ABSTRACT
Stretchable strain sensors play a crucial role in intelligent wearable systems, serving as the interface between humans and environment by translating mechanical strains into electrical signals. Traditional fiber strain sensors with intrinsic uniform axial strain distribution face challenges in achieving high sensitivity and anisotropy. Moreover, existing micro/nano-structure designs often compromise stretchability and durability. To address these challenges, a novel approach of using 3D printing to fabricate MXene-based flexible sensors with tunable micro and macrostructures. Poly(tetrafluoroethylene) (PTFE) as a pore-inducing agent is added into 3D printable inks to achieve controllable microstructural modifications. In addition to microstructure tuning, 3D printing is employed for macrostructural design modifications, guided by finite element modeling (FEM) simulations. As a result, the 3D printed sensors exhibit heightened sensitivity and anisotropy, making them suitable for tracking static and dynamic displacement changes. The proposed approach presents an efficient and economically viable solution for standardized large-scale production of advanced wire strain sensors.
ABSTRACT
Na2 Ti6 O13 (NTO) with high safety has been regarded as a promising anode candidate for sodium-ion batteries. In the present study, integrated modification of migration channels broadening, charge density re-distribution, and oxygen vacancies regulation are realized in case of Nb-doping and have obtained significantly enhanced cycling performance with 92 % reversible capacity retained after 3000â cycles at 3000â mA g-1 . Moreover, unexpected low-temperature performance with a high discharge capacity of 143â mAh g-1 at 100â mA g-1 under -15 °C is also achieved in the full cell. Theoretical investigation suggests that Nb preferentially replaces Ti3 sites, which effectively improves structural stability and lowers the diffusion energy barrier. What's more important, both the in situ X-ray diffraction (XRD) and in situ Raman furtherly confirm the robust spring effect of the Ti-O bond, making special charge compensation mechanism and respective regulation strategy to conquer the sluggish transport kinetics and low conductivity, which plays a key role in promoting electrochemical performance.
ABSTRACT
Fiber strain sensors that are directly woven into smart textiles play an important role in wearable systems. These sensors require a high sensitivity to detect the subtle strain in practical applications. However, traditional fiber strain sensors with constant diameters undergo homogeneous strain distribution in the axial direction, thereby limiting the sensitivity improvement. Herein, a novel strategy of internal or external structural design is proposed to significantly improve the sensitivity of fiber strain sensors. The fibers are produced with directional increases in diameter (internal design) or polydimethylsiloxane (PDMS) microbeads attached to surfaces (external design) by combining hollow glass tubes used as templates with PDMS drops. The structural modification of the fiber significantly impacts the sensing performance. After optimizing structural parameters, the highest gauge factor reaches 123.1 in the internal-external structure design at 25% strain. A comprehensive analysis reveals that the desirable scheme is the internal structural design, which features a high sensitivity of 110 with a 100% improvement at â¼5-20% strain. Because of the sufficiently robust interface, even at the 800th cycle, fiber sensors still possessed an excellent stable performance. The morphology evolution mechanism indicates that the resistance increase is closely related with the increased peak width and distance, and the appearance of gaps. Based on the finite element modeling simulation, the quantified effective contributions of different strategies positively correlate with the improved sensitivity. The proposed fiber strain sensors, which are woven into the two-dimensional network structure, exhibit an excellent capability for displacement monitoring and facilitate the traffic control of crossroads.
ABSTRACT
Metal sulfides have been intensively investigated for efficient sodium-ion storage due to their high capacity. However, the mechanisms behind the reaction pathways and phase transformation are still unclear. Moreover, the effects of designed nanostructure on the electrochemical behaviors are rarely reported. Herein, a hydrangea-like CuS microsphere is prepared via a facile synthetic method and displays significantly enhanced rate and cycle performance. Unlike the traditional intercalation and conversion reactions, an irreversible amorphization process is evidenced and elucidated with the help of in situ high-resolution synchrotron radiation diffraction analyses, and transmission electron microscopy. The oriented (006) crystal plane growth of the primary CuS nanosheets provide more channels and adsorption sites for Na ions intercalation and the resultant low overpotential is beneficial for the amorphous Cu-S cluster, which is consistent with the density functional theory calculation. This study can offer new insights into the correlation between the atomic-scale phase transformation and macro-scale nanostructure design and open a new principle for the electrode materials' design.
ABSTRACT
Voltage polarization during cycling, the charge potential increase of anode or discharge plateau decrease of cathode, is widely observed and would lower the output voltage. Conversely, an anomalous potential plateau negative migration phenomenon was observed in Cu xS anode of sodium-ion battery. In this study, the background mechanism was clarified from the switch of intercalation-conversion reactions and structure evolution. The dynamic cooperation between intercalation and conversion reactions may root the potential plateau negative migration during cycling. In the initial stage, the intercalation-type reaction with Na3Cu4S4 and Na4Cu2S3 products at 2.13 and 1.92 V would dominate the early migration process of potential plateaus. In the second stage, the conversion-type reaction dominated by Na2S and metallic copper formed at 1.85 and 1.53 V in the later period. The aforementioned results would provide new perspective on the electrochemical behavior of transition-metal sulfide anode and provide a clue for reducing voltage polarization.
ABSTRACT
The application of sodium titanate anodes of low cost, feasible operating voltage, and nontoxic nature were severely hindered by their inferior cycling stability and poor rate capability. Here, three-dimensional (3D) chestnut-like NaTi3O6(OH)·2H2O@N-doped carbon nanospheres (NTOH@CN) with loose crystal structures were prepared by a self-sacrificed template method. The nanospheres were composed of nanosheets and linked with nanowires, which interweaved to construct a meshwork structure. The growth mechanism of unique 3D NTOH@CN nanospheres was investigated by tracking the synthesis process of different hydrothermal durations. The rate performances of 3D NTOH@CN were superior to that of NaTi3O6(OH)·2H2O irregular spheres assembled from nanosheets (3D NTOH) and NaTi3O6(OH)·2H2O nanosheets (two-dimensional NTOH). Excellent cycling and rate performance were obtained due to their open crystal structure, unique 3D nanosphere morphology with short diffusion paths, N-doped carbon surrounding, and the solid solution reaction. In addition, the reaction mechanism, morphology change, and dynamics research during the sodium insertion/desertion process have been carefully studied. Based on varying ex situ analyses, the irreversible metallic titanium formation and the excellent structural stability of nanosphere morphology have been evidenced. The pseudocapacitive phenomenon was also detected, which effectively enhanced Na+ ion storage capability. The systematical and comprehensive study provide a holograph for the design and synthesis of sodium titanate nanostructures.
ABSTRACT
A novel complementary approach for promising anode materials is proposed. Sodium titanates with layered Na2Ti3O7 and tunnel Na2Ti6O13 hybrid structure are presented, fabricated, and characterized. The hybrid sample exhibits excellent cycling stability and superior rate performance by the inhibition of layered phase transformation and synergetic effect. The structural evolution, reaction mechanism, and reaction dynamics of hybrid electrodes during the sodium insertion/desertion process are carefully investigated. In situ synchrotron X-ray powder diffraction (SXRD) characterization is performed and the result indicates that Na+ inserts into tunnel structure with occurring solid solution reaction and intercalates into Na2Ti3O7 structure with appearing a phase transition in a low voltage. The reaction dynamics reveals that sodium ion diffusion of tunnel Na2Ti6O13 is faster than that of layered Na2Ti3O7. The synergetic complementary properties are significantly conductive to enhance electrochemical behavior of hybrid structure. This study provides a promising candidate anode for advanced sodium ion batteries (SIBs).
ABSTRACT
It is highly attractive to design FeP-based high-performance anode materials for sodium-ion batteries (SIBs). In this work, we report the development of FeP nanorod arrays on carbon cloth (FeP NAs/CC) as a flexible anode for SIBs. Such FeP NAs/CC delivers a high capacity of 829 mA h g-1 at 0.1 A g-1. At 0.2 A g-1, it still delivers 548 mA h g-1 with an excellent capacity retention of 99.8% even after 100 cycles.
ABSTRACT
Sodium-ion batteries (SIBs) have been regarded as a promising candidate for large-scale renewable energy storage system. Layered manganese oxide cathode possesses the advantages of high energy density, low cost and natural abundance while suffering from limited cycling life and poor rate capacity. To overcome these weaknesses, layer-tunnel hybrid material was developed and served as the cathode of SIB, which integrated high capacity, superior cycle ability, and rate performance. In the current work, the doping of copper was adopted to suppress the Jahn-Teller effect of Mn3+ and to affect relevant structural parameters. Multifunctions of the Cu2+ doping were carefully investigated. It was found that the structure component ratio is varied with the Cu2+ doping amount. Results demonstrated that Na+/vacancy rearrangement and phase transitions were suppressed during cycling without sacrificing the reversible capacity and enhanced electrochemical performances evidenced with 96 mA h g-1 retained after 250 cycles at 4 C and 85 mA h g-1 at 8 C. Furthermore, ex situ X-ray diffraction has demonstrated high reversibility of the Na0.6Mn0.9Cu0.1O2 cathode during Na+ extraction/insertion processes and superior air stability that results in better storage properties. This study reveals that the Cu2+ doping could be an effective strategy to tune the properties and related performances of Mn-based layer-tunnel hybrid cathode.
ABSTRACT
The capacity fluctuation phenomenon during cycling, which is closely related with solid electrolyte interphase and plays a key role for the design for advanced electrode, could be frequently observed in the titanium-based anode. However, the underlying reason for capacity fluctuation still remains unclear with rare related reports. Here, the origin of capacity fluctuation is verified with a long-life Na2Ti6O13 anode. The reaction mechanism, structural evolution and reaction kinetics during the reported sodiation/desodiation processes were carefully investigated. The gradually enhanced diffusion controlled contribution resulted in the capacity increasing. And the capacity decay could be ascribed to the irreversible reaction of metallic titanium formation and the increasing potential polarization. It is worth noting that sodium ions seem to partially reduce NTO to metallic state, which is irreversible. The present study can provide more information for the design of advanced Na2Ti6O13 anode.
ABSTRACT
Lake Qiandao is a typical subtropical man-made reservoir in China. The investigation on the seasonal and vertical dynamics of water temperature, dissolved oxygen (DO), pH value, turbidity, photosynthetic available radiation (PAR) and chlorophyll a was conducted in 2011 in order to find out the physical characteristics of Lake Qiandao. The average surface water temperature ranged from 10.4 to 32.7 degrees C. A monomictic thermal stratification was observed in Lake Qiandao, initiating in April and lasting until December. The results showed that thermal stratification had influences on vertical distribution of DO, pH value, turbidity, PAR and chlorophyll a. Very strong stratification of DO was found, inducing lower oxygen concentration in the thermocline layer and temporal hypoxia in the bottom water. The maximum turbidity was found in the thermocline layer and the precipitation affected the surface turbidity value. Moreover, the chlorophyll a concentration was higher in the surface water and lower in the bottom water as found in this study, implying that water quality was affected by stratification. Besides, the maximum photosynthesis rate and algal growth rate were found at the depth 5-10 m below the water surface. Therefore, the results can provide theoretical support for the sampling and analysis of algal blooms in Lake Qiandao.
