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.

Li-and Mn-rich cathodes (LMRs) with cationic and anionic redox reactions are considered as promising cathode materials for high-energy-density Li-ion batteries. However, the oxygen redox process leads to lattice oxygen loss and structure degradation, which would induce serious voltage fade and capacity loss and thus limit the practical application. High-valent and electrochemical inactive d 0 element doping is an effective method to tune the crystal and electronic structures, which are the main factors for the electrochemical stability. Herein, noticeably inhibited oxygen loss, reduced voltage fade, enhanced rate performance, and improved structure stability and thermal stability of LMRs have been realized by Ti 4+ and Zr 4+ dual-doping. The underlying modulation mechanisms are unraveled by combining differential electrochemical mass spectrometry, soft X-ray absorption spectroscopies, in situ XRD measurements, etc. The dual-doping reduces the covalency of the TM-O bond, mitigates the irreversible oxygen release during the oxygen redox, and stabilizes the layered framework. The expanded lithium layer facilitates the lithium diffusion kinetics and structure stability. This study may result in the fundamental understanding of crystal and electronic structure evolution in LMRs and contribute to the development of high capacity cathodes.

No abstract

The LiCoO2 cathode undergoes undesirable electrochemical performance when cycled with a high cut-off voltage (≥4.5 V versus Li/Li+). The unstable interface with poor kinetics is one of the main contributors to the performance failure. Hence, a hybrid Li-ion conductor (Li1.5Al0.5Ge1.5P3O12) and electron conductor (Al-doped ZnO) coating layer was built on the LiCoO2 surface. Characterization studies prove that a thick and conductive layer is homogeneously covered on LiCoO2 particles. The coating layer can not only enhance the interfacial ionic and electronic transport kinetics but also act as a protective layer to suppress the side reactions between the cathode and electrolyte. The modified LiCoO2 (HC-LCO) achieves an excellent cycling stability (77.1% capacity retention after 350 cycles at 1C) and rate capability (139.8 mAh g–1 at 10C) at 3.0–4.6 V. Investigations show that the protective layer can inhibit the particle cracks and Co dissolution and stabilize the cathode electrolyte interface (CEI). Furthermore, the irreversible phase transformation is still observed on the HC-LCO surface, indicating the phase transformation of the LiCoO2 surface may not be the main factor for fast performance failure. This work provides new insight of interfacial design for cathodes operating with a high cut-off voltage.

No abstract