Structural complexity of layered-spinel composite electrodes for Li-ion batteries
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Christopher S. Johnson Department of Electrochemical Energy Storage, Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439
Xiao-Qing Yang Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973
Kyung-Yoon Chung Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973; and Advanced Battery Center, Korea Institute of Science and Technology, Seoul 136-791, Korea
Won-Sub Yoona) School of Advanced Materials Engineering, Kookmin University, 861-1 Jeongneung-dong, Seongbuk-gu, Seoul 136-702, Korea
Sun-Ho Kang and Michael M. Thackeray Department of Electrochemical Energy Storage, Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439
Clare P. Greyb) Chemistry Department, State University of New York at Stony Brook, Stony Brook, New York 11794 (Received 26 January 2010; accepted 13 April 2010)
The complexity of layered-spinel yLi2MnO3(1 – y)Li1þxMn2–xO4 (Li:Mn ¼ 1.2:1; 0 x 0.33; y 0.45) composites synthesized at different temperatures has been investigated by a combination of x-ray diffraction (XRD), x-ray absorption spectroscopy (XAS), and nuclear magnetic resonance (NMR). While the layered component does not change substantially between samples, an evolution of the spinel component from a high to a low lithium excess phase has been traced with temperature by comparing with data for pure Li1þxMn2–xO4. The changes that occur to the structure of the spinel component and to the average oxidation state of the manganese ions within the composite structure as lithium is electrochemically removed in a battery have been monitored using these techniques, in some cases in situ. Our 6Li NMR results constitute the first direct observation of lithium removal from Li2MnO3 and the formation of LiMnO2 upon lithium reinsertion.
I. INTRODUCTION
The advent of Li-ion batteries has played a central role in the impressive development of portable digital and wireless technology over the past two decades. The success of this technology has triggered further efforts to use Li-ion batteries with an even larger impact on society, for example, in heavy-duty applications such as electric vehicles and energy backup for renewable energy sources. However, several challenges need to be met before these expectations can be realized, as Li-ion batteries currently do not meet the energy and power requirements of these devices.1 Despite the recent emergence of LiFePO4 as an Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/JMR.2010.0206 J. Mater. Res., Vol. 25, No. 8, Aug 2010
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alternative positive electrode,2 layered LiCoO2 is still a major player in the current Li-ion battery market.3 Given the scarcity of cobalt and the resulting high market prices, as well as concerns about the safety of Li-ion batteries, particularly in the charged state, extensive research has been carried out to find a
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