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This study examines the effects of the addition of Mn and LmNi 4.1 Al 0.25 Mn 0.3 Co 0.65 (Lm: lanthanum-rich mischmetal) alloy on the electrochemical characteristics of body centered cubic (BCC) type Ti 0.32 Cr 0.43− x Mn x V 0.25 ( x = 0–0.08) alloys as negative electrode (anode) materials for nickel–metal-hydride (Ni-MH) batteries. The activation behaviour and discharge capacity of the BCC alloys are improved significantly by ball-milling with LmNi 4.1 Al 0.25 Mn 0.3 Co 0.65 alloy because this AB 5 alloy acts as a path for hydrogen on the surface of the BCC alloy. Among the Mn-substituted alloys, a Ti 0.32 Cr 0.38 Mn 0.05 V 0.25 alloy ball-milled with the AB 5 alloy yields the greatest discharge capacity of 340 mAh g −1 . In addition, compared with the alloy without Mn, the Mn-substituted alloys exhibit a lower plateau pressure for hydrogen, a better hydrogen-storage capacity in the pressure–composition isotherms and faster surface activation.

AB 5 -type hydrogen storage alloys with MmNi 4.4− x Co 0.6 Al x (Mm-mischmetal) composition are synthesized, structurally and thermodynamically characterized, and electrochemically tested in 6 M KOH electrolyte. It is shown that an increase of the Al content in the alloy results in expansion of both the alloy lattice cell size and the unit cell volume. These structural changes lead to decrease of the plateau pressure and increase of the plateau width in the pressure-composition-temperature desorption isotherms. Improvement of the specific electrode capacity is also registered with the increase of the cell parameters. In addition to that the higher Al content is found to enhance the stability of the alloy components’ hydrides. Maximum discharge capacity of 278 mAh g −1 is measured with an electrode made from a MmNi 3.6 Co 0.6 Al 0.8 alloy. Cycle life tests of the accordingly prepared electrodes suggest a stability that is comparable to the stability of commercially available hydrogen storage electrodes.

AB 5 -type MH alloys with Mm (Misch metal) as the A part (with varied rare earth contents in Mm) were investigated for rare earth by XRF analysis and battery performance by life cycle tests with an objective of understanding the influence of rare earth content on electrochemical hydrogen storage. The La/Ce ratio was found to vary from 0.51 to 18.73. The capacity output varied between 179 and 266 mAh g −1 . The results show that the La/Ce ratio has a strong influence on the performance, with the best performance realized with samples having an La/Ce ratio of around 12. La enhancement facilitates easy activation due to refinement in grain size and interstitial dimensions. Also, an orderly influence on crystalline structure could be seen. The study demonstrates that the rare earth content is an essential factor in determining the maximum capacity output because of its influence on crystal orientation as well as an increase in the radius of the interstitials, lattice constants and cell volumes.

In a governmental funded 3-year research project a recycling process for nickel-metal hydride batteries (NiMH) has been developed. Today the discarded batteries are used in the steel industry as a cheap nickel-source. Cobalt is not paid for and rare earths (RE) are slagged and lost for reuse. Spent NiMH batteries contain 36–42% nickel, 3–4% cobalt and 8–10% mischmetal consisting of lanthanum, cerium, praseodymium and neodymium. The dismantled and processed NiMH are melted in a dc electric arc furnace producing a nickel–cobalt alloy and a slag phase highly enriched with RE-oxides. The key for success in this process was to find a suitable slag system which ensures best separation of NiCo alloy from the rare earth oxides. Different oxidic and halogenic slag systems are investigated on a laboratory and technical scale. The slag systems CaO–CaF2 and CaO–SiO2 were determined to be suitable for subsequent pilot plant trials. In these trials, the CaO–CaF2 system has shown a better melting behaviour than the CaO–SiO2 system. Nickel and cobalt were found nearly completely in the metal phase whereas the rare earths were transferred into the slag as oxides. Pyrometallurgical refining of the nickel–cobalt alloy did not make sense as investigated in technical scale trials. Within the scope of a scenario calculation the economical feasibility was demonstrated for a model scenario.

Faster activation of a multi-component AB5 based alloy metal hydride electrode through Pd nanoparticle (NP) impregnation is demonstrated. Pd nanoparticle impregnated MmNi5−xMx based alloy was prepared and characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and elemental mapping techniques. Electro-catalytic activity of laminar metal hydride electrodes containing Pd nanoparticles and micrometer size Ni particles was studied. Hydrogen absorption efficiency of the nanocomposite electrodes was compared with the metal hydride electrodes without Pd nanoparticles. The incorporation of nanostructured materials in the metal hydride alloy increased its hydrogen absorption capacity at the initial stage and activated much faster, indicating its good prospect for energy storage applications.

Two different strategies are outlined to develop both high energy density and space-efficient batteries, including the most widely applied rechargeable nickel-metal hydride (NiMH) and Li-ion batteries. The hydrogen storage capacity of fluorite-structured Mg-containing compounds are shown to have a reversible electrochemical storage capacity of more than four times that of the commonly used MischMetal-based AB5 compounds in NiMH, i.e. 1500mAh/g (5.6wt.%). The formation of octahedral sites within the crystal lattice is argued to be very crucial for the improved kinetics of hydrogen absorption and desorption. It is shown that the fluorite-structure can be conserved with both precious Sc and the less expensive Ti up to a Mg content of 80at.%. Both thermodynamic and kinetic data are presented in relation to the materials composition. In addition, the development of preshaped batteries, as the first step to battery integration, has contributed to a much higher level of design freedom for portable electronic equipment. The manufacturing process of preshaped batteries will be described together with their electrochemical characteristics. Advantageously, the mechanical stability is provided locally by polymer rivets, allowing to get rid of heavy metallic casings and to make use of a much wider range of battery shapes.

Non-stoichiometric La-rich MmNi3.55Co0.75Mn0.4Al0.3B0.3 hydrogen storage alloys using B–Ni or B–Fe alloy as additive and Ce-rich MmNi3.55Co0.75Mn0.4Al0.3B0.3 one using pure B as additive have been prepared and their microstructure, thermodynamic, and electrochemical characteristics have been examined. It is found that all investigated alloys show good activation performance and high-rate dischargeability though there is a certain decrease in electrochemical capacities compared with the commercial MmNi3.55Co0.75Mn0.4Al0.3 alloy. MmNi3.55Co0.75Mn0.4Al0.3B0.3 alloys using B–Ni alloy as additive or adopting Ce-rich mischmetal show excellent rate capability and can discharge capacity over 190 mAh/g even under 3000 mA/g current density, which display their promising use in the high-power type Ni/MH battery. The electrochemical performances of these MmNi3.55Co0.75Mn0.4Al0.3B0.3 alloys are well correlated with their microstructure, thermodynamic, and kinetic characteristics.

The electrocatalytic characteristics of a metal hydride (MH) electrode for advanced Ni/MH batteries include the hydrogen adsorption/desorption capability at the electrode/electrolyte interface. The hydrogen reactions at the MH electrode/electrolyte interface are also related to factors such as the surface area of the MH alloy powder and the nature of additives and binder materials. The high-rate discharge capability of the negative electrode in a Ni/MH battery is mainly determined by the mass transfer process in the bulk MH alloy powder and the charge transfer process at the interface between the MH alloy powder and the electrolyte. In this study, an AB 5 -type hydrogen-absorbing alloy, Mm (Ni, Co, Al, Mn) 5.02 (where Mm denotes Mischmetal, comprising 43.1 wt.% La, 3.5 wt.% Ce, 13.3 wt.% Pr and 38.9 wt.% Nd), was used as the negative MH electrode material. The MH electrode was charged and discharged for up to 200 cycles. The specific discharge capacity of the alloy electrode decreases from a maximum value of 290–250 mAh g −1 after 200 charge/discharge cycles. A cyclic voltammetry technique is used to analyze the charge transfer reactions at the electrode/electrolyte interface and the hydrogen surface coverage capacity.

An investigation is made of the effects of the solidification rate on the electrochemical properties and structure of alloys with composition MmNi 3.6 Co 0.75 Mn 0.55 Al 0.1 . By using the rapid quenching preparation technique, the electrode durability of this hydride-forming compound can be greatly improved at the expense of a small decrease in capacity compared with those of the cast alloy. Rapid quenching can also flatten and raise the discharge voltage plateau to a much more promising level, but rapidly quenched alloys generally show a lower activation speed. The higher the quenching rate, the longer the cycle life, the higher and flatter the discharge voltage plateau, but the lower the capacity. X-ray diffraction patterns and SEM observations indicated that whereas there are segregations in the master alloy, there are none in as-quenched alloys whose crystal grain is much smaller than that of the master alloy.

The charging efficiencies of MmNi 5 , MmNi 4.5 Mn 0.5 , MmNi 3.8 Co 0.7 Mn 0.5 , ZrV 0.6 Ni 1.4 , ZrV 0.6 Mn 0.4 Ni 1.0 , ZrV 0.6 Mn 0.4 Co 0.2 Ni 0.8 allay electrodes (Mm = Mischmetal) are investigated in terms of hydrogen evolution. Experiments are conducted to optimize: (i) elemental composition of the MmNi 5 system and Zr-based Laves-phase hydrogen storage alloys; (ii) additive materials, such as cobalt powder, nickel powder, Teflonized carbons, and acetylene black; (iii) the proportion of the additives in the alloy; (iv) the best percentage of the composite additives in the metal-hydride electrodes. The results show that the electrode activation, charging efficiency and high-rate discharge depend greatly on the active materials, as well as the type and the amount of the additives in the electrodes.

The effect of annealing on the hydrogen-storage properties of rapidly quenched AB 5 -type alloys is investigated by electrochemical measurements and X-ray diffraction. Annealing affects discharge capacity, voltage and cycle life. Annealing at an appropriate temperature can give a promising alloy with large capacity, high discharge voltage and long cycle life. Annealing at too high a temperature, such as 800 °C. results in the largest discharge capacity but the worst cycle life. Annealing can also flatten the discharge plateau regions. The striking difference in the phase structure between as-quenched and as-annealed alloys is that new phases occur as the product of annealing at high temperatures such as 600 and 800 °C. These phases are responsible for the deterioration in cycle durability.

Hydrogen storage properties of Mm 39.2 Ni 42.1 Mn 4.9 Al 1.25 Co 10.2 Fe 2.35 alloy have been systematically studied in the present work. An attempt is made to relate the content of hydrogen with change in resistance. It is found that the resistance of material increases with the increase in value of H / M due to hydrogen absorption. Pressure composition (P-C-T) isotherm using water displacement method has been investigated in the temperature and pressure ranges of 308 ≤ T ≤ 338 K and 0.5 ≤ P ≤ 10 bar, respectively. The P-C isotherms show the presence of two single α and β regions one mixed α + β phase. The maximum H (wt%) was found to be around 1.53 at 308 K and around 6 bar. Since enthalpy is an index of thermochemical stability of metal hydride the thermo dynamical parameters viz., the relative partial molar enthalpy (Δ H ) and relative partial molar entropy (Δ S ) of dissolved hydrogen have been calculated by plotting the Van’t Hoff plot. The variation of Δ H and Δ S with the hydrogen concentration confirm the phase boundaries.

A comparison is made of the properties of LaB 5 (BNi 3.55 Co 0.75 Mn 0.4 Al 0.3 ), La 0.7 R 0.3 B 5 (RCe, Pr, Nd) and MmB 5 (Mm is mischmetal in an atomic ratio of La:Ce:Pr:Nd = 0.7:0.2:0.05:0.05) alloy electrodes. X-ray diffraction results reveal that Ce, Pr, Nd substitute for La and decrease the unit cell volume. Pressure-composition isotherms of the electrode alloys are determined by an electrochemical method. The characteristics of the alloy electrodes, including initial activation, high-rate discharge, cycle life and self-discharge, are examined. It is found that partial replacement of La with Ce, Pr, Nd in the LaNi 5 -based alloy improves greatly the activation, high-rate discharge and cycle life of the electrode, but increases the self-discharge due to a higher dissociation pressure of the metal hydride.

The metallurgical properties of lead—strontium alloys were studied in relation to the properties required for lead—acid battery grids. The castability of all the alloys tested was as good as the corresponding alloys containing calcium. The mechanical properties of binary alloys containing 0.08% strontium or more and of ternary alloys containing 0.04% strontium or more indicated that these alloys could be handled and processed by normal production techniques. The creep and stress corrosion properties of the binary and ternary alloys were not good enough to consider them for use in deep cycled motive power batteries but the addition of up to 0.25% silver to the ternary alloys gave adequate creep and stress corrosion characteristics for this application. Ternary alloys containing 1–2% tin suffered from severe intergranular corrosion the effects of which could be overcome to some extent either by grain-refining the alloys with cerium mischmetal or by producing a fine-grained alloy grid by wrought techniques. Alloys which could be considered for battery application were lead-0.1% strontium for standby batteries, lead-0.5% tin-0.1% strontium for automotive batteries and lead-0.5% tin-0.01–0.25% silver-0.1% strontium for special motive power batteries if the cost could be afforded. A small addition of aluminium protected all the alloys from loss of alloying constituents in the molten state by oxidation.