Lithium/Oxygen Incorporation and Microstructural Evolution during Synthesis of Li‐Rich Layered Li[Li_0.2Ni_0.2Mn_0.6]O₂ Oxides

Abstract

As promising cathode materials, the lithium‐excess 3d‐transition‐metal layered oxides can deliver much higher capacities (>250 mAh g−1 at 0.1 C) than the current commercial layered oxide materials (≈180 mAh g−1 at 0.1 C) used in lithium ion batteries. Unfortunately, the original formation mechanism of these layered oxides during synthesis is not completely elucidated, that is, how is lithium and oxygen inserted into the matrix structure of the precursor during lithiation reaction? Here, a promising and practical method, a coprecipitation route followed by a microwave heating process, for controllable synthesis of cobalt‐free lithium‐excess layered compounds is reported. A series of the consistent results unambiguously confirms that oxygen atoms are successively incorporated into the precursor obtained by a coprecipitation process to maintain electroneutrality and to provide the coordination sites for inserted Li ions and transition metal cations via a high‐temperature lithiation. It is found that the electrochemical performances of the cathode materials are strongly related to the phase composition and preparation procedure. The monoclinic layered Li[Li0.2Ni0.2Mn0.6]O2 cathode materials with state‐of‐the‐art electrochemical performance and comparably high discharge capacities of 171 mAh g−1 at 10 C are obtained by microwave annealing at 750 °C for 2 h.

Phosphoric acid and thermal treatments reveal the peculiar role of surface oxygen anions in lithium and manganese-rich layered oxides

“…It is well known that the oxygen anions offer metal coordination sites in the layered structure. 11,45 The oxygen release is therefore supposed to be accompanied by surface atomic rearrangement. The intensity of the Li 1s peak in the XP spectra of LLNMO-TH4 increases, compared to that of LLNMO-H4, pointing towards Li ions from the bulk structure migrating into the empty octahedral/tetrahedral sites on the surface during annealing (i.e.…”

“…[8][9][10] Among these compounds, Li-and Mn-rich layered oxides (LMLOs) are at the forefront of this area achieving high discharge capacities above 250 mA h g À1 . 11,12 However, the oxygen redox activity always causes changes in the crystallographic structure, surface inhomogeneity and release of lattice oxygen in LMLOs, thereby resulting in structural instability and severe voltage fading. 13,14 Recently, extensive research efforts have been devoted to exploring the origin of the structural degradation of LMLOs upon high-voltage cycling.…”

Chemical, Structural, and Electronic Aspects of Formation and Degradation Behavior on Different Length Scales of Ni‐Rich NCM and Li‐Rich HE‐NCM Cathode Materials in Li‐Ion Batteries

“…[57,[231][232][233] Aluminum is a prime example of how partial substitution can dramatically improve the thermal stability of NCMs. Furthermore, by profound investigations into lithium/oxygen incorporation and microstructural evolution during synthesis of Li-rich layered oxides, recently more insights into the degradation mechanism (that involves lithium and oxygen loss and an accompanied transition to a spinel-like phase) were gained, [263] which might point to future strategies to further improve the long-term stability of such CAMs. Mater.…”

Understanding Challenges of Cathode Materials for Sodium‐Ion Batteries using Synchrotron‐Based X‐Ray Absorption Spectroscopy

“…This work highlighted the achievable approach of suppressing and restricting the electrochemical activity of Mn 4+ in Mn‐based P3‐type layered oxides. Other work also highlighted the importance of the oxygen redox chemistry …”