(An) investigation of intercalation-induced stresses generated during lithium transport through $Li_{1-δ}CoO_2$ film electrode by using a laser beam deflection method

Abstract

The present work explores the intercalation-induced stresses generated during lithium transport through sputter-deposited $Li_{1-＼delta}CoO_2$ film electrode by using a laser beam deflection method combined with galvanostatic intermittent titration technique, cyclic voltammetry and potentiostatic current transient technique. From the stress changes, Δσ, simultaneously recorded along with the galvanostatic intermittent titration charge/discharge curves and the cyclic voltammogram, it was noted that Δσ varied remarkably 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 during the lithium intercalation/deintercalation. From the comparison between the values of Δα measured experimentally and calculated theoretically, it was suggested that the origins of Δσ in the single-α-phase-region and two-phase-region are the molar volume contraction/expansion of the α-phase and the lattice parameter mismatch between the α-phase and β-phase, respectively. From Δσ simultaneously obtained along with the potentiostatic current transient, it was found that the value of Δσ due to the phase transformation was almost constant regardless of the applied potential step, and that it coincided well with the value of Δσ obtained from the Δσ vs. lithium stoichiometry curve in the two-phase-region. Furthermore, the value of Δσ decreased slightly with increasing number of cycle of the lithium intercalation/deintercalation. From the SEM micrograph of the surface morphology of the $Li_{1-＼delta}CoO_2$ film, it was noted that this stress relaxation causes the cracking of the Li_{1-＼delta}CoO_2$ film.