Lithium-ions diffusion kinetic in LiFePO4/carbon nanoparticles synthesized by microwave plasma chemical vapor deposition for lithium-ion batteries

• Published in: Applied surface science 2018-03, Vol.433, p.35-44
• Main Authors: Gao, Chao, Zhou, Jian, Liu, Guizhen, Wang, Lin
• Format: Article
• Language: English
• Subjects: Chemical diffusion coefficient; Electrochemical impedance spectroscopy; LiFePO4/carbon nanoparticles; Microwave plasma chemical vapor deposition (MPCVD)
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2017.10.034

•Nanoscale LiFePO4/carbon is first synthesized successfully using MPCVD method.•Kinetic behavior of electrode during charge/discharge process is explored by EIS.•Li-ion diffusion is slower in two-phase stage compared with that in single-phase.•Nanosize can widen fast single-phase diffusion, shorten slow two-phase diffusion.•A complete, uniform, thin carbon coating layer can ensure electron transport fast. Olivine structure LiFePO4/carbon nanoparticles are synthesized successfully using a microwave plasma chemical vapor deposition (MPCVD) method. Microwave is an effective method to synthesize nanomaterials, the LiFePO4/carbon nanoparticles with high crystallinity can shorten diffusion routes for ionic transfer and electron tunneling. Meanwhile, a high quality, complete and homogenous carbon layer with appropriate thickness coating on the surface of LiFePO4 particles during in situ chemical vapor deposition process, which can ensure that electrons are able to transfer fast enough from all sides. Electrochemical impedance spectroscopy (EIS) is carried out to collect information about the kinetic behavior of lithium diffusion in LiFePO4/carbon nanoparticles during the charging and discharging processes. The chemical diffusion coefficients of lithium ions, DLi, are calculated in the range of 10−15–10−9cm2s−1. Nanoscale LiFePO4/carbon particles show the longer regions of the faster solid-solution diffusion, and corresponding to the narrower region of the slower two-phase diffusion during the insertion/exaction of lithium ions. The CV and galvanostatic charge-discharge measurements show that the LiFePO4/carbon nanoparticles perform an excellent electrochemical performance, especially the high rate capacity and cycle life.