High-donicity anions for rechargeable potassium superoxide / peroxide batteries

Abstract

Disclosed herein is a rechargeable battery, the rechargeable battery including a cathode, an anode comprising a metal, where the metal of the anode forms a metal-ion of a superoxide-peroxide redox pair, and an electrolyte, where the electrolyte includes a non-aqueous solvent, a first electrolyte salt, and a second electrolyte salt, where the second electrolyte salt comprises an anionic moiety and a solvent moiety, and where the solvent moiety is covalently coupled to the anionic moiety. Also disclosed are methods of making the same.

Description

High-Donicity Anions for Rechargeable Potassium Superoxide / Peroxide BatteriesCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to, and the benefit of, U.S. Provisional Application Serial No. 63 / 618,537, filed January 8, 2024, the disclosure of which is expressly incorporated herein by reference in its entirety.STATEMENT OF GOVERNMENT SUPPORT

[0002] This invention was made with government support under DE-FG02-07ER46427 awarded by the Department of Energy. The government has certain rights in the invention.BACKGROUND

[0003] Potassium secondary batteries have been recognized as promising candidates for future energy storage technologies owing to their abundance, low cost, and substantial cell voltage. Among the types of potassium secondary batteries are potassium-oxygen batteries. Using oxygen (O2) as the active component at a battery cathode offers advantages in large mass-specific energy densities and low costs. In the last several decades, different alkali metal-02 batteries, such as lithium (Li)-O2, sodium-02, and potassium (K)-O2, have been actively explored. [1-6] For example, the superoxide-based K-O2 batteries system that relies on the single-electron conversion between O2 and potassium superoxide (KO2) has been developed. [7] The solution-mediated pathway allows the decomposition of primary solid KO2 to follow the “dissolution-decomposition” process, highlighted with fast reaction kinetics without requiring any catalysts. [6-8] Nevertheless, all these oxygen batteries suffer from some inherent challenges and drawbacks: an open system using O2 directly from air faces the issue of air purification and evaporation of volatile electrolytes, while a closed system using stored pure O2 would suffer from the penalty of high-pressure O2 tanks. [9] Furthermore, dissolved O2 in liquid electrolytes can cross over to consume the metal anode.

[0010] In comparison, the electrochemical conversion between solid-phase superoxide, peroxide, and oxide inherits the advantages of oxygen-based anionic redox without gaseous O2 participation / evolution.

[0004] A typical K-O2 battery of a gaseous system is shown in the equation below:whereas an oxygen anion-redox battery of a closed system is shown in the following equation:Batteries of the closed system have no gas involvement in the reaction and can be formed in a sealed cell structure.

[0005] The realization of the oxide / peroxide- and oxide-peroxide / superoxide-based cathode reaction has been demonstrated in the lithium-based system from the angle of the anion-redox cathode, allowing the use of sealed cells. [11,12] A mixed matrix of lithium oxide nanoparticles and a high-efficiency catalytic host (iridium-graphene composite or cobalt oxide) were developed previously. As for the K-based system, Lu et al. probed the electrochemistry in K-O2 battery using ambient pressure X-ray photoelectron spectroscopy and first identified both potassium peroxide (K2O2) and potassium oxide as the possible products at a high depth of discharge (DOD).

[0013] Furthermore, Zhou et al. have conducted a pioneering study on the interconversion process between K2O2 / KO2.

[0014] Such redox is highly reversible and stable in the presence of ruthenium dioxide electrocatalyst. However, the high catalyst amount (30 wt% in total cathode mass) impedes its further use for practical batteries in terms of cost. Using high-donicity solvents (e.g., dimethyl sulfoxide, DMSO) provides an elegant and efficient solution to avoid the use of electrocatalysts. As reported previously, the stable existence of solvent-separated ion pairs formation between solvated K+and superoxide anion (Ch') in high-donicity DMSO facilitates the KO2 / K2O2 interconversion.

[0015] Although DMSO solvent offers advantages, it possesses the formidable drawback of high reactivity with potassium metal, which limits further application unless a solid-state membrane of K+superionic conductor is used to protect the K metal anode.

[0015] Previous reports on lithiumsulfur batteries have suggested success using the salt-modification approach to tune the electron donicity of electrolytes. [16, 17] By changing the salt anion into one with a higher donor number (DN), the lithium sulfide growth chemistry can be modulated in a three- dimensional growth model, which effectively delays the electrode passivation and consequently results in augmented sulfur utilization.

[0016] More importantly, the electrolytes with high-DN salt anions deliver superior compatibility with a metallic Li electrode compared to the electrolyte using high-DN solvents.

[0006] To improve on state-of-the-art metal-air batteries, a battery cathode based on the superoxide / peroxide redox not only inherits the advantage of oxygen (O2) batteries in highcapacities and low costs but also overcomes the disadvantages in O2 storage, electrolyte evaporation, and anode deactivation due to O2 crossover.SUMMARY

[0007] Described herein is a rechargeable battery, the rechargeable battery including a cathode; an anode comprising a metal of a metal-ion of a superoxide-peroxide redox pair; and an electrolyte — the electrolyte comprises a non-aqueous solvent, a first electrolyte salt, and a second electrolyte salt, wherein the second electrolyte salt comprises an anionic moiety and a solvent moiety, wherein the solvent moiety is covalently coupled to the anionic moiety.

[0008] In some aspects, the second electrolyte salt is an asymmetric molecule. In some aspects, the second electrolyte salt includes a high donor number anion and a metal-ion.

[0009] In some aspects, the non-aqueous solvent includes a high donor-number solvent. In some aspects, the non-aqueous solvent is chosen from DME, DEGDME, TEGDME, DMF, DMSO, and combinations or variations thereof.

[0010] In some aspects, the first electrolyte salt includes a metal-ion.

[0011] In some aspects, the metal-ion of the redox pair, of the first electrolyte salt, and the second electrolyte salt are chosen from K, Li, Na, Rb, or Cs. In some aspects, the metalion of the redox pair, of the first electrolyte salt, and the second electrolyte salt are the same or different.

[0012] In some aspects, the electrolyte includes less than 0.50M of the second electrolyte salt in the non-aqueous solvent. In some aspects, the electrolyte includes at least 0.5M of the first electrolyte salt in the non-aqueous solvent.

[0013] In some aspects, the cathode includes a metal oxide, wherein the metal of the metal oxide comprises the metal of the superoxide-peroxide redox pair. In some aspects, the cathode comprises a binder.

[0014] In some aspects, the anode comprises a protective layer.

[0015] In some aspects, the rechargeable battery including a current collector.

[0016] In some aspects, the second electrolyte salt prevents O2 evolution in the electrolyte.

[0017] In some aspects, the rechargeable battery operates at more than 70% columbic efficiency (CE), more than 80% CE, more than 90% CE, or more than 95% CE.

[0018] In some aspects, the rechargeable battery exhibits a discharge capacity of more than 275 mAh / g-1KO2, more than 300 mAh / g-1KO2, or more than 325 mAh / g-1KO2.

[0019] In some aspects, the rechargeable battery exhibits cell stability after 100 cycles and after 120 cycles.

[0020] In some aspects, the rechargeable battery exhibits a lifespan of more than 800 hours, more than 1000 hours, more than 1200 hours, or more than 1400 hours when the battery is cycled to a depth of discharge of 85% or less.

[0021] In some aspects, the techniques described herein relate to a method to make a rechargeable battery, the rechargeable battery including a metal-ion superoxide-peroxide redox pair and an electrolyte, wherein the electrolyte includes a non-aqueous solvent, a first electrolyte salt, and a second electrolyte salt, wherein the second electrolyte salt includes an anionic moiety and a solvent moiety, wherein the solvent moiety is covalently coupled to the anionic moiety.BRIEF DESCRIPTION OF DRAWINGS

[0022] Figs. 1 A-1D show typical scanning electron microscopy (SEM) images of the (Fig. 1A) discharged and (Fig. IB) charged KO2 electrode of the K-KO2 cell using 0.5 M KPFe / DME; (Fig. 1C) the cyclic stability of K-KO2 cell at 0.5 M KPFe / DME where the current density was around ~49 mA g-1KO2 based on the KO2 mass and the initial loading of KO2 was 0.2 mAh; (Fig. ID) specific capacities and coulombic efficiencies of the K-KO2 cell based on 0.5 M KPFe / DME.

[0023] Figs. 2A-2D show an electrochemically synthesized bind-free KO2 electrode for the superoxide / peroxide redox. Fig. 2A shows the reversible charge capacities and coulombic efficiencies (CEs) upon first 10 cycles of K-O2 batteries using 0.5 M KPFe / DME. The discharge capacities were curtailed at 0.2 mAh at a current of 0.5 mA to deposit KO2 solids on the carbon paper cathode. The error bar in coulombic efficiencies shows the standard derivations of three batteries. Fig. 2B shows the representative 10th discharge (solid line) / charge (dash line) profiles of the K-O2 batteries with a depth of discharge of 0.2 mAh. The upper charge voltage limit was set at 3.0 V. Fig. 2C shows the typical morphology of KO2 solids formed in the discharged K-O2 batteries based on 0.5 M KPFe / DME electrolyte. Fig. 2D shows a K-KO2 cell assembly procedure. The binder-free KCh-deposited cathode was prepared by discharging the K-O2 battery.

[0024] Figs. 3 A-3B show evaluations of the reversible KO2 amount residue after K-KO2 cell assembly. Fig. 3 A shows the first charge profile of sealed K-KO2 cell in Ar atmosphere, and the following 2ndand 10thvoltage profiles (inset) in 0.5 M KPFe / DME. Fig. 3B shows thepressure changes of the Swagelok EL-Cell setup during the 1stcharging process of the KO2- deposited cathode based on 0.5 M KPFe / DME. The charge current was 0.1 mA.

[0025] Figs. 4A-4B show results of monitoring the cathode components evolution during the K-K02 cell cycling based on 0.5 M KPFe / DME. Fig. 4A shows typical 1stvoltage profiles of K-KO2 batteries at a current density of 49 mA g-1KO2 in the voltage range of 1.5-2.36 V. The KO2 was pre-deposited at the carbon paper with a capacity of 0.2 mAh. Fig. 4B shows Raman spectra collection at OCV, after 1stdischarge (DI) and after 1stcharge (Cl and C2) on the cathode.

[0026] Figs. 5A-5D show the effect of cation-anion / solvent interaction characterized by23Na-NMR and including (Fig. 5A) schematic concept of solvent-in-anion design and the schematic illustration of the KMPSA structure; (Fig. 5B)23Na-NMR spectra of 5 mM Na- MPSA / PFe in DME, DMSO, or Me-Im; (Fig. 5C) a plot of23Na-NMR shift versus donor numbers of NaPFe-(dark yellow) and NaMPSA-based (wine) solutions. The calculated R2value of the linear fitting curve was 99.98%; (Fig. 5D)23Na chemical shifts of electrolyte solution (0.5 M NaPFe / DME) upon different NaMPS A amounts addition. The customized coaxial NMR tubes were used to separate the deuterated solvent acetonitrile (CD3CN) and target solution.

[0027] Figs. 6A-6B show solubilities and ionic conductivities estimation of conventional high-DN K-Cl / Br / I / NO3 salt in DME. Fig. 6 A shows optical images of K-Cl / Br / I / NCh salts dissolved in DME solvent after stirring overnight. The concentrations for the recipes are 4 mM (upper) and 10 mM (lower). The arrow indicates the insoluble salt residue in DME solvent when the molarity is 10 mM. Fig. 6B shows ionic conductivities of solutions prepared by dissolving 4 mM K-Cl / Br / I / NCh in DME. The ionic conductivity of 0.5 M KPFe / DME was added for comparison.

[0028] Fig. 7 shows23Na NMR spectra of 5 mM NaPFe in various solvents, including the methyl-imidazole (Me-Im), DMSO, DMF, DME, DEGDME, and TEGDME.

[0029] Figs. 8A-8B show (Fig. 8A) the plot of23Na-NMR chemical shift versus electrolyte solution (0.5 M NaPFe / DME) upon different NaMPSA amounts addition, and (Fig. 8B)23Na-NMR spectra of 5, 20, and 200 mM NaMPSA in DME. The calculated R2value of the linear fitting curve was 99.65%.

[0030] Figs. 9A-9D demonstrate effect of cation-anion / solvent interaction observed by Raman spectroscopy including: (Fig. 9A) Raman spectra of the PF stretching mode of PF 6" anion in DME (orange), DEGDME (cyan), DMSO (sapphire), and pure KPFe (dot line) using 0.5 mol KPFe in the unit of molarit; (Fig. 9B) the anionic Raman peak of PF e in differentsolvents and pure KPFe salt; (Fig. 9C) concentration dependence of anionic Raman spectra for KMPSA / DME mixtures and pure KMPSA (dot line); (Fig. 9D) the anionic Raman peaks of MPS A’ in the KMPSA / DME and KMPSA / DMSO electrolytes with different concentrations and pure KMPSA salt. A shift toward higher wavenumbers implies more interaction between the anion and cation.

[0031] Fig. 10 shows Raman spectra of the S-N stretching mode of MPS A' anion in DMSO with the molality of 0.09 m, 0.46 m, 0.91 m, and 3.00 m. The Raman spectrum of KMPSA salt (dotted line) is added for comparison.

[0032] Figs. 11 A-l IF show stability evaluation of KMPSA against KO2 and K2O2, including: (Fig. 11 A, Fig. 11C)XH NMR and (Fig. 1 IE)19F NMR spectra of (Fig. 11 A) DME and (Fig. 11C, Fig. 1 IE) KMPSA; (Fig. 1 IB, Fig. 1 ID, Fig. 1 IF) magnified views of regions of the (Fig. 1 IB, Fig. 1 ID)JH NMR and (Fig. 1 IF)19F NMR spectra indicated by frames in (Fig. 11 A, Fig. 11C, Fig. 1 IE) before (bottom trace) and after reaction with KO2 (middle trace) or K2O2 (top tace). All the spectra were calibrated with the CD3CN (5 = 1.94 ppm). The signals of two dominant peaks in (Fig. 11 A) were ascribed to the DME solvent. TheJH NMR signal at 3.39 ppm was ascribed to the DME satelliteJH peak. The signals of Ha, Hb, Hc, and Ha peaks in (Fig. 11C)XH NMR and the signal (5 = -77.3 ppm) in (Fig. 1 IE)19F NMR were ascribed to the MPSA anion.

[0033] Fig. 12 shows a comparison of charge capacities of K-KO2 cells based on different electrolyte recipes. The cells with KMPSA additive or KMPSA / DME were cycled with the curtailed charge capacity of 292 mAh g-1KO2, while the cell with KPFe / DME was cycled in the voltage range of 1.5-2.34 V. Note that the upper voltage limit was set at 2.34 V for all the K-KO2 cells to avoid the possible O2 evolution.

[0034] Figs. 13A-13F demonstrate the reversibility of K-KO2 cells based on KPFe / DME electrolyte with KMPSA additive including: (Fig. 13A) representative 1stvoltage profiles of K-KO2 batteries in 0.5 M KPFe / DME + 1.0 wt% KMPSA (-0.04 M) at a current density of 49 mA g-1KO2, where the cubic KO2 (inset) is electrochemically deposited at the carbon paper with a capacity of 0.2 mAh; (Fig. 13B) Raman spectra collection at OCV, after 1stdischarge and after 1stcharge on the cathode; typical SEM images of the (Fig. 13C) discharged and (Fig. 13D) charged KO2 electrode of the K-KO2 cell; (Fig. 13E) the typical voltage profiles and energy efficiencies (inset) of K-KO2 cells at a current density of 49 mA g^KCh; (Fig. 13F) galvanostatic voltage profiles and energy efficiencies (inset) of K-KO2 cells at current densities of 49, 75, 100, 150, 200, and 500 mA g-1KO2. All the current densities were calculated based on the cathode KO2 mass. The voltage range was set at 1.50-2.34 V.

[0035] Fig. 14 shows the galvanostatic discharge / charge curves of the carbon paper substrate without and with KCh deposition based on the 0.5 M KPFe / DME + 1.0 wt% KMPSA recipe. The yellow point and cyan point in the charging curve represent the capacity of 292 and 342 mAh g-1KO2, respectively. The dashed line represents the “redline” for triggering the KCh decomposition with O2 evolution.

[0036] Figs. 15A-15B show (Fig. 15 A) the standard calibration curve involves O2 content and its integrated peak area and (Fig. 15B) gas evolution monitoring during cycling of the K- KO2 cell with 0.5 M KPFe / DME + 1.0 wt% KMPSA via the gas chromatography (GC) method. The inset in Fig. 15B shows the calculated O2 amount based on the integrated area in different states. Note that the presence of CEE was ascribed to the side reaction between K and DME.

[0037] Fig. 16 shows the low-magnification SEM image of the discharged KO2 electrode of the K-KO2 cell based on 0.5 M KPFe / DME + 1.0 wt% KMPSA electrolyte. The upside of the carbon paper substrate indicates the surface facing away from the separator side.

[0038] Figs. 17A-17B show (Fig. 17A) the energy converting efficiencies and (Fig. 17B) capacity retention of K-KO2 cells at a current density of 49 mA g-1KO2. The electrolyte was 0.5 M KPFe / DME + 1.0 wt% KMPSA.

[0039] Fig. 18 shows the energy converting efficiencies of K-KO2 cells at increasing current densities. The electrolyte was 0.5 M KPFe / DME + 1.0 wt% KMPSA.

[0040] Figs. 19A-19B show quantification of the KMPSA amount by NMR technique with CD3CN as the deuterated solvent including: (Fig. 19A)JH NMR spectra of standard solution with different KMPSA amount addition, where the inset in Fig. 19A is the molecule structure of KMPSA, and the peaks a, b, c, and d were ascribed to KMPSA. The CeHe (50 mM) was used as the internal standard, and the integrated area ratio of peak c in KMPSA (5 = 3.25 ppm) toJH peak in CeEE (5 = 7.37 ppm) was used for calibrating the KMPSA concentration. Additionally including: (Fig. 19B) the standard calibration curve on the KMPSA concentration. The inset image in Fig. 19B shows the titration results on the KMPSA concentration change before and after KO2 or K2O2 solid addition. Note that the KMPSA / CD3CN solution after adding KO2 or K2O2 solid was aged for 1 day before furtherJH NMR detection.

[0041] Figs. 20A-20B show (Fig. 20A) a solution-mediated mechanism for the charging process in a schematical illustration of the cell setup with the proposed strategy. The K-KO2 cell was first discharged to deposit the K2O2 product on the carbon, then the discharged cathode with K2O2 was fetched and assembled with a new carbon paper. A piece of Celgardwas added to insulate the electrical contact between the discharged cathode and the carbon paper cathode. Fig. 20B shows representative voltage-time curve of K-KO2 cell based on 0.5 M KPFe / DME + 1.0 wt% KMPSA (up) and 0.5 M KPFe / DME (down). The newly assembled cell was subject to charge, and the discharged cell was disassembled, followed by adding an extra Celgard between the discharged cathode and the carbon paper cathode.

[0042] Figs. 21A-21B show (Fig. 21A) configuration of the reassembled cells with various conditions. Note that electrolyte 1 was 0.5 M KPFe / DME + 1.0 wt% KMPSA, and electrolyte 2 was 0.5 M KPFe / DME. Cell 1 and cell 2 correspond to the data in Fig. 20B (up) and Fig. 2 IB (up), and cell 3 and cell 4 correspond to the data in Fig. 20B (down) and Fig. 2 IB (down), respectively. Fig. 2 IB show representative voltage-time curve of K-KO2 cells. One cell was discharged in 0.5 M KPFe / DME + 1.0 wt% KMPSA and charged in 0.5 M KPFe / DME (up). The other cell was discharged in 0.5 M KPFe / DME and charged in 0.5 M KPFe / DME + 1.0 wt% KMPSA (down). The discharged cell was disassembled, followed by adding an extra Celgard between the discharged cathode and the carbon paper cathode.

[0043] Figs. 22A-22C show typical voltage profiles of K-Cu half-cells based on (Fig. 22A) 0.5 M KMPSA / DME and (Fig. 22B) 0.5 M KPF6 / DME + 1.0 wt% KMPSA (-0.04 M). Fig. 22C shows a comparison of K plating / stripping efficiencies on the Cu foil among different electrolyte recipes. The test current was 0.1 mA / cm2, and the cycling capacity was curtailed at 0.1 mAh / cm2with a stripping / plating time of two hours.DETAILED DESCRIPTION OF EMBODIMENTS

[0044] Herein, an enhanced superoxide / peroxide secondary battery is disclosed and includes a high-donicity anion additive in the electrolyte. Such an anion was synthesized via a “Sol vent-in- Anion” strategy and validated to enhance the electron donicity of the electrolyte. The use of high-donicity anion could lead to enhanced capacity utilization by retarding electrode passivation and allow the full charging back of the peroxide through a solution-mediated pathway without electrocatalysts.

[0045] In some aspects, described herein is a metal-ion rechargeable battery, the rechargeable battery including a cathode, an anode including a metal, wherein the metal forms a metal-ion of a superoxide-peroxide redox pair, and an electrolyte. In some aspects, the electrolyte includes a non-aqueous solvent, a first electrolyte salt, and a second electrolyte salt. In some aspects, the second electrolyte salt includes an anionic moiety and a solvent moiety, such that the solvent moiety is covalently coupled to the anionic moiety.

[0046] In some aspects, the second electrolyte salt includes an asymmetric moiety. In some aspects, the second electrolyte salt includes a high donor number anion and a metal-ion.

[0047] In some aspects, the non-aqueous solvent includes a high donor-number solvent. For example, the non-aqueous solvent is chosen from DME, DEGDME, TEGDME, DMF, DMSO, and combinations or variations thereof.

[0048] In some aspects, the first electrolyte salt includes a metal-ion.

[0049] In some aspects, the metal-ion of the redox pair, the first electrolyte salt, and the second electrolyte salt are chosen from K, Li, Na, Rb, or Cs. In some aspects, the metal-ion of the redox pair, of the first electrolyte salt, and the second electrolyte salt are the same or different. For example, the metal-ion of the redox pair, the first electrolyte salt, and the second electrolyte salt is K. In another example, the metal-ion of the redox pair and the second electrolyte salt is K, and the metal -ion of the first electrolyte salt is one of Li, Na, Rb, or Cs.

[0050] In some aspects, the electrolyte includes less than 0.50M of the second electrolyte salt in the non-aqueous solvent.

[0051] In some aspects, the electrolyte includes at least 0.5M of the first electrolyte salt in the non-aqueous solvent.

[0052] In some aspects, the the second electrolyte salt prevents O2 evolution in the electrolyte. It is considered that the superoxide / peroxide pair, for example, shown in Equation (II), utilizes excess oxygen, therefore, preventing occurrence of O2 evolution in the electrolyte.

[0053] In some aspects, the cathode includes a metal oxide. The metal of the metal oxide being the same as the metal of the superoxide-peroxide redox pair.

[0054] In some aspects, the cathode includes a binder. In some aspects, the anode comprises a protective layer. In some aspects, the rechargeable battery includes a current collector.

[0055] In some aspects, the rechargeable battery operates at more than 70% columbic efficiency (CE), more than 80% CE, more than 90% CE, or more than 95% CE. In nonlimiting examples, the rechargeable battery operates at 75% CE, 85% CE, 92% CE, or 97% CE.

[0056] In some aspects, the rechargeable battery exhibits a discharge capacity of more than 275 mAh / g-1KO2, more than 300 mAh / g-1KO2, or more than 325 mAh / g-1KO2. In nonlimiting examples, the rechargeable battery operates at 280 mAh / g-1KO2, 290 mAh / g-1KO2, 310 mAh / g-1KO2, 320 mAh / g-1KO2, 330 mAh / g-1KO2, or 340 mAh / g-1KO2.10057] In some aspects, the rechargeable battery exhibits cell stability after 100 cycles, after 120 cycles. In non-limiting examples, the rechargeable battery exhibits cell stability after 110 cycles, after 130 cycles.

[0058] In some aspects, the rechargeable battery exhibits a lifespan of more than 800 hours, more than 1000 hours, more than 1200 hours, or more than 1400 hours when the rechargeable battery is cycled to a depth of discharge of 85% or less. In non-limiting examples, the rechargeable battery exhibits a lifespan of more than 1400 hours when the rechargeable battery is cycled to a DOD of 80%, 75%, 70%, 65%, 60%, 55%, or 50%.

[0059] This disclosure also contemplated the method of making a rechargeable battery as described herein. It is contemplated that the rechargeable battery can be made using known techniques in the field. It is further contemplated that the rechargeable battery has a form of known battery types including but not limited to coin-cell, cylinder, and pouch.EXAMPLES

[0060] The following example is put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how the compounds, compositions, articles, devices and / or methods claimed herein are made and evaluated and are intended to be purely exemplary and are not intended to limit the disclosure.

[0061] The example references L. Qin, L. Schkeryantz, Y. Wu, “Designing High- Donicity Anions for Rechargeable Potassium Superoxide / Peroxide Batteries”, Angew. Chem. Int. Ed. 2023, 62, e202213996; Angew. Chem. 2023, 135, e202213996, which is expressly incorporated herein in its entirety.

[0062] An enhanced potassium superoxide (KChJ / peroxide (K2O2) conversion is reported and facilitated by adopting a high-donicity anion additive in the ether-based electrolyte. Such an anion was synthesized via a “Solvent-in- Anion” strategy and validated to enhance the electron donicity of the electrolyte. The use of high-donicity anion could lead to enhanced KO2 utilization (-90.2%) by retarding electrode passivation and allow the full charging back of K2O2 through the solution-mediated pathway without electrocatalysts. No apparent cell degradation is observed during the first 120 cycles by controlling the reversible depth-of- discharge capacity at 292 mAh g-1KO2 within an Ch-free region. The K-KO2 cell delivers a high energy efficiency (> 84.4%) and a lifespan of over 1440 hours.

[0063] Herein, a reversible KO2 / K2O2 interconversion was observed by adding the high- donicity (3-methoxypropyl)((trifluoromethyl)sulfonyl)amide (MPS A ) anions in a moderately solvating ether-based solvent. The MPSA anion was synthesized via a solvent-in-anion strategy so as to graft a solvent moiety onto an anion. [18-20] The resulting new anion thus possessed the structural features and solvating properties of the solvent.

[0064] This solvent-in-anion design of anions tune the solubility and solvating property of electrolyte salts. When this idea was applied to MPSA , it possessed the structural features and donicity of ether solvents. Such a designed anion was demonstrated to possess a high Gutmann donor number (DN) and enhance the electron-donating capability of ether-based electrolytes even with an additive amount. The MPSA additive amount (1.0 wt%) and supporting salt / solvent choice (0.5 M potassium hexafluorophosphate / l,2-dimethoxy ethane, KPFe / DME) were optimized to achieve holistic anode-electrolyte-cathode compatibility. With MPSA as the additive, a solution-mediated process enabled the KO2 / K2O2 interconversion with a small overpotential of 216 mV. As a result, the corresponding K-KO2 full cell delivered a reversible capacity of 292 mAh g-1KO2 (calculated based on the mass of KO2) with round-trip energy efficiencies above 84.4% over 120 stable cycles at a DOD of 85.4%.

[0065] The catalyst-free KO2 cathode could significantly reduce the electrode cost. More promisingly, the reversible superoxide / peroxide conversion demonstrated here can be utilized for fulfilling the full potential of low-cost and high-energy-density superoxide batteries with commercial sealed battery technologies.

[0066] Results and Discussion.

[0067] In this study, KO2 electrodes were prepared through electrochemical reduction of O2 in a K-O2 battery cell (Figs. 2A-2D). The KCh-deposited cathode was then used to form a sealed K-KO2 cell, which represents the fully charged state for Qi / Qi2' redox. After cell assembly, the assembled K-KO2 cell was charged first to evaluate the actual KO2 amount (Figs. 3A-3B). The sealed cell delivered the first charge capacity of 0.194 mAh. The same amount of KO2 mass loading was used for all measurements in this study. Considering the onset potential of KO2 decomposition is about 2.35 V at the sealed K-KO2 cell, the upper voltage limit was set at 2.34 V to avoid O2 evolution for estimating the K-KO2 cell performance in the following electrochemical measurements unless noted otherwise.

[0068] Referring now to Figs. 2A-2D, the K-O2 batteries were cycled with a curtailed capacity of 0.20 mAh for several cycles. Based on three parallel results, the average coulombic efficiencies (CEs) reach 87.6% (1stcycle) and further increase to 97.4% (5thcycle) and 99.3% (10thcycle) (Fig. 2A). The typical 10thvoltage profile exhibits a discharge plateau at 2.41 V (vs. K+ / K) (Fig. 2B), and some discrete KO2 cubes with the particle size at several micrometers were deposited on the carbon fiber (Fig. 2C). Notably, the 10thcharging processdelivered a low overpotential of ~80 mV and a high reversible capacity of 0.199 mAh, with 99.5% capacity attributed to the KO2 formation in the former discharge process. This is consistent with prior studies indicating that the parasitic reactions of K-O2 batteries mainly occur during the 1stdischarge process.

[0034] Here, the KO2 particles were deposited on the carbon fiber by operating the K-O2 battery at the corresponding 10thdischarged state.

[0069] Referring now to Figs. 3 A-3B, the charging process of the K-KO2 cell delivers a voltage plateau at 2.41 V (KO2 + e' — > K++ O2) (Fig. 3 A). The lower KO2 decomposition potential can be ascribed to the lower O2 partial pressure in the sealed cell. The charge capacity achieved 0.194 mAh, slightly smaller than that of 0.199 mAh estimated in KO2 batteries. The capacity differences may be due to the trace KO2 residue at the separator and / or the loss during the rinse step. After correlating the O2 amount change (Ano2, calculated by the ideal gas law with the pressure change AP) with the electron flow (Ane., recorded by the battery tester), the ratio of An(e-) / An(O2) was estimated to be around 0.96 for the first charging process, corresponding to a single electron transfer for the O2 evolution during the KO2 decomposition (Fig. 3B). Notably, the sealed K-KO2 cell shows negligible capacity in the following cycles. This indicates that the evolved O2 cannot be captured for further reduction to KO2 if the cell configuration is not purged with excessive O2 priorly.

[0070] As reported in a prior study, superoxide is more stable than peroxide with the higher O2 partial pressure and lower temperature in the case of potassium. [2,7] With this knowledge, the inert argon atmosphere is a pre-requisite to realize an anionic KO2 / K2O2 redox, and it is essential to avoid further decomposition of KO2 (i.e., overcharging or O2 evolution) during operation. Otherwise, both the loss of active material of KO2 and the evolution of O2 may affect the K2O2 formation and result in fast capacity decay.

[0071] Referring now to Figs. 4A-4B, the capacity (68 mAh g-1KO2) of charge plateau (wine trace in Fig. 4A) at 2.36 V is ascribed to the oxidation of KO2 residue and oxygen evolution.

[0072] For the cyclic stability evaluation, the assembled K-KO2 cell was discharged first, followed by the charging process. A typical electrolyte recipe composed of KPFe / DME in a K-O2 battery system was first adopted as the control electrolyte to check the possibility of realizing the superoxide / peroxide redox. The K-KO2 cell based on 0.5 M KPFe / DME electrolyte was observed to deliver a first discharge capacity of 235 mAh g'1with a prominent KO2 voltage plateau at 1.90 V, slightly lower than the equilibrium potential of KO2 / K2O2 (1.92 V vs. K+ / K) (Fig. 4A). A fully discharged cathode exhibited granular particles covering the carbon paper surface with some cubic KO2 residue (Fig. 1 A),corresponding to 62.3% of KO2 utilization given the theoretical specific capacity of 377 mAh g-1KO2. The newborn particles were identified as K2O2 (760 cm’1) from the typical Raman spectrum (Fig. 4B). The subsequent first charging process exhibits a sloping voltage profile with a capacity of 167 mAh g-1KO2, leading to a low initial CE of 71.1%. The charged carbon cathode exhibited the conformal coating of smaller particles and some broken KO2 cubes (Fig. IB). It was further verified by Raman spectra that both K2O2 and KO2 (1143 cm’1) existed after charging, implying the insufficient transformation from K2O2 to KO2.

[0073] Notably, the charge capacity of the K-KO2 cell decreased in successive charging cycles within an upper voltage limitation during the cycling test, and the cell exhibited a fast decay in reversible capacity upon cycling (Fig. 1C). Specifically, the reversible charge capacity in the 30thcycle dropped to 90 mAh g-1KO2, and the average coulombic efficiency (CE) in the first 30 cycles was only 80.6% (Fig. ID). Regarding the low achievable capacity and poor reversibility of the cell, there seem to be two main challenges due to the insulating nature of K2O2: its deposition passivates the electrode surface, which limits the DODs, and the difficulty of electrochemical conversion of K2O2 back to KO2 through the solid phase.

[0074] As reported previously, the high-donicity DMSO achieves the highly reversible KO2 / K2O2 redox without catalysts. [15,21] Besides the usage of high-DN solvents, the use of conventional high-DN anions (e.g., Cl / Br / I / NO3 ) can also improve the electron donicity of electrolytes, [22,23] but these K-containing salts (Cl / Br / I / NO3 ) exhibit a low solubility (around 4 mM) in DME solvent (Figs. 6A-6B). As a result, the ionic conductivities of these electrolytes are two orders of magnitude lower than the recipe of 0.5 M KPFe / DME.Although the K-containing salts can be adopted as the additive with supporting salt (e.g., KPFe) in DME, the high K+concentration (e.g., 0.5 mol / L) in the electrolyte would significantly reduce the soluble amounts of these high-DN anions given the constant solubility product at room temperature. Recently, a “solvent-in-anion” design strategy for synthesizing high-solubility salts was reported.

[0018] For example, the K-ion asymmetric salt of potassium (3-methoxypropyl) ((trifluoromethyl)sulfonyl) amide (KMPSA) was synthesized by grafting the ether solvent moiety onto the trifluoromethanesulfonimide (TFSI) motif (Fig. 5A). Such salt was proposed to possess the combined features of a TFSI anion and an ether solvent. Guided by the like-dissolve-like principle, the KMPSA exhibited an ultrahigh solubility (-16.6 mol / kg) in DME solvent.

[0018] This strategy enabled the design of salts with tunable DN anions and high solubilities by attaching a suitable DN solvent moiety to the anion.

[0075] Referring now to Figs. 6A-6B, the K-containing salts with conventional high-DN anions (e.g., C17Br7I7NO3 ) are demonstrated to exhibit a very low solubility (-4 mM) in the moderately solvating solvent of DME at room temperature, as evidenced by the insoluble salt residue when the molarity reaches 10 mM.

[0076] Due to the lower sensitivity of39K nuclear magnetic resonance (NMR) than23Na NMR,

[0024] the electron donicity of MPSA was investigated by23Na NMR through the effect of the salt anion solvating Na+. As reported previously, the magnitude of the downfield chemical shift of the23Na signal is influenced by the electron donicity of the solvation shell around Na+ions. [25,26] When an anion is a weak donor (e.g., PFe), Na cations are fully solvated by solvent molecules; thus, the chemical shift is directly related to the donicity of the solvent, which is clearly shown in Fig. 5B and Fig. 7. Based on the known DNs for these solvents from prior reports, [27,28] a linear trend between solution DNs and NMR shifts was determined for the NaPFe-based electrolytes (dark yellow squares in Fig. 5C).

[0077] Referring now to Fig. 7, as revealed from the23Na NMR shifts of NaPFe in different solvents, the NaPFe-glyme electrolyte solutions deliver more up-field chemical shifts than DMF, DMSO, and Me-Im cases, implying the weaker electron donicity of glyme- based solvents.

[0078] When adding an anion with a Lewis basicity comparable to or even stronger than the solvent, the anion is also expected to participate in the solvation by forming contact ion pairs (CIPs), which cause a downfield shift. When comparing NaPFe / DME with NaMPSA / DME, a significant chemical shift change (above 6.1 ppm) was observed in Fig. 5B, demonstrating the higher donicity of MPSA anions than PFe. In comparison, there was no apparent influence of the anions (MPSA and PFe') on the chemical shifts in the DMSO- based solutions (less than 0.3 ppm), and the cation was mainly solvated by the high-DN DMSO solvent via the formation of solvent-separated ion pairs. Using the linear trend in Fig. 5C, the DN of a 5 mM NaMPSA / DME solution was quantified as 24.8, which is close to that of a DMSO-based system, validating that the electrolyte can still achieve a high-DN value by adopting a high-DN anion (e.g., MPSA ) even with a moderately solvating solvent of DME. Moreover, the MPSA anion can also be used as an additive. The23Na NMR spectra of 0.5 M NaPFe / DME solution exhibits a more positive shift upon addition of more NaMPSA (Fig.5D). Furthermore, there was a quasi-linear trend in NaMPSA addition amount (at least in the range of 0.02-0.10 M) against NMR shifts of base NaPFe / DME solution (Figs. 8A-8B).

[0079] Referring now to Figs. 8A-8B, in the case of NaMPSA salts, the chemical shifts are found to be independent of concentration (at least in the range of 0.005-0.2 M) when the DME is used as the solvating solvent.

[0080] It can also be concluded that increasing the MPSA' anion concentrations would result in a displacement of DME solvent and PFe' anion in the inner solvation shell of Na+ions, and the high-DN MPSA' could afford a distinct Na+solvation structure even with a small added amount given that both PFe' anion and DME solvent have a relatively lower donicity than MPSA'.

[0081] In addition to the NMR probing of cation solvation, Raman spectroscopy was used to probe the solvation around anions (Figs. 9A-9D and Fig. 10). The KMPSA-DME solutions with various molality were prepared by dissolving stoichiometric KMPSA salt and DME solvent. The S-N stretch mode in the MPSA anion was sensitive to the salt concentration in DME (Fig. 9C). The S-N Raman peak shifted to the higher wavenumber (closer to that in KMPSA solid), indicating more interaction between the K+and MPSA at a higher salt concentration. Notably, the anionic Raman peak exhibited a relatively small wavenumber change even within a very low concentration range of below 1 mol kg'1(Fig. 9D), again implying a strong interaction of high-DN MPSA with K+. Moreover, the low donicity of DME solvent provides more chances to form the CIPs once the anion possessed a high DN. Detailed information on the concentrations of the electrolyte recipe and the corresponding Raman shifts of the anionic peak can be found in Tables 1-2.

[0082] Referring now to Figs. 9A-9D, the variation in certain anionic Raman bands could give useful information on the dissociation condition of the parent salts and the coordination state of the anions. [8,9] For the KPFe-solvent mixtures, it is clearly observed that the spectral frequencies of anion were close irrespective of the solvents used and the salt concentrations (Figs. 9A-9B). This implies that solvent-separated ion pairs (SSIPs) are the dominant species, and the PFe' could hardly participate in the K+solvation even in the moderately solvating solvent of glyme.

[0083] Referring now to Fig. 10, the anionic peak of MPSA' exhibits a lower wavenumber (below 739 cm'1) when the salt KMPSA is dissolved in the DMSO, implying the dominant SSIPs species with a weaker interaction between K+and MPSA'.Table 1. Anionic Raman shifts of S-N stretching mode of MPS A- anion in DME and DMSO with different molality.Table 2. Anionic Raman shifts of P-F stretching mode of PF e anion in DME, DEGDME, and DMSO with different molality.

[0084] After demonstrating the high DN of KMPSA, the stability of KMPSA salt in the presence of KO2 or K2O2 was checked to ensure their mutual compatibility. Commercial KO2 and the as-synthesized K2O2 were added to the KMPSA / DME solution (Figs. 11 A-l IF).From the NMR spectra of the aged solution, it was observed that the MPSA anion was stable against the nucleophilic attack of KO2 or K2O2. As for the compatibility with the K anode, however, it was shown in a previous study that the K exhibits very low plating / stripping efficiencies when adopting KMPSA as the main salt in the DME system.

[0018] Therefore, the high-DN KMPSA was added as the additive with DME as the solvating solvent and KPFe as the supporting salt. The optimal amount of KMPSA in the 0.5 M KPFe / DME system was 1.0 wt% (around 0.04 M) based on the reversible capacity output of the K-KO2 cell upon cycles(Fig. 12). Such a recipe (0.5 M KPFe / DME + 1.0 wt% KMPSA) was adopted for the K-KO2 cell performance evaluation unless otherwise specified.

[0085] To verify the stability of KMPSA in the existence of superoxide and peroxide, KMPSA / DME solutions were stirred with KO2 or K2O2 powder addition. The composition of reacted solution was then subject to NMR spectroscopy to detect the possible side products. As a result, a small amount of dimethyl oxalate (5 = 3.81 ppm) was found in the bare DME solvent after treatment. The possible reaction mechanism of the DME solvent under nucleophilic attack was investigated in prior studies.

[0028] Referring now to Figs. 11 A-l IE, the typical peaks for KMPSA still exist, and no additional peaks for parasitic byproducts were observed in the NMR spectra after aging the KMPSA / DME solution with KO2 or K2O2 dissolved. This implies the superb stability of KMPSA salt.

[0086] Referring now to Fig. 12, cyclic stability evaluations are shown. After predischarging the cell to 1.5 V, all the cells were subsequently cycled with a cutoff charge depth at 292 mAh g-1KO2 to avoid undesirable O2 evolution. One exception is the case using KPFe / DME recipe, which could not achieve such a charge capacity.

[0087] As for the K-KO2 cell using the electrolyte with KMPSA additive, the discharge process was initially conducted for KO2 reduction. Specifically, the first discharge capacity reached 342 mAh g-1KO2 based on KO2 mass (90.7 % conversion vs. theoretical capacity) (yellow trace, Fig. 13 A). The same charge capacity of 342 mAh g-1KO2 was observed within the upper voltage limit of 2.34 V (top trace, Fig. 13A). The 1stcycle overpotential was estimated to be 216 mV, corresponding to a decent round-trip energy efficiency of 87.9 %. Such electrochemical behavior was distinct from the K-KO2 cell using the electrolyte without high-DN MPSA anion additive, in which the discharge plateau capacity was shortened, and the charging potential quickly rose and surpassed the oxygen evolution onset potential of -2.35 V (Fig. 1C). Notably, without the upper charging voltage limit of 2.34 V, the charging process showed two steps of oxidation as shown in Fig. 14: the oxidation of K2O2 to KO2 at a voltage below 2.34 V followed by oxygen evolution at a voltage above 2.34 V.

[0088] In Fig. 14, the first charge plateau occurs at -2.13 V, followed by the appearance of the onset of the second charge plateau at 2.34 V. The latter oxidation process is ascribed to the oxygen evolution from KO2 decomposition. In addition, the bare carbon paper substrate is demonstrated to contribute negligible capacity within the voltage range of 1.5-2.34 V.

[0089] The Raman spectra confirmed the K2O2 formation after full discharging and the KO2 regeneration after charging back (Fig. 13B). Notably, the gas chromatography measurements indicate that O2 did not participate in the electrochemical redox reaction (seeFigs. 15A-15B). The morphological change of the KO2 cathode during the discharge / charge process was monitored by SEM observation. A fully discharged cathode exhibited ribbon-like products on the carbon fiber (Fig. 13C, Fig. 16). After charging, all K2O2 ribbons disappeared, and the regenerated KO2 exhibited an entirely different morphology similar to thin pancakes sticking to the surface of carbon fibers (Fig. 13D). Because the discharge reaction was limited by electrode passivation due to the insulating K2O2 deposition in the low-DN KPFe / DME, the increase in the discharge capacity with the addition of high-DN anions suggests that electrode surface passivation was reduced. More importantly, the charge capacity reached the value of the former discharge state within the upper voltage limit, supporting the notion that all the deposited K2O2 could be completely converted back to KO2 at the end of the charge. In addition, the decreased charge polarization with the high-DN anion additive implies that K2O2 decomposition can also be accelerated under the high-DN anion environment. The observation is similar to previous studies of high-DN anions in lithium-sulfur electrochemistry. [16, 17] In the conventional ether-based electrolyte, the high- DN anion (e.g., Br ) enables a higher degree of reversibility for Li2S deposition / decomposition reactions.

[0090] It was further revealed (see Fig. 16) that the carbon paper facing away from the separator / carbon paper side tends to form more discharge products of ribbon-like K2O2, which shares a similar distribution with the parent KO2 solid.

[0091] Referring now to Figs. 15A-15B, the GC-FID was first quantitatively calibrated using a standard high-purity O2. The standard calibration curve was obtained by correlating the injected O2 amounts and the corresponding integrated peak areas. The calculated R2value of the calibration curve was estimated as 99.85%, ensuring high reliability in quantifying the gaseous O2 amounts of cycled cells. The change rates of O2 were further separately quantified via integrating the detected O2 peak areas upon one complete cycle, including the OCV, DI, and Cl states, as shown in Fig. 13 A.

[0092] Referring now to Fig. 17, turning to cyclic stability evaluation, after a predischarging step to 342 mAh g-1KO2 at the cut-off voltage of 1.5 V, the K-KO2 cell was cycled with a curtailed cut-off charge / discharge depth at 292 mAh g-1KO2 (to avoid undesired O2 evolution from KO2 decomposition). This can explain why the initial coulombic efficiency (85.4%) was below 100%, and the coulombic efficiencies of the cell in subsequent cycles were 100%. During long-term cycling, the discharge / charge overpotential has been effectively restrained, resulting in high energy efficiencies of 89.6% (10thcycle), 88.9% (20thcycle), 88.5% (30thcycle), 88.1% (50thcycle), 87.2% (80thcycle), 86.3% (100thcycle), and 84.4% (120thcycle). The detailed data and calculation process are shown in Table 3.Table 3. Detailed energy efficiencies of K-KO2 cells at different cycles calculated based on the corresponding voltage profiles in Fig. 3E. The applied current density is 49 mA g-1KO2.

[0093] After demonstrating reversibility in the first cycle, the cyclic stability was tested with the cycling capacity curtailed at 292 mAh g-1KO2 to avoid undesired O2 evolution. This corresponds to a DOD of 85.4%, given the first capacity of 342 mAh g'1(Fig. 13E). Apparent discharge and charge plateaus with stable voltage profiles were observed for the K-KO2 cell during the first 120 cycles. Nevertheless, noticeable polarization was observed at the end of the 120thcharge profile, and the charge terminal potential was close to the tipping point for O2 evolution. Despite this, the discharge / charge overpotential of the K-KO2 cell was effectively restrained during the lifespan of the cell, and a high round-trip energy efficiency of 84.4% was still observed even at the 120thcycle (Figs. 17A-17B, Table 3). The cell performance of this catalyst-free K-KO2 system with high-DN additive was comparable to the prior report on the same K-KO2 prototype based on RuCh-based catalysts (Table 4).

[0014] The rate capability of K-KO2 cells was evaluated at different current densities. Without any electrocatalyst, the round-trip energy efficiencies of the K-KO2 cells reached above 81.6 % (Fig. 18, Table 5) despite that a slightly increasing polarization was observed as the current density increased from 49 to 200 mA g-1KO2 (Fig. 13F). Although the cell delivered a reduced capacity of 182 mAh g-1KO2 at a high current of 500 mA g-1KO2, a relatively high energy efficiency of 73.0% was achieved. The energy efficiency of the K-KO2 cell demonstrated here was already comparable or even superior to that of many zinc-Ch and Li-O2 batteries using catalysts. [29-31]Table 4. Comparison of K-KO2 cell performance

[0094] The results shown in Figs. 13A-13F show that the addition of KMPSA has the dual functions of increasing the discharge capacity from KO2 to K2O2 and improving its cycling reversibility. Without the KMPSA additive, the discharge capacity is only 235 mAh g-1KO2, while the enhanced discharge capacity of 342 mAh g-1KO2 was observed after adding KMPSA. Such an increase can be explained by the difference in K2O2 morphologies. Without KMPSA, the formed K2O2 coats the carbon substrate, which passivates the substrate and limits the continuous deposition of K2O2. After adding KMPSA, the formed K2O2 are observed as ribbons growing out of the substrate, which avoids the rapid surface passivation and allows the continuous growth of K2O2. Moreover, the dramatically different morphologies of primary solid products (KO2 / K2O2) before and after adding KMPSA (Figs. 1 A-1D and Figs. 13A-13F) imply that MPSA anions tend to be preferentially adsorbed on the surface of K2O2 and KO2, and thus change the crystal growth behavior. The preferential adsorption effect of MPSA on the KO2 / K2O2 surface is further supported by the quantitative titration experiments, the results of which are shown in Figs. 19A-19B. This makes sense considering the high DN of MPSA anions imply its strong affinity to the surface K+ions on KO2 and K2O2.Table 5. Detailed energy efficiencies of K-KO2 cells at different current densities calculated based on the corresponding voltage profiles in Fig. 3F.

[0095] Referring to Figs. 19A-19B, given the distinct morphologies of primary solid products (KO2 / K2O2) in the presence of KMPSA additive (Figs. 1 A-1D and Figs. 5A-5F), it is reasonable to think that the MPSA' anion may preferentially passivate the specific plane of solids during the nucleation / growth process. To probe the interaction between the MPSA' and the formed solids in the K-KO2 cells, the KMPSA concentration was monitored before and after solid KO2 or K2O2 powder addition.

[0096] The qualification on the MPSA' anion concentration was made throughJH NMR characterization (Fig. 19A). After correlating the KMPSA concentration and the integrated area ratio of KMPSA to the internal standard of CeHe (50 mM), a good linear relationship was obtained (Fig. 19B). Notably, there was a noticeable discrepancy between the actual KMPSA concentration and the titrated concentration after adding the KO2 or K2O2 solid into KMPSA / CD3CN solution. Based on the titration results, the soluble KMPSA concentration decreased after adding the KO2 or K2O2 solid. Given the superb stability of KMPSA in the presence of superoxide and peroxide (Figs. 11 A-l IF), the decrease in the soluble KMPSA amount from the titration results may be due to the preferential adsorption of MPSA' anions on the KO2 / K2O2 surface (these adsorbed MPSA' species would not contribute to NMR signal) based on current understandings.

[0097] To further explain the enhanced reversibility and probe the charging mechanism with KMPSA additive, the K-KO2 cell was first discharged to deposit ribbon-like K2O2 on the cathode, which was then re-assembled with an additional carbon cathode. An extra separator was added to insulate the electric contact between the discharged cathode and the new cathode current collector (Fig. 20A, Fig. 21A). The newly assembled cell delivered a prominent charge plateau and capacity, which implies that the K2O2 was still electrochemically active even after losing the electrical contact, and the charging process of K2O2 proceeded via a solution-mediated pathway (sapphire trace in Fig. 20B). Nevertheless, the lower charge plateau, which corresponds to the decomposition of ribbon-like K2O2, was absent without noticeable charge capacity when changing the electrolyte to 0.5 M KPFe / DME (Fig. 2 IB, top). In comparison, the discharged K-KO2 cell could not deliver any chargecapacity in the KPFe / DME electrolyte (wine trace in Fig. 20B). It is thus proposed that the KO2 / K2O2 transformation mainly follows a surface-mediated pathway without KMPSA additive, where the electron transport and charge transfer are limited to the cathode active surface with sluggish reaction kinetics. This is also consistent with SEM observations that the growth of charge products was mainly confined to the carbon surface (Figs. 1A-1D). However, the discharged cathode in the KPFe / DME achieved the same charge capacity when adopting the electrolyte with KMPSA additive during the charging process (Fig. 2 IB, bottom). Based on the above observations, it was concluded that the K2O2 morphology was not the crucial factor affecting the charging mechanism. Instead, the strong interaction between K+and the high-DN MPS A additive and the preferential adsorption of MPS A on the formed solid were vital for regulating and promoting the K2O2 formation / decomposition via a solution-mediated process and exhibiting superior reaction kinetics and reversibility.

[0098] To explore the possible reason for the battery decay upon cycles in Fig. 13E, the influence of KMPSA salt on the K metal reversibility was evaluated by building a K-Cu halfcells. The reversibility of K plating / stripping was hindered by low CEs (around 10.4%), and the K-Cu cells quickly failed after several cycles where the cell included 0.5 M KMPSA / DME electrolyte, possibly due to the detrimental SEI formation (Fig. 22A). The average CE increased to 69.9% in the first 40 cycles when changing the main salt to KPFe with 1.0 wt% KMPSA additive (Fig. 22B). Notably, the increasing amounts of KMPSA additive resulted in ever-deteriorating cyclic stability of K-Cu half-cells as reflected by the declining CEs compared to the base electrolyte of 0.5 M KPFe / DME (Fig. 22C). Given the electrochemical performance and NMR results above, it was concluded that increased participation of MPSA in the solvation shell of K+was less favorable for the stable SEI build-up on the K surface. Actually, the inferior K reversibility upon increasing the KMPSA additive amounts in the base KPFe / DME electrolyte was also a good implication that it is difficult for the bulky PF to compete with the high-DN MPSA anions to participate in the K+solvation, since the SEI components derived from MPSA decomposition was detrimental to the K anode.

[0018] As a result, the poor stability of the SEI may facilitate the continuous consumption of MPSA anion at the K anode side upon long-term cycles, which may be responsible for the battery decay. Pre-forming a durable and ion-conductive anode protection layer on the metallic K surface is expected to further boost the K- KO2 cell performance.

[0099] One effective strategy to enhance the K anode reversibility was adding another supporting salt and reducing the MPSA' anion addition amount. Given the holistic anode- electrolyte-cathode compatibility, PF 6' is a good option because of its tendency to form amore conductive SEI than MPSA' on K anode while maintaining the superb stability against O2 and KO2 based on a prior study. [1,10]

[0100] Experimental Procedures.

[0101] Materials. Potassium hexafluorophosphate (KPFe) (Sigma-Aldrich, 99.5%), potassium iodide (KI) (Sigma-Aldrich, 99.0%), potassium bromide (KBr) (Sigma-Aldrich, 99.0%), and potassium chloride (KC1) (Sigma-Aldrich, 99.0%), were used as received. Sodium -based and potassium -based (3-methoxypropyl)((trifluoromethyl)sulfonyl)amide (NaMPSA and KMPSA) were synthesized as described previously.

[0018] All the salts were dried in a chemical drier under vacuum before transferring into the argon (Ar)-filled glovebox. 1,2-dimethoxy ethane (DME) (BASF), dimethyl sulfoxide (DMSO) (Sigma- Aldrich, 99.9%), 1 -methylimidazole (Me-Im) (Sigma-Aldrich, 99.0%), diethylene glycol dimethyl ether (DEGDME) (Sigma-Aldrich, 99.5%), tetraethylene glycol dimethyl ether (TEDEME) (Sigma-Aldrich, 99.0%), and dimethylformamide (DMF) (Sigma-Aldrich, 99.8%) were stored in a bottle filled with freshly activated molecular sieves (type 3 A) for at least two weeks before further use. The final water content was measured below 5 ppm by Karl Fisher titration.

[0102] High-purity oxygen (PRAXAIR, 99.993%) was connected to a moisture trap (RK22014, RESTEK) to further remove moisture in the cylinder. Carbon paper (Avcarb P50, Full Cell Store) was punched into round discs with a diameter of 12 mm and employed as the gas diffusion layer cathode.

[0103] Electrochemical measurements. The K-O2 batteries were assembled using custom Swagelok battery prototypes, which consist of a metallic K (Sigma-Aldrich, 98%) anode, the freestanding carbon paper cathode, and a glass fiber membrane (GF-D, Whatman) combining a tri-layer Celgard as the separator. 0.5 M KPFe in DME was used as the electrolyte, and -250 pL electrolyte was added to each K-O2 cell. An additional -500 pL DME was added into the gas reservoir to avoid solvent vaporization during tests. High-purity O2 was purged into the battery setup for one minute, followed by two hours resting before tests. The carbon paper with KO2 pre-deposition (0.2 mAh) was obtained by discharging a K-O2 cell at a current of 0.5 mA for 24 minutes. The discharged cathode was taken out, further rinsed with DME solvent, and then used for K-KO2 cell assembly.

[0104] The K-KO2 cells were assembled using 2032-type coin-cell setups, consisting of K as the reference / counter electrode and the carbon paper with KO2 pre-deposition as the working electrode. One piece of Celgard and glass fiber (GF-A, Whatman) were used as the separator, and -100 pL electrolyte was added to each K-KO2 coin-cell. Galvanostaticdischarge-charge tests were conducted using a Neware battery analyzer system (BTS3000). The voltage window for the K-KO2 batteries was set to 1.50-2.34 V. The K-Cu half-cells were assembled with K as the reference / counter electrode and the Cu foil (d = 12 mm) as the working electrode. Two pieces of Celgard soaked with ~50 pL electrolyte were used as the separator. Each K-Cu coin-cells were discharged at 0.1 mA / cm2for 1 hour and charged back to 1.0 V vs. K+ / K.

[0105] Ionic conductivity measurements. The ionic conductivities of electrolytes were measured using a homemade setup with two parallel stainless-steel plates separated by about 0.2 cm in a Teflon base. The whole setup was put inside a hermitic vial to minimize the electrolyte evaporation and air exposure. The conductivity standard solutions (1000 and 12890 pS / cm, Hach) were adopted to calibrate the setup constant, which was calculated to be 0.683 cm’1± 0.006A total of 60 pL solution was transferred into the cell, followed by aging for 20 minutes before measurements. The electrochemical impedance spectra were acquired from 1 MHz to 0.5 Hz with an alternating current amplitude of 5 mV (Gamry). The electrolyte resistance was determined as the impedance where the phase angle is close to 0°.

[0106] Characterizations. Raman spectra were recorded on a confocal Renishaw Raman microscope with a 633 nm laser wavelength, and the electrode samples were stored in a homemade airtight holder equipped with an ultrathin N-BK7 window (thickness, 0.20 mm) (TECHSPEC®). The power of the laser beam delivered to the sample surface was adjusted to 10% of the maximum laser intensity to avoid electrode sample degradation. The Raman spectrum acquisition exposure time was set as 120 seconds for five consecutive accumulations, and at least three different spots on the sample surface were detected to ensure the data reliability. The acquired Raman spectra were further processed with WIRE to subtract the background and smooth the spectra if necessary.

[0107] Scanning electron microscopy (SEM) images were acquired at an FEI Quanta 200 SEM at an accelerating voltage of 5 kV. The cycled electrode samples were disassembled in a working cell at the specific states and rinsed thoroughly by DME to remove the salt residue. After that, the air-sensitive electrode samples were transferred into an airtight holder before observation.

[0108] Synthesis ofKz h powder. K2O2 material was synthesized based on the prior report from Jansen et al.

[0032] In a typical procedure, the commercial KO2 was firstly handground for 30 minutes, followed by the heat treatment at 315 °C for one day under the dynamic vacuum condition (pressure: 2* 10'3mbar). The obtained powder was subjected to another heating treatment under the same condition to produce high-purity K2O2 powder.

[0109] Determination of donor number (DN) and detection of electrolyte byproducts using nuclear magnetic resonance (NMR).23Na NMR was carried out by preparing a 5 mM solution of Na-containing salt in various aprotic solvents, and all the spectra were collected in a 600 MHz (Bruker Avance III HD 600). The co-axial NMR tube (WGS-5BL-SP, Wilmad LabGlass) was used to avoid interference from the deuterated solvent. The deuterated acetonitrile (CD3CN) (Sigma-Aldrich, >99.8%) was refilled in the inner NMR tube, and the target electrolyte was refilled in the outer tube. By correlating the quasi-linear trend between the23Na NMR shift and the known DNs of solvents (e.g., DMSO and Me-Im [3,4]), the DNs of unknown electrolytes can be estimated from this trend.

[0110] The aged solution after stirring with KO2 or K2O2 solid was first filtrated to remove the excessive solid power. The filtration or the freshly prepared solution was then dissolved in CD3CN for 'H and19F NMR spectra, which were collected by a 400 MHz NMR spectrometer (Bruker, AVIII 400). The obtained NMR spectra were further processed with MestReNova to calibrate the data with reference to the standard deuterated solvent of CD3CN (5 = 1.94 ppm).

[0111] Operando pressure monitoring during battery cycling. An ECC-Air cell setup (EL-CELL, German) connecting with a pressure transducer (OMEGA, PX409-485) was used to monitor the pressure variation of the cell during the electrochemical cycling. The whole setup was assembled in the Ar-filled glovebox and then properly sealed with a dead-end configuration under a neat Ar atmosphere. After resting the cell at the ambient temperature condition (25 °C) for 1 hour to reach the equilibrium, the cell was subject to electrochemical cycling controlled by the Neware Battery Analyzer (BTS3000), and the corresponding pressure data was recorded by the Digital Transducer Application software (OMEGA).

[0112] The volume determination of the whole cell setup was based on the indirect liquid occupancy method. In brief, the acetone was injected into the Swagelok EL-CELL setup and the other stainless steel connection parts. The average acetone volume was determined as 5.94 mL based on four parallel trials and roughly estimated as the accessible volume for gas components (V). The evolved O2 amount (Ano2) during the K-KO2 cell charging process was calculated from the measured pressure change (Ap) based on the ideal gas law per equation 1 :An02= -7 (1) where R is the ideal gas constant (8.314 mol-1 K-l; T is temperature at ambient conditions (298 K); Ap is the pressure change during cell discharge / charge; and Lis the estimated volume of the gas reservoir inside the system.

[0113] The amount of charge (Ane_) transferred during the cell cycling was obtained by equation 2:where e is the elementary charge of one electron, NA is Avogadro constant; I is the applied current during galvanostatic discharge / charge; At is the discharge / charge duration; and AQ is the total charge transferred during discharge / charge.

[0114] Finally, the ratio value (Z), which represents the number of electrons (Ano?) transferred per evolved O2 molecule (Ane.), was estimated using equation 3 : _ Ane- An02

[0115] Gas chromatography (GC) analyses. A rubber septum was additionally mounted on the gas reservoir of the homemade Swagelok setup for collecting the GC sampling. Detailed information on the airtight Swagelok cell prototype can be found in a prior report.

[0033] A K-KO2 cell was assembled using the Swagelok cell setup in the Ar-filled glovebox, followed by aging under a neat Ar atmosphere for 1 hour before the electrochemical cycling. A gastight syringe (SGE 250 pL, Sigma-Aldrich) was used for headspace sampling, and 250 pL resulting gas samples at open circuit voltage and discharge / charge states were manually injected into a GC (Agilent Technologies 7820A), which equips with a flame ionization detector (FID) and a thermal conductivity detector (TCD). A porapak Q stainless steel packed column was employed to separate the injected gas components, and the resulting chromatograms were further processed to calculate the integrated peak area for the O2 signal in different gaseous samples. Nitrogen was adopted as the carrier gas. The total volume of the reservoir inside the homemade Swagelok cell is estimated to be around 63.6 mL based on the specifications of different components and parts.

[0116] Conclusion.

[0117] In summary, a solvent-in-anion design was introduced that tunes the solubility and electron donicity of electrolyte salts. Following the design, the MPSA anion was synthesized and further demonstrated to possess a strong electron-donating ability, which influenced the solvation structure and the DN of ether-based electrolyte based on spectroscopic analyses. By adding the high-DN MPSA anion as the additive in a moderately solvating ether-based solvent, the reversible KO2 / K2O2 interconversion with high reaction kinetics was realized via a solution-mediated pathway, and no additional electrocatalyst was required. This study demonstrated reversible superoxide / peroxide conversion as the potassium-ion battery cathodewith a considerable specific capacity (292 mAh g-1KO2), high round-trip efficiency (above 84.4%), long-term cyclic stability (over 120 cycles), and lifespan (above 1440 hours) at a DOD of 85.7%. The demonstrated anion design is of potential interest for other metal-02 and metal-sulfur batteries system.DEFINITIONS

[0118] Some references, which may include various patents, patent applications, and publications, are cited in a reference list and discussed in the disclosure provided herein. The citation and / or discussion of such references is provided merely to clarify the description of the present disclosure and is not an admission that any such reference is “prior art” to any aspects of the present disclosure described herein. In terms of notation, “[n]” corresponds to the nth reference in the list. All references cited and discussed in this specification are incorporated herein by reference in their entireties and to the same extent as if each reference was individually incorporated by reference.

[0119] Although example embodiments of the present disclosure are explained in some instances in detail herein, it is to be understood that other embodiments are contemplated. Accordingly, it is not intended that the present disclosure be limited in its scope to the details of construction and arrangement of components set forth in the following description or illustrated in the drawings. The present disclosure is capable of other embodiments and of being practiced or carried out in various ways.

[0120] It must also be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” or “5 approximately” one particular value and / or to “about” or “approximately” another particular value. When such a range is expressed, other exemplary embodiments include from the one particular value and / or to the other particular value.

[0121] By “comprising” or “containing” or “including” is meant that at least the name compound, element, particle, or method step is present in the composition or article or method, but does not exclude the presence of other compounds, materials, particles, method steps, even if the other such compounds, material, particles, method steps have the same function as what is named.

[0122] In describing example embodiments, terminology will be resorted to for the sake of clarity. It is intended that each term contemplates its broadest meaning as understood by those skilled in the art and includes all technical equivalents that operate in a similar manner to accomplish a similar purpose. It is also to be understood that the mention of one or moresteps of a method does not preclude the presence of additional method steps or intervening method steps between those steps expressly identified. Steps of a method may be performed in a different order than those described herein without departing from the scope of the present disclosure. Similarly, it is also to be understood that the mention of one or more components in a device or system does not preclude the presence of additional components or intervening components between those components expressly identified.

[0123] The expressions "ambient temperature" and "room temperature" as used herein are understood in the art and refer generally to a temperature from about 20 °C to about 35 °C.

[0124] As used herein, the term “composition” is intended to encompass a product comprising the specified ingredients in the specified amounts, as well as any product which results, directly or indirectly, from a combination of the specified ingredients in the specified amounts.

[0125] References in the specification and concluding claims to parts by weight of a particular element or component in a composition denotes the weight relationship between the element or component and any other elements or components in the composition or article for which a part by weight is expressed. Thus, in a mixture containing 2 parts by weight of component X and 5 parts by weight, components Y, X, and Y are present at a weight ratio of 2:5 and are present in such ratio regardless of whether additional components are contained in the mixture.

[0126] A weight percent (wt.%) of a component, unless specifically stated to the contrary, is based on the total weight of the formulation or composition in which the component is included.

[0127] It will be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element, or intervening elements may be present. In contrast, when an element is referred to as being "directly connected" or "directly coupled" to another element, there are no intervening elements present. Other words used to describe the relationship between elements or layers should be interpreted in a like fashion (e.g., "between" versus "directly between," "adjacent" versus "directly adjacent," "on" versus "directly on").

[0128] Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the disclosure are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in theirrespective testing measurements. Furthermore, when numerical ranges of varying scope are set forth herein, it is contemplated that any combination of these values inclusive of the recited values may be used. Further, ranges can be expressed herein as from “about” one particular value and / or to “about” another particular value. When such a range is expressed, another aspect includes from the one particular value and / or to the other particular value.

[0129] Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another aspect. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint and independently of the other endpoint. Unless stated otherwise, the term “about” means within 5% (e.g., within 2% or 1%) of the particular value modified by the term “about.”

[0130] Similarly, numerical ranges recited herein by endpoints include subranges subsumed within that range (e.g., 1 to 5 includes 1-1.5, 1.5-2, 2-2.75, 2.75-3, 3-3.90, 3.90-4, 4-4.24, 4.24-5, 2-5, 3-5, 1-4, and 2-4). It is also to be understood that all numbers and fractions thereof are presumed to be modified by the term “about.”

[0131] It will be understood that, although the terms "first," "second," etc., may be used herein to describe various elements, components, regions, layers, and / or sections. These elements, components, regions, layers, and / or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer, or section from another element, component, region, layer, or section. Thus, a first element, component, region, layer, or section discussed below could be termed a second element, component, region, layer, or section without departing from the teachings of example embodiments.

[0132] As used herein, the term "substantially" means that the subsequently described event or circumstance completely occurs or that the subsequently described event or circumstance generally, typically, or approximately occurs.

[0133] Still further, the term “substantially” can in some aspects refer to at least about 80 %, at least about 85 %, at least about 90 %, at least about 91 %, at least about 92 %, at least about 93 %, at least about 94 %, at least about 95 %, at least about 96 %, at least about 97 %, at least about 98 %, at least about 99 %, or about 100 % of the stated property, component, composition, or other condition for which substantially is used to characterize or otherwise quantify an amount.

[0134] In other aspects, as used herein, the term “substantially free,” when used in the context of a composition or component of a composition that is substantially absent, is intended to refer to an amount that is then about 1 % by weight, e.g., less than about 0.5 % byweight, less than about 0.1 % by weight, less than about 0.05 % by weight, or less than about 0.01 % by weight of the stated material, based on the total weight of the composition.

[0135] As used herein, the terms “substantially identical reference composition,” “substantially identical reference article,” or “substantially identical reference electrochemical cell” refer to a reference composition, article, or electrochemical cell comprising substantially identical components in the absence of an inventive component. In another exemplary aspect, the term "substantially," in, for example, the context "substantially identical reference composition," or “substantially identical reference article,” or “substantially identical reference electrochemical cell” refers to a reference composition, article, or an electrochemical cell comprising substantially identical components and wherein an inventive component is substituted with a common in the art component.

[0136] The devices, systems, and methods of the appended claims are not limited in scope by the specific devices, systems, and methods described herein, which are intended as illustrations of a few aspects of the claims. Any devices, systems, and methods that are functionally equivalent are intended to fall within the scope of the claims. Various modifications of the devices, systems, and methods, in addition to those shown and described herein, are intended to fall within the scope of the appended claims. Further, while only certain representative devices, systems, and method steps disclosed herein are specifically described, other combinations of the devices, systems, and method steps also are intended to fall within the scope of the appended claims, even if not specifically recited. Thus, a combination of steps, elements, components, or constituents may be explicitly mentioned herein or less; however, other combinations of steps, elements, components, and constituents are included, even though not explicitly stated.

[0137] Although several embodiments of the invention have been disclosed in the foregoing specification, it is understood by those skilled in the art that many modifications and other embodiments of the invention will come to mind to which the invention pertains, having the benefit of the teaching presented in the foregoing description and associated drawings. It is thus understood that the invention is not limited to the specific embodiments disclosed hereinabove and that many modifications and other embodiments are intended to be included within the scope of the appended claims. Moreover, although specific terms are employed herein, as well as in the claims which follow, they are used only in a generic and descriptive sense and not for the purposes of limiting the described invention nor the claims which follow.

[0138] Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of skill in the art to which the disclosed invention belongs. Publications cited herein and the materials for which they are cited are specifically incorporated by reference.

[0139] While aspects can be described and claimed in a particular statutory class, such as the system statutory class, this is for convenience only and one of ordinary skill in the art will understand that each aspect of the present invention can be described and claimed in any statutory class. Unless otherwise expressly stated, it is in no way intended that any method or aspect set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not specifically state in the claims or descriptions that the steps are to be limited to a specific order, it is in no way intended that an order be inferred in any respect. This holds for any possible non-express basis for interpretation, including matters of logic with respect to arrangement of steps or operational flow, plain meaning derived from grammatical organization or punctuation, or the number or type of aspects described in the specification.

[0140] In view of the described processes and compositions, hereinbelow are described certain more particularly described aspects of the inventions. These particularly recited aspects should not, however, be interpreted to have any limiting effect on any different claims containing different or more general teachings described herein, or that the “particular” aspects are somehow limited in some way other than the inherent meanings of the language and formulas literally used therein.

[0141] The present invention may be understood more readily by reference to the following detailed description of various aspects of the invention and the examples included therein and to the Figures and their previous and following description.REFERENCES[1] H. D. Lim, B. Lee, Y. Bae, H. Park, Y. Ko, H. Kim, J. Kim, K. Kang, Chem. Soc. Rev. 2017, 46, 2873-2888.[2] P. G. Bruce, S. A. Freunberger, L. J. Hardwick, J. M. Tarascon, Nat. Mater. 2012, 11, 19- 29.[3] P. Hartmann, C. L. Bender, M. Vracar, A. K. Durr, A. Garsuch, J. Janek, P. Adelhelm, Nat. Mater. 2013, 12, 228-232.[4] H. Yadegari, Q. Sun, X. Sun, Adv. Mater. 2016, 28, 7065-7093.[5] N. Xiao, X. Ren, W. D. McCulloch, G. Gourdin, Y. Wu, Acc. Chem. Res. 2018, 51, 2335-2343.[6] L. Qin, L. Schkeryantz, J. Zheng, N. Xiao, Y. Wu, J. Am. Chem. Soc. 2020, 142, 11629— 11640.[7] X. Ren, Y. Wu, J. Am. Chem. Soc. 2013, 135, 2923-2926.[8] L. Qin, N. Xiao, S. Zhang, X. Chen, Y. Wu, Angew. Chem. Int. Ed. 2020, 59, 10498- 10501.[9] K. G. Gallagher, S. Goebel, T. Greszler, M. Mathias, W. Oelerich, D. Eroglu, V. Srinivasan, Energy Environ. Sci. 2014, 7, 1555-1563.

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Claims

CLAIMSWhat is claimed is:

1. A rechargeable battery, the rechargeable battery comprising: a cathode; an anode comprising a metal, wherein the metal forms a metal-ion of a superoxideperoxide redox pair; and an electrolyte, wherein the electrolyte comprises a non-aqueous solvent, a first electrolyte salt, and a second electrolyte salt, wherein the second electrolyte salt comprises an anionic moiety and a solvent moiety, wherein the solvent moiety is covalently coupled to the anionic moiety.

2. The rechargeable battery of claim 1, wherein the second electrolyte salt is an asymmetric molecule.

3. The rechargeable battery of any one of the preceding claims, wherein the second electrolyte salt comprises a high donor number anion and a metal-ion.

4. The rechargeable battery of any one of the preceding claims, wherein the non-aqueous solvent comprises a high donor-number solvent.

5. The rechargeable battery of any one of the preceding claims, wherein the non-aqueous solvent is chosen from DME, DEGDME, TEGDME, DMF, DMSO, and combinations or variations thereof.

6. The rechargeable battery of any one of the preceding claims, wherein the first electrolyte salt comprises a metal-ion.

7. The rechargeable battery of any one of the preceding claims, wherein the metal-ion of the redox pair, of the first electrolyte salt, and the second electrolyte salt are chosen from K, Li, Na, Rb, or Cs.

8. The rechargeable battery of any one of the preceding claims, wherein the metal-ion of the redox pair, of the first electrolyte salt, and the second electrolyte salt are the same or different.

9. The rechargeable battery of any one of the preceding claims, wherein the electrolyte comprises less than 0.50M of the second electrolyte salt in the non-aqueous solvent.

10. The rechargeable battery of any one of the preceding claims, wherein the electrolyte comprises at least 0.5M of the first electrolyte salt in the non-aqueous solvent.

11. The rechargeable battery of any one of the preceding claims, wherein the cathode comprises a metal oxide, wherein the metal of the metal oxide comprises the metal of the superoxide-peroxide redox pair.

12. The rechargeable battery of any one of the preceding claims, wherein the cathode comprises a binder.

13. The rechargeable battery of any one of the preceding claims, wherein the anode comprises a protective layer.

14. The rechargeable battery of any one of the preceding claims, comprising a current collector.

15. The rechargeable battery of any one of the preceding claims, wherein the second electrolyte salt prevents O2 evolution in the electrolyte.

16. The rechargeable battery of any one of the preceding claims, wherein the rechargeable battery operates at more than 70% columbic efficiency (CE), more than 80% CE, more than 90% CE, or more than 95% CE.

17. The rechargeable battery of any one of the preceding claims, wherein the rechargeable battery exhibits a discharge capacity of more than 275 mAh / g-1KO2, more than 300 mAh / g-1KO2, or more than 325 m Ah / g'1K02.

18. The rechargeable battery of any one of the preceding claims, wherein the rechargeable battery exhibits cell stability after 100 cycles and after 120 cycles.

19. The rechargeable battery of any one of the preceding claims, wherein the rechargeable battery exhibits a lifespan of more than 800 hours, more than 1000 hours, more than 1200 hours, or more than 1400 hours when the rechargeable battery is cycled to a depth of discharge of 85% or less.

20. A method of making the rechargeable battery of any one of claims 1-19.

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