A Kinetically Superior Rechargeable Zinc‐Air Battery Derived from Efficient Electroseparation of Zinc, Lead, and Copper in Concentrated Solutions

Abstract

Zinc electrodeposition is currently a hot topic because of its widespread use in rechargeable zinc-air batteries. However, Zn deposition has received little attention in organic solvents with much higher ionic conductivity and current efficiency. In this study, a Zn-betaine complex is synthesized by using ZnO and betainium bis[(trifluoromethyl)sulfonyl]imide and its electrochemical behavior for six organic solvents and electrodeposited morphology are studied. Acetonitrile allowed dendrite-free Zn electrodeposition at room temperature with current efficiencies of up to 86 %. From acetonitrile solutions in which Zn, Pb, and Cu complexes are dissolved in high concentrations, Zn and Pb/ Cu are efficiently separated electrolytically under potentiostatic control, allowing the purification of solutions prepared directly from natural ores. Additionally, a highly flexible Zn anode with excellent kinetics is obtained by using a carbon fabric substrate. A rechargeable zinc-air battery with these electrodes shows an open-circuit voltage of 1.63 V, is stable for at least 75 cycles at 0.5 mA cm À 2 or 33 cycles at 20 mA cm À 2 , and allows intermediate cycling at 100 mA cm À 2 .

Electrolyte for High‐Energy‐ and Power‐Density Zinc Batteries and Ion Capacitors

“…The asymmetric stretching vibration bands of the carboxyl group at υ as (OH) = 3110-3377 cm −1 and υ as (COO) = 1761 cm −1 of [Hbet][NTf 2 ] are characteristic for the [Hbet] + cation (Figure S23a, Supporting Information). [2,11,55] In solid ZbN, the deprotonated and coordinated betaine molecule has an absorption band reaching from υ as (COO) = 1564-1716 cm −1 (Figure 4a and Figure S23a, Supporting Information). [12] The band consists of several overlapping peaks, indicating different bonding modes of the betaine ligand.…”

“…The approach is based on our earlier discovery that abundant ZnO dissolves in the ionic liquid (IL) betainium bis((trifluoromethyl)sulfonyl)imide ([Hbet] + = betainium, (CH 3 ) 3 N (+) CH 2 COOH), [Hbet][NTf 2 ]). [11] The acidic proton of the [Hbet] + cation's carboxyl group reacts with the oxide ions of ZnO to water, which is evaporated at the applied temperature of about 175 °C, and in parallel the now deprotonated carboxylate groups coordinate the metal cations (Equation ( 1)). [12] [ (1)…”

“…The approach is based on our earlier discovery that abundant ZnO dissolves in the ionic liquid (IL) betainium bis((trifluoromethyl)sulfonyl)imide ([Hbet] + = betainium, (CH 3 ) 3 N (+) CH 2 COOH), [Hbet][NTf 2 ]). [ 11 ] The acidic proton of the [Hbet] + cation's carboxyl group reacts with the oxide ions of ZnO to water, which is evaporated at the applied temperature of about 175 °C, and in parallel the now deprotonated carboxylate groups coordinate the metal cations (Equation ()). [ 12 ] $$\[{\rm{ZnO}} + 2\left[ {{\rm{Hbet}}} \right]\left[ {{\rm{NT}}{{\rm{f}}_{\rm{2}}}} \right] \to \left[ {{\rm{Zn}}{{\left( {{\rm{bet}}} \right)}_2}} \right]{\left[ {{\rm{NT}}{{\rm{f}}_2}} \right]_2} + {{\rm{H}}_2}{\rm{O}}\]$$…”

Cobalt Deposition from Ionothermally Dissolved Cobalt Oxides

“…Since homoleptic complexes with betaine ligands bear the positive charge of the metal cation, in contrast to complexes with anionic ligands, they migrate rapidly to the cathode during electrolysis. The general feasibility of ionometallurgical processing with [Hbet][NTf 2 ] has already been demonstrated for the examples of lead, [10][11][12] plutonium, [13] copper [3,12] and zinc. [10,12] This approach could also be applicable to produce cobalt by dissolving previously refined Co 3 O 4 in [Hbet][NTf 2 ] and then electrodepositing cobalt metal.…”

“…The general feasibility of ionometallurgical processing with [Hbet][NTf 2 ] has already been demonstrated for the examples of lead, [10][11][12] plutonium, [13] copper [3,12] and zinc. [10,12] This approach could also be applicable to produce cobalt by dissolving previously refined Co 3 O 4 in [Hbet][NTf 2 ] and then electrodepositing cobalt metal. Thus, the energy-intensive carbothermic or aluminothermic reduction reaction should be avoidable.…”