Power Sources For Portable Devices Research Articles

A novel Al/BiCl3/γ-Al2O3 composite for small-sized fuel cell: Fabrication, performance and mechanisms

Small-sized fuel cell is an ideal and promising power source for portable devices due to its long-term electricity supply and free of CO2 emission. However, its commercialization is obstructed by reliable hydrogen source, which should be non-corrosiveness, as compact as possible, stable and controllable high purity hydrogen supply. In this study, a novel in situ hydrogen production material Al/BiCl3/γ-Al2O3 composite is synthesized, which exhibits high hydrogen yield, fast hydrogen production rate and outstanding storage stability. The hydrogen production performance of Al/BiCl3/γ-Al2O3 can be adjusted by changing BiCl3:γ-Al2O3 weight ratio, additive content and milling time. XRD and SEM results indicate that surface cracks, active surface and metal Bi produced in fabrication process lead to the high hydrolysis activity of Al/BiCl3/γ-Al2O3. Mechanism analyses reveal that hydrogen production process is the results of pitting, microgalvanic effect and catalytic effect. Taking into account hydrogen production performance, capacity and cost, Al/5 wt%BiCl3/5 wt%γ-Al2O3 milled for 2 h is a potential hydrogen production material, which can in situ supply hydrogen for small-sized fuel cell.

Experimental study on 18650 lithium-ion battery-pack cooling system composed of heat pipe and reciprocating air flow with water mist

Lithium-ion batteries (LIBs) are critical power sources for portable devices, electric vehicles, power grids, and energy-storage systems. Effective thermal management is mandatory for achieving optimal battery performance. Although the air-cooling method has been investigated extensively owing to its simple structure, convenient maintenance, and low cost, it is insufficient for cooling large-scale battery packs because of its limited air-cooling capacity and unsatisfactory temperature uniformity. Thus, a reciprocating spray cooling system comprising a reciprocating air flow channel, heat pipe array, and spray nozzle is proposed herein for the efficient cooling of 18,650 LIB packs. The effects of the inlet air speed, spray frequency, and spray duty cycle on the cooling performance of the reciprocating mist cooling system and the corresponding optimal operating parameter range are analyzed. Additionally, the competitive mechanism between forced air convection and evaporative cooling is discussed. The results indicate that, compared with the case of natural convection cooling, the temperature increment of the battery pack decreases by 32.1 % under reciprocating mist cooling. Meanwhile, the maximum temperature difference reduces to approximately 3.41 °C with 3C of discharge. The spray frequency minimally affects the overall heat dissipation but induces surface temperature fluctuations in individual batteries. Increasing the spray duration per 10 s in a single spray duty cycle can reduce the average temperature of the battery pack by approximately 2 °C. Additionally, the power-allocation scheme affects the heat dissipation of the system. Decreasing the flow rate of spray cooling water and increasing the inlet air speed promote the evaporation of water mist inside the system, thus further improving heat dissipation. This study provides new insights into the design of air-cooled thermal management systems for battery packs.

Multifunctional PVDF film embedded with surfactant assisted-graphene with excellent piezo-capacitance, piezoelectric and triboelectric properties for various applications

Herein, we have developed multifunctional, flexible and self-poled PVDF nanocomposite films incorporated with anionic surfactant-assisted graphene nanoplatelets (S-GNP). The synergistic effect of rapid cooling process and S-GNP promoted electroactive phase content up to >97% (β + γ) of PVDF and assisted in tuning the crystallinity, tensile and dielectric properties of the PVDF/S-GNP nanocomposite (S-PGN-X) films. A flexible piezo-capacitance based pressure sensor offered an excellent response, quick recovery and high sensitivity (1.25 kPa−1) with a wide pressure sensing range (0.25–50 kPa). The sensor was integrated into a shoe sole to monitor the heel and toe pressure. Further, the S-PGN-X based triboelectric device showed excellent performance with a voltage output of >120 V and 175 μW/cm2 power density. The output of the device was sufficient to glow the LED lights, suggesting that it can be used as a sustainable power source for portable devices. Moreover, S-PGN-X based piezoelectric nanogenerator generated a voltage output of ∼19 V upon repeated application of pressure with a good power output of 1.35 μW/cm2. The piezoelectric nanogenerator could charge up a 3.3 μF capacitor up to 1.1 V under repeated finger impartation. Overall, the multifunctional S-PGN-X film with self-poling characteristics showed excellent piezo-capacitance, piezoelectric and triboelectric performance, which makes it a potential material for sensors, energy harvesting and portable electronic devices.

Development of a More Sustainable Hybrid Process for Lithium and Cobalt Recovery from Lithium-Ion Batteries

Lithium-ion batteries are widely used as a power source for portable devices and electrical vehicles (EVs). After their useful life, they can provide a secondary source from which to obtain some materials which make them up, such as lithium and cobalt. However, the metallurgical route which will be used to recover them must be considered. Therefore, is crucial that many efforts to develop more environmentally favorable recovery processes be pursued. Due to this, the present work aimed to use 1.5 M DL-malic acid and compare it to 2 M sulfuric acid, employing heat pretreatment of 1 h and 3 h to remove the powder cathode binder polyvinylidene fluoride (PVDF); for all conditions, experiments were carried out with and without adding the oxidizing agent hydrogen peroxide. The PVDF temperature degradation occurred at 630 °C. The best yields occurred in the presence of H2O2 10% v/v and heat pretreatment. With sulfuric acid (1 h) it was possible to recover 33.49% Co and 4.63% Li, and (3 h) 36.36% Co and 4.64% Li. With DL-malic acid it was possible to recover (1 h) 29.78% Co and 3.44% Li, and (3 h) 32.73% Co and 3.99% Li.

High mass-loading and binder-free flexible vanadium-based oxide cathode for zinc-ion battery via a bridge of MXene

Flexible zinc-ion batteries (ZIBs) are promising power sources for portable devices due to their high safety and low production cost. However, the low mass-loading and limited areal capacity of cathode materials are the major problems blocking the practicability of ZIBs. Herein, a high mass-loading and binder-free flexible vanadium oxide ([email protected]) cathode with a large areal capacity was fabricated via the bridge effect of MXene. The functional MXene bridge induces the growth of the vanadium oxide active layer on the carbon cloth (CC) flexible substrate. The binder-free cathode can reduce the electrochemically inactive weight of the whole electrode, which enhances the energy density of ZIBs. Consequently, the [email protected] cathode (mass-loading of ∼7 mg cm−2) delivers a desirable areal capacity (2.36 mAh cm−2) and good cycling stability (capacity retention of 86.1% after 1200 cycles at 10 mA cm−2). Moreover, several ex-situ characterization results indicate that the reaction mechanism upon battery cycling is based on the reversible Zn2+/H+ (de)intercalation in the vanadium oxide interlayer. Furthermore, the assembled quasi-solid-state [email protected]//Zn flexible battery exhibits decent performance at different bending states. Such a bridge effect strategy sheds light on the construction of high mass-loading flexible electrodes for ZIBs applications.

Recent Advances in the Development of Nanocatalysts for Direct Methanol Fuel Cells

Direct methanol fuel cells (DMFCs) have attracted much attention due to their potential application as a power source for portable devices. Their simple construction and operation, associated with compact design, high energy density, and relatively high energy-conversion efficiency, give the DMFCs an advantage over other promising energy production technologies in terms of portability. Nowadays, research on DMFCs has received increased attention in both academics and industries. However, many challenges remain before these systems become commercial, including their costs and durability. As a key material with a high-value cost, noble metal catalysts for both the anode and cathode sides face several problems, which hinder the commercialisation of DMFCs. This paper provides a detailed comprehensive review of recent progress in the development of nanocatalysts (NCs) for the anode and cathode reactions of DMFCs, based on Platinum, Platinum-hybrid, and Platinum-free materials. Particular attention is devoted to the systematisation of published experimental results tested in DMFC devices since 2015, with an emphasis on passive DMFC systems. In addition, a dedicated section was created to include modelling/theoretical studies. Some open problems and remaining challenges are also highlighted in the final section.

Textile-based moisture power generator with dual asymmetric structure and high flexibility for wearable applications

Moisture power generator (MEG) that can directly convert energy from environment into available clean electricity is ideally suitable to serve as a power source for portable devices and wearable electronics. However, the current MEG technology is lack of wearable capability and intrinsically associated with complicated fabrication processes, which have severely hindered its practical applications. Herein, we developed a facile process for the fabrication of textile-based moisture power generators (TMEGs) with a high flexibility. The newly-developed TMEGs exhibited a high open-circuit voltage of up to 1.0 V due to the rationally designed dual asymmetric structure to enhance the concentration difference of charge carriers for efficiently driving the diffusion of ions. Owing to its flexibility and superior performance, the TMEG could be used to construct a self-powered smart mask for monitoring of human’s respiration and as an efficient energy device for driving minitype electronics. More importantly, large-scale integration of TMEG units could be easily realized by directly printing electrodes array on 400 cm2 of asymmetric textile with screen-printing method, offering an enhanced electric output. Such integrated devices could be immobilized on a T-shirt as portable power source for supplying sufficient power to drive commercial wearable electronics. Compared to the existing power generation systems, therefore, TMEGs fabricated from such a simple fabrication process with all the aforementioned outstanding achievements hold promise for significant cost reduction, opening up new extensive applications as textile-based self-powered devices and wearable electronics.

Glycerol Tris(2‐cyanoethyl) Ether as an Electrolyte Additive to Enhance the Cycling Stability of Lithium Cobalt Oxide Cathode at 4.5 V

AbstractHigh‐voltage lithium cobalt oxide batteries are considered the ideal power source for portable devices, owing to their high‐energy density and accessible specific capacity. However, it is still challenging to achieve long‐term cycling stability when charging to the high cut‐off voltages (≥4.5 V vs. Li/Li+), owing to the unavoidable parasitic reactions at the cathode/electrolyte interface. Herein, we report an organic nitrile‐based molecule, glycerol tris(2‐cyanoethyl) ether (GTCE), as a novel electrolyte additive to improve the cycling stability of LiCoO2 (LCO) batteries at 2.75–4.5 V. Impressively, the LCO||Li metal half‐cell using the GTCE‐containing electrolyte (2 wt % GTCE in the base electrolyte, 1.0 M LiPF6 in EC/DEC/EMC=1/1/1, v/v) exhibits an outstanding capacity retention of 79.3 % over 150 cycles, superior to the battery with base electrolyte (only 27.4 %) under the same test conditions. It represents a feasible and valuable method to stabilize the cathode/electrolyte interface of high‐voltage lithium‐ion batteries.

Synthesis and Electrochemical Performances of Ni-Rich LiNixAl1 –XO2 (x=0.95, 0.92) Positive Electrode Materials for Li-Ion Batteries

Lithium-ion batteries (LIBs) have been put to practical use as power sources for portable devices and environmentally benign electric vehicles (EVs) because of their excellent electrochemical properties such as high specific energy, high power, and long cycle life. For the widespread use of these devices, it is necessary to improve energy density and reduce the cost. To realize high-energy density and low-cost positive electrode materials, we focused on Ni-rich (Ni content more than 80 at.%) layered positive electrode materials that do not contain Cobalt (Co), an expensive element. We have synthesized NA-based positive electrode material LiNixAl1–xO2 (x=0.92, 0.95, NA92, 95) under conditions where Ni and Al are atomically mixed. LiNiO2 (LNO), LiNi0.95Co0.05O2 (NC95) and LiNi0.95Co0.03Al0.02O2 (NCA95) with uniform particle sizes were also synthesized to clarify the effects of Al and Co substitution in Ni-rich layered positive electrode materials. Figure. 1 shows the cycle performances of the samples measured in the full cells. After 500 charge-discharge cycles in full cells under conditions of 45°C, 2 C rate, and 2.5-4.2 V, NA95 and NC95 with the same Ni ratio showed the similar capacity retention (54.1%, 56.5%), whereas NA92 showed excellent capacity retention of 75%. Compared to LNO and NC95 that do not contain Al, the increase of charge transfer resistance (R ct) with cycling was remarkably suppressed in LiNixAl1–xO2. The chemical state of Al before and after cycling was analyzed by Hard X-ray Photoelectron Spectroscopy (HAXPES). The results suggested that Al existed either as a part of the LiNixAl1–xO2 solid solution or Al oxides before cycling while it existed as the lithium aluminate and Al-F compounds. This indicates that the trace HF in the electrolyte reacted with the pristine Al compound on the topmost of electrode materials during cycling to form a Li-conductive coating layer, which suppressed the degradation during cycling. Furthermore, though the Co substitution has some effects of preventing particle cracking, the least particle cracking was observed in NA92 of all samples, indicating that both the surface degradation and the bulk degradation were suppressed with the Al substitution to produce the excellent cycle performance. The results of this study indicated that LiNixAl1–xO2 (x=0.92, 0.95) synthesized by the optimum conditions could be a promising Co-free Ni-rich layered positive electrode material. Figure 1

Synthesis of reduced graphene oxide supported nickel-cobalt-layered double hydroxide nanosheets for supercapacitors

Supercapacitors are deemed as reliable power sources for portable devices and electric vehicles. Electrode materials with high energy and power densities are greatly needed. Herein, we designed reduced-graphene-oxide supported nickel-cobalt layered double hydroxide nanosheets (NiCo-LDH/rGO) as electrode materials. The introduction of graphene could largely enhance the conductivity, and the supported NiCo-LDH could effectively prevent graphene from self-aggregation. Thanks to the synergistic effect of conductive graphene and electro-active LDH, the nanocomposites delivered a capacitance of 1675 F g−1 at 1 A g−1 and decent rate performance (capacitance retention of 83.8% at 10 A g−1); while NiCo-LDH could only exhibited a capacitance of 920 F g−1 at 1 A g−1 and 81.5% of the capacitance remained at 10 A g−1. The asymmetric supercapacitors assembled with NiCo-LDH/rGO and activated carbon (AC) delivered high energy density and power density, up to 49.9 Wh kg−1 and 3747.9 W kg−1, respectively. The appealing electrochemical performance indicates its huge application potential in supercapacitors.

Ultra-Flexible Organic Photovoltaics with Nanograting Patterns Based on CYTOP/Ag Nanowires Substrate.

In this study, we developed a method for fabricating ultrathin polymer substrates that can be used in ultra-flexible organic photovoltaics (OPVs) via a non-vacuum process using cyclic transparent optical polymer. In addition, a Ag nanowire network layer was used as a transparent electrode in a solution process. All processes were conducted on large area via spin coating. The power conversion efficiency (PCE) of the ultra-flexible OPV improved by 6.4% compared to the PCE of the ITO/Glass-based OPV. In addition, the PCE of the OPV increased to 10.12% after introducing nanostructures in the ZnO and photoactive layers. We performed 1000 cycles of compression/relaxation tests to evaluate the mechanical properties of the ultra-flexible OPV, after which, the PCE remained at 67% of the initial value. Therefore, the developed OPV system is suitable as a power source for portable devices.

A direct formate microfluidic fuel cell with cotton thread-based electrodes

A direct formate microfluidic fuel cell with cotton thread-based electrodes is proposed. The palladium catalyst is directly coated on cotton threads by repeated dipping method to prepare electrodes, which integrates the flow channel and electrode together and provides exposed active sites for enhancing the mass transfer on the anode and cathode. The aqueous anolyte and catholyte transport through cotton threads by capillary force with aid of gravity, eliminating the use of any external pump and facilitating the integration and miniaturization of the whole system. In the experiment, a three-flow channel structure is employed. The fuel is sodium formate and the oxidant is hydrogen peroxide. 1 M Na2SO4 solution is introduced into the middle channel formed by cotton threads with no catalyst to alleviate the reactant crossover. Performance is evaluated under various catalyst loadings, fuel concentrations and differences in height between the inlet and outlet. Results show that the fuel cell produces an open circuit voltage (OCV) of 1.41 V. The maximum current density of 74.56 mA cm−2 and the peak power density of 24.75 mW cm−2 are yielded when the palladium loading is 1 mg cm−1 and the difference in height between the inlet and outlet is 7 cm, using 4 M HCOONa as fuel. Furthermore, the performance of the fuel cell increases first and then decreases with increasing the palladium loading. The same variation is observed with increasing the fuel concentration. However, the performance gradually increases with increasing the difference in height from 3 cm to 7 cm. The proposed microfluidic fuel cell with cotton thread-based electrodes shows enormous potential as a micro power source for portable devices.

A New Insight in the Redox Mechanism Involved during the Delithiation/Lithiation of Spinel Materials Provided By Raman Spectroscopy

Lithium-ion batteries have been widely used as power source for portable devices and are available for applications to electric vehicles, which demand high power, high energy, inexpensive and safe batteries [1]. Their continuous improvement is tightly bound to the understanding of lithium (de)intercalation phenomena in electrode materials. Here we address for the first time the use of Raman spectroscopy to understand the mechanisms involved in high voltage spinels LiNixMn2-xO4 (x = 0; x = 0.5). Although the “classical” lithium-containing spinel LiMn2O4 (LMO) has been extensively studied, certain points remain unclear. For instance, very little is known on the nature of the intermediate composition Li0.5Mn2O4 postulated halfway during charge/discharge [2] for which attempts to model a lithium/vacancy ordering have been made [3, 4]. On the other hand, compositions within the solid solution LiNixMn2-xO4 (0 < x ≤ 0.5) are of interest as they exhibit increasing voltage upon lithium extraction. The best compromise is found for LiNi0.5Mn1.5O4 (LNMO): with a high specific capacity of 140 mAh g-1 available along a wide potential plateau at ≈ 4.7 V vs Li+/Li, LNMO is thoroughly studied as a next-generation positive electrode material for Li-ion batteries [5]. LNMO exists as two polymorphs, “disordered” (Fd-3m) where Mn/Ni occupy 16d sites randomly and “ordered” (P4332) where Ni and Mn sit on ordered 4a and 12d sites. So far, the disordered form has outperformed the ordered form from an electrochemical point of view [6]. The delithiation/lithiation mechanism of disordered LNMO has been previously investigated using mainly X-ray and neutron diffraction [7-10] and in situ synchrotron [11]. Although these methods provide a picture of the phase evolution during cycling, we still lack information about the atomic level variations as lithium ions deintercalate/intercalate in the crystal structure of LNMO. Raman spectroscopy (RS) on the other hand is a very appropriate tool to enrich the knowledge of the structure of Li intercalation compounds at the scale of the chemical bond. A wealth of structural information including symmetry changes, local disorder, changes in bond lengths, emergence of secondary phases, etc… can be extracted from the Raman study of various Li intercalated host lattices, providing therefore a better insight into the mechanisms governing the electrode performances [12]. In this work, RS is used to explore the short-range environment in LMO and "disordered" LNMO. We provide here a complete assignment of the LMO and LMNO Raman fingerprints as well as a detailed picture of structural and vibrational changes during the charge-discharge of these cathode materials. A careful RS investigation led on the LMO cathode during the charge process provides the first detailed experimental evidence of an ordering scheme at the scale of the chemical bond of the intermediate composition Li0.5Mn2O4. A combined approach using XRD and RS allows picturing changes in LNMO crystal structure and in the oxidation states of the nickel during stages of the charge-discharge process. Raman spectra collected between 3.5 and 4.9 V display rich and varying features (Figure 1). Appropriate analysis based upon Raman spectra fittings allow access to a quantitative estimation of the different Ni2+, Ni3+ and Ni4+ redox species in the LNMO spinel oxide at different oxidation-reduction states. This makes RS a powerful probe to evaluate the state of charge of the cathode material. Finally, we demonstrate the great efficiency of RS as an efficient and simple diagnostic tool of the self-discharge phenomenon occurring in the LNMO electrode.

Three-Dimensional Lattice Boltzmann Modelling the Electrode Performance of Lithium-Ion Battery

Lithium-ion batteries (LIBs) have improved significantly over the last 20 years, and have become an important power source for portable devices, such as cellular phones, laptops, cordless power tools, and electric vehicles. The porous structure of electrodes in LIBs plays a critical role in battery performance. To further improve the performance of LIBs, there have been a lot of efforts to understand the structure-performance relation and to optimize the electrode structures. Such efforts, often dominated by the experimental trial-and-error approaches, are time consuming and expensive. Computational models, on the other hand, provide an efficient way to understand the influence of electrode microstructures on battery performance, and allow us to manipulate structure parameters easily, supporting the optimization and design of electrode structures. In current study, we report our efforts in understanding the coupled transport and reaction processes in LIBs electrodes using computational modelling, which is important for improving the performance. A three-dimensional (3D) pore-scale lattice Boltzmann model, initially developed for polymer membrane fuel cells[1] and redox flow battereis[2], has been modified and adapted to simulate LIBs electrodes. The model has the capability to simulate the ion and electron transport, coupled with the electrochemical reaction at the interface between the active material and the liquid electrolyte under complex boundary conditions. The detailed 3D microstructure of the a LIB graphite anode is obtained using X-ray computed tomography(CT). The model is applied to simulate a series of electrode structures of increasing size. The work provides evidence that the 3D pore scale lattice Boltzmann model is able to simulate the complex transport processes with real electrode geometries and predict electrochemical performance. The results show that it is important to use sufficiently large electrode structure, in order to obtain reliable structural and performance information. The simulation work help to understand the impact of electrode microstructure on electrode performance, and may lead to design principles for creating electrodes with optimal microstructure for LIBs applications. Zhang, Q. Cai, S. Gu, Three-dimensional lattice-Boltzmann model for liquid water transport and oxygen diffusion in cathode of polymer electrolyte membrane fuel cell with electrochemical reaction, Electrochimica Acta, 262(2018) 282-296. Zhang, Q. Cai, O.O. Taiwo, V. Yufit, N. P. Brandon, S. Gu, The effect of wetting area in carbon paper electrode on the performance of vanadium redox flow batteries: A three-dimensional lattice Boltzmann study, Electrochimica Acta, 283(2018) 1806-1819. Acknowledgements The authors gratefully acknowledge the financial support for this work by the UK Engineering and Physical Sciences Research Council (EPSRC) projects [grant number EP/K036548/2] and [grant number EP/R021554/1]; and the EU FP7 IPACTS [grant number 268696];

High-Energy and Stable Li[Ni0.90Co0.05Mn0.05]O2 Cathode for Lithium-Ion Batteries through Microstructure Modification By Boron Doping

Lithium-ion batteries (LIBs) are emerging as one of the most promising power sources for portable devices, as well as electric vehicles (EVs) and large energy storage systems (ESS), owing to their high energy density and excellent cycle life. However, the application of LIBs in EVs to reduce CO2 emissions in internal combustion engine vehicles (ICEVs) involves some critical technical challenges, such as the driving range, safety, and cost concerns due to the properties of LIBs.1-3 For this reason, research interests and industrial efforts have focused on developing low-cost, high-energy, and safe cathode materials, which are the main component determining LIB performance and cost. Transition metal layered oxides belonging to the LiNixCoyAlzO2 (NCA) or LiNixCoyMnzO2 (NCM) family, which can increase their intrinsic capacity (above 200 mAh g-1) by increasing Ni content, are emerging as promising new cathode materials.4 However, the intrinsic drawbacks of Ni-rich cathodes, such as low Li intercalation stability over extended cycles, should be improved. In this study, we present the first successful boron doping strategy for a Ni-rich cathode material with very high Ni content. For the boron doping, we used a simple method where only a small amount of B2O3 was added during the calcination process. In addition, the structural and morphological stability of the boron-doped Ni-rich NCM cathode material was investigated before and after testing to evaluate the improved electrochemical performance; specifically, the significantly enhanced cycle performance. Thus, we conclude that the boron doping strategy is an effective and simple way to mitigate the poor stability problem of Ni-rich cathode materials for high-energy and stable LIBs. References D.-W. Jun, C. S. Yoon, U.-H. Kim, Y.-K. Sun, Chem. Mater. 2017, 29, 5048.J. H. Lee, C. S. Yoon, J.-Y. Hwang, S.-J. Kim, F. Maglia, P. Lamp, S.-T. Myung, Y.-K. Sun, Energy Environ. Sci. 2016, 9, 2152.S.-T. Myung, F. Maglia, K.-J. Park, C. S. Yoon, P. Lamp, S.-J. Kim, Y.-K. Sun, ACS Energy Lett. 2017, 2, 196.K.-S. Lee, S.-T. Myung, K. Amine, H. Yashiro, Y.-K. Sun, J. Electrochem. Soc. 2007, 154, A971.

Unraveling the Electrochemical Energy Storage Mechanism of Vanadium Hexacyanoferrate-Based Metal-Organic Frameworks As a Cathode for Aqueous Rechargeable Batteries

Considering the environmental pollution crisis caused by fossil fuel and the limited supply of those, developing alternative power stations is strongly urged. Accompanying the development of alternative power stations, the introduction of large-scale stationary energy storage systems (ESSs) connected with the electrical power grid is vital for enhanced accessibility of electricity and leveling-off the intermittent spikes in the generated power. To date, Li ion batteries (LIBs) have been successfully demonstrated as feasible power sources for portable devices. Nonetheless, the application of LIBs into ESSs faces obstacles due to the limited source and continuously increasing cost of raw lithium and high flammability and the high cost of the organic electrolytes. Consequently, aqueous rechargeable batteries (ARBs) with readily accessible electroactive guest ions of H3O+, Na+, or Mg2+, are the most suitable energy devices for ESSs. Very recently, Prussian blue analogues (PBAs) holding an important category of metal-organic frameworks have been highlighted as a promising candidate of electrode materials to be used in rechargeable batteries due to their ideal crystal structure and desirable electrochemical characteristics. Typically, PBAs have a typical cubic structure constructed with two transition metal ions (or clusters) linked via cyanide (−CN−) groups. However, the specific capacity of most PBAs obtained with aqueous electrolytes is limited to less than ≈60 mA h g−1. It indicates that the optimal combination of transition metal ions is the most crucial factor in improving their electrochemical performances, because the performance of PBA is mostly governed by the electrochemical process of the metal ions upon insertion/extraction of guest ions. Herein, new kind of PBAs constituted with vanadium and iron ions (V/Fe PBAs) were fabricated using a simple co-precipitation method, and their electrochemical performance as well as related mechanisms of energy storage was investigated under aqueous electrolytes. The V/Fe PBAs provided an improved capacity of ~ 100 mAh-1 under a C-rate of ~ 0.55 C, taking advantage of the multiple-electron redox reactions of V and Fe ions. In addition, the mechanism of energy storage and the cycling behavior were elucidated by monitoring the ex-situ X-ray absorption near-edge spectra, microstructural changes, dissolution of the transition metal ions, and changes in the resistance of charge transfer and surface layer during cycling. V/Fe PBA is the most attractive candidate cathode material for ARBs because of their high cost efficiency, simple synthesis, and the promising electrochemical performance, which is sufficient to meet the requirements of ARBs for large-scale ESSs. Figure 1

Boron-Doped Ni-Rich Layered Cathodes with Enhanced Cycling Stability

Lithium-ion batteries (LIBs) are emerging as one of the most promising power sources for portable devices, as well as electric vehicles (EVs) and large energy storage systems (ESS), owing to their high energy density and excellent cycle life. However, the application of LIBs in EVs to reduce CO2 emissions in internal combustion engine vehicles (ICEVs) involves some critical technical challenges, such as the driving range, safety, and cost concerns due to the properties of LIBs.1-3 For this reason, research interests and industrial efforts have focused on developing low-cost, high-energy, and safe cathode materials, which are the main component determining LIB performance and cost. Transition metal layered oxides belonging to the LiNixCoyAlzO2 (NCA) or LiNixCoyMnzO2 (NCM) family, which can increase their intrinsic capacity (above 200 mAh g-1) by increasing Ni content, are emerging as promising new cathode materials.4 However, the intrinsic drawbacks of Ni-rich cathodes, such as low Li intercalation stability over extended cycles, should be improved. In this study, we present the first successful boron doping strategy for a Ni-rich cathode material with very high Ni content. For the boron doping, we used a simple method where only a small amount of B2O3 was added during the calcination process. In addition, the structural and morphological stability of the boron-doped Ni-rich NCM cathode material was investigated before and after testing to evaluate the improved electrochemical performance; specifically, the significantly enhanced cycle performance. Thus, we conclude that the boron doping strategy is an effective and simple way to mitigate the poor stability problem of Ni-rich cathode materials for high-energy and stable LIBs. References D.-W. Jun, C. S. Yoon, U.-H. Kim, Y.-K. Sun, Chem. Mater. 2017, 29, 5048.J. H. Lee, C. S. Yoon, J.-Y. Hwang, S.-J. Kim, F. Maglia, P. Lamp, S.-T. Myung, Y.-K. Sun, Energy Environ. Sci. 2016, 9, 2152.S.-T. Myung, F. Maglia, K.-J. Park, C. S. Yoon, P. Lamp, S.-J. Kim, Y.-K. Sun, ACS Energy Lett. 2017, 2, 196.4. K.-S. Lee, S.-T. Myung, K. Amine, H. Yashiro, Y.-K. Sun, J. Electrochem. Soc. 2007, 154, A971.

Performance Improvements of Cobalt Oxide Cathodes for Rechargeable Lithium Batteries

AbstractLithium‐ion batteries are essential mobile power sources for portable devices and energy supplies. Among the various cathode materials, cobalt oxides are the most important materials used in lithium‐ion batteries. But the intrinsic drawbacks of cobalt oxides restrict their wide application. In this paper, we present an overview of current approaches to improve the electrochemical performance of the cathode materials, as well as the capacity and cycling capability of the lithium‐ion batteries.

Progress of phosphoric acid doped high temperature proton exchange membrane for fuel cells

High temperature proton exchange membrane fuel cells (HT-PEMFCs) have been considered as one of the most attractive power sources for portable devices, due to their high tolerance to CO, enhanced activity of the electrocatalysts and simplified water and heat managements. As the key component, high temperature proton exchange membranes (HT-PEMs) influence a lot on fuel cell performance and long term stability. In recent years, phosphoric acid (PA) doped HT-PEMs have been proved to be one of the most promising alternatives for HT-PEMFCs because of their high proton conductivity and great thermal stability. The major technical challenges of these PA doped HT-PEMs are that the increase of PA loading enhances proton conductivity while the mechanical properties significantly decrease and the PA leaching exacerbates, which limit their wide applicability in HT-PEMFCs. This monograph summarizes recent advances for PA doped HT-PEMs on the design of new polymer, physical modification, microstructure control and so on. These developments on fundamental theories and main technologies establish a good foundation for future research.

Transient investigation of passive alkaline membrane direct methanol fuel cell

Passive direct methanol fuel cell (DMFC) is considered as an attractive power source for portable devices. In this study, a transient multiphase model for passive alkaline anion exchange membrane DMFC (AAEM-DMFC) is developed. The results show that the power density decreases during the operation and is more difficult to maintain stable with higher current density or lower voltage. The fuel efficiency increases with the increment of current density or the decrement of voltage. With a certain concentration, the optimal energy density is achieved at a moderate current density or voltage. Increasing the initial methanol concentration in reservoir can improve the energy density but decrease the fuel efficiency. Anode micro-porous layer (MPL) can improve the fuel efficiency and increase the energy density with high initial concentration (or low current density) but cause negative effect on the energy density with low initial concentration (or high current density). Cathode MPL shows the similar but less significant effect. Generally, whether to use MPL should be determined by different operating conditions and the use demand.