Understanding LiOH Chemistry in a Ruthenium-Catalyzed Li-O2 Battery

Non-aqueous Li-O₂ batteries are promising for next-generation energy storage. New battery chemistries based on LiOH, rather than Li₂ O₂ , have been recently reported in systems with added water, one using a soluble additive LiI and the other using solid Ru catalysts. Here, the focus is on the mechanism of Ru-catalyzed LiOH chemistry. Using nuclear magnetic resonance, operando electrochemical pressure measurements, and mass spectrometry, it is shown that on discharging LiOH forms via a 4 e^- oxygen reduction reaction, the H in LiOH coming solely from added H₂ O and the O from both O₂ and H₂ O. On charging, quantitative LiOH oxidation occurs at 3.1 V, with O being trapped in a form of dimethyl sulfone in the electrolyte. Compared to Li₂ O₂ , LiOH formation over Ru incurs few side reactions, a critical advantage for developing a long-lived battery. An optimized metal-catalyst-electrolyte couple needs to be sought that aids LiOH oxidation and is stable towards attack by hydroxyl radicals.

Poly(vinylidene fluoride) (PVDF) Binder Degradation in Li-O2 Batteries: A Consideration for the Characterization of Lithium Superoxide

We show that a common Li-O₂ battery cathode binder, poly(vinylidene fluoride) (PVDF), degrades in the presence of reduced oxygen species during Li-O₂ discharge when adventitious impurities are present. This degradation process forms products that exhibit Raman shifts (∼1133 and 1525 cm^-1) nearly identical to those reported to belong to lithium superoxide (LiO₂), complicating the identification of LiO₂ in Li-O₂ batteries. We show that these peaks are not observed when characterizing extracted discharged cathodes that employ poly(tetrafluoroethylene) (PTFE) as a binder, even when used to bind iridium-decorated reduced graphene oxide (Ir-rGO)-based cathodes similar to those that reportedly stabilize bulk LiO₂ formation. We confirm that for all extracted discharged cathodes on which the 1133 and 1525 cm^-1 Raman shifts are observed, only a 2.0 e^-/O₂ process is identified during the discharge, and lithium peroxide (Li₂O₂) is predominantly formed (along with typical parasitic side product formation). Our results strongly suggest that bulk, stable LiO₂ formation via the 1 e^-/O₂ process is not an active discharge reaction in Li-O₂ batteries.

Recycling application of Li-MnO₂ batteries as rechargeable lithium-air batteries

The ever-increasing consumption of a huge quantity of lithium batteries, for example, Li-MnO2 cells, raises critical concern about their recycling. We demonstrate herein that decayed Li-MnO2 cells can be further utilized as rechargeable lithium-air cells with admitted oxygen. We further investigated the effects of lithiated manganese dioxide on the electrocatalytic properties of oxygen-reduction and oxygen-evolution reactions (ORR/OER). The catalytic activity was found to be correlated with the composition of Li(x)MnO2 electrodes (0<x<1) generated in situ in aprotic Li-MnO2 cells owing to tuning of the Mn valence and electronic structure. In particular, modestly lithiated Li(0.50)MnO2 exhibited superior performance with enhanced round-trip efficiency (ca. 76%), high cycling ability (190 cycles), and high discharge capacity (10,823 mA h g(carbon)(-1)). The results indicate that the use of depleted Li-MnO2 batteries can be prolonged by their application as rechargeable lithium-air batteries.

Nanostructured Mn-based oxides for electrochemical energy storage and conversion

This review summarizes recent efforts made to use nanostructured Mn-based oxides for primary batteries, Li secondary batteries, metal–air batteries, and pseudocapacitors.

Mechanistic insights for the development of Li–O2battery materials: addressing Li2O2conductivity limitations and electrolyte and cathode instabilities

This featured article provides a perspective on challenges facing Li–air battery cathode development, including Li₂O₂conductivity limitations and instabilities of electrolyte and high surface area carbon.

An advanced lithium-air battery exploiting an ionic liquid-based electrolyte

A novel lithium-oxygen battery exploiting PYR14TFSI-LiTFSI as ionic liquid-based electrolyte medium is reported. The Li/PYR14TFSI-LiTFSI/O2 battery was fully characterized by electrochemical impedance spectroscopy, capacity-limited cycling, field emission scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. The results of this extensive study demonstrate that this new Li/O2 cell is characterized by a stable electrode-electrolyte interface and a highly reversible charge-discharge cycling behavior. Most remarkably, the charge process (oxygen oxidation reaction) is characterized by a very low overvoltage, enhancing the energy efficiency to 82%, thus, addressing one of the most critical issues preventing the practical application of lithium-oxygen batteries.

The mechanisms of oxygen reduction and evolution reactions in nonaqueous lithium-oxygen batteries

A fundamental understanding of the mechanisms of both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) in nonaqueous lithium-oxygen (Li-O2) batteries is essential for the further development of these batteries. In this work, we systematically investigate the mechanisms of the ORR/OER reactions in nonaqueous Li-O2 batteries by using electron paramagnetic resonance (EPR) spectroscopy, using 5,5-dimethyl-pyrroline N-oxide as a spin trap. The study provides direct verification of the formation of the superoxide radical anion (O2(˙-)) as an intermediate in the ORR during the discharge process, while no O2(˙-) was detected in the OER during the charge process. These findings provide insight into, and an understanding of, the fundamental reaction mechanisms involving oxygen and guide the further development of this field.