In-Situ Formed Polymer Coatings in Ball-Milling: The Key to Ultra-Long Cycling Stability of Non-Sintered Garnet-Type Llzto Solid Electrolyte

Abstract

The garnet-type Li6.4La3Zr1.4Ta0.6O12 (LLZTO) solid electrolyte is promising in the fabrication of the all-solid-state lithium metal battery (LMB) for its high intrinsic lithium ionic conductivity and electrochemical stability. However, the high interfacial resistance induced by the surface contamination layer and poor interfacial contact severely hinders its practical applications. Wet ball-milling in the presence of polyacrylonitrile (PAN) was found to be extremely effective in preparation for highly conductive LLZTO. The work employs four typical polymers (PMMA, PEO, PVP, and PS) in wet ball-milling jars to prepare in-situ polymer-coated LLZTO ceramic particles. Effective lithium-ion migration channels between LLZTO particles without sintering can be constructed successfully, significantly enhancing electrochemical performances. The lithium symmetric cell exhibits long-term cycling stability of over 2000 h at 65 °C and 0.1 mA cm−2. The all-solid-state LMB assembled using the LiFePO4 cathode and the solid electrolyte made from in-situ polymer-coated LLZTO particles demonstrates a discharge capacity of 120 mAh g−1 with a capacity retention of more than 95% after 200 charge/discharge cycles at 65 °C and 0.5 C. The key mechanism underlying the much-improved performance could be the in-situ formation of polymeric protective coatings on the LLZTO fresh surfaces during the wet ball-milling process. The polymer coating prevents the LLZTO from contaminating and fills the gaps between LLZTO particles, thus facilitating lithium-ion migration.

Keywords: LLZTO, solid-state electrolyte, low interfacial resistance, polymer coating, ball-milling