Facile Synthesis of Hierarchical Micro/Nanostructured MnO Material and Its Excellent Lithium Storage Property and High Performance as Anode in a MnO/LiNi 0.5 Mn 1.5 O 4‑δ Lithium Ion Battery Gui-Liang Xu, † Yue-Feng Xu, † Jun-Chuan Fang, † Fang Fu, † Hui Sun, ‡ Ling Huang, † Shihe Yang, ‡ and Shi-Gang Sun* ,† † State Key Laboratory of Physical Chemistry of Solid Surfaces, Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China ‡ Department of Chemistry, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong * S Supporting Information ABSTRACT: Hierarchical micro/nanostructured MnO material is synthesized from a precursor of MnCO 3 with olive shape that is obtained through a facile one-pot hydrothermal procedure. The hierarchical micro/nanostructured MnO is served as anode of lithium ion battery together with a cathode of spinel LiNi 0.5 Mn 1.5 O 4‑δ material, which is synthesized also from the precursor of MnCO 3 with olive shape through a different calcination process. The structures and compositions of the as-prepared materials are characterized by TGA, XRD, BET, SEM, and TEM. Electrochemical tests of the MnO materials demonstrate that it exhibit excellent lithium storage property. The MnO material in a MnO/Li half cell can deliver a reversible capacity of 782.8 mAh g -1 after 200 cycles at a rate of 0.13 C, and a stable discharge capacity of 350 mAh g -1 at a high rate of 2.08 C. Based on the outstanding electrochemical property of the MnO material and the LiNi 0.5 Mn 1.5 O 4‑δ as well, the MnO/LiNi 0.5 Mn 1.5 O 4‑δ full cell has demonstrated a high discharge specific energy ca. 350 Wh kg -1 after 30 cycles at 0.1 C with an average high working voltage at 3.5 V and a long cycle stability. It can release a discharge specific energy of 227 Wh kg -1 after 300 cycles at a higher rate of 0.5 C. Even at a much higher rate of 20 C, the MnO/LiNi 0.5 Mn 1.5 O 4‑δ full cell can still deliver a discharge specific energy of 145.5 Wh kg -1 . The excellent lithium storage property of the MnO material and its high performance as anode in the MnO/ LiNi 0.5 Mn 1.5 O 4‑δ lithium ion battery is mainly attributed to its hierarchical micro/nanostructure, which could buffer the volume change and shorten the diffusion length of Li + during the charge/discharge processes. KEYWORDS: hierarchical micro/nanostructured, olive shape, MnO, spinel LiNi 0.5 Mn 1.5 O 4‑δ , full cell, lithium ion batteries 1. INTRODUCTION Transition metal oxides (TMOs, M = Co, Ni, Cu, Fe, Mn) have been widely investigated as anode materials for lithium ion batteries (LIBs) in the past decades since reported by Tarascon et al. in 2000. 1-3 Among the TMOs, MnO anode has attracted more and more attention in recent years, because the MnO has a high theoretical capacity of 755.6 mAh g -1 that is twice the capacity of graphite, and a lower electromotive force (1.032 V vs Li/Li + ) than other TMO anodes such as Fe 2 O 3 , Co 3 O 4 , NiO, CuO, and so forth. 4-10 Such features result in a lower voltage polarization, and make the MnO more suitable as anode material for the next generation of LIBs than other TMOs. In addition, the relatively high voltage plateau (charge, ca. 1.2 V vs Li/Li + ; discharge, 0.5 V vs Li/Li + ) of the MnO can prevent the formation of lithium dendrite during charge/discharge and thus leads to a high safety. However, large volume changes during charge/discharge cycling and the low conductivity of MnO lead to a rapid capacity fading and a poor rate capability. Morphology control synthesis of the MnO materials has been considered as an efficient way to improve its electrochemical performance. In recent years, MnO materials of different structures such as core-shell nanorods, 11 nanotubes, 12 micro- spheres, 13 nanoplates, 14 nanoflakes, 15 and so forth have been synthesized, and they all demonstrated improved cycle performance to a certain degree when they are served as anode of LIBs. To the best of our knowledge, MnO anode with both long cycle performance (≥200 cycles) and high capacity (≥700 mAh g -1 ) has been barely reported so far. Huang et al. has reported recently porous carbon-modified MnO disks 16 and mesoporous MnO/C networks; 17 the highest capacity of these anodes could reach 1224 mA h g -1 (much higher than the theoretical capacity of 755.6 mA h g -1 for MnO as anode) over 200 cycles. However, the capacity of these MnO materials presented a severe fading in the initial 50 cycles and then increased in the follow cycles of charge/discharge. On the other hand, most of the previous works concerning TMOs anodes have only investigated their electrochemical properties in TMO/Li half cells. Only few examples applying Received: April 13, 2013 Accepted: June 11, 2013 Research Article www.acsami.org © XXXX American Chemical Society A dx.doi.org/10.1021/am401355w | ACS Appl. Mater. Interfaces XXXX, XXX, XXX-XXX