent blend at 1M concentration, along with 0.3 M lithium nitrate (LiNO3) which aids in SEI formation at the Li anode surface. A baseline electrolyte of 1M salt in DOL:DME solvent blend with no fluorinated cosolvent was also prepared for each salt. Each electrolyte was incorporated into a 2032-coin cell with a lithium foil anode, sulfur cathode (loading: 3.0-3.5 mg S/cm2), and a polypropylene separator. Cells were built with both bare Li anode and protected Li with a polymer-MXene-based ASEI applied to the surface. To apply the ASEI coatings on the Li metal anode, the coating was first applied to a separate substrate and then transferred onto Li metal. The layer-by-layer (LbL) film application process was used to deposit a transferrable coating to the Li metal surface. Solutions of PEO and PAA (0.2 mg/ml, pH 2.5) were alternately sprayed onto a fluorinated ethylene propylene (FEP) substrate. Prior to deposition, the FEP substrate was plasma treated for 30 seconds followed by a single dip-coated layer. Up to 24 layers of PEO/PAA were deposited on the FEP via spray coating. After this layer was deposited, the samples were dried at 70° C. for 2 hours. Graphene oxide, MXenes and PAH were each used at a 0.2 mg/ml concentration and pH was balanced to 7.4. First, a bilayer of graphene oxide was deposited followed by a layer of poly(allylamine HCl). This layer was necessary to preserve the film integrity during the spraying process. Next, MXene and PAH solutions were alternated, spraying for 10 seconds each time with a 5 second rinse step between. Up to 40 bilayers were deposited. Once finished, the coating is air-dried. To transfer the film to Li metal, the coating was placed face-to-face with Li metal in an inert environment and sealed inside a foil pouch. This pouch was then fed through a calendar roll press twice to transfer the coating from the FEP substrate to the Li metal surface
Coin cells were assembled in an argon-filled glove box and tested on a Maccor battery cycler. Electrolyte was added at an electrolyte to sulfur (E/S) ratio of 8 μL/mg S. Electrochemical impedance spectroscopy (EIS) was performed from 10 Hz to 10000 Hz before electrochemical cycling. Following EIS screening, low temperature testing was performed in a Test Equity environmental chamber. Each coin cell was cycled three times at a C/10 rate at room temperature (RT), followed by low temperature cycling at −20° C. and −40° C. Lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) dissolved in 1:1 volume ratio DOL:DME+LiNO3 was used as the standard electrolyte. Ionic conductivity was evaluated via EIS testing and CV analysis was used to evaluate electrolyte electrochemical stability.
Ionic Conductivity. The Li-ion conductivity of each electrolyte formulation was compared to the baseline electrolyte (1M LiTFSI and 0.3 M LiNO3 in 1:1 vol. % DOL:DME), with results tabulated in Table 1:
A small solution resistance (Rs) and charge-transfer resistance (Rct) value is indicative of good ionic conductivity at room temperature (RT). Rs is determined from the Nyquist plot curve where the EIS impedance data intercepts the X-axis at the high frequency region and Rs directly translates to the ionic conductivity of the electrolyte. The Rct is associated with the electronic conductivity of the electrodes (cathode/anode) at the electrolyte interface. Each impedance plot was used to model the equivalent circuit shown in
The room temperature conductivities of the fluorinated cosolvent electrolytes are ˜10−3 S/cm, which is comparable to the baseline electrolyte. Notably, the conductivity of solvent blends comprising LiTFSI salt dissolved in DOL/DME/fluorinated co-solvent was 6 to 7-fold higher than values measured for electrolytes without fluorinated co-solvent. For example, the conductivity of electrolytes containing TFETFEE, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TFETFPE) and 2,2,2-trifluoroethyl acetate fluorinated cosolvents was 12.74 mS/cm, 15.17 mS/cm, and 12.25 mS/cm, respectively. By comparison, the conductivity of the baseline electrolyte is 2.20 mS/cm. The improved performance with fluorinated cosolvent electrolytes could be attributed to the enhanced lithium ion transport facilitated by the positive interaction of the fluorinated co-solvents with DOL and DME.
Electrochemical Impedance Spectroscopy (EIS) and Cyclic Voltammetry (CV) Analysis. The Nyquist plot of 1M LiCF3SO3+0.3M LiNO3 in DOL:DME (1:1 vol. %) shows higher solution resistance (Rs), charge transfer resistance (Rct) and interface resistance (Ri) at RT compared to electrolytes with TFETFEE cosolvent and Li anode protected with an LbL polymer-MXene ASEI, as shown in
I. CV of Baseline Cells. CV analysis was performed on 2032-coin cells constructed with a sulfur cathode, lithium anode and baseline electrolyte (1M LiTFSI+0.3M LiNO3 in 1:1 vol. % DOL:DME) at a very slow scan rate of 0.1 mV/s to register all the chemical reactions that occur during electrochemical charge-discharge cycling.
xS8+yLi++ye−⇒zLi2Sx Reaction i:
Li2Sx+mLi++me−⇒xLi2S Reaction ii:
Li2S⇒Li2Sp+nLi++ne− Reaction iii:
Li2Sp⇒S8+xLi++xe− Reaction iv:
II. Effect of Strongly Bound Li-Salt at Low-Temperature Conditions.
III. Effect of ASEI Anode on Low-Temperature Performance.
IV. Effect of Fluorinated Cosolvent on Low-Temperature Performance.
V. Combined Effect of ASEI Anode and Fluorinated Cosolvent on Low-Temperature Performance.
Flammability. Electrolyte flammability was compared to the baseline electrolyte. Self-extinguishing time (SET) measurements were used to compare electrolyte flammability. Glass filter paper disks of the same size were soaked in each electrolyte, exposed to an ignition source and time between removal of the ignition source and the flame self-extinguishing was recorded, as shown in
Electrochemical Screening at Low Temperature in Coin Cells. After impedance analysis, each composition was evaluated for electrochemical performance at RT, −20° C., and −40° C. in coin cells. Each electrolyte was run in triplicate and cycled at C/10 rate from 1.6 V to 2.8 V.
Low Temperature Electrochemical Performance. At −40° C. cycling conditions, the baseline electrolyte comprising 1 M LiTFSI in 1:1 vol. % DOL:DME is unable to provide capacity above 200 mg S/cm2 due to the incomplete conversion reaction of S8 to Li2S. However, by switching from LiTFSI to LiTFA salt, low temperature capacity was increased and a liquid phase reaction was retained, as shown in
Three additional electrolyte compositions were developed with LiCF3SO3, which provided improved low temperature performance over the baseline composition. As shown in
The composition of fluorinated co-solvent in the electrolyte was evaluated at a volume % content of 0%, 10%, 25%, and 50%, as shown in
Low Temperature Cycle Life Evaluation. Electrolyte formulations were cycled at −20° C. in coin cells. Specifically, the electrolyte systems evaluated were: 1M LiCF3SO3 dissolved in either DOL:DME or DOL:DME:TFETFEE (9:9:2 volume ratio). The baseline electrolyte (1M LiTFSI in DOL:DME) was also cycled at −20° C. for comparison. Cycle life testing is shown in
Room Temperature Cycle Life Evaluation. The following electrolytes were evaluated for RT cycle testing: (1) LiTFSI in 1,1,1,3,3,3-hexafluoropropan-2-yl acetate (HFPA), (2) LiCF3SO3 in DOL:DME, and (3) LiCF3SO3 in DOL:DME:TFETFEE (9:9:2 volume ratio) (
Room Temperature (RT) Performance Recovery after Low Temperature Exposure. One important performance requirement is the ability to recover performance after exposure to low temperature conditions. Cells were returned to room temperature cycling after completing a −40° C. cycling protocol. Electrolyte formulations (LiCF3SO3 in DOL:DME, LiCF3SO3 in DOL:DME:TFETFEE (9:9:2 volume ratio) and LiTFA in DOL:DME) were tested at RT after cycle testing at −20° C., as shown in
Electrolyte Performance in Single Layer Pouch Cells. Single layer pouch (SLP) cells with a form factor of 3.8 cm×5.5 cm and an active area of 20 cm2 were assembled, as shown in
Postmortem Analysis. Postmortem analysis was conducted on cycled and uncycled pouch cells to evaluate electrolyte compatibility and failure mechanisms. The failure mechanism in Li—S batteries is typically dictated by anode corrosion and electrolyte consumption. SLPs with the best performing electrolytes were disassembled after completion of three formation cycles. For comparison, SLPs with baseline electrolyte were also evaluated via postmortem analysis. Disassembly of SLPs assembled with the developed low temperature electrolytes (1 M LiCF3SO3 and 0.3 M LiNO3 in DOL:DME and 1 M LiCF3SO3 and 0.3 M LiNO3 in DOL:DME:TFETFEE) showed an even SEI layer coating on the Li anode surface, with no significant pitting or corrosion degradation, as shown in
Postmortem analysis was also conducted on SLPs exposed to −20° C. cycling conditions. As shown in
Preparation of Polysulfide Pre-Dissolved Electrolyte: The polysulfide pre-dissolved electrolytes were prepared by dissolving fixed concentrations of polysulfides in the baseline electrolyte (1.0 M LITFSI and 0.3 M LiNO3 in 50:50 vol % DOL:DME). First, stochiometric quantities of Li2S and sulfur (S8) were calculated using Equation 1.
xLi2S+yS8<=>xLi2S6 Equation 1
The pre-determined amounts of Li2S and S8 were then dissolved in the baseline electrolyte at 60° C. for 12 hours under argon atmosphere. Four different electrolytes with Li2S6 concentration varying between 0.01 M-0.1 M were prepared and tested in coin cells using lithium metal as anode and a baseline cathode at E/S of 8 μl/mg S. The coin cells were cycled between 1.6 V and 2.8 V at C/5 rate following 3 formation cycles at C/20 rate. Electrochemical impedance Spectroscopy (EIS) was performed on all the coin cells at the open circuit potential (OCP).
Impedance and Cycling with Pre-Dissolved Polysulfide Electrolyte:
The baseline electrolyte exhibited a fade rate of 0.23%/cycle. The polysulfide pre-dissolved electrolytes 0.01 M Li2S6, 0.025 M Li2S6, 0.05 M Li2S6 and 0.1M Li2S6 exhibited a fade rate of 0.12%, 0.09%, 0.06%, and −0.05%, respectively. All the polysulfide pre-dissolved electrolytes showed a lower fade rate compared to the baseline, the 1 M Li2S6 shows a negative fade-rate (−0.5%/cycle) due to the favorable effect of the electrolyte on the coin cell cycling which translated to 88.3%, 90.8%, 94.4% and 105.4% retention for 0.01 M, 0.025 M, 0.05 M and 0.1 M Li2S6 dissolved in baseline electrolyte, respectively. All the polysulfide pre-dissolved electrolytes also exhibit very good columbic efficiency (>98%) and capacity retention (
The relevant teachings of all patents, patent applications, and publications, including all references cited herein and above, are incorporated herein by reference in their entirety. In addition, the relevant teachings of “Electrochemical Devices Utilizing MXene-Polymer Composites,” by Castro Laicer, Mario Moreira, and Katherine Harrison, Attorney Docket No.: GIN-00225, filed on Apr. 14, 2022, are also incorporated by reference in their entirety.
This application claims the benefit of U.S. Provisional Application No. 63/175,343, filed on 15 Apr. 2021, the relevant teachings of which are incorporated herein by reference in their entirety.
This invention was made with government support under NASA SBIR Phase I Contract No. 80NSSC20C0535 awarded by the National Aeronautics and Space Administration, Shared Services Center (NSSC). The government has certain rights in the invention.
Filing Document | Filing Date | Country | Kind |
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PCT/US22/24976 | 4/15/2022 | WO |
Number | Date | Country | |
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63175343 | Apr 2021 | US |