Electrocatalytic Activity Studies of Select Metal Surfaces and Implications in Li-Air Batteries

Abstract

Rechargeable lithium-air batteries have the potential to provide Ϸ3 times higher specific energy of fully packaged batteries than conventional lithium rechargeable batteries. However, very little is known about the oxygen reduction reaction ͑ORR͒ and oxygen evolution in the presence of lithium ions in aprotic electrolytes, which hinders the improvement of low round-trip efficiencies of current lithium-air batteries. We report the intrinsic ORR activity on glassy carbon ͑GC͒ as well as polycrystalline Au and Pt electrodes, where Au is the most active with an activity trend of Au ӷ GC Ͼ Pt. Rotating disk electrode ͑RDE͒ measurements were used to obtain the kinetic current of the ORR and the reaction order with respect to oxygen partial pressure in 1 M LiClO 4 propylene carbonate:1,2-dimethoxyethane ͑1:2 v/v͒. In addition, air electrodes with Vulcan carbon or Au or Pt nanoparticles supported on Vulcan were examined in Li-O 2 single cells, where the observed discharge cell voltages follow the catalytic trend established by RDE measurements. The ORR mechanism and the rate-determining steps were discussed and contrasted with the ORR activity trend in acid and alkaline solutions.

Lithium oxides precipitation in nonaqueous Li–air batteries

“…But, it may need further investigations coupling electrochemical tests with SEM or atomic force microscopy (AFM). The LiO 2 intermediate may detach from the reaction sites as indicated in RDE tests, 41,59 and its movement and solvation within the double layer might be governed by the overpotential. This can explain the dependence of discharge capacity on the discharge rate, but still needs further study to confirm validity.…”

“…First, even when the thin film electrode is used to quantify the catalytic activity, complication may arise from the unstable solvents. For example, the ORR activity trend ranks in the descending order of Au 4 GC 4 Pt in PC + DME 41 while the trend follows the sequence of Pt 4 Au 4 GC in DME. 42 Second, the normalized current or activity based on the true surface area of catalyst or catalyst mass may not be as critical as in the PEM fuel cells, especially when non-novel catalysts are used in Li-air batteries.…”

“…5b). 41,42 Unfortunately, the ORR products following the hypothesized pathways on particular catalyst , LiO 2 and even Li 2 O 2 as well as the potential range of the air electrode, the solvent may not be chemically and electrochemically stable. It was found that employing carbonatebased solvents (propylene carbonate (PC), ethylene carbonate (EC) and dimethyl carbonate (DMC)) resulted in decomposition of carbonates to form LiCO 3 , Li alkyl carbonates and a small amount of Li 2 O 2 in the cathode, which decomposed to CO 2 upon cell charging.…”

Elucidating the Oxygen Reduction Reaction Kinetics and the Origins of the Anomalous Tafel Behavior at the Lithium–Oxygen Cell Cathode

“…1 This potential is due to the predicted pack level specific energy of Li−O 2 cells (∼500−900 Wh kg −1 ) leading to electric vehicles with a driving range approaching ∼1100 km (680 miles) for a 400 kg pack 1 as compared to automotive Li-ion cells (105 Wh kg −1 at the battery pack level) achieving a driving range of about 140 miles for the same pack weight. 2 Practical realization of Li−O 2 cells is impeded by problems of poor cycle life, high charge and discharge overpotentials resulting in low coulombic efficiency and low power density, 3 and side reactions with N 2 , CO 2 , and H 2 O during ambient air operation. 4,5 The poor cycle life is believed to be caused by the oxidative instability of the electrolyte [6][7][8]50,51 together with electrode passivation due to irreversible product deposits and high overpotentials for decomposing them.…”

First-Principles Design of Graphene-Based Active Catalysts for Oxygen Reduction and Evolution Reactions in the Aprotic Li–O2 Battery

“…To set up model systems for LiO 2 , Li 2 O 2 or (Li 2 O 2 ) 2 adsorption, we notified that thermodynamically stable structures of LiO 2 , Li 2 O 2 or (Li 2 O 2 ) 2 adsorption were already studied in previous reports, and they were utilized as our model systems. 5,24 Lu et al 33 reported that reaction intermediates in the ORR are sensitive to the nature of a catalyst in dissociating O 2 , of which activation energy is lower than binding energies with both Gr and N-Gr. 34 Furthermore, computational results 5,23 and experimental observation 4,14 proposed that nanoclusters of (Li 2 O 2 ) n are more easily form than other kinds of chemical species in Gr and N-Gr surfaces.…”