| 초록 |
The lithium ion transport through porous LiCoO2 electrode in 1M LiClO4 propylene carbonate(PC) solution was investigated by using cyclic voltammetry, galvanostatic intermittent charge-discharge experiment and potentiostatic current transient technique. The apparent chemical diffusivities of lithium ion were determined as a function of lithium charging potential during the lithium intercalation and deintercalation. In the lithium charging potential range not less than the plateau potential with intensive intercalation/deintercalation, both the cathodic and anodic current transient curves obtained from the porous oxide electrode are divided into two stages. The first stage is due to the diffusion of lithium ion through the oxide electrode and the second stage is associated with the accumulation of lithium ion at the center of the oxide particle. During the lithium intercalation, the time to the first to second stage transition decreased with decreasing lithium charging potential. This suggests that the lithium ion transport during the intercalation proceeds not by the diffusion in a single phase, but by the diffusion-controlled movement of boundary between a concentrated phase and a dilute phase. The apparent chemical diffusivity of lithium ion in the porous oxide electrode was determined to be 10-9 to 10-8 cm2 s-1 at room temperature. During the lithium deintercalation, the apparent chemical diffusivity decreased with decreasing lithium charging potential. The reduced diffusivity value is attributable to a raised lithium content in the oxide electrode. By contrast, during the lithium intercalation the apparent chemical diffusivity increased with decreasing lithium charging potential. The exact opposite dependencies of lithium ion diffusivity on lithium charging potential during the intercalation and deintercalation were discussed in terms of the phase boundary movement which is caused by the intercalation-induced stress gradient developed across phase boundary.
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