LiCoO2, discovered as a lithium‐ion intercalation material in 1980 by Prof. John B. Goodenough, is still the dominant cathode for lithium‐ion batteries (LIBs) in the portable electronics market due to its high compacted density, high energy density, excellent cycle life and reliability. In order to satisfy the increasing energy demand of portable electronics such as smartphones and laptops, the upper cutoff voltage of LiCoO2‐based batteries has been continuously raised for achieving higher energy density. However, several detrimental issues including surface degradation, damages induced by destructive phase transitions, and inhomogeneous reactions could emerge as charging to a high voltage (>4.2 V vs Li/Li+), which leads to the rapid decay of capacity, efficiency, and cycle life. In this review, the history and recent advances of LiCoO2 are introduced, and a significant section is dedicated to the fundamental failure mechanisms of LiCoO2 at high voltages (>4.2 V vs Li/Li+). Meanwhile, the modification strategies and the development of LiCoO2‐based LIBs in industry are also discussed.
Ni-rich cathode materials
LiNi
x
Co
y
Mn1–x–y
O2 (x ≥ 0.6) have attracted much attention
due to their high capacity and low cost. However, they usually suffer
from rapid capacity decay and short cycle life due to their surface/interface
instability, accompanied by the high Ni content. In this work, with
the Ni0.9Co0.05Mn0.05(OH)2 precursor serving as a coating target, a Li-ion conductor Li2SiO3 layer was uniformly coated on Ni-rich cathode
material LiNi0.9Co0.05Mn0.05O2 by a precoating and syn-lithiation method. The uniform Li2SiO3 coating layer not only improves the Li-ion
diffusion kinetics of the electrode but also reduces mechanical microstrain
and stabilizes the surface chemistry and structure with a strong Si–O
covalent bond. These results will provide further in-depth understanding
on the surface chemistry and structure stabilization mechanisms of
Ni-rich cathode materials and help to develop high-capacity cathode
materials for next-generation high-energy-density Li-ion batteries.
The lithium-rich Li[Li0.2Ni0.13Mn0.54Co0.13]O2 nanoplates were synthesized using a molten-salt method. The nanoplates showed an initial reversible discharge capacity of 233 mA·h·g−1, with a fast capacity decay. The morphology and micro-structural change, after different cycles, were studied by a scanning electron microscope (SEM) and transmission electron microscopy (TEM) to understand the mechanism of the capacity decay. Our results showed that the cracks generated from both the particle surface and the inner, and increased with long-term cycling at 0.1 C rate (C = 250 mA·g−1), together with the layered to spinel and rock-salt phase transitions. These results show that the cracks and phase transitions could be responsible for the capacity decay. The results will help us to understand capacity decay mechanisms, and to guide our future work to improve the electrochemical performance of lithium-rich cathode materials.
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