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(a) Photograph of a flexible lithium-ion battery based on a three-dimensional graphene network structure; (b) Flexible lithium-ion battery powers a light-emitting diode in a bent state; (c) Flexible lithium-ion battery in a bent and unbent state Discharge curve and (d) cycle performance chart, the battery capacity remains unchanged under bending conditions.
Thinning and flexibility are important trends in portable electronic products. Folded or bendable portable electronic products may greatly influence or even change human lifestyles in the near future. Energy storage devices are the core components of portable electronic products. Therefore, the development of high-performance flexible energy storage devices, such as flexible lithium-ion batteries, is one of the keys to the wide application of flexible electronic products.
Graphene has high electrical conductivity and good flexibility, and is an ideal candidate for flexible energy storage devices. Recently, the National Institute of Metal Research, Shenyang National Laboratory for Materials Science (Union) Laboratories, previously prepared a graphene foam with a three-dimensional network structure (Nature Materials 10 (6), 424, 2011) and proposed the use of this material as a highly conductive material. Flexible current collector, design and preparation of a flexible lithium-ion battery that can be rapidly charged and discharged. The three-dimensionally connected graphene network is used as a current collector to replace the commonly used metal current collector in the battery, which can not only effectively reduce the proportion of inactive substances in the electrode, but also provides high conductivity and porous structure of the three-dimensional graphene network for lithium ions and electrons. The fast diffusion channel enables rapid charge and discharge performance of the electrode material. In order to achieve good contact between the active material and the graphene current collector without using a binder and a conductive additive to promote electron transport and improve the stability of the electrode material during bending, the researchers developed an in-situ hydrothermal synthesis method. The graphene three-dimensional connectivity network structure directly grows active materials such as lithium iron phosphate and lithium titanate. Lithium iron phosphate/graphene and lithium titanate/graphene composite materials were used as positive and negative electrodes respectively, and a flexible silica gel was used as a package to assemble a lithium ion full battery with good flexibility (Fig. a, b). When the flexible lithium ion battery is bent, its charge and discharge characteristics remain unchanged (Figure cd), and charging can be completed within 6 minutes (up to 90% of initial capacity), and the capacity retention rate after 96 cycles is 96%.
This research proposes a new idea for the design and preparation of high-performance flexible lithium-ion batteries. This kind of quick-charged flexible lithium-ion battery has a simple preparation process and has potential practical application value. The research was published online on October 8th in the "PNAS" (PNAS, 2012, doi: 10.1073/pnas.1206839109). In addition, the research team also made full use of the excellent properties of graphene and carbon nanotubes to develop ultracapacitor and flexible electrode materials for lithium-sulfur batteries (ACS Nano 3 (7), 1745, 2009; Advanced Energy Materials 1 (5) , 917, 2011; Energy & Environmental Science 5, 8901, 2012), laying a good foundation for the development of flexible energy storage devices. The above work was funded by the National Natural Science Foundation of China, the Ministry of Science and Technology and the Chinese Academy of Sciences.
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