New Fluorinated Carbon Materials for Binder-Free Ultra-High Capacity Cathodic Materials

Abstract

Low capacity of current cathodic materials is a bottle-neck for the next generation electrochemical energy storage devices. LiMO2, LiMPO4, and mixed metal oxide lithium salts are commonly used in current lithium batteries. The heavy nature of these transition metal elements limits their capacity below 300 mAh/g. Fluorinated carbon materials are mainly used in primary lithium batteries since the 1970s. It is a high capacity cathodic material that surfers low conductivity and slow electron transfer kinetics. The preparation method, high temperature reaction between graphite and fluorine gas, also possesses significant safety threat for the production of current carbon fluoride materials. To solve the low conductivity and low discharge rate problem for carbon fluoride based cathodic materials, we designed a new type of fluorinated carbon materials that integrate conducting polymers, electron-transfer catalysts, and energy storage units, yet still have the similar composition of carbon fluoride to maintain the high specific capacity. Thus, this materials does not require additional mechanical binder and conducting materials for the cathode. The materials were characterized by electrochemical, spectroscopic, and scanning electron microscopic (SEM) methods. Electrochemical experiments were done in an Argon filled glovebox with residual O2 level less than 1 ppm. Three electrode systems were used for the characterization of this carbon fluoride cathodic materials on glassy carbon (GC) and aluminium electrodes in both 1,2-difluorobenzene (DFB)/TBAPF6 and propylene carbonate (PC)/LiPF6solution. Figure 1 shows galvanostatic discharge curve of the new carbon fluoride materials on GC WE in PC/1.0 M LIPF6 with two pieces of Li foil as CE and RE respectively at C/8 rate. The discharge result shows that this new cathodic material possesses specific capacity of 1.03 Ah/g with average voltage of 2.1 V (vs. Li+/Li) at 0.125 C rate, giving specific energy of 2.16 Wh/g. We also observed that the galvanostatic discharge of this material does not involve an initial voltage dipping as observed with current carbon fluoride materials. Searching and optimizing the electrolyte solution for rechargeable application is currently underway in this laboratory. We hope that this presentation will shed new light to the discovery of new cathodic materials. Figure 1