ABSTRACT
Lithium-sulfur batteries (LSBs) are known to be potential next-generation energy storage devices. Recently, our group reported an LSB cathode made using sulfur spheres that has been spherically templated by MXene nanosheets decorated with CoSe2 nanoparticles, forming a "loose-templating" configuration. It was postulated that the minimal restacking of the outer nanoparticle-decorated MXene layer helps to enable facile ionic transport. However, as the nanosheets do not adhere conformally to the internal sphere's surface, such a configuration can be controversial, thus requiring a more systematic understanding. In this work, we report and quantify for the first time the independent and dependent variables involved in this morphology, allowing us to identify that having smaller nanoparticles resulted in better Li+ ion transport and enhanced electrochemical performances. The optimized cathode structure exhibited an initial specific capacity of 1274 mAh/g and a 0.06% decay rate per cycle at 0.5 C over 1000 cycles in LSBs.
ABSTRACT
Lithium-sulfur (Li-S) batteries have shown exceptional theoretical energy densities, making them a promising candidate for next-generation energy storage systems. However, their practical application is limited by several challenging issues, such as uncontrollable Li dendrite growth, sluggish electrochemical kinetics, and the shuttling effect of lithium polysulfides (LiPSs). To overcome these issues, we designed and synthesized hierarchical matrixes on carbon cloth (CC) by using metal-organic frameworks (MOFs). ZnO nanosheet arrays were used as anode hosts (CC-ZnO) to enable stable Li plating and stripping. The symmetric cell with CC-ZnO@Li was demonstrated to have enhanced cycling stability, with a voltage hysteresis of â¼25 mV for over 800 h at 1 mA cm-2 and 1 mAh cm-2. To address the cathode challenges, we developed a multifunctional CC-NC-Co cathode host with physical confinement, chemical anchoring, and excellent electrocatalysis. The full cells with CC-ZnO@Li anodes and CC-NC-Co@S cathodes exhibited excellent electrochemical performance, with long cycling life (0.02% and 0.03% capacity decay per cycle when cycling 900 times at 0.5 C and 600 times at 1 C, respectively) and outstanding rate performance (793 mAh g-1 at 4 C). Additionally, the pouch cell based on the flexible CC-ZnO@Li anode and CC-NC-Co@S cathode showed good stability in different bending states. Overall, our study presents an effective strategy for preparing flexible Li and S hosts with hierarchical structures derived from MOF, which can pave the way for high-performance Li-S batteries.
ABSTRACT
Conjugated polymers have been widely adopted as active materials in hydrogel-based stretchable supercapacitors, but the relatively low conductivity and poor structural stability limit their applications. Herein, highly conductive graphene was incorporated as a substrate to anchor polyaniline (PANI) in a hydrogel-based stretchable electrode. Graphene not only provided an effective conducting network in the electrode, but also stabilized PANI during repeating charge-discharge processes due to strong π-π interaction between graphene and PANI. The obtained electrode showed high capacitance of 500.13â mF cm-2 and 100 % capacitance retention after 10000 charge-discharge cycles. The symmetrical supercapacitor using this novel stretchable electrode showed a high capacitance of 218.26â mF cm-2 , high capacitance retention of 43 % even when stretched at 150 % strain, and no capacitance decay when stretched to 100 % and then released to 0 % repeatedly for 2000 cycles, all of which were much better than the device based on the electrode without adding graphene. Such outstanding electrochemical performance shows the great application potential of highly conductive graphene in conjugated polymer-based stretchable energy storage devices.
