Tuning Co/O Redox Chemistry via Fermi Level Regulation for Stable High-Voltage LiCoO₂

Abstract

LiCoO2 (LCO) is ideal for 3C electronics due to its high tap density. However, the excessive O → Co charge transfer at high delithiation leads to irreversible Co reduction, O release, and structural degradation, deteriorating the high-voltage performance of LCO. Herein, we propose to regulate the intrinsic Fermi level via uneven trace Zr/Mg doping. First, the increase of electron density in the Fermi level mitigates both the O oxidation/coupled Co reduction through alleviating the O → Co charge transfer, restraining the formations of Co2+ and O2. This elevates Co redox activity and reduces O redox activity. In addition, the structural evolution of the cathode at delithiation is simplified. The modulated LCO delivers a high discharge capacity and a high cycling stability with 4.5 and 4.6 V ceilings. This study sheds new light on the modulation of Co/O redox chemistry and the reliable large-scale production of high-voltage LiCoO2.

Electrochemical Restoration of Battery Materials Guided by Synchrotron Radiation Technology for Sustainable Lithium‐Ion Batteries

“…The activated oxygen redox (O 2− ↔O − ) tends to be induced in excess at some specific domains, leading to an irreversible structural degradation and electrochemical performance decay. [ 45 ] Moreover, the surface O − with a higher ionic mobility than O 2− can easily escape from LCO particles. [ 46 ] The O 2 release further promotes the local structure damage and form corrosion cavities at surfaces.…”

Diffusion‐Optimized Long Lifespan 4.6 V LiCoO2: Homogenizing Cycled Bulk‐To‐Surface Li Concentration with Reduced Structure Stress

“…[ 5 ] Numerous strategies, including constructing surface protective layer for the elimination of Co dissolution, tuning Co/O electronic band structure for the reduction of lattice oxygen loss and multiple elements doping for the suppression of phase transitions, have been demonstrated effective in stabilizing the high‐delithiated‐state structure of LCO. [ 6 ] However, till now, rare studies report a long lifespan LCO (e.g., exceed 600 cycles) with a good capacity retention (e.g., >80%), which means that there are still fundamental structure‐stability problems need to be addressed.…”

Ultrathin dense LiF coverage coupled with a near-surface gradient fluorination lattice enables fast-charging long-life 4.6 V LiCoO2

“…[2][3][4][5][6][7][8][9] Essentially, these issues initially stem from near-surface lattice oxygen (O 2À ) instability and derived Co 4+ due to de-lithiation to high voltages of especially 44.5 V. More precisely, the near-surface lattice becomes highly lithium-deficient compared to the bulk lattice during deep de-lithiation causing oxygen redox (O 2À -O nÀ , n o 2) to participate in charge compensation, which can also contribute to considerable additional capacity. 3,[10][11][12][13] However, this process synchronously becomes highly irreversible as charging approaches 4.6 V. As a result, O 2À is highly susceptible to over-oxidation by Co 4+ to peroxide ions (O À ) with high mobility and activity, which will further evolve into O 2 , leading to oxygen loss. 3,5,10,11,14,15 It is reported that the large number of oxygen vacancies caused by oxygen loss triggers the collapse of the crystal structure from the surface to the bulk.…”