Unraveling the mechanism of non-monotonic C-rate-dependent electrode particle fracture

Understanding C-rate-dependent fracture in electrode particles is a key challenge for high-performance lithium-ion batteries (LIBs). Contrary to the conventional understanding that higher C-rates exacerbate particle fracture, experimental observations reveal a non-monotonic relationship between particle fracture and discharge C-rates, with the most severe fracture occurring at intermediate C-rates. Herein, through theoretical analysis, we uncover that the underlying mechanism behind the aforementioned anomalous non-monotonic relationship arises from an intricate change in the crack driving force. The change is influenced by the non-uniform distribution of lithium ions at low C-rates and the state of charge (SOC) at high C-rates. Considering microstructural heterogeneous features of polycrystalline secondary particles, such as anisotropic expansion and diffusion of primary particles, elevated diffusivity and weak fracture resistance at grain boundaries, the ubiquity of this non-monotonic relationship is confirmed. Moreover, a novel electrode particle fracture phase diagram is proposed in terms of particle size and operating conditions, which highlights a crescent-shaped unsafe domain that should be avoided to preserve mechanical integrity. Our findings not only provide unique insights into C-rate-dependent electrode particle fracture but also offer design guidelines for LIBs with superior reversible, high-rate capability.