Remaining Li-Content Dependent Structural Evolution during High Temperature Re-Heat Treatment of Quantitatively Delithiated Li-Rich Cathode Materials with Surface Defect-Spinel Phase

Abstract

Pre-extracting Li+ from Li-rich layered oxides by chemical method is considered to be a targeted strategy for improving this class of cathode material. Understanding the structural evolution of the delithiated material is very important because this is directly related to the preparation of electrochemical performance enhanced Li-rich material. Herein, we perform a high temperature reheat treatment on the quantitatively delithiated Li-rich materials with different amounts of surface defect-spinel phase and carefully investigate the structural evolution of these delithiated materials. It is found that the high temperature reheat treatment could cause the decomposition of the unstable surface defect-spinel structure, followed by the rearrangement of transition metal ions to form the thermodynamically stable phases, More importantly, we find that this process has high correlation with the remaining Li-content in the delithiated material. When the amount of extracted Li+ is relatively small (corresponding to the higher remaining Li-content), the surface defect-spinel phase could be dominantly decomposed into the LiMO2 (M = Ni, Co, and Mn) layered phase along with the significant improvement of electrochemical performance, and continuing to decrease remaining Li-content could lead to the emergence of M3O4-type spinel impurity embedding in the final product. However, when the extracted Li+ further achieves a certain amount, after the high temperature heat-treatment the Mn-rich Li2MnO3 phase (C2/m) could be separated from Ni-rich phases (including R m, Fd m, and Fm m), thus resulting in a sharp deterioration of initial capacity and voltage. These findings suggest that reheating the delithiated Li-rich material to high temperature may be a simple and effective way to improve the predelithiation modification method, but first the amount of extracted Li+ should be carefully optimized during the delithiation process.

Lewis Acidity Organoboron‐Modified Li‐Rich Cathode Materials for High‐Performance Lithium‐Ion Batteries

“…During the discharge process, an extra plateau at about 2.7 V can be observed in the SLLMO electrode, which is originated from the spinel phase on the surface. [ 38 ] In addition, the initial Coulombic efficiency increases from 79.9% of LLMO to 85.61% of SLLMO, as is well known that the surface oxygen release will lead to the migration of transition metal elements, serious side reactions and so on, all unwanted reactions will decrease the Li‐ion storage capability and finally result in the low ICE. In this experiment, BCD is directly bonded to O 2– , and stronger BO bonding can be formed after the calcination process and a relatively lower valence of transition metal ions can be realized.…”

Multi-dimensional correlation of layered Li-rich Mn-based cathode materials

“…The calcination temperature and time have an important influence on the crystallinity and morphology of a material. The higher the calcination temperature and the longer the hold time, the larger the particle size of the primary particles [116][117][118] , and even the transformation from polycrystalline secondary particles to large single crystal particles occurs, with the structure with a special morphology being more susceptible to damage during the calcination process. It may also cause excessive oxidation of TMs and a loss of Li/O, leading to increased cation mixing and phase transformation [119] .…”

Silicon‐Based Lithium Ion Battery Systems: State‐of‐the‐Art from Half and Full Cell Viewpoint

“…NCM materials have attracted widespread attention due to their high capacities and low cost. [ 269–272 ] Sun and coworkers designed a high energy Ni‐rich NCM||CNT‐Si full cell, in which the CNT‐Si anode material was obtained through a simple ball‐milling process. [ 273 ] Benefiting from the outstanding structural stability of the CNT‐Si material, the Ni‐rich NCM||CNT‐Si full cell delivered an average CE value of 99.8% and capacity retention of 81% after 500 cycles (Figure 9c).…”