Enhanced lithium storage property of Na-doped Li2Na2Ti6O14 anode materials for secondary lithium-ion batteries

Abstract

In this paper, a series of Na-doped Li₂Na₂Ti₆O₁₄ samples are synthesized by a simple solid-state reaction method through Li-site substitution with Na. Morphology observation shows that all five materials are well crystallized with a particle size in the range of 150–300 nm. Electrochemical analysis shows that Li_1.95Na_2.05Ti₆O₁₄ exhibits lower charge–discharge polarization (0.05 V) than that (0.11 V) of other Li_2−xNa_2+xTi₆O₁₄ samples (x = 0.00, 0.10, 0.15, 0.20). As a result, Li_1.95Na_2.05Ti₆O₁₄ has the highest initial charge capacity of 243.6 mA h g⁻¹, and maintains a reversible capacity of 210.7 mA h g⁻¹ after 79 cycles. For comparison, Li_2−xNa_2+xTi₆O₁₄ (x = 0.00, 0.10, 0.15 and 0.20) samples only hold a reversible capacity of 159.1, 203.5, 190.1 and 156.7 mA h g⁻¹, respectively. Moreover, Li_1.95Na_2.05Ti₆O₁₄ also delivers the best rate performance compared with the other four samples, with a charge capacity of 221.1 mA h g⁻¹ at 200 mA g⁻¹, 211.9 mA h g⁻¹ at 300 mA g⁻¹, and 198.7 mA h g⁻¹ at 400 mA g⁻¹. Besides, the reversible in situ structural evolution proves that Li_1.95Na_2.05Ti₆O₁₄ is a stable host for lithium storage. All the improved electrochemical properties of Na-doped Li₂Na₂Ti₆O₁₄ should be attributed to the Na-doping with low content, which reduces the charge–discharge polarization and improves the ionic conductivity.