Abstract
Through a facile sodium sulfide (Na2S)‐assisted hydrothermal treatment, clean and nondefective surfaces are constructed on micrometer‐sized Li4Ti5O12 particles. The remarkable improvement of surface quality shows a higher first cycle Coulombic efficiency (≈95%), a significantly enhanced cycling performance, and a better rate capability in electrochemical measurements. A combined study of Raman spectroscopy and inductive coupled plasma emission spectroscopy reveals that the evolution of Li4Ti5O12 surface in a water‐based hydrothermal environment is a hydrolysis–recrystallization process, which can introduce a new phase of anatase‐TiO2. While, with a small amount of Na2S (0.004 mol L−1 at least), the spinel‐Li4Ti5O12 phase is maintained without a second phase. During this process, the alkaline environment created by Na2S and the surface adsorption of the sulfur‐containing group (HS− or S2−) can suppress the recrystallization of anatase‐TiO2 and renew the particle surfaces. This finding gives a better understanding of the surface–property relationship on Li4Ti5O12 and guidance on preparation and modification of electrode material other than coating or doping.
Highlights
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The amorphous layer on the pristine LTO surface is probably generated during solid-phase sintering, in which some impurity elements aggregated at the surface of the LTO particles, creating defects, and preventing the ordered arrangement of the Li, Ti, and O ions.[15]
A facile modification method was introduced for Li4Ti5O12 anode materials existing of simple hydrothermal treatment with a Na2S aqueous solution
Summary
The LTO particles show a suitable morphology for battery application,[23] namely, micrometer-sized (≈12–20 μm) secondary particles (Figure 1a) composed of ≈100–500 nm primary. Through a series of analogous experiments performed with initial LTO (5 g) and different concentrations of Na2S (10 levels from 0 to 0.02 mol L−1) for 8 h (Figure S4 and Table S1, Supporting Information), it is suggested that the anatase-TiO2 phase can be inhibited when the Na2S concentration exceeds 0.004 mol L−1 resulting in a high-quality LTO surface. Some dissolved TiO32− may be absorbed again to the particle surface which recrystallized to anatase-TiO2 (Equation (4)) This explains why in the second stage the concentration of Li continues increasing while the concentration of Ti drops to a relatively small value. The hydrothermal-treated LTO with water shows another pair of redox peaks at 1.70 and 2.08 V (Figure 5c,d), attributed to lithium intercalation and deintercalation concerning the anatase-TiO2 phase.[38] While for the modified LTO by Na2S-assisted hydrothermal treatment (Figure 5e,f), no additional current peaks were observed, implying that the high-quality surface possesses better electrochemical properties. The surface–property relationship is revealed by the detailed CV analysis, supporting that the high-quality surface, without the amorphous or anatase-TiO2 surface layer, is responsible for the improved electrochemical performance
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