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Lithium-sulfur (Li-S) batteries have become prospective candidates for next-generation energy storage owing to the high energy density and low cost. However, the sluggish kinetics of the electrochemical reaction and shuttle effect result in a rapid capacity decay. Herein, a titanium nitride nanocrystal/N-doped graphene (TiN@NG) composite is developed to host elemental sulfur. The TiN nanoparticles decorated on graphene sheets attract Li polysulfides (LiPSx) and catalyze the electrochemical reduction and oxidation of LiPSx in the discharge and charge processes, respectively. These two effects effectively restrain the dissolution of the LiPSx and accelerate the electrochemical reactions, thereby, alleviating the shuttle effect. As a result, the cathode composed of TiN@NG/S delivers a remarkable reversible capacity (1390 mA h g−1 at 0.1 C) and excellent cycling performance (730 mA h g−1 after 300 cycles). We believe that this work can bring some inspiration for designing high-performance Li-S batteries.

Recycling of spent lithium-ion batteries has recently become a critical issue based on environmental concerns and a desire to reutilize resources. Among the existing recycling strategies, direct regeneration is largely encouraged from an economic and environmental perspective. However, current procedures used to separate the active cathode materials from the aluminum foil have some limitations for direct regeneration because they either destroy the structure of the cathode or use too many toxic and expensive reagents. Hence, we conducted comprehensive research on the microstructural evolution of the LiNi1−x−yCoxMnyO2 degraded electrode and then proposed a targeted method to recycle the spent cathode materials based on the increased residual lithium compounds. This separation process involves no other reagents but water, and toxic organic solvents, complicated processes, and waste treatments are unnecessary compared with the existing pretreatment strategies. Moreover, the separated cathodes are suitable for direct regeneration. Satisfactory capacity recovery of the cathode was achieved via simple sintering. Such a recycling process enables a sustainable closed-loop for the spent cathodes and provides new inspiration for the design of LIB recycling.

With the increasing demands for energy utilization and storage, the secondary lithium batteries with high energy-density and high safety performance are being continuously developed and improved. An in-depth understanding of the electrochemical process and corresponding micro-mechanism at the electrode/electrolyte interface of lithium batteries during charging and discharging is beneficial to open new avenues of guiding the optimal design of battery materials. In situ electrochemical atomic force microscopy (AFM) combines high-resolution surface-imaging of AFM with electrochemical characterizations, unraveling the direct visualization and dynamic evolution of the electrode/electrolyte interface in a working battery at nanoscale. This article reviews the latest research progress of in situ electrochemical AFM investigations into the electrode processes of lithium batteries, including the interfacial reaction process of the conversion-type cathode, the dynamic evolution of the solid electrolyte interphase film at the electrode/electrolyte interface, and the structural evolution in solid-state lithium batteries.

Unstable electrode/solid-state electrolyte interfaces and internal lithium dendrite penetration hamper the applications of solid-state lithium-metal batteries (SSLMBs), and the underlying mechanisms are not well understood. Herein, in situ optical microscopy provides insights into the lithium plating/stripping processes in a gel polymer electrolyte and reveals its dynamic evolution. Spherical lithium deposits evolve into moss-like and branch-shaped lithium dendrites with increasing current densities. Remarkably, the on-site-formed solid electrolyte interphase (SEI) shell on the lithium dendrite is distinctly captured after lithium stripping. Inducing an on-site-formed SEI shell with an enhanced modulus to wrap the lithium precipitation densely and uniformly can regulate dendrite-free behaviors. An in-depth understanding of lithium dendrite evolution and its functional SEI shell will aid in the optimization of SSLMBs.

We report a molecular investigation of a cobalt phthalocyanine (CoPc)-catalyzed CO2 reduction reaction by electrochemical scanning tunneling microscopy (ECSTM). An ordered adlayer of CoPc was prepared on Au(111). Approximately 14 % of the adsorbed species appeared with high contrast in a CO2 -purged electrolyte environment. The ECSTM experiments indicate the proportion of high-contrast species correlated with the reduction of CoII Pc (-0.2 V vs. saturated calomel electrode (SCE)). The high-contrast species is ascribed to the CoPc-CO2 complex, which is further confirmed by theoretical simulation. The sharp contrast change from CoPc-CO2 to CoPc is revealed by in situ ECSTM characterization of the reaction. Potential step experiments provide dynamic information for the initial stage of the reaction, which include the reduction of CoPc and the binding of CO2 , and the latter is the rate-limiting step. The rate constant of the formation and dissociation of CoPc-CO2 is estimated on the basis of the in situ ECSTM experiment.

Single-molecule conductance of a B-N substituted phenanthrene derivative and its isoelectronic C═C counterpart was investigated by the scanning tunneling microscopy break junction (STM-BJ) technique. The incorporation of the B-N motif results in a better single-molecule conductivity than the C═C analogue. Furthermore, the Lewis acid-base reaction between F

Sodium-ion batteries (SIBs) are promising candidates for large-scale electric energy storage with abundant sodium resources. However, their development is challenged by the availability of satisfac...

Solid-state Li-metal batteries offer a great opportunity for high-security and high-energy-density energy storage systems. However, redundant interfacial modification layers, intended to lead to an overall satisfactory interfacial stability, dramatically debase the actual energy density. Herein, a dual-interface amorphous cathode electrolyte interphase/solid electrolyte interphase CEI/SEI protection (DACP) strategy is proposed to conquer the main challenges of electrochemical side reactions and Li dendrites in hybrid solid-liquid batteries without sacrificing energy density via LiDFOB and LiBF4 in situ synergistic conversion. The amorphous CEI/SEI products have an ultralow mass proportion and act as a dynamic shield to cooperatively enforce dual electrodes with a well-preserved structure. Thus, this in situ DACP layer subtly reconciles multiple interfacial compatibilities and a high energy density, endowing the hybrid solid-liquid Li-metal battery with a sustainably brilliant cycling stability even at practical conditions, including high cathode loading, high voltage (4.5 V), and high temperature (45 °C) conditions, and enables a high-energy-density (456 Wh kg-1) pouch cell (11.2 Ah, 5 mA h cm-2) with a lean electrolyte (0.92 g Ah-1, containing solid and liquid phases). The compatible modification strategy points out a promising approach for the design of practical interfaces in future solid-state battery systems.

A hybrid solid/liquid electrolyte with superior security facilitates the implementation of high-energy-density storage devices, but it suffers from inferior chemical compatibility with cathodes. Herein, an optimal lithium difluoro(oxalato)borate salt was introduced to build in situ an amorphous cathode electrolyte interphase (CEI) between Ni-rich cathodes and hybrid electrolyte. The CEI preserves the surface structure with high compatibility, leading to enhanced interfacial stability. Meanwhile, the space-charge layer can be prominently mitigated at the solid/solid interface via harmonized chemical potentials, acquiring promoted interfacial dynamics as revealed by COMSOL simulation. Consequently, the amorphous CEI integrates the bifunctionality to provide an excellent cycling stability, high Coulombic efficiency, and favorable rate capability in high-voltage Li-metal batteries, innovating the design philosophy of functional CEI strategy for future high-energy-density batteries.

Although the significance of charge diffusion has been recognized in many high-performance energy devices, it has received very less attention in the design of electrocatalysts for the oxygen evolution reaction (OER), which is particularly crucial for highly active but less conductive OER electrocatalysts, such as two-dimensional metal hydroxides (MHs) with anisotropic conductivity. Herein, we report the elaborate design of a series of CoFe hydroxide nanosheets on graphene (CFH@G) composites to demonstrate the importance of charge diffusion regulation in improving the OER activity of MHs. It was discovered that the few-layer-thick CFH nanosheets lying on the graphene substrate provided an effective in-plane charge diffusion pathway, while keeping the substrate surface entirely covered by the laid nanosheets is necessary for providing sufficient active sites. The overly thick or stacked nanosheets are not favourable for charge diffusion, especially at large current outputs. By regulating the charge diffusion properties, the best-performing CFH@G-based material can deliver a steady OER current density of 2000 mA cm−2 at a cost of only 1.507 V under near-industrial conditions (6 M KOH and 60 °C). A practical water electrolyzer also demonstrated an impressive current output of 400 mA cm−2 at 1.694 V as well as a steady solar-to-hydrogen efficiency of 17.41%. These findings provide new insights into the role of charge diffusion in water oxidation and may open up an avenue for developing low-cost, stable and efficient electrocatalysts for practical water electrolysis and diverse energy devices.

K-ion batteries (KIBs) are drawing increasing research interest as a promising supplement of Li-ion batteries due to the natural abundance of K resource. However, due to the large size of K+, high-capacity anodes are challenged by the structural stability of the active materials which are susceptible to large volumetric deformation after incorporating with a sufficient number of K+. Herein, using SnS2/graphene as an example, we demonstrated that high-performance KIBs anode could be achieved through collaborative efforts targeting on both the active material and the prepared electrode film. The electrochemically-active species of SnS2 were controlled into small nanoparticles with their size below 5 nm to provide sufficient reactive sites for K+ storage. Meanwhile, highly-resilient electrode film based on the prepared SnS2/graphene nanocomposite was built on aluminum (Al) current collector rather than the widely-used copper foil, forming a strong anode film with high peel strength to endure the potassiation/depotassiation process. In this way, the active species was able to deliver an extraordinary reversible capacity of 610 mAh g−1 with unprecedented high-rate capability (around 290 mAh g−1 at 2A g−1) and promising cycling stability. This contribution sheds light on the rational design of high-performance electrode for KIBs and beyond.

The development of high energy electrode materials for lithium ion batteries is challenged by their inherent instabilities, which become more aggravated as the energy densities continue to climb, accordingly causing increasing concerns on battery safety and reliability. Here, taking the high voltage cathode of LiNi0.5Mn1.5O4 as an example, we demonstrate a protocol to stabilize this cathode through a systematic phase modulating on its particle surface. We are able to transfer the spinel surface into a 30 nm shell composed of two functional phases including a rock-salt one and a layered one. The former is electrochemically inert for surface stabilization while the latter is designated to provide necessary electrochemical activity. The precise synthesis control enables us to tune the ratio of these two phases, and achieve an optimized balance between improved stability against structural degradation without sacrificing its capacity. This study highlights the critical importance of well-tailored surface phase property for the cathode stabilization of high energy lithium ion batteries.

The rechargeable aluminium-sulfur (Al-S) battery is regarded as a potential alternative beyond lithium-ion battery system owing to its safety, promising energy density, and the high earth abundance of the constituent electrode materials, however, sluggish kinetic response and short life-span are the major issues that limit the battery development towards applications. In this article, we report CoII,III as an electrochemical catalyst in the sulfur cathode that renders a reduced discharge-charge voltage hysteresis and improved capacity retention and rate capability for Al-S batteries. The structural and electrochemical analysis suggest that the catalytic effect of CoII,III is closely associated with the formation of cobalt sulfides and the changes in the valence states of the CoII,III during the electrochemical reactions of the sulfur species, which lead to improved reaction kinetics and sulfur utilization in the cathode. The Al-S battery, assembled with the cathode consisting of CoII,III decorated carbon matrix, demonstrates a considerably reduced voltage hysteresis of 0.8 V, a reversible specific capacity of ≈500 mAh g-1 at 1 A g-1 after 200 discharge-charge cycles and of ≈300 mAh g-1 at 3 A g-1 .

With a remarkably high energy density and high safety, all-solid-state lithium–sulfur (ASSLS) batteries have emerged as promising next-generation energy storage systems. Direct tracking of the structural evolution at the solid–solid interfaces in an ASSLS battery is highly significant for deep understanding of the reaction mechanism to further improve the electrochemical performance. Herein, we present in situ monitoring of the evolution processes at both the cathode/electrolyte and anode/electrolyte interfaces in working ASSLS batteries via real-time optical microscope (OM) imaging. An irreversible transformation from bright-white to dark-brown in the polymer–ceramic composite electrolyte was directly captured upon discharge/charge, which indicates a shuttling process of polysulfides in the solid-state electrolyte further supported by XPS and Raman analyses. Furthermore, the in situ visualization of the temperature dependency of structural evolution clearly reveals that temperature greatly influences the polysulfide shuttling, irreversible volume-change of solid-state electrolytes and volume expansion of Li metal, which are directly correlated with the degradation of battery performance. These results provide a deep insight into the evolution processes of both structure and component in a working ASSLS battery, which could guide one to explore the electrochemical reactions at solid–solid interfaces and failure mechanism to design high performance lithium–sulfur batteries.

Cost-effective oxygen evolution reaction (OER) catalysts with both superb activity and stability are crucial for practical electrocatalytic water splitting. We herein come up with a metal carbonate hydroxide and metal sulfide (MS/MCH) heterostructure via in situ generating MS on MCH to tackle the conflict between activity and durability. The heterostructure in a unique “nanoparticle-in-nanosheet” configuration features abundant hetero-interfaces between MS and MCH, allowing for effective electron transfer from the antibonding orbital of M–S in MS to M–O in MCH and thus improving the stability of sulfides during water oxidation. Simultaneously, such coupling is able to modulate the electronic structure of the metal centre, thus enhancing the intrinsic activity. The coupled heterostructure therefore exhibits steady OER performance with an ultrasmall overpotential of 226 to deliver a current of 10 mA cm−2 and can output an industrial-level current of 1000 mA cm−2 at an overpotential of only 367 mV. Furthermore, the overall water electrolyzer with such a heterostructure as an anode presents stable hydrogen production at 100 mA cm−2 with a small cell voltage of 1.62 V and a high solar to hydrogen efficiency of 16.99%. Such superior catalytic performance demonstrates the feasibility of introducing a heterostructure to tailor the local electrocatalytic properties and opens up an avenue toward designing efficient OER catalysts for clean hydrogen production and diverse energy conversion devices.

Due to their abundant resources and potential price advantage, potassium-ion batteries (KIBs) have recently drawn increasing attention as a promising alternative to lithium-ion batteries (LIBs) for their applications in electrochemical energy storage applications. Despite the continuous progress in identifying possible electrode materials, the development of KIBs has been challenged by different problems including low reversible capacities, unsatisfactory cycling stability, and insufficient energy density, which become serious concerns for the practical application of KIBs. In this review, we will summarize the recent advancements in both cathode and anode materials with focus on their structure–performance relationship. Meanwhile, challenges and opportunities related to the future development of KIBs are also discussed.

Understanding the mechanisms of electrocatalytic reactions is essential for development of lower cost, high-efficiency electrocatalysts for electrochemical energy conversion technology. The investigation of structures and reactions of electrocatalysts at electrode surfaces with a single molecular scale resolution benefits mechanism studies as well as catalysts development. This review summarizes recent studies on investigating the structure of electrocatalysts, distribution of catalytic active sites, and in-situ monitoring of electrocatalytic processes in reactions by scanning tunneling microscope. The challenge and future development in the field are also outlined.

A pyrene-cored molecular quadripod 1,3,6,8-tetra(di(p-pyrid-4-ylphenyl)amino)pyrene (TAPyr) is presented as a noncovalent interfacial coupling reagent for the immobilization of coordination assemblies. This bench-stable molecule is readily available and has a quadripod shape with four pyridine legs and four pyridine handles on the top exterior. By a simple and short dipping procedure under ambient conditions, TAPyr is firmly immobilized on electrode surfaces in an upright fashion as probed by electrochemical, absorption spectral, atomic force microscopy, and scanning tunneling microscopy analysis. Using Pd(PhCN)2Cl2 as a metallolinker, 4-ferrocenylpyridine, a pyridine-terminated monoruthenium complex 1, and a diruthenium complex 2 with two pyridine ends have been grafted onto the ITO/TAPyr surface. The obtained thin films exhibit good electrochemical stability that is comparable or superior to those prepared by the state-of-the-art Si–O–Sn covalent functionalization. Appealing electrochromism is demonstra...

Summary Lithium-ion batteries with high energy density are being intensively pursued to meet the ever-growing demand for energy storage. However, the increase in energy density often comes with an elevated instability of electrode materials, causing major concerns about the reliability and safety of lithium-ion batteries. Here, we report a strategy for stabilizing cathode materials by modulating the vacant lattice sites on the particle surface. Using the high-voltage Li[Ni0.5Mn1.5]O4 as an example, we demonstrate that introduction of a 10-nm epitaxial surface layer with Al3+ in the empty 16c octahedral sites of the spinel Li[Ni0.5Mn1.5]O4 suppresses structural degradation during cycling by increasing the surface stability without interfering with the Li+ diffusion around the Al3+ sites. Control of the Al3+ concentration in the surface region was shown to be a facile process. The process was shown to stabilize long-term cycling of Li[Ni0.5Mn1.5]O4 to 5 V versus Li+/Li0.

Surface cobalt doping is an effective and economic way to improve the electrochemical performance of cathode materials. Herein, by tuning the precipitation kinetics of Co2+, we demonstrate an aqueous-based protocol to grow uniform basic cobaltous carbonate coating layer onto different substrates, and the thickness of the coating layer can be adjusted precisely in nanometer accuracy. Accordingly, by sintering the cobalt-coated LiNi0.5Mn1.5O4 cathode materials, an epitaxial cobalt-doped surface layer will be formed, which will act as a protective layer without hindering charge transfer. Consequently, improved battery performance is obtained because of the suppression of interfacial degradation.

The rapid capacity decay caused by the poor contact and large polarization at the interface between the cathode and solid electrolytes is still a big challenge to overcome for high-power-density solid batteries. In this study, a superior Li+ conductive transition layer Li1.4Al0.4Ti1.6(PO4)3 is introduced to coat LiNi0.6Co0.2Mn0.2O2, as a model cathode, to mitigate polarization and enhance dynamic characteristics. The critical attribute for such superior dynamics is investigated by the atomic force microscopy with boundary potential analysis, revealing that the formed interfacial transition layer provides a gradual potential slope and sustain-released polarization, and endows the battery with improved cycling stability (90% after 100 cycles) and excellent rate capability (116 mA h g–1 at 2 C) at room temperature, which enlightens the comprehension of interface engineering in the future solid batteries systems.

To gain knowledge of the most important weak interactions for supramolecular self-assembly and observe molecular structure for self-assembled architectures, the two-dimensional self-assembly of an oligo(p-phenylenevinylene)-based molecule (AS-OPV) on highly oriented pyrolytic graphite has been investigated. Accurate atomic configuration for the AS-OPV self-assembled pattern has been identified by means of multi-scale simulation combined with scanning tunneling microscopy (STM) experiments. The weak interactions which contribute to the formation of AS-OPV self-assembly are studied by analysis of non-covalent interactions existing in the system and theoretical calculation of their energy values. Investigation of the molecular structure of self-assembly and STM images at a certain temperature range is performed by molecular dynamics and density functional theory simulations. This work paves the way to explore the contribution of weak interactions for the self-assembly system, as well as providing a reference to observe the possible self-assembled structure at temperatures not convenient for direct experimental observation.

Here we show a conceptual approach to realize the scanning tunneling microscopy based induced-assembly of fullerene (C60) molecules on top of a buffer organic adlayer at room temperature in a solution environment. The realization of spatially-defined C60 assembly is attributed to the modulation of substrate-molecular interactions with the assistance of a buffer layer.

The construction of uniform core–shell nanostructures using transition-metal phosphates as the shell has been a long-standing challenge in the field of nanotechnology. Due to their extremely low solubility constants, metal phosphates are prone to precipitate independently in solution, making a heterogeneous growth around the preexisting seeds extremely hard to achieve. Here, we demonstrated that it is possible to overcome the hurdles arising from their intrinsic growth habit, and form uniform metal phosphate nanoshells with their thickness tuned with nanometer accuracy. Particularly, for the formation of different nanoshells including Ni3(PO4)2, Co3(PO4)2, and Mn3(PO4)2, it has been found that a cooperative effort to control both the solvent environment and the precipitating agent is critical to tuning the growth kinetics of these metal phosphates, making it convenient for us to grow uniform nanoshells around a large variety of seeds. The application of this synthetic protocol for the surface treatment of LiNi0.5Mn1.5O4, a well-known high voltage cathode material in lithium ion batteries, demonstrates that a 4 nm coating layer of Co3(PO4)2 can be achieved as a protective shell, which provides a much improved cycling stability to the electrode and holds promising potential for its application as a high energy cathode.

We report the potential and concentration controlled assembly of an alkyl-substituted benzo[1,2-b:4,5-b']dithiophene (DDBDT) on an Au(111) electrode by in situ electrochemical scanning tunneling microscopy (ECSTM). It is found that a lamellar structure is formed at low concentrations, while herringbone-like and rhombus structures are obtained at high concentrations. In situ STM results reveal that herringbone-like and rhombus structures could transform into lamellar structures when the electrode potential is tuned negatively. A phase diagram is obtained to illustrate the relationship and effects of concentration and substrate potential on the interfacial structures of DDBDT. Both the substrate potential and the solute concentration can modulate the self-assembly structure through changing the molecular surface density. The results provide important insights into the understanding and precise control of molecular self-assembly on solid surfaces through a combination of different approaches.

Delivery of high capacity with high thermal and air stability is a great challenge in the development of Ni-rich layered cathodes for commercialized Li-ion batteries (LIBs). Herein we present a surface concentration-gradient spherical particle with varying elemental composition from the outer end LiNi1/3Co1/3Mn1/3O2 (NCM) to the inner end LiNi0.8Co0.15Al0.05O2 (NCA). This cathode material with the merit of NCM concentration-gradient protective buffer and the inner NCA core shows high capacity retention of 99.8% after 200 cycles at 0.5 C. Furthermore, this cathode material exhibits much improved thermal and air stability compared with bare NCA. These results provide new insights into the structural design of high-performance cathodes with high energy density, long life span, and storage stability materials for LIBs in the future.

Summary Lithium metal has been deemed as the most attractive anode due to its high theoretical capacity and low anode potential. Unfortunately, its development still faces various challenges, including dendritic Li growth and low Coulombic efficiency. Here, we demonstrate that a light-weight, flexible, and free-standing 3D hollow carbon fiber (3D-HCF) container with high electroactive surface area can significantly reduce local current density and improve the Li deposition behavior. Li is confined within the interspace among the fibers and inside the hollow tubular fibers without uncontrollable Li dendrites. The Li anode in the 3D-HCFs exhibits high Coulombic efficiency (∼99.5% over 350 cycles), large areal capacity, and long-running lifespan (>1,200 hr) with an exceptionally low overpotential ( 4 cathode shows flat voltage profiles and good cycle life. We expect this work to inspire other Li container designs to promote the development of Li metal anodes.

Lithium-sulfur (Li-S) batteries have been attracting wide attention due to their promising high specific capacity. Deep understanding of Li-S interfacial mechanism including the temperature (T) effect is increasingly required to meet the burgeoning demands for battery modification and systematic researches. Herein, interfacial behavior during discharge/charge is investigated at high temperature (HT) of 60 C in electrolyte based on lithium bis(fluorosulfonyl) imide (LiFSI). By in situ atomic force microscopy (AFM), dynamic evolution of insoluble Li2S2 and Li2S is studied at the nanoscale. An in situ formed protective film can be directly monitored at 60 C after Li2S nucleation, retarding side reactions and facilitating interfacial redox. The deep insight into the interfacial processes at HT discovers a direct evidence of the existence of the protective film and reveals its dynamic behaviors, providing a new avenue for electrolyte design and performance enhancement with a long span.

Two-dimensional (2D) chiral self-assembly system of 5-(benzyloxy)-isophthalic acid derivative/(S)-(+)-2-octanol/highly oriented pyrolytic graphite was studied. A combined density functional theory/molecular mechanics/molecular dynamics (DFT/MM/MD) approach for system of 2D chiral molecular self-assembly driven by hydrogen bond at the liquid/solid interface was thus proposed. Structural models of the chiral assembly were built on the basis of scanning tunneling microscopy (STM) images and simplified for DFT geometry optimization. Merck Molecular Force Field (MMFF) was singled out as the suitable force field by comparing the optimized configurations of MM and DFT. MM and MD simulations for hexagonal unit model which better represented the 2D assemble network were then preformed with MMFF. The adhesion energy, evolution of self-assembly process and characteristic parameters of hydrogen bond were obtained and analyzed. According to the above simulation, the stabilities of the clockwise and counterclockwise enantiomorphous networks were evaluated. The calculational results were supported by STM observations and the feasibility of the simulation method was confirmed by two other systems in the presence of chiral co-absorbers (R)-(-)−2-octanol and achiral co-absorbers 1-octanol. This theoretical simulation method assesses the stability trend of 2D enantiomorphous assemblies with atomic scale and can be applied to the similar hydrogen bond driven 2D chirality of molecular self-assembly system.

Nickel-rich layered materials, such as LiNi0.80Co0.15Al0.05O2 (NCA), have been considered as one alternative cathode materials for lithium-ion batteries (LIBs) due to their high capacity and low cost. However, their poor cycle life and low thermal stability, caused by the electrode/electrolyte side reaction, prohibit their prosperity in practical application. Herein, AlPO4 has been homogeneously coated on the surface of NCA via wet chemical method towards the target of protecting NCA from the attack of electrolyte. Compared with the bare NCA, NCA@AlPO4 electrode delivers high capacity without sacrificing the discharge capacity and excellent cycling stability. After 150 cycles at 0.5 C between 3.0–4.3 V, the capacity retention of the coated material is 86.9%, much higher than that of bare NCA (66.8%). Furthermore, the thermal stability of cathode is much improved due to the protection of the uniform coating layer on the surface of NCA. These results suggest that AlPO4 coated NCA materials could act as one promising candidate for next-generation LIBs with high energy density in the near future.

© 2017 American Chemical Society. Periodically eclipsed π-stacking columns in two-dimensional covalent organic frameworks (2D COFs) could function as direct channel paths for charge carrier transport. Incorporating a well-defined 2D COF into organic electronic devices, however, is still a challenge. Herein, we have reported the solvothermal synthesis of a COFTFPy-PPDAfilm on single-layer graphene (SLG), which was constructed via covalent imine-type linkage by employing 1,3,6,8-tetrakis(p- formylphenyl)pyrene (TFPy) and p-phenylenediamine (PPDA) as building blocks. A vertical field-effect transistor (VFET) based on the heterostructure of COFTFPy-PPDAfilm and SLG shows ambipolar charge carrier behavior under lower modulating voltages. Work-function-tunable contact between SLG and COFTFPy-PPDAfilm and suitable injection barriers of charge carriers lead to the ambipolar transport with high current density on/off ratio (>105) and high on-current density (>4.1 A cm-2). Interfacing 2D COF with graphene for VFET could shed light on the promising application prospect of 2D COFs in organic electronics and optoelectronics.

High-capacity Li-rich cathode materials can significantly improve the energy density of lithium-ion batteries, which is the key limitation to miniaturization of electronic devices and further improvement of electrical-vehicle mileage. However, severe voltage decay hinders the further commercialization of these materials. Insights into the relationship between the inherent structural stability and external appearance of the voltage decay in high-energy Li-rich cathode materials are critical to solve this problem. Here, we demonstrate that structural evolution can be significantly inhibited by the intentional introduction of certain adventive cations (such as Ni2+) or by premeditated reservation of some of the original Li+ ions in the Li slab in the delithiated state. The voltage decay of Li-rich cathode materials over 100 cycles decreased from 500 to 90 or 40 mV upon introducing Ni2+ or retaining some Li+ ions in the Li slab, respectively. The cations in the Li slab can serve as stabilizers to reduce the repulsion between the two neighboring oxygen layers, leading to improved thermodynamic stability. Meanwhile, the cations also suppress transition metal ion migration into the Li slab, thereby inhibiting structural evolution and mitigating voltage decay. These findings provide insights into the origin of voltage decay in Li-rich cathode materials and set new guidelines for designing these materials for high-energy-density Li-ion batteries.

We demonstrated a rechargeable aqueous Al-S battery based on a water-in-salt electrolyte with the configuration Al‖Al(OTF)3 + LiTFSI + HCl‖S/C. The superconcentrated LiTFSI trapped water molecules to inhibit the hydrolysis of aluminum polysulfides in the cathode, and the HCl additive provided a mild acidic environment to enable repeatable oxidation-reduction reactions in the anode.

Co-crystallization of organic molecules is an important strategy for the fabrication of molecular materials. In this contribution, we investigated the mixing behavior of 5-(benzyloxy)-isophthalic acid homologues (BIC-Cn, n = 6, 8, 10, 12, and 14) at the liquid/solid interface using a scanning tunneling microscope. Deposition of the single component of BIC-Cn always results in typical honeycomb networks, whereas co-deposition of two BIC-Cn homologues leads to hybrid double-walled honeycomb networks or phase separation depending on the difference in the length of their alkyl chains. 2D co-crystallization can only be realized for BIC-C6/BIC-C10 or BIC-C8/BIC-C12 which have a four-methyl unit difference in their alkyl chains. The size complementarity of the alkyl chains in the two components suggests that it is responsible for the 2D co-crystallization, though hydrogen bonding contributes a lot both to the pristine honeycomb network and to the hybrid co-crystal. This result is of importance for understanding the role of van der Waals interaction and its interplay with hydrogen bonding in 2D co-crystallization.

A tri-stable structural switching between different polymorphisms is presented in the 2D molecular assembly of a 5-(benzyloxy)isophthalic acid derivative (BIC-C12) at the liquid/solid interface. The assembled structure of BIC-C12 is sensitive to the applied voltage between the STM tip and the sample surface. A compact lamellar structure is exclusively observed at positive sample bias, while a porous honeycomb structure or a quadrangular structure is preferred at negative sample bias. Selective switching between the lamellar structure and the honeycomb structure or the quadrangular structure is realized by controlling the polarity and magnitude of the sample bias. The transition between the honeycomb structure and the quadrangular structure is, however, absent in the assembly. This tri-stable structural switching is closely related to the molecular concentration in the liquid phase. This result provides insights into the effect of external electric field on molecular assembly and benefits the design and construction of switchable molecular architectures on surfaces.

A self-hollowing process was demonstrated for the creation of hollow MoS2 nanospheres starting from their amorphous solid precursor, which were spontaneously transformed into a hollow structure during the rearrangement of crystal lattices initiated by a high-temperature treatment, forming hollow-structured materials favorable for their application in sodium ion batteries.

The development of high-performance potassium-ion batteries (PIBs) is challenged by the availability of stable cathode materials, which are known to undergo complex phase transitions and irreversible structural degradation especially charged to high voltage. Here, we reported a P2-type cathode in formula of K0.6Mn0.8Ni0.1Ti0.1O2 (KMNT), which exhibited a highly reversible K+ (de)intercalation capability up to 4.2 V. We demonstrated that the coexistence of Ni and Ti was able to not only suppress the structural damage related to the Jahn-Teller effect of Mn3+, a critical factor accounting for the performance degradation of Mn-based PIBs cathodes, but also restrain the detrimental lattice sliding of transition metal layers at high voltage. Accordingly, the structurally engineered KMNT showed a much favored solid-solution reaction with a successful elimination of the destructive phase degradation at deep depotassiation state. Our results highlighted the essential role played by the lattice design of cathode materials in modulating their electrochemical behavior for stable and high-performance PIBs.

Quantum dot sensitized solar cell (QDSSC) has been considered as a promising candidate for the low-cost third-generation photovoltaics due to the unique optoelectronic properties of quantum dot light absorbers. Over the past years, QDSSCs have witnessed tremendous progress with a rapid rising of the power conversion efficiency from sub-5% in 2010 to 11.6% in 2016. Herein, we present a comprehensively review on the recent progresses in QDSSCs with an emphasis on the design and fabrication of three-dimensional (3D) nanostructured electrodes for efficient photoanodes and counter electrodes (CEs). By increasing QD loading at photoanode and catalyst loading at CEs, enlarging solid-liquid interface to reduce charge transfer resistance, facilitating charger transport and mass transfer, and enhancing the light harvesting, 3D nanostructured electrodes have demonstrated their promising potentials for the construction of efficient photoanodes and CEs. Together with the efforts on the surface engineering to inhibit the interfacial charge recombination and the exploration of efficient quantum dot absorbers and electrolytes, such 3D nanostructured photoanodes and CEs will open up great opportunities to achieve high-performance QDSSCs with industrially appealing PCEs and stability for practical applications.

Here we applied ionic interactions as the driving force to fabricate well-ordered bicomponent assemblies by using two porphyrin ions equipped with oppositely-charged groups. Two kinds of bimolecular chessboard structures were successfully constructed on Au(111) and investigated by scanning tunneling microscopy (STM).

We have studied the self-assembly structure of meso-diphenyltetrathia [22]-annulene [2,1,2,1] (DPTTA) on highly oriented pyrolytic graphite (HOPG), Au(111), and single-layer graphene (SLG) modified Au(111) substrates. High resolution scanning tunneling microscopy (STM) reveals that DPTTA molecules pack into one dimensionally ordered row structure on graphene and HOPG surfaces, while assemble into two dimensional close-packed structure on Au(111) surface. We ascribe this difference to the effect of the substrate. The addition of C60 molecules on these DPTTA modified substrates further reveals that the structural difference in DPTTA adlayer can affect its ability to form donor-acceptor (D-A) hierarchical structure with C60 molecules. The results provide an example of substrate effect in self-assemblies of functional molecules, which is significant for the design of molecular based devices.

We report an in situ electrochemical scanning tunneling microscopy (ECSTM) investigation of the 5,10,15,20-tetraphenyl-21H,23H-porphine cobalt(II) (CoTPP)-catalyzed oxygen reduction reaction (ORR). A highly ordered CoTPP adlayer is revealed on the Au(111) electrode. High-contrast adsorbed species are monitored in CoTPP adlayer in electrolyte containing oxygen, and are attributed to the formation of CoTPP–O2 complexes. In situ STM results reveal the sharp contrast changes upon switching the substrate potential to trigger the ORR. The results benefit the understanding of the catalytic role of metal porphyrins (MPs) in the ORR, which is important for the design of MP-based catalysts.

Designing specific structured electrode materials is essential for efficient electrochemical energy storage. Graphene owns unique 2D structure and possesses excellent electrical conductivity, ultrahigh specific surface areas, as well as colloidal self-assembling behavior, which make it an ideal candidate for constructing hybrid electrode materials with remarkably enhanced electrochemical performances. This article reviews the recent research progress made on various 3D graphene-based electrode materials and their applications in electrochemical energy storage such as Li-ion and Li-S batteries. Based on the recent works made by our group, we highlight the principles of designing graphene-based materials, and discuss various advanced structures of graphene-based electrodes. Furthermore, future research directions for the development of novel and more efficient graphene-based electrode materials are proposed.

Microspace-confined sulfur molecules as cathodes for lithium-sulfur (Li-S) batteries have shown great significance in both scientific and technical aspects. A study of different microspace-confined sulfur will not only promote the advancement of Li-S batteries but also arouse a wide interest in sulfur chemistry and related applications. Herein, we choose two-dimensional (2D) graphene interlayer as host and construct 2D space-confined sulfur model systems by simple intercalation chemistry of graphite oxide. Two routes, including solvothermal method and interlamellar reaction approach, are developed, and sulfur can be easily intercalated into sub-nanometer-sized graphene interlayers, forming a graphene confined sulfur structure. The 2D space-confined sulfur can work well in a carbonate-based electrolyte and show similar electrochemical behaviors of small sulfur molecules, indicating the special molecular form of sulfur in graphene layers. The 2D space-confined sulfur concept will be helpful for further understanding the electrochemical character of confined sulfur molecules and designing a high-performance sulfur cathode.

A subzero-temperature cathode material is obtained by nucleating cubic prussian blue crystals at inhomogeneities in carbon nanotubes. Due to fast ionic/electronic transport kinetics even at -25 °C, the cathode shows an outstanding low-temperature performance in terms of specific energy, high-rate capability, and cycle life, providing a practical sodium-ion battery powering an electric vehicle in frigid regions.

Room-temperature sodium-ion batteries (SIBs) have shown great promise in grid-scale energy storage, portable electronics, and electric vehicles because of the abundance of low-cost sodium. Sodium-based layered oxides with a P2-type layered framework have been considered as one of the most promising cathode materials for SIBs. However, they suffer from the undesired P2-O2 phase transition, which leads to rapid capacity decay and limited reversible capacities. Herein, we show that this problem can be significantly mitigated by substituting some of the nickel ions with magnesium to obtain Na0.67 Mn0.67 Ni0.33-x Mgx O2 (0≤x≤0.33). Both the reversible capacity and the capacity retention of the P2-type cathode material were remarkably improved as the P2-O2 phase transition was thus suppressed during cycling. This strategy might also be applicable to the modulation of the physical and chemical properties of layered oxides and provides new insight into the rational design of high-capacity and highly stable cathode materials for SIBs.

Hollow hybrid microspheres have found great potential in different areas, such as drug delivery, nanoreactors, photonics, and lithium-ion batteries. Here, we report a simple and scalable approach to construct high-quality hollow hybrid microspheres through a previously unexplored growth mechanism. Starting from uniform solid microspheres with low crystallinity, we identified that a hollowing process can happen through the progressive inward crystallization process initiated on the particle surface: the gradual encroachment of the crystallization frontline toward the core leads to the depletion of the center and forms the central cavity. We showed that such a synthetic platform was versatile and can be applicable for a large variety of materials. By using the production of Li4Ti5O12-carbon hollow hybrid microspheres as an example, we demonstrated that high-performance anode materials could be achieved through synthesis and structure control. We expect that our findings offer new perspectives in different areas ranging from materials chemistry, energy storage devices, catalysis, to drug delivery.

Because of their high theoretical energy density and low cost, lithium–sulfur (Li–S) batteries are promising next-generation energy storage devices. The electrochemical performance of Li–S batteries largely depends on the efficient reversible conversion of Li polysulfides to Li2S in discharge and to elemental S during charging. Here, we report on our discovery that monodisperse cobalt atoms embedded in nitrogen-doped graphene (Co–N/G) can trigger the surface-mediated reaction of Li polysulfides. Using a combination of operando X-ray absorption spectroscopy and first-principles calculation, we reveal that the Co–N–C coordination center serves as a bifunctional electrocatalyst to facilitate both the formation and the decomposition of Li2S in discharge and charge processes, respectively. The S@Co–N/G composite, with a high S mass ratio of 90 wt %, can deliver a gravimetric capacity of 1210 mAh g–1, and it exhibits an areal capacity of 5.1 mAh cm–2 with capacity fading rate of 0.029% per cycle over 100 cycles...

Coherent anti-Stokes Raman scattering (CARS) is able to enhance molecular signals by vibrational coherence compared to weak Raman signal. The surface or tip enhancement are successful technologies, which make it possible for Raman to detect single molecule with nanometer resolution. However, due to technical difficulties, tip-enhanced CARS (TECARS) is not as successful as expected. For single molecular detection, high sensitivity and resolution are two main challenges. Here, we reported the first single atom layer TECARS imaging on Graphene with the highest resolution about 20[Formula: see text]nm, which has ever been reported. The highest EF[Formula: see text] is about 104, the similar order of magnitude with SECARS (EF of tip is usually smaller than that of substrates). Such resolution and sensitivity is promising for medical, biology and chemical applications in the future.