Studies of Li and Mn-Rich Li_x[MnNiCo]O₂Electrodes: Electrochemical Performance, Structure, and the Effect of the Aluminum Fluoride Coating

Abstract

We report herein on the study of Li and Mn rich Lix[MnNiCo]O2 cathode materials with an emphasis on the effect of AlF3 coating on their electrochemical performance. The initial stoichiometry of these materials was xLi2MnO3.(1-x)LiMnyNizCowO2 where x is in the range 0.4-0.5 and the y:z:w ratio was as we previously reported. Their structure was considered on the basis of two-components model, namely monoclinic Li2MnO3 (C2/m) and rhombohedral LiMO2 (R-3m) (M = Mn, Ni, Co) that are structurally compatible and closely integrated phases. Based on TEM studies we concluded that the coating had a crystalline tetragonal structure t-AlF3 (P4nmm symmetry) and AlF3 nano-crystals were regularly distributed over the particles surface. Amorphous clusters of AlF3 and/or other Al-containing species, like AlFxOy, Al[FOH], etc. may also present, as it follows from solid-state NMR measurements. It was shown that electrodes comprising the AlF3-coated material exhibited higher reversible capacities of ∼250 mAh/g at a C/5 rate, more stable cycling behavior, higher lithium storage capability at 60°C, and lower impedance measured during Li-deinteraclation comparing to electrodes prepared from the uncoated material. An important finding is that Lix[MnNiCo]O2 /AlF3 materials revealed much higher thermal stability both in the pristine (lithiated) and cycled (delithiated) states than their uncoated counterparts.

Study of Cathode Materials for Lithium-Ion Batteries: Recent Progress and New Challenges

“…The onset temperature of charged NCM622 (4.3 V) was measured to be ~290 °C, while a 0.5 wt % SiO2 coating could lower the onset to ~270 °C ( Figure 20) [113]. It must be emphasized that DSC measurements of charged samples are often run with dry powder, but a more realistic picture would need the addition of the electrolyte solution as well [16]. Nonetheless, trends can also be observed from measurements on dry powder.…”

“…A wide variety of materials was investigated for use as coatings, including the metal oxides SnO, Al 2 O 3 , TiO 2 , MgO and ZrO 2 [44][45][46][47], fluorides such as AlF 3 and ZrF x [48,49], and phosphates such as AlPO 4 [50]. Recently, we studied the structural characteristics and electrochemical behavior of electrodes comprising Li-and Mn-rich Li x [MnNiCo]O 2 cathode materials (prepared at BASF, Ludwigshafen, Germany) with the stoichiometry of xLi 2 MnO 3 ·(1 − x)LiMn y Ni z Co w O 2 at 60 • C (x is in the range 0.4-0.5, and the y:z:w ratio was already reported, coated with AlF 3 (about 2-3 wt %)) [16]. Special emphasis was given to the possible structural transformation during the activation and cycling of these electrodes, to solution and interfacial reactions, and to the stability of the AlF 3 coating during prolonged charge/discharge cycling at 60 • C. We also studied possible interactions between the aluminum fluoride and the core of the active material, to better understand the effect of this coating on all the chemical, electrochemical and thermal processes of the electrodes.…”

“…The AlF 3 coating appears as thin crystalline layers covering the particle surface, indicated by arrows in the inset (c). We have previously shown that xLi2MnO3·(1 − x)Li [MnyNizCow]O2 (x around 0.5, y:z:w around 2:2:1) electrodes can be effectively cycled at both 30 and 60 °C, with reversible capacities of about 220-250 mAh·g −1 at a rate of C/5 [16]. The AlF3-coated electrodes also exhibit stable charge/discharge behavior, providing higher capacities and lower fade upon prolonged cycling at 60 °C ( Figure 3A,B).…”

“…The layers of AlF 3 are indicated by arrows. The coating crystallizes into the tetragonal structure t-AlF 3 described by the P4nmm symmetry, possessing a unit cell with the parameters a = 10.1843 Å and c = 7.1738 Å. Reprinted from [16].…”

Review—Recent Advances and Remaining Challenges for Lithium Ion Battery Cathodes

“…93 Another coating with interesting results comes from AlF 3 , also explored by our group. 37,94,95 AlF 3 was coated on Li-rich material via pH controlled aqueous solution, and annealed at 400…”