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1. BiFeO3 Coupled Polysulfide Trapping in C/S Composite Cathode Material for Li-S Batteries as Large Efficiency and High Rate Performance

   https://doi.org/10.3390/en14248362  

   Tripathi, Balram; Katiyar, Rajesh K.; Morell, Gerardo; Dixit, Ambesh; Katiyar, Ram S. (December 2021, Energies)

   We demonstrated the efficient coupling of BiFeO3 (BFO) ferroelectric material within the carbon–sulfur (C-S) composite cathode, where polysulfides are trapped in BFO mesh, reducing the polysulfide shuttle impact, and thus resulting in an improved cyclic performance and an increase in capacity in Li-S batteries. Here, the built-in internal field due to BFO enhances polysulfide trapping. The observation of a difference in the diffusion behavior of polysulfides in BFO-coupled composites suggests more efficient trapping in BFO-modified C-S electrodes compared to pristine C-S composite cathodes. The X-ray diffraction results of BFO–C-S composite cathodes show an orthorhombic structure, while Raman spectra substantiate efficient coupling of BFO in C-S composites, in agreement with SEM images, showing the interconnected network of submicron-size sulfur composites. Two plateaus were observed at 1.75 V and 2.1 V in the charge/discharge characteristics of BFO–C-S composite cathodes. The observed capacity of ~1600 mAh g−1 in a 1.5–2.5 V operating window for BFO30-C10-S60 composite cathodes, and the high cyclic stability substantiate the superior performance of the designed cathode materials due to the efficient reduction in the polysulfide shuttle effect in these composite cathodes. 

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2. Creating Effective Nanoreactors on Carbon Nanotubes with Mechanochemical Treatments for High‐Areal‐Capacity Sulfur Cathodes and Lithium Anodes

   https://doi.org/10.1002/adfm.201800595  

   Yang, Gang; Tan, Jian; Jin, Ho; Kim, Young_Heon; Yang, Xinyu; Son, Dong_Hee; Ahn, Sangjung; Zhou, Hongcai; Yu, Choongho (June 2018, Advanced Functional Materials)

   Abstract Li‐S batteries can potentially deliver high energy density and power, but polysulfide shuttle and lithium dendrite formations on Li metal anode have been the major hurdle. The polysulfide shuttle becomes severe particularly when the areal loading of the active material (sulfur) is increased to deliver the high energy density and the charge/discharge current density is raised to deliver high power. This study reports a novel mechanochemical method to create trenches on the surface of carbon nanotubes (CNTs) in free‐standing 3D porous CNT sponges. Unique spiral trenches are created by pressures during the chemical treatment process, providing polysulfide‐philic surfaces for cathode and lithiophilic surfaces for anode. The Li‐S cells made from manufacturing‐friendly sulfur‐sandwiched cathodes and lithium‐infused anodes using the mechanochemically treated electrodes exhibit a strikingly high areal capacity as high as 13.3 mAh cm⁻², which is only marginally reduced even with a tenfold increase in current density (16 mA cm⁻²), demonstrating both high “cell‐level” energy density and power. The outstanding performance can be attributed to the significantly improved reaction kinetics and lowered overpotentials coming from the reduced interfacial resistance and charge transfer resistance at both cathodes and anodes. The trench–wall CNT sponge simultaneously tackles the most critical problems on both the cathodes and anodes of Li‐S batteries, and this method can be utilized in designing new electrode materials for energy storage and beyond. 

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3. A simple and scalable pre-lithiation approach for high energy and low cost lithium ion sulfur batteries

   Chao Shen, Donghao Ye (January 2020, Journal of the Electrochemical Society)

   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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4. Tailoring Mesopores and Nitrogen Groups of Carbon Nanofibers for Polysulfide Entrapment in Lithium–Sulfur Batteries

   https://doi.org/10.3390/polym14071342  

   Sarkar, Snatika; Won, Jong Sung; An, Meichun; Zhang, Rui; Lee, Jin Hong; Lee, Seung Goo; Joo, Yong Lak (April 2022, Polymers)

   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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5. Unlocking Li2CO3-Li2SO4 as Cathodes for Li-ion Batteries

   https://doi.org/10.26434/chemrxiv-2024-732b5  

   Yu, Mingliang; Li, Bo; Wang, Jing; Xu, Yaobin; Zhang, Nan; Jung, Min Soo; Xue, Zhichen; Cho, Yukio; Kim, Min-Jae; Feng, Guangxia; et al (June 2024, ChemRxiv)

   Amidst the rapid expansion of the electric vehicle industry, the need for alternative battery technologies that balance economic viability with sustainability has never been more critical. Here, we report that common lithium salts of Li2CO3 and Li2SO4 are transformed into cathode active mass in Li-ion batteries by ball milling to form a composite with Cu2S. The optimal composite cathode comprising Li2CO3, Li2SO4, and Cu2S, with a practical active mass loading of 12.5-13.0 mg/cm2, demonstrates a reversible capacity of 247 mAh/g based on the total mass of Cu2S and the lithium salts, a specific energy of 716 Wh/kg, and a stable cycle life. This cathode chemistry rivals layered oxide cathodes of Li-ion batteries in energy density but at substantially reduced cost and ecological footprint. Mechanistic investigations reveal that in the composite Li2CO3 serves as the primary active mass, Li2SO4 enhances kinetic properties and reversibility, and Cu2S stabilizes the resulting anionic radicals for reversibility as a binding agent. Our findings pave the way for directly using precursor lithium salts as cathodes for Li-ion batteries to meet the ever-increasing market demands sustainably. 

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