The Influence of Surface Chemistry on Critical Current Density for Garnet Electrolyte

Abstract

Garnet‐based solid state lithium batteries have attracted a lot of attention due to their potential advantages in safety and energy density. However, the high electrode–electrolyte interfacial resistance and low critical current density (CCD) related with lithium dendrite penetration have seriously hindered their further development and practical application. Here, for garnet‐type solid electrolyte, the surface Li2CO3, interlayer species, lithium wettability, interfacial impedance, and CCD are systematically investigated. It turns out that Li2CO3‐free garnet electrolyte is intrinsically lithiophilic, and the interfacial impedance is mainly affected by the amount of surface Li2CO3. In addition, the CCD values are manipulated by the interfacial impedance rather than the apparent Li wettability. This study provides a comprehensive understanding about the interrelationships among surface chemistry, lithium wettability, interfacial impedance, and critical current density for garnet‐type solid electrolytes.

Temperature and Pressure Effects on Unrecoverable Voids in Li Metal Solid-State Batteries

“…Comparison of room-temperature (20–25 °C) critical current densities (CCD) reported for Li metal and LLZO. “Bare LLZO” represents CCD of Li–LLZO without any interlayer or surface alterations. − “Interlayers/Alloys” represents CCD, where a thin interlayer or alloying mechanism was used to increase the wettability. − “Interlayers/Alloys” represents CCD where the surface structure of LLZO was modified by patterning , (c).…”

Molten Salt Driven Conversion Reaction Enabling Lithiophilic and Air‐Stable Garnet Surface for Solid‐State Lithium Batteries

“…The detection of Li 2 CO 3 characteristic peak at ≈21.4° in XRD pattern, together with CO 3 2− vibration peak at 1089 cm −1 in Raman spectrum of fresh LLZTO indicates the formation of surface contaminants even during the preparation of garnet pellets. [53,54] The amount of surface Li 2 CO 3 continuously increases with increasing exposure time to air. In order to remove the surface contaminants, the LLZTO was treated by molten NH 4 H 2 PO 4 salt at 185 °C based on its conversion reaction with Li 2 CO 3 as shown in Equation 1. )…”

Revealing the Influence of Surface Microstructure on Li Wettability and Interfacial Ionic Transportation for Garnet‐Type Electrolytes

“…Particularly, the cubic garnet-type Li 7 La 3 Zr 2 O 12 (LLZO) is considered an attractive option because of its excellent stability against lithium metal, wide electrochemical window, and high ion conductivity (≈1 mS cm −1 ) at room temperature. [16,17] However, the poor chemical stability of LLZO causes the formation of lithiophobic species (e.g., Li 2 CO 3 and LiOH) on its surface upon contact with water and air, [18][19][20] which compromises the electrodeelectrolyte contact and leads to high interfacial impedance (R int ) and the consequent low critical current density (CCD). [9,[21][22][23] In addition to that, the poor contact between LLZO and lithium metal will also cause inhomogeneous lithium-ion flux through the interface, triggering unfavorable dendrites growth/propagation, especially at locations such as defects and cracks.…”