➀ Argonne National Laboratory has identified a failure mode in sodium-ion batteries; ➁ The study focused on sodium-ion oxide cathodes made from transition-metal core-shell particles; ➂ The research revealed that cracks develop deep within the particles and not at the surface; ➃ The findings suggest that slow heating during the cathode synthesis process can prevent cracks, leading to cathode particles with no loss of storage capacity over 400 operating cycles.