Nanoscale-engineered LiCoO2as a high energy cathode for wide temperature lithium-ion battery applications-role of coating chemistry and thickness

Extending the charge cutoff voltage of LiCoO₂(LCO) beyond 4.2 V is considered as a key parameter to obtain higher energy densities. Following gaps have been identified based on a thorough literature survey especially for higher cutoff voltage of nanoscale engineered LCO cathodes, (i) different metal oxides and metal fluoride surface coatings have been mostly done independently by different groups, (ii) room temperature performance was the focus with limited investigations at high temperature, (iii) nonexistence of low temperature cycling studies and (iv) no reports on high rate capability of LCO beyond 4.5 V (especially at 4.8 V) needs to be investigated. Herein, we report the effect of nanoscale engineering of LCO along with the role of coating chemistry and thickness to study its electrochemical performance at higher voltages and at wide operating temperatures. Surface coating was implemented with different metal oxides and a metal fluoride with tunable thickness. At 4.5 V, 5 wt% Al₂O₃coated LiCoO₂(LCO@Al₂O₃-5) delivered a reversible capacity of 169 mAh g^-1at 100 mA g^-1and 151 mAh g^-1at high rate of 10 C (2 A g^-1) and 72% retention at the end of 500 cycles. At 55 °C, it exhibited better stability over 500 cycles at 5 C and even at -12.5 °C it maintained 72% of its initial capacity after 100 cycles at 200 mA g^-1. At 4.8 V cut-off, LCO@Al₂O₃-5 rendered reversible capacity of 213 mAh g^-1at 100 mA g^-1, a high value compared to literatures reported for LCO. Also noted that it delivered a capacity of 126 mAh g^-1at a current density of 1 A g^-1, whereas bare could only exhibit 66 mAh g^-1under same testing conditions. Enhanced performance of LCO@Al₂O₃-5 can be ascribed to the lower charge transfer resistance derived from the stable solid solution formation on the interface.Ex situXRD andex situRaman analysis at different stages of charge/discharge cycles correlates the enhanced performance of LCO@Al₂O₃-5 with its structural stability and minimal structural degradation.

Constructing compatible interface between Li7La3Zr2O12 solid electrolyte and LiCoO2 cathode for stable cycling performances at 4.5 V

With high theoretical capacity and tap density, LiCoO2 (LCO) cathode has been extensively utilized in lithium-ion batteries (LIBs) for energy storage devices. However, the bottleneck of structural and interfacial instabilities upon cycling severely restricts its practical application at high cut-off voltage. From another perspective, the compatibility between the electrode and electrolyte is highly valued in the development of all-solid-state batteries. Herein, we construct a compatible interface between Li7La3Zr2O12 (LLZO) and LCO through a facile surface modification strategy, which significantly improves the cycling stability of LCO at a high cut-off voltage of 4.5 V. Characterization results demonstrate that the LCO@1.0 LLZO sample delivers a desirable capacity retention of 76.8% even after 1000 cycles at 3.0-4.5 V with the current density of 1 C (1 C = 274 mA g-1). Further investigation indicates that the LLZO modification layer could protect the LCO electrode through effectively alleviating the side reactions, which not only facilitates the Li+ transportation at the interface but also mitigates the bulk structure degradation. Moreover, it is also established that a small amount of La and Zr ions could gradiently migrate into the surface lattice of LCO to generate a thin layer of the surface solid solution Li-Co-La-Zr-O. Thus formed pinning region between surface modified LLZO and LCO cathode could contribute both to their mechanical compatibility and Li+ kinetics behavior upon repeated cycling. This work not only provides a strategy in broadening the operation potential and extracting higher capacity of LCO but also sheds light on constructing compatible interfaces in LIBs, especially for all-solid-state energy storage and conversion devices.

Reviving lithium cobalt oxide-based lithium secondary batteries-toward a higher energy density

This review summarizes the key challenges, effective modification strategies and perspectives regarding reviving lithium cobalt oxide-based lithium secondary batteries-toward a higher energy density.