Metal Oxide Coated Lithium Cobalt Fluorophosphate Cathode Materials for Lithium Secondary Batteries—Effect of Aging and Temperature

Abstract

Lithium cobalt fluorophosphate (Li2CoPO4F) is a promising 5 V class cathode material for lithium secondary batteries. In this study, surface coating with ZrO2 improved the electrochemical activity of Li2CoPO4F with a maximum discharge capacity of 144 mA h g(-1). The effectiveness of ZrO2 coating was evaluated using aging analysis with a commercial electrolyte, i.e., 1 M LiPF6 in EC:DMC (1:1, v/v). The metal ion dissolution was reduced to 1/8th of that observed in the non-coated Li2CoPO4F. It was found that the thin coating layer had less or no contribution to the additional resistance for the cell, both at an open circuit potential and at a fully charged state; hence, the capacity of the cell was retained over cycling. Elevated temperature aging did not affect the intrinsic property of the coated Li2CoPO4F, as observed from the complete anodic and cathodic peaks from cyclic voltammetry studies after 30 days of storage at 50 degrees C. An increase in impedance was observed for aged cells, which could be due to the thick SEI layer formed during storage. The ZrO2 coating over Li2CoPO4F was crucial for the improved performance of electrode active material at higher operating potentials of up to 5.2 V.

Enhancing the energy density of safer Li-ion batteries by combining high-voltage lithium cobalt fluorophosphate cathodes and nanostructured titania anodes

“…However, recent studies have indicated that Li 2 CoPO 4 F can reach a maximum reversible capacity of 150 mA h g −1 , with an outstanding high-voltage operation of ~5 V vs. Li +  /Li111527282930. Because of the high inefficiency from the first to the second cycle observable in Li 2 CoPO 4 F, these electrodes were subjected to activation cycles before being used in the complete lithium-ion cell (see Supplementary Fig.…”

Interface chemistry engineering in electrode systems for electrochemical energy storage

“…[114][115][116] Moreover, surface coatings onto cathode material with oxides (NiO or MnO 2 ) can essentially shield from direct exposure to the electrolyte solution, improving the structural integrity of the cathode material and suppressing phase transitions. 117,118 For the supercapacitors, a conducting polymer such as polypyrrole (PPy) usually is used to coat the surface of the electrode materials to, which lead to signicantly improved electron transport within every nanostructures. PPy was chosen not only because it has greater density and better degree of exibility, but also itself can undergo a fast redox reaction to store charge.…”