Energy and the environment are two major issues faced by mankind today and have been highly valued by countries in the world. They are listed as major areas of science and technology for priority development. The development of clean energy systems such as lithium batteries, wind power and solar power has become the mainstream of the modern energy industry. Lithium batteries have an important position in the field of energy storage due to their superior performance and technological innovations, but the development of electronic equipment and electric vehicles also places higher demands on lithium batteries.
Emerging energy storage systems - lithium-sulfur batteries have the advantages of high theoretical energy density, low cost, and environmental friendliness. Their theoretical specific capacities and energy densities are 1675 mA h g-1 and 2600 Wh/kg, respectively, much higher than current lithium ions. Batteries have quickly become a research hotspot in the scientific and industrial fields and have attracted the attention of researchers at home and abroad in the field of new energy power batteries.
Under the support of the National Natural Science Foundation of China and the Chinese Academy of Sciences, Zhang Yuegang, a researcher at the Suzhou Institute of Nanotechnology and Nanobionics of the Chinese Academy of Sciences, has conducted extensive research around the synthesis of nano-sulfur and graphene composite materials and the application fields of lithium-sulfur batteries. The researchers used polyaniline to improve graphene oxide nano-sulfur composites, effectively reducing the charge transfer resistance of the electrode material, inhibiting the dissolution of lithium polysulfide, and improving the specific discharge capacity, coulomb efficiency, and cycle stability of the composite (Nano Research, 2014 ,7,1355-1363). In order to further improve the electrical conductivity of the composite sulfur graphene nanomaterials and suppress the shuttling effect of lithium polysulfide, the members of the research group further improved the graphene oxide, nitrided the graphene oxide using ammonia, and encapsulated the nanoparticles into nitrogen. Doped graphene sheets (S@NG).
The lithium-sulfur battery assembled with the composite material exhibits higher specific capacity and stability at different magnifications, for example, 1167 mA h g-1 at 0.2C and 1058 mA h g-1 at 0.5C; 1C The time was 971 mA h g-1; at 2C it was 802 mA h g-1; at 5C it was 606 mA h g-1. The battery has an extremely long cycle life, and the average capacity decay rate per cycle obtained after 2000 charge and discharge tests is only 0.028%. The excellent properties of this material are attributed to the excellent adsorption of N-functional groups in lithium-doped graphene sheets to lithium polysulfide, and the excellent conductivity of nitrogen-doped graphene. The results of this study are also confirmed based on S@NG composites. Lithium-sulfur batteries have great application prospects in the field of energy storage such as portable electronics and new power sources (Nano Letters, 2014, 14, 4821−4827). In addition, the members of the research group used low-temperature reactions to slow down the rate of chemical reactions, loaded a uniform sulfur film on the 3D reduced graphene oxide, and dried in the air to shrink the pores of the 3D reduced graphene oxide, resulting in a dense SG composite material. The adhesion to reduced graphene oxide, the immobilization of nano-sulfur and the inhibition of polysulfide dissolution loss increase the specific capacity and cycle stability of S-graphene composites (Nano Energy, 2015, 12, 468-475).
In the past year, Zhang Yuegang's research group also made progress in lithium ion batteries, super capacitors, and photoelectric materials, such as research on vanadium pentoxide micro flower as cathode material for lithium ion batteries (J. Mater. Chem. A, 2015, 3, 1103-1109), Studies on Oxide Nanosheets as Cathode Materials for Lithium-Ion Batteries (Scientific Reports 2015, 5, 8326), Performance of Carbon Nanomaterials High Energy Flexible Capacitors (Chem. Mater., 2015, 27, 1194–1200) Photocatalytic performance of multi-stage bifurcated titanium dioxide nanostructures (J. Mater. Chem. A, 2015, 3, 4004-4009).
This series of work has received substantial funding from the National Natural Science Foundation of China and the Chinese Academy of Sciences, and has been supported by the printed electronics department, testing and processing platform of Suzhou Nanometer Institute.
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