Enhancing the electrochemistry performance of Li4Ti5O12 for Li-ion battery anodes by a sol–gel assisted molten salt method and graphene modification

Abstract

Graphene modified Li₄Ti₅O₁₂ composites (G-LTO) were prepared via a sol–gel assisted molten salt synthesis process. The product was fabricated by controlled hydrolysis of tetrabutyl titanate in the presence of graphene oxide, glacial acetic acid and LiCl–KCl molten salts in a mixed solvent of ethanol and water, followed by calcination treatment and a washing process. For comparison, pure LTO and carbon modified LTO were also synthesized by the same process without graphene oxide addition and with urea, respectively. The results reveal that pure LTO has a decreased particle size, and primary particles aggregation and agglomeration is effectively avoided by this method. Besides, the introduction of graphene sheets leads to the most uniform distribution particle size of LTO, and enhances the conductivity between the adjacent LTO particles. Hence, G-LTO composites present an improved rate performance (111.3 mA h g⁻¹ at 10C) and cycling stability (the capacity loss of 11.9% after 500 cycles at 1C). Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) well explain the electrode kinetics. The charge transfer resistance at the LTO active substance/electrolyte interface is reduced from 316.9 Ω to 151.8 Ω. The Li⁺ diffusion coefficient in the G-LTO electrode is 7.83 × 10⁻¹¹ cm² s⁻¹, which is larger than the 5.49 × 10⁻¹¹ cm² s⁻¹ of the P-LTO electrode. The results could be attributed to the smaller particle size, reduced aggregation and improved electronic conductivity as a result of the improved synthetic method and the presence of graphene sheets.