Atomic‐Scale Revealing the Structure Distribution between LiMO₂ and Li₂MnO₃ in Li‐Rich and Mn‐Based Oxide Cathode Materials

Abstract

Lithium‐rich and manganese‐based oxide (LRMO) cathode materials are regarded as promising cathode materials for lithium‐ion batteries with anionic redox characteristics and higher specific energy density. However, the complex initial structure and complicated reaction mechanism of LRMO is controversial. Herein, the reaction mechanism and unusual electrochemical phenomena are reconsidered after proposing the concept of structure distribution between Li2MnO3 and LiMO2 structures. The initial structure states show different types of composition characteristics of Li2MnO3 and LiMO2, including “large and isolated distribution” and “uniformly dispersed distribution” characteristics, as summarized by multiple aberration correction scanning transmission electron microscopy observations at the atomic‐scale for cross sectional samples. Based on the density functional theory calculations, X‐ray absorption spectroscopy, and atomic‐scale observations during the different voltage states, the results accordingly suggest that the distribution characteristic is the essential cause of the unusual behavior in LRMO. It governs the reaction behavior, leading to the changes in electronic structure of O2p and TM3d, and the maintenance of layered structure, reversibility of the anionic redox, as well as, the voltage hysteresis. This work constructs the interrelationships of electrochemical behavior—distribution characteristic—reaction mechanism, contributing to the further application of LRMO materials in the electric vehicle market.

Tuning Li2MnO3-Like Domain Size and Surface Structure Enables Highly Stabilized Li-Rich Layered Oxide Cathodes

“…As shown in Figure S14, the D Li + values of LNMO-0.1 are greater than that of LNMO-20 in the whole potential range, implying better Li + diffusion kinetics of LNMO-0.1. Therefore, in summary, the Li + migration kinetics in the uniformly dispersed Li 2 MnO 3 -like domain structure was significantly boosted …”

“…As shown in Figure S6b, the peaks of the Li 2 MnO 3 -like domains become weaker, and the full width at half-maximum (fwhm) increases from LNMO-20 to LNMO-0.01, while the (020) M peaks are similar in shape for all samples. The phenomenon is attributed to the reduction of the size of the Li 2 MnO 3 -like domains, since the increase in stacking faults tends to cause asymmetric broadening of the (020) M peak. ,, According to the Scherrer equation, the average grain size of Li 2 MnO 3 -like domains decreases from 56.25 nm for LNMO-20 to 23.57 nm for LNMO-0.1, while the average grain size of LiTMO 2 domains is almost unchanged (Table S4). Moreover, the results of two-phase Rietveld refinements show that the contents of Li 2 MnO 3 components are 55.25% and 30.78% for LNMO-20 and LNMO-0.1, respectively (Figure a,b, Figure S7, and Table S5).…”

“…Therefore, in summary, the Li + migration kinetics in the uniformly dispersed Li 2 MnO 3 -like domain structure was significantly boosted. 49 The cycling performances of all samples were evaluated at 1 C in the potential range of 2.0−4.6 V, as shown in Figure 3c and Table S7. Reassuringly, LNMO-0.1 exhibits a reversible capacity of 192.3 mAh g −1 , with an excellent capacity retention rate of 85.4% after 300 cycles, which is higher than that of LNMO-20 (181.8 mAh g −1 , 64.6%).…”

Effects of Bending on Nucleation and Injection of Oxygen Vacancies into the Bulk Lattice of Li‐Rich Layered Cathodes

“…The Li/TM ratios for each set are as follows: LMR55-1 with a Li/TM ratio of 1.206/0.794, LMR55-2 with a Li/TM ratio of 1.189/0.811, and LMR55-3 with a Li/TM ratio of 1.178/0.822 (Note S6 of the Supporting Information for details of the synthesis). In our previous work, [46] it has been demonstrated that the enhancement of lattice oxygen activity through this biphasic dispersed distribution leads to an increase in the first cycle discharge capacity of LMR. Moreover, STEM imaging enabled us to study the two-phase distribution in the three samples, as shown in Figure 5d-f.…”

Lithium-Ion Conductor Li2ZrO3-Coated Primary Particles To Optimize the Performance of Li-Rich Mn-Based Cathode Materials

“…However, the LRMC still faces all-round challenges including high first irreversible capacity, poor Coulombic efficiency, poor rate capacity, and voltage decay, which have restricted the large-scale use and industrialization of the LRMC. − Therefore, numerous scholars have made a series of important research in enhancing the performance of the LRMC. It has been found that the main failure mechanisms of the materials include lattice oxygen release, transition metal ion migration, and electrode/electrolyte interface side reactions. − …”