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

Abstract

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 LFP||Li full cell shows a remarkable capacity retention of 99.54 % after 300 cycles at 0.5C, and 95.58 % with a higher Coulombic efficiency (CE) of 99 % after 600 cycles at 1C. In addition, the cell with this CSE and NCM811 cathode exhibits excellent capacity retention of 78 % after 150 cycles at 0.5C. This approach to designing interfacial layers offers new avenues for advancing solid-state lithium-metal batteries.