Origin of Structural Evolution in Capacity Degradation for Overcharged NMC622 via Operando Coupled Investigation

Abstract

The nickel-rich layered oxide materials have been selected as promising cathode materials for the next generation lithium ion batteries because of their large capacity and comparably high operating voltage. However, at high voltage (beyond 4.30 V vs Li/Li), the members of this family are all suffering from a rapid capacity decay, which was commonly concerned with crystal lattice distortion and related cation disordering. In this work, the quasi-spherical Ni-rich layered LiNiCoMnO (QS-NMC622) material was successfully synthesized through the carbonate co-precipitation method. A coupled measurement, which is a combination of potentiostatic intermittent titration technique (PITT) and in situ X-ray diffraction (XRD), was deployed to simultaneously capture the structural changes and lithium ion diffusion coefficient of QS-NMC622 material during the first cycle. With help of in situ XRD patterns and high-resolution transmission electron microscope (HR-TEM) images, a defective spinel framework of Fd3̅m space group was detected along with a rapid decreasing lattice-parameter c and lattice distortion at deep delithiated state, which causes poor kinetics related to lithium ion mobility. The new-born framework seems to transform and remain as full spinel structure in the parent phase to the end of charge/discharge with high voltage, which could deteriorate both the surface and body structure stability during the subsequent cycles. This established coupled in situ measurement could be applied to simultaneously investigate the structure transformation and kinetics of cathode materials during charge/discharge.

In Situ Probing Multiple‐Scale Structures of Energy Materials for Li‐Ion Batteries

“…The peak evolution profiles of selected angles (d) from 17.7° to 20.2° and (e) from 62.5° to 67.5° for the as‐prepared NCM622 cathode material. Reproduced with permission . Copyright 2017, American Chemical Society.…”

“…Thus, the NCM811 electrode is more likely to suffer from accelerated capacity attenuation caused by the intergranular fracture. In addition, Wang et al combined the potentiostatic intermittent titration and in situ XRD techniques to simultaneously capture the structural changes and lithium ion diffusion coefficients of NMC622 electrode during the initial cycle . From the continuous XRD peak profiles (Figure d,e), the splitting feature of the Bragg peaks, corresponding to R ‐3 m layered structure, transformed into a single‐peak feature ( Fd ‐3 m ) at high voltage.…”

The effect of chelating agent on synthesis and electrochemical properties of LiNi0.6Co0.2Mn0.2O2

“…The lattice parameters were obtained via refining and calculating in Bruker DIFFRAC EVA software, as showed in Table 1. The value of c/a reflects the trigonometric distortion of the main structure, and the higher the value, the more complete of layered hexagonal structure [29,30]. It can be observed in the Table 1 ordered a-NaFeO 2 structure among the three samples, which indicate that it has the best structural stability.…”

“…The average primary particle size of S-622 is the largest, C-622 and G-622 are almost same. It is generally believed that when the primary particle size is small, the active particles can be sufficiently infiltrated by the electrolyte, which is favorable for electrochemical performance via enhanced insertion/ discharge of Li + [21,22]. In order to study the agglomeration of primary particles, the specific surface area of three samples were measured by automatic surface area and pore size distribution analyzer.…”

Layer‐Based Heterostructured Cathodes for Lithium‐Ion and Sodium‐Ion Batteries

“…As demonstrated in Figure a, the crystallographic configuration of layered LiMO 2 is arrayed in rhombohedral ( R m ) α‐NaFeO 2 symmetry with alternate Li and M layers formed by edge sharing octahedral unit cells . The close‐packed orientation of the MO 6 octahedrons in the M layers obstructs vertical diffusion of Li + along the c axis, which is responsible for the comparatively low Li + diffusion coefficients of layered materials (10 −9 –10 −10 cm 2 s −1 ) . Moreover, site replacements between Li + and Ni 2+ are also common in Ni‐containing LiMO 2 , as the Ni 2+ and Li + ions have similar ionic radius .…”