Effect of A-site High-Entropy Doping on the Structure and Electricity Performance of Li 0.25 La 0.25 NbO 3 Perovskite- type Solid Electrolyte
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High-entropy doping has emerged as a promising strategy to tailor the properties of solid electrolyte materials for advanced lithium-ion batteries. In this study, we systematically investigate the influence of A-site high-entropy doping on the structural, microstructural, and electrochemical properties of perovskite-type Li 0.25 La 0.25 NbO 3 (LLNO) ceramics. A series of compositions with the general formula Li 0.25 La 0.25−x M x NbO 3 (M = Al 3+ , Mg 2+ , Y 3+ , Ba 2+ , Na + ; x = 0, 0.01, 0.02, 0.03, 0.04) were synthesized via solid-state reaction at sintering temperatures of 1100°C and 1050°C. X-ray diffraction (XRD) analysis reveals that the perovskite structure is retained only at low doping levels (x ≤ 0.02), while higher concentrations lead to the formation of multiple secondary phases and the degradation of the main phase. Scanning electron microscopy (SEM) observations indicate that moderate doping (sintering at 1100°C with x ≤ 0.03; sintering at 1050°C with x ≤ 0.01) maintains uniform grain morphology and favorable densification, whereas excessive doping leads to microstructural degradation. Alternating current (AC) impedance spectroscopy and direct current (DC) polarization measurements demonstrate that appropriately doped samples (LLNO-1100, Q1-LLNO-1100, Q2-LLNO-1100, LLNO-1050, and Q1-LLNO-1050 ) exhibit stable ionic conductivity (2.74 × 10 − 6 , 1.52 × 10 − 6 , 1.06 × 10 − 6 , 3.06 × 10 − 6 , and 1.42 × 10 − 6 S·cm − 1 ) and reduced electronic conductivity (10 − 8 – 10 − 9 S·cm − 1 ), contributing to enhanced lithium-ion transference. This indicates that all samples belong to the solid-state electrolytes. The activation energy for ionic conduction remains within a favorable range for low doping concentrations, suggesting potential for further optimization. These findings provide valuable insights into the structural stability and transport behavior of high-entropy doped LLNO ceramics.
