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Smart Merit Combination of Sulfur, Selenium and Electrode Engineering to Build Better Sustainable Li-Storage Batteries Ting Meng, Yani Liu, Linpo Li, Jianhui Zhu, Jiechang Gao, Han Zhang, Lai Ma, Chang Ming Li, and Jian Jiang ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b04395 • Publication Date (Web): 01 Dec 2018 Downloaded from http://pubs.acs.org on December 6, 2018
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ACS Sustainable Chemistry & Engineering
Smart Merit Combination of Sulfur, Selenium and Electrode Engineering to Build Better Sustainable Li-Storage Batteries Ting Meng,a,c Yani Liu,a,c Linpo Li,a,c Jianhui Zhu,b Jiechang Gao,a,c Han Zhang,
a,c
Lai Ma, a,c Chang
Ming Li,a,c* Jian Jiang,a,c,* aInstitute
for Clean Energy & Advanced Materials, Faculty of Materials and Energy, Southwest University, No.2
Tiansheng Road, BeiBei District, Chongqing 400715, P.R. China. bChongqing
Key Laboratory for Advanced Materials and Technologies of Clean Energies, No.2 Tiansheng Road,
BeiBei District, Chongqing 400715, P.R. China. cSchool
of Physical Science and Technology, Southwest University, No.2 Tiansheng Road, BeiBei District,
Chongqing 400715, P.R. China. To whom correspondence should be addressed: Tel: +86-23-68254842. *E-mail:
[email protected] (C.M. Li);
[email protected] (J. Jiang).
Abstract: Given the giant theoretical capacity and great natural abundance of sulfur (S), Li-S batteries have been regarded as one of most promising sustainable power sources in future. However, they have to suffer from issues of short cyclic lifespan, low Coulombic efficiency and poor rate behaviors unfortunately due to the insulating nature for S actives and negative polysulfide intermediates dissolution. As a congener, the conducting selenium (Se) shows the similar Li-storage chemistry to S, with comparable volumetric capacity, superb rate capability but unluckily low gravimetric capacity and limited cyclic life. To build sustained power systems with preferable behaviors, we put forward an efficient battery promotion strategy by combining merits of S, Se and smart electrode engineering. Herein, Se and S are successively infused into carbon black (CB) matrix and further packaged by thin nickel nitrate hydroxide layers (S/Se@CB⊂NNH) so as to suppress the actives diffusion losses. Such integrated S/Se@CB⊂NNH hybrids well inherit the superiorities of S, Se and benefit from the integrated electrode design, capable of showing high reversible specific capacities (~913 mAh g-1), excellent rate capability and cyclic stability (almost 100% Coulombic efficiency) and greatly prolonged lifetime. Our present work may provide an efficient, scalable and applicable way to develop reliable and superior cathodes for sustainable Li storage applications.
Keywords: S and Se Cathodes; Electrode Engineering; Merit Combination; Sustainable Li Storage
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Introduction Along with the ever-increasing demands in energy supply, the continual development of power systems with upper energy density, superb rate capability, long lifespan and prominent safety/sustainability becomes highly pursued.1 Lithium-sulfur (Li-S) batteries are nowadays considered as one of most promising power sources in near future due to their large theoretical energy density (~2600 Wh kg-1),2 great natural abundance of S (the 5th most common element on earth, readily available in/near volcanic regions and rather cheap; much beneficial to our scalable energy-storage applications in a pretty long period).3 Also, they could be the most applicable and sustainable power sources in near future given a fact that the elemental S cathodes can be greatly evolved from the petroleum coke wastes, or extracted from cysteine/methionine-rich biomasses using the green and sustained fermentation technology (synthetic route: high-sulfur organics → hydrogen sulfide → S).4 Besides, the efficient recycling of S resources in used Li-S batteries can be readily achieved by the physical thermal separation techniques. Nevertheless, their implementation progress still remains sluggish due to the troublesome problems like low actives utilization, poor energy-storage efficiency and limited cyclic lifetime. This is mainly induced by the intrinsically insulating nature of S (~5 × 10-28 S m-1) and undesirable dissolution of high-order polysulfide species.5-7 Additionally, the large volume changes of S in lithiation/delithiation would inevitably lead to the structural damages of cathodes, accelerating the capacity decay and ultimately causing the battery device failure.8-12 The selenium (Se), another significant element in the VI A group with far superior electrical conductivity (~1 × 10-3 S m-1; almost ~25 order of magnitudes larger than that of S), is regarded as an attractive cathode alternative for Li storage on account of its large volumetric capacity (~3254 mA h cm-1) and outstanding rate capabilities.13 Also, the Se resources can be easily recycled via the thermal treatment. In spite of overwhelming advantages aforementioned, Se cathodes also have to face formidable challenges comprising unsatisifactory gravimetric capacity (~675 mA h g-1) and adverse polyselenide dissolution/diffusion losses upon continual cycling.14 Aimed to build better battery systems with preferable performances (e.g., remarkable energy and power densities) in Li storage, the combination of large-capacity S and electrically conducting Se could be a feasible and rational way.15,16 Recently, a series of SexSy cathode materials have been reported, capable of showing enhanced reaction kinetics, prolonged cyclic lifespan and particularly greater specific capacities/energy densities than single-phased S or Se.12, 17 Typically for example,
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Qian et al. reported an amorphous S0.94Se0.06/C cathode, which owns outstanding electrochemical behaviors with a stable capacity of ~1105 mA h g-1 at 0.2 A g-1 and a good rate capability of 617 mA h g-1 even at 20 A g-1.18 This performance promotion is greatly attributed to a fact that S and Se can complement each other's advantages. Though using this combination may well offset the S/Se shortcomings and improve the electrode reaction kinetics, it still fails to address cyclic issues led by actives dissolution losses due to the lack of effective protective layers to prevent the diffusion out of polar polysulfide/polyselenide molecules in repeated charge/discharge procedures.19 Trying to extend the battery operation period, great efforts and achievements suggest that some polar species (e.g., transition metal oxides/sulfide/hydroxides) can function as exterior encapsulation layers and connect with these soluble intermediates via the chemical bonds formation, thereby mitigating the dissolution problems, preventing the adverse shutting effect and promoting the long-lasting cyclic endurance.20, 21
In this regard, besides the synergistic combination of S and Se, a rational core-shell functionalized
electrode configuration design is highly required to upgrade the battery behaviors. Inspired by above classic literatures and our previous work, we herein propose an efficient battery promotion strategy by the merit combination of S, Se and smart hybrid electrode engineering. In our case, the elemental Se and S are step by step infused into porous carbon black (CB) matrix via a melt-diffusion method under distinct temperature conditions. The as-formed nanopowders are then dispersed and encapsulated within ultra-thin functionalized nickel nitrate hydroxide layers (denoted as S/Se@CB⊂NNH) so as to prevent actives dissolution/diffusion losses. By using such core-shell integrated S/Se@CB⊂NNH hybrid products as the cathode materials, we eventually achieve a maximum specific capacity of ~913 mA h g-1 at 0.2 A g-1, excellent rate capability (~488 mA h g-1 at ~5 A g-1) and pronged cycling life period over 500 cycles (~almost 100% Coulombic efficiency and pretty low capacity decay rate). Our present S/Se complementary strategy and the rational/useful structural design may guide the future development of superior cathodes for sustainable Li storage.
Experimental Section Synthesis of S/Se@CB and S/Se@CB⊂NNH composites All involved chemicals (analytical grade) were purchased from Sigma-Aldrich and used directly without any purification. S and Se were infused into the CB matrix via a traditional melt-diffusion method. Typically, CB nanoparticles were mixed with Se powders in a mass ratio of 1:1 and milled
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in a planetary ball mill at 500 rpm for 12 h. The powder mixture was transferred into a quartz tube that is then vacuumed and heated at 240 oC for 12 h in order to obtain Se@CB hybrid samples. Later, the hybrid products of S/Se@CB were made by grounding Se@CB hybrid powders with S (specific weight ratio of Se/S: 1:3) and undergoing a heating procedure at 155°C in a vacuum condition for 12 h. Afterwards, S/Se@CB powders (~50 mg), hexamethylenetetramine (~50 mg), Ni(NO3)2∙6H2O (~25 mg) and distilled water (~50 ml) was mixed and magnetically stirred for 30 min, transferred into a sealed glass container and held at 95 oC for 6 h. The ultimate powder samples were then collected, washed by distilled water several times and dried at 60 oC in an electronic oven.
Material characterization and Electrochemical testing X-ray diffraction (XRD, Bruker D8 Advance diffractometer with Cu Kα radiation, λ=1.5418 Å) was used to identify the crystalline structure and phase of samples. The morphology was characterized by using a JEOL JSM-7800F field emission scanning electron microscope (FESEM) equipped with energy dispersive X-ray spectroscopy (EDS), and JEM 2010F transmission electron microscope (TEM). The X-ray photoelectron spectroscopy (XPS) was used to study the materials’ surface chemistry on a Perkin-Elmer model PHI 5600 XPS system (XPS; Thermo Electron, VG ESCALAB 250 spectrometer) with a resolution of 0.3-0.5 eV from a monochromated Al anode X-ray source. The Raman spectrum was recorded by Witech CRM200 spectrometer with 532 nm laser at room temperature. TGA analysis was performed by a SDT600 apparatus in N2 atmosphere. For battery testing, all working electrodes were made by mixing electrode materials, CB and sodium alginate (SA, Sigma-Aldrich) binders (weight ratio: 8:1:1) in distilled water to form a slurry. The homogeneous slurry was then pasted onto an Al foil and dried in a vacuum oven at 60 oC for 8h. The 2032-type coin cells were assembled in an Ar-filled glove box (MIKROUNA; H2O
