Assessing the roles of mechanical cracks in Ni-rich layered cathodes in the capacity decay of liquid and solid-state batteries

Abstract

Cracks are ubiquitous in Ni-rich layered cathodes upon cycling in liquid electrolyte-lithium-ion batteries (LELIBs); however, their roles in the capacity decay are unclear. Furthermore, how cracks affect the performance of all solid-state batteries (ASSBs) has not been explored yet. Herein, cracks are created by mechanical compression in the pristine single crystal LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811) and their roles in the capacity decay in solid-state batteries are asserted. These mechanically created fresh cracks are predominantly along the (003) planes with minor cracks along the planes slanted to the (003) planes, and both types of cracks contain little or no rock-salt phase, which is in sharp contrast to the chemomechanical cracks in NMC811 where rock-salt phase formation is ubiquitous. We reveal that mechanical cracks cause a significant initial capacity loss in ASSBs but little capacity decay during the subsequent cycling. In contrast, the capacity decay in LELIBs is principally governed by the rock salt phase and interfacial side reactions and thus does not result in an initial capacity loss, but a severe capacity decay during cycling.