The high-rate charge/discharge performance of L3DC alloy is improved by heat treatment in pure Ar or 10% H2/Ar atmosphere at 300°C and 400°C. L3DC, a commercially available LaNi5-type alloy, is used as the negative electrode for high-power nickel–metal hydride batteries. The structural modification, morphology, and surface composition of the heat-treated alloys are examined through X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray energy dispersive spectrometry (EDS). Electrochemical performance of the alloy is also tested with an electrochemical workstation and a charge/discharge tester. Results show that the low- and room-temperature rate discharge performance and high-temperature rate charge performance of the alloy can be improved by heat treatment in 10% H2/Ar atmosphere. Moreover, the low- and room-temperature rate charge performance and high-temperature rate discharge performance can only be enhanced by heat treatment in pure Ar atmosphere. Heat treatment can affect not only the speed of proton transport in the solid phase, but also the hydrogen reaction on the alloy surface.