context: The electrochemical performance of LTO electrodes coated with various materials was evaluated by linear sweep voltammetry (Fig. 3). Hydrogen evolution began at ∼1.8 V vs. Li on the pristine LTO surface, which was higher than its lithiation potential (1.55 V). The HER process (rather than lithiation of LTO) dominated the cathodic reaction during the scan. The carbon coating enhanced the electronic conductivity of LTO, thus accelerating the HER (as evidenced by the higher currents and positively shifted HER potential). The TiO2 coating also positively shifted the cathodic limit due to its high catalytic activity. In contrast, the ZnO coating and Al2O3 costing negatively shifted the cathodic limit potential by 0.1 V. In addition, the HER currents on the ZnO-coated and Al2O3-coated LTO electrode were much lower compared with those on pristine LTO. The capability of HER suppression as quantified by the onset potential of the HER should increase in the order TiO2 < carbon < LTO < ZnO < Al2O3, which was consistent with the prediction in Fig. 1. The Al2O3 coating not only suppressed the HER catalytic activity but also acted as a kinetic barrier to slow down electron transfer from the electrode bulk to protons in the electrolyte. Al2O3 coating shifted the HER potential to <1.5 V, so Li+ intercalation was enabled before the HER, as evidenced by a sharp lithiation peak at 1.55 V (Fig. 4a). Using a similar approach, we also evaluated the effect of surface coating on the oxygen evolution reaction (OER). Al2O3 coating and TiO2 coating on LiNi0.5Mn1.5O4 reduced the side reactions on this high-voltage (4.8 V) cathode material only slightly (Fig. S3†).