On the Mechanism of Nonaqueous Li–O₂ Electrochemistry on C and Its Kinetic Overpotentials: Some Implications for Li–Air Batteries

Abstract

Quantitative differential electrochemical mass spectrometry and cyclic voltammetry have been combined to probe possible mechanisms and the kinetic overpotentials, responsible for discharge and charge in a Li−O 2 battery, using C as the cathode and an electrolyte based on dimethoxyethane as the solvent. Previous spectroscopy experiments (X-ray diffraction, μRaman, IR, XPS) have shown that Li 2 O 2 is the principle product formed during Li−O 2 discharge using this electrolyte/cathode combination. At all discharge potentials and charge potentials <4.0 V, the observed electrochemistry is ∼2e − /O 2 consumed or produced, also implying that Li 2 O 2 is the dominant thermodynamically stable species formed and consumed in the electrochemistry. No evidence exists at any potential for formation of stable LiO 2 (1e − /O 2 ) or Li 2 O (4e − /O 2 ) during discharge. At charging potentials >4.0 V, the electrochemistry requires significantly more than 2e − /O 2 , and we take this as evidence for electrolyte decomposition. We find that sequential concerted (Li + + e − ) ion transfers to/from adsorbed O 2 * and LiO 2 * to produce/consume Li 2 O 2 is the mechanism that is most compatible with these experiments. The kinetic overpotentials are extremely low relative to aqueous O 2 reduction and evolution, and this implies that in principle a discharge−charge Li−O 2 cycle is possible with high voltaic efficiency (∼85%) if electrolyte and cathode stability issues are resolved.

The Lithium/Air Battery: Still an Emerging System or a Practical Reality?

“…The mechanism of the formation/decomposition of Li 2 O 2 has not yet been established with certainty. [125][126][127][128][129][130] The non-conductive solid Li 2 O 2 precipitate [ 11,82,130,131 ] can accumulate on the porous substrate structure, causing blockage of the available surface area for further formation of Li 2 O 2 . The transfer pathway for oxygen gas and lithium ions can also be clogged by Li 2 O 2 precipitate, resulting in an increase in cell resistance.…”

Experimental and Computational Analysis of the Solvent‐Dependent O2/Li+‐O2− Redox Couple: Standard Potentials, Coupling Strength, and Implications for Lithium–Oxygen Batteries

“…[11][12][13][14] [14,15] A number of studies have attributed the formation of large Li 2 O 2 particles and high discharge capacities observed at low rates (< 10 mA cm À2 in ethers [16,17] ), to high availability of soluble Li + -O 2 À . Abraham and co-workers [13,14,18] have suggested that the stability of Li + -O 2 À increases with solvent donor number (DN), which is a measure of the solvation enthalpy of the Lewis acid SbCl 5 in a given solvent .…”

A Mini-Review on Non-Aqueous Lithium-Oxygen Batteries - Electrochemistry and Cathode Materials

“…Cyclic voltammetry (CV) [31][32][33][34] has been employed on different electrodes and electrolytes to define the reaction mechanism of the Li-O 2 battery. In the CV measurements, an O 2 reduction part of the CV curve is equivalent to battery discharging, and the oxidation part is equivalent to charging.…”

“…The observed O 2 reduction and oxidation peaks were explained based on the electrochemical and chemical reactions described in Eqs. (3)- (6) [31][32][33][34][35]:…”