A new aqueous TiO 2 /Ni(OH) 2 rechargeable battery system with a high voltage, consisting of a-phase nickel hydroxides as the cathode and TiO 2 nanotube arrays as the anode, is proposed for the first time. It is a feasible strategy to combine two different reaction mechanisms in an aqueous alkaline electrolyte: proton and lithium insertion/extraction reactions.Lithium-ion batteries (LIBs) are the most successful electrochemical devices with a high energy density in organic electrolytes. However, the safety issue arising from the flammable organic electrolytes handicaps their extensive applications in electric vehicles (EVs) and hybrid electric vehicles (HEVs). As the most ideal electrolyte solvent, water is abundant and friendly to the environment. Alkaline aqueous rechargeable batteries are the most promising power sources, especially for their large-scale application in EVs and HEVs based on the issue of safety. 1,2 In recent years, a new type of rechargeable lithium batteries with intercalation compounds as electrode-active materials in aqueous electrolytes containing Li ions has been proposed 1 and studied extensively, such as VO 2 (B)

Rechargeable aqueous TiO2/LiMn2O4 lithium-ion battery is fabricated by combining the TiO2 nanotube arrays on metallic titanium foil as anode and LiMn2O4 as cathode in aqueous solution with mixed lithium salts (LiCl and Li2SO4). It is shown from cyclic voltammograms that the lithium insertion/extraction peaks of the cathode are highly symmetrical before the oxygen evolution, which can ensure a good lithium utilization of the LiMn2O4. Importantly, a higher anodic hydrogen evolution overpotential in TiO2 anode is observed, which is essential for the facile lithium insertion in preference to the hydrogen evolution. Meanwhile, the gas (hydrogen and oxygen) evolution in the anodic and cathodic processes can be effectively suppressed in aqueous electrolyte with mixed lithium salts as compared with that in pure LiCl and Li2SO4 solution, respectively. Correspondingly, the fabricated TiO2/LiMn2O4 battery presents a high discharge voltage plateau of above 2 V, which is well beyond the average discharge voltage of current aqueous battery system. Therefore, the combination of the appropriate anode/cathode-active materials with a relatively large potential difference and high gas evolution overpotential is an ideal strategy for developing new aqueous battery system based on reversible lithium insertion/extraction reactions in aqueous electrolyte.

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