Studies of LiNi0.5Mn1.5O4 as a Positive Electrode for Li-Ion Batteries: M3+ Doping (M = Al, Fe, Co and Cr), Electrolyte Salts and LiNi0.5Mn1.5O4/Li4Ti5O12 Cells

Al, Co, Fe, Cr-substituted and pure LiNi0.5Mn1.5O4 with specific surface area between 0.25 and 0.55 m(2)/g were synthesized from co-precipitated precursors. XRD, SEM, FTIR, BET and electrochemical tests were performed to develop comparisons between the substituted and pure LNMO. LNMO/Li cells and LNMO-limited LNMO/LTO full cells with the substituted LNMO materials were fabricated and tested using currents corresponding to C/20, C/10, C/2, 1C and 2C and at temperatures of 30, 40 and 50 degrees C to measure the coulombic efficiency (CE) as well as the charge/discharge capacity end point slippages. There was no magic improvement of the CE in LNMO-limited LNMO/LTO cells when the substituents M = Al, Co, Fe or Cr were added to make LiM0.1Ni0.45Mn1.45O4 suggesting that these substituents do not impact electrolyte oxidation at the positive electrode surface. LNMO/LTO cells with 1 M LiPF6 as the electrolyte salt show better CE and smaller charge end point capacity slippage compared to cells with 1 M LiBF4, 1 M LiClO4 or 0.6 M LiBOB in EC/DMC. Measurements of CE versus cycling rate for LNMO-limited LNMO/LTO cells at C/20, C/2, 1C and 2C show that the observed increase of CE is proportional to the cycling current. This indicates that parasitic reactions in the cells proceed at the same rate, independent of the applied current. It is our opinion that more research is needed to improve the CE, along with decreasing the charge end point capacity slippage, before commercial applications of LNMO can be contemplated. (C) 2013 The Electrochemical Society. All rights reserved.