Gongchang Peng

Facile Fabrication of Ethoxy-Functional Polysiloxane Wrapped LiNi0.6Co0.2Mn0.2O2 Cathode with Improved Cycling Performance for Rechargeable Li-Ion Battery

Dealing with the water molecule on the surface of LiNi0.6Co0.2Mn0.2O2 (NCM) cathode and hydrogen fluoride in the electrolyte is one of the most difficult challenges in Li-ion battery research. In this paper, the surface polymerization of tetraethyl orthosilicate (TEOS) on NCM to generate ethoxy-functional polysiloxane (EPS) wrapped NCM (E-NCM) cathode under mild conditions and without any additions is utilized to solve this intractable problem. The differential scanning calorimetry, transmission electron microscopy, and X-ray photoelectron spectroscopy results show that the formed amorphous coating can provide a protective shell to improve the NCM thermal stability, suppress the thickening of the solid electrolyte interphase (SEI) layer, and scavenge HF in the electrolyte. The E-NCM composite with 2 mol % EPS delivers a high discharge capacity retention of 84.9% after 100 cycles at a 1 C discharge rate in the 2.8-4.3 V potential range at 55 °C. Moreover, electrochemical impedance spectroscopy measurements reveal that the EPS coating could alleviate the impedance rise during cycling especially at an elevated temperature. Therefore, the fabricated E-NCM cathode with long-term cycling and thermal stability is a promising candidate for use in a high-energy Li-ion battery.

Effects of functional groups of graphene oxide on the electrochemical performance of lithium-ion batteries

Graphene oxide (GO) with different ratios of functional groups are prepared via low temperature direct thermal reduction technology and re-oxidization by nitric acid, respectively. The structural, elemental, and oxygen-containing functional group compositions and electrochemical behaviors of the prepared GO are characterized using Fourier infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, Raman spectroscopy, and X-ray photoelectron spectroscopy, as well as charge/discharge curves and electrochemical impedance spectra measurements. Compared with graphite and graphene, the enhanced reversible capacity of GO is attributed to the oxygen-containing functional groups and the improved capacities are attributed predominantly to carbonyl and carboxyl groups. Besides, labile oxygen functionalities, such as epoxy groups, have a negative effect on the electrochemical properties, which lower the initial coulomb efficiency of graphene oxide anode materials. These findings may be beneficial to the material design of graphene-based anode materials with a high energy density.