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

Abstract

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.

Influence of dry‐ and wet‐milled LLZTO particles on the sintered pellets

“…For the WM‐powder, the peaks corresponding to Li 2 CO 3 and LiOH ⋅H 2 O get much stronger; the new and broad peak for υ (C–H) at 2800 cm −1 can be attributed to the residual IPA solvent appears. This implies that the O 2− on the LLZTO lattice surface tends to attract the H on –OH in the IPA solvent 2 . Obviously, the LLZTO powder will have more side reactions during wet milling than dry milling.…”

“…Lithium‐ion batteries (LIBs) have been widely used in portable electronics and are transitioning to new applications in electric vehicles and stationary energy storage systems 1 . However, safety concerns and demands for high energy density require a revolution in LIBs 2 . As a result, extensive research has been conducted on all‐solid‐state LIBs (ASSLIBs) in recent years with the expectation to develop intrinsically safe batteries with high energy density.…”

“…Grinding solid electrolyte powder with organic solvents, that is, wet grinding, may have the following problems: (1) Most organic solvents have side reactions with LLZO. The compounds with acidic hydroxyl groups such as isopropanol (IPA) and N ‐methyl pyrrolidone (NMP) may react with the basic LLZO and considerably change the LLZO lattice parameters 2 . (2) The organic solvents are typically toxic and flammable, harmful to the operators, and unfriendly to the environment 8–10 .…”

Ion transport in composite polymer electrolytes

“…have some significant advantages, such as high ionic conductivity (10 À4 to 10 À2 S cm À1 ), high ionic transference number (B1), wide electrochemical window (46 V), excellent thermal stability and high mechanical strength. [13][14][15][16][17] However, high impedance and polarization during cycling, originating from poor interfacial contacts between electrolytes State Key Laboratory of Material Processing and Die & Mould Technology, School of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, P. R. China. E-mail: xguo@hust.edu.cn…”

“…have some significant advantages, such as high ionic conductivity (10 −4 to 10 −2 S cm −1 ), high ionic transference number (∼1), wide electrochemical window (>6 V), excellent thermal stability and high mechanical strength. 13–17 However, high impedance and polarization during cycling, originating from poor interfacial contacts between electrolytes and electrodes, seriously limit their applications. 18,19 In contrast, solid polymer electrolytes have the advantages of high flexibility, remarkable processability, and favorable interfacial contacts with electrodes, therefore, are emerging as the most promising candidates for solid-state batteries.…”