The shield-like nano-sized Si3N4 derivatives to defend against the attack of lithium dendrites.

The unrestrained Li dendrite growth impedes the performance of Li metal batteries (LMBs) and brings safety concerns. To mitigate the unfavorable effect of Li dendrites, in this work, a shield-like artificial interlayer composed of Si3N4 is employed to achieve the desirable electrochemical performance of LMBs. The Si3N4-based interlayer can in-situ electrochemically react with Li to generate inorganic Li3N and LixSi alloys: the former with high ionic conductivity can effectively enhance the Li+ transference, while the latter with reversibility for Li+ insertion/deinsertion can act as Li+ reservoir to modulate Li+ platting/stripping. Thus, the Si3N4-derived compound shield effectively defends against the attack of Li dendrites and suppresses their growth, with which the Li||Li cells can cycle at 1 mA cm-2 (1 mAh cm-2) up to 500 h and the LiFePO4 (LFP) ||Li batteries can operate 400 cycles at 1C with 91.5 % capacity retention.

The inhibited Li dendrite growth via bulk/liquid dual-phase modulation.

Li metal is a potential anode material for the next generation high-energy-density batteries because of its high theoretical specific capacity. However, the inhomogeneous lithium dendrite growth restrains corresponding electrochemical performance and brings safety concerns. In this contribution, the Li3Bi/Li2O/LiI fillers are generated by the in-situ reaction between Li and BiOI nanoflakes, which promises corresponding Li anodes (BiOI@Li) showing favorable electrochemical performance. This can be attributed to the bulk/liquid dual modulations: (1) The three-dimensional Bi-based framework in the bulk-phase lowers the local current density and accommodates the volume variation; (2) The LiI dispersed within Li metal is slowly released and dissolved into the electrolyte with the consumption of Li, which will form I-/I3- electron pair and further reactivate the inactive Li species. Specifically, the BiOI@Li//BiOI@Li symmetrical cell shows small overpotential and enhanced cycle stability over 600 h at 1 mA cm-2. Matched with an S-based cathode, the full Li-S battery demonstrates desirable rate performance and cycling stability.

"Grafting" NiSe onto Cu2-xSe with twinborn structure embedded in carbon-based nanofibers to weave freestanding sodium-ion storage electrode.

The fabrication of freestanding electrodes for Na+ storage is necessary to achieve high energy density. However, the large radius of Na+ results in a large volume fluctuation and sluggish reaction kinetics of active materials, particularly at a high active material content, thereby impeding electrochemical performance with undesirable cycling performance or rate capability. In this study, a freestanding electrode based on the "NiSe grafted on Cu2-xSe" heterostructure with double-carbon protective shells (NiSe/Cu2-xSe@C@NCNFs) was successfully constructed for Na+ storage. In this microstructure, N-doped carbon nanofibers (NCNFs) serve as the stem of the twinborn NiSe/Cu2-xSe heterostructure with a built-in electric field, where NiSe improves Na+ absorption and Cu2-xSe enhances Na+ diffusion. The "graft" design enabled the freestanding NiSe/Cu2-xSe@C@NCNFs electrode with a high active mass content of 76.1 wt% to exhibit superior electrochemical performance for Na+ storage (75 mAh g-1 at 2 A g-1) compared to those of Cu2-xSe@C@NCNFs (26 mAh g-1 at 2 A g-1) and NiSe@C@NCNFs (9 mAh g-1 at 2 A g-1).

The Inducement and "Rejuvenation" of Li Dendrites by Space Confinement and Positive Fe/Co-Sites.

The high reactivity of Li metal and the inhomogeneous Li deposition leads to the formation of Li dendrites and "dead" Li, which impedes the performance of Li metal batteries (LMBs) with high energy density. The regulating and guiding the Li dendrite nucleation is a desirable tactic to realize concentrated distribution of Li dendrites instead of completely inhibiting dendrite formation. Here, a Fe-Co-based Prussian blue analog with hollow and open framework (H-PBA) is employed to modify the commercial polypropylene separator (PP@H-PBA). This functional PP@H-PBA can guide the lithium dendrite growth to form uniform lithium deposition and activate the inactive Li. In details, the H-PBA with macroporous structure and open framework can induce the growth of lithium dendrites via space confinement, while the positive Fe/Co-sites lowered by polar cyanide (-CN) of PBA can reactivate the inactive Li. Thus, the Li|PP@H-PBA|Li symmetric cells exhibit long-term stability at 1 mA cm-2 for 1 mAh cm-2 over 500 h. And the Li-S batteries with PP@H-PBA deliver favorable cycling performance at 500 mA g-1 for 200 cycles.

The Multi-Functional Effects of CuS as Modifier to Fabricate Efficient Interlayer for Li-S Batteries.

The shuttle effect of lithium polysulfides in lithium-sulfur batteries (LSBs) has a detrimental impact on their electrochemical performance. To effectively mitigate the shuttle effect, in this study, the coral-like CuS is introduced to modify the carbon nanotube (CNTs), which is coated on commercial separator and served as the S cathode interlayer (PE@CuS/CNTs). The CuS/CNTs interlayer possesses efficient physical impediment and chemisorption to polysulfide anions. When achieving maximum adsorption to polysulfide anions, a "polysulfide-phobic" surface would be formed as a shield to restrain the polysulfide anions in the cathode region. Simultaneously, the CuS/CNTs interlayer can improve the lithium ion diffusion and guarantee desirable electrochemical reaction kinetics. Consequently, the LSBs with PE@CuS/CNTs show an initial discharge capacity of 1242.4 mAh g-1 at 0.5 C (1 C = 1675 mA g-1 ) and retain a long-term cycling stability (568.5 mAh g-1 after 1000 cycles, 2 C), corresponding to an ultra-low capacity fading rate of only 0.05% per cycle. Also, the LSBs with PE@CuS/CNTs exhibit high resistance to self-discharge and favorable performance under high S loading (4.5 mg cm-2 ) and lean electrolyte (9.4 mLElectrolyte  g S -1 ).

Li3Bi/LiF/Li2O derived from mechanical rolling of Li metal with BiOF nanoplates as stable filler for dendrite-free Li metal batteries.

Li is attractive anode for next-generation high-energy batteries. The high chemical activity, dendrite growth, and huge volume fluctuation of Li hinder its practical application. In this work, a Li-BiOF composite anode (LBOF) is obtained by combining Li metal with BiOF nanoplates through facile folding and mechanical cold rolling. Further, Li3Bi/LiF/Li2O filler is formed by the in-situ reactions of BiOF with contacted Li. In the filler, the Li3Bi, with high ionic conductivity and a lithiophilic nature, provides a mutually permeable channel for Li+ diffusion. The low surface diffusion energy barrier of Li3Bi and LiF can further promote the uniform deposition of Li. The conductive lithiophilic filler can reduce the local current density and provide a spatial limitation to the deposited Li. Consequently, the symmetrical LBOF||LBOF cell can cycle stably at 1 mA cm-2 for over 1300 h. Additionally, the surface of LBOF is flat with suppressed dendrite formation and free of dead Li accumulation, and the change in electrode volume is significantly alleviated. Furthermore, the LBOF||LiFePO4 full battery can maintain a stable cycle of more than 200 times with high capacity retention of 88.7% in a corrosive ester-based electrolyte. This simple mechanical approach is compatible with the current industrial route and is inspiring to solve the long-standing lithium-dendrite problem.

Fe7Se8 encapsulated in N-doped carbon nanofibers as a stable anode material for sodium ion batteries.

Transition metal chalcogenides especially Fe-based selenides for sodium storage have the advantages of high electric conductivity, low cost, abundant active sites, and high theoretical capacity. Herein, we proposed a facile synthesis of Fe7Se8 embedded in carbon nanofibers (denoted as Fe7Se8-NCFs). The Fe7Se8-NCFs with a 1D electron transfer network can facilitate Na+ transportation to ensure fast reaction kinetics. Moreover, Fe7Se8 encapsulated in carbon nanofibers, Fe7Se8-NCFs, can effectively adapt the volume variation to keep structural integrity during a continuous Na+ insertion and extraction process. As a result, Fe7Se8-NCFs present improved rate performance and remarkable cycling stability for sodium storage. The Fe7Se8-NCFs exhibit practical feasibility with a reasonable specific capacity of 109 mA h g-1 after 200 cycles and a favorable rate capability of 136 mA h g-1 at a high rate of 2 A g-1 when coupled with Na3V2(PO4)3 to assemble full sodium ion batteries.

Highly conductive VC embedded in carbon matrix as effective trapper and catalyst for Li-S batteries.

Vanadium carbide embedded in a nitrogen-doped carbon matrix (VC@NCM) is synthesized as a 3D freestanding sulfur host. Owing to the high electrical conductivity (1.6 × 104 S cm-1) of VC and strong chemisorption and catalytic effect on sulfur species, Li-S batteries with VC@NCM deliver enhanced redox kinetics with ultralow capacity decay of 0.01% per cycle after 1000 cycles at 1C. This work identifies the effect of strong chemisorption and high electrical conductivity on high S utilization and cycle stability in Li-S batteries.

Constructing Co3S4 Nanosheets Coating N-Doped Carbon Nanofibers as Freestanding Sulfur Host for High-Performance Lithium-Sulfur Batteries.

Lithium-sulfur batteries (LSBs) have shown great potential as a rival for next generation batteries, for its relatively high theoretical capacity and eco-friendly properties. Nevertheless, blocked by the shuttle effect of lithium polysulfides (LPSs, Li2S4-Li2S8) and insulation of sulfur, LSBs show rapid capacity loss and cannot achieve the practical application. Herein, a composite of carbon nanofibers coated by Co3S4 nanosheets (denoted as CNF@Co3S4) is successfully synthesized as freestanding sulfur host to optimize the interaction with sulfur species. The combination of the two materials can lead extraordinary cycling and rate performance by alleviating the shuttle of LPSs effectively. N-doped carbon nanofibers serve as long-range conductive networks and Co3S4 nanosheets can accelerate the conversion of LPSs through its electrocatalytic and chemical adsorption ability. Benefiting from the unique structure, the transporting rate of Li+ can be enhanced. Distribution of Li+ is uniform for enough exposed negative active sites. As a result, the cell with CNF@Co3S4 as sulfur host is able to stabilize at 710 mA h g-1 at 1 C after 200 cycles with average coulombic efficiency of 97.8% in a sulfur loading of 1.7 mg cm-2 and deliver 4.1 mA h cm-2 at 0.1 C even in 6.8 mg cm-2 for 100 cycles.

Promoting Ge Alloying Reaction via Heterostructure Engineering for High Efficient and Ultra-Stable Sodium-Ion Storage.

Germanium (Ge)-based materials have been considered as potential anode materials for sodium-ion batteries owing to their high theoretical specific capacity. However, the poor conductivity and Na+ diffusivity of Ge-based materials result in retardant ion/electron transportation and insufficient sodium storage efficiency, leading to sluggish reaction kinetics. To intrinsically maximize the sodium storage capability of Ge, the nitrogen doped carbon-coated Cu3Ge/Ge heterostructure material (Cu3Ge/Ge@N-C) is developed for enhanced sodium storage. The pod-like structure of Cu3Ge/Ge@N-C exposes numerous active surface to shorten ion transportation pathway while the uniform encapsulation of carbon shell improves the electron transportation, leading to enhanced reaction kinetics. Theoretical calculation reveals that Cu3Ge/Ge heterostructure can offer decent electron conduction and lower the Na+ diffusion barrier, which further promotes Ge alloying reaction and improves its sodium storage capability close to its theoretical value. In addition, the uniform encapsulation of nitrogen-doped carbon on Cu3Ge/Ge heterostructure material efficiently alleviates its volume expansion and prevents its decomposition, further ensuring its structural integrity upon cycling. Attributed to these unique superiorities, the as-prepared Cu3Ge/Ge@N-C electrode demonstrates admirable discharge capacity, outstanding rate capability and prolonged cycle lifespan (178 mAh g-1 at 4.0 A g-1 after 4000 cycles).

A Full Li-S Battery with Ultralow Excessive Li Enabled via Lithiophilic and Sulfilic W2 C Modulation.

The practical application of Li-S batteries demands low cell balance (Licapacity /Scapacity ), which involves uniform Li growth, restrained shuttle effect, and fast redox reaction kinetics of S species simultaneously. Herein, with the aid of W2 C nanocrystals, a freestanding 3D current collector is applied as both Li and S hosts owing to its lithiophilic and sulfilic property. On the one hand, the highly conductive W2 C can reduce Li nucleation overpotentials, thus guiding uniform Li nucleation and deposition to suppress Li dendrite growth. On the other hand, the polar W2 C with catalytic effect can enhance the chemisorption affinity to lithium polysulfides (LiPSs) and guarantee fast redox kinetics to restrain S species in cathode region and promote the utilization of S. Surprisingly, a full Li-S battery with ultralow cell balance of 1.5:1 and high sulfur loading of 6.06 mg cm-2 shows obvious redox plateaus of S and maintains high reversible specific capacity of 1020 mAh g-1 (6.2 mAh cm-2 ) after 200 cycles. This work may shed new sights on the facile design of full Li-S battery with low excessive Li supply.

Conductive FeOOH as Multifunctional Interlayer for Superior Lithium-Sulfur Batteries.

The commercial course of Li-S batteries (LSBs) is impeded by several severe problems, such as low electrical conductivity of S, Li2 S2 , and Li2 S, considerable volume variation up to 80% during multiphase transformation and severe intermediation lithium polysulfides (LiPSs) shuttle effect. To solve above problems, conductive FeOOH interlayer is designed as an effective trapper and catalyst to accelerate the conversion of LiPSs in LSBs. FeOOH nanorod is effectively affinitive to S that Fe atoms act as Lewis acid sites to capture LiPSs via strong chemical anchoring capability and dispersion interaction. The excellent electrocatalytic effect enables that reduced charging potential barrier and enhanced electron/ion transport is realized on the FeOOH interlayer to promote LiPSs conversion. Significantly, Li2 S oxidation process is improved on the FeOOH interlayer determined as a combination of reduced Li2 S decomposition energy barrier and enhanced Li-ion transport. Therefore, the multifunctional FeOOH interlayer with conductive and catalytic features show strong chemisorption with LiPSs and accelerated LiPSs redox kinetics. As a result, LSBs with FeOOH interlayer displays high discharge capacity of 1449 mAh g-1 at 0.05 C and low capacity decay of 0.05% per cycle at 1 C, as well as excellent rate capability (449 mAh g-1 at 2 C).

Hematite photoanode modified with inexpensive hole-storage layer for highly efficient solar water oxidation.

Hematite is recognized as an excellent photocatalyst for photoelectrochemical photoanodes for water oxidation because of its favorable band gap, excellent anti-photocorrosion and structural stability in alkaline solution. However, slow charge transport and fast carrier recombination in the bulk and at the hematite photoanode/electrolyte interface, have limited its applications for water splitting. Herein, we report a highly efficient hematite/ferrhydrite (Fh) core-shell photoanode system, consisting of hematite (α-Fe2O3) semiconductor nanorods which dramatically enhance light harvesting, and ferrhydrite as the hole-storage shell. Our integrated hematite/ferrhydrite core-shell photoanode shows 2.7 times increased photo-current density under simulated sun light irradiation.

MnSe embedded in carbon nanofibers as advanced anode material for sodium ion batteries.

MnSe with high theoretical capacity and reversibility is considered as a promising material for the anode of sodium ion batteries. In this study, MnSe nanoparticles embedded in 1D carbon nanofibers (MnSe-NC) are successfully prepared via facile electrospinning and subsequent selenization. A carbon framework can effectively protect MnSe dispersed in it from agglomeration and can accommodate volume variation in the conversion reaction between MnSe and Na+ to guarantee cycling stability. The 1D fiber structure can increase the area of contact between electrode and electrolyte to shorten the diffusion path of Na+ and facilitate its transfer. According to the kinetic analysis, the storage process of sodium by MnSe-NC is a surface pseudocapacitive-controlled process with promising rate capability. Impressively, An MnSe-NC anode in sodium ion full cells is investigated by pairing with an Na3V2(PO4)2@rGO cathode, which exhibits a reversible capacity of 195 mA h g-1 at 0.1 A g-1.

Co3V2O8 Nanoparticles Supported on Reduced Graphene Oxide for Efficient Lithium Storage.

Co3V2O8 (CVO) with high theoretical specific capacity derived from the multiple oxidation states of V and Co is regarded as a potential electrode material for lithium-ion batteries (LIBs). Herein, reduced graphene oxide (rGO)-supported ultrafine CVO (rGO@CVO) nanoparticles are successfully prepared via the hydrothermal and subsequent annealing processes. The CVO supported on 2D rGO nanosheets possess excellent structural compatibility for the accommodation of volume variation to maintain the structural integrity of an electrode during the repeated lithiation/delithiation process. On the other hand, the rGO, as a highly-conductive network in the rGO@CVO composite, facilitates rapid charge transfer to ensure fast reaction kinetics. Moreover, the CV kinetic analysis indicates that the capacity of rGO@CVO is mainly dominated by a pseudocapacitive process with favorable rate capability. As a result, the rGO@CVO composite exhibits improved specific capacity (1132 mAh g-1, 0.1 A g-1) and promising rate capability (482 mAh g-1, 10 A g-1).

Cu2Se Nanoparticles Encapsulated by Nitrogen-Doped Carbon Nanofibers for Efficient Sodium Storage.

Cu2Se with high theoretical capacity and good electronic conductivity have attracted particular attention as anode materials for sodium ion batteries (SIBs). However, during electrochemical reactions, the large volume change of Cu2Se results in poor rate performance and cycling stability. To solve this issue, nanosized-Cu2Se is encapsulated in 1D nitrogen-doped carbon nanofibers (Cu2Se-NC) so that the unique structure of 1D carbon fiber network ensures a high contact area between the electrolyte and Cu2Se with a short Na+ diffusion path and provides a protective matrix to accommodate the volume variation. The kinetic analysis and DNa+ calculation indicates that the dominant contribution to the capacity is surface pseudocapacitance with fast Na+ migration, which guarantees the favorable rate performance of Cu2Se-NC for SIBs.

Double Morphology of Co9S8 Coated by N, S Co-doped Carbon as Efficient Anode Materials for Sodium-Ion Batteries.

Co9S8 is a potential anode material for its high sodium storage performance, easy accessibility, and thermostability. However, the volume expansion is a great hindrance to its development. Herein, a composite containing Co9S8 nanofibers and hollow Co9S8 nanospheres with N, S co-doped carbon layer (Co9S8@NSC) is successfully synthesized through a facile solvothermal process and a high-temperature carbonization. Ascribed to the carbon coating and the large specific surface area, severe volume stress can be effectively alleviated. In particular, with N and S heteroatoms introduced into the carbon layer, which is conducive to the Na+ adsorption and diffusion on the carbon surface, Co9S8@NSC can perform more capacitive sodium storage mechanism. As a result, the electrode can exhibit a favorable reversible capacity of 226 mA h g-1 at 5 A g-1 and a favorable capacity retention of 83.1% at 1 A g-1 after 800 cycles. The unique design provides an innovative thought for enhancing the sodium storage performance.

Lotus Root-Like Nitrogen-Doped Carbon Nanofiber Structure Assembled with VN Catalysts as a Multifunctional Host for Superior Lithium-Sulfur Batteries.

Lithium-sulfur batteries (LSBs) are regarded as one of the most promising energy-recycling storage systems due to their high energy density (up to 2600 Wh kg-1), high theoretical specific capacity (as much as 1672 mAh g-1), environmental friendliness, and low cost. Originating from the complicated redox of lithium polysulfide intermediates, Li-S batteries suffer from several problems, restricting their application and commercialization. Such problems include the shuttle effect of polysulfides (Li2Sx (2 < x ≤ 8)), low electronic conductivity of S/Li2S/Li2S2, and large volumetric expansion of S upon lithiation. In this study, a lotus root-like nitrogen-doped carbon nanofiber (NCNF) structure, assembled with vanadium nitride (VN) catalysts, was fabricated as a 3D freestanding current collector for high performance LSBs. The lotus root-like NCNF structure, which had a multichannel porous nanostructure, was able to provide excellent (ionically/electronically) conductive networks, which promoted ion transport and physical confinement of lithium polysulfides. Further, the structure provided good electrolyte penetration, thereby enhancing the interface contact with active S. VN, with its narrow resolved band gap, showed high electrical conductivity, high catalytic effect and polar chemical adsorption of lithium polysulfides, which is ideal for accelerating the reversible redox kinetics of intermediate polysulfides to improve the utilization of S. Tests showed that the VN-decorated multichannel porous carbon nanofiber structure retained a high specific capacity of 1325 mAh g-1 after 100 cycles at 0.1 C, with a low capacity decay of 0.05% per cycle, and demonstrated excellent rate capability.

Modified Nanopillar Arrays for Highly Stable and Efficient Photoelectrochemical Water Splitting.

Atomically modified graphitic carbon nitride quantum dots (QDs), characterized by strongly increased reactivity and stability, are developed. These are deposited on arrays of TiO2 nanopillars used as a photoanode for the photoelectrochemical water splitting. This photoanode shows excellent stability, with 111 h of continuous work without any performance loss, which outperforms the best-reported results by a factor of 10. Remarkably, our photoanode produces hydrogen even at zero bias. The excellent performance is attributed to the enhancement of photoabsorption, as well as to the promotion of charge separation between TiO2 nanopillars and the QDs.

Enhanced Photocatalytic H2 Evolution over ZnIn2S4 Flower-Like Microspheres Doped with Black Phosphorus Quantum Dots.

In this work, black phosphorus quantum dots (BPQDs) were decorated on hexagonal ZnIn2S4 flower-like microspheres to form zero-dimensional/two-dimensional (0D/2D) structures. Interface interactions between the BPQDs and ZnIn2S4 resulted in optimum effective charge transfer, thereby improving the photocatalytic performance of the material. Thus, the 0.2% BPQD-ZnIn2S4 sample showed 30% higher H2 evolution rates compared to pure ZnIn2S4. This study provides a simple route for the synthesis of photocatalysts. The results obtained herein can pave the way for designing effective catalysts for solar-to-chemical energy conversion and feasible approaches to obtain cheap, clean, and efficient photocatalysts.