US 2016.0006089A1 (19) United States (12) Patent Application Publication (10) Pub. No.: US 2016/0006089 A1 Wu et al. (43) Pub. Date: Jan. 7, 2016
(54) POTASSIUM-OXYGEN BATTERIES BASED Publication Classification ON POTASSIUMSUPEROXDE (51) Int. Cl. (71) Applicants: Yiying WU, Columbus, OH (US); EY 2. 3. Xiaodi REN, Columbus, OH (US) HOLM. I.2/02 (2006.01) HOLM 4/96 2006.O1 (72) Inventors: Yiying Wu, Columbus, OH (US); Xiaodi (52) U.S. Cl. ( ) Ren, Columbus, OH (US) CPC ...... H0IM 12/08 (2013.01); H01 M 4/96 (2013.01); H0IM 4/9041 (2013.01); H0IM (21) Appl. No.: 14/762,768 12/02 (2013.01); HOIM2220/30 (2013.01); HOIM 2300/0028 (2013.01) (22) PCT Fled: Jan. 23, 2014 (57) ABSTRACT Potassium-oxvgenygen (K( O.)2) batteries based on ppotassium (86). PCT No.: PCT/US14/12730 superoxide (KO) are provided. The K-O batteries can S371 (c)(1), exhibit high specific energy a low discharge?charge potential (2) Date: UL 22, 2015 gap (e.g., a discharge?charge potential gap of less than 50 mV. 9 at a current density of 0.16 mA/cm) without the use of any catalysts. The discharge product of the K-O batteries is O O K—O, which is both kinetically stable and thermodynami Related U.S. Application Data cally stable. As a consequence of the stability of the discharge (60) Provisional application No. 61/755,753, filed on Jan. product, the K-O batteries can exhibit improved opera 23, 2013. tional stability relative to other metal-air batteries.
DISCHARGE K+e CHARGE
K"+O+e DISCHARGE
K K" ELECTROLYTE POROUS CARBON Patent Application Publication Jan. 7, 2016 Sheet 1 of 10 US 2016/0006089 A1
Patent Application Publication Jan. 7, 2016 Sheet 2 of 10 US 2016/0006089 A1
O D E O O
CC Y Z (u0/Wu)ALISN3OLN3&Juno Patent Application Publication Jan. 7, 2016 Sheet 3 of 10 US 2016/0006089 A1 Q D E C CN lii s Z CC O CMO (u0/Wu) ALISN3OLN3&Yno Patent Application Publication Jan. 7, 2016 Sheet 4 of 10 US 2016/0006089 A1 AHELIVEºo-) (W) WLOA Patent Application Publication Jan. 7, 2016 Sheet 5 of 10 US 2016/0006089 A1 (W) WITOW Patent Application Publication Jan. 7, 2016 Sheet 6 of 10 US 2016/0006089 A1 (n'e) ALISNLN Patent Application Publication Jan. 7, 2016 Sheet 7 of 10 US 2016/0006089 A1 s L L 2 CD a. Y C a. O 5 C/O S. C/O ?h OO ?h Y O L L a. ? O O S (n'e) ALISNLN Patent Application Publication Jan. 7, 2016 Sheet 8 of 10 US 2016/0006089 A1 g s ?h Z s co E Y is Lo Y O O d N cy cN N (W) SWIION Patent Application Publication Jan. 7, 2016 Sheet 9 of 10 US 2016/0006089 A1 LL CD Y cC C CD |CO d St. cy CN ce (W) SWITOW Patent Application Publication Jan. 7, 2016 Sheet 10 of 10 US 2016/0006089 A1 S CN E CD - E CO Sto E. c i? N FH is O O s s (W) SWLION US 2016/0006089 A1 Jan. 7, 2016 POTASSUM-OXYGEN BATTERIES BASED potassium salt can be, for example, KPF. The K-O batter ON POTASSIUMSUPEROXDE ies can further comprise a separator that mechanically sepa rates the first electrode and the second electrode (e.g., a glassy STATEMENT REGARDING FEDERALLY fiber separator). SPONSORED RESEARCH ORDEVELOPMENT 0008. The K-O batteries are based on the one-electron 0001. This invention was made with Government Support reduction of oxygen to Superoxide. During discharge of the under Grant No. DMR-0955471 awarded by the National potassium-oxygen battery, a discharge product can beformed Science Foundation. The Government has certain rights in the at the second electrode that is thermodynamically stable and invention. kinetically stable. During discharge of the K-O batteries, the one-electron reduction of oxygen at the second electrode TECHNICAL FIELD can form a Superoxide (O). Once formed, the Superoxide is captured by potassium ions, forming KO. During discharge 0002 This application relates generally to potassium-oxy of the K-O battery, reaction (1) occurs at the second elec gen (K-O.) batteries based on potassium Superoxide (KO). trode BACKGROUND 0003 Metal-air batteries (MABs) have attracted interest and during charge of the K-O battery, reaction (2) occurs at for a variety of energy storage applications, largely because the second electrode MABs exhibit much larger specific energies than current KO-->O+e +K" (2). Li-ion batteries. In particular, Li-O batteries have attracted attention from researchers due to their high specific energy. The net discharge reaction for the K-O battery is 0004. In spite of their potential, lithium-oxygen batteries K+O->KO (AG'=-239.4 kJ/mol, E=2.48 V), correspond have significant shortcomings that have hampered their wide ing to a theoretical energy density of 935 Wh/kg for the spread adoption. The discharge process in Li-O batteries battery (based on the mass of KO). involves the reduction of oxygen to Superoxide (O), the 0009. By exploiting the one-electron quasi-reversible formation of LiO, and subsequent disproportionation of the O/O redox couple, K-O batteries can be designed that LiO into LiO and O, the charge process in Li-O batter possess a high specific energy, a low discharge?charge poten ies is the direct oxidation of LiO into O. As a result of the tial gap (e.g., a discharge?charge potential gap of less than 50 asymmetric reaction mechanism, the charge reaction in mV at a current density of 0.16 mA/cm), high round-trip Li O batteries has a much higher overpotential (-1-1.5V) energy efficiency (e.g., that possess a round-trip energy effi than the discharge reaction (-0.3 V). As a consequence, ciency of >95%), and good recyclability (e.g., that are Li O batteries exhibit a relatively low round-trip energy rechargeable). efficiency of around 60%. In addition, the instability of the electrolyte and carbon electrode under the high charging DESCRIPTION OF DRAWINGS potential (>3.5 V) contributes to the low rechargeability of 0010 FIG. 1 is a schematic illustration of a K-O battery. Li-O batteries. In addition, the insulating nature of LiO. 0011 FIG. 2A is a plot of cyclic voltammograms for oxy hinders the charge transfer reactions and result in a limited gen reduction and oxidation on a glassy carbon electrode battery capacity. (three-electrode setup) in oxygen-Saturated acetonitrile con 0005 Improved battery designs are needed to provide taining 0.1 MTBAPF, 0.1 M LiCIO, and 0.1 M KPF. The MABs that overcome the shortcomings of existing Li-O. current density of the oxygen reduction and oxidation in the battery designs. presence of the LiClO electrolyte was enlarged three times for clarity. Good reversibility of the O/O redox couple can SUMMARY be observed in the presence of the tetrabutylammonium cat 0006 Potassium-oxygen (K-O.) batteries based on ion (TBA) due to its large size (and thus low charge density). potassium Superoxide (KO) are provided. Potassium-oxy 0012 FIG. 2B is a plot of cyclic voltammograms for oxy gen batteries can comprise a first electrode comprising potas gen reduction and oxidation on a porous carbon electrode sium, a second electrode, and an electrolyte disposed between (two-electrode battery setup) in oxygen-Saturated the first electrode and the second electrode. dimethoxyethane (DME) containing 0.5 M KPF6. Oxygen 0007. The first electrode can comprise potassium metal pressure during measurement was 1 atm. (e.g., potassium metal foil). The second electrode can com (0013 FIG. 3A is a plot of voltage over time for the first prise a porous carbon electrode. The porous carbon electrode discharge and the first charge cycle of a K-O battery includ can comprise a metal foam framework (e.g., a Nifoam frame ing 0.5 M KPF in DME as an electrolyte. Following mea work), carbon (e.g., a carbon black powder), and a binder surement of the first discharge curve, the K metal electrode (e.g., a polymeric binder Such as polytetrafluoroethylene was replaced with a fresh K metal electrode prior to measure (PTFE)). After discharge of the K-O battery, the second ment of the first charge curve. Both the first discharge curve electrode can further comprise KO. The electrolyte can be a and the first charge curve were measured at a current density liquid electrolyte comprising potassium cations and an apro of 0.16 mA/cm. The electrode geometric area was 0.64 cm. tic solvent. For example, the electrolyte can be a K" electro The horizontal dash line indicates the calculated thermody lyte solution comprising an ether solvent and a potassium salt. namic potential of the K-O battery. In some embodiments, the ether solvent can comprise a sol (0014 FIG. 3B is a plot of voltage over time for the first vent selected from the group consisting of dimethoxyethane discharge and the first charge cycle of a Li-O battery (DME), diglyme, tetraglyme, and butyl diglyme. In certain including 1 M LiCFSO intetraglyme as an electrolyte. Both embodiments, the ether solvent can comprise a mixture of the first discharge curve and the first charge curve were mea diglyme and butyl diglyme (e.g., in a Volume ratio of 2:5). The sured at a current density of 0.16 mA/cm. The electrode US 2016/0006089 A1 Jan. 7, 2016 geometric area was 0.64 cm. The horizontal dash line indi 0023. As described above, the first electrode of the K-O- cates the calculated thermodynamic potential of the Li-O. batteries (e.g., the anode of the K-O batteries) can comprise battery. potassium. The potassium can be, for example, potassium 0015 FIG. 4A is a plot of the overlayed X-ray diffraction metal (e.g., a potassium foil). The first electrode can be fab (XRD) pattern of a carbon electrode after the discharging ricated in any suitable geometry so as to afford a functioning process (bottom trace) and a KO-loaded electrode after the K-O battery having the dimensions and performance char charging process (top trace). Also included are lines repre acteristics desired for a particular application. For example, senting the standard XRD pattern of KO (JCPDF No. the first electrode can be in the form of a metal wire, metal 43-1020). grid, metal mesh, expanded metal, metal foil, or metal sheet. 0016 FIG. 4B is a plot of the overlayed Raman spectra of In certain embodiments, the first electrode can comprise a carbon electrode before the discharging process (bottom potassium metal foil. trace) and after the discharging process (top trace). 0024. The K-O, batteries further comprise a second elec 0017 FIG. 5 is a plot of voltage over time for the charging trode. The second electrode functions as a cathode during process of a K-O battery including an artificial discharged discharge of the battery. The second electrode can be fabri electrode (a KO-loaded electrode). The charge curve were cated in any suitable geometry so as to afford a functioning measured at a current density of 0.16 mA/cm K-O battery having the dimensions and performance char 0018 FIG. 6 is a plot of the first two continuous battery acteristics desired for a particular application. For example, discharge-charge cycles of a K-O battery including 0.5 M during discharge of the K-O battery, the second electrode KPF in a butyl diglyme/diglyme mixture (volume ratio 2:5) reacts with molecular oxygen (e.g., air or O gas). Accord as an electrolyte. Both the discharge curves and the charge ingly, the second electrode can be an electrode configured to curves were measured at a current density of 0.16 mA/cm. facilitate an electrochemical reaction with O gas. For 0019 FIG. 7 is a plot of the voltage profile of potassium example, the second electrode can be a gas diffusion elec electrodeposition and dissolution at 0.16 mA/cm in a KIK trode. Gas diffusion electrodes that are permeable to oxidiz symmetric cell (electrolyte=0.5 M KPF in a mixture of butyl ing gases (e.g., that are permeable to O.) are known in the art. diglyme and diglyme (volume ratio of 2:5)). Ether and poly Suitable electrodes can comprise a porous electrode body ether solvents, particularly those containing terminal oxygen through which oxygen or air can diffuse without the applica moieties, can coordinate to alkali metal ions and generate tion of elevated pressure. Solvated electrons or metal anions. These species can be 0025. The second electrode can be fabricated from a mate highly reductive in nature, and may induce the decomposition rial or composition that conducts electrical current. For of the electrolyte. Mixtures of butyl diglyme and diglyme example, the second electrode can comprise a metal mesh or (e.g., in a volume ratio of 2:5) were found to stable in cells foam (e.g., a nickel foam), a conductive fabric (e.g., a woven containing a potassium metal electrode due to the limited or nonwoven fabric formed from conductive fibers such as tendency of butyl diglyme and diglyme to coordinate potas carbon fibers or metal filaments), a gas diffusion media com sium cations. posed of carbon, or carbon on a metal mesh or foam (e.g., carbon on a nickel foam). DETAILED DESCRIPTION 0026. In some embodiments, the second electrode com prises a porous carbon electrode. The porous carbon electrode 0020 Disclosed herein are potassium-oxygen batteries. can comprise a metal foam framework (e.g., a Nifoam frame Potassium-oxygen batteries can comprise a first electrode work), carbon (e.g., a carbon powder, Such as carbon black comprising potassium, a second electrode, and an electrolyte powders commercially available under the trade name disposed between the first electrode and the second electrode. SUPER PR from TIMCAL Ltd.), and a binder (e.g., a poly 0021. The K-O batteries are based on the one-electron meric binder such as polytetrafluoroethylene (PTFE)). After reduction of oxygen to Superoxide. The discharge product of discharge of the battery, the second electrode can further the K-O batteries (e.g., KO) can be both kinetically stable comprise potassium Superoxide (KO), in particular solid and thermodynamically stable. During discharge of the KO. The solid potassium Superoxide can be amorphous or K-O battery, the one-electron reduction of oxygen at the crystalline. In certain embodiments, the Solid potassium second electrode forms Superoxide. Once formed, the Super Superoxide comprises crystalline KO. oxide is captured by potassium ions, forming potassium superoxide. By exploiting the quasi-reversible O/O redox 0027. The second electrode can optionally further com couple, K-O batteries can be designed that possess a high prise an electrocatalyst. For example, the second electrode specific energy, a low discharge?charge potential gap, high can comprise a catalyst for the reduction of oxygen to Super round-trip energy efficiency, and good recyclability. oxide in the course of discharging, a catalyst for the oxidation of Superoxide to oxygen in the course of charging, or a com 0022. During discharge of the K-O battery, reaction (1) bination thereof (e.g., a single electocatalyst that catalyzes occurs at the second electrode both the reduction of oxygen to Superoxide and the oxidation O+e +K"->KO, (1) of Superoxide to oxygen, or a first electocatalyst that catalyzes and during charge of the K-O battery, reaction (2) occurs at both the reduction of oxygen to Superoxide and a second the second electrode electrocatalyst that catalyzes the oxidation of Superoxide to oxygen). In certain embodiments, the second electrode does not comprise an electrocatalyst. The net discharge reaction for the K-O battery is 0028. The electrolyte can be any suitable electrolyte. The K+O->KO (AG'=-239.4 kJ/mol, E=2.48 V), correspond electrolyte can be a liquid electrolyte comprising potassium ing to a theoretical energy density of 935 Wh/kg for the cations and an aprotic solvent. For example, the electrolyte battery (based on the mass of KO). can be a K" electrolyte solution comprising an ether solvent. US 2016/0006089 A1 Jan. 7, 2016 0029. The ether solvent can be, for example, an aprotic KO. The KO can be dissolved in the liquid electrolyte, glycol diether, such as a mono- or oligoalkylene glycol deposited on the second electrode during discharging, or diether (e.g., a mono- or oligo-C-C-alkylene glycol diether combinations thereof. Once formed, the KO can be isolate in Such as a mono- or oligoethylene glycol diether). In certain Solid form, in particular in crystalline form, from the second embodiments, the ether solvent comprises an aprotic glycol electrode by mechanical means after disassembling the diether that does not include terminal oxygen moieties (e.g., K—O battery. The KO can also be isolate from the liquid an aprotic glycol diether capped with methyl or ethyl groups). electrolyte, for example by crystallization. The isolation of Examples of suitable ether solvents include dimethoxyethane KO from the liquid electrolyte can be done batch-wise or (DME), diglyme (bis(2-methoxyethyl)ether), butyl diglyme, continuously. For example in a continuous process new liquid triglyme (triethylene glycol dimethyl ether), tetraglyme (tet electrolyte is added to the battery while liquid electrolyte raethylene glycol dimethyl ether), as well as mixtures thereof. comprising KO is removed during discharging in Such a 0030. In some embodiments, the ether solvent comprises a Solvent selected from the group consisting of dimethoxy manner, that the total volume of the electrolyte in the cell is ethane, diglyme, tetraglyme, and butyl diglyme. In certain kept constant. embodiments, the ether solvent comprises a mixture of dig 0038. The examples below are intended to further illus lyme and butyl diglyme (e.g., in a Volume ratio of 2:5). trate certain aspects of the devices described herein, and are 0031. The electrolyte can comprise any suitable potas not intended to limit the scope of the claims. sium-containing conductive salt that is soluble in the aprotic Solvent. Suitable potassium salts are known in the art, and include, for example, KPF, KBF, KCIO, KASF EXAMPLES KCFSO, potassium bis(oxalato)borate, potassium difluoro 0039. Overview Lithium-oxygen (Li-O.) batteries are (Oxalate)borate, KSiF. KSbF. KC(CFSO), regarded as one of the most promisingenergy storage systems KN(CFSO), and combinations thereof. In certain embodi for future applications. However, the energy efficiencies of ments, the K electrolyte solution comprises KPF. Li-O batteries are greatly undermined by the large overpo 0032. If desired, the electrolyte can further comprise addi tentials of the discharge (formation of LiO) and charge tional components, including additional aprotic solvents, or a (oxidation of LiO) reactions. In existing Li-O batteries, crown ether (e.g., 1,4,7,10,13,16-hexaoxacyclooctadecane). parasitic reactions of the electrolyte and the carbon electrode 0033. The K-O batteries can further comprise a separa induced by the high charging potential cause a decay of tor that mechanically separates the first electrode and the capacity and limit the battery life. Potassium-oxygen second electrode. The separator can be disposed between the (K-O.) batteries are described below that use K" ions to first electrode and the second electrode, so as to keep the two capture O to form a thermodynamically stable KO as the electrodes apart to prevent electrical short circuits. The sepa discharge product. This allows for the batteries to operate rator can be fabricated from any suitable material that allows through the one-electron redox process of O/O. Without for the transport of ionic charge carriers between the two the use of catalysts, these K-O batteries show a low dis electrodes. charge?charge potential gap of less than 50 mV at modest 0034 Suitable separators are known in the art, and include current densities. polymer films (e.g., porous polymer films, such as porous polyolefin films), polymeric nonwovens, and inorganic non 0040 Introduction wovens (e.g., glass fiber nonwovens and ceramic fiber non 0041 Li O, batteries have attracted attention from wovens). In some embodiments, the separator can comprise a researchers due to their high specific energy. Non-aqueous glassy fiber separator. lithium-oxygen batteries, which are based on the net reaction 0035. The K-O batteries can be rechargeable. The of 2Li+O 0042. Materials and Methods Li O batteries is that LiO is unstable due to the high 0043 Swagelok Cell Assembly charge density of Li". Based on Hard-Soft Acid-Base 0044 SUPER PR carbon powder (obtained from TIM (HSAB) theory, O should be increasingly stable with CAL Ltd.) was ground with polytetrafluoroethylene (PTFE) decreasing cation charge density. Potassium ions carry a powder (Sigma Aldrich, 1 micron size) (weight ratio=1:1). A lower charge density than both lithium and sodium ions. This slurry was then formed by addition of a solution of 0.5 M explains why, in contrast to LiO and NaO, KO is commer KPF (Sigma Aldrich, 99.9%) in 1,2-dimethoxyethane cially available and stable up to its melting point (560° C.). (DME, Novolyte Tech.) or diglyme (Sigma Aldrich, 99.5%). 0051 Cyclic voltammograms for oxygen reduction and The slurry was casted into a Nickel foam disk (outer diam oxidation on a glassy carbon electrode in the presence of a 0.1 eter=12 mm; thickness=1.7 mm) to form a porous carbon air M solution of three different cations (tertbutylammonium electrode. The Swagelok cell was assembled by Stacking a cations, 0.1 MTBAPF; lithium cations, 0.1 M LiClO; and potassium metal foil (Sigma Aldrich, 99.5%), a Whatman potassium cations, 0.1 M KPF) in an aprotic Solvent (oxy glass fiber separator (saturated with an electrolyte (0.5 M gen-saturated acetonitrile) are shown in FIG. 2A. In the pres KPF dissolved in either DME or diglyme)), and the air elec ence of the K electrolyte, the gap between the oxygen reduc trode. The cell was sealed with an O-ring (Macro Rubber, tion potential and the oxygen oxidation potential is much Viton) except for valves introducing dried oxygen gas at a Smaller than the gap between the oxygen reduction potential pressure of 1 atm. and the oxygen oxidation potential in the presence of a Li 0045 An artificial discharged battery was constructed as electrolyte. The higher current density in the presence of the described above, except that the electrode was formed using K" electrolyte may be the result of the higher conductivity of a slurry of carbon powder, PTFE, and KO (Sigma Aldrich) KO, (~10 S/cm at 10° C.). These results suggest that a (ratio=1:1:1). All solvents, including diethylene glycol dibu K Obattery could operate at lower overpotentials (and thus tyl ether (butyl diglyme, Sigma Aldrich, >99%) and tetrag significantly higher round-trip energy efficiency) than a lyme (Novolyte), were dried over 4. A molecular sieves. Cell Li-O battery. The reactions expected to occur on the porous assembly was performed in a glovebox filled with high purity carbon electrode during discharging and charging of the bat Argon. tery would be as follows: 0046 Electrochemical Tests Dishcharge: O+e +K'->KO (1) 0047 Batteries were tested using a Maccortesting station (model 4304), with discharge and charge current density of Charge: KO-->O+e +K" (2) 0.16 mA/cm (geometric area) and within a voltage range of The net discharge reaction for the battery would be between 2.0 V and 3.2V (vs. K"/K). To study the influence of K+O->KO (AG'=-239.4 kJ/mol, E=2.48 V), correspond different cations, oxygen reduction reactions were performed ing to a theoretical energy density of 935 Wh/kg for the in the presence of 0.1 M of different salts, e.g. tetrabutylam battery (based on the mass of KO). monium hexafluorophosphate (TBAPF, Sigma Aldrich, 0.052 A Swagelok battery was fabricated containing a electrochemical grade), LiClO4 (Alfa Aesar, electrochemical potassium metal foil, a glassy fiber separator and a porous grade) and KPF. Cyclic voltammetry studies were carried carbon electrode prepared from a mixture of a SUPER PR) out in a three-electrode system using a Gamry potentiostat, carbon powder and a binder in a Ni foam framework. 0.5 M with a glassy carbon working electrode (3 mm diameter), a KPF in an ether solvent (1,2-dimethoxyethane (DME) or platinum wire counter electrode, and a Ag"/Ag non-aqueous diglyme) were used as the electrolyte. For purposes of com reference electrode (10 mM AgNO in acetonitrile, from CHI parison, a Li-O battery was constructed in a similar man Inc.). Acetonitrile was distilled with CaH prior to use. ner, except that a 1 M solution of LiCFSO intetraglyme was 0.048 Characterization used as the electrolyte. 0049. After battery tests, air electrodes were washed with 0053. The electrochemical behavior of the carbon cathode DME to remove residual conducting salt, and then dried in the K-O battery was investigated by cyclic Voltammetry under vacuum. The structure of discharge product was char in the two-electrode battery setup (K metal served as the acterized by X-ray diffractometer (Bruker D8 Advance, Cu counter and reference electrode). The cyclic Voltammograms KC. Source, 40 kV, 50 mA) using an air-sensitive sample are shown in FIG. 2B. Before oxygen was purged into the holder equipped with a moisture barrier film. Raman spectra two-electrode battery setup, only the double layer capacitor of the discharged air electrodes were obtained using a micro behavior of carbon was observed. Once oxygen was intro scope Raman spectrometer (in Via, Renishaw) at a 633 nm duced into the two-electrode battery setup, oxygen reduction excitation wavelength (laser power 6 mW) using an air-sen and oxidation processes could be clearly seen. The difference sitive sample holder equipped with a ZnSe optical window. between the onset potential for oxygen reduction and the Side products in the air electrodes were extracted with DO onset potential for oxygen oxidation is relatively small. The (Sigma Aldrich, 99.9 atom % D) and characterized using "H oxidation process observed at potentials above 3.5V is attrib NMR spectroscopy (Bruker, 400 MHz). uted to the decomposition of carbon electrode or electrolyte. 0050 Results and Discussion Improved battery designs This suggests that the oxidation process can be complete and chemistries offer the potential to provide batteries that within a potential range where the carbon electrode and the overcome the shortcomings of existing Li-O battery electrolyte are relatively stable. designs. The O/O, redox couple offers an attractive elec 0054 The first discharge and charge voltage profiles of the trochemical platform for battery development. The O/O. K—O battery and the Li-O battery are shown in FIGS.3A redox couple is quasi-reversible in aprotic solvents. As Sug and 3B respectively. The stable discharge plateau is at 2.70V gested by the fact that O. has a bond length (1.28-1.33 A) (overpotential mast 26 mV) for the Li-O, battery and at closer to O. (1.21 A) than to O(1.49A), the energy barrier 2.47V (m-10 mV) for the K-O, battery. More impor for the conversion of Oto O is lower than the energy barrier tantly, in the Subsequent charging processes, the Voltage is as for the conversion of O, to O. However, a key problem in low as 2.50-2.52 V for the K-O battery. The charge over US 2016/0006089 A1 Jan. 7, 2016 potential (m) of ~20-40 mV observed for the K-O bat lyte after battery discharge. The stable voltage profile of tery is significantly smaller than charge overpotential potassium electrodeposition and electrodissolution cycles observed for the Li O battery. Moreover, within this small (FIG. 7) suggest that the electrolyte itself is stable when used charging potential range, almost 90% of the discharged prod in conjunction with a potassium metal electrode. However, uct can be oxidized. In contrast, in the case of the Li-O. when side products diffuse to the metal electrode, they can battery, only half of the discharged product could be removed easily react with potassium, forming an insulating layer on even when the voltage reaches 4.0V, where the ether electro the surface of the metal electrode. This phenomenon was lyte and the carbon electrode become unstable. The charge/ visually observed when the K-O batteries were disas discharge potential gap of about 50 mV observed for the sembled and inspected after the tests described above. The K-O battery is the lowest/discharge potential gap ever accumulation of this insulating layer during the course of reported for a metal-oxygen battery. Compared to the Li-O. several cycles of rechargeability likely results in the observed battery, which has a potential gap of 1V, the K-O battery decay in battery capacity. can provide an exceptional round-trip energy efficiency of 0059 Conclusions >95%. 0060. In conclusion, a major obstacle for developing 0055 To confirm the formation of KO during discharge, highly efficient Li O batteries lies in the large overpoten the discharged cathode was characterized by X-ray diffrac tials of the electrochemical reactions (i.e., the discharge and tion and Raman spectroscopy. As shown in FIG. 4A, X-ray charge reactions). Described above is a K-O battery that diffraction (XRD) analysis confirmed that crystalline KO takes advantage of the reversibility of the O/O, redox was the dominant discharge product, as the peaks in the XRD couple. The discharge and charge reactions in the K-O- pattern after discharge correspond to peaks in the standard battery exhibit significantly lower overpotentials than the XRD pattern of KO. No evidence of other potassium oxides, discharge and charge reactions in Li-O batteries. The Such as potassiumperoxide (KO) or potassium oxide (KO) K-O battery exhibits a charge/discharge potential gap was seen. Raman spectra of the cathode (see FIG. 4B) also smaller than 50 mV at a current density of 0.16 mA/cm. showed the characteristic intense peak of potassium SuperoX XRD analysis and Raman spectroscopy have confirmed the ide at 1142 cm. The other two broad peaks in the formation of KO during discharge. Experiments with an 0056 Raman spectra can be assigned to the G band (1582 artificial discharged battery have confirmed that the reaction cm) and D band (1350 cm) of the carbon material in the in the charging process is the oxidation of KO. The discharge electrode. product (KO) is both kinetically and thermodynamically 0057 The oxidation of KO, at a low overpotential was stable. As a consequence of the stability of the discharge further confirmed by charging an artificial discharged elec product (KO), the K-O batteries can operate under a wider trode. The artificial discharged electrode was prepared by range of temperatures. loading slurry of hand-milled KO. carbon powder, and binder (weight ratio=1:2:1) into a Ni foam. The charge volt 0061 The devices of the appended claims are not limited age profiles of the K-O battery containing the artificial in scope by the specific devices described herein, which are discharged electrode is shown in FIG. 5. As shown in FIG. 5, intended as illustrations of a few aspects of the claims. Any the main charge process remains at a low Voltage range devices that are functionally equivalent are intended to fall between 2.55 and 2.90V. In the absence of KO, the voltage within the scope of the claims. Various modifications of the goes beyond 4.0 V in less than 10 minutes, suggesting that the devices in addition to those shown and described herein are reaction observed is the oxidation of KO, not the oxidation of intended to fall within the scope of the appended claims. the electrolyte. The slight increase in potential relative to the Further, while only certain representative devices disclosed potential shown in FIG. 3A likely results from the fact that herein are specifically described, other combinations of the electronic contact between this the mechanically mixed KO devices also are intended to fall within the scope of the and carbon in the artificial discharged electrode is not as good appended claims, even if not specifically recited. Thus, a as that formed by the electrochemical reaction in the K-O- combination of steps, elements, components, or constituents battery. The amount of KO calculated from the total charge may be explicitly mentioned herein or less, however, other flow in the oxidation process was about 6.9 mg, whereas the combinations of steps, elements, components, and constitu amount of loaded KO was 8.0 mg. The small difference may ents are included, even though not explicitly stated. be due to some of the initial KO2 particles being loosely 0062. The term “comprising and variations thereof as bound to the carbon particles. This finding, along with the used herein is used synonymously with the term “including XRD characterization of the electrode (FIG. 4A) following and variations thereof and are open, non-limiting terms. the charging process that shows only peaks from the Substrate Although the terms “comprising and “including have been Ni foam (with no apparent KO peaks remaining), confirms used hereinto describe various embodiments, the terms “con that the reaction in the charging process is the oxidation of sisting essentially of and "consisting of can be used in place KO. of “comprising and “including to provide for more specific 0058. The K-O battery shows several cycles of embodiments of the invention and are also disclosed. Other rechargeability, although the capacity decays with increasing than where noted, all numbers expressing geometries, dimen cycle number. As shown in FIG. 6, the charge capacity of the sions, and so forth used in the specification and claims are to 2nd cycle is only half of the 1st cycle, and the charge Voltage be understood at the very least, and not as an attempt to limit is also higher. The recyclability of the K-O battery still the application of the doctrine of equivalents to the scope of suffers due to issues with electrolyte stability. Specifically, the claims, to be construed in light of the number of signifi reactive superoxide ions react with the ether solvent during cant digits and ordinary rounding approaches. battery cycling, forming species Such as H2O, potassium 0063. Unless defined otherwise, all technical and scien formate (HCOOK) and potassium acetate (CHCOOK). tific terms used herein have the same meanings as commonly These species could be identified by H NMR in the electro understood by one of skill in the art to which the disclosed US 2016/0006089 A1 Jan. 7, 2016 invention belongs. Publications cited herein and the materials 17. The potassium-oxygen battery of claim 16, wherein the for which they are cited are specifically incorporated by ref ether solvent comprises a solvent selected from the group CCC. consisting of dimethoxyethane, diglyme, tetraglyme, and 1. A potassium-oxygen battery comprising: butyl diglyme. a first electrode comprising potassium; 18. The potassium-oxygen battery of claim 16, wherein the a second electrode; and ether solvent comprises a mixture of diglyme and butyl dig a K" electrolyte solution comprising an ether solvent. lyme. 2. The potassium-oxygen battery of claim 1, wherein the 19. The potassium-oxygen battery of claim 16, wherein the first electrode comprises potassium metal. K" electrolyte solution comprises KPF. 3. The potassium-oxygen battery of claim 1, wherein the 20. The potassium-oxygen battery of claim 16, wherein the second electrode comprises a porous carbon electrode. potassium-oxygen battery further comprises a separator. 4. The potassium-oxygen battery of claim 1, wherein after 21. The potassium-oxygen battery of claim 20, wherein the discharging the battery, the second electrode comprises separator comprises a glassy fiber separator. potassium Superoxide (KO). 22. The potassium-oxygen battery of claim 16, wherein the 5. The potassium-oxygen battery of claim 1, wherein the potassium-oxygen battery exhibits a discharge?charge poten ether solvent comprises a solvent selected from the group tial gap of less than 50 mV at a current density of 0.16 consisting of dimethoxyethane, diglyme, tetraglyme, and mA/cm. butyl diglyme. 23-32. (canceled) 6. The potassium-oxygen battery of claim 1, wherein the 33. A potassium-oxygen battery comprising ether solvent comprises a mixture of diglyme and butyl dig a first electrode comprising potassium; lyme. a second electrode; and 7. The potassium-oxygen battery of claim 1, wherein the an electrolyte; K" electrolyte solution comprises KPF. wherein during discharge of the potassium-oxygen battery, 8. The potassium-oxygen battery of claim 1, wherein the a discharge product is formed that is thermodynamically potassium-oxygen battery further comprises a separator. stable and kinetically stable. 9. The potassium-oxygen battery of claim 8, wherein the 34. The potassium-oxygen battery of claim 33, wherein the separator comprises a glassy fiber separator. first electrode comprises potassium metal. 10. The potassium-oxygen battery of claim 1, wherein the 35. The potassium-oxygen battery of claim 33, wherein the potassium-oxygen battery exhibits a discharge?charge poten second electrode comprises a porous carbon electrode. tial gap of less than 50 mV at a current density of 0.16 36. The potassium-oxygen battery of claim 33, wherein the mA/cm. discharge product comprises potassium Superoxide (KO), 11. The potassium-oxygen battery of claim 1, wherein the and after discharging the battery, the second electrode com potassium-oxygen battery is rechargeable. prises potassium Superoxide (KO). 12. A potassium-oxygen battery comprising: 37. The potassium-oxygen battery of claim 33, wherein the first electrode comprising potassium; electrolyte comprises a K" electrolyte Solution comprising an a second electrode; and ether solvent. an electrolyte; 38. The potassium-oxygen battery of claim 37, wherein the wherein during discharge of the potassium-oxygen battery, ether solvent comprises a solvent selected from the group reaction (1) occurs at the second electrode consisting of dimethoxyethane, diglyme, tetraglyme, and butyl diglyme. 39. The potassium-oxygen battery of claim 37 or 38 claim and wherein during charge of the potassium-oxygen bat 37, wherein the ether solvent comprises a mixture of diglyme tery, reaction (2) occurs at the second electrode and butyl diglyme. 40. The potassium-oxygen battery of claim 37, wherein the 13. The potassium-oxygenbattery of claim 12, wherein the K" electrolyte solution comprises KPF. first electrode comprises potassium metal. 41. The potassium-oxygen battery of claim 33, wherein the 14. The potassium-oxygenbattery of claim 12, wherein the potassium-oxygen battery further comprises a separator. second electrode comprises a porous carbon electrode. 42. The potassium-oxygen battery of claim 41, wherein the 15. The potassium-oxygen battery of claim 12, wherein separator comprises a glassy fiber separator. after discharging the battery, the second electrode comprises 43. The potassium-oxygen battery of claim 33, wherein the potassium Superoxide (KO). potassium-oxygen battery exhibits a discharge?charge poten 16. The potassium-oxygenbattery of claim 12, wherein the tial gap of less than 50 mV at a current density of 0.16 electrolyte comprises a K" electrolyte Solution comprising an mA/cm. ether solvent.