Structure Tailoring and Material Modification of the Thick Cathode for Fast Charging and Long Lifespan Li-S Batteries

It is urgent to develop both affordable and sustainable batteries with high energy density and fast charging speed to alleviate the range anxiety of electric vehicles.^1,2 The lithium-sulfur (Li-S) system is especially attractive because of its high theoretical specific energy (around 2600 W h kg^-1), low cost, and low toxicity. However, the application of sulfur cathodes to date has been hindered by several obstacles, including low active material loading, low electronic conductivity, shuttle effects, and sluggish sulfur conversion kinetics.<br/>Herein, we combine a material-agnostic approach based on the asymmetric cathode structure design with a controllable vapor-deposited polymer to realize fast charging Li-S batteries with high sulfur loading.³ Specifically, the active materials and the tortuosity of the cathode were tailored by the 3D printing (stereolithography technique), which distributed in an inhomogeneous way to compensate for the gradient distribution of Li ions originated in the cathode depth direction, leading to less polarization in the electrode scale. The as-printed cathode is then sintered at 900 °C in an N₂ atmosphere to generate a carbon skeleton (i.e.: carbonization of resin) with intrinsic carbon defects. The structure design and defects engineering are expected to synergistically create favorable sulfur conversion conditions and mitigate the polarization in thick electrodes. The oCVD technique is leveraged to produce a conformal coating layer to eliminate shuttle effects for the elongated battery life. In-situ XRD diffractograms show a distinguishable difference between the printed cathode and the 2D planer cathode with similar mass loading, confirming an eminent sulfur conversion kinetic condition.<br/>Overall, the customized cathode delivered 820 mAh g^-1 at 4 C with a mass loading of 8.3 mg cm^-2, and the cathode with oCVD polymer showcased high-capacity retention (85% after 300 cycles), which indicates high mass loading with elevated sulfur utilization ratio, accelerated reaction kinetics, and stabilized electrochemical process have been achieved on the sulfur cathode by implementing this innovative cathode design strategy. The results of this study suggest a promising way of employing structural optimization and material modification for the higher energy and power density battery.<br/><br/>1 Zhang, Y., Nanoscale 15, 4195-4218 (2023).<br/>2 Zhang, Y., Energy Storage Materials 48, 1-11 (2022).<br/>3 Xu, R., Advanced Energy Materials 5, 1500408 (2015).<br/><br/>Acknowledgments<br/>This work was partially supported by National Science Foundation, Award number ECCS-1931088 and CBET-2207302. S.L. and H.W.S. acknowledge the support from the Improvement of Measurement Standards and Technology for Mechanical Metrology (Grant No. 23011043) by KRISS.