We report in situ measurements of stress evolution in a silicon thin-filmelectrode during electrochemical lithiation and delithiation by using theMulti-beam Optical Sensor (MOS) technique. Upon lithiation, due to substrateconstraint, the silicon electrode initially undergoes elastic deformation,resulting in rapid rise of compressive stress. The electrode begins to deformplastically at a compressive stress of ca. -1.75 GPa; subsequent lithiationresults in continued plastic strain, dissipating mechanical energy. Upondelithiation, the electrode first undergoes elastic straining in the oppositedirection, leading to a tensile stress of ca. 1 GPa; subsequently, it deformsplastically during the rest of delithiation. The plastic flow stress evolvescontinuously with lithium concentration. Thus, mechanical energy is dissipatedin plastic deformation during both lithiation and delithiation, and it can becalculated from the stress measurements; we show that it is comparable to thepolarization loss. Upon current interrupt, both the film stress and theelectrode potential relax with similar time-constants, suggesting that stresscontributes significantly to the chemical potential of lithiated-silicon.
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