The Origin of Solvent Deprotonation in LiI-added Aprotic Electrolytes for Li-O2 Batteries

Spheroidization: The Impact of Precursor Morphology on Solid-State Lithiation Process for High-Quality Ultrahigh-Nickel Oxide Cathodes

Layered oxides with ultrahigh nickel content are considered promising high energy cathode materials. However, their cycle stability is constrained by a series of heterogeneous structural transformations during the complex solid-state lithiation process. By in-depth investigation into the solid-state lithiation process of LiNi0.92Co0.04Mn0.04O2, it is found that the protruded parts on the surface of precursor particles tend to be surrounded by locally excessive LiOH, which promotes the formation of a rigid and denseR 3 - m ${{\rm { R}}\mathrel{\mathop{{\rm { 3}}}\limits^{{\rm -}}}{\rm { m}}}$ shell during the early stage of lithiation process. The shell will hinder the diffusion of lithium and topotactic lithiation within the particles, culminating in spatially heterogeneous intermediates that can impair the electrochemical properties of the cathode material. The spheroidization of the precursor can enhance uniformity in structural evolution during solid-phase lithiation. Ultrahigh nickel cathodes derived from spherical precursors demonstrate high initial discharge specific capacity (234.2 mAh g-1, in the range of 2.7-4.3 V) and capacity retention (89.3 % after 200 cycles), significantly superior to the non-spherical samples. This study not only sheds light on the intricate relationship between precursor shape and structural transformation but also introduces a novel strategy for enhancing cathode performance through precursor spheroidization.

Insights into the LiI Redox Mediation in Aprotic Li-O2 Batteries: Solvation Effects and Singlet Oxygen Evolution

Lithium-oxygen aprotic batteries (aLOBs) are highly promising next-generation secondary batteries due to their high theoretical energy density. However, the practical implementation of these batteries is hindered by parasitic reactions that negatively impact their reversibility and cycle life. One of the challenges lies in the oxidation of Li2O2, which requires large overpotentials if not catalyzed. To address this issue, redox mediators (RMs) have been proposed to reduce the oxygen evolution reaction (OER) overpotentials. In this study, we focus on a lithium iodide RM and investigate its role on the degradation chemistry and the release of singlet oxygen in aLOBs, in different solvent environments. Specifically, we compare the impact of a polar solvent, dimethyl sulfoxide (DMSO), and a low polarity solvent, tetraglyme (G4). We demonstrate a strong interplay between solvation, degradation, and redox mediation in OER by LiI in aLOBs. The results show that LiI in DMSO-based electrolytes leads to extensive degradation and to 1O2 release, affecting the cell performance, while in G4-based electrolytes, the release of 1O2 appears to be suppressed, resulting in better cyclability.

Understanding Catalytic Mechanisms and Cathode Interface Kinetics in Nonaqueous Mg-CO2 Batteries

We leverage first-principles density functional theory (DFT) calculations to understand the electrocatalytic processes in Mg-CO2 batteries, considering ruthenium oxide (RuO2) as an archetypical cathode catalyst. Our goal is to establish a mechanistic framework for understanding the charging and discharging reaction pathways and their influence on overpotentials. On the RuO2 (211) surface, we found reaction initiation through thermodynamically favorable adsorption of Mg followed by interactions with CO2. However, we found that the formation of carbonate (CO32-) and oxalate (C2O42-) intermediates via the activation of CO2 at the catalytic site is thermodynamically unfavorable. We predict that MgC2O4 will form as the discharge product due to its lower overpotential compared to MgCO3. However, MgC2O4 is thermodynamically unstable and is expected to decompose into MgCO3, MgO, and C as final discharge products. Through Bader charge analysis, we investigate the covalent interactions between intermediates and catalyst sites. Moreover, we study the electrochemical free energy profiles of the most favorable reaction pathways and determine discharge and charge overpotentials of 1.30 and 1.35 V, respectively. Our results underscore the importance of catalyst design for the cathode material to overcome performance limitations in nonaqueous Mg-CO2 batteries.