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Due to the large demand of lithium-ion batteries (LIBs) for energy storage in daily life and the limited lifetime of commercial LIB cells, exploring green and sustainable recycling methods becomes an urgent need to mitigate the environmental and economic issues associated with waste LIBs. In this work, we demonstrate an efficient direct recycling method to regenerate degraded lithium manganese oxide (LMO) cathodes to restore their high capacity, long cycling stability, and high rate performance, on par with pristine LMO materials. This one-step regeneration, achieved by a hydrothermal reaction in dilution Li-containing solution, enables the reconstruction of desired stoichiometry and microphase purity, which is further validated by testing spent LIBs with different states of health. Life-cycle analysis suggested the great environmental and economic benefits enabled by this direct regeneration method compared with today’s pyro- and hydrometallurgical processes. This work not only represents a fundamental understanding of the relithiation mechanism of spent cathodes but also provides a potential solution for sustainable and closed-loop recycling and remanufacturing of energy materials.

In this work, Li-rich Li1.2Mn0.43+Mnx4+Ti0.4–xO2(LMMxTO, 0 ≤ x≤ 0.4) oxides have been studied for the first time. X-ray diffraction (XRD) patterns show a cation-disordered rocksalt structure when xranges from 0 to 0.2. After Mn4+substitution, LMM0.2TO delivers a high specific capacity of 322 mAh g–1at room temperature (30 °C, 30 mA g–1) and even 352 mAh g–1(45 °C, 30 mA g–1) with an energy density of 1041 Wh kg–1. The reason for such a high capacity of LMM0.2TO is ascribed to the increase of both cationic (Mn) and anionic (O) redox after Mn4+substitution, which is proved by dQ/dVcurves, X-ray absorption near edge structure, DFT calculations, and in situXRD results. In addition, the roles of Mn3+and Ti4+in LMM0.2TO are also discussed in detail. A ternary phase diagram is established to comprehend and further optimize the earth-abundant Mn3+–Mn4+–Ti4+system. This work gives an innovative strategy to improve the energy density, broadening the ideas of designing Li-rich materials with better performance.

Cation-disordered rock-salt oxides with the 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 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, X-ray absorption near-edge spectroscopy, differential electrochemical mass spectrometry, transmission electron microscopy, and electrochemical analyses. It is concluded that the redox reaction of 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 results in an encouraging cycling performance. In summary, we elucidate the degradation of cationic–anionic redox processes in cation-disordered cathode materials and propose strategies for adjusting the electronic/ionic conductivity of the electrodes to modulate the oxygen redox reactions, setting a new direction for the design of better cation-disordered oxides.

Spontaneous and anisotropic surface segregation of W cations in LiMn1.5Ni0.5O4particles can alter the Wulff shape and improve surface stability, thereby significantly improving the electrochemical performance. An Auger electron nanoprobe was employed to identify the anisotropic surface segregation, whereby W cations prefer to segregate to {110} surface facets to decrease its relative surface energy according to Gibbs adsorption theory and subsequently increase its surface area according to Wulff theory. Consequently, the rate performance is improved (e.g., by ∼5-fold at a high rate of 25C) because the {110} facets have more open channels for fast lithium ion diffusion. Furthermore, X-ray photoelectron spectroscopy (XPS) depth profiling suggested that the surface segregation and partial reduction of W cation inhibit the formation of Mn3+on surfaces to improve cycling stability via enhancing the cathode electrolyte interphase (CEI) stability at high charging voltages. This is the first report of using anisotropic surface segregation to thermodynamically control the particle morphology as well as enhancing CEI stability as a facile, and potentially general, method to significantly improve the electrochemical performance of battery electrodes. Combining neutron diffraction, an Auger electron nanoprobe, XPS, and other characterizations, we depict the underlying mechanisms of improved ionic transport and CEI stability in high-voltage LiMn1.5Ni0.5O4spinel materials.

In this work we prepared Li1.2Ni0.2Mn0.6O2(LNMO) using a hydroxide co-precipitation method and investigated the effect of co-modification with NH4F and Al2O3. After surface co-modification, the first cycle Coulombic efficiency of Li1.2Ni0.2Mn0.6O2improved from 82.7% to 87.5%, and the reversible discharge capacity improved from 253 to 287 mAh g–1at C/20. Moreover, the rate capability also increased significantly. A combination of neutron diffraction (ND), high-resolution transmission electron microscopy (HRTEM), aberration-corrected scanning transmission electron microscopy (a-STEM)/electron energy loss spectroscopy (EELS), and X-ray photoelectron spectroscopy (XPS) revealed the changes of surface structure and chemistry after NH4F and Al2O3surface co-modification while the bulk properties showed relatively no changes. These complex changes on the material’s surface include the formation of an amorphous Al2O3coating, the transformation of layered material to a spinel-like phase on the surface, the formation of nanoislands of active material, and the partial chemical reduction of surface Mn4+. Such enhanced discharge capacity of the modified material can be primarily assigned to three aspects: decreased irreversible oxygen loss, the activation of cathode material facilitated with preactivated Mn3+on the surface, and stabilization of the Ni-redox pair. These insights will provide guidance for the surface modification in high-voltage-cathode battery materials of the future.