Lithium batteries are becoming ubiquitous in portable and transportation energy storage systems. Unfortunately, severe degradation occurs and results in a solid electrolyte interphase (SEI) between the electrode and the electrolyte. On the other hand, the SEI can prevent the exfoliation of electrode materials and inhibit further electrolyte decomposition. It is believed that SEI cracks due to either of its unstable structure or the cracking of electrode during electrochemical cycling. However, our understanding of the fracture in the SEI remains tenuous due to the complexity of experimentation as well as numerically tracking the interface motion explicitly upon cycling. The phase-field method that can handle complex interfacial evolution without tracking the interface motion explicitly upon cycling. In addition, the phase-field method integrates morphological with electrochemical analysis as well as shed light on mechanical reliability. Thus, we adopt phase-field method to investigate the cracking of the SEI in Lithium batteries. Without loss of generality, we propose a nanoparticle agglomerate structure (i.e., primary particles and binder) to represent a secondary particle wildly adopted by different lithium batteries. Two types of SEI are considered herein, the compact layer and the porous layer. The location where has the maximum lithium concentration gradient will be picked up to investigate the crack propagation in the compact layer and the porous layer of SEI. The flux vector of lithium diffusion is assumed to be proportional to the gradient of the chemical potential. The main capacity loss due to the SEI fracture will also be estimated in this work.