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

Abstract

Three fluorine-doped lithium nickel oxide samples series (LiNiO 2−x F x , LiNi 1−x Mg x O 2−x F x ; Li 1+x/2 Ni 1−x/2 O 2−x F x ) were prepared and investigated. It is suggested that fluorine was introduced into the lattice structure during the calcination. As fluorine is introduced into LiNiO 2−x F x and LiNi 1−x Mg x O 2−x F x the percentage of Ni (or Ni and Mg) in the Li layer increases for x > 0.05. However, adding excess Li in Li 1+x/2 Ni 1−x/2 O 2−x F x sucessfully balances the charge differential introduced by fluorine doping therefore very little Ni 2+ was created and the lithium layers remain “uncontaminated” by other metals. Data from Li/LiNiO 2−x F x , Li/LiNi 1−x Mg x O 2−x F x and Li/Li 1+x/2 Ni 1−x/2 O 2−x F x cells mirror the percent of cation mixing as determined by X-ray diffraction (XRD) and Rietveld refinement in each case. In situ XRD of Li 1.1−x Ni 0.9 O 1.8 F 0.2 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, Li 2 O or Li 2 CO 3 ). No evidence of residual LiF was found.