The Importance of Nanometric Passivating Films on Cathodes for Li–Air Batteries

Abstract

Recently, there has been a transition from fully carbonaceous positive electrodes for the aprotic lithium oxygen battery to alternative materials and the use of redox mediator additives, in an attempt to lower the large electrochemical overpotentials associated with the charge reaction. However, the stabilizing or catalytic effect of these materials can become complicated due to the presence of major side-reactions observed during dis(charge). Here, we isolate the charge reaction from the discharge by utilizing electrodes prefilled with commercial lithium peroxide with a crystallite size of about 200-800 nm. Using a combination of S/TEM, online mass spectrometry, XPS, and electrochemical methods to probe the nature of surface films on carbon and conductive Ti-based nanoparticles, we show that oxygen evolution from lithium peroxide is strongly dependent on their surface properties. Insulating TiO2 surface layers on TiC and TiN - even as thin as 3 nm-can completely inhibit the charge reaction under these conditions. On the other hand, TiC, which lacks this oxide film, readily facilitates oxidation of the bulk Li2O2 crystallites, at a much lower overpotential relative to carbon. Since oxidation of lithium oxygen battery cathodes is inevitable in these systems, precise control of the surface chemistry at the nanoscale becomes of upmost importance.

A Carbon‐ and Binder‐Free Nanostructured Cathode for High‐Performance Nonaqueous Li‐O2 Battery

“…This significantly improved round‐trip efficiency of TiN NTA can be ascribed to the enhanced electronic conductivity of this unique binder‐free nanostructrure. Compared with previous reports of promising noncarbon substrates, this self‐standing TiN NTA also delivered satisfactory capacity and energy efficiency 19, 20…”

“…To achieve a carbon‐free electrode, titanium‐based materials (such as TiC and TiSi 2 ) have been reported to deliver promising performance for nonaqueous Li–O 2 battery 15, 16, 17, 18, 19. Among them, titanium nitride (TiN), which has been widely used as cathode support for the electrocatalyst of oxygen reduction in aqueous electrolyte, has also attracted extensive attention 20, 21, 22.…”

“…Among them, titanium nitride (TiN), which has been widely used as cathode support for the electrocatalyst of oxygen reduction in aqueous electrolyte, has also attracted extensive attention 20, 21, 22. However, the reported TiN carbon‐free cathode was fabricated with nanoparticles and only exhibited poor capacities with serious polarization 15, 19. These nanoparticles may be severely blocked by the deposition of Li 2 O 2 during discharge due to the unclear pore/porosity and poor electronic contact at grain boundary with the presence of insulating binder, leading to higher overpotential during charging process.…”

Recent Progress in Electrocatalyst for Li‐O2 Batteries

“…Other kinds of factors which can correlate with the performances, such as the catalyst size, [171,172] the crystal facet, [173,174] and the conductivity are reported. [175] Among these efforts, Zhu…”

Antimony Doped Tin Oxide–Synthesis, Characterization and Application as Cathode Material in Li-O2Cells: Implications on the Prospect of Carbon-Free Cathodes for Rechargeable Lithium-Air Batteries

“…6 Furthermore, the performance of carbides and nitrides, which are potentially prone to oxidation, has been found to be strongly dependent on the formation of nanometric oxide surface films. 26,27 To circumvent these issues, electrically conductive metal oxides are promising materials due to their inherent stability against oxidation. Hence, the magnéli phase Ti 4 O 7 28 as well as Pt supported on TiO 2 nanofibers 29 have been proposed as eligible compounds for Li-O 2 cathodes.…”