No abstract

The application of lithium metal as a negative electrode in all-solid-state batteries shows promise for optimizing battery safety and energy density. However, further development relies on a detailed understanding of the chemo-mechanical issues at the interface between the lithium metal and solid electrolyte (SE). In this study, crack formation inside the sulfide SE (Li3PS4: LPS) layers during battery operation was visualized using in situ X-ray computed tomography (X-ray CT). Moreover, the degradation mechanism that causes short-circuiting was proposed based on a combination of the X-ray CT results and scanning electron microscopy images after short-circuiting. The primary cause of short-circuiting was a chemical reaction in which LPS was reduced at the lithium interface. The LPS expanded during decomposition, thereby forming small cracks. Lithium penetrated the small cracks to form new interfaces with fresh LPS on the interior of the LPS layers. This combination of reduction–expansion–cracking of LPS was repeated at these new interfaces. Lithium clusters eventually formed, thereby generating large cracks due to stress concentration. Lithium penetrated these large cracks easily, finally causing short-circuiting. Therefore, preventing the reduction reaction at the interface between the SE and lithium metal is effective in suppressing degradation. In fact, LPS-LiI electrolytes, which are highly stable to reduction, were demonstrated to prevent the repeated degradation mechanism. These findings will promote all-solid-state lithium-metal battery development by providing valuable insight into the design of the interface between SEs and lithium, where the selection of a suitable SE is vital.

Li metal is very attractive as a negative electrode material for high-energy-density all-solid-state batteries owing to its high specific capacity and low electrochemical potential. However, short-circuiting of batteries upon formation of Li dendrites is a serious issue that hinders its successful practical application. An advantage of all-solid-state batteries is their inherent safety at high temperatures. In this study, the high-temperature performance of all-solid-state Li-metal batteries containing sulfide-glass electrolytes was investigated. Symmetric cells with Li 3 PS 4 electrolytes exhibited better Li dissolution-deposition performance at 100 • C than at 25 • C. In addition, inserting Au thin films at the Li/Li 3 PS 4 interface enabled stable operation of the symmetric cells at high current density (1.3 mA cm −2 ) and large areal capacity (6.5 mAh cm −2 ) without short-circuiting. All-solid-state Li-metal batteries with Au thin films (Li/Au/Li 3 PS 4 /LiNi 1/3 Mn 1/3 Co 1/3 O 2 ) exhibited high rate performance at 2.4 mA cm −2 and long lives of over 200 cycles at 100 • C. The dissolution of the Au thin films into the Li metal is a possible reason for the enhanced electrochemical performance. These results indicate that interface modification and optimizing operating temperature are promising strategies to achieve all-solid-state batteries with high energy densities.

All-solid-state batteries (ASSBs) are potentially safe energy storage devices. The 90Li3BO3·10Li2SO4 (mol %) glass-ceramic is one of the promising oxide electrolytes due to its high ductility and ionic conductivity. Utilization of Li metal negative electrode enhances the energy density of ASSBs. Herein, the high electrochemical stability of the 90Li3BO3·10Li2SO4 electrolyte against Li metal negative electrode was demonstrated. The symmetric cells using a dense electrolyte body with relative density of 99% synthesized by the hot-pressing technique showed excellent cycle performance for the Li dissolution and deposition reactions. Finally, the all-solid-state (Li/80LiNi0.5Mn0.3Co0.2O2·20Li2SO4) full cell operated as a secondary battery at 100 °C.

The electronic and ionic conductivities of the interphase that forms between Li metal and solid electrolytes (SEs) are key parameters in determining battery cell performance. In this study, we evaluated the effect of the interphase on Li dissolution/deposition behaviors. The reduction of Li2S–P2S5 glasses to Li2S and Li3P by Li metal occurred at the Li/SE interface. The Li dissolution/deposition performance at 100 °C was improved by increasing the Li3P content in the interphase, and the cell with a Li4P2S6 glass electrolyte functioned without short-circuiting at a current density of 1.3 mA cm−2. The ionic conductivity of the Li/SE interphase was evaluated by preparing Li–SE compounds using mechanochemical processing. The milled sample prepared from Li metal and Li4P2S6 glass showed a one order of magnitude higher conductivity of 10−4 S cm−1 at 100 °C than that of the Li–Li3PS4 milled sample, indicating that the ionic conductivity of the interphase formed at the Li/SE interface is an important factor for improving the short-circuiting tolerance of all-solid-state Li-metal batteries.