The submicron single crystals of LiCoPO 4 with 500 nm diameter are prepared by solvothermal method . The carbon coated sample is obtained using sucrose as carbon source under 650 °C subsequently. It is investigated that the solvent composition has an effect on the morphology and the electrochemical performance of the cathode material . The as-prepared samples are characterized with X-ray diffraction, scanning electron microscopy, transmission electron microscopy , X-ray photoelectron spectroscopic, dynamic light scattering , and Fourier transform infrared spectra. The electrochemical performance is evaluated by cyclic voltammetry , galvanostatic charge–discharge, and electrochemical impedance spectroscopy . The LiCoPO 4 /C cathode can reach an initial discharge capacity of 123.8 mA h g −1 at 0.1C, with a retention of 83% after 100 cycles. A discharge capacity of 84.9 mA h g −1 is still attainable when the rate is up to 2C. The good cycling performance and rate capability are contributed to the decrease of particle size along with the lower antisite defect concentration in the LCP crystals, and uniform carbon coating.
Jian Wei,Houfei Xiong,Hao Zhang,Xueting Li,Yanyi Liu,Zongmo Shi
The challenge of commercial layered-structure nickel-rich cathodes in lithium-ion batteries (LIBs) are the rapid capacity/voltage degradation at high rate capability and thermal runaway. The wide operational voltage range and excellent electrochemical stability of the coating material are key points to improve electrochemical performance and thermal stability at high voltage and high rate conditions. The uniformly olivine-type LiCoPO 4 (LCP) coatings were successfully prepared on the surface of LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) cathode combining sol–gel method and heat treatment. The capacity retention and operating voltage stability of the cathode at high cutoff voltage of 4.6 V were dramatically improved due to the ultrathin and stable interface is designed. The modified NCM811 exhibited a high cycling capacity of 157.7 mAh·g −1 at 5 C with a capacity loss of only 12.1 %. In high nickel cathode coating modification, LCP as the thinnest phosphate coating effectively improves the capacity decay of the cathode at high rate. The interface reconstruction provided a stable channel of Li + transport, which suppressed the cathode/electrolyte interface reaction to enhance the stability. The formation of strong covalent P O bonds at the interface significantly reduced the oxidizing activity on the NCM811 surface, further inhibiting the oxygen release and irreversible phase transition.
LiCoPO 4 (LCP) synthesized particles, which used a conventional solid-state method, were applied as activators for the first time to activate peroxymonosulfate (PMS) with diethyl phthalate (DEP) as the target pollutant. Contrast tests presented that LCP possessed excellent ability of activating PMS for pollutant removal without controlling pH. About 98.6% of DEP could be removed in 6 min with 0.1 g L −1 LCP and 0.15 g L −1 PMS. Rating under different concentrations of Co 2+ and leaching solution, activation tests indicated that LCP/PMS system involved in heterogeneous and homogeneous reaction. To reduce the homogeneous effect of Co 2+ ions, LCP dose decreased to 0.01 g L −1 , and the time for entire removal of DEP was extended to 60 min. Technologies such as Scanning electron microscope (SEM), X-ray diffraction (XRD), Raman and X-ray photoelectron spectroscopy (XPS) were employed to characterize the particles before and after the reaction. It was found that characterizations of samples had little change and that the DEP removal efficiencies showed no significant reduction after 3 cycles. Sulfate radicals and hydroxyl radicals existed together to make great contributions. This study presented the proposed mechanism of radical production in LCP/PMS system for the DEP removal. Co 2+ /Co 3+ cycle in heterogeneous surface and homogeneous solution play important roles in the process of PMS activation . This report would help to understand the mechanism of PMS activation on LCP and offered an alternative environment-friendly scheme for pollutant removal.
Bo Xiao,Dongjia Li,Xinyi Dai,Yawei Wei,Yunchao Liao,Chao Wang,Fangli Ji,Fuzhong Wu
The low cycling stability of LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) is due to structural instability during lithium insertion and removal and strong surface reactivity, and it limits widespread application. In this study, a layer of LiCoPO 4 was coated on NCM811, and electrochemical tests showed that the material had excellent high-voltage electrochemical properties. The NCM811 sample coated with 1.0 wt% LiCoPO 4 (NCM-LCP1) had a capacity of 156.5 mAh g −1 after 100 cycles at 3–4.6 V and a retention rate of 87.47%. In contrast, the capacity of unmodified NCM811 was only 96.9 mAh g −1 , with a retention rate of 55.9%. An NCM-LCP1/graphite full cell demonstrated a capacity retention rate of 87.46% over 200 cycles at 3–4.3 V. By combining EIS and postcycle analyses, the stability and protection mechanism of the LiCoPO 4 layer under high voltage was confirmed. The LiCoPO 4 layer effectively prevented particle fragmentation and kept the structure stable. It also suppressed side reactions on the cathode surface. This work offers a new methodology for modifying NCM811 materials operated at 4.6 V.
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