Applications of Carbon Nanotubes in CF x Electrodes for High-power Li/CF x Batteries
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Applications of Carbon Nanotubes in CFx Electrodes for High-power Li/CFx Batteries Qing Zhang,a Kenneth J. Takeuchi,a, b* Esther S. Takeuchi,a, b, c* and Amy C. Marschilok a, b* a
Department of Materials Science and Engineering, Stony Brook University, Stony Brook, NY 11794-2275, U.S.A. b Department of Chemistry, Stony Brook University, Stony Brook, NY 11794-3400, U.S.A. c Brookhaven National Laboratory, Upton, NY 11973-5000, U.S.A. *corresponding authors: [email protected], [email protected], [email protected] ABSTRACT Carbon monofluoride (CFx) has been extensively used as a reliable cathode material in lithium primary batteries because of its high energy density and long shelf life. However, the implementation of Li/ CFx batteries in high-power applications is limited by the low power capability resulting from the insulative nature of CFx material. In this work, we incorporated multi-walled carbon nanotubes into CFx electrodes and studied the impact on the electrochemical performances when CNTs were used as a conductive additive material and current collector substrate. Our work demonstrated the promising utilization of CNTs in CFx electrodes in improving the practical capacity and power capability of Li/ CFx batteries. INTRODUCTION The CFx (carbon fluoride) material was commercialized as a cathode material for lithium primary batteries in the 1970s.1, 2 CFx compounds are usually made from fluorination of carbon sources such as graphite and carbon fiber, and are usually non-stoichiometric with x varying between 0 and 1.3. Most of the CFx compounds synthesized for battery cathode applications have x values above 1. The overall discharge reaction of a Li/ CFx battery is “ ”, and the theoretical capacity of CFx is 865 mAh·g-1 assuming x equals 1.3, 4 The high energy density and low self-discharge characteristics of Li/ CFx batteries result in a variety of applications in industrial, commercial, military and medical devices markets.5-11 However, the insulative nature of CFx (x > 1) material and the complex solvation process during CFx discharge give rise to the low power capability of Li/ CFx batteries.12, 13 Thus the applications of Li/CFx batteries are currently limited to devices which require low-to-medium level currents.14, 15 Multi-walled carbon nanotubes (CNTs) have drawn significant attention due to their outstanding electrical (106 to 107 S·m-1) and thermal conductivity (> 300 W·m-1·K-1), chemical stability and mechanical flexibility.16-21 They have been explored as different battery components in lithium primary and secondary batteries including conductive additives, free-standing electrodes and current collectors.22-25 In the present work, we first investigated the effects of CNTs in Li/CFx batteries when CNTs are used as conductive additives in the CFx electrodes and compared them with electrodes using conventional carbon black. To tackle the issue of CNTs aggregation, we studied
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functionalized CNTs and illustrated the relationship between dispersion and ele
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