La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ (LSCF) is recognized as one of the most promising cathode materials for the highly-desired intermediate-temperature solid oxide fuel cell (IT-SOFC) technology. However, it is still challenged by polarization losses due to reduced operation temperatures. In this work, a series of Ba²⁺-doped La_0.6−xBa_xSr_0.4Co_0.2Fe_0.8O_3−δ (LBSCFx, x = 0.05, 0.10, 0.15, and 0.20) materials are successfully synthesized and their electrochemical performances are evaluated as a cathode for IT-SOFC technology. The study shows that, compared to the un-doped LSCF, the Ba²⁺-doped LBSCF possess higher electrical conductivities at 500–800 °C and display lower polarization resistances to oxygen adsorption/dissociation. As a result, the Ni-SDC|SDC|LBSCF0.20 cell (SDC = samarium-doped cerium, Sm_0.2Ce_0.8O_1.9) delivers a high maximum power density of 0.704 W/cm² at 750 °C, which is > 30% higher than the Ni-SDC|SDC|LSCF cell. This work reveals that Ba ²⁺-doping is effective in enhancing oxygen catalytic activity of LSCF-based cathode materials, demonstrating a new and commercial-feasible strategy in developing high performance cathode materials for the IT-SOFC technology.