Abstract
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.
Highlights
In the last two decades, various approaches have been proposed to improve the electrochemical properties of hydrogen storage alloys (HSAs), such as composition optimization[13], surface modification[14,15], preparation techniques modification[16], processing methods optimization[17] etc
The HSAs/NPNi hybrid electrode pellets were fabricated with a facile procedure, which involves hydrothermal synthesis of Ni(OH)[2], integration of Ni(OH)[2] with the master alloy (LaCe)0.9Y0.1Ni3.7Co0.75(MnAl)0.65, thermal reduction of Ni(OH)[2] by annealing treatment of the composites under an Ar/H2 atmosphere, and cold pressing the mixture of as-prepared composites and carbonyl nickel powders (Fig. 1a,b)
It is found that the peaks of Ni phase are broadened, which is attributed to the formation of nanoscale polycrystals [NPNi as demonstrated by scanning electron microscope (SEM) and transmission electron microscope (TEM) images below] during the annealing treatment[42]
Summary
In the last two decades, various approaches have been proposed to improve the electrochemical properties of HSAs, such as composition optimization[13], surface modification[14,15], preparation techniques modification[16], processing methods optimization[17] etc. Nanoporous metals have unique porous structures with large surface/volume ratio They could be used to (i) increase the electrochemical active area and to improve electrochemical reaction kinetics; and (ii) decrease the internal resistance and polarization and to enhance the conductivity of a metallic hydride electrode. The major aim of this work is to develop a new type of hybrid electrode (HSAs/NPNi) by incorporating HSAs powders with a current collector of three-dimensional bicontinuous nanoporous Ni for applications in Ni-MH batteries Such a composite shows excellent HRD performance where its discharge capacity is 2.4 times that of the bare HSAs at a discharge current density of 3000 mA g−1. It is found that the NPNi introduced into the composite decreases RC and RCT, and accelerates the diffusion rate of hydrogen atoms in HSAs. The findings in this work provide a new strategy to improve the HRD performance of Ni-MH batteries, which can be utilized to design other electrode materials
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