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The phase diagram of the Gd-Ni-V ternary system at 500 888888 , the phase structure and electrochemical performance of V2.1TiNi0.4Gdx（x=0-0.09） alloys were investigated systematically by X-ray diffraction （XRD）, differential thermal analysis （DTA）, scanning electron microscopy （SEM） techniques and electrochemical measurements in this paper.The results of investigation and analysing of the ternary phase diagram of the Gd-Ni-V alloy system were presented. It consists of 14 single-phase regions, 25 two-phase regions and 12 three-phase regions. The 14 single-phase regions are:α（Gd）,β（Gd3Ni）,γ（GdNi）,δ（GdNi2）,ε（GdNi3）,ζ（Gd2Ni7）,η（GdNi5）,θ（Gd2Ni+（17））,κ（Ni3V）,λ（Ni2V）,ι（Ni）,μ（Ni2V3）,μ（NiV3）,ω（V）. The 25 two-phase regions are:α+β,β+γ,γ+δ,δ+ε,ε+ζ,ζ+η,η+θ,θ+ι,ι+κ,κ+λ,λ+μ,μ+ν,ν+ω,α+ω,β+ω,γ+ω,γ+ν,γ+μ,δ+μ,ε+μ,ε+λ,ε+κ,ζ+κ,η+κ,θ+κ. The 12 three-phase regions are:α+β+ω,β+γ+ω,γ+ν+ω,γ+μ+ν,γ+δ+μ,δ+ε+μ,ε+λ+μ,ε+λ+κ,ε+κ+ζ,ζ+κ+η,κ+θ+θ,θ+κ+ι. The maximum solid solubility of V in GdNi5, GdNi2 and Gd2Ni17, is about 3 at.%, 2.5 at.% and 3 at.%V, respectively. The maximum solid solubility of Gd in Ni, Ni3V, Ni2V, Ni2V3, NiV3 and V, is about less than I at.% Gd.The study on the microstructure and electrochemical properties of V2.1TiNi0.4Gdx （x=0-0.09） alloys shows that all alloys consist of a V-based solid solution main phase with a bcc structure and a secondary phase. For the alloy with x≤0.03, the secondary phase is the TiNi-based phase. However, the secondary phase in the alloy changes into the GdNi5 phase as x>0.03. And the lattice constants of the main phase expand with the increase of Gd content. The addition of Gd leads to a difficult activation, a lower maximum diacharge capacities and a depressed high-rate dischargeability comparing with V2.1TiNi0.4 alloy. However, when the Gd content reached 0.05, the cycling stability is improved significantly and its capacity retention after 30 charging/discharging is 24.67%.
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