Revealing crack-healing mechanism of NCM composite cathode for sustainable cyclability of sulfide-based solid-state batteries

Understanding the interfacial phenomena in composite cathodes is essential for achieving excellent cycle performance in all-solid-state batteries (ASSBs), which exhibit high safety performance and energy densities. Herein, we report on the spontaneous crack-healing mechanism in a composite cathode consisting of LiNi0.7Co0.15Mn0.15O2 (NCM) and Li6PS5Cl0.5Br0.5. This cathode exhibited excellent cycle performance during cell tests owing to the stack pressure, which enhanced the ionic and electrical transfers at the material interfaces by remarkably reducing macrocracks between the materials in the composite cathode. Apart from the mechanical effects, a cathode electrolyte interface (CEI) composed of carbon, sulfur, bromine, and oxygen was formed at the interface of NCM and the binder, as decomposing the SSE adjacent to the NCM particles during electrochemical cycles. By contrast, the migration of sulfur and carbon species filled the microcracks between the NCM primary particles inside the secondary particles, thus improving the crucial crack issue of ASSBs. Furthermore, sufficient stack pressure and binding materials played a key role in maintaining the conductive pathway of the cathode by contributing to mechanical crack healing and chemical CEI formation. In this manner, achieving a better understanding of the healing behavior of microcracks and macrocracks in composite cathodes can facilitate the development of ASSBs with a long cycle performance.