Critical roles of microstructure and interphase on the stability of microsized germanium anode

Abstract Creating a certain degree of porosity is a widely adopted strategy in maintaining the cyclic stability of alloy anodes in Li-ion batteries (LIBs). The free space provided by the nanopores enables to partly alleviate the large strains during lithiation for increasing structural integrity. Instead of fabricating a nanostructured electrode with pre-designed pores, nanopores are in-situ created during lithiation/de-lithiation of Ge electrodes, enabling the direct utilization of microsized Ge particles. Assisting by scanning transmission electron microscopy (STEM), we systematically explore the microstructure evolution of Ge particles during cycling. It reveals the vital role of pore development, which is closely related to the solid electrolyte interphase (SEI), in maintaining the stable cyclic performance. The nanostructure of SEI is further resolved by cryo-transmission electron microscopy (cryo-TEM), which suggests that the amorphous inorganic component is essential to the fast kinetics for inducing sufficient porosity. Compared to the classic lithium hexafluorophosphate (LiPF6) salt in the electrolyte, the lithium difluoro(oxalato)borate (LiDFOB) shows great advantages in constructing a highly ionic conductive SEI layer for facilitating the nanopore growth. This work demonstrates the critical roles of interphase and the resulted microstructure in stabilizing the alloy microparticles.