Amorphous Dual-Layer Coating: Enabling High Li-Ion Conductivity of Non-Sintered Garnet-Type Solid Electrolyte

Garnet-type oxide Li6.4La3Zr1.4Ta0.6O12 (LLZTO) has attracted considerable attention as a highly promising solid state electrolyte. However, its high ionic conductivity is achievable only after high temperature sintering (approximate to 1200 degrees C) to form dense pellets but with detrimental brittleness and poor contact with electrodes. Herein, a novel strategy to achieve high Li+ ion conductivity of LLZTO without sintering is demonstrated. This is realized by ball milling LLZTO together with LiBH4, which results in a LLZTO composite with unique amorphous dual coating: LiBO2 as the inner layer and LiBH4 as the outer layer. After cold pressing the LLZTO composite powders under 300 MPa to form electrolyte pellets, a high Li+ ion conductivity of 8.02 x 10(-5) S cm(-1) is obtained at 30 degrees C, which is four orders of magnitude higher than that of the non-sintered pristine LLZTO pellets (4.17 x 10(-9) S cm(-1)). The composite electrolyte displays an ultrahigh Li+ transference number of 0.9999 and enables symmetric Li-Li cells to be cycled for 1000 h at 60 degrees C and 300 h at 30 degrees C. The significant improvements are attributed to the continuous ionic conductive network among LLZTO particles facilitated by LiBH4 that is chemically compatible and electrochemically stable with Li metal electrode.

Automated summary

A novel strategy to achieve high Li+ ion conductivity of Garnet-type oxide Li6.4La3Zr1.4Ta0.6O12(LLZTO) without sintering is demonstrated by ball milling LLZTO together with LiBH4 to form a composite electrolyte with unique amorphous dual coating. The composite electrolyte displays an ultra-high Li+ transference number and enables long-term cycling of symmetric Li-Li cells.