In this paper, we propose a novel in-situ technique to characterize electrochemical processes in lithium ion batteries (LIB) by monitoring the frequency shift of microcan-tilevers. The fabricated cantilevers coated with battery electrodes were tested in a home made liquid cell, and their mass changes associated with SEI formation and lithium insertion were monitored by a laser vibrometer. The resonant frequency of cantilevers before cycling was 18,400Hz and shifted to 16,800Hz after lithiation. The initial mass of the cantilever before cycling was measured 45.35 μg. Therefore, the lithium stored in the silicon anode during the first lithiation was estimated 7.89μg.