TEM failure analysis of electrochemically delithiated LiNi 0.5 Mn 1.5 O 4 spinel
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MRS Advances © 2020 Materials Research Society DOI: 10.1557/adv.2020.105
TEM failure analysis of electrochemically delithiated LiNi0.5Mn1.5O4 spinel Xiangyun Song1, Yanbao Fu1, Chengyu Song2, Vincent Battaglia1 1
Energy Storage and Distributed Resources (ESDR) Department, Lawrence Berkeley National Laboratory, University of California 2 National Center for Electron Microscopy of Molecular Foundry, Lawrence Berkeley National Laboratory, University of California
Abstract: LiNi0.5Mn1.5O4 cathode material, which has a higher working voltage (4.7 v) than NCM and a moderate specific capacity (148 mAh/g theoretical), has been studied to understand the source of capacity fade during the first 100 cycles in a half cell. The work mainly consisted of high resolution TEM observations and analysis of the surface microstructural properties, before and after cycling. We found that the pristine material consisted almost entirely of large FCC spinal domains but with cycling appears small simple cubic spinel domains at the surface. It is proposed that these small changes of the surface microstructure leads to impedance rise that results in the premature arrival to the upper cutoff voltage of 4.85V during charging and the subsequent loss of capacity with cycling.
INTRODUCTION: LiNi0.5Mn1.5O4 with the spinel structure is among one of the more popular cathode materials for lithium ion rechargeable batteries due to its high Mn content, low cost, favorable charge density, high electronic conductivity, good stability on overcharge, suitable electrode potential, and environmental friendliness. Due to these advantages, LiNi0.5Mn1.5O4 spinel material has been a proposed cathode candidate in large format Liion batteries for applications in hybrid and electric vehicles [1-4]. Up to now, most research on this material has focused on the electrochemical properties achieved through different preparation techniques [5-14]. However, due to the electrode’s complexity and environmental sensitivity, there are very few papers investigating its microstructural properties. In particular, TEM sample preparation of the material is especially difficult after cycling.
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In this paper, LiNi0.5Mn1.5O4 (hereon abbreviated as LMNO) spinel samples before and after cycling were studied and compared mainly via high resolution transmission electron microscopy (TEM), with a focus on the possible lattice structural changes of the LNMO particles. Our TEM observations of the cycled LNMO particles found an increase in lattice distortion, stress, overlapping, defects, and nanoparticles on the primary particle surfaces. Further TEM analysis performed by indexing the lattice fringes with fast Fourier transform (FFT) patterns revealed that there are more ordered LNMO simple cubic - P4332 grains (hereon abbreviated as SC-P4332
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