Conversion mechanism of nickel fluoride and NiO-doped nickel fluoride in Li ion batteries

• Published in: Electrochimica acta 2012, Vol.59, p.213-221
• Main Authors: Lee, Dae Hoe, Carroll, Kyler J., Calvin, Scott, Jin, Sungho, Meng, Ying Shirley
• Format: Article
• Language: English
• Subjects: Applied sciences; Conversion; Conversion mechanism; Direct energy conversion and energy accumulation; Electrical engineering. Electrical power engineering; Electrical power engineering; Electrochemical conversion: primary and secondary batteries, fuel cells; energy storage (including batteries and capacitors), defects, charge transport, materials and chemistry by design, synthesis (novel materials); Exact sciences and technology; Nanostructure; Nickel; Nickel fluoride; Nickel fluorides; NiO-doped nickel fluoride; Nucleation and growth of Ni; SQUIDs; Superconducting quantum interference devices; Superparamagnetism; X-ray photoelectron spectroscopy; X-rays
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/j.electacta.2011.10.105

The conversion mechanism of NiF 2 and NiO-doped NiF 2 during electrochemical cycling was investigated using a combination of structural analysis by ex situ X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS) and magnetic analysis by superconducting quantum interference device (SQUID) magnetometry. It was observed that the conversion reactions in both cathode materials were partially reversible; however, they differ in their conversion rate. NiO-doped NiF 2 exhibited enhanced electrochemical properties in terms of the conversion potential and reversibility due to the presence of a NiO phase, which has slightly higher electronic conductivity than NiF 2. It is suggested that the NiO doping reduced the nucleation sites for Ni nanoparticles, subsequently enhancing the kinetics of the conversion reaction involving the growth of Ni particles formed during lithiation. The ex situ XRD and the magnetic hysteresis data ( H C and M S) indicate that the average dimension of the Ni particles formed along with LiF in pristine NiF 2 and NiO-doped NiF 2 during the 1st lithiation was in the superparamagnetic regime, with 4–5 nm and 8–9 nm particle sizes, respectively. Although the particle size was decreased to the nanoscale, the original NiF 2 phase was regenerated by re-lithiation.