In this study, we compare the performance of two phases of MoS2 monolayers: 1T' and 2H, about their ability to adsorb lithium and sodium ions. Employing the density functional theory and molecular dynamics, we include the ion concentration to analyze the electronic structure, ion kinetics, and battery performance. The pristine 2H-MoS2 monolayer is the ground state. However, the charge transfer effects above a critical ion concentration yield a stability change, where the 1T'-MoS2 monolayer with adsorbed ions becomes more stable than the 2H counterpart. The diffusion of ions onto the 1T' monolayer is anisotropic, being more efficient at ion adsorption than the 2H phase. Finally, we calculate the open circuit voltage and specific capacity, confirming that the 1T'-MoS2 phase has great potential for developing lithium/sodium ion batteries. © 2023 Elsevier B.V.