Nonmacrocyclic Iron(II) Soluble Redox Mediators Leading to High-Rate Li–O ₂ Battery

Open AccessCCS ChemistryRESEARCH ARTICLE1 May 2021Nonmacrocyclic Iron(II) Soluble Redox Mediators Leading to High-Rate Li–O2 Battery Baoxing Wang, Xiao Xueyi Cheng, Jing Zhang, Minglei Yan, Guochang Li, Lijun Yang, Qiang Wu, Xizhang Wang and Zheng Hu Key Laboratory of Mesoscopic Chemistry MOE, Jiangsu Provincial for Nanotechnology, School Chemical Engineering, Nanjing University, 210023 Google Scholar More articles by this author , Cheng Zhang Yan Li Yang Wu *Corresponding authors: E-mail Address: [email protected] https://doi.org/10.31635/ccschem.020.202000313 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd favoritesTrack Citations ShareFacebookTwitterLinked InEmail The lithium–oxygen (Li–O2) battery is highly promising but suffers from poor cycling life, especially at high rates; hence, the need high-efficient accelerating agents crucial. Recently macrocyclic Fe-based redox mediators, such as iron(II) phthalocyanine (FePc) heme, have been developed anticipated be ideal due their bifunctional charge superoxide shuttling capabilities. However, they still operate far below expectations, which could result low concentrations in electrolyte strong π–π interaction carbon cathode. Herein, authors report a new type nonmacrocyclic acetylacetonate [Fe(acac)2] glycinate [Fe(gly)2], weak with cathode, thus, remain electrolyte. Fe(gly)2@Li–O2 reaches long life 321 cycles 0.5 A g−1, much superior counterpart typical FePc, particularly exhibits 167 2.0 g−1 136 ultrahigh 5.0 g−1. This study demonstrates an efficient strategy achieve high-rate performance batteries developing mediators electron shuttling. Download figure PowerPoint Introduction With depletion fossil fuels, high-performance electrochemical energy storage devices attracted increasing interests alternative supplies.1,2 rechargeable candidate owing its theoretical density, compared that gasoline.3–6 Despite significant progress enhancing capacity stability recent years,7–18 rate battery, date, quite limited usually < ⁢ g c t h o d e − 1 challenge, especially, conversion applications.4,5 In stored via oxygen evolution reaction (OER) process released reduction (ORR) process, both occur on cathode.18,19 depends Li2O2 uptake, accommodated porous cathode material, while correlates positively reversibility ORR OER.20,21 For achievement capacity, sp2 materials large specific surface area, suitable pore structure conductivity are most commonly used cathodes.22–24 improving stability, usually, two categories electrocatalysts developed, is, heterogeneous catalysts decorated carbon-based cathode12–16,24–26 soluble employed electrolyte.7–11,18,27–31 catalysts, insulated product densely deposits surface, leading separation catalytic sites exposed electrolyte.5,9,31,32 Accordingly, OER retarded some extent increased resistance transfer deposit, capability. contrast, act shuttles between electrode electrolyte, reversibly donate or accept electrons facile conversions O2 Li2O2. case, avoids drawback insulation. Besides, mediator also enhance dimethyl sulphoxide (DMSO), combining active species harmful stability.31 Therefore, intrinsic advantage over facilitating charge/discharge capability thereof.5,33,34 should mainly rely sufficient transport.4,8,20 Unfortunately, traditional tetrathiafulvalene (TTF) lithium iodide (LiI),27,29 solubility too limitation Henry’s law. recently heme either shuttle carrier.35,36 But causes marked concentration might lead short supply O2, similar case mediators. until now, yet demonstrate we avoiding Consequently, capability, full discharge counterparts FePc mediator. Experimental Methods Materials synthesis characterizations three-dimensional (3D) few-layer graphene-like (3DG) was material batteries, prepared situ Cu template method, described our study.37 Specifically, basic copper carbonate [CuCO3·Cu(OH)2·xH2O; 20 g] mixed polymethyl methacrylate (PMMA; 3.0 g), ball milled 8 h. mixture transferred horizontal quartz tube, then heated 250 °C maintained 6 10 vol % H2/Ar atmosphere flow mL min−1. Subsequently, temperature system raised rapidly 900 held as-prepared sample treated solutions H2O:HCl:H2O2 (4∶3∶1 volume) remove washed repeatedly deionized water. Finally, 3DG obtained after vacuum drying 70 12 Scanning microscopy (SEM; Hitachi S4800 kV; Japan), transmission (TEM; JEOL JEM-2100F operating 200 powder X-ray diffraction (PXRD; Bruker D8 Advance XRD instrument using Kα radiation; Germany) were morphologies structures samples. UV–Vis spectroscopy (Shimadzu UV-3600; Japan) measure adsorption different Fe(II) 3DG. Nitrogen adsorption/desorption isotherms measured Thermo Fisher Scientific Surfer Gas Adsorption Porosimeter (Italy). area size distribution calculated Brunauer–Emmett–Teller (BET), Horvath–Kawazoe (HK; micropores <2 nm), Barrett–Joyner–Halenda (BJH; pores >2 nm) methods, same paper.37 bulk reference report.38 Fabrication homogeneously mixing 95 wt 5 poly(vinylidene difluoride) (PVDF; 60 dispersion water), rolled current collector (carbon cloth) diameter 1.4 cm, followed mass ∼0.3 mg (Sartorius Ultra Microbalance MSE2.7S 2.1 g/0.1 µg; Germany). assembled foil (0.38 mm thickness; Sigma-Aldrich, Shanghai, China), borosilicate glass fiber separators (Whatman, soaked 0.1 into CR2032 coin cell seven home-made holes side flowing ( Supporting Information Figure S1). consists 1.0 mol L−1 bis(trifluoromethylsulphonyl)imide (LiTFSI; China)/DMSO (Greagent) without Fe(acac)2 (Adamas, Beijing, China; 50.0 mmol L−1), Fe(gly)2 (Adamas; L−1). sealed 150 chamber argon (Ar)-filled glovebox. flushed gas min−1 saturated DMSO vapor (to depress loss solvent) clear out Ar. Then performed under condition. galvanostatic tests LAND CT2001A testing (Wuhan, China). cyclic voltammetry (CV) linear scan (LSV) measurements workstation (CHI760E; CH Instruments, China) rotating disk (RDE; Pine Research USA). glassy covered working electrode. Platinum (Pt) wire Ag/AgCl counter electrodes, respectively. CV tests, 50 LiTFSI/DMSO H-type Ar-filled curves Ar- O2-saturated corresponding flushing, LSV conducted four-neck bottle equipped RDE. Density functional theory calculation (DFT) calculations carried DMol3 code Studio (version 8.0; BIOVIA, San Diego, CA) through spin-unrestricted all-electron method.39,40 All generalized gradient-corrected Perdew–Burke–Ernzerhof (GGA/PBE) double numerical basis set polarization function (DNP). electronic coordinates relaxation, tolerances energy, maximum force, displacement × 10−5 Ha, 2 10−3 Ha Å−1, Å, solution effect accounted conductor-like screening model (COSMO). Monkhorst–Pack k-point mesh 4 1, global orbital cutoff Å. Results Discussion shows results experimental Fe(II)-based molecule molecules [Fe(gly)2 Fe(acac)2] energies −1.61 −2.37 eV Fe(acac)2, respectively, smaller than −5.27 indicating weaker (Figure 1a). point confirmed results. when amount (0.30 mg) added µL Fe(gly)2, residual contents one order higher 1b S2). suggested majority promote performances, minimal concentration. | Adsorptions (a) configurations sheet energies. (b) adsorption. initial L−1. Electrochemical performances series any mediator, M possessed abundant micro–, meso–, macropores, volume (3.15 cm3 g−1), (1290 m2 (679 Sm−1) S3).37 denoted Fe(gly)2@Li–O2, Fe(acac)2@Li–O2, protected]–O2, protected]–O2. Their presented 2. exhibited discharging capacities above 20,000 mAh terminal voltage V 2a), uptake cathode.20 protected]–O2 difference >2800 demonstrated promotion capacity. Discharge profiles V. Terminal vs cycle number densities. (c) density visual comparison, replotted gray. Note: reversible 800 (b, c) Note (a, b) more reflected capabilities batteries. At only 30 times, addition increases numbers. led (Figures 2b). It worth mentioning increment evident times remained record Tables S1 apparent improvement indicated exceptional contribution Additionally, >400 overpotentials lower 2b S4). Increasing prolong further 156 193 2c). Briefly, preparing and/or prototype species. better Fe(acac)2@Li–O2 attributable during long-time noteworthy survived long-term even S5). Origin To get insight origin processes investigated example overpotential. elucidated simulated shown 3. Without curve featureless Ar-purged atmosphere, peak 2.45 (Ered,1) oxidation 3.12 (Eox,1) O2-purged occurred formation decomposition 3a).35,36 showed pairs peaks 3b S6), resulted Fe species,35,36,41 2.58 (E’red,2) 2.79 (E’ox,2) FeII(acac)2/FeI(acac)2 pair, ∼2.91 (E’red,3) ∼2.95 (E’ox,3) FeIII(acac)2/FeII(acac)2 pair. Under besides mentioned above, pair appeared (Ered,1, Eox,1), ascribed ORR/OER Li2O2, per Fe(acac)2. Interestingly, all shifted Table S3), shifts ∼2.85 (Ered,2) 2.91 3.30 (Ered,3) caused coordination 3.24 (Eox,2) 2.95 3.46 (Eox,3) arose Fe(acac)2–Li2O2, cases mediators.35,36 Moreover, Eox,1) dramatically intensity decreased ∼0.15 potential gap, those 3a 3b), enhanced activity boosted situation FePc.35 3 curves. scanning mV s−1. speed s−1 1200 rpm, RDE 3c). stages. first stage, it gave comparable potential, consistent results, originated FeII(acac)2–O2 FeI(acac)2–O2 ↔ II acac ) – O one-electron based Levich equation,35 second FeII(acac)2–O2Li2to FeII(acac)2-O2Li2, larger confirms boost formation, agreement rollback (the arrowed) observed absence “Li2O2 blocking effect” insulation coating layer significantly alleviated vital Based analysis, assistance speculated Scheme S1), noting reported vanadium(III) [V(acac)3] Nonetheless, mechanism V(acac)3 LiO2 Fe(gly)2.31 combines Li+ form Li+V(acac)3, has affinity intermediate produce V(acac)3–LiO2.31 taking example, Fe(acac)2–O2, easy assemble accepting electron, combine Fe(acac)2–LiO2. other words, intermediates formed V(acac)3. because acts carrier increase promotes transport does not. Since crucial capability,4,8,20,35 rates ones Morphology We examined morphological products three cases, i.e., non-macrocyclic blank case. SEM images cathodes (discharge) subsequent (charge) depth 10,000 composed small particles uniform ∼200 nm, forming 4a S7). discharged undulating morphology 3DG, particle-like product, relatively dense 4c). displayed 4b), particle Fe(acac)2@Li–O2. influence products. After successive almost decomposed 4d–4f). According observations, realized. tends coordinate center atoms S8); complex accepted efficiently combined attached “redox mechanism.”42,43 subsequently deposited supersaturation, accompanied release Thanks nuclei initially. shuttled shallow (face flow) acting carriers continuously nuclei, 4g). reduced gradually defect-rich layer, defects “surface mechanism” 4i).43 growth” Meanwhile, coexisted coexistence 4h). Generally, 4a) favorable, 4b 4c) unfavorable process.44 blank, high-concentration great Collectively, understanding helpful design Morphologic schematic diagram process. (a–c) (d–f) Corresponding charge. (g–i) Conclusion fabrication sustained π