To improve the electrochemical properties of AB₅-type hydrogen storage alloy used as negative electrodes of Ni-MH batteries, La_0.58Ce_0.20Zr_0.02Sm_0.2 (Ni_0.85Co_0.03Mn_0.05Al_0.07)_5+x (x=0, 0.10, 0.15, 0.30, 0.45) hydrogen storage alloys were prepared by medium-frequency induction vacuum melting method, and the effect of x value on the phase structure and electrochemical properties of hydrogen storage alloys was systematically investigated. The results show that hydrogen storage alloys with different x values are mainly composed of main LaNi₅ phase and Ni₂MnAl phase. As x increases from 0 to 0.45, the abundance of LaNi₅ phase first increases and then decreases; lattice parameter a decreases gradually; c first increases and then decreases; c/a ratio rises gradually; and cell volume presents a decreasing trend. The hydrogen desorption plateau pressures of alloy electrodes with x ranging from 0 to 0.45 meet the requirement of 0.01-0.5 MPa for negative electrode materials of automotive Ni-MH batteries. With the increase of x, the maximum discharge capacity C_max decreases sequentially, while the capacity retention rate S₁₀₀ increases first and then decreases. The alloy electrode with x=0.15 exhibits optimal comprehensive properties: C_max of 313.2 mAh/g, S₁₀₀ of 94.69%, and high-rate discharge ability HRD_{3 000} of 60.35% at discharge current density of 3 000 mA/g. The high-rate discharge performance of hydrogen storage alloy electrodes with different x values is determined by both charge transfer rate and hydrogen diffusion rate.