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
- NSF-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 All‐solid‐state batteries with metallic lithium (LiBCC) anode and solid electrolyte (SE) are under active development. However, an unstable SE/LiBCCinterface due to electrochemical and mechanical instabilities hinders their operation. Herein, an ultra‐thin nanoporous mixed ionic and electronic conductor (MIEC) interlayer (≈3.25 µm), which regulates LiBCCdeposition and stripping, serving as a 3D scaffold for Li0ad‐atom formation, LiBCCnucleation, and long‐range transport of ions and electrons at SE/LiBCCinterface is demonstrated. Consisting of lithium silicide and carbon nanotubes, the MIEC interlayer is thermodynamically stable against LiBCCand highly lithiophilic. Moreover, its nanopores (<100 nm) confine the deposited LiBCCto the size regime where LiBCCexhibits “smaller is much softer” size‐dependent plasticity governed by diffusive deformation mechanisms. The LiBCCthus remains soft enough not to mechanically penetrate SE in contact. Upon further plating, LiBCCgrows in between the current collector and the MIEC interlayer, not directly contacting the SE. As a result, a full‐cell having Li3.75Si‐CNT/LiBCCfoil as an anode and LiNi0.8Co0.1Mn0.1O2as a cathode displays a high specific capacity of 207.8 mAh g−1, 92.0% initial Coulombic efficiency, 88.9% capacity retention after 200 cycles (Coulombic efficiency reaches 99.9% after tens of cycles), and excellent rate capability (76% at 5 C).
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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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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.
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Abstract Nonaqueous metal–gas batteries based on halogenated reactants exhibit strong potential for future high‐energy electrochemical systems. The lithium–sulfur hexafluoride (Li–SF6) primary battery, which utilizes a safe, noncombustible, energy‐dense gas as cathode, demonstrates attractive eight‐electron transfer reduction during discharge and high attainable capacities (>3000 mAh g−1carbon) at voltages above 2.2 VLi. However, improved rate capability is needed for practical applications. Here, two viable strategies are reported to achieve this by targeting the solubility of the passivating discharge product, lithium fluoride (LiF). Operating at moderately elevated temperatures, e.g., 50 °C, in DMSO dramatically improves LiF solubility and promotes sparser and larger LiF nuclei on gas diffusion layer electrodes, leading to capacity improvements of ≈10× at 120 µA cm−2. More aggressive chemical modification of the electrolyte by including a tris(pentafluorophenyl)borane anion receptor further promotes LiF solubilization; capacity increases even at room temperature by a factor of 25 at 120 µA cm−2, with attainable capacities up to 3 mAh cm−2. This work shows that bulk fluoride‐forming conversion reactions can be strongly manipulated by tuning the electrolyte environment to be solvating toward F−, and that significantly improved rates can be achieved, leading a step closer to practical applications.
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/polym14071342
