New cathode materials for lithium-sulfur batteries have achieved a substantial increase in volumetric energy density

Since the cathode material sulfur has significant advantages such as high theoretical specific capacity, abundant natural reserves, low cost and environmental friendliness, lithium-sulfur batteries are considered to be the most promising next-generation energy storage system. In the traditional method of using conductive carbonaceous material as the sulfur main body to construct the sulfur cathode, due to the weak interaction between low-polarity carbon and high-polarity LiPS, the physical isolation and physical adsorption provided by carbon-based materials are effective in inhibiting battery capacity degradation. The effect is limited, especially for highly loaded sulfur electrodes. In addition, the poor affinity between carbon-based materials and LiPS also hinders effective interfacial charge transfer and slows down the reaction kinetics of sulfur species. Moreover, the existence of a large amount of low tap density carbon greatly sacrifices the volumetric energy density of the battery. It is of great significance to design a sulfur host material with high conductivity and abundant exposed active sites to replace conductive carbon to obtain high area and volume capacity.

With funding from the National Natural Science Foundation of China (21601191, 21673241, 21471151), the Strategic Leading Science and Technology Project of the Chinese Academy of Sciences (XDB20000000), and the Natural Science Foundation of Fujian Province (2018J01030), Wang Ruihu, a researcher at the State Key Laboratory of Structural Chemistry, Fujian Institute of the Structure of Matter, Chinese Academy of Sciences, adopted a sodium alginate-induced chemical bond tailoring strategy and proposed MXene-based Ti3C2Tx (Tx stands for surface functional groups) nanodots-dispersed Ti3C2Tx nanosheets (TCD-TCS) ) In order to realize the restricted fixation and conversion of active substance sulfur under high sulfur loading conditions. The abundant surface polarity sites in TCD-TCS enhance the structural integrity of the electrode, and the absence of carbon-based materials and conductive additives makes the positive electrode material with high tap density. The TCD-TCS/S electrode exhibits almost theoretical specific discharge capacity at a medium sulfur load of 1.8 mgcm-2. Under the high sulfur load of 13.8mgcm-2, ultra-high capacity (1957mAhcm-3) and high area capacity (13.7mAhcm-2) are simultaneously realized. The study of the mechanism of sulfur precipitation during discharge shows the importance of the integration of MXene-based nanodots and nanosheets in Li-S batteries. The above work was published in ACSNano (UltrafineTi3C2MXeneNanodots-InterspersedNanosheet for High-Energy-DensityLithium-SulfurBatteries, ACSNano, 2019, 13, 3608-3617). The first author of the paper is assistant researcher Xiao Zhubing.

Previously, Xiao Zhubing et al. aimed to improve the area capacity and volume capacity of lithium-sulfur batteries, using flower-like porous Ti3C2Tx (FLPT) based without any carbon conductive additives. The positive electrode system has achieved a double increase in the area capacity and volume capacity of lithium-sulfur batteries (ACSNano, 2019, 13, 3404-3412). In addition, highly conductive transition metal sulfides (TiS2 and NbS2) have been used as additives in lithium-sulfur battery cathodes to increase battery area capacity and high current discharge capacity (EnergyStorageMater.2018,12,252-259; ACSNano2017,11,8488-8498; ACSAppl.Mater.Interfaces2017,9,18845-18855). The reduced graphene oxide/vanadium sulfide (rGO/VS2) composite material was obtained by hydrothermal method and applied to the ternary sulfur cathode system, and the rGO/VS2-S cathode material with a close-packed sandwich structure was prepared, and the volume energy density was realized. The substantial increase (Adv.EnergyMater.2018,7,1702337).