Green synthesis of LiFePO4/graphene coated Carbon Fiber cathodes for high performance structural batteries

Abstract

Carbon fibers (CF), also known as graphite fibers, can be used as multifunctional conductive electrodes in "structural batteries" that simultaneously store electrical energy and carry mechanical loads without additional current collectors. However, there are several challenges in the commercialization of structural batteries. For example, CF-based cathode composites usually suffer from their low energy capacity due to the poor adhesion of active materials on CF surface, and the current fabrication techniques (such as blade coating or spray coating) need to use toxic organic solvents such as N-methyl pyrrolidone (NMP). In this thesis, we report a green approach that utilizes electrophoretic deposition (EPD) to fabricate novel cathode composites consisting of lithium iron phosphate (LiFePO4) and graphene nanosheets. Ethanol was used as a green solvent to replace NMP. Meanwhile, Different commercial graphene materials, including 3 kinds of graphene nanoplatelets, 4 kinds of reduced graphene oxide were tested and systematically compared with our homemade graphene. Most of the graphene additives can significantly improve our structural battery performance, with the highest specific capacity of 125 mAhg1 and over 80% retention at 2C over 500 cycles. Morphological and structural analyses were conducted by scanning electron microscopy (SEM) and Raman spectroscopy to further understand how the surface and quality of different kinds of graphene can impact the relative battery performance.