Active Dendrite Suppression by Ferroelectric Membrane Separators in Rechargeable Batteries.

Anodic dendrite formation is a critical issue in rechargeable batteries and often leads to poor cycling stability and quick capacity loss. Prevailing strategies for dendrite suppression aim at slowing down the growth rate kinetically but still leaving possibilities for dendrite evolution over time. Herein, we report a complete dendrite elimination strategy using a mesoporous ferroelectric polymer membrane as the battery separator. The dendrite suppression is realized by spontaneously reversing the surface energetics for metal ion reduction at the protrusion front, where a positive piezoelectric polarization is generated and superimposed as the protrusion compresses the separator. This effect is demonstrated first in a Zn electroplating process, and further in Zn-Zn symmetric cells and Zn-NaV3O8·1.5H2O full cells, where the dendritic Zn anode surfaces are completely turned into featureless flat surfaces. Consequently, a substantially longer charging/discharging cycle is achieved. This study provides a promising pathway toward high-performance dendrite-free rechargeable batteries.

Nucleation Kinetics and Structure Evolution of Quasi-Two-Dimensional ZnO at the Air-Water Interface: An In Situ Time-Resolved Grazing Incidence X-ray Scattering Study.

The design and synthesis of high-quality two-dimensional (2D) materials with desired morphology are essential for property control. One critical challenge that impedes the understanding and control of 2D crystal nucleation and growth is the inability of direct observation of the nanocrystal evolution process with high enough time resolution. Here, we demonstrated an in situ X-ray scattering approach that directly reveals 2D wurtzite ZnO nanosheet growth at the air-water interface. The time-resolved grazing incidence X-ray diffraction (GID) and grazing incidence X-ray off-specular scattering (GIXOS) results uncovered a lateral to vertical growth kinetics switch phenomenon in the ZnO nanosheet growth. This switch represents the 2D to three-dimensional (3D) crystal structure evolution, which governs the size and thickness of nanosheets, respectively. This phenomenon can guide 2D nanocrystal synthesis with rationally controlled size and thickness. Our work opens a new pathway toward the understanding of 2D nanomaterial growth kinetics based on time-resolved liquid surface grazing incidence X-ray techniques.

Understanding the High-Performance Anode Material of CoC2 O4 ⋠2 H2 O Microrods Wrapped by Reduced Graphene Oxide for Lithium-Ion and Sodium-Ion Batteries.

Metal oxalate has become a most promising candidate as an anode material for lithium-ion and sodium-ion batteries. However, capacity decrease owing to the volume expansion of the active material during cycling is a problem. Herein, a rod-like CoC2 O4 ⋅2 H2 O/rGO hybrid is fabricated through a novel multistep solvo/hydrothermal strategy. The structural characteristics of the CoC2 O4 ⋅2 H2 O microrod wrapped using rGO sheets not only inhibit the volume variation of the hybrid electrode during cycling, but also accelerate the transfer of electrons and ions in the 3 D graphene network, thereby improving the electrochemical properties of CoC2 O4 ⋅2 H2 O. The CoC2 O4 ⋅2 H2 O/rGO electrode delivers a specific capacity of 1011.5 mA h g-1 at 0.2 A g-1 after 200 cycles for lithium storage, and a high capacity of 221.1 mA h g-1 at 0.2 A g-1 after 100 cycles for sodium storage. Moreover, the full cell CoC2 O4 ⋅2 H2 O/rGO//LiCoO2 consisting of the CoC2 O4 ⋅2 H2 O/rGO anode and LiCoO2 cathode maintains 138.1 mA h g-1 after 200 cycles at 0.2 A g-1 and has superior long-cycle stability. In addition, in situ Raman spectroscopy and in situ and ex situ X-ray diffraction techniques provide a unique opportunity to understand fully the reaction mechanism of CoC2 O4 ⋅2 H2 O/rGO. This work also gives a new perspective and solid research basis for the application of metal oxalate materials in high-performance lithium-ion and sodium-ion batteries.

Self-powered liquid chemical sensors based on solid-liquid contact electrification.

Triboelectric nanogenerators (TENGs) have attracted many research endeavors as self-powered sensors for force, velocity, and gas detection based on solid-solid or solid-air interactions. Recently, triboelectrification at liquid-solid interfaces also showed intriguing capability in converting physical contacts into electricity. Here, we report a self-powered triboelectric sensor for liquid chemical sensing based on liquid-solid electrification. As a liquid droplet passed across the tribo-negative sensor surface, the induced surface charge balanced with the electrical double layer charge in the liquid droplet. The competition between the double layer charge and surface charge generated characteristic positive and negative voltage spikes, which may serve as a "binary feature" to identify the chemical compound. The sensor showed distinct sensitivity to three amino acids including glycine, lysine and phenylalanine as a function of their concentration. The versatile sensing ability was further demonstrated on several other inorganic and organic chemical compounds dissolved in DI water. This work demonstrated a promising sensing application based on the triboelectrification principle for biofluid sensor development.

Multifunctional Artificial Artery from Direct 3D Printing with Built-In Ferroelectricity and Tissue-Matching Modulus for Real-Time Sensing and Occlusion Monitoring.

Treating vascular grafts failure requires complex surgery procedures and is associated with high risks. A real-time monitoring vascular system enables quick and reliable identification of complications and initiates safer treatments early. Here, an electric fieldassisted 3D printing technology is developed to fabricate in situ-poled ferroelectric artificial arteries that offer battery-free real-time blood pressure sensing and occlusion monitoring capability. The functional artery architecture is made possible by the development of a ferroelectric biocomposite which can be quickly polarized during printing and reshaped into devised objects. The synergistic effect from the potassium sodium niobite particles and the polyvinylidene fluoride polymer matrix yields a superb piezoelectric performance (bulk-scale d 33 > 12 pC N-1). The sinusoidal architecture brings the mechanical modulus close to the level of blood vessels. The desired piezoelectric and mechanical properties of the artificial artery provide an excellent sensitivity to pressure change (0.306 mV mmHg-1, R 2 > 0.99) within the range of human blood pressure (11.25-225.00 mmHg). The high pressure sensitivity and the ability to detect subtle vessel motion pattern change enable early detection of partial occlusion (e.g., thrombosis), allowing for preventing grafts failure. This work demonstrates a promising strategy of incorporating multifunctionality to artificial biological systems for smart healthcare systems.

Embedding ultrafine ZnSnO3 nanoparticles into reduced graphene oxide composites as high-performance electrodes for lithium ion batteries.

Ultrafine ZnSnO3 nanoparticles, with an average diameter of 45 nm, homogeneously grown on reduced graphene oxide (rGO) have been successfully fabricated via methods of low temperature coprecipitation, colloid electrostatic self-assembly, and hydrothermal treatment. The uniformly distributed ZnSnO3 nanocrystals could inhibit the restacking of rGO sheets. In turn, the existence of rGO could hinder the growth and aggregation of ZnSnO3 nanoparticles in the synthesis process, increase the conductivity of the composite, and buffer the volume expansion of the ZnSnO3 nanocrystals upon lithium ion insertion and extraction. The obtained ZnSnO3/rGO exhibited superior cycling stability with a discharge/charge capacity of 718/696 mA h g-1 after 100 cycles at a current density of 0.1 A g-1.

Efficient Hydrogen Evolution Electrocatalysis Using Cobalt Nanotubes Decorated with Titanium Dioxide Nanodots.

TiO2 Co nanotubes decorated with nanodots (TiO2 NDs/Co NSNTs-CFs) are reported as high-performance earth-abundant electrocatalysts for the hydrogen evolution reaction (HER) in alkaline solution. TiO2 NDs/Co NSNTs can promote water adsorption and optimize the free energy of hydrogen adsorption. More importantly, the absorbed water can be easily activated in the presence of the TiO2 -Co hybrid structure. These advantages will significantly promote HER. TiO2 NDs/Co NSNTs-CFs as electrocatalysts show a high catalytic performance towards HER in alkaline solution. This study will open up a new avenue for designing and fabricating low-cost high-performance HER catalysts.

FeOOH/Co/FeOOH Hybrid Nanotube Arrays as High-Performance Electrocatalysts for the Oxygen Evolution Reaction.

Herein, we developed FeOOH/Co/FeOOH hybrid nanotube arrays (HNTAs) supported on Ni foams for oxygen evolution reaction (OER). The inner Co metal cores serve as highly conductive layers to provide reliable electronic transmission, and can overcome the poor electrical conductivity of FeOOH efficiently. DFT calculations demonstrate the strong electronic interactions between Co and FeOOH in the FeOOH/Co/FeOOH HNTAs, and the hybrid structure can lower the energy barriers of intermediates and thus promote the catalytic reactions. The FeOOH/Co/FeOOH HNTAs exhibit high electrocatalytic performance for OER, such as low onset potential, small Tafel slope, and excellent long-term durability, and they are promising electrocatalysts for OER in alkaline solution.

Applications, prospects and challenges of metal borides in lithium sulfur batteries.

Although the lithium-sulfur (Li-S) battery has a theoretical capacity of up to 1675 mA h g-1, its practical application is limited owing to some problems, such as the shuttle effect of soluble lithium polysulfides (LiPSs) and the growth of Li dendrites. It has been verified that some transition metal compounds exhibit strong polarity, good chemical adsorption and high electrocatalytic activities, which are beneficial for the rapid conversion of intermediate product in order to effectively inhibit the "shuttle effect". Remarkably, being different from other metal compounds, it is a significant characteristic that both metal and boron atoms of transition metal borides (TMBs) can bind to LiPSs, which have shown great potential in recent years. Here, for the first time, almost all existing studies on TMBs employed in Li-S cells are comprehensively summarized. We firstly clarify special structures and electronic features of metal borides to show their great potential, and then existing strategies to improve the electrochemical properties of TMBs are summarized and discussed in the focus sections, such as carbon-matrix construction, morphology control, heteroatomic doping, heterostructure formation, phase engineering, preparation techniques. Finally, the remaining challenges and perspectives are proposed to point out a direction for realizing high-energy and long-life Li-S batteries.

Ultrastable piezoelectric biomaterial nanofibers and fabrics as an implantable and conformal electromechanical sensor patch.

Poly(l-lactic acid) (PLLA) is a widely used U.S. Food and Drug Administration-approved implantable biomaterial that also possesses strong piezoelectricity. However, the intrinsically low stability of its high-energy piezoelectric ß phase and random domain orientations associated with current synthesis approaches remain a critical roadblock to practical applications. Here, we report an interfacial anchoring strategy for fabricating core/shell PLLA/glycine (Gly) nanofibers (NFs) by electrospinning, which show a high ratio of piezoelectric ß phase and excellent orientation alignment. The self-assembled core/shell structure offers strong intermolecular interactions between the -OH groups on Gly and C=O groups on PLLA, which promotes the crystallization of oriented PLLA polymer chains and stabilizes the ß phase structure. As-received core/shell NFs exhibit substantially enhanced piezoelectric performance and excellent stability. An all NF-based nonwoven fabric is fabricated and assembled as a flexible nanogenerator. The device offers excellent conformality to heavily wrinkled surfaces and thus can precisely detect complex physiological motions often found from biological organs.

Surface Ligand Modification on Ultrathin Ni(OH)2 Nanosheets Enabling Enhanced Alkaline Ethanol Oxidation Kinetics.

The ethanol oxidation reaction (EOR) is an economical pathway in many electrochemical systems for clean energy, such as ethanol fuel cells and the anodic reaction in hydrogen generation. Noble metals, such as platinum, are benchmark catalysts for EOR owing to their superb electrochemical capability. To improve sustainability and product selectivity, nickel (Ni)-based electrocatalysts are considered promising alternatives to noble-metal EOR. Although Ni-based electrocatalysts are relieved from intermediate poisoning, their performances are largely limited by their relatively high onset potential. Therefore, the EOR usually competes with the oxygen evolution reaction (OER) at working potentials, resulting in a low EOR efficiency. Here, we demonstrate a strategy to modify the surface ligands on ultrathin Ni(OH)2 nanosheets, which substantially improved their catalytic properties for the alkaline EOR. Chemisorbed octadecylamine ligands could create an alcoholophilic layer at the nanosheet surface to promote alcohol diffusion and adsorption, resulting in outstanding EOR activity and selectivity over the OER at higher potential. These non-noble-metal-based 2D electrocatalysts and surface ligand engineering showcase a promising strategy for achieving high-efficiency electrocatalysis of EOR in many practical electrochemical processes.

Experimentally informed structure optimization of amorphous TiO2 films grown by atomic layer deposition.

Amorphous titanium dioxide TiO2 (a-TiO2) has been widely studied, particularly as a protective coating layer on semiconductors to prevent corrosion and promote electron-hole conduction in photoelectrochemical reactions. The stability and longevity of a-TiO2 is strongly affected by the thickness and structural heterogeneity, implying that understanding the structure properties of a-TiO2 is crucial for improving the performance. This study characterized the structural and electronic properties of a-TiO2 thin films (∼17 nm) grown on Si by atomic layer deposition (ALD). Fluctuation spectra V(k) and angular correlation functions were determined with 4-dimensional scanning transmission electron microscopy (4D-STEM), which revealed the distinctive medium-range ordering in the a-TiO2 film. A realistic atomic model of a-TiO2 was established guided by the medium-range ordering and the previously reported short-range ordering of a-TiO2 film, as well as the interatomic potential. The structure was optimized by the StructOpt code using a genetic algorithm that simultaneously minimizes energy and maximizes the match to experimental short- and medium-range ordering. The StructOpt a-TiO2 model presents improved agreements with the medium-range ordering and the k-space location of the dominant 2-fold angular correlations compared with a traditional melt-quenched model. The electronic structure of the StructOpt a-TiO2 model was studied by ab initio calculations and compared to the crystalline phases and experimental results. This work uncovered the medium-range ordering in a-TiO2 thin films and provided a realistic a-TiO2 structure model for further investigation of structure-property relationships and materials design. In addition, the improved multi-objective optimization package StructOpt was provided for structure determination of complex materials guided by experiments and simulations.

Strong Room-Temperature Ferromagnetism in Ultrathin NiOOH Nanosheets through Surfactant Manipulation.

Two-dimensional (2D) ferromagnetic (FM) materials with nanoscale thickness and spontaneous net magnetization have emerged as a promising class of functional materials for applications in next-generation spintronics, quantum processing, and data storage devices. However, most 2D materials exhibit weak FM even at low temperatures, limiting their potential applications in many technological fields. The fabrication of strong room-temperature FM 2D materials is highly desirable for the development of practical applications. Here, we demonstrate an ionic layer epitaxy strategy to synthesize few-layered NiOOH nanosheets with strong room-temperature FM and a saturation magnetization up to 409.86 emu cm-3 at 300 K. The results are consistent with the ab initio predictions of a stable FM NiOOH nanolayer structure with an FM configuration. The FM strength of the NiOOH nanosheets can be tuned by controlling the surfactant monolayer density and annealing. This work offers a promising strategy for achieving strong high-temperature FM in 2D materials for spintronic applications.

Improving performances of Lithium-Sulfur cells via regulating of VSe2 functional mediator with Doping-Defect engineering and Electrode-Separator integration strategy.

The sluggish redox kinetics and the severe shuttle effect of soluble lithium polysulfides (LiPSs) are the main key issues which would hinder the development of lithium-sulfur (Li-S) batteries. In this work, a nickel-doped vanadium selenide in-situ grows on reduced graphene oxide(rGO) to form a two-dimensional (2D) composite Ni-VSe2/rGO by a simple solvothermal method. When it is used as a modified separator in Li-S batteries, the Ni-VSe2/rGO material with the doped defect and super-thin layered structure can greatly adsorb LiPSs and catalyze the conversion reaction of LiPSs, resulting in effectively reducing LiPSs diffusion and suppressing the shuttle effect. More importantly, the cathode-separator bonding body is first developed as a new strategy of electrode-separator integration in Li-S batteries, which not only could decrease the LiPSs dissolution and improve the catalysis performance of the functional separator as the upper current-collector, but also is good for the high sulfur loading and the low electrolyte/sulfur (E/S) ratio for high energy density Li-S batteries. When the Ni-VSe2/rGO-PP (polypropylene, Celgard 2400) modified separator is applied, the Li-S cell can retain 510.3 mA h g-1 capacity after 1190 cycles at 0.5C. In the electrode-separator integrated system, the Li-S cell can still maintain 552.9 mA h g-1 for 190 cycles at a sulfur loading 6.4 mg cm-2 and 4.9 mA h cm-2 for 100 cycles at a sulfur loading 7.0 mg cm-2. The experimental results indicate that both the doped defect engineering and the super-thin layered structure design might optimally be chosen to fabricate a new modified separator material, and especially, the electrode-separator integration strategy would open a practical way to promote the electrochemical behavior of Li-S batteries with high sulfur loading and low E/S ratio.

The role of selenium vacancies functionalized mediator of bimetal (Co, Fe) selenide for high-energy-density lithium-sulfur batteries.

Lithium-sulfur (Li-S) batteries are currently only in the basic research stage and have not been commercialized, which is mainly affected by the poor conductivity of sulfur/lithium sulfide (S/Li2S), volume expansion effect of sulfur and the shuttle effect of lithium polysulfides (LiPSs). Herein, a three dimensional (3D) carbon nanotubes (CNTs) decorated cubic Co9Se8-x/FeSe2-y (0 ï¼œ x ï¼œ 8, 0 ï¼œ y ï¼œ 2) composite (Co9Se8-x/FeSe2-y@CNTs) is developed, and used as the functionalized mediator on polypropylene (PP) in Li-S batteries. Benefiting from the good electrical conductivity, large number of Se vacancies and the triple block/adsorption/catalytic effects of Co9Se8-x/FeSe2-y@CNTs, the cell with Co9Se8-x/FeSe2-y@CNTs//PP modified separator delivers a high reversible capacity (1103.5 mA h g-1) at 1C after three cycles activation at 0.5C and remains 446 mA g h-1 after 750 cycles with a 0.08% capacity decay rate each cycle. Moreover, at 0.2C, a high areal capacity of 3.63 mA h cm-2 after 100 cycles with a high sulfur loading of 4.1 mg cm-2 is obtained. The in-situ XRD tests revealing the transition path of α-S8 â†’ Li2S â†’ ß-S8 during the first charge-discharge process, then ß-S8 â†’ Li2S â†’ ß-S8 conversion reaction in the next cycles, and firstly determine the sulfur-selenide active intermediates (Se1.1S6.9) during cycles. The work provides a new insight into the development of bimetallic selenide composites by defect engineering with highly adsorptive and catalytic properties for Li-S batteries.

Novel hydrothermal synthesis of Mn-TaS3@rGO nanocomposite as a superior multifunctional mediator for advanced Li-S batteries.

Because of its high theoretical capacity and energy density, the lithium-sulfur (Li-S) battery is a desirable next-generation energy storage technology. However, the shuttle effect of lithium polysulfide and the slow sulfur reaction kinetics remain significant barriers to Li-S battery application. In this work, tantalum trisulfide (TaS3) and selective manganese-doped tantalum trisulfide (Mn-TaS3) nanocomposites on reduced graphene oxide surface were developed via a one-step hydrothermal method for the first time and introduced as a novel multifunctional mediator in the Li-S battery. The surface engineering of Mn-TaS3@rGO with abundant defects not only exhibits the strong adsorption performance on lithium polysulfides (LiPSs) but also demonstrates the remarkable electrocatalytic effect on both the LiPSs conversion reaction in symmetric cell and the Li2S nucleation/dissolution processes in potentiostatic experiments, which would substantially promote the electrochemical performance of LSB. The cell assembled with Mn-TaS3@rGO/PP modified separator could significantly improve the cell conductivity and effectively accelerate the redox conversion of active sulfur during the charging/discharging process, which delivers exceptional long-term cycling with 683 mA h g-1 retention capacity after the 1000th cycle at 0.3C under the sulfur loading of 2.7 mg cm-2. Even at the E/S ratio as low as 5.0 µL mg-1, the reversible specific capacity of 692 mA h g-1 can be offered at 0.2C over 300 cycles. This research indicates that the novel Mn-TaS3@rGO multifunctional mediator is successfully fabricated and applied in Li-S batteries with extraordinary electrochemical performances and gives a strategy to explore the construction of a modified functional separator.

Two-birds with one stone: Improving both cathode and anode electrochemical performances via two-dimensional Te-CoTe2/rGO ultrathin nanosheets as sulfur hosts in lithium-sulfur batteries.

A Te-doped CoTe2 film could be grown in situ on reduced graphene oxide (rGO) to develop a Te-CoTe2/rGO composite with an ultrathin layered structure, which has multiple protective effects on both the sulfur positive electrode and lithium negative electrode in lithium sulfur (Li-S) batteries. The Te-CoTe2/rGO composite as a sulfur host not only shows a strong adsorbing ability for lithium polysulfides (LiPSs) but can also accelerate the conversion reaction of active material sulfur during the charging/discharging process. More importantly, this host can turn the shuttle effect from an unfavorable factor to a favorable factor, which could improve the electrochemical performance of the lithium anode with uniform lithium plating/stripping resulting from the intermediate polytellurosulfide species (Li2TexSy), which could be generated on the cathode surface via Te reacting with soluble Li2Sn (4 ≤ n ≤ 8). As a result, the S@Te-CoTe2/rGO cathode shows a discharge capacity of 970.0 mA h g-1 in the first cycle at 1 C and retains a high capacity of 545.5 mA h g-1 after 1000 cycles, corresponding to a low capacity decay rate of only 0.043% per cycle. In addition, in situ X-ray diffraction (XRD) and in situ Raman were used to explore the sulfur conversion process. This study not only demonstrates that a two-dimensional (2D) ultrathin Te-CoTe2/rGO composite is successfully developed with multiple effects on Li-S batteries but also opens a new pathway for designing unique sulfur hosts to promote the electrochemical performance of Li-S batteries.