Effects of Fluorine Doping on Nickel-Rich Positive Electrode Materials for Lithium-Ion Batteries

Three fluorine-doped lithium nickel oxide samples series (LiNiO2-xFx, LiNi1-xMgxO2-xFx; Li1+x/2O2Ni1-x/2O2-xFx) were prepared and investigated. It is suggested that fluorine was introduced into the lattice structure during the calcination. As fluorine is introduced into LiNiO2-xFx and LiNi1-xMgxO2-xFx the percentage of Ni (or Ni and Mg) in the Li layer increases for x > 0.05. However, adding excess Li inLi(1+x/2)O(2)Ni(1-x/2)O(2-x)F(x) sucessfully balances the charge differential introduced by fluorine doping therefore very little Ni2+ was created and the lithium layers remain uncontaminated by other metals. Data from Li/LiNiO2-xFx, Li/LiNi1-xMgxO2-xFx and Li/Li1+x/2O2Ni1-x/2O2-xFx cells mirror the percent of cation mixing as determined by X-ray diffraction (XRD) and Rietveld refinement in each case. In situ XRD of Li1.1-xNi0.9O1.8F0.2 shows no multipule phase transitions which further suggests fluorine was successfully doped into the lattice. Acclelerating rate calorimetry (ARC) experiments show a potential safety advantage brought by fluorine doping. pH titration was used to explore if residual LiF (if any) at the surface converted to other lithium compounds (LiOH, Li2O or Li2CO3). No evidence of residual LiF was found. (C) 2020 The Author(s). Published on behalf of The Electrochemical Society by IOP Publishing Limited.