Effects of Mg Doping at Different Positions in Li-Rich Mn-Based Cathode Material on Electrochemical Performance

Abstract

Li-rich Mn-based layered oxides are among the most promising cathode materials for next-generation lithium-ion batteries, yet they suffer from capacity fading and voltage decay during cycling. The electrochemical performance of the material can be improved by doping with Mg. However, the effect of Mg doping at different positions (lithium or transition metals) remains unclear. Li1.2Mn0.54Ni0.13Co0.13O2 (LR) was synthesized by coprecipitation followed by a solid-state reaction. The coprecipitation stage was used to introduce Mg in TM layers (sample LR-Mg), and the solid-state reaction (st) was used to dope Mg in Li layers (LR-Mg(st)). The presence of magnesium at different positions was confirmed by XRD, XPS, and electrochemical studies. The investigations have shown that the introduction of Mg in TM layers is preferable in terms of the electrochemical performance. The sample doped with Mg at the TM positions shows better cyclability and higher discharge capacity than the undoped sample. The poor electrochemical properties of the sample doped with Mg at Li positions are due to the kinetic hindrance of oxidation of the manganese-containing species formed after activation of the Li2MnO3 component of the composite oxide. The oxide LR-Mg(st) demonstrates the lowest lithium-ion diffusion coefficient and the greatest polarization resistance compared to LR and LR-Mg.

Cobalt-Free Oxide Cathode Material with Phase Composition Control to High Electrochemical Performance in Li-Ion Batteries

“…S5 (region B) of the supporting information. This oxidation peak is related to the irreversible process of Li 2 MnO 3 activation, which is accompanied by lithium and oxygen release or oxygen redox, according to the reports of Ma et al 28 and Makhonica et al 44 In addition, the Li 2 MnO 3 suffers a structure rearrangement and transforms to a new phase. i.e., the transition from a layer structure to a cubic spinel-like framework occurs.…”

“…Moreover, most of the literature attributes the intensity ratio increase to the doping in the structure. 44 However, the balance between the good crystallinity and the low ratio of cation mixing is limited by the Ni amount in the layer material. In addition, the combination of the high thermal treatment temperature and high nickel content in the samples could lead to phase transformation.…”

Modification Strategies and Challenges of High‐Performance Lithium‐Rich Manganese‐Based Cathode Materials

“…Elemental doping can be categorized into three types based on their charge properties: cationic doping (Mg 2þ , Al 3þ , Na þ , Nb 5þ , Fe 3þ , etc. ), [22,23,25,43,44] anionic doping (F À , S 2À , etc. ), [45,46] and multi-ion co-doping.…”

Enhancing Ionic Transport and Structural Stability of Lithium‐Rich Layered Oxide Cathodes via Local Structure Regulation

“…[10] Doping elements can form strong M-O bonds with nearby oxygen atoms, thereby suppressing irreversible phase transitions caused by cation mixing and lattice oxygen loss. Various ion doping has been studied, such as Na, [11] Mg, [12] Ti, [13] Nb, [14] etc., and the results show that the doping elements significantly affecting the structural stability and electrochemical properties of crystalline materials. Similarly, introducing a secondary phase or constructing a multiphase structure in layered crystal structures provides an alternative approach for crystal structure design.…”