Xinyi Dai

Improved Electrochemical Performance of LiCoO2 Electrodes with ZnO Coating by Radio Frequency Magnetron Sputtering

Surface modification of LiCoO2 is an effective method to improve its energy density and elongate its cycle life in an extended operation voltage window. In this study, ZnO was directly coated on as-prepared LiCoO2 composite electrodes via radio frequency (RF) magnetron sputtering. ZnO is not only coated on the electrode as thin film but also diffuses through the whole electrode due to the intrinsic porosity of the composite electrode and the high diffusivity of the deposited species. It was found that ZnO coating can significantly improve the cycling performance and the rate capability of the LiCoO2 electrodes in the voltage range of 3.0-4.5 V. The sample with an optimum coating thickness of 17 nm exhibits an initial discharge capacity of 191 mAh g(-1) at 0.2 C, and the capacity retention is 81% after 200 cycles. It also delivers superior rate performance with a reversible capacity of 106 mAh g(-1) at 10 C. The enhanced cycling performance and rate capability are attributed to the stabilized phase structure and improved lithium ion diffusion coefficient induced by ZnO coating as evidenced by X-ray diffraction, cyclic voltammetry, respectively.

Dicarboxylate CaC8H4O4 as a high-performance anode for Li-ion batteries

Currently, many organic materials are being considered as electrode materials and display good electrochemical behavior. However, the most critical issues related to the wide use of organic electrodes are their low thermal stability and poor cycling performance due to their high solubility in electrolytes. Focusing on one of the most conventional carboxylate organic materials, namely lithium terephthalate Li2C8H4O4, we tackle these typical disadvantages via modifying its molecular structure by cation substitution. CaC8H4O4 and Al2(C8H4O4)3 are prepared via a facile cation exchange reaction. Of these, CaC8H4O4 presents the best cycling performance with thermal stability up to 570 °C and capacity of 399 mA·h·g−1, without any capacity decay in the voltage window of 0.005–3.0 V. The molecular, crystal structure, and morphology of CaC8H4O4 are retained during cycling. This cation-substitution strategy brings new perspectives in the synthesis of new materials as well as broadening the applications of organic materials in Li/Na-ion batteries.

Enhanced reversibility and electrochemical performances of mechanically alloyed Cu3P achieved by Fe addition

Cu3P is a potential anode material for lithium-ion batteries with its comparable gravimetric capacity, but several times higher volumetric capacity (4732 mA h cm−3) than graphite. However, the cycling stability of Cu3P is poor at low discharge potentials and high current densities. In this work, Fe addition is employed as a simple strategy to modulate the composition and phase constitution of Cu3P nanopowders synthesized by wet mechanical alloying, and thereby to tune the electrochemical performance of the anode. The addition of Fe results in a composite constitute containing Cu3P as the major phase and some other minor phases including Cu, α-Fe and FeP, which are combinationally determined by X-ray diffraction, energy dispersive X-ray spectroscopy and Mossbauer spectroscopy. Electrochemical tests reveal that both the cycling stability and the rate capability of the electrodes are improved by Fe addition. The Cu3P electrode with 10% Fe addition shows the best cell performance, with the capacity being remarkably improved by over 100%, from 82 mA h g−1 to 178 mA h g−1 after 50 cycles at 0.75C between 2.0 V and 0.5 V vs. Li/Li+. The improvement of the electrochemical performance is engendered by a synergetic effect of the microstructure change of the powders and the presence of Fe-related minor phases, leading to increased electronic conductivity as well as enhanced electrochemical reversibility of the electrode.