RESUMO
A lithium-sulfur (Li-S) battery is widely regarded as one of the most promising technologies for energy storage because of its high theoretical energy density and cost advantage. However, the shuttling of soluble polysulfides between the cathode and the anode and the consequent lithium anode degradation strongly limit the safety and electrochemical performance in the Li-S battery. Herein, a metal-organic-framework (MOF)-modified gel polymer electrolyte (GPE) is employed in a Li-S battery in order to stablize the lithium anode. In view of the abundant pores in the MOF skeleton, the as-prepared GPE not only immobilizes the large-size polysulfide anions but also cages electrolyte anions into the pores, thus facilitating a uniform flux of Li ions and homogeneous Li deposition. Cooperated with a sulfur-carbon composite cathode, the lithium with MOF-modified GPE exhibits a uniform surface morphology and dense solid electrolyte interphase (SEI) film, thus delivering good cycle stability and high-rate capability.
RESUMO
Biomineralization technology is a feasible and promising route to fabricate phosphate cathode materials with hierarchical nanostructure for high-performance lithium-ion batteries (LIBs). In this work, to improve the electrochemical performance of LiMn0.8Fe0.2PO4 (LMFP), hierarchical LMFP/carbon nanospheres are wrapped in situ with N-doped graphene nanoribbons (GNRs) via biomineralization by using yeast cells as the nucleating agent, self-assembly template, and carbon source. Such LMFP nanospheres are assembled by more fine nanocrystals with an average size of 18.3 nm. Moreover, the preferential crystal orientation along the [010] direction and certain antisite lattice defects can be identified in LMFP nanocrystals, which promote rapid diffusion of Li ions and generate more active sites for the electrochemical reaction. Moreover, such N-doped GNR networks, wrapped between LMFP/carbon nanospheres, are beneficial to the fast mobility of electrons and good penetration of the electrolyte. As expected, the as-prepared LMFP/carbon multicomposite presents the outstanding electrochemical performance, including the large initial discharge capacity of 168.8 mA h g-1, good rate capability, and excellent long-term cycling stability over 2000 cycles. Therefore, the biomineralization method is demonstrated here to be effective to manipulate the microstructure of multicomponent phosphate cathode materials based on the requirement of capacity, rate capability, and cycle stability for LIBs.
RESUMO
Microporous carbon polyhedrons (MCPs) are encapsulated into polyacrylonitrile (PAN) nanofibers by electrospinning the mixture of MCPs and PAN. Subsequently, the as-prepared MCPs-PAN nanofibers are employed as sulfur immobilizer for lithium-sulfur battery. Here, the S/MCPs-PAN multicomposites integrate the advantage of sulfur/microporous carbon and sulfurized PAN. Specifically, with large pore volume, MCPs inside PAN nanofibers provide a sufficient sulfur loading. While PAN-based nanofibers offer a conductive path and matrix. Therefore, the electrochemical performance is significantly improved for the S/MCPs-PAN multicomposite with a suitable sulfur content in carbonate-based electrolyte. At the current density of 160 mA g-1sulfur, the S/MPCPs-PAN composite delivers a large discharge capacity of 789.7 mAh g-1composite, high Coulombic efficiency of about 100% except in the first cycle, and good capacity retention after 200 cycles. In particular, even at 4 C rate, the S/MCPs-PAN composite can still release the discharge capacity of 370 mAh g-1composite. On the contrary, the formation of the thick SEI layer on the surface of nanofibers with a high sulfur content are observed, which is responsible for the quick capacity deterioration of the sulfur-based composite in carbonate-based electrolyte. This design of the S/MCPs-PAN multicomposite is helpful for the fabrication of stable Li-S battery.
