Reaction Mechanisms of Ta-Substituted Cubic Li7La3Zr2O12 with Solvents During Storage.

The reactivity of garnet solid electrolytes toward humid air hinders their practical application despite their attractive, superior properties such as high Li+ conductivity and wide electrochemical window. Sealing garnets with organic solvents can not only prevent them from reacting with humid air but also render them compatible with other processing technologies. Therefore, the chemical and structural stability of garnets in organic solvents must be studied. In this study, we selected several commonly used organic solvents with different representative functional groups to investigate their stability with garnets and reaction mechanisms. The experiments and theoretical calculations revealed that all of the solvents reacted with garnets through Li-H exchange, and solvent acidity determined the reaction strength. Furthermore, the solvent acidity was closely correlated to the functional groups connected to H atoms, which can affect charge distribution. Solvents or the tautomer of the solvents with hydroxyl groups such as alcohol, acetone, and N-methyl pyrrolidone, which are relatively more acidic, can lead to a violent reaction with changes in the lattice parameters of garnets. Ether compounds and saturated aliphatic hydrocarbons with relatively low acidity are highly stable against garnets. The proposed reaction mechanisms and rules may help in selecting appropriate solvents for different applications of garnets.

Interfaces Between Cathode and Electrolyte in Solid State Lithium Batteries: Challenges and Perspectives.

Solid state lithium batteries are widely accepted as promising candidates for next generation of various energy storage devices with the probability to realize improved energy density and superior safety performances. However, the interface between electrode and solid electrolyte remain a key issue that hinders practical development of solid state lithium batteries. In this review, we specifically focus on the interface between solid electrolytes and prevailing cathodes. The basic principles of interface layer formation are summarized and three kinds of interface layers can be categorized. For typical solid state lithium batteries, a most common and daunting challenge is to achieve and sustain intimate solid-solid contact. Meanwhile, different specific issues occur on various types of solid electrolytes, depending on the intrinsic properties of adjacent solid components. Our discussion mostly involves following electrolytes, including solid polymer electrolyte, inorganic solid oxide and sulfide electrolytes as well as composite electrolytes. The effective strategies to overcome the interface instabilities are also summarized. In order to clarify interfacial behaviors fundamentally, advanced characterization techniques with time, and atomic-scale resolution are required to gain more insights from different perspectives. And recent progresses achieved from advanced characterization are also reviewed here. We highlight that the cooperative characterization of diverse advanced characterization techniques is necessary to gain the final clarification of interface behavior, and stress that the combination of diverse interfacial modification strategies is required to build up decent cathode-electrolyte interface for superior solid state lithium batteries.