Understanding improved electrochemical properties of NiO-doped NiF sub(2)-C composite conversion materials by X-ray absorption spectroscopy and pair distribution function analysis

• Published in: Physical chemistry chemical physics : PCCP Vol. 16; no. 7; pp. 3095 - 3102
• Main Authors: Lee, Dae Hoe, Carroll, Kyler J, Chapman, Karena W, Borkiewicz, Olaf J, Calvin, Scott, Fullerton, Eric E, Meng, Ying Shirley
• Format: Journal Article
• Language: English
• Published: 01.01.2014
• Subjects: Absorption spectroscopy; Composite materials; Conversion; Discharge; Distribution functions; Electronics; Nanoparticles; Nickel; X-rays
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c3cp54431a

The conversion reactions of pure NiF sub(2) and the NiO-doped NiF sub(2)-C composite (NiO-NiF sub(2)-C) were investigated using X-ray absorption spectroscopy (XAS) and pair distribution function (PDF) analysis. The enhanced electronic conductivity of NiO-NiF sub(2)-C is associated with a significant improvement in the reversibility of the conversion reaction compared to pure NiF sub(2). Different evolutions of the size distributions of the Ni nanoparticles formed during discharge were observed. While a bimodal nanoparticle size distribution was maintained for NiO-NiF sub(2)-C following the 1st and 2nd discharge, for pure NiF sub(2) only smaller nanoparticles ( similar to 14 Aa) remained following the 2nd discharge. We postulate that the solid electrolyte interphase formed upon the 1st discharge at large overpotential retards the growth of metallic Ni leading to formation of smaller Ni particles during the 2nd discharge. In contrast, the NiO doping and the carbon layer covering the NiO-NiF sub(2)-C possibly facilitate the conversion process on the surface preserving the reaction kinetics upon the 2nd discharge. Based on the electronic conductivity and surface properties, the resulting size of the Ni nanoparticles is associated with the conversion kinetics and consequently the cyclability.