Sulfur-polyacrylonitrile (S-PAN) composite has been developed as a novel composite cathode material to address many issues with conventional Li-S batteries (LSBs). In this study, a freestanding S-PAN-CNT composite is first developed as the cathode material for LSBs, which is capable to deliver a high specific capacity of 1458 mAh g-1 at 0.2C and a desirable high-rate performance of 1097 mAh g-1 at 2.0 C. Furthermore, a Li2S-PAN-CNT cathode is obtained via in-situ direct pre-lithiation of S-PAN-CNT composite, which exhibits an even improved discharge capacity, cycling performance, and rate capability. Lastly, we develop Li-ion sulfur full batteries based on both S-PAN-CNT and Li2S-PAN-CNT cathode. The excellent electrochemical performance and corresponding theoretical estimation both demonstrate that the proposed system as a promising metal-free Li-ion battery with a high specific capacity, good cycle life, and low cost.
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Tailoring Mesopores and Nitrogen Groups of Carbon Nanofibers for Polysulfide Entrapment in Lithium–Sulfur Batteries
In the current work, we combined different physical and chemical modifications of carbon nanofibers through the creation of micro-, meso-, and macro-pores as well as the incorporation of nitrogen groups in cyclic polyacrylonitrile (CPAN) using gas-assisted electrospinning and air-controlled electrospray processes. We incorporated them into electrode and interlayer in Li–Sulfur batteries. First, we controlled pore size and distributions in mesoporous carbon fibers (mpCNF) via adding polymethyl methacrylate as a sacrificial polymer to the polyacrylonitrile carbon precursor, followed by varying activation conditions. Secondly, nitrogen groups were introduced via cyclization of PAN on mesoporous carbon nanofibers (mpCPAN). We compared the synergistic effects of all these features in cathode substrate and interlayer on the performance Li–Sulfur batteries and used various characterization tools to understand them. Our results revealed that coating CPAN on both mesoporous carbon cathode and interlayer greatly enhanced the rate capability and capacity retention, leading to the capacity of 1000 mAh/g at 2 C and 1200 mAh/g at 0.5 C with the capability retention of 88% after 100 cycles. The presence of nitrogen groups and mesopores in both cathodes and interlayers resulted in more effective polysulfide confinement and also show more promise for higher loading systems.
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- Award ID(s):
- 1719875
- PAR ID:
- 10325669
- Date Published:
- Journal Name:
- Polymers
- Volume:
- 14
- Issue:
- 7
- ISSN:
- 2073-4360
- Page Range / eLocation ID:
- 1342
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract The abundance and environmental friendliness in nature of sulfur (S) make Li–S batteries more attractive in addition to the high theoretical capacity (1675 mAh g−1) and energy density (2600 Wh kg−1) of the batteries. In this study, a bio‐based S cathode with graphene (Gr) coating, capable of effectively suppressing the shuttle effect of polysulfides, is enabled via networking soy protein (SP) and polydopamine (PDA) to form a functional bio‐binder (SP‐PDA). Dopamine self‐polymerization in SP not only generates the interpenetrated network for the bio‐binder but also makes the denatured structure of SP with rich functional groups effective for trapping polysulfides. Meanwhile, the Gr coating with low impedance, and high electronic and ionic conductivity on the cathode surface further significantly reduces polysulfide dissolution. Consequently, the Li–S batteries with the bio‐cathode (SP‐PDA@Gr) demonstrate excellent rate performance and long cycling capacity. In specific, under the current density of 0.5 A g−1at 70% (500 mAh g−1) capacity retention, the cycle life of the Li–S cell with SP‐PDA@Gr cathode is 600 cycles, i.e.,100 times longer than that of the cell with PVDF binder. This study provides a sustainable strategy for enhancing the performance of Li–S batteries through networking natural proteins to form functional bio‐binders.
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Abstract All‐solid‐state lithium‐sulfur batteries (ASSLSBs) based on sulfide solid‐state electrolytes (SSEs) provide prospectively high energy density and safety. However, the low conductivity and sluggish reaction kinetic of sulfur cathode limit its commercialization. The use of carbon additives can improve the electrical conductivity but accelerates the decomposition of SSEs. Herein, a highly conductive carbon fiber decorated with hybrid 1T/2H MoS2nanosheets is designed. The high chemical and electrochemical compatibility among MoS2and sulfide SSE can greatly improve the stability of the cathode and therefore maintain pristine interfaces. The uniform distribution of electrical‐conductive metallic 1T MoS2on carbon fiber benefits the electron transfer between carbon and sulfur. Meanwhile, the layered structure of MoS2can be intercalated by a large amount of Li ions facilitating ionic and electronic conductivity. In consequence, the charge transfer and reaction kinetics are greatly enhanced, and the decomposition of SSEs is successfully relieved. As a result, the ASSLSB delivers an ultrahigh initial discharge and charge capacity of 1456 and 1470 mAh g−1at 0.05 C individually with ultrahigh coulombic efficiency and maintains high capacity retention of 78% after 220 cycles. The batteries also obtain a remarkable rate performance of 1069 mAh g−1at 1 C.
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Lithium–sulfur (Li–S) batteries are regarded as one of the most promising next-generation electrochemical cells. However, shuttling of lithium polysulfide intermediates and sluggish kinetics in random deposition of lithium sulfide (Li 2 S) have significantly degraded their capacity, rate and cycling performance. Herein, few-layered MoS 2 nanosheets enriched with sulfur vacancies are anchored inside hollow mesoporous carbon (MoS 2−x /HMC) via S–C bonding and proposed as a novel functional mediator for Li–S batteries. Ultrathin MoS 2 sheets with abundant sulfur vacancies have strong chemical affinity to polysulfides and in the meantime catalyze their fast redox conversion with enhanced reaction kinetics as proved by experimental observations and first-principles density functional theory (DFT) calculations. At a current density of 1C, the MoS 2−x /HMC-S composite cathode exhibits a high initial capacity of 945 mA h g −1 with a high retained capacity of 526 mA h g −1 and a coulombic efficiency of nearly 100% after 500 cycles. The present work sheds light on the design of novel functional electrodes for next-generation electrochemical cells based on a simple yet effective vacancy engineering strategy.more » « less
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Abstract The significant performance decay in conventional graphite anodes under low‐temperature conditions is attributed to the slow diffusion of alkali metal ions, requiring new strategies to enhance the charge storage kinetics at low temperatures. Here, nitrogen (N)‐doped defective crumpled graphene (NCG) is employed as a promising anode to enable stable low‐temperature operation of alkali metal‐ion storage by exploiting the surface‐controlled charge storage mechanisms. At a low temperature of −40 °C, the NCG anodes maintain high capacities of ≈172 mAh g−1for lithium (Li)‐ion, ≈107 mAh g−1for sodium (Na)‐ion, and ≈118 mAh g−1for potassium (K)‐ion at 0.01 A g−1with outstanding rate‐capability and cycling stability. A combination of density functional theory (DFT) and electrochemical analysis further reveals the role of the N‐functional groups and defect sites in improving the utilization of the surface‐controlled charge storage mechanisms. In addition, the full cell with the NCG anode and a LiFePO4cathode shows a high capacity of ≈73 mAh g−1at 0.5 °C even at −40 °C. The results highlight the importance of utilizing the surface‐controlled charge storage mechanisms with controlled defect structures and functional groups on the carbon surface to improve the charge storage performance of alkali metal‐ion under low‐temperature conditions.
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/polym14071342
