Interfacial Reaction Kinetics Research Articles

Construction of MoS2/NiS2 heterostructure with fast interfacial reaction kinetics for ultrafast sodium storage

Constructing heterostructure is a valid method to reinforcing sodium storage performance of transition metal chalcogenides materials. Herein, a simple, safe and controllable one step hydrothermal method is proposed to synthesize MoS2/NiS2 heterostructure. Due to the difference in band gaps and work functions of MoS2 and NiS2, the charges are redistributed at the MoS2/NiS2 heterointerfaces, thereby accelerating the migration of electrons and Na+. The heterointerfaces provide extra active sites for storing Na+, thus increasing the sodium storage capacity of the heterostructure. Furthermore, the distinct redox potentials of NiS2 and MoS2 promote the structural stability of MoS2/NiS2 heterostructure during the electrochemical reaction processes. Consequently, the obtained MoS2/NiS2 heterostructure exhibits superior rate properties (339.4 mAh g−1 at 10 A g−1) and ultra-stable cycling stability (480.5 mAh g−1 after 350 cycles at 1 A g−1). This paper presents a valid strategy for creating heterostructure anodes with excellent sodium storage properties.

Electrochemical Reduction of N2 to Ammonia Promoted by Hydrated Cation Ions: Mechanistic Insights from a Combined Computational and Experimental Study.

Alkali ions, major components at the electrode-electrolyte interface, are crucial to modulating reaction activity and selectivity of catalyst materials. However, the underlying mechanism of how the alkali ions catalyze the N2 reduction reaction (NRR) into ammonia remains elusive, posing challenges for experimentalists to select appropriate electrolyte solutions. In this work, by employing a combined experimental and computational approach, we proposed four essential roles of cation ions at Fe electrodes for N2 fixation: (i) promoting NN bond cleavage; (ii) stabilizing NRR intermediates; (iii) suppressing the competing hydrogen evolution reaction (HER); and (iv) modulating the interfacial charge distribution at the electrode-electrolyte interface. For N2 adsorption on an Fe electrode with cation ions, our constrained ab initio molecular dynamic (c-AIMD) results demonstrate a barrierless process, while an extra 0.52 eV barrier requires to be overcome to adsorb N2 for the pure Fe-water interface. For the formation of *NNH species within the N2 reduction process, the calculated free energy barrier is 0.50 eV at the Li+-Fe-water interface. However, the calculated barrier reaches 0.81 eV in pure Fe-water interface. Furthermore, experiments demonstrate a high Faradaic efficiency for ammonia synthesis on a Li+-Fe-water interface, reaching 27.93% at a working potential of -0.3 V vs RHE and pH = 6.8. These results emphasize how alkali metal cations and local reaction environments on the electrode surface play crucial roles in influencing the kinetics of interfacial reactions.

Controlled growth of 3D CdS-branched ZnO nanorod arrays for efficient solar driven photoelectrochemical water splitting

While world energy consumption is rising every year, the development of clean and renewable energy sources becomes very important for keeping the standard of living and preserving the environment. Solar driven photoelectrochemical (PEC) water splitting to produce hydrogen and oxygen is a promising method to contribute to the energy increasing demand. The development of the photoelectrode is a key factor for improving the PEC performance. A new morphology of 3D CdS-branched ZnO nanorod array nanocomposite has successfully been synthesized via solution routes as a photoanode. The present nanocomposite provides the highest photocurrent density of 2.5 mA/cm2 at a potential 1.23 V vs. RHE, which is about 83.3 times compared to a photocurrent density of about 0.03 mA/cm2 of the bare ZnO nanorod array photoelectrode. The boost of the PEC performance is improved due to the improvement of light absorption capacity, the enhanced energy band alignment (type-II heterostructure) promoting the charge transfer and separation, and the improvement of the electrode-electrolyte interface reaction kinetics. The result will be useful for further research on energy conversion and energy storage devices.

Design method of immiscible dissimilar welding (Mg/Fe) based on CALPHAD and thermodynamic modelling

Joining dissimilar metals is a major challenge in joining technology; the weldability of immiscible systems is especially challenging. In this study, a design methodology for dissimilar welding is suggested. The Miedema model and Toop model are developed to calculate the thermodynamics of quaternary alloy systems (Mg-Fe-Al-Cu). Finite element modelling (FEM) of temperature fields and the calculation of phase diagrams (CALPHAD) are combined to provide prerequisite information for modelling. As a test subject, laser welded lap configuration joints of AZ31B magnesium alloy and DP590 steel with a copper coating were put into the design scheme. The interfacial elemental diffusion and formation of intermetallics (IMCs) along the interface during the welding process are predicted. This simulation design scheme predicts the interfacial reaction kinetics and identifies whether the intermediate element works or not. The effects of the Cu coating thickness on the weld constitution, interfacial microstructures and mechanical properties were studied. Cu coating promotes the weld formation fostering the metallurgical reaction of the fusion zone (FZ) with the steel brazing interface. The mechanism of interfacial reactions during the welding-brazing process has been clarified. The Vickers hardness distribution across the interface shows that the Cu-IMCs are ductile.

From Fundamental Interfacial Reaction Kinetics to Macroscopic Current–Voltage Characteristics: Case Study of Solid Acid Fuel Cell Limitations and Possibilities

AbstractThe unique properties of solid acid electrolytes, in particular CsH2PO4, are in many ways ideal for fuel cell operation. However, the technology is constrained by high cathode overpotentials. Here a simplified cathode geometry is employed to obtain the fundamental electrochemical parameters (exchange current density and charge transfer coefficient) describing the oxygen reduction reaction (ORR) at the CsH2PO4‐Pt‐gas interface. The parameters are incorporated into a 1D model of the voltage–current characteristics of realistic SAFC cathodes, which reproduced the measured polarization behavior of such cathodes without recourse to fitting adjustable parameters. Following this validation, the model is utilized to evaluate the impact of changes to cathode properties, microstructure, and operating conditions. Of these, the charge transfer coefficient, measured to have a value of ≈0.6 for ORR on Pt in the SAFC cathode environment, is found to have the greatest impact on power output. Nevertheless, even without material modifications, a combination of microstructural and operational modifications are identified with projected performance metrics meeting Department of Energy targets (0.8 V at 300 mA cm−2, and peak power density of 1 W cm−2), albeit at high Pt loadings. However, the analysis indicates that truly meaningful advances will likely necessitate the discovery of alternative ORR catalysts.

Duodecuple H‐Bonded NH4+ Storage in Multi‐Redox‐Site N‐Heterocyclic Cathode for Six‐Electron Zinc–Organic Batteries

AbstractDesigning multiple redox sites in electroactive organic cathodes that allow more electron transfer is a permanent target for energy storage. Here, six‐electron zinc–organic batteries are reported accessed by duodecuple H‐bonded NH4+ storage in N‐heterocyclic dipyrazino[2,3‐f:2′,3′‐h]quinoxaline‐2,3,6,7,10,11‐hexacarbonitrile (DQH) cathode. DQH features an extended π‐conjugated aromatic planarity enriched with super electron delocalization routes and dodecahedral‐active imine/cyano motifs, achieving a high capacity up to 385 mAh g−1 at 0.5 A g−1. Besides, DQH cathode redox‐exclusively couples with small‐hydration‐size and low‐desolvation‐energy‐barrier NH4+ ions (0.33 nm and 0.19 eV vs 0.86 nm and 0.36 eV of Zn2+) via flexible H‐bonding interactions. NH4+ topo‐coordination enables DQH anti‐dissolution in aqueous electrolytes to avoid common capacity decay of small organic molecules, and solves the instability and low interfacial reaction kinetics issues caused by rigidly and sluggishly repeated insertion of Zn2+ ions. This gives zinc–organic battery high‐rate ability (30 A g−1) and high lifespan (30 000 cycles at 10 A g−1).

Fast Interfacial Defluorination Kinetics Enables Stable Cycling of Low-Temperature Lithium Metal Batteries.

The development of low-temperature lithium metal batteries (LMBs) encounters significant challenges because of severe dendritic lithium growth during the charging/discharging processes. To date, the precise origin of lithium dendrite formation still remains elusive due to the intricate interplay between the highly reactive lithium metal anode and organic electrolytes. Herein, we unveil the critical role of interfacial defluorination kinetics of localized high-concentration electrolytes (LHCEs) in regulating lithium dendrite formation, thereby determining the performance of low-temperature LMBs. We investigate the impact of solvation structures of LHCEs on low-temperature LMBs by employing tetrahydrofuran (THF) and 2-methyltetrahydrofuran (2-MeTHF) as comparative solvents. The combination of comprehensive characterizations and theoretical simulations reveals that the THF-based LHCE featured with a strong solvation strength exhibits fast interfacial defluorination reaction kinetics, thus leading to the formation of an amorphous and inorganic-rich solid-electrolyte interphase (SEI) that can effectively suppress the growth of lithium dendrites. As a result, the highly reversible Li metal anode achieves an exceptional Coulombic efficiency (CE) of up to ∼99.63% at a low temperature of -30 °C, thereby enabling stable cycling of low-temperature LMB full cells. These findings underscore the crucial role of electrolyte interfacial reaction kinetics in shaping SEI formation and provide valuable insights into the fundamental understanding of electrolyte chemistry in LMBs.

Cell membrane-inspired regulation of reactant diffusion for active agent microencapsulation via interface engineering

Microencapsulation of hydrophilic amines in nonaqueous emulsions provides opportunities for a variety of applications, such as CO2 absorbents, and adhesives, but also presents challenges due to the intense reactant diffusion and disruptive interfacial reaction kinetics. Drawing inspiration from cellular systems, where cell membranes effectively regulate mass transfer for essential activities, we propose an interface engineering approach to manage interfacial reactant diffusion. This strategy obviates the modification of emulsion phases with additives in literature, which lowered effective core content. To achieve this, a solvent-induced polymer self-assembling method is adopted. The self-assembled polymer effectively formed a stabilizing viscoelastic film, which kinetically traps the microdroplets, serves as a viscous barrier lowering intense amine diffusion and interfacial polymerization kinetics, and provides protection for the microdroplets against the destructive forces from reaction turbulence and emulsion collision. This approach possesses high tolerance against microencapsulation conditions and is technically friendly, laying the groundwork for scalable microencapsulation of amines to meet industrial demands. We successfully synthesized Tetraethylenepentamine (TEPA)-loaded microcapsules with adjustable shell tightness, hierarchical shell structures, high shell strength and high core content. The method's versatility is further evidenced with different species containing reactive hydrogens. The demonstrated potential of TEPA-loaded microcapsules in effective CO2 capture and instant adhesives provides a fresh perspective on the microencapsulation of distinct polar payloads through interface engineering and its wide-ranging applications.

Multifunctional Supramolecular Hydrogel Modulated Heterojunction Interface Carrier Transport Engineering Facilitates Sensitive Photoelectrochemical Immunosensing.

Highly responsive interface of semiconductor nanophotoelectrochemical materials provides a broad development prospect for the identification of low-abundance cancer marker molecules. This work innovatively proposes an efficient blank WO3/SnIn4S8 heterojunction interface formed by self-assembly on the working electrode for interface regulation and photoregulation. Different from the traditional biomolecular layered interface, a hydrogel layer containing manganese dioxide with a wide light absorption range is formed at the interface after an accurate response to external immune recognition. The formation of the hydrogel layer hinders the effective contact between the heterojunction interface and the electrolyte solution, and manganese dioxide in the hydrogel layer forms a strong competition between the light source and the substrate photoelectric material. The process effectively improves the carrier recombination efficiency at the interface, reduces the interface reaction kinetics and photoelectric conversion efficiency, and thus provides strong support for target identification. Taking advantage of the process, the resulting biosensors are being explored for sensitive detection of human epidermal growth factor receptor 2, with a limit of detection as low as 0.037 pg/mL. Also, this study contributes to the advancement of photoelectrochemical biosensing technology and opens up new avenues for the development of sensitive and accurate analytical tools in the field of bioanalysis.

Boosting interfacial reaction kinetics in yarn-shaped zinc-V2O5·nH2O batteries through carbon nanotube intermediate layer integration

Flexible yarn-shaped batteries are promising candidates for the wearable electronics owing to their good flexibility, tiny volume, compatibility with textiles. However, their practical applications are hindered by low capacity, active material mass loading, and energy density. Herein, we develop a coaxially wrapping strategy to fabricate an advanced yarn-shaped aqueous zinc-ion batteries (AZIBs) incorporating core-sheath carbon nanotube (CNT)/V2O5·nH2O composite yarns as cathodes and zinc wire as anodes. The as-wrapped CNT intermediate layer not only enhances the surface's conductivity, but the nano-array porous layer can also accelerate the mixing of ion concentration between the electrode surface and the electrolyte fluid through the turbulence effect, thereby improving the interfacial ion/electron kinetics. As a result, the energy storage mechanism of CNT/V2O5·nH2O yarn AZIBs transformed from capacitive-dominant to diffusion-controlled process, and the batteries demonstrate exceptional discharge capacity of 566.7 mAh g−1 at 0.1 A g−1, surpassing the state-of-art yarn-based AZIBs and approaching the theoretical zinc storage capacity (589 mAh g−1). In addition, they exhibit a high energy density of 471 Wh kg−1 at 25.5 W kg−1 and excellent cycling performance. This work opens a new and efficient avenue for the structure design of high-performance electrode materials for flexible yarn-based batteries.

Slag Electrical Conductivity and Its Effect on Mass Transport and Interfacial Reaction Kinetics

Pyrometallurgical refining typically involves slag–metal reactions which are commonly controlled by transport of reactants in the slag or metal phase. For the simplicity of analysis, mass transport in slag is generally treated on a phenomenological basis as transport of molecules. Although this approach works well for many of the reaction systems over narrow ranges of conditions, it can fail when extrapolated over a wide range of conditions. In many refining processes, transport of oxygen in slag determines the kinetics of major reactions. Transport of oxygen in slag is strongly influenced by the electrical conductivity of slag. Whilst this has been well understood since the 1950s, there have been relatively few attempts to quantify the effects of slag electrical properties on the refining kinetics. Herein, an overview is presented focusing on the electrical properties of slags and their effects on the transport kinetics in steelmaking reactions. An analysis is conducted based on a modified version of the approach taken by Wagner to describe oxygen transport in solid oxides. Data from the literature including work from the authors’ laboratory is discussed in an evaluation of literature oxygen transport in CaO–SiO2–FetO, CaO–SiO2–Al2O3–FetO, and PbO–Fe2O3 slags.

Reconstructing Inorganic‐Rich Interphases by Nonflammable Electrolytes for High‐Voltage and Low‐Temperature LiNi0.5Mn1.5O4 Cathodes

AbstractCobalt‐free and spinel LiNi0.5Mn1.5O4 (LNMO) cathodes commonly suffer from undesirable solvent decomposition, serious transition‐metal dissolution, and unstable cathode electrolyte interphase (CEI) layers, incurring rapid capacity decay at high voltages and low temperatures. Herein, these issues are well addressed by utilizing fluorinated solvents with a low coordination number and ethyl propionate with a low melting point. A Li2CO3/LiF‐rich heterostructured CEI layer, which possesses good electron blocking capability of LiF, fast Li+ transport kinetics of Li2CO3 and good mechanical stability, is generated by the synergistic decomposition of hybrid solvents. The robust, homogeneous, and well‐balanced CEI layers subsequently prevent catalyzed parasitic side reactions, prohibit transition‐metal dissolution, and ensure fast interfacial reaction kinetics crossover to the LNMO cathode, thus improving its cycling stability. Consequently, the LNMO cathode delivers a high‐capacity retention of 95.8% over 500 cycles at 25 °C and 97.5% after 180 cycles at −20 °C. This work provides an encouraging alternative to design the high‐voltage and low‐temperature electrolyte for pushing the ongoing research to stabilize Co‐free LNMO materials toward practical applications.

Weak Electrostatic Force on K+ in Gel Polymer Electrolyte Realizes High Ion Transference Number for Quasi Solid-State Potassium Ion Batteries.

Quasi-solid-state potassium-ion batteries (SSPIBs) are of great potential for commercial use due to the abundant reserves and cost-effectiveness of resources, as well as high safety. Gel polymer electrolytes (GPEs) with high ionic conductivity and fast interfacial charge transport are necessary for SSPIBs. Here, the weak electrostatic force between K+ and electronegative functional groups in the ethoxylated trimethylolpropane triacrylate (ETPTA) polymer chains, which can promote fast migration of free K+, is revealed. To further enhance the interfacial reaction kinetics, a multilayered GPE by in situ growth of poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP) on ETPTA (PVDF-HFP|ETPTA|PVDF-HFP) is constructed to improve the interface contact and provide sufficient K+ concentration in PVDF-HFP. A high ion transference number (0.92) and a superior ionic conductivity (5.15 × 10-3 S cm-1) are achieved. Consequently, the SSPIBs with both intercalation-type (PB) and conversion-type (PTCDA) cathodes show the best battery performance among all reported SSPIBs of the same cathode. These findings demonstrate that potassium-ion batteries have the potential to surpass Li/Na ion batteries in solid-state systems.

In Situ Molecular Engineering Strategy to Construct Hierarchical MoS2 Double-Layer Nanotubes for Ultralong Lifespan "Rocking-Chair" Aqueous Zinc-Ion Batteries.

Rechargeable aqueous zinc ion batteries (AZIBs) have gained considerable attention owing to their low cost and high safety, but dendrite growth, low plating/stripping efficiency, surface passivation, and self-erosion of the Zn metal anode are hindering their application. Herein, a one-step in situ molecular engineering strategy for the simultaneous construction of hierarchical MoS2 double-layer nanotubes (MoS2-DLTs) with expanded layer-spacing, oxygen doping, structural defects, and an abundant 1T-phase is proposed, which are designed as an intercalation-type anode for "rocking-chair" AZIBs, avoiding the Zn anode issues and therefore displaying a long cycling life. Benefiting from the structural optimization and molecular engineering, the Zn2+ diffusion efficiency and interface reaction kinetics of MoS2-DLTs are enhanced. When coupled with a homemade ZnMn2O4 cathode, the assembled MoS2-DLTs//ZnMn2O4 full battery exhibited impressive cycling stability with a capacity retention of 86.6% over 10 000 cycles under 1 A g-1anode, outperforming most of the reported "rocking-chair" AZIBs. The Zn2+/H+ cointercalation mechanism of MoS2-DLTs is investigated by synchrotron in situ powder X-ray diffraction and multiple ex situ characterizations. This research demonstrates the feasibility of MoS2 for Zn-storage anodes that can be used to construct reliable aqueous full batteries.

Boosting Photoresponse of Self‐Powered Photoelectrochemical Photodetectors via Planar Interdigital Electrodes

AbstractUnderwater optical communications (UOC) and light imaging have aroused tremendous attention due to the ever‐growing exploration of marine resources. Photoelectrochemical‐type photodetectors (PEC PDs) have good application potential in underwater optoelectronic devices because of their intrinsic aqueous operation characteristics with a self‐powered function and high sensitivity. However, most of the currently reported PEC PDs consist of sandwich‐like device structures, increasing the weight, volume, and complexity of the devices. Here, a planar interdigital electrode (IE) structure for high‐performance self‐powered PEC PDs for the first time is proposed. The CuO‐based IE PEC PDs achieve good photoresponse in the wide region of 365–850 nm with a high responsivity of 21.86 mA W−1 (455 nm irradiation), a fast response time (0.02/0.17 s), and good stability in artificial seawater. The good photoresponse is attributed to the promotion of interfacial electrochemical reaction kinetics and the accelerated charge transport by IE structure. Moreover, the CuO‐based IE PEC PDs show good UOC and underwater light imaging capability. Furthermore, the IE structure successfully applies in p‐Se and CuSe PEC PDs, demonstrating its good universality. The simpler structure and good photoresponse demonstrate that IE structure provides a new perspective for designing high‐performance, low‐cost, and self‐powered PEC PDs.

An efficient approach to compartmentalize double layer effects on kinetics of interfacial proton-electron transfer reactions

Activation barriers for elementary electrochemical reactions can show strong dependence on the composition and structure of the electrode–electrolyte interface, the electrochemical double layer (EDL), due to the highly polar nature of ion/electron transfer transition states. A compartmentalized analytical framework, built upon DFT calculations, is developed to consider complex interactions between reaction intermediates and the EDL. The approach analytically captures how altering interfacial properties, such as the dielectric constant or distribution of electrolyte charges, impact electrocatalytic activation barriers. Dipole moment changes along the reaction path plays the largest role in dictating the extent to which interfacial properties impact elementary electrochemical kinetics. The compartmentalization and uncertainty quantification capability of the developed framework is illustrated employing a Helmholtz model with two parameters, dielectric constant and double layer thickness. The framework translates routine DFT analysis of (water-assisted) hydrogenation activation barriers to proton-coupled electron transfer barriers that depend analytically on electrode potential and EDL properties.

Photocatalytic overall water splitting endowed by modulation of internal and external energy fields.

The pursuit of sustainable and clean energy sources has driven extensive research into the generation and use of novel energy vectors. The photocatalytic overall water splitting (POWS) reaction has been identified as a promising approach for harnessing solar energy to produce hydrogen to be used as a clean energy carrier. Materials chemistry and associated photocatalyst design are key to the further improvement of the efficiency of the POWS reaction through the optimization of charge carrier separation, migration and interfacial reaction kinetics. This review examines the latest progress in POWS, ranging from key catalyst materials to modification strategies and reaction design. Critical analysis focuses on carrier separation and promotion from the perspective of internal and external energy fields, aiming to trace the driving force behind the POWS process and explore the potential for industrial development of this technology. This review concludes by presenting perspectives on the emerging opportunities for this technology, and the challenges to be overcome by future studies.

Carbonate weakens the interactions between potassium and calcareous soil.

The ion interfacial transport driven by ion-surface interactions in calcareous soil has a profound impact on the nutrient storage and environmental buffer capacity of the main agricultural soils in dry and semi-arid areas. The roles that carbonate plays in preserving the soil's inorganic carbon pool and soil structure stability have been widely investigated, but its significance in the aforementioned microscopic processes, especially the influence of carbonate on the interfacial reaction kinetics of nutrient elements, is yet to be determined. In this study, potassium (K) was used as an indicator ion to investigate its affinity in carbonate-removed (CREM) and carbonate-reserved (CRES) calcareous soil using the general theory of ion diffusion in an external electric field. We discovered that (1) at a given initial K concentration, the carbonate in CRES soil retards the adsorption rate and diminishes the adsorption amount of K in calcareous soil, reducing the interfacial transport properties of nutrient ions at the solid-liquid interface of calcareous soils compared with CREM soil; and (2) this weakening of the interfacial transport effect on nutrient K originates from the soil carbonate, which prefers to weaken the electrostatic interaction intensity between K and the calcareous soil surface. Furthermore, this is due to the carbonate shielding effect on the surface adsorption sites of other soil components and the competitive relationship between K+ and cations released by carbonate dissolution. The influence of carbonate on the nutrient ion transport at the solid-liquid interface of calcareous soil has been investigated by soil electrochemistry theory-based ion adsorption kinetics, and the links between kinetic features and ion-surface binding energy have been clarified.

(Invited) A "Master Curve" for Plating Onset, Reaction Inhomogeneity during Fast Charging: Experiment and Theory

Inhomogeneous intercalation in porous anodes may lead to accelerated lithium plating during fast charging. This reaction inhomogeneity can occur both at the particle level or at the length scale set by the electrode thickness. Many studies have investigated the effects of various physical and electrochemical properties (e.g., ionic and mass transport, interface reaction kinetics, electrode thermodynamic behavior) on reaction inhomogeneity. However, their effect on accelerated lithium plating at high C-rates has not been fully elucidated. In this work, theory and experiment are used to study how reaction inhomogeneity and plating are related at high C-rates. It is shown that a non-dimensional number, the “reaction inhomogeneity parameter” λ, can be used to predict plating onset in graphite half-cells with a simple analytical solution derived from porous electrode theory, so long as anode particles are sufficiently small. Experiments measuring lithium plating onset in a small-particle graphite at various C-rates and thicknesses can be normalized to a single “master curve” for plating onset when plotted as a function of λ. These comparisons validate the theoretical predictions from both analytical and numerical modeling. Further, experiments with in situ visual inspection of local intercalation in graphite demonstrate that this λ parameter can predict reaction inhomogeneity measured using various metrics. These combined results support the numerical prediction that reaction inhomogeneity on the electrode length scale is responsible for accelerated plating at high charge rates for small-particle graphite. Further, it is shown with theory that this normalization procedure may be applicable for varied porosity, tortuosity, electrolyte materials and different anode materials. Finally, it is demonstrated that use of this “master curve” can be extended to patterned electrodes where channeled architectures are used to improve high C-rate charging.

Crystal Orientation-Dependent Interface Compatibility in the Oxide Composite Cathode by in Situ Heating Transmission Electron Microscopy

All-solid-state batteries (ASSBs) with oxide-based solid electrolytes are getting prominence as a forthcoming battery system capable of overcoming the drawbacks of current lithium-ion batteries by satisfying the expanding demand for high energy density and safety. However, the poor interfacial contact between cathode active materials and solid electrolytes, at which lithium ions diffuse and the charge transfer occurs, is a major concern for practical utilization. Although the co-sintering process at high temperatures is essential to achieve an intimate interface contact, excessive thermal energy reversely accelerates the interfacial degradation reaction, of which the mechanism has been still unexplored. Here, using an epitaxial model system in which the crystal orientations of the Li(Ni1/3Co1/3Mn1/3)O2 cathode and Li3xLa(2/3)-x⎕(1/3)-2xTiO3 solid electrolyte are controlled, we directly probe the interfacial reaction in real-time during heating by in situ heating transmission electron microscopy, and investigate the impact of the crystal orientation at the interface on the interfacial reaction mechanism and kinetics. In situ observation reveals that the interfacial reactions are highly dependent on the crystal orientation at the interface involving the onset temperature of the reaction, the diffusion behavior of lithium ions, the intermediate states, and the overall degradation mechanism between the active material and the solid electrolyte. The interfacial degradation during heating increases the charge transfer resistance between the cathode active material and the solid electrolyte, and the increasing tendency of the resistance is closely related to the crystal orientation-dependent interfacial degradation.