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

Abstract

Three fluorine-doped lithium nickel oxide samples series (LiNiO2−xFx, LiNi1−xMgxO2−xFx; Li1+x/2Ni1−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 in Li1+x/2Ni1−x/2O2−xFx 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/2Ni1−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.

Surface Stabilization with Fluorine of Layered Ultrahigh-Nickel Oxide Cathodes for Lithium-Ion Batteries

“…39 Recently, by means of XRD, Rietveld refinement, and pH titration, Dahn et al showed fluorine is being introduced into the lattice of high-nickel materials. 34 They observed an increase in the a and c parameters along with reduction in particle size after fluorination. In our study, no significant changes in the lattice parameters are observed, indicating that fluorine is not significantly doping into the lattice but rather stays on the surface due to the low enough calcination temperature (400 °C) with NH 4 F. The presence of fluorine at the surface was further confirmed by STEM energy-dispersive X-ray spectroscopy (EDS) mapping and line scanning (Figure S2).…”

“…With XRD and 7 Li as well as 19 F magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy, Croguennec et al suggested that fluorine does not get doped into the structure by substituting oxygen but stays as small LiF particles at the grain boundaries . Recently, by means of XRD, Rietveld refinement, and pH titration, Dahn et al showed fluorine is being introduced into the lattice of high-nickel materials . They observed an increase in the a and c parameters along with reduction in particle size after fluorination.…”

“…), fluorides (AlF 3 , MgF 2 , CaF 2 , etc. ), phosphates (AlPO 4 , Li 3 PO 4 ), and so on. − Fluorine coating has been shown to improve the electrochemical performance due to cathode–electrolyte interface stabilization and reduced rock-salt phase formation. − The effect of coatings can vary depending on thickness, uniformity, and conductivity. For fluorine coating, NH 4 F and NH 4 F·HF are the most widely used source.…”

New Insights into Structural Evolution of LiNiO2 Revealed by Operando Neutron Diffraction

“…[11] Hence, concerns have been expressed about its electrochemical [12][13][14] and thermal [15,16] performance especially at high degrees of delithiation (> 4.3 V vs. Li/Li + ). Although extensive works [17,18] have shown that cation-substituted Ni-rich cathodes, e. g., LiNi 1-x-y Mn x Co y O 2 (1-x-y � 0.8), can improve the structural/thermal stability and cyclability, the renaissance of research interest in LiNiO 2 has been underway, [19][20][21][22][23] to meet the harsher criteria for EVs batteries. [1,2] Among the challenges such as parasitic surface reactions [24,25] and formation of disordered rock-salt (NiO) impurity [26,27] at high state-of-charge (SOC), the sequential phase transition (H1-M-H2-H3) [28,29] might play a more profound role in altering the structural stability.…”

Enhancing the Structure and Interface Stability of LiNi0.83Co0.12Mn0.05O2 Cathode Material for Li-Ion Batteries via Facile CeP2O7 Coating

“…The XRD patterns and Rietveld refined results of different samples are shown in Figure and Table . According to Figure a, three samples of P-LNCM83, W-LNCM83, and Aq-LNCM83@CPPO all have a α-NaFeO 2 type layered structure, and the diffraction peaks of the impurities are not observed in the diffraction pattern of the three samples. What’s more, from the enlarged diffraction peak of (003) and (104) planes, it is found that the W-LNCM83 and Aq-LNCM83@CPPO samples’ peak positions are slightly shifted to the left side compared to that of P-LNCM83.…”