Reducing Co/O Band Overlap through Spin State Modulation for Stabilized High Capability of 4.6 V LiCoO₂

Abstract

High-voltage LiCoO2 (LCO) attracts great interest because of its large specific capacity, but it suffers from oxygen release, structural degradation, and quick capacity drop. These daunting issues root from the inferior thermodynamics and kinetics of the triggered oxygen anion redox (OAR) at high voltages. Herein, a tuned redox mechanism with almost only Co redox is demonstrated by atomically engineered high-spin LCO. The high-spin Co network reduces the Co/O band overlap, eliminates the adverse phase transition of O3 → H1–3, delays the exceeding of the O 2p band over the Fermi level, and suppresses excessive O → Co charge transfer at high voltages. This function intrinsically promotes Co redox and restrains O redox, fundamentally addressing the issues of O2 release and coupled detrimental Co reduction. Moreover, the chemomechanical heterogeneity caused by different kinetics of Co/O redox centers and the inferior rate performance limited by slow O redox kinetics is simultaneously improved owing to the suppression of slow OAR and the excitation of fast Co redox. The modulated LCO delivers ultrahigh rate capacities of 216 mAh g–1 (1C) and 195 mAh g–1(5C), as well as high capacity retentions of 90.4% (@100 cycles) and 86.9% (@500 cycles). This work sheds new light on the design for a wide range of O redox cathodes.

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

“…The (003) peak exhibits two-phase characters in the charged LCOM and LCOF, which could be assigned to two hexagonal phases with varied lattice parameters. Such two-phase co-existence might arise from two reasons: (1) the partial suppression of the high-voltage phase transitions and (2) the chemomechanical heterogeneity caused by different kinetics of Co/O redox centers . Combining the results from in-situ XRD and ex-situ XPS, a strong stabilization effect induced by the MROs in LCOMF could be confirmed, beneficial in maintaining the CoO 2 layers and homogeneity of the particles.…”

Ultrathin Titanium Dioxide Coating Enables High-Rate and Long-Life Lithium Cobalt Oxide

“…In addition, the content of Li 2 CO 3 (589.8 eV) in the C1s spectra of bare LCO is higher than that of LCO-ALD50, suggesting that the bare LCO has a greater reduction by the carbonate solvent during charging and discharging [ 20 ]. The deconvoluted peaks at 530.9 eV and 530.3 eV in the O1s spectra can be ascribed to Li x PF y O z and M-O, respectively [ 7 , 12 ]. The intensity of M-O can be used as an indicator of the thickness of the CEI layer.…”

“…Strategies have been demonstrated to address the above problem of high-voltage LCO (HV-LCO), including nano-structuring [ 5 ], surface coating [ 6 , 7 ], electrolyte modification [ 8 ] and cation doping [ 9 , 10 ]. Surface coating with highly ionic/electronic conductors or metal oxides can effectively improve the rate performance and long-cycling stability of HV-LCO [ 10 , 11 , 12 ].…”

Structural Understanding for High‐Voltage Stabilization of Lithium Cobalt Oxide

“…As a result, oxygen loss from Li x CoO 2 ( x ≤ 0.5) can be further triggered to propel the compositions within the LiCoO 2 ‐Li 0.5 CoO 2 ‐Co 3 O 4 tie‐line triangle in the Li–Co–O ternary phase diagram, [ 68 ] while resulting oxygen vacancies may also cause spin flip or even electron injection in nearby Co 3 d electronic structure. Oxygen redox in LCO may be restrained by HS Co, [ 69 ] but various studies have shown that O, especially that in the surface, mainly and passively compensates for charge above 4.4 V. [ 63 ] Similar anionic redox is found in other layered oxides like LMRO and Li 2 MnO 3 but is more severe.…”