Power Sources For Electronics Research Articles

A Multidirectional Forearm Electromagnetic Generator Designed via Numerical Simulations

Harvesting biomechanical energy from daily human body motions provides a promising and sustainable power solution for wearable electronics, whose current power supplies, i.e., batteries, have unsatisfactory capacity and durability due to volume, shape, and flexibility constraints. Electromagnetic generators (EMGs) are favorable energy transducers because of their high energy-conversion efficiency, low dependence on frequencies, and long-term stability. However, an EMG that can effectively harvest energy from multi-directional arm motions at aperiodic low frequencies are yet to be created. Here, we introduce a unique EMG configuration by combining a linear and a helix frame into a monolithic unit (EMG-LH), enabling the EMG to scavenge energy from all kinds of arm motions up to 6 degrees of freedom (DOFs) (movement along XYZ axes and forearm rotations). The EMG frame geometry is designed and optimized according to numerical simulations. To clarify the working mechanism and maximize the power output, the copper coils’ winding pattern, the magnets’ velocity profiles, and the resulting voltage output are numerically simulated and then experimentally verified. Our EMG-LH outperforms linear EMGs (EMG-Ls) and helix EMGs (EMG-Hs) in harvesting energy from all arm motions. This work explicitly presents a forearm-wearable energy harvester as a sustainable power source for wearable electronics.

Highly robust zinc metal anode directed by organic–inorganic synergistic interfaces for wearable aqueous zinc battery

AbstractFlexible aqueous zinc batteries (FAZBs) with high safety and environmental friendliness are promising smart power sources for smart wearable electronics. However, the bare zinc anode usually suffers from damnable dendrite growth and rampant side reaction on the surface, greatly impeding practical applications in FAZBs. Herein, a composite polymer interface layer is artificially self‐assembled on the surface of the zinc anode by graft‐modified fluorinated monomer (polyacrylic acid‐2‐(Trifluoromethyl)propenoic acid, PAA‐TFPA), on which an organic–inorganic hybrid (PAA‐Zn/ZnF2) solid electrolyte interface (SEI) with excellent ionic conductivity is formed by interacting with Zn2+. Both the pouch cell and fiber zinc anode exhibit excellent plating/stripping reversibility after protecting by this organic–inorganic SEI, which can be stably cycled more than 3000 h in symmetric Zn||Zn cells or 550 h in fiber Zn||Zn cells. Additionally, this interface layer preserves zinc anode with excellent mechanical durability under various mechanical deformation (stably working for another 1200 h after bending 100 h). The corresponding PAA‐Zn/ZnF2@Zn||MnO2 full cell displays an ultra‐long life span (79% capacity retention after 3000 cycles) and mechanical robustness (85% of the initial capacity for another 3000 cycles after bending 100 times). More importantly, the as‐assembled cells can easily power smart wearable devices to monitor the user's health condition.

Highly Stretchable and Flexible Electrospinning‐Based Biofuel Cell for Implantable Electronic

AbstractWith the emerging demand of implantable microelectronics, it essentially requires the fully integrated and reliable power supplies. The study reports a stretchable and flexible electrospinning‐based glucose/O2 biofuel cell with glucose oxidase bioanode, Pt/C cathode and thermoplastic polyurethane substrate, which is capable for adapting to the various stresses and strains caused by individual movement. The rigid benzene rings and elastic chain segments of thermoplastic polyurethane ensure its superior tensile property. Furthermore, the stable covalent connections between the activated carbon nanotubes (CNTs‐COOH) and glucose oxidase inside 3D thermoplastic polyurethane network are established by amide reaction to ensure the rapid direct electron transfer of bioanode and stable power output of device in flexible environments. The biofuel cell exhibits an open circuit voltage of 0.575 V, and high‐power density of 57 µW cm−2 in 5 mM glucose. Moreover, the power‐generation properties of implantable biofuel cell keep steady, and its power density exhibits limited fluctuations on the dorsum of rat when bending, stretching, and twisting in 28 days. There is no obvious local inflammation or systemic abnormalities in rats. It satisfies the impressive biocompatible requirement, demonstrating the promising potential of electrospinning‐based biofuel cell as a robust self‐sustained power source for implantable electronics.

Wearable Rectenna With Integrated Miniaturized Feeding Slot and Rectifier Structure

A low-cost hybrid textile/PCB wearable rectenna is designed for smart on-body applications. It is an integration of a textile patch antenna and a highly efficient rectifier on a small PCB substrate, where the feeding aperture of the antenna is significantly miniaturized by exploiting an LC loading technique in order to have an effective integration with the rectifier. The feeding-rectifying circuitry is attached to the back of the antenna by normal sewing threads. The essential components are soldered on the small rigid PCB for a robust connection. The size of the rectenna is 0.817 × 0.817 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> while the rigid substrate area for the feeding-rectifying circuitry is only 0.278 × 0.147 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (3.4 cm × 1.8 cm) at 2.45 GHz. The intrinsic dielectric/conduction loss of textile feedlines, the loss of antenna-to-rectifier interconnectors, the loss of soldering or gluing on textiles, and the loss due to body absorption from typical large feeding slots are constitutively reduced. The soldering points and the consequent hard-to-be-characterized parasitic effects on textiles are avoided. The proposed integration approach reduces the cost and eases the rectenna design, fabrication, and integration. As a result, the power conversion efficiency (PCE) of the rectifier reaches up to 39.5% at -20 dBm input power level whilst the experimental rectenna prototype achieves the state-of-the-art PCE of 41% at an extremely low incident power density of 0.4 μW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The maximum PCE is 56% at the -5 dBm input power. Finally, the possibility of harvesting datalink energy from PC/mobile phones as power source for wearable electronics is investigated.

MOF-derived porous Ni/C material for high-performance hybrid nanogenerator and self-powered wearable sensor

This study proposed a self-powered bio-sensing positioning system driven by MOF-derived porous Ni/C material-based hybrid nanogenerator. The porous structure of Ni/C nanoparticles provides a high specific surface area, increases the capacitance of the nano-composite, and traps more charges due to the formation of micro-capacitors, which boost the performance of TENGs. The as-fabricated enhanced TENG achieved a peak voltage of 820 V and a power density of 10.1 W/m2. An optimal bilayer structure was determined through experiments and simulations to obtain the maximum output performance. Flexible TENGs are placed on various parts of the body to achieve biomechanical energy harvesting and motion monitoring, and provide power sources for small electronics. By combining with electromagnetic generator (EMG), a wearable self-powered positioning system is constructed. This work provides a new idea to enhance the output of TENG, and broadens the application of TENG in self-powered wearable systems.

Comparative assessment of single-loop droop controlled grid-forming converter and its damping enhancement

As the penetration of power electronic interfaced power sources increases rapidly, grid-forming controlled voltage source converters (VSCs) are deemed as an effective alternative to synchronous generators. As a typical grid-forming control scheme, droop control is commonly utilized due to its simplicity of construction and stability of operation. VSCs driven by droop controls, such as multi-loop droop control (MLDC) and single-loop droop control (SLDC) are capable of actively establishing voltage and frequency of grid-forming converters. However, the transient performance of SLDC at different faults is less explored to date. In this work, an in-depth comparative assessment of large-signal stability against the established MLDC is first presented by means of phase portrait. It is revealed that, both control strategies have similar transient behaviors with their basic scheme. However, with the introducing of the low-pass filters which can emulate the inertia, SLDC generally exhibits a larger power angle overshoot during the fault and therefore has poorer transient stability as compared that of MLDC. To address this issue, this work improves the damping of SLDC by incorporating differential compensation link into it. Furthermore, a parameter design guideline that balances damping and inertia, hence the transient stability and frequency stability, is proposed. The analysis is supported by real-time hardware-in-the-loop experimental results.

Design and characteristic analysis of a novel deformation-controllable piezoelectric vibration energy harvester for low frequency

Vibration energy harvesting using the piezoelectric effect is becoming a promising solution to the sustainable green power source for low-power portable and wireless electronics. To harvest low-frequency vibration energy and prevent the damage of piezoelectric vibrator due to the excessive deformation, a novel deformation-controllable piezoelectric vibration energy harvester (D-CPVEH) by using a wedge cam to limit the maximum deformation of the cantilevered piezoelectric vibrator is proposed in this paper. The cam structure can drive the pre-bending piezoelectric vibrator to produce a controllable-amplitude and unidirectional deformation, thereby improving the reliability of the harvester significantly. To verify the feasibility of the proposed principle and design, theoretical analysis and numerical simulation are firstly performed, and then the influences of system parameters on the dynamic response of the D-CPVEH are analyzed in terms of amplitude ratio of the cam and deformation of the vibrator. Afterwards, a prototype is fabricated and tested in terms of frequency response characteristics. The simulation and experimental results show that the maximum deformation of the piezoelectric vibrator can effectively be limited by introducing the cam structure. Besides, it demonstrates that the spring stiffness, additional mass, cam lift, cam angle and excitation frequency exert a significant effect on the amplitude ratio of the cam, the deformation of the piezoelectric vibrator, the output voltage and the maximum voltage of the harvester, and the optimal operating bandwidth. The maximum generated voltage increases while the corresponding optimal operating bandwidth decreases with the increase of the cam lift. It is found that the maximum voltage is basically independent of other structural parameters except for the cam lift. Furthermore, the optimal operating bandwidth can be effectively adjusted by the spring stiffness, additional mass and cam angle to adapt to the broadband low-frequency vibration environments. The testing result shows that the D-CPVEH can achieve the maximum power of 2.58 mW at 5.5 Hz with the optimal load resistance of 30 kΩ.

Nature-Driven Biocompatible Epidermal Electronic Skin for Real-Time Wireless Monitoring of Human Physiological Signals.

Wearable bioelectronic patches are creating a transformative effect in the health care industry for human physiological signal monitoring. However, the use of such patches is restricted due to the unavailability of a proper power source. Ideal biodevices should be thin, soft, robust, energy-efficient, and biocompatible. Here, we report development of a flexible, lightweight, and biocompatible electronic skin-cum-portable power source for wearable bioelectronics by using a processed chicken feather fiber. The device is fabricated with a novel, breathable composite of biowaste chicken feather and organic poly(vinylidene fluoride) (PVDF) polymer, where the chicken feather fiber constitutes the "microbones" of the PVDF, enhancing its piezoelectric phase content, biocompatibility, and crystallinity. Thanks to its outstanding pressure sensitivity, the fabricated electronic skin is used for the monitoring of different human physiological signals such as body motion, finger and joint bending, throat activities, and pulse rate with excellent sensitivity. A wireless system is developed to remotely receive the different physiological signals as captured by the electronic skin. We also explore the capabilities of the device as a power source for other small electronics. The piezoelectric energy harvesting device can harvest a maximum output voltage of ∼28 V and an area power density of 1.4 μW·cm-2 from the human finger imparting. The improved energy harvesting property of the device is related to the induced higher fraction of the electroactive phase in the composite. The easy process ability, natural biocompatibility, superior piezoelectric performance, high pressure sensitivity, and alignment toward wireless transmission of the captured data make the device a promising candidate for wearable bioelectronic patches and power sources.

Atomically dispersed Fe-Ni dual sites in heteroatom doped carbon tyres for efficient oxygen electrocatalysis in rechargeable Zn-Air battery

The electronic and functional synergies between the twin metal centers make dual single-atom catalysts (DACs) attractive for oxygen electrocatalysis. The catalytic activities of DACs are largely decided by their surrounding micro-environment and supporting substrates. Modulating the micro-environment as well as engineering the efficient support is challenging tasks. Moreover, both are critical to optimizing the performance of DACs. Herein, a novel bio-cooperative strategy is developed to synthesize FeNi-DAC wherein Fe-Ni dual-atom sites are embedded in the N, P codoped tyre shaped carbon matrix. The configuration matching of Fe-Ni dual centers together with the local electronic engineering of N, P heteroatoms synergistically boost the catalytic activity on the oxygen reaction. Furthermore, the central-hollow highly-porous carbon matrix not only gives rise to a large amount of active sites, but also facilitates fast kinetics. Taking advantage of both the DAC and the substrate, the FeNi-NPC hollow tyre (HT) catalyst scores high in both oxygen reduction and evolution reactions, which exhibits the narrow potential difference and excellent durability. The aqueous Zn-air full battery (ZAB) integrating the FeNi-NPC HT air cathode has a high power density and a good stability over long-term cycling. Moreover, the flexible solid-state ZAB assembled with the polymer electrolyte obtains the high reliability over a wide range of temperatures or under diverse outside deformations. Therefore, this work offers a new green approach to prepare highly efficient DACs with built-in modulated micro-environment and tailor-made substrates. Moreover, it also paves a new way to develop highly-pliable power source for flexible electronics.

Moisture-Enabled Germination of Heat-Activated Bacillus Endospores for Rapid and Practical Bioelectricity Generation: Toward Portable, Storable Bacteria-Powered Biobatteries.

Small-scale battery-like microbial fuel cells (MFCs) are a promising alternative power source for future low-power electronics. Controllable microbial electrocatalytic activity in a miniaturized MFC with unlimited biodegradable energy resources would enable simple power generation in various environmental settings. However, the short shelf-life of living biocatalysts, few ways to activate the stored biocatalysts, and extremely low electrocatalytic capabilities render the miniature MFCs unsuitable for practical use. Here, heat-activated Bacillus subtilis spores are revolutionarily used as a dormant biocatalyst that can survive storage and rapidly germinate when exposed to special nutrients that are preloaded in the device. A microporous, graphene hydrogel allows the adsorption of moisture from the air, moves the nutrients to the spores, and triggers their germination for power generation. In particular, forming a CuO-hydrogel anode and an Ag2 O-hydrogel cathode promotes superior electrocatalytic activities leading to an exceptionally high electrical performance in the MFC. The battery-type MFC device is readily activated by moisture harvesting, producing a maximum power density of 0.4mW cm-2 and a maximum current density of 2.2mA cm-2 . The MFC configuration is readily stackable in series and a three-MFC pack produces enough power for several low-power applications, demonstrating its practical feasibility as a sole power source.

Flexible photo-charging power sources for wearable electronics

Sustainable power supply is one of the key guarantees for wearable electronics. However, the trend of multifunctionality in integrated miniatured platform and higher operational expectation for modern untethered electronics raises great challenges. A flexible photo-charging system that harvests light energy from ambient environment and simultaneously charges the energy storage devices would be a promising power solution other than manual battery replacement or frequently recharging. In this review, we discuss the state-of-the-art flexible photo-charging technologies as power sources for wearable electronics. Planar photo-charging devices and wearable photo-charging fibers/textiles are summarized, including the materials engineering, device designs, and performances. Then we will briefly present their current applications in sensing and health monitoring. This review concludes with some key challenges and perspectives for further research and development.

Adaptive Control Strategy for Frequency Support From MTDC Connected Offshore Wind Power Plants

Grid integration of large-scale power electronic interfaced renewable energy sources leads to a low inertia system, thus resulting in a high rate of change of frequency (RoCoF) and frequency deviations in the power system following a credible contingency. In this article, a realistic adaptive communication-independent control strategy for effective inertial and primary frequency support from multiterminal HVDC (MTDC) connected offshore wind farms (OWFs) has been proposed. The proposed strategy can identify and distinguish the grid under disturbance among the other healthy grids in the MTDC system by an adaptive droop frequency support (ADFS) scheme at each receiving end converter (REC). On the OWF side, the control system of wind turbine generators has been designed to coordinate with the ADFS scheme to comply with the grid code regulations (GCRs) for inertial and primary frequency support. The proposed ADFS control scheme ensures that while providing frequency support to the grid under disturbance, frequency deviation limits of the healthy neighboring grids are not breached. Moreover, the proposed strategy complies adequately with the maximum permissible limits of HVDC voltage deviation. Furthermore, the proposed strategy is dependent on only local measurements and can be easily customized to comply with any applicable GCR. The reliability and effectiveness of the proposed robust control strategy have been demonstrated on three power systems interconnected through the MTDC system to two OWFs.

Highly flexible triboelectric nanogenerators with electrospun PVDF-TrFE nanofibers on MWCNTs/PDMS/AgNWs composite electrodes

With an increasing demand for flexible and portable power sources, triboelectric nanogenerators (TENGs) have been attracted as self-powered systems. In this study, we fabricated highly flexible TENGs composed of directly electrospun a poly(vinylidene fluoride co-trifluoroethylene) (PVDF-TrFE) nanofiber membranes on the multi-walled carbon nanotubes (MWCNTs)/poly(dimethylsiloxane) (PDMS)/silver nanowires (AgNWs) composite electrodes. Adjusting the PDMS mixing ratio could enhance the adhesive strength and decrease Young's modulus of the composite electrode, resulting in the fabrication of highly flexible TENGs. The TENG (30 mm × 30 mm2) yielded a power density of 5.28 W/m2. In addition, it was demonstrated the TENG could stably harvest electric energy under various conditions. It is expected that the proposed TENGs could be applied as electrical power sources for flexible electronics due to its sufficient electrical performance and flexibility.

Study of Nitrogen-Doped Carbon Nanotubes for Creation of Piezoelectric Nanogenerator

The creation of sustainable power sources for wearable electronics and self-powered systems is a promising direction of modern electronics. At the moment, a search for functional materials with high values of piezoelectric coefficient and elasticity, as well as non-toxicity, is underway to generate such power sources. In this paper, nitrogen-doped carbon nanotubes (N-CNTs) are considered as a functional material for a piezoelectric nanogenerator capable of converting nanoscale deformations into electrical energy. The effect of defectiveness and of geometric and mechanical parameters of N-CNTs on the current generated during their deformation is studied. It was established that the piezoelectric response of N-CNTs increased nonlinearly with an increase in the Young’s modulus and the aspect ratio of the length to diameter of the nanotube and, on the contrary, decreased with an increase in defectiveness not caused by the incorporation of nitrogen atoms. The advantages of using N-CNT to create energy-efficient piezoelectric nanogenerators are shown.

A Self-Healing PVA-Linked Phytic Acid Hydrogel-Based Electrolyte for High-Performance Flexible Supercapacitors.

Flexible supercapacitors can be ideal flexible power sources for wearable electronics due to their ultra-high power density and high cycle life. In daily applications, wearable devices will inevitably cause damage or short circuit during bending, stretching, and compression. Therefore, it is necessary to develop proper energy storage devices to meet the requirements of various wearable electronic devices. Herein, Poly(vinyl alcohol) linked various content of phytic acid (PVA-PAx) hydrogels are synthesized with high transparency and high toughness by a one-step freeze-thaw method. The effects of different raw material ratios and agents on the ionic conductivity and mechanical properties of the hydrogel electrolyte are investigated. The PVA-PA21% with 2 M H2SO4 solution (PVA-PA21%-2 M H2SO4) shows a high ionic conductivity of 62.75 mS cm-1. Based on this, flexible supercapacitors fabricated with PVA-PA21%-2 M H2SO4 hydrogel present a high specific capacitance at 1 A g-1 after bending at 90° (64.8 F g-1) and for 30 times (67.3 F g-1), respectively. Moreover, the device shows energy densities of 13.5 Wh kg-1 and 14.0 Wh kg-1 at a power density of 300 W kg-1 after bending at 90° and for 30 times during 10,000 cycles. It provides inspiration for the design and development of electrolytes for related energy electrochemical devices.

REDUCING THE SHOOTING OF HYBRID PHOTOVOLTAIC PLANTS ON SCR AND LI-GRIDS

The main threat by comparable methods lately is the temporary downtime for accurate-current network dispatch errors. Throughout a temporary outage, Power Electronic based power sources stop operating, giving rise to possible security defiance towards the network, in this research, the potentially viable choice to serve continuous work temporarily for the scheme is provided with consideration of identifying upgrades to existing photovoltaic generators (photovoltaic generators discrete) and an upgrade in the separate establishment of existing “photovoltaic” and “Energy Storage Systems” discrete hybrid photovoltaics. This study aims to find a series of power sources with Power Electronic interfaces that are connected to a low “Short Circuit Ratio” network and “Low Inertia” grid to operate without a moment's stoppage.&#x0D; The proposed method was proved by adopting PSS/e on a method where power electronics-occupying assets produce the majority of energy. Inverter models along with temporary shutdown through an equal 3-period fault were advanced in PSS/e. together with increasing infiltration of “Power Electronics” established multitude and resources, progressive completion is needed to improve network stability in low a) areas and low inertia networks. The requirements for progressive solvent arose out of the steady variation in the paradigm of the power grid from the dominant systems of traditional electric machines to the high penetration of systems based on power electronics. A technical comparison was made between distinct categories of resolution (divergent photovoltaic and divergent hybrid photovoltaic) to operate a photovoltaic generator's weak “Short Circuit Ratios” also “Low Inertia” grating (grid).&#x0D; The results of this study indicate that the proposed solution is calculated nether disparate running term and error class adopting the Electromagnetic Transient model. Moreover, to analyze distinct solvents, a specialized proportion is served on discrete hybrid photovoltaic generators. The proposed solution is the development of conventional increase as well as contemporary condensers, deter capacitors, and reducers to advanced photovoltaic generators and hybrid photovoltaic generators to provide voltage support to ensure continuous working through lopsided dispatch streak disturbances, and another solution is photovoltaic-energy generation. Integrated storage system connected to High Voltage dc and high voltage ac transmission network.

Constructing Carbon Nanotube Hybrid Fiber Electrodes with Unique Hierarchical Microcrack Structure for High-Voltage, Ultrahigh-Rate, and Ultralong-Life Flexible Aqueous Zinc Batteries.

Flexible aqueous zinc batteries are promising candidates as safe power sources for fast-growing portable and wearable electronics. However, the low working voltage, poor rate capability, and cycling stability have greatly restricted their development and applications. Here, a new family of flexible bimetallic phosphide/carbon nanotube hybrid fiber electrodes with unique macroscopic microcrack structure and microscopic porous nanoflower structure is reported. The hierarchical microcrack structure not only facilitates the penetration of electrolyte for effective exposure of active sites, but also can serve as buffers to relieve the stress concentrations of the fiber electrode under deformations, enabling impressive electrochemical performance and mechanical flexibility. Particularly, the fabricated flexible aqueous zinc batteries demonstrate high working voltage plateau and specific capacity (≈1.7V, 258.9 mAh g-1 at 2 A g-1 ), ultrahigh rate capability (135.8 mAh g-1 at 50 A g-1 , fully charged in only 9.8 s) and impressive power density of 79 000W kg-1 . Moreover, the flexible batteries show ultralong cycling life with 74.6% capacity retention after 20 000 cycles. The fiber batteries are also highly flexible and can be easily knitted into soft electronic textiles to power a smartphone, which are particularly promising for the next-generation of flexible and wearable electronics.

State relevance and modal analysis in electrical microgrids with high penetration of electronic generation

A clean electricity sector requires distributed generation through electronic power sources with very fast voltage, frequency, and current responses. Therefore, unlike in conventional power systems with slow generators, fast power-line dynamics may not always be negligible compared to generators’ dynamics. In this scenario, this paper proposes an algorithm to calculate the relevance of each state of a linear system in the system input–output response systematically. It explores its application to a linearised model of an electrical microgrid to decide which dynamics are relevant to be included for analysis and/or simulation. This algorithm uses a non-physical balanced realisation of the linear system, where the energy of each state variable in the system output can be calculated. Both the balanced realisation and the original system have the same eigenvalues. A “relevance coefficient” (RC) of each one of the state variables of the original linear system has been defined by combining the relevance of the states of the balanced system with the mode-in-state participation factors of the system eigenvalues of both systems. The usefulness of the proposed RC was validated by comparing detailed nonlinear simulations of an electrical microgrid with nonlinear simulations of reduced models as informed by the RC. Results show that the proposed RC gives sensible and clear recommendations even in systems without a clear time separation between system dynamics.

Quantum view of Li-ion high mobility at carbon-coated cathode interfaces

Lithium-ion batteries (LIBs) are among the most promising power sources for electric vehicles, portable electronics and smart grids. In LIBs, the cathode is a major bottleneck, with a particular reference to its low electrical conductivity and Li-ion diffusivity. The coating with carbon layers is generally employed to enhance the electrical conductivity and to protect the active material from degradation during operation. Here, we demonstrate that this layer has a primary role in the lithium diffusivity into the cathode nanoparticles. Positron is a useful quantum probe at the electroactive materials/carbon interface to sense the mobility of Li-ion. Broadband electrical spectroscopy demonstrates that only a small number of Li-ions are moving, and that their diffusion strongly depends on the type of carbon additive. Positron annihilation and broadband electrical spectroscopies are crucial complementary tools to investigate the electronic effect of the carbon phase on the cathode performance and Li-ion dynamics in electroactive materials.

A potential flexible fuel cell with dual-functional hydrogel based on multi-component crosslinked hybrid polyvinyl alcohol

The flexible energy supplies are urgently needed considering with the rapid development of portable wearable electronic devices. The fuel cells possess the highest theoretical power density compared with batteries and super-capacitors. However, the flexible and bendable applications are hindered by the inconvenient fuel/electrolyte storage and existence of physical membrane. It is necessary to develop one kind of power sources with a straightforward system and integrated fuel/electrolyte supply-storage system. Herein, a new type of hydrogel based on polyvinyl alcohol-polyvinyl pyrrolidone-sulfosuccinic acid semi-interpenetrating network, is synthesized and applied by doping and blending various functional groups. The hydrogel possess the characteristics of high swelling ratio, superior ionic conductivity, good mechanical properties and integrated dual functions. The flexible fuel cell integrated with fuel storage/supply hydrogel is assembled without any external auxiliary system. It delivers a maximum power density of 2.83 mW cm−2 and operates normally under various flexible situations such as bending, twisting, fatigue bending and needling states. Both high flexibility and stability of the hydrogel-based micro fuel cells have been demonstrated upon the wearable and bendable applications. The work illustrates a pathway for designing power sources for flexible electronics with integrated fuel/electrolyte storage and matched mechanical properties.