SEI-Coated Carbon Particles: Electrochemomechanical Fracture Mechanisms

By starting from fundamental physical principles, a generalized theoretical framework was developed to engineer the intercalation-induced mechanical degradation in SEI-coated carbon particles from the surrounding electrolyte in rechargeable lithium-ion batteries (LIBs). Six elemental regimes of fracture formation in spherical electrochemically active carbon particles of radius, r p , coated with an SEI layer of thickness, delta MUCH LESS-THAN r p , have been identified: The pristine regime, the SEI debonding regime, the SEI surface flaw regime, the surface carbon flaw regime (delithiation), the internal circular carbon flaw regime (lithiation), and the carbon exfoliation regime (lithiation); as well as four combined regimes during delithiation and four combined regimes during lithiation. Results are summarized in terms of C-Rate versus particle size, degradation maps, to identify LIB operation conditions where the performance can be optimized, while suppressing the decrepitation of the SEI-coated carbon particle system. Improved porous electrode layers that deliver longer battery life are possible by selecting electrolytes that considering the design of SEI-coated carbon particles of tailored elastic stiffness and critical stress intensity factor, so that they are safe from developing a chemomechanically induced flaw, exfoliation, or carbon re-forming, during both lithiation or delithiation in the 1 to 10 mu m size particle, and C-Rates < 1 C.