Effective Solution toward the Issues of Zn-Based Anodes for Advanced Alkaline Ni-Zn Batteries

Alkaline nickel-zinc (Ni-Zn) batteries, as traditional rechargeable aqueous batteries, possess an obvious advantage in terms of energy density, but their development has been hindered by the anode-concerned problems, Zn dendrites, self-corrosion, passivation, deformation, and hydrogen evolution reaction (HER). Herein, to solve these problems, a dual protective strategy is proposed toward the anode using ZnO as an initial active material, including a C coating on ZnO (ZnO@C) and a thin poly(vinyl alcohol) (PVA) layer coating on the electrode (ZnO@C-PVA). In a three-electrode configuration, the reversible capacity can reach 600 mAh g^-1 for the ZnO@C-PVA. Using excessive commercial Ni(OH)₂ as the cathode, the alkaline Ni-Zn cells exhibit good electrochemical performance: Discharge capacity can be as high as 640-650 mAh g^-1 at 4 A g^-1 with a Coulomb efficiency (CE) as high as 97-99% after activity, suggesting low self-corrosion and HER. Capacity retention is 97% after 1200 cycles, indicating rather good durability. The discharge capacity is even slightly increased with the increase of charge/discharge current density (≤8 A g^-1), implying good rate performance. Additionally, the discharge voltage can reach 1.8 V (midpoint value) at various current densities, reflecting the fast reaction kinetics of the anode. Most importantly, no Zn dendrites and passivation are observed after long-term cycling. The strategy proposed here can solve the anode-concerned problems effectively, exhibiting a high application prospect.

Removal of car battery heavy metals from wastewater by activated carbons: a brief review

Spent automobile batteries are one of the most significant secondary sources of harmful heavy metals for the environment. After being incorporated into the aquatic ecosystems, these metals disseminate to various plants, microorganisms, and the human body and cause multiple adverse effects. Activated carbons (ACs) have long been used as an effective adsorbent for different heavy metals in wastewater treatment processes. Although numerous research works have been published to date on this topic, they are scattered in the literature. In this review, we have assembled these works and provided an extensive overview of the application of ACs for treating spent car battery heavy metals (CBHMs) from aquatic systems. The preparation of ACs from different precursor materials, their application in the adsorption of CBHMs, the adsorption mechanism, kinetics, adsorption isotherms and various parameters that may affect the adsorption processes have been discussed in detail. A brief comparative analysis of the adsorption performances of ACs prepared from different precursor materials is also provided. Finally, recommendations for future research works are also offered.

Connecting battery technologies for electric vehicles from battery materials to management

Vehicle electrification has always been a hot topic and gradually become a major role in the automobile manufacturing industry over the last two decades. This paper presented comprehensive discussions and insightful evaluations of both conventional electric vehicle (EV) batteries (such as lead-acid, nickel-based, lithium-ion batteries, etc.) and the state-of-the-art battery technologies (such as all-solid-state, silicon-based, lithium-sulphur, metal-air batteries, etc.). Battery major component materials, operating characteristics, theoretical models, manufacturing processes, and end-of-life management were thoroughly reviewed. Different from other reviews focusing on theoretical studies, this review emphasized the key aspects of battery technologies, commercial applications, and lifecycle management. Useful battery managing technologies such as health prediction, charging and discharging, as well as thermal runaway prevention were thoroughly discussed. Two novel hexagon radar charts of all-round evaluations of most reigning and potential EV battery technologies were created to predict the development trend of the EV battery technologies. It showed that lithium-ion batteries (3.9 points) would be still the dominant product for the current commercial EV power battery market in a short term. However, some cutting-edge technologies such as an all-solid-state battery (3.55 points) and silicon-based battery (3.3 points) are highly likely to be the next-generation EV onboard batteries with both higher specific power and better safety performance.

Crystal and electronic structure manipulation of Laves intermetallics for boosting hydrogen evolution reaction

Since the 1970s, Laves intermetallics (AB₂) have been widely used in hydrogen storage technology (e.g., nickel-metal hydride batteries) due to the abundant interstitial sites and moderate metal-hydrogen bond strength (E_M-H). They, however, have been rarely used in the hydrogen evolution reaction (HER) because of the same reason (i.e. moderate E_M-H), which results in poor HER efficiency. In this study, by applying lanthanide contraction and ligand effect, we have successfully lowered the E_M-H and substantially boosted the HER activity of Laves intermetallics (RECo₂ and RERu_0.5Co_1.5 (RE = Pr, Tb, Y and Er)) to outperform those of commercial Pt/C catalyst. Hydrogen overpotential decreases from ErCo₂ (η₁₀ = 169 mV) to PrCo₂ (η₁₀ = 113 mV) and then to PrRu_0.5Co_1.5 (η₁₀ = 29 mV). The expansion of lattice constants for PrCo₂ may alleviate the obstacle of H atom diffusing through interstitial sites, while the inclusion of Ru element can raise the antibonding population of Co-Co/Ru bonds, which consequently lowers E_M-H and thus elevates HER activity according to the Sabatier principle. This outcome indicates that the manipulation of the crystal structure and electronic structure factor is an efficient strategy to boost the HER activity of Laves intermetallics.

Porous Carbon Architecture Assembled by Cross-Linked Carbon Leaves with Implanted Atomic Cobalt for High-Performance Li-S Batteries

The practical application of lithium-sulfur batteries is severely hampered by the poor conductivity, polysulfide shuttle effect and sluggish reaction kinetics of sulfur cathodes. Herein, a hierarchically porous three-dimension (3D) carbon architecture assembled by cross-linked carbon leaves with implanted atomic Co-N₄ has been delicately developed as an advanced sulfur host through a SiO₂-mediated zeolitic imidazolate framework-L (ZIF-L) strategy. The unique 3D architectures not only provide a highly conductive network for fast electron transfer and buffer the volume change upon lithiation-delithiation process but also endow rich interface with full exposure of Co-N₄ active sites to boost the lithium polysulfides adsorption and conversion. Owing to the accelerated kinetics and suppressed shuttle effect, the as-prepared sulfur cathode exhibits a superior electrochemical performance with a high reversible specific capacity of 695 mAh g^-1 at 5 C and a low capacity fading rate of 0.053% per cycle over 500 cycles at 1 C. This work may provide a promising solution for the design of an advanced sulfur-based cathode toward high-performance Li-S batteries.

Effects of the Chromium Content in (TiVNb)100−xCrx Body-Centered Cubic High Entropy Alloys Designed for Hydrogen Storage Applications

In this paper, we report an investigation of adding a non-hydride forming element in the multicomponent Ti-V-Nb-M system. By the Calculation of Phase Diagrams approach (CALPHAD), the thermodynamic phase stability of the TiVNbT (T = Cr, Mn, Fe, Co, and Ni) was investigated, and Cr was selected as the fourth alloying element due its high tendency to stabilize body-centered cubic solid solutions (BCC). The (TiVNb)100−xCrx alloys (with x = 15, 25, and 35 at.% Cr) were synthesized by arc-melting. The structural characterization reveals that the three alloys were composed of a major BCC phase, which agrees with the thermodynamic calculations. The three alloys absorb hydrogen at room temperature without any activation treatment, achieving a hydrogen uptake of about H/M = 2. The Pressure-Composition-Isotherms curves (PCI) has shown that increasing the Cr amount increases the equilibrium pressures, indicating that tunable H storage properties can be achieved by controlling the alloys’ Cr content.

Dual-carbon coupled Co5.47N composites for capacitive lithium-ion storage

Transition metal nitrides are of great interest as potential anodes for lithium-ion batteries (LIBs) owing to their high theoretical capacity. However, poor cycling stability and rate performance greatly hinder their practical applications. To better alleviate these problems, a unique 3D hierarchical nanocomposite constructed by dual carbon-coated Co_5.47N nano-grains wrapped with carbon and reduced graphene oxide (Co_5.47N@C@rGO) was synthesized through one-step simultaneous nitridation and carbonization of zeolitic imidazolate frameworks@GO precursor. The 3D hierarchical Co_5.47N@C@rGO composite can combine the good conductivity and mechanical strength of rGO and a high theoretical capacity of Co_5.47N. When explored as anode material for LIBs, Co_5.47N@C@rGO exhibits a high reversible capacity of ~860 mAh g^-1 at a current density of 1.0 A g^-1 after 500 cycles and excellent high-rate capability (665 and 573 mAh g^-1 at current densities of 3.2 and 6.4 A g^-1, respectively). The excellent electrochemical performance of Co_5.47N@C@rGO can be ascribed to its hierarchically porous structure and the synergistic effect between Co_5.47N nano-grains and rGO.

Hydrogen storage behavior of nanocrystalline and amorphous Mg-Ni-Cu-La alloys

Alloying and structural modification are two effective ways to enhance the hydrogen storage kinetics and decrease the thermal stability of Mg and Mg-based alloys. In order to enhance the characteristics of Mg₂Ni-type alloys, Cu and La were added to an Mg₂Ni-type alloy, and the sample alloys (Mg₂₄Ni₁₀Cu₂)_100−xLa_x (x = 0, 5, 10, 15, 20) were prepared by melt spinning. The influences of La content and spinning rate on the gaseous and electrochemical hydrogen storage properties of the sample alloys were explored in detail. The structural identification carried out by XRD and TEM indicates that the main phase of the alloys is Mg₂Ni and the addition of La results in the formation of the secondary phases LaMg₃ and La₂Mg₁₇. The as-spun alloys have amorphous and nanocrystalline structures, and the addition of La promotes glass formation. The electrochemical properties examined by an automatic galvanostatic system show that the samples possess a good activation capability and achieve their maximal discharge capacities within three cycles. The discharge potential characteristics were vastly ameliorated by melt spinning and La addition. The discharge capacities of the samples achieve their maximal values as the La content changes, and the discharge capacities always increase with increasing spinning rate. The addition of La leads to a decline in hydrogen absorption capacity, but it can effectively enhance the rate of hydrogen absorption. The addition of La and melt spinning significantly increase the hydrogen desorption rate due to the reduced activation energy.

In order to enhance the characteristics of Mg₂Ni-type alloys, Cu and La were added to an Mg₂Ni-type alloy, and sample alloys were prepared by melt spinning. The effects of La content and spinning rate on the hydrogen storage properties were explored.

Vacancy Occupation-Driven Polymorphic Transformation in Cobalt Ditelluride for Boosted Oxygen Evolution Reaction

Transition-metal dichalcogenides (TMDs) hold great potential as an advanced electrocatalyst for oxygen evolution reaction (OER), but to date the activity of transition metal telluride catalysts are demonstrated to be poor for this reaction. In this study, we report the activation of CoTe₂ for OER by doping secondary anions into Te vacancies to trigger a structural transition from the hexagonal to the orthorhombic phase. The achieved orthorhombic CoTe₂ with partial vacancies occupied by P-doping exhibits an exceptional OER catalytic activity with an overpotential of only 241 mV at 10 mA cm^-2 and a robust stability more than 24 h. The combined experimental and theoretical studies suggest that the defective phase transformation is controllable and allows the synergism of vacancy, doping as well as the reconstructed crystallographic structure, ensuring more exposure of catalytic active sites, rapid charge transfer, and energetically favorable intermediates. This vacancy occupation-driven strategy of structural transformation can also be manipulated by S- and Se-doping, which may offer useful guidance for developing tellurides-based electrocatalyst for OER.

An alternative for the anode materials of nickel metal hydride batteries: an AB3-type La0.6Gd0.2Mg0.2Ni2.6Co0.3Al0.1 hydrogen storage alloy

In order to satisfy the demand for the cyclic stability of commercial Ni-MH anodes, a PuNi3-type La0.6Gd0.2Mg0.2Ni2.6Co0.3Al0.1 alloy with excellent overall electrochemical properties was prepared by annealing the as-cast alloy sample at different temperatures for a week. The alloy had the highest PuNi3-type content of 86.9 wt% (1073 K), which offered a capacity retention of 69.6% after 100 cycles. However, 23.7 wt% PuNi3 type phase of the alloy constantly converted into the Ce2Ni7 type phase within a temperature increase of 50 °C, which improved the capacity retention by 12.1% under the same discharge capacity. We found that the addition of Gd did not change the stacked [LaMgNi4]/[LaNi5] superlattice and it maintained the structural stability of the crystal as well as its anti-corrosion, which is also a key factor to improve cyclic stability. These findings imply that alloys with both PuNi3-type and Ce2Ni7-type multiphase structures can be considered as a new choice for hydrogen storage.

Battery Technologies for Grid-Level Large-Scale Electrical Energy Storage

Grid-level large-scale electrical energy storage (GLEES) is an essential approach for balancing the supply–demand of electricity generation, distribution, and usage. Compared with conventional energy storage methods, battery technologies are desirable energy storage devices for GLEES due to their easy modularization, rapid response, flexible installation, and short construction cycles. In general, battery energy storage technologies are expected to meet the requirements of GLEES such as peak shaving and load leveling, voltage and frequency regulation, and emergency response, which are highlighted in this perspective. Furthermore, several types of battery technologies, including lead–acid, nickel–cadmium, nickel–metal hydride, sodium–sulfur, lithium-ion, and flow batteries, are discussed in detail for the application of GLEES. Moreover, some possible developing directions to facilitate efforts in this area are presented to establish a perspective on battery technology, provide a road map for guiding future studies, and promote the commercial application of batteries for GLEES.

Multifunctional Electrocatalysis on a Porous N-Doped NiCo2O4@C Nanonetwork

Developing a multifunctional electrocatalyst with eminent activity, strong durability, and cheapness for the hydrogen/oxygen evolution reaction (HER/OER) and oxygen reduction reaction (ORR) is critical to overall water splitting and regenerative fuel cells. Herein, a nitrogen-doped nanonetwork assembled by porous and defective NiCo₂O₄@C nanowires grown on nickel foam (N-NiCo₂O₄@C@NF) is crafted via biomimetic mineralization and following carbonization of phase-transited lysozyme (PTL)-coupled NiCo₂O₄. The as-obtained N-NiCo₂O₄@C@NF electrocatalysts exhibit an exceptional catalytic activity with ultralow overpotentials for the HER (42 mV) and OER (242 mV) to afford 10 mA cm^-2 while maintaining good stability in alkaline media. Meanwhile, the N-NiCo2O4@C electrocatalysts presents a superior catalytic activity for ORR and a favorable four-electron pathway. The unprecedented catalytic performance arises from a highly porous structure and abundant defects and synergistic effects of components. This work may offer a new possibility in the exploration of multifunctional electrocatalysts for various energy-related electrocatalytic reactions.

Superior "green" electrode materials for secondary batteries: through the footprint family indicators to analyze their environmental friendliness

As secondary batteries are becoming the popular production of industry, especial for lithium ion batteries (LIBs), the degree of environmental friendliness will gather increasing attention to their products of the whole life cycle. The research combines the life cycle assessment (LCA) and footprint family definition to establish a framework to calculate the footprint family of secondary battery materials. Through the method, we calculated the values of carbon footprint, water footprint, and ecological footprint about this eight kinds of secondary cathode battery materials with Ni-MH, Li_1.2Ni_0.2Mn_0.6O₂/C, LiNi_1/3Co_1/3Mn_1/3O₂/C, LiNi₀.₈Co_0.2O₂/C, LiFePO₄/C, LiFe_0.98Mn_0.02PO₄/C, FeF₃(H₂O)₃/C, and NaFePO₄/C. When comparing and analyzing their values in each footprint, it can summarize the evaluation method for some secondary batteries by footprint indicators and construct the evaluation system. Through the comprehensive evaluation of footprint family system, the NaFePO₄/C battery gets the best performance of three main footprints when combining 1 kg of cathode materials, while Ni-MH is opposite. Hence, among these eight batteries environmental impacts evaluation, the NaFePO₄/C battery is regarded as the superior "green" battery, albeit the current application is restricted because of the synthesis limitation on large scale and energy density of storage. In LIBs comparison, the FeF₃(H₂O)₃ material shows its characteristics of environmental friendliness, which is expected to be a greener battery material of LIB. In conventional LIBs, the iron-containing cathode materials show lower environmental burden than ternary cathode materials. We can reduce environmental impacts through developing new advanced materials and reducing the content of high sensitivity element in raw materials.

3D β-Ni(OH)2 nanowires/RGO composite prepared by phase transformation method for superior electrochemical performance

In order to improve the capacity and rate performance of nickel-metal hydride (Ni-MH) batteries, we proposed a simple phase transformation method to synthesis 3D β-nickel hydroxide nanowires/reduced graphene oxide (β-Ni(OH)₂ NWs/RGO) composite. β-Ni(OH)₂ nanowires with diameters of 20-30 nm and lengths up to several micrometers were decorated on RGO layers, forming 3D network structure. The 3D β-Ni(OH)₂ NWs/RGO composite displayed a discharge capacity of 343.2 mAh/g at 0.2C, and the capacity values has almost no loss after 100th cycles. When the discharge rate was at 5C, the capacity reached a value of 272.7 mAh/g, and its capacity retention was 79.5%. It showed good capacity and rate performance as a positive material for Ni-MH batteries.

Suitability Evaluation of LaNi5 as Hydrogen-Storage-Alloy Actuator by In-Situ Displacement Measurement during Hydrogen Pressure Change

The swelling ability of LaNi₅ for application to hydrogen-storage-alloy (HSA) actuator is discussed through the measurement of the swelling ratio in hydrogen. The HSA actuator is driven by hydrogen pressure change causing the swelling of HSA. LaNi₅ is one of the candidate materials for HSA actuators as well as palladium. Some prototypes of HSA actuators using LaNi₅ have been fabricated; however, the kinetic swelling ability of LaNi₅ itself has been not investigated. In this paper, the authors investigated the static and kinetic swelling ability of LaNi₅ powder under hydrogen atmosphere. The results showed that the swelling ratio increased by 0.12 at the phase transition pressure. Response time decreased with an increase in the charged pressure during absorption, while it remained constant during discharge. Reaction kinetics revealed that these swelling behaviors were explained by hydrogen absorption and lattice expansion. The swelling ability of LaNi₅ was also compared with that of palladium. The results show that LaNi₅ swells 1.8 times more than palladium under 0.5 MPa. LaNi₅ is suitable for an actuator driven repeatedly under more than the phase transition pressure. Palladium can be used for one-way-operation actuator even under 0.1 MPa since its response time during the evacuation was much longer than during the pressurization.

Phase-Transited Lysozyme-Driven Formation of Self-Supported Co3O4@C Nanomeshes for Overall Water Splitting

The development of highly efficient catalysts for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is of paramount importance in water splitting. Herein, a phase-transited lysozyme (PTL) is employed as the platform to synthesize nitrogen-doped Co3O4@C nanomesh with rich oxygen vacancies supported on the nickel foam (N-Co3O4@C@NF). This PTL-driven N-Co3O4@C@NF integrates the advantages of porous structure, high exposure of surface atoms, strong synergetic effect between the components and unique 3D electrode configuration, imparting exceptional activity in catalyzing both HER and OER. Remarkably, an alkaline electrolyzer assembled by N-Co3O4@C@NF as both cathode and anode delivers a current density of 10 mA cm-2 at an ultralow cell voltage of 1.40 V, which is not only much lower than that of the commercially noble Pt/C and IrO2/C catalyst couple (≈1.61 V) but also a new record for the overall water splitting. The finding may open new possibilities for the design of bifunctional electrocatalysts for application in practical water electrolysis.

Iron-Doping-Induced Phase Transformation in Dual-Carbon-Confined Cobalt Diselenide Enabling Superior Lithium Storage

Transition metal chalcogenides (TMCs) have been investigated as promising anodes for high-performance lithium-ion batteries, but they usually suffer from poor conductivity and large volume variation, thus leading to unsatisfactory performance. Although nanostructure engineering and hybridization with conductive materials have been proposed to address this concern, a better performance toward practical device applications is still highly desired. Herein, we report an iron-doping-induced structural phase transition from pyrite-type (cubic) to marcasite-type (orthorhombic) phases in porous carbon/rGO-coupled CoSe₂. The dual-carbon-confined orthorhombic CoSe₂ ( o-Fe _xCo_{1- x}Se₂@NC@rGO) composites exhibit dramatically enhanced lithium storage performance (920 mAh g^-1 after 1000 cycles at 1.0 A g^-1) over cubic CoSe₂-based composites ( c-CoSe₂@NC@rGO). The combined experimental studies and density functional theory calculations reveal that this doping-induced structural phase transformation strategy could create a favorable electronic structure and ensure a rapid charge transfer. These results demonstrate that the phase-transformation engineering may provide another opportunity in the design of high-performance TMC-based electrodes.

Experimental Study on Storage and Maintenance Method of Ni-MH Battery Modules for Hybrid Electric Vehicles

This paper investigates the performance changes of nickel–metal hydride (Ni-MH) battery modules for hybrid electric vehicles (HEVs) using different storage and maintenance methods. The effects of charge–discharge mode, maintenance period, rest time, charge rate, and storage state of charge (SOC) on the storage performance of Ni-MH battery modules are studied. Based on the experimental results and engineering application requirements, this paper proposes some important recommendations and methods for storage and maintenance of Ni-MH battery modules for HEVs. The experimental results show that, compared with the six benchmark methods, the proposed storage and maintenance method provides superior storage and maintenance outcomes and significantly saves maintenance time.

An All-Solid-State Rechargeable Chloride Ion Battery

The chloride ion battery has been developed as one of the alternative battery chemistries beyond lithium ion, toward abundant material resources and high energy density. Its application, however, is limited by the dissolution of electrode materials and side reactions in the liquid electrolyte. Herein, a solid polymer electrolyte allowing chloride ion transfer and consisting of poly(ethylene oxide) as the polymer matrix, tributylmethylammonium chloride as the chloride salt, and succinonitrile as the solid plasticizer is reported. The as-prepared polymer electrolyte shows conductivities of 10-5-10-4 S cm-1 in the temperature range of 298-343 K. When it is assembled with the iron oxychloride/lithium electrode system, reversible electrochemical redox reactions of FeOCl/FeO at the cathode side and Li/LiCl at the anode side are realized, demonstrating the first all-solid-state rechargeable chloride ion battery.

Porous hollow composites assembled by NixCo1-xSe2 nanosheets rooted on carbon polyhedra for superior lithium storage capability

Transition metal chalcogenides (TMCs) have attracted considerable interest owing to their satisfied theoretical capacity, good safety and environmentally benign nature in lithium-ion batteries (LIBs). However, the poor conductivity as well as the severe volume changes during the discharge-charge process cause capacity fading rapidly, which severely impede the practical applications of TMCs. To address this challenge, a hollow hybrid architecture assembled by Ni_xCo_1-xSe₂ nanosheets and strongly coupled porous carbon have been rational designed. Within this structure, the integration of nanosheets rooted on the surface of porous carbon not only provide three-dimensional conductive network but also offer plentiful pathways and active sites for electrolyte penetration and Li storage, and buffer a large volume expansion/contraction caused by lithium intercalation/deintercalation. As evidenced by electrochemical measurements, the Ni_xCo_1-xSe₂/C composites used as anodes in LIBs exhibit a superior reversible high capacity of 1667 mA h g^-1 at current density of 2.0 A g^-1 over 600 cycles and an outstanding rate capability (1580 and 1093 mA h g^-1 at 3.2 and 6.4 A g^-1, respectively).

Formation of multi-shelled nickel-based sulfide hollow spheres for rechargeable alkaline batteries

Metal sulfides with multi-shelled hollow structures are promising electrode materials for rechargeable alkaline batteries due to their abundant redox centers and electrochemically active sites.

Improved hydrogen storage kinetics of nanocrystalline and amorphous Ce–Mg–Ni-based CeMg12-type alloys synthesized by mechanical milling

Addition of Ni and milling are beneficial for forming nanocrystalline and amorphous structures, thus enhancing the hydrogen storage kinetics of CeMg₁₂-type alloys.

An investigation of gaseous hydrogen storage characterizations of Mg–Y–Ni–Cu alloys synthesized by melt spinning

Melt spinning was successfully utilized to prepare Mg_25−xY_xNi₉Cu (x = 0, 1, 3, 5, 7) alloys, producing nanocrystalline and amorphous structures with improved hydrogenation and dehydrogenation performances. The influence of spinning rate on hydrogenation and dehydrogenation thermodynamics and kinetics was studied in detail. XRD and TEM were utilized to characterize the alloy structures. Hydrogenation and dehydrogenation performances were investigated by Sievert apparatus, DSC and TGA connected to a H₂ detector. Dehydrogenation activation energies were estimated using both Arrhenius and Kissinger methods. Results show that melt spinning significantly decreases thermodynamic parameters (ΔH and ΔS) and ameliorates desorption kinetics. Dehydrogenation activation energy markedly lowers with increase in spinning rate and is the real driver of amelioration of dehydrogenation kinetics caused by increasing Y content.

Melt spinning enables the crystalline alloy to be strongly disordered and nanostructured, thus enhancing the hydrogen storage kinetics of Mg_25−xY_xNi₉Cu.

A Novel Type of Battery-Supercapacitor Hybrid Device with Highly Switchable Dual Performances Based on a Carbon Skeleton/Mg2Ni Free-Standing Hydrogen Storage Electrode

The sharp proliferation of high power electronics and electrical vehicles has promoted growing demands for power sources with both high energy and power densities. Under these circumstances, battery-supercapacitor hybrid devices are attracting considerable attention as they combine the advantages of both batteries and supercapacitors. Here, a novel type of hybrid device based on a carbon skeleton/Mg₂Ni free-standing electrode without the traditional nickel foam current collector is reported, which has been designed and fabricated through a dispersing-freeze-drying method by employing reduced graphene oxide (rGO) and multiwalled carbon nanotubes (MWCNTs) as a hybrid skeleton. As a result, the Mg₂Ni alloy is able to deliver a high discharge capacity of 644 mAh g^-1 and, more importantly, a high cycling stability with a retention of over 78% after 50 charge/discharge cycles have been achieved, which exceeds almost all the results ever reported on the Mg₂Ni alloy. Simultaneously, the electrode could also exhibit excellent supercapacitor performances including high specific capacities (296 F g^-1) and outstanding cycling stability (100% retention after 100 cycles). Moreover, the hybrid device can switch between battery and supercapacitor modes immediately as needed during application. These features make the C skeleton/alloy electrode a highly promising candidate for battery-supercapacitor hybrid devices with high power/energy density and favorable cycling stability.

Design of Hydrogen Storage Alloys/Nanoporous Metals Hybrid Electrodes for Nickel-Metal Hydride Batteries

Nickel metal hydride (Ni-MH) batteries have demonstrated key technology advantages for applications in new-energy vehicles, which play an important role in reducing greenhouse gas emissions and the world's dependence on fossil fuels. However, the poor high-rate dischargeability of the negative electrode materials-hydrogen storage alloys (HSAs) limits applications of Ni-MH batteries in high-power fields due to large polarization. Here we design a hybrid electrode by integrating HSAs with a current collector of three-dimensional bicontinuous nanoporous Ni. The electrode shows enhanced high-rate dischargeability with the capacity retention rate reaching 44.6% at a discharge current density of 3000 mA g(-1), which is 2.4 times that of bare HSAs (18.8%). Such a unique hybrid architecture not only enhances charge transfer between nanoporous Ni and HSAs, but also facilitates rapid diffusion of hydrogen atoms in HSAs. The developed HSAs/nanoporous metals hybrid structures exhibit great potential to be candidates as electrodes in high-performance Ni-MH batteries towards applications in new-energy vehicles.