Stability Enhancement and Microstructural Modification of Ni-Rich Cathodes via Halide Doping

Abstract

Elemental doping is an effective strategy to modify surface and bulk chemistry in NMC cathode materials. By adding small amounts of lithium halide salts during the calcination process, the Ni-rich NMC811 cathode is doped with Br, Cl, or F halogens. The dopant type has a significant impact on the lithiation process and heavily influences the final cathode porosity and surface morphology. Utilizing a variety of electrochemical, surface, and bulk characterization techniques, it is demonstrated that an initial content of 5 mol % LiBr or LiCl in the lithium source is effective in improving capacity retention while also providing excellent rate performance. The improvements are attributed to a substantial increase in specific surface area, the formation of a stable cathode electrolyte interface (CEI) layer, and suppressed surface reconstruction. In addition, the particle microstructure is better equipped to handle cyclic volume changes with increased values of critical crack lengths. Overall, it is demonstrated that anion doping via the addition of lithium halide salts is a facile approach toward Ni-rich NMC modification for enhanced cathode performance.

High Voltage Cycling Stability of LiF-Coated NMC811 Electrode

“…16,44,57−60 After 100 charge/discharge cycles, the samples experience a higher degree of polarization, indicated by the shift of oxidation and reduction peaks to higher and lower potentials, respectively. 59 Additionally, the intensity reduction of the anodic/cathodic peaks signifies capacity decline, in line with the cycling performance in Figure 5. The root cause of these behaviors can be traced back to the detrimental effect of high-cutoff voltage cycling.…”

“…After the initial formation cycles, both samples show three distinct pairs of anodic/cathodic peaks assigned to the multiphase transition of a Ni-rich layered oxide cathode material. In the anodic scan, the first peak is assigned to the transition from a hexagonal (H1) phase to a monoclinic (M) phase, followed by a second peak for the transition to another hexagonal (H2) phase, and then a third peak for the transition to the hexagonal (H3) phase. ,,− After 100 charge/discharge cycles, the samples experience a higher degree of polarization, indicated by the shift of oxidation and reduction peaks to higher and lower potentials, respectively . Additionally, the intensity reduction of the anodic/cathodic peaks signifies capacity decline, in line with the cycling performance in Figure .…”

A review on nickel-rich nickel–cobalt–manganese ternary cathode materials LiNi0.6Co0.2Mn0.2O2 for lithium-ion batteries: performance enhancement by modification

“…In addition to the improved cycling performance, cyclic voltammetry and AC impedance tests fully demonstrate that the fluorine modification facilitates the reduction of polarization and charge transfer impedance. In addition, the highly electronegative elements chlorine, 91 sulfur, 92 and bromine 93 ions also enable good bonding between TM cations and anions. In recent years, the relatively novel doping of polyanions (borate, 94 phosphate, 95 silicate, 96 etc. )…”

Limiting voltage and capacity fade of lithium-rich, low cobalt Li1.2Ni0.13Mn0.54Fe0.1Co0.03O2 by controlling the upper cut-off voltage

“…To improve the structural stability and the electrochemical performance of Li(NiMnCo)O 2 based materials, various metal doping such as Al, Cr, Fe, Mo, Mg, Zr, and Si has been studied. [17][18][19][20][21][22] Recently, Layered lithium-rich NMC (Li-rich NMC) has been extensively studied due to its enhanced performances, especially the high discharge capacity (>250 mA h g −1 ). [23][24][25][26][27][28][29][30] However, Li-rich NMC cathodes still suffer from serious drawbacks such as the poor rate capabilities and the non-stable electrochemical performances (capacity and voltage fading) caused by the transition metals leaching during cycling and the crystal structures changes.…”

“…To improve the structural stability and the electrochemical performance of Li(NiMnCo)O 2 based materials, various metal doping such as Al, Cr, Fe, Mo, Mg, Zr, and Si has been studied. 17–22…”