Enhanced electrochemical performance of Li-rich cathode materials through microstructural control

Abstract

The microstructural complexity of Li-rich cathode materials has so far hampered understanding the critical link between size, morphology and structural defects with both capacity and voltage fadings that this family of materials exhibits. Li2MnO3 is used here as a model material to extract reliable structure-property relationships that can be further exploited for the development of high-performing and long-lasting Li-rich oxides. A series of samples with microstructural variability have been prepared and thoroughly characterized using the FAULTS software, which allows quantification of planar defects and extraction of average crystallite sizes. Together with transmission electron microscopy (TEM) and density functional theory (DFT) results, the successful application of FAULTS analysis to Li2MnO3 has allowed rationalizing the synthesis conditions and identifying the individual impact of concurrent microstructural features on both voltage and capacity fadings, a necessary step for the development of high-capacity Li-ion cathode materials with enhanced cycle life.

DFT-Assisted Solid-State NMR Characterization of Defects in Li2MnO3

“…(a) As in all Li-rich materials, stacking faults resulting from planar shifts of the mixed Li/Mn layer are energetically favorable although their extent strongly depends on the synthesis conditions (precursors, temperature and time). 38,39,42,43…”

Solid state chemistry for developing better metal-ion batteries

“…5a, b ), faulted close-packing sequence due to the “cubic-to-hexagonal” transformation of the close-packed layers, and incomplete Li/M ordering depending on the x value. Although the theory of diffraction from faulted structures is well-known and corresponding software is developed 59 , it is still rarely used, most probably because of the complexity of modeling faulted stacking sequences, but more so owing to their dynamical behavior upon Li + uptake and removal 60 , 61 . Tracing the defect structure evolution throughout charge/discharge is still a challenge.…”

“…The profiles of the reflections originating from the “honeycomb” ordering (outlined in green) are affected by stacking faults in various concentrations (reproduced from ref. 61 with permission from the Royal Society of Chemistry). c Electron diffraction tomography experiment in a TEM cell with liquid electrolyte and Si 3 N 4 windows: scheme of the cell and data collection procedure, 3D reciprocal space reconstruction (domains of diffracted intensity at the Bragg positions are shown in green) and difference Fourier map showing the Li positions in the LiFePO 4 structure.…”

Synthetic Pathway Determines the Non-equilibrium Crystallography of Li- and Mn-rich Layered Oxides

“…FAULTS facilitates the refinement of stacking faulted structures, thereby enabling an investigation of the degree of faulting within the structure in addition to other structural parameters. The single-phase stacking-faulted LMNCO structure model was obtained by adapting a previously reported Li2MnO3 structure 31 to the LMNCO structure and approximating the TM species to Mn (i.e., Li1.2Mn0.54Ni0.13Co0.13O2 = Li1.2Mn0.8O2), to avoid over-parameterization. The difference between the TM electronic charges before and after this approximation is ~5.8% and therefore, is reasonable.…”

“…The difference between the TM electronic charges before and after this approximation is ~5.8% and therefore, is reasonable. For SS-LMNCO, a two-phase model comprising of stacking-faulted Li2MnO3 31 and LiNi0.33Mn0.33Co0.33O2 10 phases was used, with the latter being incorporated as a background phase. Refinements against neutron diffraction data was carried out without using stacking faulted structure models.…”