Surface modification of LiCoO2 (LCO) gained much attention as it could play a prominent role in improving electrochemical performance and structural stability. Herein, we report an ultra‐thin TiO2 coating on LiCoO2 (LCO‐TiO2) as a potential candidate to overcome the electrochemical, structural instability and interface issues of the bare‐LCO. The structural properties as well as electrochemical performances of bare‐LCO and LCO‐TiO2 were investigated by X‐Ray diffraction, Transmission Electron Microscopy (TEM), X‐ray Photoelectron Spectroscopy (XPS), Galvanostatic charge‐discharge and electrochemical impedance spectroscopy (EIS). At the end of 100 cycles, 1C rate capacity retention was about 50% and 90% for bare‐LCO and LCO‐TiO2 respectively. Rate studies showed that the bare LCO exhibited a specific capacity of ∼120 mAh/g and only 16 mAh/g at 1C and 60 discharge rates respectively whereas, the TiO2 coated LCO showed a capacity of ∼132 mAh/g and nearly 98 mAh/g at 1C and 60C discharge rates respectively. The implementation of TiO2 coating over LiCoO2 enhanced the electrochemical performance, cell stability as well as efficiency.
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.% Al2O3 coated LiCoO2 (LCO@Al2O3-5) delivered a reversible capacity of 169 mAh/g at 100 mA/g and 151 mAh/g at high rate of 10C (2 A/g) and 72% retention at the end of 500 cycles. At 55 ⁰C, it exhibited better stability over 500 cycles at 5C and even at -12.5 ℃ it maintained 72% of its initial capacity after 100 cycles at 200 mA/g. At 4.8 V cut-off, LCO@Al2O3-5 rendered reversible capacity of 213 mAh/g at 100 mA/g, a high value compared to literatures reported for LCO. Also noted that it delivered a capacity of 126 mAh/g at a current density of 1 A/g, whereas bare could only exhibit 66 mAh/g under 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-situ XRD and ex-situ Raman analysis at different stages of charge/discharge cycles correlates the enhanced performance of LCO@Al2O3-5 with its structural stability and minimal structural degradation.
Lithium ion batteries (LIB) are the domain power house that gratifies the growing energy needs of the modern society. Statistical records highlight the future demand of LIB for transportation and other high energy applications. Cathodes play a significant role in enhancement of electrochemical performance of a battery, especially in terms of energy density. Therefore, numerous innovative studies have been reported for the development of new cathode materials as well as improving the performance of existing ones. Literature designate stable cathode-electrolyte interface (CEI) is vital for safe and prolonged high performance of LIBs at different cycling conditions. Considering the context, many groups shed light on stabilizing the CEI with different strategies like surface coating, surface doping and electrolyte modulation. Local temperature variation across the globe is another major factor that influences the application and deployment of LIB chemistries. In this review, we discuss the importance of nano-scale engineering strategies on different class of cathode materials for their improved CEI and hence their low and high temperature performances. Based on the literature reviewed, the best nano-scale engineering strategies investigated for each cathode material have been identified and described. Finally, we discuss the advantages, limitations and future directions for enabling high performance cathode materials for a wide range of applications.
Germanium thin-film anodes for Li-ion battery applications are the focus of the present work. As part of this chapter, we shall briefly review the use of germanium thin films in Li-ion batteries, and subsequently, new results pertaining to the effect of vinylene carbonate (VC) as electrolyte additive on the electrochemical performance are presented. We have used cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy to investigate the performance. Thin-film electrode performance with 0 wt. %, 5 wt. %, and 10 wt.% VC as electrolyte additive was compared to understand the role of additive's concentration. The cell with 5 wt.% VC as electrolyte additive exhibited best performance with high specific capacity of 975 mAh/g, with a retention of 94 and 99% Coulombic efficiency at the end of 100 cycles. Ex situ surface chemical analysis of the solid-electrolyte interphase (SEI) layer has been studied in detail using X-ray photoelectron spectroscopy and correlated with the electrochemical performance.
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