COMMUNICATION www.MaterialsViews.com www.advenergymat.de © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim (1 of 6) 1300912 wileyonlinelibrary.com Adv. Energy Mater. 2014, 4, 1300912 Three-Dimensionally “Curved” NiO Nanomembranes as Ultrahigh Rate Capability Anodes for Li-Ion Batteries with Long Cycle Lifetimes Xiaolei Sun, Chenglin Yan,* Yao Chen, Wenping Si, Junwen Deng, Steffen Oswald, Lifeng Liu, and Oliver G. Schmidt X. Sun, Dr. C. Yan, Dr. Y. Chen, W. Si, J. Deng, Prof. O. G. Schmidt Institute for Integrative Nanosciences IFW Dresden, Helmholtzstrasse 20 Dresden, 01069, Germany E-mail: c.yan@ifw-dresden.de X. Sun, W. Si, J. Deng, Prof. O. G. Schmidt Material Systems for Nanoelectronics Chemnitz University of Technology Reichenhainer Strasse 70, Chemnitz, 09107, Germany S. Oswald Institute for Complex Materials IFW Dresden, Helmholtzstrasse 20 Dresden, 01069, Germany L. Liu International Iberian Nanotechnology Laboratory (INL) 4715–330, Braga, Portugal O. G. Schmidt Cluster of Excellence MERGE Reichenhainer Strasse 70, Chemnitz, 09126, Germany DOI: 10.1002/aenm.201300912 The depletion of traditional energy resources has stimulated significant research interest in developing renewable energy sources, including solar radiation, wind, and waves. [1] Because of the intermittent availability of these resources, the exploita- tion of their full potential requires the development of energy storage systems. Lithium-ion batteries (LIBs), as a class of energy storage devices, are now attracting great attention for applications in portable electronic devices and electrical vehi- cles. [1–8] To meet the ever-increasing demand for efficient energy storage systems in hybrid electric vehicles and plug- in hybrid electric vehicles, LIBs must be developed further to improve their ability to deliver high power and their energy density with ensured safety in operation and reduced cost. [1,9] As a transition metal oxide, nickel oxide (NiO) is low cost, environmentally friendly, and abundant in nature. It is consid- ered as one of the most appealing anode materials due to its high lithium storage capacity. However, the performance of the NiO anode has been limited by its poor electrochemical reac- tivity and large volume variation during the lithium uptake/ release process. [10] To address these issues, various nanostruc- tured NiO anode materials have been fabricated to achieve improved electrochemical performance. [11–16] Despite signifi- cant progress, the NiO electrodes are still far from commer- cialization. Therefore, new strategies for building advanced NiO electrodes with ultrafast power rates and long lifespans are urgently needed. Recently, curved nanomembranes, an important family of functional materials, have attracted considerable interest because of their properties and potential applications in energy storage, fluidic sensor, biocatalysis, etc. [17–20] In terms of LIBs, the large interstitial space in the curved nanostructure can effi- ciently increase the surface area accessible to the electrolyte, which allows lithium ions to intercalate at the interior and exte- rior of the curved nanomembranes and to accommodate large and frequent mechanical strain from the electrochemical reac- tions of the active materials with lithium ions. [17,21] Here, we report three-dimensionally “curved” NiO nanomem- branes made using a simple fabrication technique followed by a thermal oxidation process, based on above considerations. [22] The curved NiO nanomembranes exhibit both superior power rate and ultralong cycle life when utilized as the anode material for LIBs. The electrodes deliver a high capacity of 721 mAh g -1 at 1.5 C (1 C = 718 mA g -1 ) after 1400 cycles. Notably, even after cycling at an extremely high C-rate of 50 C (i.e., current density of 35 400 mA g -1 ), the capacity is able to recover to the initial value when the current rate is set back to 0.2 C after 110 cycles. To the best of our knowledge, such impressive superior power rate and ultralong lifespan for nickel-oxide-based electrodes have not been reported previously. The chemical composition of the product was determined by X-ray powder diffraction (XRD), as shown in Figure 1 a. All three characteristic diffraction peaks can be assigned to NiO in the face-centered cubic phase (JCPDS card No. 47–1049). The corresponding Raman spectrum (see Supporting Information, Figure S1) reveals five broad peaks centered at 402, 520, 695, 879, and 1069 cm -1 , which are of vibrational origin and cor- respond to the one-phonon first-order transverse optical mode (TO, at 402 cm -1 ), one-phonon longitudinal optical mode (LO, at 520 cm -1 ), two-phonon modes (2TO, at 695 cm -1 ), TO + LO (at 879 cm -1 ), and 2LO (at 1069 cm -1 ) modes, respectively. [23] Further, the composition and valence states of the material were investigated by X-ray photoelectron spectroscopy (XPS; Supporting Information, Figure S2), where the O 1s and Ni 2p core levels were examined. The O 1s spectrum consists of a main peak at 530.7 eV with a shoulder at 532.4 eV. The two regions in the Ni 2p spectrum could be assigned to the Ni 2p 1/2 (870–885 eV) and Ni 2p 3/2 (850–865 eV) spin-orbit levels, respectively. From these spectra it follows that Ni is at the sur- face, mainly in the Ni 2+ state with some Ni 3+ contribution, and no metallic Ni is observed. [24] The low-magnification scanning electron microscopy (SEM) image in Figure 1b provides an overview of the morphology