Lithium-ion batteries (LIBs) have gained widespread popularity for energy storage systems due to their enhanced performance, extended cycle life and minimal self-discharge rates. Polycrystalline NMC particles are widely used active materials in high energy density LIBs for electric vehicle applications. They offer high specific capacity and low cost but despite these promising features, the service life of LIB system is considerably limited by the degradation of active material in positive electrode upon repeated charge-discharge cycles. Under typical operating conditions, Ni-rich NMC particles are susceptible to an accelerated degradation mechanism that can detrimentally affect the battery's long-term performance. Among these mechanisms, mechanical degradation stands out as an area that presents challenges and uncertainties. The polycrystalline NMC particle is composed of numerous primary active particles, and particle cracking or mechanical breakdown of active particle is a very likely degradation mechanism. The potential of computational simulations based on theoretical modeling to predict battery behavior is recognized. LIB modeling is a complex, multi-scale, and multi-physics problem, encompassing mechanical, electrochemical, and thermal phenomena with diverse effects and interactions occurring across various length scales. This study aims to develop a 3D numerical model that integrates both mechanical and electrochemical processes within LIBs. The model incorporates a phase field damage approach to simulate crack growth and mechanical failure of active materials, enabling the investigation of their impact on battery performance. Exploring various factors that contribute to the degradation process offers opportunities to design advanced electrodes for high-performance next generation lithium-ion batteries.