Operando Nanomechanical Mapping of Amorphous Silicon Thin Film Electrodes in All-Solid-State Lithium-Ion Battery Configuration during Electrochemical Lithiation and Delithiation.

An operando bimodal atomic force microscopy system was constructed to perform nanomechanical mapping of an amorphous Si thin film electrode deposited on a Li6.6La3Zr1.6Ta0.4O12 solid electrolyte sheet during electrochemical lithiation/delithiation. The evolution of Young's modulus maps of the Si electrode was successfully tracked as a function of apparent Li content x in lithium silicide (LixSi) simultaneously with real-time surface topography observation. At the initial stage of lithiation, the average modulus steeply decreased due to the generation of LixSi from intrinsic Si, followed by a moderate modulus reduction until the electrode capacity reached 3300 mAh g-1 (Li content x = 3.46). In the following delithiation, the gradual recovery of the average modulus of LixSi was observed up to 1467 mAh g-1 (Li content x = 1.54) at which delithiation stopped due to the significant volume change induced by phase transformation of LixSi.

Deciphering the Dynamic Processes at the Electrode-Electrolyte Interface for Stable Deposition of Lithium.

Realization of lithium-metal (Li) batteries is plagued by the dendritic deposition of Li leading to internal short-circuit and low Coulombic efficiency. The Li-deposition process largely depends on the liquid electrolyte that reacts with the Li metal and forms a solid electrolyte interphase (SEI) layer with diverse chemical and physical properties. Moreover, the electrolyte possesses characteristic ion transport behaviors and directly affects the deposition kinetics at the electrode surface. As a result, the convolution of interfacial, ion transport, and kinetic effects of an electrolyte obscures the understanding of Li deposition in Li-metal batteries. Herein, the dynamic processes and the interfacial properties of Li-metal electrodes are precisely delineated in representative ether electrolytes. It is found that a combination of homogeneous SEI and slow deposition kinetics produces layer-by-layer epitaxial growth of Li. In contrast, the dendritic growth of Li is observed when the SEI is inhomogeneous and the reaction rate is fast. Nevertheless, it is shown that a homogeneous SEI is not a prerequisite in suppressing Li dendrites when the adverse effect of an unfavorable SEI can be subdued by proper kinetic tuning at the interface. Furthermore, an otherwise kinetically unstable electrolyte can also be made compatible with the Li-metal electrode when covered with a properly designed SEI. This delineation of the roles of SEI and deposition kinetics gives deep insight into designing efficient electrolytes in Li-metal batteries.