Antioxidative Lithium Reservoir Based on Interstitial Channels of

May 29, 2019 - First, the adsorption energy (ΔELi) of Li was calculated at different positions (schematically depicted in Figure 1a) of the SWCNT bun...
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Antioxidative Lithium Reservoir Based on Interstitial Channels of Carbon Nanotube Bundles Seok-Kyu Cho,† Gwan Yeong Jung,† Keun-Ho Choi,‡ Jiyun Lee,† JongTae Yoo,*,§ Sang Kyu Kwak,*,† and Sang-Young Lee*,† †

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Department of Energy Engineering, School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan 44919, Republic of Korea ‡ ubatt Inc., Migun Techno World 2-116, Daejeon 34025, Republic of Korea § R&D Investment Planning Team, Korea Institute of S&T Evaluation and Planning (KISTEP), Seoul 06775, Republic of Korea S Supporting Information *

ABSTRACT: Lithium (Li) metal has garnered considerable attention in next-generation battery anodes. However, its environmental vulnerability, along with the electrochemical instability and safety failures, poses a formidable challenge to commercial use. Here, we describe a new class of antioxidative Li reservoir based on interstitial channels of single-walled carbon nanotube (SWCNT) bundles. The Li preferentially confined in the interstitial channels exhibits unusual thermodynamic stability and exceptional capacity even after exposure to harsh environmental conditions, thereby enabling us to propose a new lithiation/delithiation mechanism in carbon nanotubes. To explore practical application of this approach, the Li confined in the SWCNT bundles is electrochemically extracted and subsequently plated on a copper foil. The resulting Li-plated copper foil shows reliable charge/discharge behavior comparable to those of pristine Li foils. Benefiting from the confinement effect of the interstitial channels, the SWCNT bundles hold great promise as an environmentally tolerant, high-capacity Li reservoir. KEYWORDS: Carbon nanotube bundles, interstitial channels, antioxidation, lithium reservoir, nanoconfinement

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shielding,7,8 conductive 3D scaffolds,9,10 and other strategies.11,12 Note that most previous works have focused on improving the electrochemical performance of Li metal after cell assembly. However, to achieve commercial viability of Li metal, its environmental vulnerability (e.g., notorious reactivity upon exposure to air and water) should be resolved as an indispensable prerequisite in addition to resolving the concerns on cell performance and safety. Here, we report a new class of antioxidative Li reservoir based on interstitial channels of single-walled carbon nanotube (SWCNT) bundles to address the longstanding challenges of Li metal described above. The SWCNT bundles are constructed by assembling SWCNT strands via van der

ithium (Li) metal has recently attracted much interest as an ideal battery anode material due to its high theoretical specific capacity (3860 mAh g−1) and low redox potential (−3.04 V vs standard hydrogen electrode (SHE)).1,2 However, commercial application of Li metal has been staggering by its electrochemical instability with electrolytes and safety failures.3,4 In particular, nonuniform plating/stripping behavior on Li metal continuously consumes electrolytes to create new solid electrolyte interphase (SEI) layers, frequently resulting in electrically isolated, dead Li. This Li-consuming parasitic reaction results in low Coulombic efficiency (C.E.) and poor cycling retention. Additionally, the random growth of Li dendrites tends to provoke an internal short circuit problem between electrodes, thus triggering thermal runaway of the batteries. Enormous research efforts have been undertaken to address the aforementioned problems of Li metal, which include the stabilization of SEI layers,5,6 mechanical/electrochemical © XXXX American Chemical Society

Received: April 1, 2019 Revised: May 11, 2019 Published: May 29, 2019 A

DOI: 10.1021/acs.nanolett.9b01334 Nano Lett. XXXX, XXX, XXX−XXX

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Figure 1. Theoretical elucidation of the specific recognition and confinement of Li in SWCNT nanospaces. (a) Schematic of three possible adsorption sites (i.e., interstitial channel, external groove, and surface) in the SWCNT bundles. (b) Adsorption energy (ΔELi) of Li in the SWCNT bundles with different tube diameters ((4,4), (5,5), (7,7), and (10,10), respectively). (c) Configurations of MD model systems for the SWCNT bundles embedded in liquid electrolyte (= LiPF6 in EC/DEC solvent mixture, chosen as an example). Depending on their positions in the SWCNTs, the Li atoms are classified as follows: Li confined inside the bundle (denoted as Li(confined)), Li adsorbed on the outer surface of the SWCNTs (Li(adsorbed)), and Li freely moving in the bulk electrolyte (Li(free)). (d) Self-diffusion coefficients (D) of Li (at different positions in the SWCNTs) wereestimated from MSD analysis. The error bars represent the standard deviations of each value.

nanospaces is highly stable and difficult to extract compared to the Li in the SWCNT surface, which appears consistent with the findings of previous studies.13−15 The ΔELi at the interstitial channel was highest in the (4,4) SWCNT bundle and decreased with increasing SWCNT diameter, eventually approaching the ΔELi of the external groove. This result was attributed to the enlarged void space at the larger SWCNT diameter in which the Li adsorption geometry of the interstitial channel resembles that of the groove site (Figure S1). To further understand the Li storage behavior in the interstitial channel, we calculated the Li−Li (ΔELi−Li) and Li−CNT (ΔELi−CNT) interactions as a function of Li number density (Supplementary Note 1, Figures S2 and S3). As the Li number density increased, ΔELi−Li tended to increase and then surpassed ΔELi−CNT, whereas ΔELi(total) remained almost unchanged, indicating that the thermodynamic stability of Li stored in the interstitial channels has little dependence on the Li number density. Next, we calculated the Li diffusivity in the SWCNT bundles to investigate lithiation/delithiation kinetics (Figure 1c). The Li-containing SWCNT bundle was introduced into a conventional liquid electrolyte (for calculation details, see MD simulations in the Supporting Information and Figures S4 and S5), and three regions were considered for this theoretical analysis: Li confined inside the SWCNT bundle (denoted as “Li(confined)”), Li adsorbed on the outer surface of the SWCNTs (denoted as “Li(adsorbed)”), and Li in the bulk

Waals interactions, eventually producing one-dimensional (1D) nanospaces (specifically, interstitial channels and external grooves). The 1D nanospaces of the SWCNT bundles can store Li up to 0.47 kgLi kgSWCNT−1 by tuning the degree of the SWCNT bundles. More notably, Li preferentially stored in the interstitial channels of the SWCNT bundles (55% of the total Li storage capacity) is chemically stable after exposure to air and even water. Note that the SWCNT bundles presented herein are explored as an antioxidative Li reservoir, not a conventional Li host which has been widely investigated in Li metal anodes. To examine the practical applicability of this concept, the Li confined in the SWCNT bundles is electrochemically extracted and subsequently plated on a copper (Cu) foil. The resulting Li-plated Cu foil shows normal and stable charge/discharge behavior comparable to those of pristine Li foils, thereby demonstrating the promising potential of this antioxidative Li reservoir approach. The specific recognition and confinement of Li stored in the SWCNT nanospaces were theoretically elucidated. First, the adsorption energy (ΔELi) of Li was calculated at different positions (schematically depicted in Figure 1a) of the SWCNT bundles via density functional theory (DFT) calculations (for calculation details, see DFT calculations in the Supporting Information). The interstitial channel and external groove sites showed larger ΔELi than the surface, and the tube diameters of the SWCNTs had little effect on the overall tendency (Figure 1b). This result indicates that the Li in the SWCNT B

DOI: 10.1021/acs.nanolett.9b01334 Nano Lett. XXXX, XXX, XXX−XXX

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Figure 2. Lithiation and delithiation behaviors of the SWCNT bundles. (a) Galvanostatic voltage profiles as a function of specific capacity under a voltage range of 0−4.7 V (vs Li/Li+). Qconfined represents the delithiation capacity in a voltage range of 3.0−4.7 V. (b) Ex situ Raman analysis as a function of lithiation/delithiation voltage in which the characteristic peak at 267 cm−1 is considered a bundle marker. The spectra were repeatedly measured three times (depicted in black/red/blue colors) to ensure reliability. (c) Galvanostatic lithiation profiles as a function of bundle degree at a constant current density of 35 mA g−1. (d) PITT analysis during delithiation up to 4.7 V. The black line and red dots represent the voltage step and current response, respectively.

electrolyte (denoted as “Li(free)”). The self-diffusion coefficients (D) of Li in the above-mentioned regions were calculated using mean square displacement (MSD) analysis (Figure 1d, Figure S6, and Supplementary Note 3). The Li diffusivity tended to decrease in the order of Li(free) > Li(adsorbed) > Li(confined), indicating that the Li confined in the interstitial channel is most sluggish and requires a larger energy for migration. From this theoretical understanding, we propose a new lithiation/delithiation mechanism in the SWCNT bundles, which is conceptually illustrated along with the free energy landscape (Figure S7). During the lithiation, Li preferentially enters the interstitial channels due to its high binding affinity (step I). Subsequently, Li adsorbs onto the outer surface of the SWCNTs (step II). The delithiation from the SWCNT bundles occurs in the reverse order via endothermic reaction pathways (from step III to step IV). Note that a significantly high energy is required to extract the Li confined in the interstitial channel (step IV). On the basis of the theoretical investigation described above, the lithiation/delithiation behavior of the SWCNT bundles was experimentally investigated. Figure 2a shows the voltage profile of the SWCNT bundles as a function of specific capacity. High lithiation/delithiation capacities (1.8 Ah gSWCNT−1 = 0.47 kgLi kgSWCNT−1) and reversible storage behavior (C.E. = ∼100%) were observed in a voltage range of 0−4.7 V (vs Li/Li+). By comparison, a significantly large amount of Li (Qconfined = 1.46 Ah gSWCNT−1 = 0.38 kgLi kgSWCNT−1 in Figure 2a) remained in the SWCNT upon delithiation to 3.0 V. Almost all previous studies16−23 investigated the lithiation/delithiation behavior of CNTs in the voltage range of 0−3.0 V and ascribed the initial capacity difference to SEI layer formation (accompanying irreversible

capacity loss) on the CNT surface. However, our results revealed that the main cause for the initial capacity difference observed in the voltage range of 0−3.0 V was not related to SEI formation on CNT surface (Table S1). In the voltage range of 0−3.0 V, a considerable amount of Li was not yet electrochemically extracted but remained in the interstitial channels of the SWCNT bundles. This result is consistent with the previous theoretical investigation, which shows the highest migration energy for Li confined in the interstitial channels. To further elucidate this unusual electrochemical behavior of the SWCNT bundles, their structural change during lithiation/ delithiation was traced by ex situ Raman spectroscopy under 785 nm laser excitation. The Raman spectra of SWCNTs provide information on their bundle degree24,25 in which the relative intensity of the radial breathing mode (RBM) at 267 cm−1 (corresponding to (10,2) SWCNT) is considered a bundle marker. As a model system, the (10,2) nanotubeincluding SWCNT electrode was fabricated by adding highpressure carbon monoxide (HiPco) SWCNTs in the suspension (Figure S9). Figure 2b shows a sharp decrease in I267 at the end of the lithiation plateau (0.8 V in Figure 2a), similar to those observed in isolated SWCNTs.24,25 I267 recovered upon delithiation to 4.7 V. This result indicates that the lithiation/delithiation in the SWCNT bundles contributes to reversible disassembly and assembly of SWCNTs. This strong dependence of SWCNT aggregation is clear evidence of the viable role of the interstitial channels of the SWCNT bundles as a Li reservoir. The Li storage capacities of the SWCNT bundles were investigated as a function of bundle degree. The bundle degree was varied by changing the SWCNT concentration in the suspension (Figures S10 and S11). Figure 2c shows that the C

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Figure 3. Environmental stability of the SWCNT bundles. (a) XRD profiles of the fully lithiated SWCNT bundles after exposure to ambient conditions for 1 day as a function of delithiation voltage. (b) Change in the pH of water (with a thymol blue indicator, initially acidic condition) containing the LiIC−SWCNT and control samples (lithiated graphite and Li foil). The change in the color of the solutions is shown in the inset. (c) Voltage profiles of the LiIC−SWCNT upon delithiation (before and after exposure to oxidative environments). The full-range voltage profile before environmental exposure is shown in the inset. (d) SEM and optical (inset) images of the Li layer (electrochemically extracted from the LiIC− SWCNT) on Cu foil. (e) Voltage profiles of Li-ion cells (Li-deposited Cu foil anode/LiCoO2 cathode) at a charge/discharge current density of 1.0 C/1.0 C. (f) Comparison of thermodynamic stability and Li storage capacity (LiIC−SWCNT vs conventional Li storage materials).

These results spurred us to conduct an in-depth investigation of the physicochemical properties of the SWCNT bundles. The environmental stability of Li at different positions of the SWCNT bundles was investigated using ex situ X-ray diffraction (XRD) measurements after exposure to ambient conditions for 1 day. For this analysis, the fully lithiated SWCNT bundles were delithiated to predetermined potentials, thus yielding various degrees of Li storage states in the SWCNT bundle. Figure 3a shows that all samples examined herein presented an intense peak at 2θ = 26.5° corresponding to the characteristic intertube spacing of SWCNT bundles.19,21 In addition, the broad peaks at 2θ = ∼31° and ∼36° that signifies oxidized Li species 26 were detected upon partial extraction to 0.01 and 3.0 V. These peaks may be due to oxidation of Li residing on the

voltage plateaus at 0.8 V were extended with increasing bundle degree, revealing the significance of the bundle degree for Li storage. This finding is in complete contrast to previously reported results (Table S1) that ascribed the voltage plateau at 0.8 V to irreversible capacity loss arising from SEI formation on the CNT surface. To provide additional evidence, we conducted a potentiostatic intermittent titration technique (PITT) analysis. The PITT responses at 0.8 (upon lithiation, Figure S12) and 4.5 V (upon delithiation, Figure 2d) showed a slow rise and decline in the current, in comparison to the results observed at other voltages. This kinetically sluggish lithiation (at 0.8 V)/delithiation (at 4.5 V) behavior is highly consistent with the high binding energy and low diffusivity of the Li stored in the interstitial channels discussed in the previous theoretical investigation. D

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compared to the conventional LIB anode materials which tend to spontaneously oxidize upon contact with water due to their lower oxidation potential. Another noteworthy advantage of the LiIC−SWCNT is the substantially higher Li storage capacity than currently available intercalation-based LIB cathode materials. Future works will focus on lowering the delithiation overpotential of the LiIC−SWCNT without impairing its environmental stability. In summary, we have demonstrated an antioxidative Li reservoir based on the interstitial channels of SWCNT bundles. The Li preferentially confined in the interstitial channels showed the unusual thermodynamic stability and electrochemical behavior. The theoretical/experimental elucidation of the interstitial channels allowed us to suggest a new lithiation/ delithiation mechanism that is different from those of previous studies reporting the SEI formation-induced irreversible loss in the Li storage capacity of CNTs. Notably, the LiIC−SWCNT provided an exceptional Li storage capacity (∼0.26 kgLi kgSWCNT−1) that lies far beyond those of conventional Li storage materials. Furthermore, the delithiation capacity of the LiIC−SWCNT was hardly impaired after exposure to air and water, exhibiting its environmental stability. The potential application of the LiIC−SWCNT as an antioxidative Li reservoir was verified by the reliable electrochemical performance of the Li-ion cells (assembled with LiCoO2 cathodes and Li-deposited Cu foil anodes that were prepared by extracting Li from the LiIC−SWCNT. We envision that this SWCNT nanospace strategy will open a new avenue for development of environmentally tolerant, high-capacity Li reservoir materials.

external surfaces of the SWCNTs. By comparison, the characteristic peaks were not observed in the delithiation to 4.3 V as well as the full delithiation to 4.7 V. This result demonstrates that the Li stored in the voltage range of 4.3−4.7 V, which predominantly exists in the interstitial channels of the SWCNT bundles, is chemically stable against ambient conditions. The environmental stability of the partially delithiated (to 4.3 V) SWCNT (hereafter denoted as LiIC (Interstitial Channels)− SWCNT) was further investigated under much harsher conditions. Upon contact with water, Li is oxidized and yields hydroxide ions.26 Therefore, the pH change of water is a reliable criterion for evaluating the water stability of samples. Here, the pH of water with a thymol blue indicator was initially set at 1.773 for the apparent comparison between samples. Pristine Li metal (200 μm) and lithiated graphite (its Li content equal to that of LiIC−SWCNT) were chosen as control samples. When the control samples were immersed in water (initially, red color), the color and pH of the solution changed drastically (Figure 3b). The Li metal and lithiated graphite produced blue (pH = 11.3) and yellow color (pH = 7.3), respectively. By contrast, no significant changes in color and pH were observed in the LiIC−SWCNT, which showed little difference from the blank solution. This unusual environmental stability of the LiIC−SWCNT was verified by theoretically investigating the possibility of intermolecular collision between Li and water. MD simulations (Figure S13) showed that the minimum distance between the Li stored in the SWCNT interstitial channels and water molecules was 4.1 Å, much larger than that of hydrated Li+ ion (∼1.9 Å).27 This result indicates that the Li in the SWCNT interstitial channels is isolated from water molecules, thus enabling exceptional environmental stability compared to conventional Li storage materials such as Li metal and lithiated graphite. After exposure to air and water, the Li in the LiIC−SWCNT was fully extracted to 4.7 V. Figure 3c shows that Li was successfully extracted from the LiIC−SWCNT before and even after exposure to oxidative environments. The relative delithiation capacity (= delithiation capacity after exposure/ delithiation capacity before exposure) was estimated to be 91% (after exposure to ambient air) and 95% (water), respectively. In addition, the LiIC−SWCNT was placed in an oven at 200 °C (higher than the melting temperature of Li) for 1 h. After exposure to such harsh thermal conditions, the retention ratio of delithiation capacity was 85%. We explored the feasibility of the LiIC−SWCNT as a new concept of a Li reservoir for battery applications. The Li stored in the LiIC−SWCNT was galvanostatically extracted and plated on a Cu foil. The plated Li layer appeared shiny silver white overall and exhibited round-shaped smooth edges (Figure 3d). The electrochemical properties of the Li-deposited Cu were investigated using a LiCoO2-paired Li-ion cell. The Li-ion cell containing the Li-deposited Cu showed normal charge/ discharge voltage profiles and stable cycling performance (Figure 3e and Figure S14), comparable to those of a control cell assembled with the pristine Li. This result demonstrates the potential application of the Li-deposited Cu as an alternative anode. To highlight the excellence of the LiIC−SWCNT, its thermodynamic stability and Li storage capacity were compared with those of previously reported Li storage materials (Figure 3f and Table S2). Note that the LiIC− SWCNT showed the exceptional waterproof characteristic

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.nanolett.9b01334. Materials and methods, supplementary notes about calculation details, supplementary simulation, Raman, AFM, and electrochemical results, summary of Li storage behavior of the previously reported CNTs (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. *E-mail: [email protected]. ORCID

Sang Kyu Kwak: 0000-0002-0332-1534 Sang-Young Lee: 0000-0001-7153-0517 Author Contributions

S.-K.C. and G.Y.J. contributed equally. S.-K.C., K.-H.C., and J.Y. designed all experiments and analyzed experimental results. G.Y.J. and J.L. designed and performed all theoretical calculations. S.-K.C., G.Y.J., K.-H.C., J.L., J.Y., S.K.K, and S.Y.L. prepared the manuscript. J.Y., S.K.K., and S.-Y.L. revised the manuscript critically. All authors have given approval to the final version of the manuscript. Notes

The authors declare no competing financial interest. E

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(16) Gao, B.; Kleinhammes, A.; Tang, X.; Bower, C.; Fleming, L.; Wu, Y.; Zhou, O. Electrochemical intercalation of single-walled carbon nanotubes with lithium. Chem. Phys. Lett. 1999, 307 (3−4), 153−157. (17) Maurin, G.; Bousquet, C.; Henn, F.; Bernier, P.; Almairac, R.; Simon, B. Electrochemical intercalation of lithium into multiwall carbon nanotubes. Chem. Phys. Lett. 1999, 312 (1), 14−18. (18) Frackowiak, E.; Gautier, S.; Gaucher, H.; Bonnamy, S.; Beguin, F. Electrochemical storage of lithium in multiwalled carbon nanotubes. Carbon 1999, 37 (1), 61−69. (19) Claye, A. S.; Fischer, J. E.; Huffman, C. B.; Rinzler, A. G.; Smalley, R. E. Solid-State Electrochemistry of the Li Single Wall Carbon Nanotube System. J. Electrochem. Soc. 2000, 147 (8), 2845− 2852. (20) Kim, Y. A.; Kojima, M.; Muramatsu, H.; Umemoto, S.; Watanabe, T.; Yoshida, K.; Sato, K.; Ikeda, T.; Hayashi, T.; Endo, M.; Terrones, M.; Dresselhaus, M. S. In Situ Raman Study on Single- and Double-Walled Carbon Nanotubes as a Function of Lithium Insertion. Small 2006, 2 (5), 667−676. (21) Landi, B. J.; Ganter, M. J.; Schauerman, C. M.; Cress, C. D.; Raffaelle, R. P. Lithium Ion Capacity of Single Wall Carbon Nanotube Paper Electrodes. J. Phys. Chem. C 2008, 112 (19), 7509−7515. (22) Yoon, S.; Lee, S.; Kim, S.; Park, K.-W.; Cho, D.; Jeong, Y. Carbon nanotube film anodes for flexible lithium ion batteries. J. Power Sources 2015, 279, 495−501. (23) Ren, J.; Ren, R. P.; Lv, Y. K. A New Anode for Lithium-Ion Batteries Based on Single-Walled Carbon Nanotubes and Graphene: Improved Performance through a Binary Network Design. Chem. Asian J. 2018, 13 (9), 1223−1227. (24) Heller, D. A.; Barone, P. W.; Swanson, J. P.; Mayrhofer, R. M.; Strano, M. S. Using Raman Spectroscopy to Elucidate the Aggregation State of Single-Walled Carbon Nanotubes. J. Phys. Chem. B 2004, 108 (22), 6905−6909. (25) O’Connell, M. J.; Sivaram, S.; Doorn, S. K. Near-infrared resonance Raman excitation profile studies of single-walled carbon nanotube intertube interactions: A direct comparison of bundled and individually dispersed HiPco nanotubes. Phys. Rev. B: Condens. Matter Mater. Phys. 2004, 69 (23), 235415. (26) Adams, B. D.; Radtke, C.; Black, R.; Trudeau, M. L.; Zaghib, K.; Nazar, L. F. Current density dependence of peroxide formation in the Li−O2 battery and its effect on charge. Energy Environ. Sci. 2013, 6, 1772−1778. (27) Rudolph, W.; Brooker, M. H.; Pye, C. C. Hydration of Lithium Ion in Aqueous Solution. J. Phys. Chem. 1995, 99 (11), 3793−3797.

ACKNOWLEDGMENTS This work was supported by the Basic Science Research Program (2017M1A2A2087810, 2017M1A2A2044501, 2018R1A2A1A05019733, and 22018M3D1A1058624), Wearable Platform Materials Technology Center (2016R1A5A1009926) through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT, and future Planning and Batteries R&D of LG Chem. S.K.K. acknowledges the financial support from the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (NRF-2018M1A2A2063341) and computational resources from UNIST-HPC.

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REFERENCES

(1) Choi, J. W.; Aurbach, D. Promise and reality of post-lithium-ion batteries with high energy densities. Nat. Rev. Mater. 2016, 1, 16013. (2) Cheng, X.-B.; Zhang, R.; Zhao, C.-Z.; Zhang, Q. Toward Safe Lithium Metal Anode in Rechargeable Batteries: A Review. Chem. Rev. 2017, 117 (15), 10403−10473. (3) Tikekar, M. D.; Choudhury, S.; Tu, Z.; Archer, L. A. Design principles for electrolytes and interfaces for stable lithium-metal batteries. Nat. Energy 2016, 1, 1−7. (4) Zhao, J.; Zhou, G.; Yan, K.; Xie, J.; Li, Y.; Liao, L.; Jin, Y.; Liu, K.; Hsu, P.-C.; Wang, J.; Cheng, H.-M.; Cui, Y. Air-stable and freestanding lithium alloy/graphene foil as an alternative to lithium metal anodes. Nat. Nanotechnol. 2017, 12, 993−999. (5) Li, N.-W.; Yin, Y.-X.; Yang, C.-P.; Guo, Y.-G. An Artificial Solid Electrolyte Interphase Layer for Stable Lithium Metal Anodes. Adv. Mater. 2016, 28 (9), 1853−1858. (6) Kim, M. S.; Ryu, J.-H.; Deepika; Lim, Y. R.; Nah, I. W.; Lee, K.R.; Archer, L. A.; Cho, W. I. Langmuir−Blodgett artificial solidelectrolyte interphases for practical lithium metal batteries. Nat. Energy 2018, 3, 889−898. (7) Ding, F.; Xu, W.; Graff, G. L.; Zhang, J.; Sushko, M. L.; Chen, X.; Shao, Y.; Engelhard, M. H.; Nie, Z.; Xiao, J.; Liu, X.; Sushko, P. V.; Liu, J.; Zhang, J.-G. Dendrite-Free Lithium Deposition via SelfHealing Electrostatic Shield Mechanism. J. Am. Chem. Soc. 2013, 135 (11), 4450−4456. (8) Nguyen, H.-D.; Kim, G.-T.; Shi, J.; Paillard, E.; Judeinstein, P.; Lyonnard, S.; Bresser, D.; Iojoiu, C. Nanostructured multi-block copolymer single-ion conductors for safer high-performance lithium batteries. Energy Environ. Sci. 2018, 11, 3298−3309. (9) Zhang, Y.; Luo, W.; Wang, C.; Li, Y.; Chen, C.; Song, J.; Dai, J.; Hitz, E. M.; Xu, S.; Yang, C.; Wang, Y.; Hu, L. High-capacity, lowtortuosity, and channel-guided lithium metal anode. Proc. Natl. Acad. Sci. U. S. A. 2017, 114 (14), 3584−3589. (10) Zhang, H.; Liao, X.; Guan, Y.; Xiang, Y.; Li, M.; Zhang, W.; Zhu, X.; Ming, H.; Lu, L.; Qiu, J.; Huang, Y.; Cao, G.; Yang, Y.; Mai, L.; Zhao, Y.; Zhang, H. Lithiophilic-lithiophobic gradient interfacial layer for a highly stable lithium metal anode. Nat. Commun. 2018, 9, 3729. (11) Li, L.; Basu, S.; Wang, Y.; Chen, Z.; Hundekar, P.; Wang, B.; Shi, J.; Shi, Y.; Narayanan, S.; Koratkar, N. Self-heating−induced healing of lithium dendrites. Science 2018, 359 (6383), 1513−1516. (12) Li, Q.; Tan, S.; Li, L.; Lu, Y.; He, Y. Understanding the molecular mechanism of pulse current charging for stable lithiummetal batteries. Sci. Adv. 2017, 3, e1701246. (13) Zhao, J.; Buldum, A.; Han, J.; Lu, J. P. First-Principles Study of Li-Intercalated Carbon Nanotube Ropes. Phys. Rev. Lett. 2000, 85 (8), 1706−1709. (14) Meunier, V.; Kephart, J.; Roland, C.; Bernholc, J. Ab Initio Investigations of Lithium Diffusion in Carbon Nanotube Systems. Phys. Rev. Lett. 2002, 88 (7), 075506. (15) Song, B.; Yang, J.; Zhao, J.; Fang, H. Intercalation and diffusion of lithium ions in a carbon nanotubebundle by ab initio molecular dynamics simulations. Energy Environ. Sci. 2011, 4, 1379−1384. F

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