Development of the Negative Electrode Using Coin-Stacked CNF for Li Ion Battery

Abstract

In general, graphite materials are used for the negative electrode material for lithium-ion batteries (LIBs). Charge/discharge mechanism of LIBs occurs by Li ion intercalation/deintercalation into/from graphite layers. More high-performance LIBs have been demanded for usage as a power source such as electric vehicles. We focused on the structure of carbon nanofilaments (CNF). The diameter of CNF is very small compared to graphite. CNF has a similar layered structure with graphite. Three distinct structure types of CNF has been identified based on the angle of graphene layers with respect to the filament axis, coin-stacked, cup-stacked, and tubular. CNF has remarkable electronic properties and many other unique characteristics. For this reason, CNF has received much attention. Therefore, in this study, we investigated that coin-stacked CNF (CSCNF) was synthesized by the chemical vapor deposition (CVD) method, and CSCNF negative electrode for LIBs was evaluated. For CNF synthesis, nano metal particles loaded on oxidized diamond were used. Oxidized diamond has oxygen-containing functional groups arranged regularly. Therefore, nano metal particles is a highly dispersed on it. Pd metal was used for loaded metal. Pd metal could synthesized CNF having coin-stacked structures. Pd metal was loaded on oxidized diamond by metal nano-colloidal method. C2H4 as a feedstock for CSCNF was used. Synthesized CSCNF was used for the negative electrode material. Electrochemical properties of the negative electrode were evaluated half-cell test. Half-cell was assembled in a glove box under an argon atmosphere. Oxidation-reduction reaction of the negative electrode was evaluated by cyclic voltammogram (CV) measurement. Capacity of the negative electrode was evaluated by a constant current charge and discharge (CC) measurement. CV and CC measurement were observed that CSCNF had a different discharge behavior as compared to graphite. Electrochemical measurements indicated that CSCNF negative electrode displayed discharged capacity (514 mAh/g) over the theoretical discharged capacity of graphite intercalation compounds (372 mAh/g). From the results, it seems that Li ion was intercalated into CNF layers and adsorbed on the surface of CNF. For this reason, adsorption of Li ion was gained high capacity of the negative electrode with CNF. The negative electrode with CNF was thus found to be appropriate materials for the use in LIBs.