For lithium-selenium batteries, commercial applications are hindered by the inferior electrical conductivity of selenium and the low utilization ratio of the active selenium. Here, we report a new baked-in-salt approach to enable Se to better infiltrate into metal-complex-derived porous carbon (Se/MnMC-B). The approach uses the confined, narrow space that is sandwiched between two compact NaCl solid disks, thus avoiding the need for protection with argon or a vacuum environment during processing. The electrochemical properties for both lithium and sodium storage of our Se/MnMC-B cathode were found to be outstanding. For lithium storage, the Se/MnMC-B cathode (with 72% selenium loading) exhibited a capacity of 580 mA h g(-1) after 1000 cycles at 1 C, and an excellent rate capability was achieved at 20 C and 510 mA h g(-1). For sodium storage, a specific capacity of 535 mA h g(-1) was achieved at 0.1 C after 150 cycles. These results demonstrate the potential of this approach as a new effective general synthesis method for confining other low melting point materials into a porous carbon matrix.