The formation of dendrites is a critical drawback for the utilization of Li and other metals in secondary batteries. These emorphous crystals can pierce into the polymer electrolyte and short the cell. Therefore the design/selection criterion requires the dendrite-polymer mechanical compatibility. Hereby we characterize the dendrites morphological evolution based on the intrinsic material property (surface energy). Consequently, we perform force field calculations on the created microstructures to extract the effective mechanical properties such as elastic modulus and poission ratio. In particular, our study is also useful for understanding the mechanics of amorphous structures.