The Roles of Ni and Mn in the Thermal Stability of Lithium-Rich Manganese-Rich Oxide Cathode

摘要

The pursuit of high-energy-density lithium-ion batteries (LIBs) has broughtextensive research on the high-capacity lithium-rich manganese-rich oxidecathode (LRMO). However, practical applications of LRMO require a comprehensiveunderstanding of its thermal stability, which determines theboundary for the safe use of LIBs. Here, systematic investigations of thethermal stability of LRMO are carried out by using in situ X-ray diffractionand full-field transmission X-ray microscopy combined with X-ray absorptionnear edge structure. The roles of Ni and Mn in affecting the thermal stabilityof LRMO are uncovered. It is surprising that Ni, despite being in the minority,acts as a key factor that governs the onset temperature of thermal decomposition.Unlike in lithium nickel-cobalt-manganese oxide cathodes where ahigher content of Mn is believed to stabilize the structure with reduced heatrelease, in LRMO it causes more heat release which can be attributed to thelithium excess environment around Mn. In addition, it is revealed that theincomplete coverage of solid polymer electrolytes over the LRMO particlesurface may lead to the deterioration of thermal stability. These findingsprovide mechanistic insights into the thermal behavior of LRMO cathodesfor developing high-capacity cathodes with improved safety, particularly, forfuture applications in solid-state batteries.