Unveiling the Roles of Trace Fe and F Co-doped into High-Ni Li-Rich Layered Oxides in Performance Improvement

Abstract

High-Ni Li-rich layered oxides (HNLOs) derived from Li-rich Mn-based layered oxides (LRMLOs) can effectively mitigate the voltage decay of LRMLOs but normally suffered from decreased capacity and cycling stability. Herein, an effective, simple, and up-scalable co-doping strategy of trace Fe and F ions via a facile expanded graphite template-sacrificed approach was proposed for improving the performance of HNLOs. The trace Fe and F codoping can far more effectively improve both its rate capability and cycling stability in a synergistic manner compared to the introduction of individual Fe cations and F anions. The co-doping of Fe and F increased the Li−O bonds by a magnitude far larger than the summation of the increments by their individual doping, quite favorable for the performance. The trace Fe doping can escalate the capacity and enhance the rate capability significantly by increasing the components of lower valence transition metals to activate their redox reactions more effectively and improving both the electronic and ionic conduction. In contrast, trace F can improve the cycling stability remarkably by lowering the O 2p band top to suppress the lattice oxygen escape effectively which were revealed by density functional theory calculations. The co-doped cathode exhibited excellent cycling stability with a superior capacity retention of 90% after 200 cycles at 1 C, much higher than 64% for the pristine sample. This study offers an idea for synergistically improving the performance of Li-rich layered oxides by co-doping trace Fe cations and F anions simultaneously, which play a complementary role in performance improvement.

Endowing Cobalt-Free Li-Rich Li1.2Ni0.2Mn0.6O2 with Superior Electrochemical Performance via Simultaneous Surface Coating and Ion Co-Doping

“…The Mn 2p 3/2 peak further splits into two characteristic bands corresponding to Mn 4+ with a binding energy of 642.9 eV and Mn 3+ with a binding energy of 642.2 eV. 37,38 A closer look reveals that the difference in the Mn 2p XPS spectra of the LNM and LTP-LNM materials is negligible, suggesting that the LTP modification exhibits little impact on the structure of the Li 2 MnO 3 domain (C2/m space group). In contrast, a significant variation in the Ni 2p XPS spectra of the materials was observed (Figure 3c).…”

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

“…[18] Based on this mechanism, doping and structural modulation have been explored to mitigate voltage attenuation. [31][32][33][34][35][36][37] The voltage decay of the cathode material can be understood as a failure to maintain the integrity and orderability of the layered structure during high cutoff voltage cycling, including oxygen release, phase transitions, and defects. [38] These factors are not isolated but are intrinsically linked.…”

Boosting LiMn2O4 Diffusion Coefficients and Stability via Fe/Mg Doping and MWCNT Synergistically Modulating Microstructure

“…Li et al found that Fe-doped Ni hydroxide powders experienced an enhanced lithium-ion storage capacity with improved cycling stability and rate capability [7]. A similar study claimed that the replacement of Mn by Fe can effectively activate the redox reactions and improve the ionicelectronic conductivities through increasing the lower oxidation state transition metal ions [8]. Te nontransition metal, manganese has also been shown to provide additional storage capacity and suppress capacity fading by increasing the average valence state of Mn which improves the difusion kinetics during Li insertion/extraction.…”