Solid composite electrolyte with a Cs doped fluorapatite-interfacial layer enabling dendrite-free anodes for solid-state lithium batteries

To address the issue of lithium metal deposition, a Cs doped FA interlayer was constructed on the surface of CSE. The CSE with this interfacial layer exhibits enhanced ionic conductivity, high Li+ transference number, a wide electrochemical window, and excellent flame-retardant property. Furthermore, the Li||Li symmetric cell assembled using the CSE with this interfacial layer demonstrates stable electroplating/stripping tests over 2000h at 0.2 mA cm−2. In addition, the full cells with the Cs doped FA interlayer and LFP or NCM811 cathode exhibit remarkable electrochemical performance. [Display omitted] •DFT shows that Cs-doped FA contributes to the decomposition of LiTFSI to produce more freedom Li+.•The Cs doped FA interfacial layer can effectively inhibit lithium dendrite growth.•The symmetric Li||Li cell exhibits an exceptionally long life of more than 2000 h at 0.2 mA cm−2.•Solid-state lithium metal batteries with LiFePO4 and NCM811 exhibit excellent cycling performance. Composite electrolytes have garnered considerable attention owing to ease of processing, flexibility, and cost-effectiveness. Nevertheless, their practical applicability has been hindered by the insufficient ionic conductivity and the formation of dendrites duo to solid–solid interfacial interactions. In this work, an interfacial layer with Cs-doped fluorapatite (Ca5(PO4)3F, FA) as the filler was constructed to enhance the flame-retardant property of the composite electrolyte and inhibit dendrite growth during cycling process. The CSE with the Cs doped FA interfacial layer exhibits significant flame-retardant properties. Furthermore, the self-healing electrostatic shielding (SHES) mechanism of Cs+ effectively inhibits the growth of lithium dendrite and promotes uniform lithium deposition. The solid electrolyte integrated with the Cs doped FA interfacial layer exhibits a broad voltage window of 5.58 V vs. Li+/Li, high ionic conductivity of 5.43 × 10-4 S cm−1, and Li+ transference number of 0.716. Density functional theory (DFT) calculations reveal a competitive interaction between Cs+ and Li+ for TFSI- coordination, leading to reduced binding energy of LiTFSI and thus increasing the availability of free lithium ions, enhancing lithium ions mobility. Additionally, the symmetrical cell with the Cs doped FA interfacial layer demonstrates cyclic stability over 2000 h at 0.2 mA cm−2 due to the lower nucleation overpotential, demonstrating excellent lithium plating/stripping capabilities. The