Lithium, the lightest metal with the lowest standard reduction potential, has been long considered as the ultimate anode material for next‐generation high‐energy‐density batteries. However, an ...unexpected Li dendrite formation, which causes poor reversibility of electrochemical reactions and safety concerns, is a major problem that has to be solved for the commercialization of Li metal anodes. For the implementation of stable Li metal anodes, complete understanding on the dendritic Li formation and its dissolution is essential for electrode material design, which requires the development of advanced characterization techniques. Specifically, compared to an ex situ characterization as a postmortem analysis, in situ/operando characterizations allow dynamic structural and chemical evolution to be directly observed in a realistic battery cell, which helps unravel the complex reactions and degradation mechanisms in Li metal anodes. Here, recent progress in the understanding of electrochemical behavior in Li metal anodes upon deposition and dissolution, verified by the in situ/operando analytical techniques using light, electron, X‐ray, neutron, and magnetism‐based characterizations, is covered. This progress report provides a fundamental understanding of Li deposition and dissolution mechanisms and highlights the critical role of in situ/operando analyses in developing stable Li metal anodes.
A fundamental understanding of dendrite formation and dissolution mechanisms is an important issue for Li metal batteries. This progress report summarizes recent work on the mechanistic understanding of Li deposition and dissolution by in situ/operando analytical techniques using light, electron, X‐ray, neutron, and magnetism‐based characterizations, highlighting the critical role of in situ/operando analyses in developing stable Li metal batteries.
Developing high‐energy‐density electrodes for lithium ion batteries (LIBs) is of primary importance to meet the challenges in electronics and automobile industries in the near future. Conversion ...reaction‐based transition metal oxides are attractive candidates for LIB anodes because of their high theoretical capacities. This review summarizes recent advances on the development of nanostructured transition metal oxides for use in lithium ion battery anodes based on conversion reactions. The oxide materials covered in this review include oxides of iron, manganese, cobalt, copper, nickel, molybdenum, zinc, ruthenium, chromium, and tungsten, and mixed metal oxides. Various kinds of nanostructured materials including nanowires, nanosheets, hollow structures, porous structures, and oxide/carbon nanocomposites are discussed in terms of their LIB anode applications.
Conversion reaction‐based oxides are considered promising anode materials to replace graphite due to their high theoretical capacity. This review summarizes recent advances in the development of nanostructured transition metal oxides for use in lithium ion battery anodes based on conversion reactions. Moreover, some important aspects and future directions for designing high‐performance anodes are discussed.
Galvanic replacement reactions provide a simple and versatile route for producing hollow nanostructures with controllable pore structures and compositions. However, these reactions have previously ...been limited to the chemical transformation of metallic nanostructures. We demonstrated galvanic replacement reactions in metal oxide nanocrystals as well. When manganese oxide (Mn₃O₄) nanocrystals were reacted with iron(ll) perchlorate, hollow box-shaped nanocrystals of Mn₃O₄/γ-Fw₂O₃ ("nanoboxes") were produced. These nanoboxes ultimately transformed into hollow cagelike nanocrystals of γ-Fe₂O₃ ("nanocages"). Because of their nonequilibrium compositions and hollow structures, these nanoboxes and nanocages exhibited good performance as anode materials for lithium ion batteries. The generality of this approach was demonstrated with other metal pairs, including Co₃O₄/SnO₂ and Mn₃O₄/SnO₂.
Lithium‐ion capacitors (LICs) exhibit superior power density and cyclability compared to lithium‐ion batteries. However, the low initial Coulombic efficiency (ICE) of amorphous carbon anodes (e.g., ...hard carbon (HC) and soft carbon (SC)) limits the energy density of LICs by underutilizing cathode capacity. Here, a solution‐based deep prelithiation strategy for carbon anodes is applied using a contact‐ion pair dominant solution, offering high energy density based on a systematic electrode balancing based on the cathode capacity increased beyond the original theoretical limit. Increasing the anode ICE to 150% over 100%, the activated carbon (AC) capacity is doubled by activating Li+ cation storage, which unleashes rocking‐chair LIC operation alongside the dual‐ion‐storage mechanism. The increased AC capacity results in an energy density of 106.6 Wh kg−1AC+SC, equivalent to 281% of that of LICs without prelithiation. Moreover, this process lowers the cathode‐anode mass ratio, reducing the cell thickness by 67% without compromising the cell capacity. This solution‐based deep chemical prelithiation promises high‐energy LICs based on transition metal‐free, earth‐abundant active materials to meet the practical demands of power‐intensive applications.
A solution‐based deep prelithiation of carbon anodes is proposed to maximize the energy density of lithium‐ion capacitors, enabled by the spontaneous charge transfer from contact‐ion pair dominant solutions to the anodes. The deep prelithiation, achieving 150% anode ICE, unleashes Li+ ion storage in cathodes, doubling the cathode capacity. This results in a reduced cell thickness by 67% without compromising capacity.
Although Li metal has long been considered to be the ideal anode material for Li rechargeable batteries, our limited understanding of the complex mechanism of Li plating has hindered the widespread ...deployment of Li metal anodes. Therefore, operando studies are required to unambiguously reveal the complex mechanistic steps involved. In this study, we employed synchrotron-based X-ray imaging methods to visualize the evolution of Li plating/stripping under operando and, more importantly, practical conditions for battery operation, providing detailed insights into morphology evolution during Li plating. The effects of critical battery operating parameters, including concentration of Li salts, current density, ionic strength, and various electrolytes and additives, on Li plating/stripping have been studied. The delicate interplay of these conditions on the resulting Li metal morphology has been characterized for the first time.
All‐solid‐state batteries (ASSBs) based on ceramic materials are considered a key technology for automobiles and energy storage systems owing to their high safety and stability. However, contact ...issues between the electrode and solid‐electrolyte materials and undesired chemical reaction occurring at interfaces have hindered their development. Herein, the chemical compatibility and structural stability of composite mixtures of the layered cathode materials Li1−xNi0.5Co0.2Mn0.3O2 (NCM523) with the garnet‐type solid electrolyte Li6.25Ga0.25La3Zr2O12 (LLZO‐Ga) during high‐temperature co‐sintering under various gas flowing conditions are investigated. In situ high‐temperature X‐ray diffraction analysis of the composite materials reveals that Li diffusion from LLZO‐Ga to NCM523 occurs at high temperature under synthetic air atmosphere, resulting in the decomposition of LLZO‐Ga into La2Zr2O7 and the recovery of charged NCM523 to the as‐prepared state. The structural stability of the composite mixture at high temperature is further investigated under N2 atmosphere, revealing that Li diffuses toward the opposite direction and involves the phase transition of LLZO‐Ga from a cubic to tetragonal structure and the reduction of the NCM523 cathode to Ni metal. These findings provide insight into the structural stability of layered cathode and garnet‐type solid‐electrolyte composite materials and the design of stable interfaces between them via co‐sintering for ASSBs.
Co‐sintering is an efficient approach to solve the contact issues between electrode and solid‐electrolyte materials. However, undesired chemical reaction occurring at interface hinders their development, thus understanding the chemical compatibility of battery materials is crucial for improving interface. In this study, structural stability and chemical compatibility between layered cathode and garnet‐type solid electrolyte are explored via co‐sintering for all‐solid‐state batteries.
Single‐atom M‒N‒C catalysts have attracted tremendous attention for their application to electrocatalysis. Nitrogen‐coordinated mononuclear metal moieties (MNx moities) are bio‐inspired active sites ...that are analogous to various metal‐porphyrin cofactors. Given that the functions of metal‐porphyrin cofactors are highly dependent on the local coordination environments around the mononuclear active site, engineering MNx active sites in heterogeneous M‒N‒C catalysts would provide an additional degree of freedom for boosting their electrocatalytic activity. This work presents a local coordination structure modification of FeN4 moieties via morphological engineering of graphene support. Introducing highly wrinkled structure in graphene matrix induces nonplanar distortion of FeN4 moieties, resulting in the modification of electronic structure of mononuclear Fe. Electrochemical analysis combined with first‐principles calculations reveal that enhanced electrocatalytic lithium polysulfide conversion, especially the Li2S redox step, is attributed to the local structure modified FeN4 active sites, while increased specific surface area also contributes to improved performance at low C‐rates. Owing to the synergistic combination of atomic‐level modified FeN4 active sites and morphological advantage of graphene support, Fe‒N‒C catalysts with wrinkled graphene morphology show superior lithium–sulfur battery performance at both low and high C‐rates (particularly 915.9 mAh g−1 at 5 C) with promising cycling stability.
Atomic‐level engineering of MNx active sites is a desirable strategy to enhance and fine‐tune electrocatalytic performance of M‒N‒C catalysts. FeN4 active sites on wrinkled graphene support exhibits different structural and electronic properties compared to square‐planar FeN4 moieties. The synergistic combination of modified FeN4 active sites and morphological advantage of wrinkled graphene support improves the electrocatalytic performance for lithium–sulfur conversion chemistry.
Abstract
The complex interplay and only partial understanding of the multi-step phase transitions and reaction kinetics of redox processes in lithium–sulfur batteries are the main stumbling blocks ...that hinder the advancement and broad deployment of this electrochemical energy storage system. To better understand these aspects, here we report
operando
confocal Raman microscopy measurements to investigate the reaction kinetics of Li–S redox processes and provide mechanistic insights into polysulfide generation/evolution and sulfur deposition.
Operando
visualization and quantification of the reactants and intermediates enabled the characterization of potential-dependent rates during Li–S redox and the linking of the electronic conductivity of the sulfur-based electrode and concentrations of polysulfides to the cell performance. We also report the visualization of the interfacial evolution and diffusion processes of different polysulfides that demonstrate stepwise discharge and parallel recharge mechanisms during cell operation. These results provide fundamental insights into the mechanisms and kinetics of Li–S redox reactions.
N‐coordinated Ni single atom (Ni–NC) is one of the best catalysts for the CO2 reduction reaction (CO2RR) to produce CO. However, no bulk Ni materials have exhibited high catalytic activity for CO2RR. ...Herein, it is shown that NiS nanoparticles mimicking the electronic structure of Ni–NC in real‐time enhance the CO2RR activity in a zero‐gap electrolyzer. In situ/Operando X‐ray absorption spectroscopy suggests that under a cathodic potential, the electronic structure of NiS changes similarly to that of Ni–NC and modulated Ox–zSy ligands with similar properties to Ni ligands, resulting in a mimicked electronic structure. However, NiS exhibits low stability owing to the loss of S species, key to mimicking N ligands. The future challenges in finding a stable mimicked electronic structure are discussed. Moreover, this work provides new insights into the development of catalysts from materials that have not generally been considered previously.
NiS exhibits enhanced catalytic activity for CO2 reduction in a zero‐gap electrolyzer. Operando X‐ray absorption spectroscopy suggests that NiS mimics single atom catalysts with the ideal electronic structure for CO2 reduction. It is expected that the NiS successfully mimics the electronic structure of NiNC due to its broken D4h symmetry and modulated Ox–zSy ligands under a cathodic potential.
The limited lifespan of aqueous zinc‐ion batteries (with vanadium‐oxide based cathodes) is constrained by practical applications due to corrosion accelerated by vanadium ions leaching from the ...cathode and uneven dendrite growth on the zinc metal anode. To address these issues, the difference in size between hydrated zinc ions (4.30 Å) in electrolyte and vanadium ions (8.34 Å) is considered. Uniformly coating the MOF‐801 nanoparticles (with a pore size of 6.0 Å) on the zinc foil formed a selective ion transport layer. The uniform zinc ion flux generated by the selective ion transport layer allows hydrated zinc ions to be transported evenly and promotes uniform zinc deposition, leading to a low overpotential (17.4 mV) and high cycle stability (1000 h) in the symmetric cell. Moreover, the selective ion transport layer, having pores smaller than vanadium ions, blocked vanadium ions from migrating toward the zinc anode, thereby reducing its corrosion and contributing to a capacity retention of 86% after 2000 cycles under full‐cell conditions. This study demonstrates that the pore size of the coating layer influences the long‐term stability of aqueous zinc‐ion batteries and may serve as a guide when selecting interface modification materials for various metal batteries.
The commercialization of aqueous zinc‐ion batteries has been hindered by considerable drawbacks, such as dendritic zinc growth and cathode dissolution in mildly acidic electrolytes. Here, uniform Zn deposition, suppression of corrosion, and vanadium oxide‐based cathode dissolution are achieved via a selective ion transport layer composed of MOF‐801, which improved the performance and stability of aqueous zinc‐ion batteries.
