Elucidating and Mitigating the Degradation of Cationic–Anionic Redox Processes in Li1.2Mn0.4Ti0.4O2 Cation-Disordered Cathode Materials

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Abstract
Cation-disordered rock-salt oxides with O2-/O2n- redox reaction, such as Li1.2Mn0.4Ti0.4O2 (LMTO), are critical Li-rich cathode materials for designing high-energy-density batteries. Understanding the cationic-anionic redox accompanying with the structural evolution process is really imperative to further improve the performance. In this work, the cationic-anionic redox and capacity degradation mechanism of carbon coated LMTO during (dis)charge processes are elucidated by combining in-situ X-ray diffraction (XRD), X-ray absorption near edge spectroscopy (XANES), differential electrochemical mass spectrometer (DEMS), transmission electron microscope (TEM) and electrochemical analyses. It is concluded that the redox reaction of the Mn2+/Mn4+ is quite stable, while the severe degradation is mainly caused by the O2-/O2n- redox process. Moreover, we clearly clarify how the cationic-anionic interplay governs sluggish kinetics, large polarization, and capacity fading in LMTO, and reveal for the first time that a certain amount of carbon coating is capable of suppressing the irreversible lattice oxygen loss and result in encouraging cyclic performance. In summary, we elucidate the degradation of cationic-anionic redox processes in cation disordered cathode materials and propose strategies of adjusting electronic/ionic conductivity of the electrodes to modulate the oxygen redox reactions, setting a new direction for the design of better cation-disordered oxides.
Funding Information
  • Ministry of Science and Technology of the People's Republic of China (2018YFB0905400, 2016YFB0901500)
  • National Natural Science Foundation of China (21761132030, 21935009)

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