[en] The stress change, Δσ, generated during lithium transport through the rf sputter-deposited Li_1-δCoO₂ film was exactly determined as a function of the lithium stoichiometry, (1 - δ), using a laser beam deflection method (LBDM) combined with cyclic voltammetry, galvanostatic intermittent titration technique and potentiostatic current transient technique. Tensile and compressive stresses were generated during the lithium intercalation and deintercalation, respectively. Δσ varied remarkably with (1 - δ) in the single-α-phase region as well as in the two-phase region, but it remained almost constant in the single-β-phase region. Δσ generated during a real potential step between an initial electrode potential and a final applied potential was uniquely specified by (1 - δ). The value of Δσ coincided well with that value derived from the Δσ versus (1 - δ) curve (stress transient) measured simultaneously along with the galvanostatic intermittent titration discharge curve. From the comparison between the values of Δσ measured experimentally and calculated theoretically, it was suggested that Δσ in the single-α-phase region and the two-phase region originate from the molar volume change of the α-phase and from the lattice parameter mismatch between the α-phase and β-phase, respectively