Abstract
The Ni‐rich layered oxides with a Ni content of >0.5 are drawing much attention recently to increase the energy density of lithium‐ion batteries. However, the Ni‐rich layered oxides suffer from aggressive reaction of the cathode surface with the organic electrolyte at the higher operating voltages, resulting in consequent impedance rise and capacity fade. To overcome this difficulty, we present here a heterostructure composed of a Ni‐rich LiNi0.7Co0.15Mn0.15O2 core and a Li‐rich Li1.2− xNi0.2Mn0.6O2 shell, incorporating the advantageous features of the structural stability of the core and chemical stability of the shell. With a unique chemical treatment for the activation of the Li2MnO3 phase of the shell, a high capacity is realized with the Li‐rich shell material. Aberration‐corrected scanning transmission electron microscopy (STEM) provides direct evidence for the formation of surface Li‐rich shell layer. As a result, the heterostructure exhibits a high capacity retention of 98% and a discharge‐voltage retention of 97% during 100 cycles with a discharge capacity of 190 mA h g−1 (at 2.0–4.5 V under C/3 rate, 1C = 200 mA g−1).
Highlights
The Ni-rich layered oxides with a Ni content of >0.5 are drawing much attennone of the efforts could completely elimition recently to increase the energy density of lithium-ion batteries
Many studies have recently pointed out that these deteriorations start at the active material surface, and they extend to the bulk.[6,11,13,14]
Small nanoparticles are formed at the surface of the secondary particles (Figure 2b–d)
Summary
The 20LNM-AlF3-LNCM sample shows an initial discharge capacity of 203 mA h g−1 and a Coulombic efficiency of 81.3%, which are comparable to those of the bare LNCM, even with a high coating amount of 10 wt%. The 20LNM-ALF3-coated LNCM sample shows superior cyclability with a capacity retention of 98% during 100 cycles, even when it is cycled with a high state of charge (SOC) between 2.0 and 4.5 V.
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