Irreversible Transition from GaO₆ Octahedra to GaO₄ Tetrahedra for Improved Electrochemical Stability in Ga-Doped Li(Ni_0.9Co_0.1)O₂

Abstract

Trace doping is an efficient way to improve the stability of nickel-rich layered cathodes for lithium-ion batteries, but the structural origin of such improvement, rather than a simple replacement, has been rarely explored. Herein, Ga dopants have been introduced into a nickel-rich host, LiNi 0.9 Co 0.1 O 2 , by a combination of coprecipitation and the solid-state sintering method. Structural analyses based on high-resolution synchrotron powder diffraction data and X-ray absorption spectra suggest that Ga preferentially sits in the NiO 6 slabs, resulting in reduced Ni/Li cationic mixing and depressed lattice vibration. Due to the smaller dissociation energy of Ga−O bonds, some Ga 3+ cations migrate first toward Li layers upon delithiation and form the GaO 4 tetrahedral symmetry irreversibly during the electrochemical process, which acts as a pillar in the subsequent electrochemical processes. As a result, the doped material exhibits both improved cycling performance and rate capability under a high operating voltage (4.5 V) due to the stabilized structure in the lithiation/delithiation process. This study illustrates how a dopant enhances the electrochemical stability in views of both pristine and charged structure and suggests that a positive effect is expected from the dopant favoring the tetrahedral symmetry (e.g., Al).

Regulating Pseudo-Jahn–Teller Effect and Superstructure in Layered Cathode Materials for Reversible Alkali-Ion Intercalation

“…Many heavy-elemental dopants (i.e., Sn, La) have been reported to improve the electrochemical stability of LiCoO 2 at a high voltage, likely resulting from the relieved lattice vibration reducing the vibronic couplings. , Following this line, we also demonstrate the high efficiency of a W dopant in LiCoO 2 (Figure S17, SI). In addition, other dopants (i.e., Al, Ga) that prefer tetrahedral geometry, also could be effective for enhancing the structural stability and electrochemical performance of O3-type layered cathodes that are constructed with transition-metal oxide octahedra as a basic unit because the resulting tetrahedra from Al or Ga could significantly suppress the pseudo-JTE in the octahedral geometry. , Regulating the pseudo-JTE appears mandatory for fundamentally stabilizing the structure of layered cathodes and thereby maximizing their electrochemical performances.…”

“…In addition, other dopants (i.e., Al, Ga) that prefer tetrahedral geometry, also could be effective for enhancing the structural stability and electrochemical performance of O3-type layered cathodes that are constructed with transition-metal oxide octahedra as a basic unit because the resulting tetrahedra from Al or Ga could significantly suppress the pseudo-JTE in the octahedral geometry. 35,36 Regulating the pseudo-JTE appears mandatory for fundamentally stabilizing the structure of layered cathodes and thereby maximizing their electrochemical performances.…”

Reversible Li Intercalation in Layered Cathodes Enabled by Dopant-Induced Medium-Range Orders

“…The deviation from the exact Li site suggests that the Mg atom appears as MgO 4 tetrahedral configuration, similar to the Al and Ga dopants. 25 The tetrahedral bonds are generally much stronger than their octahedral counterparts, which could inhibit the slipping of CoO 2 layers more effectively. The tetrahedral oxygen ligands typically have higher electron density than the octahedral oxygen ligands; 26 this helps to suppress electron transfer from the octahedral ligand to Co, which will in turn depress the PJTE upon battery operation.…”

Galvanostatic Electrodeposition of Durable IrOx Films on Low-Iridium-Supported Titanium for an Acidic Oxygen Evolution Reaction

“…Theoretically, the impact of the OER at 0.05 mA cm –2 is weakest, but because of the small amount of deposition, the IrO x deposition layer cannot cover the substrate, resulting in bare titanium being oxidized by air during the heat treatment. Considering the limitations of the XRD experiment, the material cannot be characterized as its volume fraction is less than 5%. , Therefore, few IrO 2 grains or forming a thin film may not be detected, which also can be used to explain the inability of the rutile phase peak of iridium oxide to appear at low current density.…”

“…Considering the limitations of the XRD experiment, the material cannot be characterized as its volume fraction is less than 5%. 48,49 Therefore, few IrO 2 grains or forming a thin film may not be detected, which also can be used to explain the inability of the rutile phase peak of iridium oxide to appear at low current density.…”