Revealing the Correlations between Morphological Evolution and Surface Reactivity of Catalytic Cathodes in Lithium-Oxygen Batteries

Upcycling Spent Lithium-Ion Batteries: Constructing Bifunctional Catalysts Featuring Long-Range Order and Short-Range Disorder for Lithium-Oxygen Batteries

Upcycling of high-value metals (M = Ni, Co, Mn) from spent ternary lithium-ion batteries to the field of lithium-oxygen batteries is highly appealing, yet remains a huge challenge. In particular, the alloying of the recovered M components with Pt and applied as cathode catalysts have not yet been reported. Herein, a fresh L12-type Pt3 M medium-entropy intermetallic nanoparticle is first proposed, confined on N-doped carbon matrix (L12-Pt3(Ni1/3Co1/3Mn1/3)@N-C) based on spent 111 typed LiNi1-x-yMnxCoyO2 cathode. This well-defined catalyst combines both features of long-range order L12 face-centered cubic structure and short-range disorder in M sites. The former contributes to enhancing the structural stability, and the latter further facilitates deeply activating the catalytic activity of Pt sites. Experiments and theoretical results demonstrate that the local coordination environment and electronic distribution of Pt are both fundamentally modulated via surrounding disordered Ni, Co, and Mn atoms, which greatly optimize the affinity toward oxygen-containing intermediates and facilitate the deposition/decomposition kinetics of the thin-film Li2O2 discharge products. Specifically, the L12-Pt3(Ni1/3Co1/3Mn1/3)@N-C catalyst exhibits an ultra-low overpotential of 0.48 V and achieves 220 cycles at 400 mA g-1 under 1000 mAh g-1. The work provides important insights for the recycling of spent lithium-ion batteries into advanced catalyst-related applications.

Construction of an Oxygen-Vacancy-Rich CeO2@CoO Heterojunction toward High-Performance Lithium-Oxygen Batteries

Lithium-oxygen (Li-O2) batteries theoretically possess an exceptional energy density comparable to gasoline (up to 3500 W h kg-1), but in practical applications, the discharge products are difficult to effectively decompose, which leads to clogging of the cathode, resulting in severe polarization, limited actual capacity, and shortened battery life for Li-O2 batteries. Herein, we construct a highly active and stable catalyst with d-f electronic orbit coupling as a redox center by anchoring CeO2 onto CoO, simultaneously, oxygen vacancy (Ov) and CeO2 coactivated CoO. By leveraging the effects of interface engineering and defect engineering on the electronic structure of the catalyst, the adsorption energy for LiO2 can be adjusted to an ideal range. This not only avoids surface passivation caused by excessively strong binding energy but also overcomes the issue of sluggish Li2O2 decomposition efficiency due to excessively weak binding energy. Bracingly, the CeO2/CoO-based Li-O2 batteries exhibit an ultralow charge-discharge polarization, and Li2O2 was successfully induced to nucleate uniformly in nanoflower-like shapes, which could promote the reversible decomposition of the discharge products during the charging process and thereby enhance the electrochemical performance of Li-O2 batteries. Therefore, the CeO2@CoO/CC cathode exhibited an ultralow overpotential of 0.57 V and achieved a high discharge capacity of 19,850 mA h g-1. This work provides an important reference for designing the structure of cathode catalysts for Li-O2 batteries and regulating the growth paths and morphologies of discharge products.

Cobalt nanoparticles decorated hollow N-doped carbon nanospindles enable high-performance lithium-oxygen batteries

Despite the ultrahigh theoretical energy density and cost-effectiveness, aprotic lithium-oxygen (Li-O2) batteries suffer from slow oxygen redox kinetics at cathodes and large voltage hysteresis. Here, we well-design ultrafine Co nanoparticles supported by N-doped mesoporous hollow carbon nanospindles (Co@HCNs) to serve as efficient electrocatalysts for Li-O2 battery. Benefiting from strong metal-support interactions, the obtained Co@HCNs manifest high affinity for the LiO2 intermediate, promoting formation of ultrathin nanosheet-like Li2O2 with low-impedance contact interface on the Co@HCNs cathode surface, which facilitates the reversible decomposition upon charging. The mesoporous hollow nanospindles can provide abundant electron/ions transport channels to synergistically accelerate the formation and decomposition of discharge products. The Li-O2 battery based on Co@HCNs displays remarkably reduced discharge/charge polarization of 0.92 V, impressive rate performance, and stable operation for 250 cycles. This work will provide a new avenue to design advanced oxygen electrocatalysts for high-performance Li-O2 battery.

Understanding the Dynamic Evolution of Active Sites among Single Atoms, Clusters, and Nanoparticles

Catalysis remains a cornerstone of chemical research, with the active sites of catalysts being crucial for their functionality. Identifying active sites, particularly during the reaction process, is crucial for elucidating the relationship between a catalyst's structure and its catalytic property. However, the dynamic evolution of active sites within heterogeneous metal catalysts presents a substantial challenge for accurately pinpointing the real active sites. The advent of in situ and operando characterization techniques has illuminated the path toward understanding the dynamic changes of active sites, offering robust scientific evidence to support the rational design of catalysts. There is a pressing need for a comprehensive review that systematically explores the dynamic evolution among single atoms, clusters, and nanoparticles as active sites during the reaction process, utilizing in situ and operando characterization techniques. This review aims to delineate the effects of various reaction factors on dynamic evolution of active sites among single atoms, clusters, and nanoparticles. Moreover, several in situ and operando techniques are elaborated with emphases on tracking the dynamic evolution of active sites, linking them to catalytic properties. Finally, it discusses challenges and future perspectives in identifying active sites during the reaction process and advancing in situ and operando characterization techniques.

Nanoengineering of Cathode Catalysts for Li-O2 Batteries

Lithium-oxygen (Li-O2) batteries have obtained widespread attention as next-generation energy storage systems due to their extremely high energy density. However, the high charge overpotential, attributed to the insulating property of Li2O2, significantly limits the energy efficiency and triggers solvent degradation. The high electrochemical activities of oxygen reduction reactions (ORR) and oxygen evolution reactions (OER) on the cathode are crucial for alleviating the high charging polarizations and enhancing the lifetime of Li-O2 batteries, which are also top challenges of state-of-art research. In this review, the scientific challenges and the proposed solutions in the development of cathode catalysts have been summarized. The recent research advancements on the nanoengineering of cathode catalysts for Li-O2 batteries have been comprehensively discussed, and the perspectives on the structure optimization are presented. Meanwhile, we have elucidated the structure-performance relationship between the electronic state and performance of the cathode catalysts at the nanoscale level. This review intends to provide guidelines for the design and construction of cathode catalysts in advanced Li-O2 batteries.

Revealing the CO2 Conversion at Electrode/Electrolyte Interfaces in Li-CO2 Batteries via Nanoscale Visualization Methods

Lithium-carbon dioxide (Li-CO2 ) battery technology presents a promising opportunity for carbon capture and energy storage. Despite tremendous efforts in Li-CO2 batteries, the complex electrode/electrolyte/CO2 triple-phase interfacial processes remain poorly understood, in particular at the nanoscale. Here, using in situ atomic force microscopy and laser confocal microscopy-differential interference contrast microscopy, we directly observed the CO2 conversion processes in Li-CO2 batteries at the nanoscale, and further revealed a laser-tuned reaction pathway based on the real-time observations. During discharge, a bi-component composite, Li2 CO3 /C, deposits as micron-sized clusters through a 3D progressive growth model, followed by a 3D decomposition pathway during the subsequent recharge. When the cell operates under laser (λ=405 nm) irradiation, densely packed Li2 CO3 /C flakes deposit rapidly during discharge. Upon the recharge, they predominantly decompose at the interfaces of the flake and electrode, detaching themselves from the electrode and causing irreversible capacity degradation. In situ Raman shows that the laser promotes the formation of poorly soluble intermediates, Li2 C2 O4 , which in turn affects growth/decomposition pathways of Li2 CO3 /C and the cell performance. Our findings provide mechanistic insights into interfacial evolution in Li-CO2 batteries and the laser-tuned CO2 conversion reactions, which can inspire strategies of monitoring and controlling the multistep and multiphase interfacial reactions in advanced electrochemical devices.

Adsorbate-Induced Adatom Formation on Lithium, Iron, Cobalt, Ruthenium, and Rhenium Surfaces

Recent experimental and theoretical studies have demonstrated the reaction-driven metal-metal bond breaking in metal catalytic surfaces even under relatively mild conditions. Here, we construct a density functional theory (DFT) database for the adsorbate-induced adatom formation energy on the close-packed facets of three hexagonal close-packed metals (Co, Ru, and Re) and two body-centered cubic metals (Li and Fe), where the source of the ejected metal atom is either a step edge or a close-packed surface. For Co and Ru, we also considered their metastable face-centered cubic structures. We studied 18 different adsorbates relevant to catalytic processes and predicted noticeably easier adatom formation on Li and Fe compared to the other three metals. The NH3- and CO-induced adatom formation on Fe(110) is possible at room temperature, a result relevant to NH3 synthesis and Fischer-Tropsch synthesis, respectively. There also exist other systems with favorable adsorbate effects for adatom formation relevant to catalytic processes at elevated temperatures (500-700 K). Our results offer insight into the reaction-driven formation of metal clusters, which could play the role of active sites in reactions catalyzed by Li, Fe, Co, Ru, and Re catalysts.

Double spatial confinement on ruthenium nanoparticles inside carbon frameworks as durable catalysts for a quasi‐solid‐state Li–O2 battery

The rational design of large‐area exposure, nonagglomeration, and long‐range dispersion of metal nanoparticles (NPs) in the catalysts is critical for the development of energy storage and conversion systems. Little attention has been focused on modulating and developing catalyst interface contact engineering between a carbon substrate and dispersed metal. Here, a highly dispersed ultrafine ruthenium (Ru) NP strategy by double spatial confinement is proposed, that is, incorporating directed growth of metal–organic framework crystals into a bacterial cellulose templating substrate to integrate their respective merits as an excellent electrocatalytic cathode catalyst for a quasi‐solid‐state Li–O2 battery. The porous carbon matrix with highly dispersed ultrafine Ru NPs is well designed and used as cathode catalysts in a Li–O2 battery, demonstrating a high discharge areal capacity of 6.82 mAh cm–2 at 0.02 mA cm–2, a high‐rate capability of 4.93 mAh cm–2 at 0.2 mA cm–2, and stable discharge/charge cycling for up to 500 cycles (2000 h) with low overpotentials of ~1.4 V. This fundamental understanding of the structure–performance relationship demonstrates a new and promising approach to optimize highly efficient cathode catalysts for solid‐state Li–O2 batteries.

Electrochemical Atomic Force Microscopy Study on the Dynamic Evolution of Lithium Deposition

Lithium metal is one of the most promising anode materials for lithium-ion batteries; however, lithium dendrite growth hinders its large-scale development. So far, the dendrite formation mechanism is unclear. Herein, the dynamic evolution of lithium deposition in etheryl-based and ethylene carbonate (EC)-based electrolytes was obtained by combining an in situ electrochemical atomic force microscope (EC-AFM) with an electrochemical workstation. Three growth modes of lithium particles are proposed: preferential, merged, and independent growth. In addition, a lithium deposition schematic is proposed to clearly describe the morphological changes in lithium deposition. This schematic shows the process of lithium deposition, thus providing a theoretical basis for solving the problem of lithium dendrite growth.

A Review of In-Situ Techniques for Probing Active Sites and Mechanisms of Electrocatalytic Oxygen Reduction Reactions

Electrocatalytic oxygen reduction reaction (ORR) is one of the most important reactions in electrochemical energy technologies such as fuel cells and metal-O2/air batteries, etc. However, the essential catalysts to overcome its slow reaction kinetic always undergo a complex dynamic evolution in the actual catalytic process, and the concomitant intermediates and catalytic products also occur continuous conversion and reconstruction. This makes them difficult to be accurately captured, making the identification of ORR active sites and the elucidation of ORR mechanisms difficult. Thus, it is necessary to use extensive in-situ characterization techniques to proceed the real-time monitoring of the catalyst structure and the evolution state of intermediates and products during ORR. This work reviews the major advances in the use of various in-situ techniques to characterize the catalytic processes of various catalysts. Specifically, the catalyst structure evolutions revealed directly by in-situ techniques are systematically summarized, such as phase, valence, electronic transfer, coordination, and spin states varies. In-situ revelation of intermediate adsorption/desorption behavior, and the real-time monitoring of the product nucleation, growth, and reconstruction evolution are equally emphasized in the discussion. Other interference factors, as well as in-situ signal assignment with the aid of theoretical calculations, are also covered. Finally, some major challenges and prospects of in-situ techniques for future catalysts research in the ORR process are proposed.

Surface Degradation of Single-crystalline Ni-rich Cathode and Regulation Mechanism by Atomic Layer Deposition in Solid-State Lithium Batteries

Single-crystalline Ni-rich cathode (SC-NCM) has attracted increasing interest owing to its greater capacity retention in advanced solid-state lithium batteries (SSLBs), while suffers from severe interfacial instability during cycling. Here, via atomic layer deposition, Li3 PO4 is introduced to coat SC-NCM (L-NCM), to suppress undesired side reaction and enhance interfacial stability. The dynamic degradation and surface regulation of SC-NCM are investigated inside a working SSLB by in situ atomic force microscopy (AFM). We directly observe the uneven cathode electrolyte interphase (CEI) and surface defects on pristine SC-NCM particle. Remarkably, the formed amorphous LiF-rich CEI on L-NCM maintains its initial structure upon cycling, and thus endows the battery with improved cycling stability and excellent rate capability. Such on-site tracking provides deep insights into surface mechanism and structure-reactivity correlation of SC-NCM, and thus benefits the optimizations of SSLBs.

Reacquainting the Sudden-Death and Reaction Routes of Li-O2 Batteries by Ex Situ Observation of Li2O2 Distribution Inside a Highly Ordered Air Electrode

The unclear Li₂O₂ distribution inside an air electrode stems from the difficulty of conducting observation techniques inside a porous electrode. In this work, an integrated air electrode is prepared with highly ordered channels. The morphological composition and distribution of Li₂O₂ inside the real air electrode are clearly observed for the first time. The results show that the toroidal Li₂O₂ is constrained by the channel size and exhibits a larger diameter on the separator side at high currents. In contrast to the reported single-factor experiments, the coupling effects of charge transfer impedance and concentration polarization on sudden death are analyzed in-depth at low and high currents. The growth model suggests that toroidal Li₂O₂ exhibits a high dependence on the electrode surface structure. A new route is proposed in which the Li₂O₂/electrode interface of a toroid is controlled partially by the second single-electron reduction.

On-Surface Synthesis toward Two-Dimensional Polymers

Two-dimensional (2D) polymers have garnered widespread interest because of their intriguing physicochemical properties. Envisaged applications in fields including nanodevices, solid-state chemistry, physical organic chemistry, and condensed matter physics, however, demand high-quality and large-scale production. In this perspective, we first introduce exotic band structures of organic frameworks holding honeycomb, kagome, and Lieb lattices. We further discuss how mesoscale ordered 2D polymers can be synthesized by means of choosing suitable monomers and optimizing growth conditions. We describe successful polymerization strategies to introducing a non-benzenoid subunit into a π-conjugated carbon lattice via delicately designed monomer precursors. Also, to obviate transfer and restore the intrinsic properties of π-conjugated polymers, new paradigms of aryl-aryl coupling on inert surfaces are discussed. Recent achievements in the photopolymerization demonstrate the need for monomer design. We conclude the potential applications of these organic networks and project the future possibilities in providing new insights into on-surface polymerization.