Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M12/00—Hybrid cells; Manufacture thereof
  • H01M12/08—Hybrid cells; Manufacture thereof composed of a half-cell of a fuel-cell type and a half-cell of the secondary-cell type
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M12/00—Hybrid cells; Manufacture thereof
  • H01M12/02—Details
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
  • H01M4/96—Carbon-based electrodes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/409—Separators, membranes or diaphragms characterised by the material
  • H01M50/411—Organic material
  • H01M50/429—Natural polymers
  • H01M50/4295—Natural cotton, cellulose or wood
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M2300/00—Electrolytes
  • H01M2300/0002—Aqueous electrolytes
  • H01M2300/0014—Alkaline electrolytes
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries

Definitions

• the invention relates to a novel Zn-air rechargeable battery with charcoal/graphite cathode and dicarboxyl telechelic polyethylene glycol containing additive, e.g. PEG or POLOXAMER.
• dicarboxyl telechelic PEGs were successfully applied to suppress the formation of dendritic and mossy deposits on the surface of the zinc electrode. The weight of the electrode did not change after the long term test.
• zinc-air batteries over those of based on Li-ions is that zinc is an abundant element in the Earth's crust as opposite to lithium, furthermore, oxygen is available directly from the air.
• the other advantages of the zinc-air batteries are their high energy densities (1350 Wh/kg) and in addition, the aqueous-based electrolytes provide safe operation condition for the high capacity rechargeable batteries.
• the chargeability of these batteries can be granted by developing bifunctional cathodes, which can promote the oxygen evolution reaction (OER, for charging) and oxygen-reduction reaction (ORR, for discharging) [9]
• OER oxygen evolution reaction
• ORR oxygen-reduction reaction
• different electrodes were applied for the charging and discharging processes (using different catalysts) [12-15], while others developed cathode with bifunctional activity providing both reactions using only one electrode [16-19]
• the development of catalyst with high OER activity seems to be a big challenge; and in addition, the control of the morphology of the zinc deposited during the charging process is also a frequently occurring problem [20-23]
• the morphology of the zinc deposition depends mainly on the operation conditions, for instance, at low current density mossy structure is formed., Moreover, upon increasing current densities layer-like deposition (at middle density) can occur, while at high current densities formation of zinc dendrites is expected to take place.
• the morphology of the surface of the zinc electrode can be controlled by appropriate charging protocols [24]
• STAC trimethyloctadecylammonium chloride
• tetrabutylammonium bromide [25]
• nickel, indium [26] dissolved in the electrolyte have been shown to suppress dendrite formation.
• mossy zinc deposition could be reduced using fluorinated surfactants [28]
• Banik and Akolkar used low molecular weight poly(ethylene glycol-diol) (PEG200) for that purpose and report a model that predicts an order of magnitude reduction in the zinc dendrite growth rates in the presence of high concentration of PEG (10000 ppm), consistent with experimental findings [27]
• the invention relates to a rechargeable Zn-air alkaline battery with charcoal-based air cathode and zinc anode, said alkaline battery comprising a dicarboxyl telechelic polymer of C 2 -C 3 alkylene glycol units (subunits or monomeric units), preferably said dicarboxyl telechelic polymer comprising ethylene-oxide units.
• the invention also relates to a rechargeable Zn-air alkaline battery with charcoal-based air cathode and zinc anode, said alkaline battery comprising a dicarboxyl telechelic polymer comprising ethylene-oxide units.
• said dicarboxyl telechelic polymer is used as additive in the electrolyte of the battery.
• said dicarboxyl telechelic polymer reduces the rate of charge transfer process.
• said dicarboxyl telechelic polymer reduces preferably avoids the formation of dendritic and or other type deposits on the Zn electrode.
• poly(alkylene-glycol) according to the invention has a molecular weight, preferably an average molecular weight of not higher than 3500 Da, preferably not higher than 2000 Da, more preferably not higher than 1000 Da.
• the additives are preferably chelating the Zn(ll) ions.
• the Zn-poly-alkylene-glycol(COO) 2 reduce the rate of charge transfer process and, preferably, adsorb onto the surface of the Zn-electrode.
• the dicarboxyl telechelic polymer means a,w dicarboxyl polymer comprising C 2 -C 3 alkylene glycol subunits, wherein the monomers of the polymer are selected from 1,2-ethanediol, 1,2- propanediol, 1,3-propanediol.
• the monomers of the polymer are selected from 1,2-ethanediol, 1,2- propanediol, 1,3-propanediol.
• at least a part of the subunits are ethylene-glycol subunits.
• at least 10% (w/w), at least 20% (w/w), more preferably at least 30% (w/w) or in particular at least 40% (w/w) of the dicarboxyl telechelic polymer consists of ethylene-glycol subunits.
• the dicarboxyl telechelic polymer is dicarboxyl telechelic PEG (a, co dicarboxyl-poly(ethylene glycol)).
• the molecular weight of the dicarboxyl telechelic PEG is not higher than 3300 Da, preferably not higher than 1500 Da.
• dicarboxyl telechelic PEG600 is disclaimed.
• dicarboxyl telechelic PEG, in particular bi-carboxy methyl ether (PEG BCME) is disclaimed.
• PEG BCME bi-carboxy methyl ether
• the molecular weight of the dicarboxyl telechelic PEG is at least 100 or at least 200 Da.
• the molecular weight of the dicarboxyl telechelic PEG is 100 to 1400 Da, preferably 200 to 1000 Da, in particular 300 to 900 Da, highly preferably 400 to 800 Da or 200 to 600 Da, particularly preferably about 600 Da, e.g. 500 to 700 Da.
• dicarboxyl telechelic polymer is a a,w dicarboxyl-poly(ethylene- glycol)-poly(propylene glycol)-poly(ethylene glycol) copolymer (POLOXAMER).
• POLOXAMER dicarboxyl-poly(ethylene- glycol)-poly(propylene glycol)-poly(ethylene glycol) copolymer
• at least 10% (w/w), at least 20% (w/w), more preferably at least 30% (w/w) or in particular at least 40% (w/w) of the dicarboxyl telechelic polymer consists of ethylene-glycol subunits.
• the propylene glycol content of the POLOXAMER is 30-70% w / w, preferably 40-60% w/ w, highly preferably about 50% w/ w.
• the molecular weight of which is not higher than 5000 Da preferably is about 1800 Da.
• the cathode consists (essentially) of graphite and charcoal.
• the battery has an initial cell potential of 1.2 V to 1.6 V, preferably 1.25 V.
• the rechargeable Zn-air alkaline battery cellophane i.e. regenerated cellulose serves as the semi-permeable membrane, i.e., the separator (or diaphragm).
• the electrolyte of the battery contains alkaline hydroxide solution, preferably potassium-hydroxide solution and the dicarboxyl telechelic poly(alkylene-glycol) of the invention as additive.
• the electrolyte of the battery contains only KOH and [Zn(OH) 4 ] 2 and said non-toxic dicarboxyl telechelic PEG additives.
• the battery has an initial cell potential of 1.2 V to 1.6 V, preferably 1.25 V.
• the anode comprises a Zn plate
• the air cathode comprises or consists of graphite and charcoal
• the separator is a semi-permeable membrane made of regenerated cellulose (cellophane)
• the electrolyte comprises KOH and [Zn(OH) 4 ] 2 and non-toxic dicarboxyl telechelic poly(alkylene- glycol) as an additive.
• the concentration of the KOH is 2 to 10 M, preferably about 6 M, and the concentration of the [Zn(OH) 4 ] 2 is 0.1 to 0.5 M, preferably 0.25 M at the initial stage of the battery.
• the battery has an initial cell potential of 1.2 V to 1.6 V, preferably 1.25 V.
• the battery during normal operation of the battery no H 2 gas is developed.
• the anode comprises a Zn plate
• the air cathode comprises or consists of graphite and charcoal
• the separator is a semi-permeable membrane made of regenerated cellulose (cellophane)
• the electrolyte comprises KOH and [Zn(OH) 4 ] 2 and non-toxic dicarboxyl telechelic PEG additives.
• the concentration of the KOH and [Zn(OH) 4 ] 2 is as defined in paragraphe i).
• the concentration of the non-toxic dicarboxyl telechelic PEG additives is 50 to 500 ppm, preferably 50 to 190 ppm, in particular 80 to 160 ppm.
• the concentration of the non-toxic dicarboxyl telechelic PEG additives is 0.5 to 5 x 10 4 M, preferably 1 to 3 x 10 4 M, in particular 1.5. to 2.5 x 10 4 M.
• the dicarboxyl telechelic PEG is 300 to 900 Da, highly preferably 400 to 800 Da or particularly preferably 200 to 500 Da or 200 to 600 Da or about 600 Da, e.g. 500 to 700 Da.
• the anode comprises a Zn plate
• the air cathode comprises or consists of graphite and charcoal
• the separator is a semi-permeable membrane made of regenerated cellulose (cellophane)
• the electrolyte comprises KOH and [Zn(OH) 4 ] 2 and non-toxic dicarboxyl telechelic a,w dicarboxyl- poly(ethylene-glycol)-poly(propylene glycol)-poly(ethylene glycol) copolymer as additive.
• the concentration of the KOH and [Zn(OH) 4 ] 2 is as defined in paragraph ')
• the concentration of the non-toxic dicarboxyl telechelic poly(ethylene-glycol)- poly(propylene-glycol) copolymer (preferably dicarboxyl telechelic POLOXAMER) additives is 0.5 to 5 x 10 4 M, preferably 1 to 3 x 10 4 M, in particular 1.5 to 2.5 x 10 4 M.
• the copolymer is 300 to 2000 Da, highly preferably 300 to 1500 Da or 500 to 1800 Da.
• the electrolyte of the battery contains only KOH and [Zn(OH) 4 ] 2 and non toxic dicarboxyl telechelic PEG additives
• the cathode consists of graphite and charcoal, wherein cellophane serves as the semi-permeable membrane, i.e., the separator, and the cathode skeleton comprises preferably polyethylene and cottonn wherein the battery has an initial cell potential of 1.2 V to 1.6 V, preferably 1.25 V.
• the battery has rectangular cells.
• the charcoal-based air cathode comprises a graphite body.
• the 20 cathode graphite body is a 21 graphite rod whereas th charcoal is 22 activated carbon.
• the 10 anode comprises an 11 Zn plate. At least during operation of the battery both to the cathode and to the anode 60 electric wires are connected.
• the invention relates to the following: 1.
• the invention relates to a rechargeable Zn-air alkaline battery with charcoal-based air cathode and zinc anode, said alkaline battery comprising a dicarboxyl telechelic polymer comprising ethylene-oxide units.
• dicarboxyl telechelic polymer is dicarboxyl telechelic PEG (a,w dicarboxyl-poly(ethylene glycol)) as additive in the electrolyte of the battery, wherein preferably the molecular weight of the dicarboxyl telechelic PEG is not higher than 3300 Da, preferably not higher than 1500 Da.
• dicarboxyl telechelic polymer is polyethylene glycol-polypropylene glycol-polyethylene glycol (POLOXAMER) preferably the molecular weight of which is not higher than 5000 Da, preferably is about 1800 Da.
• POLOXAMER polyethylene glycol-polypropylene glycol-polyethylene glycol
• polyethylene and cotton is the skeleton of the electrode.
• a “dicarboxyl telechelic polymer” means herein an a,w dicarboxyl polymer.
• the dicarboxyl telechelic polymer comprises C 2 -C 3 alkylene glycol subunits.
• a poly(alkylene-glycol) polymer means here a polymer of alkylene-glycol monomers, in particular a polymer of 1,2-ethanediol, 1,2-propanediol and/or 1,3-propanediol derivable by polycondensation with the elimination of water.
• Poly(alkylene-glycol), poly(alkylene-oxide), polyalkylene-glycol or poly(alkylene- oxide are used interchangeably herein and the same type of alternative names may applied to, mutatis mutandis, poly(ethylene-glycols) and poly(propylene-glycols) as well.
• a poly(alkylene-glycol) (or polyalkylene-glycol, used interchangeably) polymer may be a homopolymer of a single type of alkylene glycol subunits or copolymer of more than one type of alkylene glycol subunits.
• the poly(alkylene-glycol) polymer comprises ethylene glycol and/or propylene glycol subunits, preferably comprises at least ethylene glycol subunits.
• Suitable PAGs include polyethylene glycol (PEG) and copolymers of ethylene glycol with propylene glycol (e.g. poloxamers, meroxapols; e.g., PLURONIC ® surfactants.)
• poly(alkylene-glycol) preferably "PEG” or “poly(ethylene glycol),” or a copolymer of ethylene glycol with propylene glycol as used herein, is meant to encompass any water- soluble poly(alkylene-glycol).
• terminal groups and architecture of the poly(alkylene-glycol) polymers, preferably polyethylene glycol) comprising polymers of the invention are carboxylate groups.
• PEG poly(alkylene-glycol)
• Most PEGs include molecules with a distribution of molecular weights (i.e. they are polydisperse).
• Molecular weight refers to the average molecular mass (or “molecular weight”) of a polymer, typically determined by any appropriate method, e.g. size exclusion chromatography or light scattering techniques or can be measured by mass spectrometry or any other appropriate means.
• the size distribution can be characterized statistically by weight average molecular weight (Mw) or by number average molecular weight (Mn), the ratio of which is called the polydispersity index.
• Electrode refers to a substance that is capable of conducting electric current as a result of comprising positively and negatively charged ions, which are able to migrate in the electrolyte, wherein preferably the electrolyte is a solution wherein migration of ions takes place negative and positive terminals (cathode and anode) of an electric circuit, respectively.
• a “separator” is used herein as a permeable membrane placed between a battery's anode and cathode.
• the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.
• FIG. 1 The MALDI-TOF mass spectrum of the dicarboxyl telechelic PEG1500.
• the main series corresponds to the potassiated dicarboxyl telechelic polyethylene glycol.
• the inset reveals the two additional series appearing in the mass spectrum. The numbers on the top of these peaks show the measured and the theoretical m/z values (for the main series, these are shown in brackets).
• the potassium salt of dicarboxyl telechelic PEG ionized by potassium ion is denoted by series A, while series B corresponds to the potassiated monocarboxyl PEG.
• FIG. 3a Long-term discharging of cylindrical primary battery.
• the red solid line represents the fitted curve using a stretched exponential function (equation 1).
• FIG. 4 Charging and discharging of the cylindrical rechargeable battery.
• the charging steps operated at a current density of 7.5 mAcm 2 , while the discharging current density was 0.625 mAcm 2 .
• dicarboxyl telechelic PEG M n : 1500 Da, 2xl0 4 M was added. (Insets show the real time images of the zinc electrode)
• Figure 7 Discharging of the rectangular Zn-Air rechargeable battery in the absence and presence of dicarboxyl telechelic PEG additives during the cycling test: in the absence of dicarboxyl telechelic PEG additives (a), in the presence of dicarboxyl telechelic PEG600 (b), PEG1500 (c) and PEG3300 (d).
• the black solid lines represent the fitted curves by eq. 1.
• Figure 9 The SEM images of the zinc electrode after 68-hour cyclic performance test with the current density of 2 mAcm 2 . with no additive, and with carboxyl telechelic PEG600, PEG1500 and PEG3300, respectively.
• FIG. 12 Charge-discharge test of a battery containing additive dicarboxylic telechelic POLOXAMER (Figure 12a). Magnified diagram of charge-discharge cycles ( Figure 12b). Battery coulomb efficiency over 270 cycles used ( Figure 12c).
• Deposit formation on the surface of Zn-electrode is expected if the charge transfer process is much faster than that of the incorporation of the metallic Zn formed into the crystalline lattice of the Zn electrode. Accordingly, if deposit formation is to be avoided one should fundamentally define conditions to slow down the charge transfer process, i.e., the charge transfer process should be the rate determining step in the overall recharging process.
• the dicarboxylic telechelic poly(alkylene-glycols) used in the batteries of the invention can be prepared from e.g. poly(alkylene-glycols) which are well-known and commercially available and can be obtained from commercial sources.
• terminal carboxyl groups can be synthesized by methods known in the art, e.g. as disclosed in US8067505B2 or by a method described by Fishman, A et al [29] and references cited therein.
• the present inventors focused on the construction of a Zn-air rechargeable battery with heavy metal- free, charcoal-based air cathode applying a,w dicarboxyl-poly(ethylene glycol) electrolyte additives.
• a,w dicarboxyl-poly(ethylene glycol) electrolyte additives were synthesized.
• cylindrical and rectangular cells were made to test the electrochemical performance of the system.
• cyclic voltammetry measurements were carried out to understand the effect of dicarboxyl telechelic additives.
• the invention relates to a novel rechargeable Zn-air alkaline battery developed with charcoal/graphite cathode and zinc anode.
• charcoal/graphite cathode Using of charcoal/graphite cathode, continuous oxygen supply was achieved and it was demonstrated by long-term performance tests that it is an appropriate electrode in the rechargeable Zn-air alkaline battery.
• dicarboxyl telechelic PEGs of different molecular weights 600 Da, 1500 Da, and 3300 Da
• the rechargeable Zn-air alkaline battery of the invention comprises charcoal- based air cathode comprising a graphite body or member, e.g. a 20 graphite rod and a Zn-anode preferably a 11 Zn-plate anode arranged in a cell wherein the anode space and the cathode space are separated by a separator (diaphragm) made of a cellulose membrane e.g. a regenerated cellulose, e.g. cellophane.
• the cell has a rectangular arrangement.
• the 20 cathode is fixed within the cell, e.g. is placed in a frame, e.g.
• the telechelic dicarboxyl poly(alkylene-glycol) is present in the electrolyte, preferably is placed to the same place as the anode, preferably the 11 Zn plate anode, i.e. the anode side of the separator.
• the electrode comprises electrolyte ions for which the separator is permeable.
• the electrode has a flat arrangement.
• the graphite/charcoal air 20 cathode is present in a flat 50 frame to provide mechanical strenth
• the 30 separator to separate the cathode space from the anode space is cellulose and the anode comprises a flat 11 Zn plate surrounded by a 70 reservoir.
• the rechargeable Zn-air alkaline battery is a flexible rechargeable Zn-air alkaline battery, wherein the rechargeable Zn-air alkaline battery has significantly improved mechanical flexibility under repeated bending deformation compared to the conventional Zn-air battery technologies.
• the cell of the flexible rechargeable Zn-air alkaline battery has a planar arrangement with a bendable structure characteristics, e.g. the cells are placed in a frame or separated by a separator or cross-linked each other within the planar arrangement.
• the flexible rechargeable Zn-air alkaline battery may be used for wearable electronics applications.
• dicarboxyl telechelic poly(alkylene-glycol) is used in the electrolyte as additive to reduce In the Zn electrode preferably a Zn plate is used.
• the battery has an initial cell potential of 1.2 V to 1.6 V, preferably 1.25 V.
• Zinc foil 100 x 100 x 0.25mm, 99.9%
• POLOXAMER Mn, starting: 1800 g / mol, propylene glycol content 50% w / w).
• activated carbon i.e., charcoal, (analytical grade), Chromium(VI) oxide (analytical grade), Sulfuric acid (analytical grade), Sodium chloride (analytical grade), Magnesium sulfate (analytical grade) were received from Merck (Darmstadt, Germany).
• the Zn electrodes were cleaned by rinsing them with n-hexane and dried before use.
• Graphite rod with spectroscopic grade was used as graphite rod (Ceramics Praha, Czech Republic, Prague).
• Dichloromethane HPLC grade
• n-Hexane HPLC grade
• Diethyl ether reagent grade
• Zinc oxide analytical grade
• Potassium hydroxide analytical grade
• the Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF MS) measurements were carried out with a Bruker Autoflex Speed mass spectrometer. In all cases 19 kV acceleration voltage was used in the positive ion mode. Ions were detected in the reflectron mode and 21 kV and 9.55 kV were applied as reflectron voltage 1 and voltage 2, respectively. A solid phase laser (355 nm, >100 pJ/pulse) operating at 500 Hz was applied to produce laser desorption and 2000 shots were summed.
• Samples were dissolved in a mixture of water and methanol (80/20 V/V) at a concentration of 10 mg/mL.
• Samples for MALDI-TOF MS were prepared with 2,5-dihydroxy benzoic acid (DHB) matrix. The matrix at a concentration of 20 mg/mL was dissolved in the same water/methanol mixture as the sample.
• the matrix solution, the sample solution and potassiumtrifluoroacetate solution (5 mg/mL in water/methanol (80/20 V/V)), used as the cationization agent, were mixed in a 10:2:1 (v/v/v) ratio (matrix/analyte/cationization agent).
• a volume of 0.5 pL of the solution was deposited onto a metal sample plate and allowed to air-dry.
• the dropping funnel was charged with 2,62 g (26.2 mmol) of Cr0 3 dissolved in 5 mL of water.
• the oxidizing agent was introduced into the reactor for 20 minutes - the highest temperature was 55 °C.
• the reaction mixture was stirred for additional three hours. The color of the mixture changed from orange to green-blue showing the completion of the reaction.
• 25 mL of water was added to the reaction mixture, transferred into a separation funnel and extracted with 3 x 100 mL of CH 2 CI 2 .
• the Zinc-air rechargeable batteries were constructed using charcoal/graphite cathode and zinc anode with two different geometries.
• the 20 cathode compartment was fabricated from polyethylene (PE) skeleton with cylinder (with 4 cm diameter) or rectangular prism (with dimensions: 3 x 3 x 9.5 cm (length x width x height)) shape.
• Cotton finger or lining was connected to the 50 frame (PE skeleton) forming cotton textile walls inside the cylinder or the rectangular prism.
• cellophane used as a semipermeable membrane, i.e. the 30 separator, was inserted inside the cotton cavity.
• the interior space was filled with charcoal (approx.
• the prepared cell was inserted into a 70 reservoir (beaker) with 200 mL volume and filled out through the charcoal bed with 6 M aqueous potassium hydroxide solution containing ZnO at a concentration of 0.25 M.
• the level of the solution in the 70 reservoir (beaker) was kept constant (the height of the lye was 8 cm).
• these PEG derivatives were dissolved and/or emulsified in the KOH/ZnO solution at a concentration of 2 x 10 4 M.
• the electrolyte of the battery contains only KOH and [Zn(OH) 4 ] 2 and non-toxic dicarboxyl telechelic PEG additives.
• the cathode consists of graphite and charcoal. In such configuration, polyethylene and cotton is the skeleton of the electrode, while cellophane serves as the semi-permeable membrane, i.e., the separator. All of the materials used for the construction of Zn-air rechargeable battery are easily available, non-toxic and are met the main criteria of green and sustainable chemistry. Arrangement and a picture from the novel Zn-air rechargeable battery are shown in Fig. 2.
• Fig. 3. shows that the discharge process is stable and the operation of the Zn-air cell is sustainable with the application of charcoal/graphite cathode.
• Fig. 3. shows that the discharge process is stable and the operation of the Zn-air cell is sustainable with the application of charcoal/graphite cathode.
• the discharge curve can well be described using stretched exponential function as shown in Fig. 3. where AE S is the potential change.
• the k s is the rate coefficient of the decay and m is the stretched exponential factor, while the £ is the terminal potential.
• the fitted parameters for £ , AE S , k s and m are 1.22 V, 0.029 V, 0.058 h 1 and 0.606, respectively.
• the charging current density in this case was 7.5 mAcm 2 .
• intensive deposit formation was observed as it is demonstrated in Fig. 4.
• the deposit is more expanded near the side of the electrode due to the higher local current density.
• the structure of the deposit is mainly mossy type, however, dendrite-like crystals have also appeared.
• the intensive charging event was followed by discharging with a current density of 0.625 mAcm 2 . This step removed most of the deposition from the surface of the Zn-electrode, confirming the presence of mossy-type deposit, indicating that deposition and dissolution are overwhelmingly reversible.
• dicarboxyl telechelic PEG1500 was added to the electrolyte.
• the surface of the electrode after the charging remained almost the same as before.
• significant amount of new deposits was not observed in the presence of dicarboxyl telechelic PEG additive, only the size of some deposit increased, which formed during the first cycle.
• the dicarboxyl telechelic PEG shows high efficiency in the suppression of the deposit formation.
• the working, the counter and the reference electrode were zinc wire, graphite and zinc wire, respectively.
• the voltammograms were recorded in the range of -0.5-0.55 V vs. Zn/Zn 2+ .
• the cathodic peaks are detected at a lower potential than -0.1 V, while anodic peaks are around 0.1 V.
• the anodic/cathodic peak separations are higher than in the additive-free system.
• Shimizu et. al. [20] for the anodic peak applying anionic additives in the electrolyte.
• the difference between the position of anodic and cathodic peaks reveals higher overpotential, however, the difference is low compared to other types of additives applied by Trudgeon et. al.
• the CV figures reveal the shifts for both the anodic and cathodic peak positions.
• the cathodic shifts are 25 mV, 24 mV and 52 mV, while the shifts of the anodic peaks are 50 mV, 7 mV, 65 mV compared to the additive-free system for the dicarboxyl telechelic PEGs with the molecular weights of 600, 1500 and 3300 Da, respectively.
• the highest anodic/cathodic peak separation was observed for the dicarboxyl telechelic PEG3300, which might be the result of the incomplete solution of the polymer in the concentrated KOH solution.
• Rectangular rechargeable Zn-air battery with telechelic PEG The cyclic performance of the novel Zn-air rechargeable battery with different additives was tested with the current density of 2 mAcm 2 for charging and discharging. The time limit of the steps was 5 min, while the potential limits were 1.0 and 1.8 V. The battery potential was around 1.27 V. It is clearly visible in Fig. 6., that the additive-free system has an increasing battery potential range with time (efficiency and capacity curves are shown in the supporting information). The change of potential suggests the formation of irreversible deposit on the surface of the zinc electrode. Moreover, the dicarboxyl telechelic PEGs of different molecular weights have a favorable effect on the stability of the potentials.
• the dicarboxyl telechelic PEG600 gives the most stable charging-discharging curves (Fig. 6), very small changes can be observed in the case of dicarboxyl telechelic PEG1500, while in the presence of dicarboxyl telechelic PEG3300 distorted cycles were obtained.
• the observed trend in the performance of dicarboxyl telechelic PEG additives may be due to the fact that the chelating ability of the carboxylate groups at the chain-end of PEGs towards the Zn(ll) ions decreases with the increasing chain-length.
• Zn-PEG(COO) 2 complexes may adsorb onto the surface of the Zn- electrode and thus reduce the rate of charge transfer process.
• the Coulomb efficiency of the tested batteries were near 100 % indicating high reproducibility of the charging/discharging cycles.
• the battery potential change was investigated for the 20 th discharge cycles of each measurement (with and without additives) to visualize the effect of the dicarboxyl telechelic PEG additives (Fig. 7.).
• Ebattery where AE f and AE S are the potential change corresponding to fast and slow decay, respectively.
• the k f and k s are the rate coefficients of the fast and slow decay, respectively, and m is the stretched exponential factor, while the E plin is the terminal potential.
• Eq. 2 consist of two exponential terms in which the first term represents a fast decay of E battery indicating a fast rearrangement of the structure of electric double layer thus reducing the overpotential of the zinc electrode.
• the second term involves the stretched exponential function.
• the value of the stretched exponential factor (m) decreases as the chain length of dicarboxyl telechelic PEGs increases, while the corresponding k s values does not change significantly in the case of PEG1500 and PEG3300.ln order to prove the long term stability of the novel Zn-air rechargeable battery, the cyclic performance measurements were extended up to more than 450 cycles (65 hours) in the presence of dicarboxyl telechelic PEG600 (Fig. 8.).
• the maximum potential of the cycles is slightly increasing, however, stable cycles were observed.
• the stability of the Zn-electrode is also confirmed by the capacity curve. It was found that the capacity remained constant during the investigated period and high Coulomb efficiency was obtained (near 100%).
• the reversibility of charging/discharging of the battery was also confirmed by measurement of the mass of the zinc-electrode before and after the long-term cycling performance measurements and no significant changes in the mass of the electrode was observed.
• Fig. 9. shows the recorded images of electrodes after long-term cyclic performance tests (68-hour) at different magnifications in the presence and in the absence of dicarboxyl telechelic PEG600 additives.
• the applied current density was 2 mAcm 2 .
• Mossy-like and porous deposition is formed on the surface of the electrode in the absence of dicarboxyl telechelic PEG additive.
• the deposit occupies large area on the electrode surface.
• the application of dicarboxyl telechelic PEG600 yielded highly improved morphology.
• the electrode surface is relatively smooth, needle-like dendritic, or mossy protrusions were not recognized.
• the elemental composition of deposits was proved to be metallic zinc by energy dispersive spectroscopy (EDS) measurements. A typical EDS spectrum is shown in Fig. 10.
• EDS energy dispersive spectroscopy
• Novel Zn-air rechargeable battery with telechelic polyethyleneglycol-propyleneglycol- polyethyleneglycol POLOXAMER
• the design of the experimental equipment was identical to that described for the dicarboxyl telechelical PEG 600 experiments (Fig. 11).
• the composition of the electrolyte used was also the same as that of the electrolyte used in the previous experiments, except that the dicarboxyl telecelical additive PEG 600 was replaced by a dicarboxyl telechelic POLOXAMER derivative.
• the dicarboxylic POLOXAMER derivative When mixed with 6 M potassium hydroxide solution, the dicarboxylic POLOXAMER derivative was not completely dissolved but formed an opaque emulsion.
• the Zn-air batteries are promising energy storage devices because of their high storage capacity and inexpensive constructions.
• a novel Zn-air rechargeable battery with charcoal/graphite cathode and dicarboxyl telechelic polyethylene glycol (PEG) additives with different molecular weights (M n : 600 Da, 1500 Da, 3300 Da) is reported.
• the battery is free of heavy metals and all of the used materials are easily available and non-toxic.
• the synthesized dicarboxyl telechelic PEGs were successfully applied to suppress the formation of dendritic and mossy deposits on the surface of the zinc electrode at both 7.5 and 2 mAcm 2 charging current density.
• the stability of the rechargeable battery was tested, where stable operation was achieved with all the synthesized dicarboxyl telechelic PEG additives. Cyclic voltammetry measurements were also carried out to understand the effect of dicarboxyl telechelic additives. Furthermore, the long-term cyclic performance was investigated with charging/discharging cycles up to 68 hours, where stable battery potentials were obtained with near 100% Coulombic efficiency during the entire measurement. In the presence of additives, the discharging steps were also mathematically modeled. The electrode surface after the tests were analyzed by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). The additive-free systems resulted in mossy-like deposition, while in the presence of dicarboxyl telechelic PEG additives the surface of the zinc electrode remained smooth and the weight of the electrode did not change after the long-term test.
• SEM Scanning Electron Microscopy
• EDS Energy Dispersive Spectroscopy

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• 2021
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