Search

Li metal anodes (LMAs) has attracted extensive research interest because of its extremely high theoretical capacity (3860 mAh/g) at low redox potential (−3.04 V vs. standard hydrogen electrode). However, the extremely high chemical reactivity and the intrinsic “hostless” nature of LMAs bring about serious dendritic growth and dramatic volume change during the plating/strapping process, thus resulting in poor Coulombic efficiency, short lifespan, and severe safety concerns. Of various strategies, the construction of three-dimensional carbonaceous scaffolds for LMAs can substantially reduce the local current density, inhibit Li dendrite growth, and accommodate volume variation. Electrospinning is a simple yet effective strategy to fabricate carbon nanofibers (CNFs), which have been regarded as promising skeletons for LMAs, owing to their large surface areas, good electrical conductivity, and high porosity. In this Mini Review, we briefly introduce the fabrication of CNFs using electrospinning and the modification of CNFs. We highlight the recent advances in electrospun CNF skeletons for LMAs, including pure CNF and CNF-based composite scaffolds. Finally, we discuss the remaining challenges of electrospun CNF scaffolds for LMAs and provide possible solutions to push forward the advancement in this field.

Na metal is a promising candidate as anode material owing to its high theoretical energy density and abundance on earth, but suffers from dendrite growth, extremely large volume change, and poor Coulombic efficiency. Herein, a low-cost and effective strategy is developed to discourage the dendrite growth by in situ formation of an artificial NaF-rich protective layer on Na metal. The protective layer facilitates the formation of highly stable, NaF-rich solid electrolyte interphase (SEI) capable of preventing continuous electrolyte depletion during charge/discharge cycles. The depth profiling experiment confirms functional gradient of SEI through its thickness with wealthier NaF species towards the Na metal. The symmetric cells assembled using the Na anode with a protective layer exhibit excellent cyclic stability with low overpotentials of 8, 50, and 70 mV, at areal currents of 1, 5 and 10 mA cm−2, respectively, thanks to its high dendrite suppression ability as proven by theoretical calculations. The full battery prepared with a Na3V2(PO4)3 cathode delivers 99% retention of Coulombic efficiency after 400 and 600 cycles at 1C in ether- and carbonate-based electrolytes, respectively. The SEI layer design strategy presented here can shed some important insights into the development of high-performance dendrite-free Na metal batteries and interface engineering for solid electrolytes.

Separators are indispensable components of modern electrochemical energy storage devices such as lithium-ion batteries (LIBs). They perform the critical function of physically separating the electrodes to prevent short-circuits while permitting the ions to pass through. While conventional separators using polypropylene (PP) and polyethylene (PE) are prone to shrinkage and melting at relatively high temperatures (150 °C or above) causing short circuits and thermal runaway, separators made of thermally stable polyimides (PIs) are electrochemically stable and resistant to high temperatures, and possess good mechanical strength—making them a promising solution to the safety concerns of LIBs. In this review, the research progress on PI separators for use in LIBs is summarized with a special focus on molecular design and microstructural control. In view of the significant progress in advanced chemistries beyond LIBs, recent advances in PI-based membranes for applications in lithium-sulfur, lithium-metal, and solid-state batteries are also reviewed. Finally, practical issues are also discussed along with their prospects.

Solid polymer electrolytes (SPEs) and gel polymer electrolytes (GPEs) show great promise for the realization of commercial, high performance Li-metal batteries (LMBs). However, the interfacial and high-temperature instability of GPEs, and the low room-temperature ionic conductivity of SPEs still limit their practical implementation. This article presents a solid-like dual-salt polymer electrolyte (DSPE), consisting of coordinated solvents and thermally stable Li-salts within a temperature-resistant polymer matrix, as a promising new strategy for addressing these issues. The developed DSPE demonstrates high ionic conductivity of 0.16, 0.73, and 1.93 mS cm−1 at −20, 20, and 100 °C, respectively. Li|DSPE|LiFePO4 batteries using this DSPE deliver an initial discharge capacity of 151 mAh g−1 at 0.5C, a rate performance of 123 mAh g−1 at 3C, and excellent long-term stability with a retained capacity of 143 mAh g−1 after 500 cycles at 0.5C and 23 °C. Further, the battery shows stable cycling between −10 °C and 80 °C. This impressive electrochemical performance is ascribed to the high Li+ conductivity of the membrane, the stabilization of the Al current collector, and the formation of a robust, LiF-rich solid-electrolyte interphase containing conductive Li-B-O-based species.

With the rapid growth of lithium-ion battery (LIB) market raising concerns about limited lithium resources and their surging prices, rechargeable sodium-ion batteries (SIBs) have attracted growing attention as an alternative to LIBs because of abundance and low cost of sodium precursors and significantly reduced fabrication costs arising from the use of Al as the anode current collector. Metal chalcogenides (MCs) have emerged as potential anodes of SIBs thanks to a large variety of available species, abundance, low cost, unique physical and chemical properties, and high theoretical capacities. However, MCs face several challenges like large volume changes during sodiation and desodiation, poor electrical conductivities, and lack of large-scale production. Hence, various strategies have been employed to address these issues for practical applications of SIBs. This review is dedicated to integrating recent progress in rational design of nanostructured MCs for SIBs. Layer- and non-layer structured MCs assembled with nanocarbon materials are discussed along with their underlying reaction mechanisms. A special focus is placed on discussion of the findings from advanced in situ/operando characterization techniques and atomistic and molecular level simulations with various examples to shed comprehensive mechanistic insights into the sodiation and desodiation processes. Finally, the challenges, potential solutions, and future perspectives for exploring new SIB electrode materials are highlighted.

With the rapid development of wearable devices, there is an increasing demand for ultra-safe flexible lithium-ion batteries (LIBs) capable of delivering high energy density. Because it can provide the highest possible capacity of 3860 mAh g-1, lithium metal has drawn tremendous research attention. However, Li is a highly reactive metal that grows dendrites during the cycling of lithium-metal batteries (LMBs). To resolve the problem, we developed a new non-flammable elastic quasi-solid electrolyte (QSE), which can be polymerized in situ and whose composition is tailored to achieve high elasticity. Moreover, the incorporation of trimethyl phosphate (TMP) renders the electrolyte non-flammable. Thanks to the solid electrolyte interphase (SEI) formed, the LMB with QSE displays excellent cycling stability as it can be operated for 500 cycles, with a capacity retention of 94%. The corresponding symmetric cell cycled stably for more than 500 h. Scanning electron microscopy (SEM) and density functional theory (DFT) calculations reveal that fluoroethylene carbonate (FEC) is critical in forming the LiF-rich SEI that enables long-term cycling stability. In brief, a non-flammable, elastic, and stable QSE is reported for the first time, which is very promising in the application of the next-generation wearable devices.

Sb2Se3 based anodes are widely studied for advanced Na-ion batteries. However, their Na storage performance at high rates is limited to 2000 mA g−1 because of poor kinetics of redox reactions. Here, the heterointerfacial interactions taking place between Sb2Se3 and functionalized CNTs are probed to understand the formation of Sb–O–C and Se–C bonds in the amorphous a-Sb2Se3/CNT composite using the density functional theory and ab-initio molecular dynamics simulations. The distinct morphologies and thicknesses of solid electrolyte interface layers formed on crystalline c-Sb2Se3 and a-Sb2Se3/CNT composite electrodes are revealed by advanced cryogenic transmission electron microscopy and their influences on the kinetics of redox reactions in the corresponding electrodes are identified. The structurally robust a-Sb2Se3/CNT composite electrode exhibits four orders of magnitude higher Na-ion diffusion coefficient than the crystalline c-Sb2Se3 counterpart, giving rise to an exceptional high-rate capacity of 454 mA h g−1 at 12800 mA g−1 and capacity retention of over 62% after 200 cycles at 10000 mA g−1. The full cells containing the composite electrodes present energy and power densities of ∼175 Wh kg−1 at 0.5C and ∼5784 W kg−1 at 80C, respectively, and stable cyclic performance up to 120 cycles.

Room temperature (RT) sodium-sulfur (Na-S) batteries are a promising technology for stationary energy storage thanks to their high energy density of 1274 Wh kg−1 and low cost. However, RT Na-S batteries are hazardous because they use highly volatile and flammable electrolytes. Here, we develop a new nonflammable electrolyte for RT Na-S batteries, consisting of sodium trifluoromethanesulfonimide (NaTFSI) in a mixture of trimethyl phosphate (TMP) and fluoroethylene carbonate (FEC). The nonflammable electrolyte facilitates highly stable and reversible Na plating/stripping during cycles. The dendrite-free Na-S battery with the NaTFSI/TMP+FEC electrolyte delivers a remarkable reversible capacity of 788 ​mAh g−1 after 300 cycles at 1C, corresponding to a negligible capacity decay below 0.04% per cycle. The ab initio molecular dynamics simulations and surface analysis reveal the formation of a NaF-rich solid electrolyte interphase (SEI) film with reduced interfacial resistance thanks to the introduction of FEC into the electrolyte. The formed NaF SEI layer suppresses the growth of Na dendrites on the anode, enhancing the electrochemical performance of the RT Na-S batteries. The new findings reported here will shed new light on dendrite-free RT Na-S batteries by the rational design of nonflammable electrolytes.

Few-layer 2D Sb2S3 (2D-SS) nanosheets are synthesized using a simple and scalable exfoliation method assisted by Li intercalation, which are employed as bifunctional anodes for both lithium ion batteries (LIBs) and sodium ion batteries (SIBs) for the first time. The 2D-SS nanosheets present a well-defined layered structure with an ultrathin thickness of 3.8 nm and a lateral size as large as several tens of micrometers, giving rise to an extremely large aspect ratio and surface area, compared to their bulk form before exfoliation. These ameliorating features of 2D-SS nanosheets offer fast high-rate transportation of Li+/Na+ ions through the short diffusion paths and abundant active sites. The 2D-SS electrode delivers a steady cyclic stability and an outstanding rate capability of 607 mA h g−1 at 2.0 A g−1 in LIBs, while exhibiting a decent capacity of ~680 mA h g−1 at 0.05 A g−1 in SIBs. Remarkably, the 2D-SS anodes present comparable or even better pseudocapacitive behaviors in SIBs than in LIBs, and the anomaly is explained by the better diffusion characteristics of Na atoms than Li atoms along with improved structural integrity after Na adsorption according to the first-principles calculations. Both the Li and Na atoms exhibit higher mobilities on the exfoliated 2D-SS nanosheets than on the bulk counterpart, responsible for the enhanced pseudocapacitive behaviors of the 2D-SS electrode. These new findings will help rationally design high-performance bifunctional anodes for next-generation alkali metal ion batteries.

Solid-state batteries (SSBs) with Li7La3Zr2O12 (LLZO) ceramic oxide electrolytes are attracting significant interest because of LLZO’s non-flammability, excellent ionic conductivity, electrochemical stability against Li metal anodes, and processability in air. However, the poor solid-solid contact between the electrolyte and the electrodes leads to large interfacial impedances, which are detrimental to the functioning of LLZO-based SSBs. In this work, we modified the electrode|Ta-doped-LLZO (LLZTO) interfaces by employing a plastic crystal interlayer based on succinonitrile with a fluoroethylene carbonate additive. The interlayer, which can be easily applied, drastically reduces the interfacial resistances and allows the stable operation of Li-metal based batteries. A Li|LLZTO|LiFePO4 battery with this interlayer can stably cycle at room-temperature for 50 times at 0.1 C while still retaining a capacity of 140 mAh g-1. The symmetric Li|LLZTO|Li cell with the interlayer can cycle at 0.2 mA cm-2 for over 150 hours. It also has a higher critical current density for the growth of dendrites compared with an analogous cell without the interlayer. In short, this work provides a facile and efficient methodology to enhance the effective Li transportation rates at the electrode|electrolyte interfaces of SSBs and can be readily applied to other types of electrolytes beyond LLZO.

The dissolution of Mn ions from Mn-containing cathodes and the growth of Na dendrites are two critical issues that deteriorate the life time of Na batteries. In this work, we develop a novel solid-state composite-polymer-electrolyte based on a polyvinylidene fluoride matrix and Na3Zr2Si2PO12 fillers to simultaneously tackle these two problems. Elemental and morphology analysis show that the composite-polymer-electrolyte effectively impedes the dissolution and migration of Mn ions from the Na0.67MnO2 cathode as well as facilitates the uniform deposition of Na on the anode. A facile interface modification is applied to improve the contact between the composite-polymer-electrolyte and electrodes, which reduces the interfacial resistances and greatly delays the growth of Na dendrites. Consequently, the Na0.67MnO2/Na cell with the composite-polymer-electrolyte displays a significant improvement in cyclic stability and rate performance, without sacrificing the specific capacity, compared to that of a cell using an organic-liquid-electrolyte. Therefore, this work provides an effective way to improve the cycle life of Na batteries by stabilizing both electrodes with a composite-polymer-electrolyte and can be readily applied to other batteries, e.g. Li batteries.

Highly conductive carbon microspheres (CMSs) with a hierarchical porous structure are prepared by electrospraying polystyrene/polyvinylpyrrolidine (PS/PVP) solution containing Ketjen carbon black (KB) nanoparticles. The branched KB particles serve as the structural skeleton to support CMSs while the hybrid polymer precursor forms multiscale pores upon pyrolysis. The CMSs possessing an extremely large pore volume of 2.08 cm3 g−1 and a large specific surface area of 756 m2 g−1 are melt-infiltrated with sulfur to form sulfur/CMS composite cathode for lithium-sulfur batteries. The cathode delivers a remarkable initial capacity of 1006 mAh g−1 at 1 C with high retention of 67.5% after 1000 cycles, and an initial capacity of 728 mAh g−1 at 2 C with high retention of 68.5% after 2000 cycles. The excellent electrochemical performance is attributed to the distinct functional and structural features of CMS framework: namely, microscale grain size, closely packed KB particles, large pore volume and hierarchical pore size, as well as superior conductive framework, which in turn suppress the shuttling of dissoluble polysulfides and boost the utilization of encapsulated sulfur. The above findings may offer insights into designing new carbon frameworks for other types of high performance rechargeable batteries.

Solid electrolyte interphase (SEI) is an electrically insulating and ionically conductive passivation layer which is formed on the electrode surface through electrolyte decomposition. SEI is crucial to battery performance because it plays a vital role to determine the Coulombic efficiency, cycle life, capacity, and safety. Given the intricated formation mechanisms and the complicated structures and compositions of SEI, the in-depth understanding of SEI is still challenging. This review is dedicated to critical discussion on recent advances in understanding the formation mechanisms of SEI. The important factors, including electrolyte components, temperature, areal current, and electrode materials, that affect the formation, morphology, structure, composition, and properties of SEI layers are discussed. In situ/operando characterization techniques used to look into the surface morphology, electrochemical performance, chemical composition, structure, and mechanical properties of SEI layers are emphasized. The recent progress of the state-of-the-art cryogenic electron microscopy aimed at atomistic visualization of SEI is highlighted. Multi-scale theoretical simulations employed to study the thermodynamic and kinetic properties of SEI are also discussed. In addition, the SEIs formed on various anodes using solid-state electrolytes are also presented. Finally, the outstanding challenges and future directions in understanding SEI are presented. This review is envisioned to offer new insights into rationally designing the SEI layers for the development of next-generation high-performance rechargeable batteries.

The potential application of metallic Na anodes for high energy density batteries is plagued by dendrite formation accompanied by rapid consumption of electrolyte and Na metal. Herein, coaxially electrospun, hollow and mesoporous carbon nanofiber (HpCNF) hosts possessing strong affinity with Na are developed for Na metal batteries. The combined in situ and cryogenic microscopy along with theoretical simulations reveal that the highly sodiophilic HpCNFs with abundant defects and nitrogen functional groups enable compact, uniform plating of Na with excellent reversibility aided by the resilient, fluorine-rich SEI layer. Thanks to the optimized Na deposition in the entire structure, the Na@HpCNF anodes present an average Coulombic efficiency of 99.7% after 1,400 cycles at a current density of 3 mA cm−2 and a plating/striping capacity of 6 mAh cm−2. Their symmetric cell maintains stable cycles for over 1000 hr at 5 mA cm−2 and 5 mAh cm−2, which is among the best when compared with state-of-the-art electrodes. The full cells paired with a Na3V2(PO4)2F3 cathode deliver remarkable specific capacities of 115 and 93 mAh cm−2 after 500 cycles at 1 C and 200 cycles at 4 C, respectively. These findings highlight new insight into rationally-designed metal anodes towards the development of high-performance metal batteries.

The silicon/carbon (Si/C) hybrid fibers with a hierarchical core–shell structure are prepared by encapsulating Si nanoparticles in the interconnected hollow carbon fibers (Si@IHCFs) based on a dual coaxial electrospinning technique. For the hierarchical structure, Si nanoparticles are embedded in the honeycomb-like carbon framework in the fiber core, which is further wrapped by the interlocked cobweb-like carbon shell network. As lithium-ion battery anode, the well-defined Si@IHCFs demonstrates a reversible capacity of 903 mAh g −1 and a capacity retention of 89% after 100 cycles with a current density of 0.2 A g −1 . With the current density gradually increasing to 2.0 A g −1 , the electrode shows a specific capacity of 743 mAh g −1 , exhibiting superior rate capability compared to the Si/C fibers with a core–shell but unconnected structure. The excellent electrochemical properties are attributed to the hierarchical core–shell structure and cross-linked network for the Si/C composite fibers. The carbon framework in the core region accommodates the volume expansion of Si by the honeycomb-like pores. And the interconnected carbon shell can not only prevent electrolyte from permeating into the core section, but also improve the electronic conductivity by the connections in the fiber network.

Sodium-ion batteries have been considered a cost-effective alternative to lithium-ion batteries because of the cheap and abundant sodium reserves. However, the sluggish kinetics arising from the slow ion and electron transport, particularly at high rates, is the main bottleneck of fast sodium storage. Here, few-layer MoSe2 encapsulated by nitrogen/phosphorus (N/P) co-doped carbon and reduced graphene oxide (MoSe2@NPC/rGO) composites are fabricated through a simple polymerization reaction followed by selenization. The two-dimensional composite nanosheets effectively shorten the ion diffusion length while the few-layer MoSe2 exposes a large surface area to the electrolyte. The NPC/rGO sheets intercalated within the composites function as channels for fast electron transfer and surface reactions. First-principles calculations show quick Na transport rates on the surface of MoSe2, and quantitative kinetics analysis reveals a pseudocapacitance-dominated Na+ storage mechanism at high rates. Thanks to the ameliorating functional features and highly reversible conversion reactions, the MoSe2@NPC/rGO electrode delivers a reversible capacity of ~340 mA h g−1 after 500 cycles at 0.5 A g−1 with a high contribution by surface capacitance. It also possesses a high reversible capacity of ~100 mA h g−1 even at an extremely high current density of 50 A g−1, presenting potential application as anodes for high-power sodium-ion batteries.

Rechargeable batteries have significantly helped to effectively use renewable energy sources as well as to intensively expand the electrification of vehicles. To achieve such goals, new advanced materials are urgently required. Atomically dispersed materials (ADMs) with single-atom metals supported on substrates feature uniform metallic sites and represent the utmost utilization of atoms, demonstrating wide applications in catalysis. These structural and morphological characteristics also make ADMs attractive materials for rechargeable batteries. Herein, we highlight and summarize the recent advances in synthetic methods for ADMs by physical confinement and chemical bonding. Subsequently, we summarize the recent progress in the design of diverse ADMs for lithium metal, lithium-sulfur, sodium-sulfur, lithium-oxygen, and zinc-air batteries and unveil the corresponding roles of ADMs from atomistic perspectives. Finally, the challenges and perspectives in this field are discussed.

Nanostructured metal chalcogenides (MCs) and their composites are studied for high performance sodium-ion batteries (SIBs). Herein, we report the assembly of an emerging MC, Sb2Te3, with functionalized carbon nanotubes (CNTs) to form composite anodes. The role of oxygenated functional groups on CNTs in fostering the chemical interactions with Sb2Te3 for enhanced structural integrity of electrodes is elucidated by density functional theory combined with ab-initio molecular dynamics simulations and X-ray photoelectron spectroscopy analysis. Remarkably, cryogenic transmission electron microscopy (TEM) analysis reveals a uniform and thin solid electrolyte interface (SEI) layer of ~19.1 nm on the Sb2Te3/CNT composite while the neat Sb2Te3 presents an irregular and ~67.3 nm thick SEI. The ex-situ X-ray diffraction (XRD) and ex-situ/in-situ TEM analyses offer mechanistic explanations of phase transition and volume changes during sodiation. The Sb2Te3/CNT composite electrode with an optimal content of 10 wt% CNTs delivers excellent reversible gravimetric and volumetric capacities of 422 mA h g−1 and 1232 mA h cm−3, respectively, at 100 mA g−1 with ~97.5% capacity retention after 300 cycles. The excellent high-rate capability of 318 mA h g−1 at 6400 mA g−1 corroborates the structural robustness of the composite electrode. Sodium-ion full cells (SIFCs) are assembled by pairing the above anode with a Na3V2(PO4)2F3 cathode, which exhibit remarkable energy density of ~229 Wh kg−1 at 0.5 C and excellent cyclic stability of over 71% and 66% capacity retention at 5 C and 10 C, respectively, after 200 cycles. Even at 40 C, an ultrahigh power density of 5384 W kg−1 is delivered. Furthermore, the pouch-type SIFCs prove excellent flexibility with ~85% capacity retention after 1000 bending cycles and satisfactory operation under temperatures ranging from 40 to −20 °C. The design strategy developed here can also be employed to other electrode materials to achieve better SEI stability and excellent Na storage performance.

Fe3O4 nanoparticles encapsulated in porous carbon fibers (Fe3O4@PCFs) as anode materials in lithium ion batteries are fabricated by a facile single-nozzle electrospinning technique followed by heat treatment. A mixed solution of polyacrylonitrile (PAN) and polystyrene (PS) containing Fe3O4 nanoparticles is utilized to prepare hybrid precursor fibers of Fe3O4@PS/PAN. The resulted porous Fe3O4/carbon hybrid fibers composed of compact carbon shell and Fe3O4-embeded honeycomb-like carbon core are formed due to the thermal decomposition of PS and PAN. The Fe3O4@PCF composite demonstrates an initial reversible capacity of 1015 mAh g−1 with 84.4% capacity retention after 80 cycles at a current density of 0.2 A g−1. This electrode also exhibits superior rate capability with current density increasing from 0.1 to 2.0 A g−1, and capacity retention of 91% after 200 cycles at 2.0 A g−1. The exceptionally high performances are attributed to the high electric conductivity and structural stability of the porous carbon fibers with unique structure, which not only buffers the volume change of Fe3O4 with the internal space, but also acts as high-efficient transport pathways for ions and electrons. Furthermore, the compact carbon shell can promote the formation of stable solid electrolyte interphase on the fiber surface.

Silicon (Si) has been regarded as one of the most attractive anode materials for the next generation lithium-ion batteries because of its large theoretical capacity, high safety, low cost and environmental benignity. However, the architecture of Si-based anode material still needs to be well designed to overcome the structure degradation and instability of the solid-electrolyte interphase caused by a large volume change during cycling. Here we report the electrochemical performances of a novel binder-free Si/carbon composite film consisting of alternatively stacked Si-porous carbon layers and graphene layers, which is synthesized by electrostatic spray deposition followed by heat treatment. For this composite film, Si nanoparticles are embedded in the porous carbon layer composed of nitrogen-doped carbon framework, carbon black and carbon nanotubes. And the combined Si-porous carbon layer is further sandwiched by flexible and conductive graphene sheets. The multilayered Si-porous carbon/graphene electrode shows a maximum reversible capacity of 1020 mAh g −1 with 75% capacity retention after 100 cycles and a good rate capability on the basis of the total electrode weight. The excellent electrochemical performances are attributed to the fact that the layer-by-layer porous carbon matrix can accommodate the volume change of Si particles and maintain the structural and electrical integrities.

Silicon/carbon composite microspheres with hierarchical core–shell structure were prepared by spray drying polyvinyl alcohol (PVA) solution containing silicon (Si) nanoparticles, followed by surface coating with polyacrylonitrile (PAN) and heat treatment. For the hierarchical structure, the core section (Si/po-C) was composed of PVA-based porous carbon framework and the embedded Si nanoparticles, and the desired Si/po-C@C microspheres were formed by encapsulating the Si/po-C core with PAN-based carbon shell. The Si/po-C@C anode gave rise to stable cycling performances with high capacity and excellent rate capability attributed to the hierarchical structure. The compact PAN-based carbon shell was able to block electrolyte to contact with Si effectively, promoting the formation of stable solid-electrolyte interphase. The porous carbon framework could accommodate the volume change of embedded Si nanoparticles and enhance the internal conductivity. Keywords: Si/C anode, Core–shell structure, Electrochemical properties, Lithium ion battery, Spray drying

Semicontinuous niobium and silver films were made in an ultra-high-vacuum (UHV) chamber and in-situ d.c. resistance measurements were performed. After interrupting the deposition, we investigated the immediate ageing phenomenon (relaxation) of the sample resistance on a time scale of about 10 min. Resistance increase and decrease were observed for niobium and silver samples, respectively. The intensity of the relaxation is sensitive to substrate temperature and film thickness. We suggest that edge diffusion and coalescence of islands due to thermomigration of the metal atoms are responsible for the resistance relaxation.

In situ DC resistance measurements were performed on semicontinuous niobium and silver films, which were made on mica and fullerene substrates in an ultra-high-vacuum(UHV) chamber. Right after the interruption of the deposition, we investigated the changes(relaxation) of the sample resistance on a time scale of about 10 minutes. Resistance increase was observed for Nb/mica and Ag C 60 systems, and decrease for Ag/mica system. The relaxation is sensitive to substrate temperature and film thickness. We suggest that the edge diffusion and mergence of islands due to thermomigration of the metal atoms are responsible for the resistance relaxation. The intensity and direction of the relaxation reflect the interfacial activity of the metal/substrate system. The heterogeneities on substrate may also play an important role during this process.