The Intriguing Nature of Fluorine Doping on Li₂CuO₂ and the Reasons Behind the Inhibition of Oxygen Evolution

Abstract

Oxygen evolution is a major contributor to the degradation of lithium metal oxide cathode materials during initial charging, leading to low initial capacities and poor cyclability. The introduction of different ions to modify the electrochemical behavior of these materials and combat oxygen evolution is commonplace; while the benefits of these modifications are evident, the nature of these modifications are not fully understood. Herein, a multiangle approach is utilized to elucidate the effects of fluorine doping on the evolution of oxygen in Li 2 CuO 2 . Through XRD, the presence of fluorine is confirmed in the synthesized samples via the detection of the contraction in the unit cell of Li 2 CuO 2 in the a and c directions, and the results are verified through solid-state 19 F NMR. As a result of F-doping, the electrochemical results suggest a modification of the bulk properties, showing an increased reversible capacity. Li 2 CuO 2 only discharges 83 mAh g −1 on the 10th cycle, while the cuprate doped with 5.0 mol % fluorine achieved a discharge capacity of 133 mAh g −1 . This improvement is attributed to the presence of F in the structure of Li 2 CuO 2 , as determined via in situ DEMS experiments. Lastly, ab initio calculations further support the hypothesis that fluorine doping changes the density of states close to the Fermi level, altering the bulk properties and the likelihood for oxygen evolution.

Enhanced Cycling Performance of a Li-Excess Li2CuO2 Cathode Additive by Cosubstitution Nanoarchitectonics of Ni and Mn for Lithium-Ion Batteries

“…35 In principle, such bands are related to three different vibration modes, such as one A g and two B g in the crystal structure of CuO. 36 As confirmed in the XRD pattern, the signals for the secondary phase (i.e., Li 2 MnO 3 ) were clearly identified at 498 and 613 cm −1 in the spectrum of LCMO with a high concentration of Mn. 37 As proposed, single-phase LCNMO can be retained without any impurity or secondary phase after the Ni/Mn cosubstitution due to the low concentration of Mn.…”

“…The Raman spectra of Li 2 CuO 2 also showed three distinctive bands at 368, 387, and 583 cm –1 , corresponding to copper oxides with a divalent Cu 2+ such as CuO (Figure c) . In principle, such bands are related to three different vibration modes, such as one A g and two B g in the crystal structure of CuO . As confirmed in the XRD pattern, the signals for the secondary phase (i.e., Li 2 MnO 3 ) were clearly identified at 498 and 613 cm –1 in the spectrum of LCMO with a high concentration of Mn .…”

Estudio de cuprato de litio modificado con iones de metales de transición como cátodo alternativo para baterías de ion litio

“…La tabla 1. Entre los materiales propuestos para utilizarse como cátodo para baterías de ion litio, el cuprato de litio (Li2CuO2) ha sido estudiado debido principalmente a dos factores: La abundancia de Cu en el planeta, permitiéndole ser un metal económico y, la alta capacidad teórica (490 mAhg -1 ) que posee el material, debido a los dos iones de litio presentes en la estructura [28].…”