Yuhai Hu

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

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.

Flexible rechargeable lithium ion batteries: advances and challenges in materials and process technologies

Flexible batteries possess several unique features including high flexibility, lightweight and easy portability, high specific power and energy density, and remarkable rate capability, etc. So far, many different kinds of flexible batteries have been invented. The batteries, according to the electrochemical processes in a cell, can be categorized as flexible alkaline batteries, plastic batteries (or all-polymer batteries), polymer lithium-metal batteries (with lithium foil as an anode), and flexible rechargeable lithium ion batteries (LIBs), etc. Among these, flexible LIBs attract more rapidly increasing attention. As compared to the conventional rechargeable LIBs, fabrication of flexible LIBs is more challenging. An optimal match among the core components, i.e., nanostructured electrode materials, shape-conformable solid electrolytes, and soft current collectors should be achieved, so that the batteries maintain stable electrochemical performances even though they are deformed to fit the powered devices. Thus, fabrication of such batteries is not cost-effective and hence, is also inefficient. In the search for the potential core components for flexible LIBs, much progress has been made in screening solid state electrolytes, soft current collectors and electrode materials, and in electrode design and full LIB cell assembly (particularly in managing to get the three core components to work harmonically). There are also studies focusing on fundamental understanding and simulation of fully flexible LIBs. They reliably anticipate and describe the battery performances that are not easily explored experimentally using the present state-of-the-art technologies. In this review, we systematically summarize the advances in flexible LIBs research, with focus on the development of flexible electrodes. The review proceeds in terms of the processes for making electrodes and full LIB cells so as to emphasize the materials and process technologies. The development of solid state electrolytes and the fundamental understanding and simulation of flexible LIBs are also addressed. The review concludes with a perspective according to the authors experience in the related field, and the potential application of printing processes in flexible LIB fabrication is especially emphasized.

Novel approach toward a binder-free and current collector-free anode configuration: highly flexible nanoporous carbon nanotube electrodes with strong mechanical strength harvesting improved lithium storage

In this work, we developed a novel flexible nanoporous carbon nanotube film to use as a binder-free and current collector-free anode electrode for lithium ion batteries, providing a new approach to flexible energy devices. The proposed novel anode configuration shows better cycling performance and rate capability than the conventional electrode architecture. Moreover, this unique configuration exhibits good flexibility and robust mechanical strength, which has the potential to be applied to flexible lithium ion batteries. Our findings may provide a new anode configuration for lithium ion batteries with improved cycling stability and rate capability.