图1 2D层状材料构筑定向离子传输通道示意图

Fig. 1 Schematic diagrams of constructing directional ion transport channels using 2D layered materials (a) Microscopic ion transport channel structure between 2D layered materials; (b) Microscopically disordered ion transport pathways; (c) Microscopically ordered and vertically arranged ion transport pathways

图2 2D层状材料在电极材料中构建定向离子通道的应用[42,45,50]

Fig. 2 Application of 2D layered materials in constructing directional ion channels in electrode materials[42,45,50] (a) Schematic diagram of vertical alignment of VOPO4 nanosheets induced by solvent evaporation[42]; (b) Rate capability of conventional electrodes as a function of mass loading[42]; (c) Rate capability of vertically aligned nanosheets (VANS) electrode at 5 mg·cm−2[42]; (d, e) HRTEM images of Ti2CTx/C (d) before and (e) after Sn4+ intercalation[45]; (f) Rate performance of Ti2AlC/C, Ti2CTx/C, and Sn4+-Ti2CTx/C electrodes[45]; (g) Schematic fabrication of flexible V-rGO/tannic acid (TA)/laser-pretreated graphite paper (LGP) electrodes via laser assistance[50]; (h) Galvanostatic charge-discharge curves of the quasi-solid-state aqueous zinc-ion hybrid capacitors[50]

图3 2D层状材料的排列方式对锂沉积均匀性与循环寿命的影响[52,54]

Fig. 3 Influence of the arrangement of 2D layered materials on the uniformity of lithium deposition and cycle life[52,54] (a-c) Schematics of Li deposition in (a) horizontally aligned rGO aerogel (HGA), (b) randomly arranged rGO aerogel (RGA), and (c) vertically aligned rGO aerogel (VGA)[52]; (d-f) Cross-sectional scanning electron microscope (SEM) images of (d) HGA and (e) RGA after 40 cycles, and (f) VGA after 100 cycles (cycling current density: 3 mA·cm-2, capacity: 3 mAh·cm-2, carbonate electrolyte)[52]; (g) Rate capability and long-term cycling performances of LFP||Li cells[52]; (h) Synthesis and SEM images of v-Ti3C2Tx electrodes[54]; (i) Coulombic efficiencies of V-Ti3C2Tx and H-Ti3C2Tx electrodes at 1.0 mAh·cm-2[54]

图4 2D层状材料在SPEs中构建定向离子通道的应用[64,68,70]

Fig. 4 Application of 2D layered materials in constructing directional ion channels in SPEs[64,68,70] (a) Schematic illustration of the synthesis of composite solid-state electrolytes (CSEs) with NFO nanosheets and a rational mechanism for ion transport in CSEs applied in lithium metal batteries[64]; (b) Arrhenius curves of CSEs with vertically aligned NFO-PEO (ANFO-PEO), random aligned NFO-PEO (RNFO-PEO), and PEO-LiTFSI (PL)[64]; (c) Average values of transference number along with their standard errors[64]; (d-f) Cross-sectional SEM images of (d) VAVS and (e) VAVS-CSPE (UV etched), (f) Li electrode surface after test for about half-month with VAVS-CSPE electrolytes[68]; (g) Galvanostatic cycling performance of Li/SPE/Li symmetric cells measured at 35 ℃ with 0.5 mA·cm-2 current density[68]; (h) Schematic illustration of the preparation of VALS-CSPE[70]; (i) Galvanostatic tests of Li|Li cells at 0.10 mA·cm−2[70]

图5 Cu-MMT/明胶垂直阵列实现PEO基固态电解质高临界电流密度与无枝晶锂沉积[72]

Fig. 5 High critical current density and dendrite free lithium deposition of PEO-based solid electrolyte by Cu-MMT/gelatin vertical array[72] (a) Cross-scale synergistic rectification strategy through the ion rectifier; (b) Top view SEM images of ion rectifier of the vertical channel surface; (c) Chemical structure and electron density distribution of tripeptide (hydroxyproline-proline-glycine, Hyp-Pro-Gly) abundantly present in gelatin (top), binding energies of Hyp-Pro-Gly and PEO chain segments with Li+, respectively (bottom); (d, e) Critical current density tests of (d) CGVA-PEO/LiTFSI and (e) PEO/LiTFSI; (f) Ionic conductivity−temperature curves of different electrolytes; (g) Current variation with polarization of Li//CGVA-PEO/LiTFSI//Li symmetrical cell with an applied potential of 10 mV with inset showing electrochemical impedance spectroscopy (EIS) plots before and after polarization; (h) Top-view SEM images (top) and corresponding X-ray computed tomography (X-CT) images (bottom) of Li anodes with different electrolyte membranes after 20 cycles at 0.1 mA·cm−2 and 0.1 mAh·cm−2

图6 2D层状材料在GPEs中构建定向离子通道的应用[22,79]

Fig. 6 Application of 2D layered materials in constructing directional ion channels in GPEs[22,79] (a) Top-view SEM image of VAMMT[22]; (b) Cross-sectional SEM image of VAMMT[22]; (c) Arrhenius ionic conductivity (σ) plots of CMP/VAMMT, CMP/MMT and pure CMP[22]; (d) Li+ transference numbers of different electrolytes[22]; (e) Schematic illustration for the in situ polymerization of COF-templated method (PDCM)[79]; (f) 2D wide-angle X-ray scattering (WAXS) patterns of COF powder and COF membrane (COFM)[79]; (g) SEM images of the fracture surface for PDCM[79]; (h) Galvanostatic cycling curves of the Li||Li symmetric cells assembled with PDCM and PDOL@PP (PDPP)[79]

图7 2D层状材料在隔膜中构建定向离子通道的应用[82-83,85]

Fig. 7 Application of 2D layered materials in constructing directional ion channels in separator[82-83,85] (a) SEM morphologies of homogeneous membrane synthesized by low-temperature crystallization method (LTCM) (scale bar: 5 μm) with inset showing the optical image with the dimensions of 6 cm×6 cm[82]; (b) Cross-sectional SEM morphologies of TpPa-SO3H FSF (Tp: 1,3,5-triformylphloroglucinol; Pa-SO3H: 2,5-diaminobenzenesulfonic acid; FSF: free-standing form) homogeneous membrane (scale bar: 10 μm)[82]; (c) Migration number results of TpPa-SO3H HPF (HPF: high-pressure form) and TpPa-SO3H FSF in Zn-Zn symmetric batteries[82]; (d) Long cycling performance of zinc-iodine batteries using TpPa-SO3H FSF separator under the condition of 2 A·g−1 with an active mass loading of 5 mg·cm−2 with insets showing the photo of Zn anode foil after cycling (scale bar: 8 mm) and the corresponding XRD patterns[82]; (e) Coulombic efficiency (CE), voltage efficiency (VE), and energy efficiency (EE) during the charge-discharge cycling of zinc-iodine flow battery (20 mA·cm−2) using TpPa-SO3H FSF separator with inset showing the first 10 charge-discharge curves[82]; (f) Schematic of aligned ASU-LDH nanosheets under applied-electric field[83]; (g) Durability test of σ values of xDA-MMT films and Nafion NR211 film with a 25.4 μm thickness[85]; (h, i) Single-cell performances of (h) vertically aligned polydopamine-intercalated montmorillonite membrane (VAPMM)-based and (i) N117-based membrane electrode assembly from 30 to 75 ℃ with 100% relative humidity (RH)[85]

图8 2D层状材料促进电化学储能过程的离子传输机理[22,46,61,79]

Fig. 8 Ionic transport mechanisms of 2D layered materials promoting electrochemical energy storage process[22,46,61,79] (a) 6Li solid state nuclear magnetic resonance (SSNMR) spectra of CMP/VAMMT before (left) and after (right) discharge in the 6Li‖Cu cell[22]; (b) Synchrotron radiation X-ray diffraction (λ=0.2073 Å) patterns of pristine MMT, pristine CMP/VAMMT, cycled CMP/VAMMT, and the glass window[22]; (c) Raman spectra and fitting curves of PHL1.25 and PHL1.25BN5 electrolytes in 730-760 cm−1 (CIP: contact ion pair; AGG: aggregated ion pair)[61]; (d) Quantitative analysis of CIPs and AGGs of PHL1.25 and PHL1.25BN5 electrolytes[61]; (e) COMSOL multiphysics simulation results of the Zn2+ ions distribution behaviors of LH-Ti3C2Tx and H-Ti3C2Tx[46]; (f) Zn2+ ions concentration distribution versus diffusion depth through the cathode of LH-Ti3C2Tx and H-Ti3C2Tx[46]; (g) Distribution profiles of CF3SO32− detected by time-of-flight secondary ion mass spectrometer (TOF-SIMS) from the cycled Zn anodes in Zn||LH-Ti3C2Tx and Zn||H-Ti3C2Tx[46]; (h) 2D contour plots of the in situ XRD test results within one charge/discharge cycle of Zn||LH-Ti3C2Tx ZHCs[46]; (i, j) 1H-13C cross polarization-heteronuclear correlation nuclear magnetic resonance (CP-HETCOR NMR) spectra of (i) PDOL-COF physical mixture and (j) PDCM composite[79]; (k) Theoretical elucidation of Li+ migration behaviors in PDCM and COFM (initial, intermediate, transition, and final states are abbreviated as IS, IM, TS, and FS, respectively)[79]