High Discharge Current Density Research Articles

A self fire-extinguishing and high rate lithium-fluorinated carbon battery realized by ethoxy (pentafluoro) cyclotriphosphazene electrolyte additive design

The lithium/carbon fluoride (Li/CFx) battery has attracted significant attention due to its highest energy density among all commercially available lithium primary batteries. However, its high energy density also poses a significant risk during thermal runaway events, and its poor electrochemical performance at high discharge current densities limits its application in high-power devices. In this study, we propose a flame-retardant and interface-affinity enhancing electrolyte additive, ethoxy (pentafluoro) cyclotriphosphazene (PFPN), to regulate the electrolyte in Li/CFx batteries. The PFPN molecules participate in the lithium solvation shell, and its fluorine groups shows better affinity with the carbon fluoride cathode compared to traditional carbonate electrolytes. Furthermore, as a bulky molecule, PFPN reduces the desolvation energy of Li+ ions after participating in lithium ion coordination, making it easier for Li+ ions to be utilized at the carbon fluoride cathode, significantly enhancing the battery's rate performance. In a carbonate electrolyte containing 16 % PFPN additive (1 M LiBF4/EC+DMC, volume ratio 1:1), the CFx cathode delivers 277 % higher capacity at a current density of 1 A g−1 compared to a CFx cathode without the additive. Additionally, due to the ability of PFPN to produce fluorine and phosphorus radicals at high temperatures that interrupt the combustion chain reaction, the electrolyte can achieve up to 10 instances of zero-second self-extinguishing, reducing the battery self-extinguishing time by 90 %. This study is the first to investigate the safety and flame-retardant electrolyte design of carbon fluoride batteries, providing a method to improve the power performance and safety of Li/CFx batteries at the same time.

Reusable Cell Design for High-Temperature (600 °C) Liquid Metal Battery Cycling

This paper presents the cycling of a novel low-cost Na-Zn liquid metal battery. Its 600 °C operating temperature presents multiple challenges that must be overcome to achieve commercial viability, both from a structural and electrochemical perspective. To enable long-term cycling of the Na-Zn battery in a realistic environment, we have developed a reusable, hermetically sealed, high temperature and sufficiently corrosion resistant cell concept. The design as well as various approaches for assembling and filling the cell are presented. The factors considered when selecting specific components are documented and explained. The active volume of the cell design can be up to 40 ml, corresponding to a nominal capacity of 1 A h, while the entire cell body weighs around 800 g and costs approximately €200 ($215). The performance of the cell is demonstrated in terms of longevity (1000 h) and high discharge current density (100 mA cm-2). The manuscript not only presents the first long-term cycling performance of the novel Na-Zn chemistry achieving Coulombic efficiency of up to 80%, but also demonstrates the design’s versatility with in situ dynamic neutron radiography of the cell.

Forming Robust and Highly Li‐Ion Conductive Interfaces in High‐Performance Lithium Metal Batteries Using Chloroethylene Carbonate Additive

Developing high‐rate Li metal batteries (LMBs) is challenging because of dendrite growth and irreversible parasitic reactions of the Li metal. Herein, a robust and highly ion‐conductive solid electrolyte interphase (SEI) layer is designed on a Li metal anode and a Ni‐rich layered cathode by incorporating chloroethylene carbonate (ClEC) as an additive in fluoroethylene carbonate‐based electrolytes. ClEC induces the formation of LiCl, which facilitates Li‐ion diffusion in the robust LiF‐rich SEI layer, thereby improving the cycle stability of the Li metal anode and suppressing microcracking of the Ni‐rich layered cathode, especially during charging and discharging at high current densities. By using the newly developed combination of electrolyte solution, an LMB featuring the Li[Ni0.78Co0.1Mn0.12]O2 cathode (2.3 mAh cm−2, 0.1 C) affords a superior capacity retention of 80.2% over 400 cycles at high charge and discharge current densities of 2.0 C (3.6 mA cm−2) and 5.0 C (9.0 mA cm−2). This study provides insights into the use of ClEC as an electrolyte additive and highlights the importance of constructing robust and highly ion‐conductive interfaces on both Li metal anodes and Ni‐rich cathodes for high‐performance LMBs.

The Effect of C45 Carbon Black-Phosphomolybdic Acid Nanocomposite on Hydrogenation and Corrosion Resistance of La2Ni9Co Hydrogen Storage Alloy

In this paper, we analysed the influence of corrosion processes and the addition of a carbon black-heteropoly phosphomolybdic acid (C45-MPA) nanocomposite on the operating parameters of a hydride electrode obtained on the basis of the intermetallic compound La2Ni9Co. The electrochemical properties of negative electrodes for NiMH batteries were studied using galvanostatic charge/discharge curves, the potentiostatic method, and electrochemical impedance spectroscopy (EIS). The morphology and chemical composition analysis of the studied electrodes were investigated by means of scanning electron microscopy (SEM) with supporting energy-dispersive X-ray analysis (EDS). For more structural information, FTIR analysis was performed. The results indicate that the presence of the C45-MPA nanocomposite in the electrode material increased both the discharge capacity of the hydride electrode and the exchange current density of the H2O/H2 system. The heteropoly acid-modified electrode is also more resistant to high discharge current densities due to its catalytic activity.

Planar Sodium‐Nickel Chloride Batteries with High Areal Capacity for Sustainable Energy Storage

AbstractHigh‐temperature sodium‐nickel chloride (Na‐NiCl2) batteries are a promising solution for stationary energy storage, but the complex tubular geometry of the solid electrolyte represents a challenge for manufacturing. A planar electrolyte and cell design is more compatible with automated mass production. However, the planar cell design also faces a series of challenges, such as the management of molten phases during cycling. As a result, cycling of planar high‐temperature cells until now focused on moderate areal capacities and current densities. In this work, planar cells capable of integrating cost‐efficient nickel/iron electrodes at a substantially enhanced areal capacity of 150 mAh cm−2 is presented. Due to a low cell resistance during operation at 300 °C, these cells deliver a specific discharge energy of 300 Wh kg−1 at high discharge current densities of 80 mA cm−2 (C/2, 10%–100% state‐of‐charge). This results represent the first demonstration of planar Na‐NiCl2 cells at a commercially relevant combination of areal capacity, cycling rate, and energy efficiency. It is further identified the secondary molten NaAlCl4 electrolyte to contribute to the cell capacity during cycling. Mitigating electrochemical decomposition of NaAlCl4 will play an important role in further enhancing both cycling rates and cycle life of high temperature Na‐NiCl2 batteries.

Rare-metal-free Zn–air batteries with ultrahigh voltage and high power density achieved by iron azaphthalocyanine unimolecular layer (AZUL) electrocatalysts and acid/alkaline tandem aqueous electrolyte cells

Zn–air batteries have only been used in limited applications, such as hearing aid batteries, due to their low power density and standard voltage of around 1.4 V. Therefore, to use Zn–air batteries as a drive power source in cutting-edge devices such as drones, it is essential to improve the drive voltage and output power density. Here, we propose Zn–air batteries with a high potential (∼2.25 V) and high power density (∼318 mW/cm2) by using the newly designed iron azaphthalocyanine unimolecular layer (AZUL) electrocatalyst and a tandem Zn–air battery cell. The AZUL electrocatalyst in this new type of cell had a high electrochemical stability and high oxygen reduction reaction performance in the ultralow pH region, in which Pt and other metallic and inorganic electrocatalysts cannot be used. Furthermore, the tandem-electrolyte cells had a cell voltage of over 1.0 V at a high discharge current density of 200 mA/cm2, and the output power density was 1139 mWh/g(Zn) at 100 mA/cm2 discharge.

Successful Charge–Discharge Experiments of Anthraquinone-Bromate Flow Battery: First Report

The proposed anthraquinone-bromate cell combines the advantages of anthraquinone-bromine redox flow batteries and novel hybrid hydrogen-bromate flow batteries. The anthraquinone-2,7-disulfonic acid is of interest as a promising organic negolyte due its high solubility, rapid kinetics of electrode reactions and suitable redox potentials combined with a high chemical stability during redox reactions. Lithium or sodium bromates as posolytes provide an anomalously high discharge current density of order ~A cm−2 due to a novel autocatalytic mechanism. Combining these two systems, we developed a single cell of novel anthraquinone-bromate flow battery, which showed a power density of 1.08 W cm−2, energy density of 16.1 W h L−1 and energy efficiency of 72% after 10 charge–discharge cycles.

Portable integrated photo-charging storage device operating at 3 V

The integration of an energy harvesting device and an energy storage device into one unit has been widely studied as a distributed power source. Herein, we propose a high-voltage-driven photo-charging storage device, integrating a series-connected perovskite solar cell and an ionogel-based solid supercapacitor. The photo-charging storage device exhibits high overall efficiencies of 13.17 % and 9.87 % at 1 mA cm−2 and 20 mA cm−2, respectively, attributed to its high storage efficiency of over ∼ 70 % at all discharge current densities. This high discharge current density of 20 mA cm−2 is the record value for all reported integrated solar cells and electric double-layer capacitor systems. Moreover, the photo-charging storage device maintains 78.6 % of its overall efficiency after 100 cycles under AM 1.5 G illumination and exhibits remarkable cycle performance under indoor light illumination. To understand the interfacial behavior of the photo-charging storage device, impedance spectroscopy is performed for the first time. In addition, to avoid the decomposition of the perovskite solar cell active layer with moisture, an encapsulation process is conducted, which enables the device to remain operational at 3 V after 8 weeks. These results underline the high potential of this photo-charging storage device as a portable power source.

Multi-cationic ionic liquid combination enabling 86-fold enhancement in frequency response and superior energy density in all-solid-state supercapacitors

Polymer ionic-conductor electrolytes with seamless electrode-electrolyte interface are indispensable for extracting the full potential of all-solid-state electrochemical double layer capacitors. While ionic liquids are among the best ionic conductors in liquid state and offer a wide potential window, translating their ionic mobility and activity to solid-state is important, yet challenging. In this direction, we report a mixed ionic liquid based solid electrolyte with an ionic conductivity of 1 mS/cm that delivers 86-fold higher scan-rate operability and 2.6 times lower relaxation time constant than their individual constituents. Specifically, a flexible polymeric matrix impregnated with a mixture of monocationic (1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (BMIm TFSI)) and a dicationic ionic liquid (1,4-di(vinylimidazolium) butane bisbromide ([DVIM]Br)) facilitates rapid and extensive formation of electrical double layer when integrated with carbon-based electrodes. The resulting all-solid-sate flexible supercapacitor achieves superior scan rate operability (15,000 mV/s) and ultralow relaxation time constant (7.8 ms), translating to high discharge current density (>1 mA/cm2), energy density (26.4 Wh/kg) and power density (61,127 W/kg). The improved rate capability (~83 %) and energy storage performance is attributed to a synergistic interplay of ionic strength, conductivity and ion mobility of the mixed ionic-liquid that unfold newer avenues towards solid-electrolyte engineering for energy storage devices.

Highly-porous Super-Growth carbon nanotube sheet cathode develops high-power Lithium-Air Batteries

Lithium-Air Battery (LAB) is expected to develop ultra-high energy density batteries, but the low rate performance and poor cycle life of present LAB cells hinder practical development. Here we report that a highly porous carbon nanotube (CNT) cathode dramatically enhances the rate capability of LAB. Single-walled CNTs (SWCNTs) with wavy patterns prepared from the Super-Growth (SG) method successfully provided CNT sheets with high porosity of up to 94%. The pore structure was characterized by two distinct pores in size, namely, highly extended mesoscale (approximately 5–200 nm) pores formed inside CNT bundles that provide large surface area for oxygen reduction reaction (ORR) and inter-bundle gaps in a micrometer scale that works for oxygen diffusion path. This porous CNT sheet cathode significantly increased the discharge rate of LAB cells, specifically enabling a high discharge current density of 3.0 mA/cm2 securing practical cell capacity of 3.3 mAh/cm2, which is comparable to the current LiB technology that provides ∼3 mAh/cm2 cell capacity at ∼1C rate (∼3 mA/cm2) discharge. Furthermore, this highly porous cathode was also effective for extending the cycle life of LAB cells. Such bimodal pore architecture of the CNT sheet cathode paves the new strategy for developing high-power energy-dense LAB.

Healable Lithium Alloy Anode with Ultrahigh Capacity.

Effective recycling of spent Li metal anodes is an urgent need for energy/resource conservation and environmental protection, making Li metal batteries more affordable and sustainable. For the first time, we explore a unique sustainable healable lithium alloy anode inspired by the intrinsic healing ability of liquid metal. This lithium alloy anode can transform back to the liquid state through Li-completed extraction, and then the structure degradation generated during operation could be healed. Therefore, an ultralong cycle life of more than 1300 times can be successfully realized under harsh conditions of 5 mA h cm-2 capacitance by a process of two healing behaviors. This design improves the sustainable utilization of Li metal to a great extent, bringing about unexpected effects in the field of lithium-based anodes even at an unprecedentedly high discharge current density (up to 25 mA cm-2) and capacity (up to 50 mA h cm-2).

Simultaneously Realizing Superior Energy Storage Properties and Outstanding Charge-Discharge Performances in Tungsten Bronze-Based Ceramic for Capacitor Applications.

The development of lead-free ceramics with appropriate energy storage properties is essential for the successful practical application of advanced electronic devices. In this study, a site engineering strategy was proposed to concurrently decrease grain size, increase the band-gap, and enhance the relaxor nature in Ta-doped tungsten bronze ceramics (Sr2NaNb5-xTaxO15) for the improvement of the dielectric breakdown strength and the polarization difference. As a result, the ceramic with x = 1.5, that is, Sr2NaNb3.5Ta1.5O15, exhibited superior energy density (∼3.99 J/cm3) and outstanding energy efficiency (∼91.7%) (@380 kV/cm) as well as good thermal stability and remarkable fatigue endurance. In addition, the ceramic demonstrated an ultrashort discharge time (τ0.9 < 57 ns), a high discharge current density (925.8 A/cm2) along with a high power density (78.7 MW/cm3). The energy storage properties in combination with good stability achieved in this work indicate the powerful potential of Sr2NaNb5-xTaxO15 tungsten bronze ceramics for high-performance capacitor applications. This material can be considered as a complement to the widely studied perovskite-based relaxor ceramics and should be further investigated in the future.

Gaseous electrolyte additive BF3 for high-power Li/CFx primary batteries

Lithium/graphite fluoride (Li/CFx) batteries have attracted great attention because of the highest energy density among all commercially available lithium primary batteries. However, the inferior electrochemical performances at high discharge current densities impede their applications in high-power devices. Herein, we have found a novel and low-cost gaseous electrolyte additive BF3 that can remarkably improve the rate capability of the Li/CFx batteries. The CFx (x=1.15) cathode in the carbonate electrolyte with 0.01M BF3 additive can deliver a maximum power density of 23040 W kg−1 with a high gravimetric energy density of 722.8 Wh kg−1. By contrast, the CFx cathodes in the electrolyte without additive can barely provide capacity at discharge rates above 5C. Such significant enhancement can be attributed to the ability of the BF3 additive to dissolve the insulating discharge product LiF without passivating the cathode surface and impeding the intercalation of lithium ions. This work provides a way that enables Li/CFx batteries to have an ultrahigh power density comparable to that of supercapacitors while maintaining high energy densities.

Development of high-performance hydrogen storage alloys for applications in nickel-metal hydride batteries at ultra-low temperature

The main challenge for the applications of nickel-metal hydride (Ni-MH) batteries in low-temperature regions derives from the sluggish kinetics of its negative electrode materials—hydrogen storage alloys (HSAs). Here we design and fabricate a series of Co-free HSAs, exhibiting superior electrochemical reaction kinetics and low-temperature dischargeability performance. One novel candidate, La0.95Y0.05Ni4.5Mn0.4Al0.35, shows the highest discharge specific capacity of 283.5 mAh g−1 among reported data of AB5-type HSAs at a high discharge current density of 3000 mA g−1, which is 4.3 times that of the alloy synthesized with the same composition as a commercial alloy (MmNi3.55Co0.75Mn0.4Al0.3) electrode (65.9 mAh g−1). Moreover, this Co-free La0.95Y0.05Ni4.5Mn0.4Al0.35 alloy electrode can remain a discharge specific capacity of 255.8 mAh g−1 at a low temperature of 233 K while the synthesized MmNi3.55Co0.75Mn0.4Al0.3 alloy electrode shows a specific capacity of only 9.5 mAh g−1. The discharge specific capacity of the above Co-free alloy electrode can reach 30.0 mAh g−1 228 K, making it a promising candidate as a negative electrode material for applications in Ni-MH batteries at ultra-low temperature.

Synergistic optimization of antiferroelectric ceramics with superior energy storage properties via phase structure engineering

Dielectric capacitors with high energy storage density and high efficiency exhibit potential applications in lightweight, miniaturized microelectronic devices. Here, (Pb, La)(Zr, Sn)O3 (PLZS) based ceramics with Ba substitution were selected and studied with in-situ Raman spectra and in-situ synchrotron X-ray diffraction. Results show that the room temperature phase structure consists of two coexisting antiferroelectric phases of OI and OII (O refers to orthorhombic), and between them the latter possesses lower forward phase-switching electric field (EAF) and should be the origin of FE(I). Meanwhile, Polarization-electric field (P-E) loops and Raman spectrum under variable temperature reveal optimal Ba content of 0.02. Suitable Ba substitution forms balanced coexisting structure and therefore achieves ultrahigh recoverable energy storage density (Wrec) of 12.8 J/cm3 and simultaneously high energy storage efficiency (η) of 84.2% under an electric field of 450 kV/cm. Extremely short discharge period of 51.6 ns and high Wrec support ultrahigh power density (PD) of 327 MW/cm3 and high discharge current density (Ddis) of 1815 A/cm2. Reasonable phase structure design after clarifying the relationship between structure and performance shows guiding significance, and the improved ultra-high Wrec and PD enhance the possibility of applications of antiferroelectric ceramics in pulsed power capacitor.

Facile fabrication of novel Ti3C2Tx-supported fallen leaf-like Bi2S3 nanopieces by a combined local-repulsion and macroscopic attraction strategy with enhanced symmetrical supercapacitor performance

Hybrid electrode materials with superior electrochemical performance are highly desired to fulfil the ever-increasing energy-density demands of supercapacitors. Herein, a facile and efficient ion-attraction strategy is demonstrated for the construction of a uniform heterostructure of Bi2S3/Ti3C2Tx (BSTC) nanocomposites, in which fallen leaf-like Bi2S3 nanopieces are firstly planted on the surface of Ti3C2Tx due to the local-repulsion of Ti atoms and the macroscopic attraction of functional groups (OH/O/F) to Bi3+. The DFT calculation was conducted to explain the morphology transformation mechanism from nanoparticles to nanopieces and the enhancement of the electrical conductivity of Bi2S3 is due to the incorporation of Ti3C2Tx. When used as a supercapacitor electrode, the BSTC-29 (Ti3C2Tx content: 29 wt.%) nanocomposite exhibits a superior electrochemical performance with an enhanced capacity of 615 C g-1 at a high discharge current density of 3 A g-1, and a high capacitance retention up to 91% is also obtained due to the enhanced structural stability. Furthermore, the assembled symmetrical supercapacitor exhibits both a high energy density of 27.6 Wh kg-1 and a power density of 24.3 kW kg-1, respectively, surpassing those of Bi2S3 and Ti3C2Tx in this study and many other related composites in literature. This study presents a new promising strategy for the synthesis of high-performance supercapacitor electrode materials.

Sulfur-doped carbon nanotubes as a conducting agent in supercapacitor electrodes

The electrochemical performance of sulfur-doped carbon nanotubes (S-CNTs) was investigated to confirm the S-doping effects and the possibility of their application as conducting agents in supercapacitor electrodes. S-CNTs were successfully synthesized via chemical vapor deposition using dimethyl disulfide as the carbon source. They were purified to obtain purified S-CNTs (P–S-CNTs) with diameters 30–50 nm and S content of 0.65 at%. The doped S atoms were removed partially from the P–S-CNTs by heat treatment in H2 atmosphere (De-P-S-CNTs). To compare the electrochemical performances of various conducting materials for supercapacitor electrodes, commercial activated carbon (MSP20) was used as the active material and commercial conducting agent (Super-P), commercial multi-walled CNTs (MWCNTs), De-P-S-CNTs, and P–S-CNTs were used as the conducting agents. The electrode with P–S-CNTs exhibited the highest specific capacitance at a high discharge current density of 100 mA cm−2 (120.2 F g−1) and the lowest charge-transfer resistance (6.19 Ω) that are significantly superior to those of Super-P (83.9 F g−1 and 15.16 Ω), MWCNTs (87.8 F g−1 and 17.02 Ω), and De-P-S-CNTs (90.1 F g−1 and 22.33 Ω). The superior electrochemical performance of P–S-CNTs can be attributed to the excellent electrical conductivity and pseudocapacitive contribution of the S-doping effect.

Study on leaf-shaped cobalt-based metal-organic frameworks synthesized by solvothermal method as high discharge current density air cathode catalyst for lithium-oxygen batteries

A type of leaf-shaped cobalt-based metal-organic framework material is synthesized by solvothermal method with 1.3:1 cobalt and terephthalic acid ratio and uses as the air electrode catalyst for lithium-oxygen batteries working at high discharge current density. Physical characterization displays that the interaction between cobalt and terephthalic acid can produce a crystal material and the different proportions have a certain influence on their structure and crystallinity. In addition, micromorphology with cobalt and terephthalic acid 1.3:1 shows a leaf-like structure, and synaptic structure on the leaf surface may be beneficial to improve the catalytic activity. Electrochemical tests present that air electrode using this leaf-like structure catalyst materials has good reversibility and the specific discharge capacities can achieve to 3573.90 mAh g−1 at 0.5 mA cm−2 current densities. However, compared with existing catalysts, these leaf-shaped catalyst materials have no obvious advantage in improving the cycle life.

Modification of LiCoO2 through rough coating with lithium lanthanum zirconium tantalum oxide for high-voltage performance in lithium ion batteries

In this study, the spray-drying technique was used to apply a 0.5 at%, 1 at%, and 1.25 at% of lithium lanthanum zirconium tantalum oxide (Li6.75La3Zr1.75Ta0.25O12) powder coating on the surface of lithium cobalt oxide (LiCoO2) cathode materials. Subsequently, these materials were sintered for either 5 or 10 h at 800 °C to obtain LiCoO2 cathode materials with a rough coating. X-ray diffraction, cyclic voltammetry, electrochemical impedance spectroscopy, and differential scanning calorimetry were then conducted to analyze differences in the structure, electrochemical properties, and thermostability of the materials before and after surface modification. The modified LiCoO2 cathodes with Li6.75La3Zr1.75Ta0.25O12 rough coating had more than twice the discharge capacity as the bare LiCoO2 cathode at a high discharge current density when the cutoff voltage ranged from 2.8 to 4.5 V. In addition, 1 at% Li6.75La3Zr1.75Ta0.25O12 coating and 5 h of sintering at 800 °C resulted in the optimal capacity retention of 85.4% after 80 cycles and a slower exothermic reaction than that of the bare LiCoO2 cathode. Thus, rough coating an adequate quantity of Li6.75La3Zr1.75Ta0.25O12 powder on a LiCoO2 cathode mitigated the reaction between the cathode material surface and electrolyte, stabilizing the main structure and enhancing the ionic conductivity and electrochemical characteristics of the material.

Hydrides of Laves type Ti–Zr alloys with enhanced H storage capacity as advanced metal hydride battery anodes

The present work was focused on the studies of the effect of variation of stoichiometric composition of Ti–Zr based AB2±x Laves phase alloys by changing the ratio between A (Ti + Zr) and B (Mn + V + Fe + Ni) components belonging to both hypo-stoichiometric (AB1.90, AB1.95) and over-stoichiometric (AB2.08) alloys further to the stoichiometric AB2.0 composition to optimize their hydrogen storage behaviours and performances as the alloy anodes of nickel metal hydride batteries.AB2-xLa0.03 Laves type alloys (A = Ti0.15Zr0.85; B = Mn0.64–0.69V0.11–0.119Fe0.11–0.119Ni1.097–1.184; x = 0, 0.05 and 0.1) were arc melted and then homogenized by annealing.The studies involved probing of the phase-structural composition by X-Ray diffraction (XRD), together with studies of the microstructural state, hydrogen absorption–desorption and thermodynamic characteristics of gas–solid reactions and electrochemical charge-discharge performance, further to the impedance spectroscopy characterization. The alloys were probed using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and XRD.These studies concluded that the alloys contained the main C15 FCC Laves type AB2 intermetallic co-existing with a secondary C14 hexagonal Laves phase and a small amount of LaNi intermetallic. The gaseous H storage capacity and electrochemical performances were found to be closely dependent on the stoichiometric compositions of the alloys. High discharge capacities approaching 500 mAh/g were achieved for the AB1.95 alloy. At 500 mA/g current density, the discharge capacity was maintained as high as 80%, with very low capacity retention after 500 cycles. The alloy which had the highest capacity retention after 500 cycles was found to be AB2.0 alloy. Furthermore, AB2.0 alloy showed an excellent cyclic stability together with a high hydrogen diffusion coefficient. Studies of hydrogen diffusion coefficients showed that annealing enhanced the H diffusion rates allowing advanced performance at high discharge current densities. This has been related to a higher content of C15 Laves compound which allows to reach a higher H mobility in contrast with higher storage capacity observed for the C14 Laves type polymorph.