Dendrite-free solid-state lithium batteries enabled by a fluorine doped Li7La3Zr2O12 composite electrolyte and LiAlF4 interphase

Abstract

Solid-state lithium metal batteries (SSLMBs) have gained much interest owing to their advantages of high specific energy density and safety performance. Nevertheless, the low ionic conductivity of the solid electrolyte and poor contact between lithium metal and electrolyte have hindered their widespread application. In this work, fluorine doped Li₇La₃Zr₂O₁₂ (LLZOF_x) was used to improve the ionic conductivity of the composite electrolyte, and then AlF₃ was employed to construct a lithophilic layer on the surface of the lithium anode, which can effectively improve the conformity of the electrolyte and lithium metal. The LLZOF_0.2 CSE exhibits not only a high ionic conductivity of 3.9 × 10⁻⁴ S cm⁻¹ but also a wide electrochemical window of 5.44 V and an improved Li⁺ transference number of 0.61. Furthermore, the adsorption and binding energies of lithium bis(trifluoromethanesulfonyl)imide (LITFSI) on LLZOF_0.2 were determined through calculations. The results indicate that LLZOF_0.2 can reduce the binding energy of LiTFSI, and adsorb TFSI⁻, therefore increasing the amount of free lithium ions. In addition, a lithophilic layer was constructed on the surface of the lithium metal. This layer composed of LiF and LiAlF₄ effectively reduces interfacial resistance, lowers the overpotential of the symmetric cell, and inhibits the growth of dendrites. The experimental results indicate that the cell composed of the LLZOF_0.2 based CSE and Li@AlF₃ demonstrates outstanding electrochemical performance. The capacity retention of the cell with the LLZOF_0.2 based CSE and LiAlF₄ interphase is 86.9% after 300 cycles at 1C.