Artificial Thiophdiyne Ultrathin Layer as an Enhanced Solid Electrolyte

Research Article Cite This: ACS Appl. Mater. Interfaces 2019, 11, 23990−23999

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Artificial Thiophdiyne Ultrathin Layer as an Enhanced Solid Electrolyte Interphase for the Aluminum Foil of Dual-Ion Batteries Kun Wang,†,‡ Xiaodong Li,†,‡,§ Yu Xie,† Jianjiang He,†,‡ Ze Yang,†,‡ Xiangyan Shen,†,‡,§ Ning Wang,†,‡ and Changshui Huang*,†,‡ †

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Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Songling Road 189, Qingdao 266101, China ‡ Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China § University of Chinese Academy of Sciences, No. 19A Yuquan Road, Beijing 100049, China S Supporting Information *

ABSTRACT: In this study, we design a novel carbon-based material containing thiophene and acetylenic linkers as functional groups named thiophdiyne (Thi-Dy) and apply it as an ultrathin artificial protective layer for the commercially available aluminum (Al) foil of dual-ion batteries (DIBs). The Thi-Dy films can be grown easily and directly on the Al foil through a mild Glaser−Hay coupling reaction. The as-proposed thiophene and acetylenic linker functional groups in Thi-Dy layers act as energetic active sites for the effective fabrication of a stable hybrid solid electrolyte interphase (SEI) during the electrochemical process, which is revealed through the ex situ measurement. The Thi-Dy-enhanced SEI layer contributes to offer a more effective and regulated lithium intercalation and diffusion pathway and delay the pulverization and huge volume expansion of the Al−Li alloy during long cycles, which are confirmed by the improvement on the cyclic stability of DIBs. Those studies are expected to provide novel thiophene-containing functional materials and mass-produced surface modification approach for metal anode protection, which will promote the research for the next-generation rechargeable battery. KEYWORDS: thiophene-containing, thiophdiyne, cycling stability, dual-ion batteries, solid electrolyte interphase

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density and cyclic stability, aluminum (Al) was first reported by Lee et al. as a potential negative electrode candidate through the formation of Al−Li alloy for lithium-ion-based DIBs with advantages of higher capacities, abundant resource, and low costs.12 However, Al is seriously hindered for practical applications because it easily fails and leads to pulverization and huge volume expansion because of the formation of Al−Li alloy.13,14 Many attempts, including the stabilizing Al-electrolyte interface, construction of Al−carbon nanoarchitectures, or building 3D porous Al, are reported to facilitate a stable, uniform solid electrolyte interphase (SEI) to withstand the volume expansion of the Al electrode.15−18 Recently, carbonbased interlayers or high-polarity polymer has been reported as

INTRODUCTION Over the past decades, lithium-ion batteries (LIBs) are considered as the most potential energy storage system and have been widespread applied for consumer electronics and electric vehicles. Yet, LIBs still need further improvement because of the limited lithium resource and increasing costs with the rapid growth demanding.1,2 A new type of low-cost energy storage systems such as aluminum-ion batteries, potassium−organic batteries, alkali metal ion-based dual-ion batteries (DIBs), dual-ion capacitors, even multi-ions batteries have aroused extensive interest for their advantages in terms of low cost, safety, and sustainability.3−9 The mentioned novel batteries show different energy storage mechanisms with conventional LIBs. Among such alternative systems, DIBs were first introduced by McCullough in earlier 1980s, relying on the intercalation and deintercalation of cations/anions during the cycle process.10,11 To improve the poor energy © 2019 American Chemical Society

Received: February 23, 2019 Accepted: June 12, 2019 Published: June 12, 2019 23990

DOI: 10.1021/acsami.9b03250 ACS Appl. Mater. Interfaces 2019, 11, 23990−23999

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ACS Applied Materials & Interfaces

Figure 1. (a) Schematic of synthetic route of the Thi-Dy compounds; (b) schematic illustration of the DIBs with Thi-Dy layer-modified Al foil.

Figure 2. (a) Solid-state 13C NMR of Thi-Dy powder as an exfoliated sample; XPS survey of S 2p (b) and C 1s (c) binding energy of Thi-Dy; (d) nitrogen adsorption−desorption isotherms of Thi-Dy as an exfoliated sample (inner: pore-size distribution); (e) Raman spectrum of the Thi-Dymodified Al foil; (f) current−voltage (I−V) curve of the Thi-Dy-modified Al foil.

during the lithiation/delithiation. An artificial SEI layer is an effective approach to stabilize the fragile natural SEI on the silicon surface to survive the huge internal stress fluctuations. It provides us the referential ideas to design an artificial layer with effective electronic and ionic pathways, rich electrolyte active

a protective layer to stabilize the Li metal anode surface, delaying the Li dendrite growth during cycling process.19 This research approach is also considered to solve the volume expansion problem of the silicon anode because of the enormous volume change for the formation of Li15Si4 alloy 23991


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preparation process are diagrammatized in Figure S1 in the Supporting Information. The chemical construction of the asprepared Thi-Dy layers is confirmed through solid-state 13C NMR, as shown in Figure 2a. The multiple peaks located in the range of 107 and 128 ppm can be attributed to the carbon atoms on the thiophene moieties which are connected to the four acetylenic linkages. The mixed peaks in the range of 90.6 and 73.0 ppm could be connected to Csp−Csp and Csp−Csp2 interlinkages, respectively.29,30 Notably, the asymmetric configuration of the thiophene units results in the different chemical bonding environments of the carbon atoms which might be because of the multiplet in the chemical shifts located at 128, 115, and 107 ppm. It corresponds to the carbon bonded with thiophene group in the acetylenic linkages. To study the possible stable configurations of Thi-Dy, we employed first-principles free-energy calculations with two tetragon-like structures for Thi-Dy. The corresponding total free energies of the configurations of Thi-Dy (A) and Thi-Dy (B) involving 50 atoms in either of them are −421.9 and −416.3 eV per unit, respectively (shown in Scheme S1). The energies are nearly the same, indicating that A and B conformations are probable to coexist in the products. The combining ability of Al and Thi-Dy has been studied. The results show that both configurations of Thi-Dy are conducive to the adsorption of Al atoms with free electrons, and there is little difference in adsorption energy (Eb). The X-ray photoelectron spectroscopy (XPS) scan results suggest that the S 2p region originated from the thiophene functional group in Figure 2b. The prominent S 2p peaks at around 164.1 eV for S 2p3/2, 165.2 eV for S 2p3/2 and S 2p1/2, and 168.6 eV for C− SOx−C binding are assigned to the characteristics of thiophene.36 It also suggests that the synthetic products have both Csp2 (284.3 eV) and Csp (285 eV) hybrid carbons with portion of C−O and CO bonds exists, probably because of the strong adsorption of O2 by tetragon-like intramolecular pores of Thi-Dy (Figure 2c).28 In addition, the Fouriertransform infrared spectroscopy (FT-IR) and UV−vis spectra of Thi-Dy layers are described in Figure S2b,c as the Supporting Information. Two bands attributed to the C−S asymmetric and symmetric stretching vibrations are found at 1395 and 892 cm−1, respectively.37 The band around 2250 cm−1 could be assigned to the typical acetylene stretching vibration. UV−vis spectra show sharp peaks around 255 nm. It is attributed to a typical π−π* transition derived from the conjugated thiophene and acetylenic bond. In Figure 2d, the nitrogen adsorption−desorption measurement suggests the abundant micropore in the Thi-Dy as an exfoliated sample. The tiny adsorption hysteresis and coincident isotherms confirm the existence of mesoporous of Thi-Dy. The Brunauer−Emmett−Teller result of Thi-Dy is calculated at around 77.6 m2 g−1. The pore distribution result future confirms the existing of mesoporous and micropores in the Thi-Dy structure according to the formed tetragon-like intramolecular pores and macropore network. Raman spectra could observe a wide bond region from 1300 to 1600 cm−1 in Figure 2e. It is noted that an unconspicuous D band at around 1380 cm−1 could be considered as the Cβ−Cβ stretching and a strong G band at around 1598 cm−1 attributed to the asymmetric CC stretching. Two small bands are derived from the diyne linkage at around 1939 and 2190 cm−1.26,38 In Figure S2a, the X-ray diffraction (XRD) result of the exfoliated Thi-Dy sample shows a broad peak around 22.5°, suggesting a interlayer spacing of 0.381 nm, similar to the reported

sites, excellent chemical stability, and layer-forming ability for the modified Al foil.20 As a candidate, conductive polymers containing a high-polarity functional group such as polythiophene (PT) have been studied for battery applications because of the properties of high electrical conductivity, filmforming ability, chemical stability, and a variety of designability.21,22 Recently, Zhang et al. reported the structure design for the thiophene functional group containing microporous polymers with excellent electrochemical performance.23 Kwon et al. used PT derivatives as an active bridge between various anode materials with high capacity.24 Li et al. prepared a self-formed SEI layer using sulfur-containing polymers served as a “plasticizer” to enhance the mechanical flexibility and improve the toughness of SEI layers.25 Those research studies show thiophene-containing compounds with superiority in microporous structure design and strong binding ability with lithium ions. However, there has been less report related to the direct application of such compounds for the surface modification of a metal anode because the PTs are usually obtained through oxidation polymerization with the acidic medium and strong oxidant.22 To prepare the thiophenecontaining materials and maintain the activity of thiophene groups with excellent ionic transmission as well as diffusion performance, it still needs an innovative study. Recently, graphdiyne is reported as a new kind of carbon allotrope that contains a number of intramolecular pores with rich acetylenic linkers, impelling high capacities and excellent rate capability for various energy storage devices.26−28 The chemical synthetic route for graphdiyne-based carbons has inspired us to a new research approach to design heteroatomicsubstituted carbon-rich materials such as boron-, halogen-, or nitrogen-substituted graphdiyne.29−33 The combination of the heteroatomic functional active site to the conjugated carbon framework through a simple cross-coupling solution reaction shows great convenience and benefits than complex pyrolyzation or chemical vapor deposition.34 In addition, it also provides an in situ and facile method to obtain the uniform conjugated carbon framework on metal arbitrary substrates such as Al with mass-produced conditions because the graphdiyne can be easily synthesized on arbitrary substrates through the controlled release of copper ion.35 Therefore, we design to substitute H atom positions of thiophene ring to introduce acetylenic bond as functional groups and prepare the PT derivatives named thiophdiyne (Thi-Dy) (Figure 1a). The artificial Thi-Dy films are expected to enhance the formation of hybrid SEI layer on the Al foil and act as an active bridge to improve the flexibility and toughness of enhanced SEI layers. Meanwhile, the Thi-Dy-enhanced hybrid SEI layer for the Al− Li alloy is supposed to provide more efficient pathway for lithium-ion transmission and diffusion and reduce the formation of microdefects and delay the pulverization failure and huge volume changes during long cycles for the application of DIBs (as shown in Figure 1b).

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RESULTS AND DISCUSSION The synthesis of tetra (trimethylsilyl) ethynyl thiophene was proceeded by following a typical Negishi coupling reaction. The preparation of Thi-Dy layer-modified commercial Al is operated through a typical envelope method of immersing an Al foil covered with copper in the mixture solution containing pyridine and tetraethynythiophene, as reported previously.35 The nuclear magnetic resonance (NMR) spectra of the tetra (trimethylsilyl) ethynyl thiophene monomer and the detailed 23992


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Figure 3. Morphology of the obtained Thi-Dy layers: (a) surface morphologies of Thi-Dy-modified Al samples; (b) cross-sectional SEM image of Thi-Dy layers as an exfoliated free-standing layer; (c) cross-sectional SEM image of Thi-Dy-modified Al foil (the inset scheme is the schematic of the cross-sectional view for Thi-Dy layers on Al); element mapping of the cross-sectional Thi-Dy-modified Al negative electrode with respect to Al (d), C (e), and S (f) element distribution, respectively; (g) optical photographs of free-standing Thi-Dy layers, commercial Al and Thi-Dy-modified Al samples, respectively; TEM (h,i) and HRTEM images of Thi-Dy layers.

Figure 4. (a) Ex situ XPS survey of the as-prepared Thi-Dy-modified Al negative electrode at potential from 4.2 to 4.8 V at the initial charge process with a current rate of 100 mA g−1. Chemical composition analysis of the XPS survey for P 2p (b), S 2p (C), C 1s (d), and F 1s (e) element.

m−1, which indicates a better charge-transfer ability than that of GDY and undoped polythiophene.26,41 The structure of

GDY.39,40 As shown in Figure 2d, the electrical conductivity of the Thi-Dy layer is calculated to be around 3.125 × 10−2 S 23993


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Figure 5. Morphologies and cross-sectional view of commercial Al foil (a,b) and Thi-Dy-modified Al (Thi-Dy/Al) negative electrode (c,d) at potentials of 4.2 and 4.8 V during the initial charge process with different resolutions, respectively. The ex situ XRD patterns (e) and ex situ Raman spectra (f) of the Thi-Dy-modified Al negative electrode at different potentials during the initial charge process with a current rate of 100 mA g−1.

scale as shown Figure S4, revealing the potential application of thus mass-produced surface modification approach for the metal electrode. In Figure 3h,i, the high-resolution TEM (HRTEM) images of Thi-Dy can only observe lateral stacking without the cross-structure, revealing the layer structure with an interlayer spacing around 0.38 nm of Thi-Dy. As mentioned above, it is proven that the designed Thi-Dy layers are successfully combining thiophene and acetylenic functional groups with in-plane intramolecular pores and layer structure. The unique morphology and functional structural features of Thi-Dy are hopeful to promote an enhanced SEI layer on Al and expected to be applied for long-cycle DIBs (as suggested in Figure 1b). Successively, to explore the synergistic effect of the interaction between thiophene and acetylenic functional groups with carbonate electrolyte and lithium ions for the formation of the enhanced SEI layer, we fabricate 2032-type DIB cells using the Thi-Dy-modified Al foil as a negative electrode. Commercial graphite is used as a positive electrode. LiPF6 (4 M) is dissolved in ethyl-methyl carbonate and applied as the high-concentration electrolyte. The cell is disassembled

Thi-Dy layers on an Al foil is confirmed and contained the thiophene and acetylenic groups with tetragon-like intramolecular pores and layered structure as we design. The morphology of the Thi-Dy layers on an Al foil is measured using transmission electron microscope (TEM) and scanning electron microscope (SEM). The Thi-Dy layer shows a rough surface with a large number of granules on an Al foil, as shown in Figure 3a. The thickness of the free-standing ThiDy layer is estimated around 20 nm as an exfoliated sample by etching the Al foil in an acidic solution, as suggested in Figure 3b. In Figure 3c, there is no clear boundary between the ThiDy protective layer with the Al foil, proving that the Thi-Dy is firmly and densely grown on an Al foil. The distribution of C and S atoms is further revealed by the element mapping measurement, suggesting that the C and S atoms are uniformly dispersed, as shown in Figure 3e,f. Figure 3g shows that the free-standing Thi-Dy layers present translucent yellowishbrown on the larger scale with the flexibility of the Thi-Dy layer, suggesting the excellent film forming ability because of the incorporation of thiophene and acetylenic functional groups. The Thi-Dy-modified Al can also be made at a large 23994


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Figure 6. Electrochemical performance of assembled DIB cells: (a) CV profiles of Thi-Dy-modified Al foil-based cells for the initial three cycles with scan rate as 0.1 mV s−1; (b) charge−discharge curves of Al and Thi-Dy-modified Al foil-based cells at the current rate of 100 mA g−1 at the first cycle; (c) rate performance of Al (blue) and Thi-Dy-modified Al (red) for DIB cells; (d) Nyquist plots of Al and Thi-Dy-modified Al foil-based cells at initial states; and (e) cycle performance of the Al and Thi-Dy-modified Al foil-based cells with a current density of 100 mA g−1.

and washed by the pure ethyl-methyl carbonate electrolyte when it was charged at certain voltages at the initial cycle to study the changes in surface morphology and structure of ThiDy layers.15,17 Figure 4a shows the ex situ XPS survey of the Thi-Dy-modified Al foil at different potentials from 4.2 to 4.8 V at a certain current density around 100 mA g−1. It observed a obvious decrease on the Al 2p at around 78 eV and increase on the hybrid lithium metal and lithium salts on the Li 1s bond at around 56 eV, revealing that the formation of the SEI layer is covered on the Thi-Dy/Al foil and grown on the Li−Al alloy with the potential from 4.2 to 4.8 V.17,42 In P 2p bonding energy profiles (Figure 4b), a series of signals are identified at 134.8 and 136.2 eV, which are attributed to feature P−C and PO bonding, respectively.43,44 The P−C and PO bonding are original from the P containing phosphate and carbonate electrolyte decomposition and bonded with the thiophene and acetylenic groups to form a SEI layer beginning at 4.2 V. It obviously observed a decrease and shift to high bonding energy range on the PO bond with the increased potential, revealing that the thicker and stable SEI layer continuously covered on the thiophene-containing Thi-Dy layer with the potential increasing. It is speculated that phosphate and carbonate electrolyte decomposition and bonding with active

sites are mainly deposited on the surface of Thi-Dy at a lower potential. As shown in Figure 4c, the series of signals for S 2p bonding energy profiles is assigned to bonds at around 164.2 eV for S 2p3/2, 165.2 eV for S 2p3/2 and S 2p1/2, and 168.6 eV for C−SOx−C.36 With the potential increased, S 2p3/2 and S 2p1/2 binding became weak, revealing that the near perfect SEI covered on the Thi-Dy layer. Meanwhile, the relative intensity of the C−SOx−C bond is increasing, probably because the polar thiophene functional group plays a more important role for the interaction with the carbonate electrolyte at a high potential. The C 1s XPS spectra exhibit major difference among the potential changes in Figure 4d. With the increased potential at 4.2 and 4.4 V, the C 1s spectrum of the Thi-Dy surface shows prominent peaks around 284.5 eV for Csp2, 285 eV for Csp, 286.5 eV for C−O, and 288.5 eV for CO binding, which are corresponding to C 2H5OLi, C−C, C2H5CO3Li, and Li2CO3, representing the composition of the SEI layer on carbon materials as reported.45 After 4.4 V to 4.8 V, the C−O and CO peaks are disappeared and shifted nearby 288.8 and 289.5 eV because of the higher bonding energy at high potential. A peak around 290.5 eV is appeared at potential reached to 4.6 V and shifted to a higher bonding energy region around 291.2 eV at 4.8 V, which may cause from 23995


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ACS Applied Materials & Interfaces the formation of −CF3 originated from the interaction between nomadic F− containing electrolyte and thiophene and acetylenic active groups.46 Moreover, two peaks at 685.2 and 686.5 eV could be assigned to the F 1s binding derived from F− (LiF) and −CF3, as shown in Figure 4e.32,46 The LiF is the original form of the decomposition product of LiPF6. For the F 1s profiles, the tiny shift to the low bonding energy region for LiF is probably due to the interaction between nomadic F− and Thi-Dy functional group to form the −CF3 at higher potential, corresponding to the shift of C 1s spectra.47 As a consequence, it is confirmed that the Thi-Dy layer acts as an artificial protective layer on Al, which is energetically participated in the formation of SEI layer containing electrolyte decomposition compound and Thi-Dy itself. It also speculated that phosphate and carbonate electrolyte decomposition and bonding with active sites are mainly deposited on the surface of Thi-Dy at a lower potential from 4.2 V, and the deposition of LiF plays a major role as the higher potential. The SEI layer is grown and keeping stable during the Al−Li alloying process even at a high potential, suggesting that the Thi-Dy layer is served as a “plasticizer” to improve the flexibility and toughness of the enhanced SEI layer. These results are more evidenced that the thiophene and acetylenic functional groups play an important role to form an enhanced SEI during the electrochemical process. In additional, further characterizations of the Thi-Dycontaining electrode are carried out through ex situ Raman, XRD, and SEM tests when it is charged to different potentials. The surface morphology of Thi-Dy- or Al-based cells charged to different potentials is presented as contrast in Figure 5a−d (the morphologies at potentials of 4.4 and 4.6 V for Al and Thi-Dy-modified Al are shown in Figures S6 and S7). It is directly seen that the formation of Al−Li alloy nucleated on the surface of the Al electrode with higher potential forms 4.2 V. Meanwhile, the growth and fracture of the microdefects on the commercial Al surface are gradually increased. The dendrite-like structure is observed at a potential of 4.8 V, as shown in Figure 5b. The high-concentration electrolyte could be enriched around the protrusion of the Al surface for the fast Li deposition and alloying, resulting in a fast nucleated and surface fracture.15 Benefitting from the Thi-Dy-enhanced SEI layer, the concentration of the electrolyte is probably inhibited with a slower lithium deposition and the formation of the Al− Li alloy process. The microdefects, granules, and fractures on the Thi-Dy-modified Al surface are much smaller than those on the commercial Al foil, as suggested in Figure 5c,d. It is reasonable to consider that the Thi-Dy-enhanced SEI could provide fast transmission channels for regulated Li intercalation and diffusion, significantly attributed to the tetragon-like intramolecular pores and layered structure in Thi-Dy. Meanwhile, the granular protuberance for commercial Al and ThiDy-modified Al electrodes is observed in Figure 5a−d as the profile images. A more obvious and thicker SEI layer is observed on the surface of Thi-Dy-modified Al, reducing the depth of microdefect penetration and delay the massive volume expansion at high potential because the Thi-Dyenhanced SEI provides a controlled lithium intercalation and diffusion. The ex situ Raman and XRD test results are suggested in Figure 5e,f. Inconspicuous diffraction peaks at around 24.5° and 39.6° appear at each potential, implying the formation of Al−Li alloy.12,48 In Figure 5f, the Raman intensity of Thi-Dy-based electrodes becomes weaken gradually with increasing potential because of the deposition and decom-

position of the carbonate electrolyte and the formation of SEI on the surface. For the full battery test, Figure 6a shows the cyclic voltammetry (CV) profiles of Thi-Dy-modified Al cells with a certain scan rate of 0.1 mV s−1. With the potential increased, the anodic peaks are observed at around 3.65 V for the Al electrode and 4.2 V for the Thi-Dy-modified Al electrode. This is initially associated with the formation of Al−Li and SEI layer in the first cycle, as our previous confirmed.49,50 Meanwhile, the Al and Thi-Dy-modified Al foil for Li half cells were assembled in CR2032 cells. A flat plateau around 0.2 V versus Li/Li+ is observed for Thi-Dy foil-based Li half cells, which corresponds to the Al−Li alloy formation process (Figure S11a). It is noted that the Thi-Dy-modified Al electrode shows a delayed voltage drop, probably because of the presence of the Thi-Dy protective layer on Al. Meanwhile, the presence of the Thi-Dy layer on Al can greatly improve the electrochemical performance of Li half cells, as shown in Figure S11b. In Figure 6b, it is observed that the galvanostatic charge−discharge (GCD) curve appeared as a plateau after 4.2 V, revealing the formation of Al−Li alloy process.15 The GCDs of the Thi-Dymodified Al electrode observed a faster voltage rise than that of the Al electrode, revealing that the Thi-Dy layer could retard the alloy speed and lead to the polarization of Li ions. It is noted that a weak platform at around 1.5 V is only existence in the first charge−discharge curves and almost disappeared from the second cycle in Figure S12. It is reasonable to speculate such platform probably because of the irreversible decomposition of unstable SEI components. The capacity of the ThiDy-based cell remains stable around 132, 122, 110, 108, and 106 mA h g−1 with different current densities of 100, 200, 300, and 400 mA g−1, as suggested in Figure 6c. The capacities are randomly changed from 500 mA g−1 and returned to 120 mA h g−1 when the current density backs to 100 mA g−1. For Albased cells, the capacities are decreased greatly from 300 mA g−1. It is suggested that the Al-based cells exhibited a weaker rate capability because of the fast and random growth of the alloy. Figure S13 shows the capacity retention ability of Al and Thi-Dy-modified Al anode-based anode. It intuitively shows that the presence of the Thi-Dy film is helpful to optimize the rate and cycle behavior of the assembled DIBs, mainly because of the inhibiting effect on the pulverization and volume expansion of Al. The Nyquist plots for each cell are shown in Figure 6d. Thi-Dy-based cell exhibits a higher resistance compared to the Al foil because the Thi-Dy layer could result in the regulated Li intercalation. It is seen that the Nyquist plots of Thi-Dy-containing cells show an extra and obvious semicircle at the high-frequency region, which directly proves the formation of a hybrid and more stable SEI with Thi-Dy.51 In Figure 6e, the capacity of the Thi-Dy-based DIB remains at a high capacity around 112 mA h g−1 for 550 cycles and reaches to 82% capacity retention. Meanwhile, the Al electrode shows a weaker capacity retention and drops greatly after 80 cycles. The Thi-Dy-containing electrode shows a better capacity retention than the Al electrode, revealing that the modified Thi-Dy plays an important function on the improvement of cycle performance. The Coulombic efficiency for both Al and Thi-Dy electrodes is maintained at around 90%, as suggested in Figure 6e. The relatively low Coulombic efficiency is due to the unstable SEI formed on both graphite and Thi-Dy-coated Al electrodes and the decomposition of high-concentration electrolyte on electrodes at both sides. To further optimize the electrochemical performance of obtained 23996


ACS Applied Materials & Interfaces DIBs, an in-depth study such as constructing the more stable SEI layer, suitable electrolyte additives, or developing new anion-hosting cathode is continued undergoing. In order to further reveal the failure mechanism for the DIB electrode, additional experiments are operated. The Nyquist plots and CV profiles of Thi-Dy-based cells after 300 and 500 cycles are contrasted in Figures S9 and S10, respectively. The greater semicircle at the high-frequency region, as well as more oblique line at the low-frequency region, is observed, suggesting that the SEI interface impedance and diffusion impedance became larger after long cycles. Figure S16 shows the cross-sectional morphologies of the Thi-Dy-modified Al electrode after 10 and 300 cycles. The Thi-Dy-modified Al electrode exhibited a finite expansion and only pulverized near the surface part, which is benefited by the existence of ThiDy.52 Hence, the alloying process on the Thi-Dy-modified Al foil could be summarized as proposed schematic diagrams in Figure 7. It is illustrated that the artificial Thi-Dy layers act as

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CONCLUSIONS

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ASSOCIATED CONTENT

In summary, we successfully designed and prepared novel carbon-based ultrathin Thi-Dy films on a commercial Al foil, which suitably acts as an artificial protective layer for DIBs’ negative electrode materials with improved cycling stability. The morphology and chemical structure of the Thi-Dy layers on the Al surface are confirmed. By combination of thiophene and acetylenic functional groups with tetragon-like intramolecular pores and layered structure, the artificial Thi-Dy layers could enhance the formation of enhanced hybrid SEI layer because of the strong interaction between the introduced thiophene and acetylenic functional groups with the electrolyte. The synergistic effects for the formation of enhanced SEI layer with artificial Thi-Dy layers are confirmed through the ex situ measurement. The hybrid and enhanced SEI layer is confirmed to offer more efficient pathway for regulated Li intercalation and diffusion and delay the pulverization and volume expansion of the Al electrode. Therefore, the Thi-Dybased DIB cells could deliver a higher capacity and better capacity retention rate with longer cyclic ability than the commercial Al foil. Meanwhile, this research also provides a mass-produced surface modification approach for the protection of the metal electrode for next-generation energy storage devices.

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.9b03250. Detailed experimental operation; NMR spectra of the prepared monomer; XPS survey, XRD patterns, FT-IR spectra, and density functional theory calculation results of the Thi-Dy sample; photos of Thi-Dy layers at a large scale; morphologies of Al and Thi-Dy-modified Al electrodes at potentials of 4.4 and 4.6 V; photos of obtained Thi-Dy layers; CV and Nyquist plots of Thi-Dy cells with different cycles; Li half cell behavior of Thi-Dy cells; morphologies and charge−discharge curves of ThiDy prepared with more HBE monomer; the capacity retention for Al and Thi-Dy cells; the ex situ XRD patterns and Raman spectra; and XPS survey of Thi-Dy with different cycles (PDF)

Figure 7. Proposed schematic diagrams of the lithium-ion intercalation and deintercalation process in the Thi-Dy-modified Al foil for the DIB cell configuration [(I) initial state of Thi-Dy-modified Al foil; (II and III) Li intercalation and deintercalation process in ThiDy-modified Al, respectively; and (IV) Li intercalation process in ThiDy after long cycles].

an enhanced SEI layer and protective layer on the Al surface. The introduced thiophene and acetylenic functional groups could enhance the interaction between the Thi-Dy protective layer and carbonate/lithium electrolyte, promote the electrolyte decomposition, and bond with active sites together to serve as a plasticizer to form an enhanced SEI layer (Figure 7(I)). When the Li ion is alloying with Al during the charging process, a slower Li deposition and Al−Li alloy formation occur because of the regulated Li concentration. The surface fractures and microdefects of the Thi-Dy-modified Al foil are comparatively smaller than those of commercial Al, as shown in Figure 7(II). The Thi-Dy-based SEI layer reconstructed a smooth and robust interface and kept a relatively stable structure of the Al surface when the lithium ion is dealloying with Al during the discharging process, as shown in Figure 7(III). For long cycles form Figure 7(I−IV), the Thi-Dyenhanced SEI provides flexibility and toughness to the robust protective film for regulated Li intercalation and alloying with Al, significantly reducing the pulverization failure and volume change as we proposed.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Yu Xie: 0000-0001-8925-6958 Changshui Huang: 0000-0001-5169-0855 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This study was supported by the National Natural Science Foundation of China (21771187, 51822208, 21790050, and 21790051), the Frontier Science Research Project (QYZDBSSW-JSC052) of the Chinese Academy of Sciences, and the Natural Science Foundation of Shandong Province (China) for Distinguished Young Scholars (JQ201610). 23997


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Artificial Thiophdiyne Ultrathin Layer as an Enhanced Solid Electrolyte

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