LiFePO4–graphene as a superior cathode material for rechargeable lithium batteries: impact of stacked graphene and unfolded graphene

Abstract

In this work, we describe the use of unfolded graphene as a three dimensional (3D) conducting network for LiFePO₄ nanoparticle growth. Compared with stacked graphene, which has a wrinkled structure, the use of unfolded graphene enables better dispersion of LiFePO₄ and restricts the LiFePO₄ particle size at the nanoscale. More importantly, it allows each LiFePO₄ particle to be attached to the conducting layer, which could greatly enhance the electronic conductivity, thereby realizing the full potential of the active materials. Based on its superior structure, after post-treatment for 12 hours, the LiFePO₄–unfolded graphene nanocomposite achieved a discharge capacity of 166.2 mA h g⁻¹ in the 1st cycle, which is 98% of the theoretical capacity (170 mA h g⁻¹). The composite also displayed stable cycling behavior up to 100 cycles, whereas the LiFePO₄–stacked graphene composite with a similar carbon content could deliver a discharge capacity of only 77 mA h g⁻¹ in the 1st cycle. X-ray absorption near-edge spectroscopy (XANES) provided spectroscopic understanding of the crystallinity of LiFePO₄ and chemical bonding between LiFePO₄ and unfolded graphene.