The structural stability of nanosized ZnO-coated LiMn2O4 was characterized by its cycling behavior at 30 and 55°C. The structural degradation and Mn dissolution of the as-prepared and ZnO-coated LiMn2O4 electrodes before and after cycling were studied. The ZnO-coating significantly improved cycling performance at 55°C. The reason for the excellent cycling performance of ZnO-coated LiMn2O4 electrode is largely attributed to ZnO’s role of HF collection from the electrolyte. © 2003 The Electrochemical Society. All rights reserved.

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Operating voltage enhancement is an effective route for high energy density supercapacitors. Unfortunately, widely used activated carbon electrode generally suffers from poor electrochemical stability over 2.5 V. Here we present atomic layer deposition (ALD) encapsulation of activated carbons for high voltage stable supercapacitors. Two-nanometer-thick Al2O3 dielectric layers are conformally coated at activated carbon surface by ALD, well-maintaining microporous morphology. Resultant electrodes exhibit excellent stability at 3 V operation with 39% energy density enhancement from 2.5 V operation. Because of the protection of surface functional groups and reduction of electrolyte degradation, 74% of initial voltage was maintained 50 h after full charge, and 88% of capacitance was retained after 5000 cycles at 70 °C accelerated test, which correspond to 31 and 17% improvements from bare activated carbon, respectively. This ALD-based surface modification offers a general method to enhance electrochemical stability of carbon materials for diverse energy and environmental applications.