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Title: Electronic and Electrochemical Properties of Li 1–x Mn 1.5 Ni 0.5 O 4 Spinel Cathodes As a Function of Lithium Content and Cation Ordering

The electronic and electrochemical properties of the high-voltage spinel LiMn1.5Ni0.5O4 as a function of cation ordering and lithium content have been investigated. Conductivity and activation energy measurements confirm that charge transfer occurs by small polaron hopping and the charge carrier conduction is easier in the Ni:3d band than in the in Mn:3d band. Seebeck coefficient data reveal that the Ni2+/3+. and Ni3+/4+ redox couples are combined in a single,3d band, and that maximum charge carrier concentration occurs where the average Ni oxidation state is close to 3+, corresponding to x = 0.5 in Li Li1-xMn1.5Ni0.5O4. Furthermore, maximum electronic conductivity is found at x = 0.5, regardless of cation ordering. The thermodynamically stable phases formed during cycling were investigated by recording the X-ray diffraction (XRD) of chemically delithiated powders. The more ordered spinels maintained two separate two-phase regions upon lithium extraction, while the more disordered samples exhibited a solid-solubility region from LiMn1.5Ni0.5O4 to Li0.5Mn1.5Ni0.5O4. The conductivity and phase-transformation data of four samples with varying degrees of cation ordering were compared to the electrochemical data collected with lithium cells. Only the most ordered spinel showed inferior rate performance, while the sample annealed for a shorter time performed comparable to the unannealed ormore » disordered samples. Our results challenge the most common beliefs about high-voltage spinel: (i) low Mn3+ content is responsible for poor rate performance and (ii) thermodynamically stable solid-solubility is critical for fast kinetics.« less
 [1] ;  [2] ;  [1] ;  [1]
  1. Univ. of Texas, Austin, TX (United States)
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
OSTI Identifier:
Grant/Contract Number:
AC05-00OR22725; DMR-1122603
Accepted Manuscript
Journal Name:
Chemistry of Materials
Additional Journal Information:
Journal Volume: 27; Journal Issue: 20; Journal ID: ISSN 0897-4756
American Chemical Society (ACS)
Research Org:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Spallation Neutron Source
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States