[en] Li-CO${}_2$ batteries with a high theoretical energy density (1876 Wh kg${}^{-<!--\; ???\; -->1}$) have unique benefits for reversible carbon fixation for energy storage systems. However, due to lack of stable and highly active catalysts, the long-term operation of Li-CO${}_2$ batteries is limited to low current densities (mainly <0.2 mA cm${}^{-<!--\; ???\; -->2}$) that are far from practical conditions. In this work, it is discovered that, with an ionic liquid-based electrolyte, highly active and stable transition metal trichalcogenide alloy catalysts of Sb${}_{0.67}$Bi${}_{1.33}$X${}_3$ (X = S, Te) enable operation of the Li-CO${}_2$ battery at a very high current rate of 1 mA cm${}^{-<!--\; ???\; -->2}$ for up to 220 cycles. It is revealed that: i) the type of chalcogenide (Te vs S) significantly affects the electronic and catalytic properties of the catalysts, ii) a coupled cation-electron charge transfer process facilitates the carbon dioxide reduction reaction (CO${}_2$RR) occurring during discharge, and iii) the concentration of ionic liquid in the electrolyte controls the number of participating CO${}_2$ molecules in reactions. A combination of these key factors is found to be crucial for a successful operation of the Li-CO${}_2$ chemistry at high current rates. This work introduces a new class of catalysts with potential to fundamentally solve challenges of this type of batteries. (© 2024 The Authors. Advanced Energy Materials published by Wiley‐VCH GmbH)

[en] Highlights: • Reveal the relationship between the solvating power of electrolyte solvents and the fading mechanism of high-voltage LIBs. • A LFER was discovered between the solvating power of the electrolyte and the extent of cathode parasitic reactions at high voltage. • There was no evidence correlating the solvation ability of electrolyte with the decay of the high-voltage cathode LNMO. • The major decaying mechanism of the NMC/graphite cell cycled at a high voltage (> 4.5 V vs. Li/Li⁺) is solvation-driven. Understanding the decaying mechanism in lithium-ion batteries (LIBs) is critical to establishing a stable electrolyte system. Despite the advent of various novel electrolyte solvents designated for high-voltage LIBs, their working principles are not fully understood. Currently, oxidative decomposition of electrolytes is believed to be the major cause of capacity fade, and tremendous effort has been devoted to discovering a new electrolyte with enhanced anodic stability. However, the oxidative decomposition process cannot solely explain the rapid decay of some electrolyte systems with intrinsic high anodic stability when used with a high-nickel layered oxide cathode such as LiNi_0.6Mn_0.2Co_0.2O₂ (NMC622). In this report, a study of the quantitative structure-activity relationship was conducted to deepen the mechanistic understanding of the decay in high-voltage LIBs. The results obtained from the newly introduced molecular pair analysis and linear free-energy relationship (LFER) studies were highly consistent with the solvation-involved decaying mechanism in a high-nickel layered oxide cathode cycling at high voltage (> 4.5 V vs. Li/Li⁺). There was no evidence correlating the solvation ability of electrolyte solvents with the decay of a high-nickel layered oxide cathode cycling at a relatively low voltage (vs. Li/Li⁺), nor with the high^-voltage spinel cathode LiNi_0.5Mn_1.5O₄ (LNMO). Undoubtedly, the unveiled mechanistic insight provides a critical guideline for the development of an appropriate electrolyte system targeting different high-voltage cathode materials.

[en] The garnet-type phase Li${}_7$La${}_3$Zr${}_2$O${}_{12}$ (LLZO) attracts significant attention as an oxide solid electrolyte to enable safe and robust solid-state batteries (SSBs) with potentially high energy density. However, while significant progress has been made in demonstrating compatibility with Li metal, integrating LLZO into composite cathodes remains a challenge. The current perspective focuses on the critical issues that need to be addressed to achieve the ultimate goal of an all-solid-state LLZO-based battery that delivers safety, durability, and pack-level performance characteristics that are unobtainable with state-of-the-art Li-ion batteries. This perspective complements existing reviews of solid/solid interfaces with more emphasis on understanding numerous homo- and heteroionic interfaces in a pure oxide-based SSB and the various phenomena that accompany the evolution of the chemical, electrochemical, structural, morphological, and mechanical properties of those interfaces during processing and operation. Finally, the insights gained from a comprehensive literature survey of LLZO-cathode interfaces are used to guide efforts for the development of LLZO-based SSBs. (© 2022 The Authors. Advanced Energy Materials published by Wiley‐VCH GmbH)

[en] Lithium-air batteries based on CO${}_2$ reactant (Li-CO${}_2$) have recently been of interest because it has been found that reversible Li/CO${}_2$ electrochemistry is feasible. In this study, a new medium-entropy cathode catalyst, (NbTa)${}_{0.5}$BiS${}_3$, that enables the reversible electrochemistry to operate at high rates is presented. This medium entropy cathode catalyst is combined with an ionic liquid-based electrolyte blend to give a Li-CO${}_2$ battery that operates at high current density of 5000 mA g${}^{-<!--\; ???\; -->1}$ and capacity of 5000 mAh g${}^{-<!--\; ???\; -->1}$ for up to 125 cycles, far exceeding reported values in the literature for this type of battery. The higher rate performance is believed to be due to the greater stability of the multi-element (NbTa)${}_{0.5}$BiS${}_3$ catalyst because of its higher entropy compared to previously used catalysts with a smaller number of elements with lower entropies. Evidence for this comes from computational studies giving very low surface energies (high surface stability) for (NbTa)${}_{0.5}$BiS${}_3$ and transmission electron microscopystudies showing the structure being retained after cycling. In addition, the calculations indicate that Nb-terminated surface promotes Li-CO${}_2$ electrochemistry resulting in Li${}_2$CO${}_3$ and carbon formation, consistent with the products found in the cell. These results open new direction to design and develop high-performance Li-CO${}_2$ batteries. (© 2023 The Authors. Advanced Functional Materials published by Wiley‐VCH GmbH)