First-principles calculations were performed to investigate the electrochemical stability of lithium solid electrolyte materials in all-solid-state Li-ion batteries. The common solid electrolytes were found to have a limited electrochemical window. Our results suggest that the outstanding stability of the solid electrolyte materials is not thermodynamically intrinsic but is originated from kinetic stabilizations. The sluggish kinetics of the decomposition reactions cause a high overpotential leading to a nominally wide electrochemical window observed in many experiments. The decomposition products, similar to the solid-electrolyte-interphases, mitigate the extreme chemical potential from the electrodes and protect the solid electrolyte from further decompositions. With the aid of the first-principles calculations, we revealed the passivation mechanism of these decomposition interphases and quantified the extensions of the electrochemical window from the interphases. We also found that the artificial coating layers applied at the solid electrolyte and electrode interfaces have a similar effect of passivating the solid electrolyte. Our newly gained understanding provided general principles for developing solid electrolyte materials with enhanced stability and for engineering interfaces in all-solid-state Li-ion batteries.

This study provides the understanding and design strategy of solid electrolyte–electrode interfaces to improve electrochemical performance of all-solid-state Li-ion batteries.

Super-ionic conductor materials have great potential to enable novel technologies in energy storage and conversion. However, it is not yet understood why only a few materials can deliver exceptionally higher ionic conductivity than typical solids or how one can design fast ion conductors following simple principles. Using ab initio modelling, here we show that fast diffusion in super-ionic conductors does not occur through isolated ion hopping as is typical in solids, but instead proceeds through concerted migrations of multiple ions with low energy barriers. Furthermore, we elucidate that the low energy barriers of the concerted ionic diffusion are a result of unique mobile ion configurations and strong mobile ion interactions in super-ionic conductors. Our results provide a general framework and universal strategy to design solid materials with fast ionic diffusion.

electrochemical stability window, and (3) chemical compatibility with the anode and cathode. In the past few years, major advances have been achieved in increasing the Li ionic conductivity of the solid electrolytes. The state-of-the-art solid electrolyte materials, such as Li-garnet Li 7 La 3 Zr 2 O 12 (LLZO) and Li 10 GeP 2 S 12 (LGPS) have achieved an ionic conductivity of 10 −3 to 10 −2 S cm −1 , [ 1,2 ] which are comparable to commercial organic liquid electrolytes. The high ionic conductivity in solid electrolytes has ignited the research of all-solid-state Li-ion batteries. After achieving adequate Li ionic conductivity in the solid electrolyte materials, current research efforts turned to enhancing the electrochemical stability of the solid electrolytes and chemical compatibility between the solid electrolytes and electrodes, so that Li metal anode and high voltage cathode materials can achieve higher energy density in all-solid-state Li-ion batteries. To enable the highest voltage output of the solid-state battery by coupling a lithium metal anode with a high voltage cathode material, a very wide electrochemical stability window (0.0-5.0 V) is desired for an ideal solid electrolyte. The electrochemical stability window of solid electrolyte was typically obtained by applying the linear polarization on the Li/solid electrolyte/ inert metal (e.g., Pt) semiblocking electrode. Tested by this method, very wide electrochemical stability windows of 0.0 to 5.0 V were reported for both LGPS and LLZO. [ 2,3 ] However, the electrochemical performances of the bulk-type all-solid-state battery batteries assembled with these solid electrolytes [ 2,4 ] are far worse than the liquid-electrolyte based batteries even though the solid electrolyte has a comparable ionic conductivity to the liquid electrolyte. The high interfacial resistance is often blamed as the main limiting factor for the performance of the solid state battery. [ 5 ] The origin of the interfacial resistance, though still not fully understood, is often attributed to the poor physical interfacial contact, the formation of space charge layers, [ 6 ] and/or the formation of interphase layers due to the chemical reactions between the electrolyte and electrode. [ 7 ] Although a variety of interfacial processing techniques, such as dynamic pressing, [ 8 ] nanosizing, [ 9 ] cosintering, [ 10 ] screen printing, [ 11 ] surface coatings [ 12,13 ] have been attempted to engineer the interfaces between the electrodes and electrolytes, the performances of the solid-state battery are still much lower than the liquidelectrolyte based batteries. The limited electrochemical stabilityThe electrochemical stability window of solid electrolyte is overestimated by the conventional experimental method using a Li/electrolyte/inert metal semiblocking electrode because of the limited contact area between solid electrolyte and inert metal. Since the battery is cycled in the overestimated stability window, the decomposition of the solid electrolyte at the interfaces occurs but has be...

Strategy to change the wettability of the solid-state electrolyte against Li and reduce interface resistance.