Abstract
Aqueous lithium-ion batteries are gaining increasing interest as a potential candidate for the next generation batteries. These batteries provide much higher safety and reduced cost of manufacturing as the prime advantages. Aqueous electrolytes also offer higher ionic motilities for lithium ions which could pave the way for faster charging batteries. Despite the advantages, a huge drawback in aqueous batteries is the lower electrochemical stability window for water-based electrolytes. Titanium dioxide (TiO2) is one candidate electrode material that can offer a high capacity, but the redox potential for TiO2 is much lower than the hydrogen evolution potential for water. Here we report on our efforts to increase the over-potential for hydrogen evolution on the anode in order to achieve good cycle stability of TiO2 in aqueous electrolytes. By using a combination of in-situ and ex-situ surface coatings on the anode and tuning the composition and molarity of aqueous electrolytes, we demonstrate that the over-potential for hydrogen evolution can be suppressed to sufficiently low potentials to allow reversible Li insertion and extraction to/from TiO2. These achieved results are critically important for the development of high voltage aqueous batteries. Materials characterization of TiO2 electrodes using scanning and transmission electron microscopy (SEM and TEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction and vibrational spectroscopy studies (Raman and FTIR) before and after electrochemical cycling will be reported. Results of electrochemical characterization tests, such as cyclic voltammetry (CV) conducted at different sweep rates, charge-discharge (C-D) conducted at different current densities and different temperatures and electrochemical impedance spectroscopy (EIS) studies, show the relationships between the composition of cell components and cell electrochemical performance.
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