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May 16, 2017 - Poly(ethyl α‑cyanoacrylate)-Based Artificial Solid Electrolyte. Interphase Layer for Enhanced Interface Stability of Li Metal Anodes...
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Poly(ethyl α‑cyanoacrylate)-Based Artificial Solid Electrolyte Interphase Layer for Enhanced Interface Stability of Li Metal Anodes Zhenglin Hu,†,§ Shu Zhang,† Shanmu Dong,*,† Wenjun Li,‡,§ Hong Li,‡ Guanglei Cui,*,† and Liquan Chen†,‡ †

Qingdao Industrial Energy Storage Research Institute, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao 266101, P. R. China ‡ Key Laboratory for Renewable Energy, Beijing Key Laboratory for New Energy Materials and Devices, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, P. R. China § University of Chinese Academy of Sciences, Beijing 100049, P. R. China S Supporting Information *

ABSTRACT: The inhomogeneous deposition/dissolution of Li metal and an unstable SEI layer are still tough issues for lithium metal batteries, causing severe safety problems and low Coulombic efficiency. In this paper, we design an artificial SEI layer based on in situ polymerization of ethyl α-cyanoacrylate precursor with LiNO3 additive. The CN− and NO3− groups can react with lithium metal during cycling to form a nitrogenous interface inorganic layer, facilitating ions conduction and blocking further undesirable interface reaction. The poly(ethyl α-cyanoacrylate) with excellent mechanical property presents as the dominate organic species in the artificial SEI layer to offer a uniform and firm protective outer layer. A lithium metal battery with this artificial SEI film exhibits a capacity retention of 93% even after 500 cycles at a rate of 2C. A smooth surface morphology of the lithium metal anode is obtained without any cracks and dendrites.

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INTRODUCTION Lithium-ion batteries (LIBs) have achieved great success in the markets of consumable electronic equipment in the past decades.1 However, LIBs are gradually reaching the theoretical capacity and cannot meet the rapid growth for various electronic devices. Modern portable electronics and electric automobiles have proposed an urgent requirement for high energy density energy storage systems.2 To achieve higher energy density, lithium metal is regarded as the “Holy Grail” for its extremely high theoretical capacity (3860 mAh g−1), low density (0.534 g cm−3), and the lowest negative electrochemical potential3,4 (−3.040 V vs standard hydrogen electrode). Consequently, it has drawn worldwide interests for nextgeneration rechargeable high energy density batteries, such as Li-S and Li-air batteries.5,6 Despite extensive research efforts since decades ago, several fundamental challenges with the lithium metal anode still remain unsolved. Lithium metal can react with most of the organic solvents due to its high activity, forming a solid-electrolyte-interphase (SEI) layer.7 The compounds in the SEI layer have been reported as complex lithium-containing inorganic and organic species. The inorganic compounds, such as LiF and Li2CO3, are mostly formed on the early stage of cycling, while a gradual formation of the organic species occurs constantly.8 The unstable species in the native © 2017 American Chemical Society

SEI tend to partially decompose in the subsequent cycles, leading to inhomogeneous coverage of lithium metal. The fracture and regeneration of the SEI layer causes severe consumption of lithium metal and the electrolyte, which results in irreversible capacity and low Coulombic efficiency.9 Furthermore, the surface heterogeneity of lithium foils contributes to an uneven electric field and nucleation sites, accelerating the formation of dendritic lithium and further cracking the SEI layer.10 To achieve a stable SEI layer, we design an artificial protection layer by in situ polymerization of ethyl αcyanoacrylate (ECA) monomers on the lithium anode. LiNO3 is introduced into the prepolymer as a critical additive. As a natural SEI layer, the CN− functional group in ECA and NO3− from LiNO3 can easily react with the lithium anode to in situ generate a uniform inorganic nitrogenous interface layer during cycles. The poly(ethyl α-cyanoacrylate) serves as the dominate organic species in the artificial SEI film, offering the strong adhesion strength with lithium metal, which can bear the volume change and release the internal stress during the lithium Received: January 9, 2017 Revised: May 16, 2017 Published: May 16, 2017 4682

DOI: 10.1021/acs.chemmater.7b00091 Chem. Mater. 2017, 29, 4682−4689

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Chemistry of Materials

lithium anodes, electrochemical impedance spectroscopy (EIS) was tested by an electrochemical working station (VMP-300) over a frequency range of 0.1−106 Hz with a perturbation amplitude of 5 mV.

plating/stripping process. The excellent mechanical property and homogeneous distribution of the PECA outer layer can protect the inner inorganic interface layer from severe fragment caused by heterogeneous lithium deposition. Furthermore, poly(ethyl α-cyanoacrylate) bulk can dissociate the lithium salt effectively to facilitate ionic transport, resulting in greatly enhanced electrochemical behaviors of the lithium metal anode.11 On the basis of its excellent mechanical and electrochemcial properties, the PECA-based artificial SEI layer is suitable for potential industrialization of a lithium metal battery in the conventional production condition.

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RESULTS AND DISCUSSION Pretreatment of Li Metal Anode. The pretreatment process of the metal lithium anode is schematically presented in Figure 1. The lithium strip was first polished by stirring it in

EXPERIMENTAL SECTION

Pretreatment of Lithium Metal Anode. Lithium metal foil (FMC-Lithuim, 150 μm) was received and stored in an argon atmosphere glovebox. Aurbach and co-workers reported that the native passive film of lithium metal including Li2CO3, LiOH, and Li2O suffers from the partial dissolution, leading to the sustainable consumption of the lithium metal anode.12 Thus, the removal of the surface passive film is essential. Various methods have been reported previously, such as scraping with a razor blade13,14 or with a polyethylene block,15 to remove surface impurity from the as received lithium strip. In this work, an untreated lithium strip (size: 0.15 × 50 mm) was immersed into n-pentane solvent for at least 3 min with vigorous stirring, and the surface of the lithium strip shows metallic luster after polishing.16 ECA monomers dissolved in anhydrous acetone (AE, Aldrich) solvent as the film-forming solution, and the volume ratio of ECA/AE is 1:5. Meanwhile, lithium nitrate (LiNO3) is the additive and dissolved in acetone solvent with a molar concentration of 0.1 M (relative to AE). Then, the lithium strip was coated with the film-forming solution via blade-coating by using a doctor blade of 200 μm. The coated lithium strip was dried under argon flow in a glovebox, and ECA monomer molecules polymerize with the initiation of hydroxy on the surface of lithium metal. Preparation of LiFePO4 Cathode. A LiFePO4 cathode slurry was prepared by grinding LiFePO4 powder (battery grade), Super P, and polyvinylidene difluoride (PVDF, Alfa Aesar) with mass fractions of 80, 10, and 10%, respectively. The PVDF dissolved in N-methyl pyrrolidone (NMP, Aldrich) with a mass fraction of 6% was used as the binder. The obtained cathode slurry was coated on aluminum foils and dried at 120 °C for 12 h in a vacuum oven. Then, the cathode foil was punched into small plates with a diameter of 12 mm. The specific capacity of the commercial LiFePO4 with carbon coating is about 150 mAh g−1, and the areal capacity of the LFP cathode is approximately 1.04 mAh cm−2. Assembling of Coin Cells. LiFePO4 was chosen as the cathode material, and the electrolyte was 1.0 M LiPF6 in 1:1 (V/V) EC/DMC (Aldrich). The PECA coated lithium strip was punched into little wafers with a diameter of 14 mm as the anodes and the coin cells were assembled in a glovebox with an argon gas environment. Characterization. Symmetric cells were employed to evaluate the cycling stability and cycle life of different samples. They were assembled using CR2032-type coin cells and cycled at 1.0 mA cm−2 for 1 h in each half cycle. The cycling performance of different samples in LiFePO4|Li cells was tested between 2.5 and 4 V under a LAND CT2001A test system. A scanning electron microscope (FE-SEM, Hitachi S-4800) was used to obtain the surface morphology of lithium metal. The element compositions were examined by energy dispersive X-ray spectroscopy (EDX, Horiba 7593-H). The X-ray photoelectron spectroscopy (XPS) was employed to detect the surface composition, and it was performed on a Thermo Scientific ESCALab 250Xi. Secondary ion mass spectroscopy (SIMS) was used to detect the element content on the surface of different samples. For SIMS analysis, the samples were protected by argon and quickly transferred into the vacuum chamber via a glovebag. Atomic force microscopy (Multimode 8, AFM) with PFT-QNM mode was employed to measure the surface morphology and the Young’s modulus of the PECA modified lithium anode. In order to investigate the interface impedance of different

Figure 1. Schematics of the pretreatment process of metal lithium and the corresponding polymerization mechanism of ECA monomers.

anhydrous n-pentane to remove the surface impurity such as Li2CO3, LiOH, and Li2O. The film-forming solution composed of ethyl α-cyanoacrylate (ECA) monomers, LiNO3 additive, and anhydrous acetone was dropped on the surface of polished lithium metal uniformly using the doctor blade. Then, the filmforming solution was dried under an argon gas environment to obtain a compact and homogeneous PECA-based artificial SEI layer (Figure 2a,b). The anionic polymerization mechanism of

Figure 2. (a) The photo of lithium foils with (right) or without (left) PECA-based SEI film. (b) The cross-sectional SEM image of lithium anode with PECA-based SEI film. (c) AFM image of Li(PECA+ LiNO3) anode and (d) the corresponding Young’s modulus mapping.

ECA monomers is also depicted in Figure 1, and the tightly bound monolayer consisting of hydroxyl groups on the surface of lithium metal works as the initiating agent.14,17 The in situ polymerization is beneficial for the interfacial contact between the lithium anode and the PECA-based SEI film, contributing to better mechanical properties and interfacial compatibility of electrodes.18 Atomic force microscopy (AFM) was employed to 4683

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Figure 3. Voltage profiles of three different samples cycled in Li|Li symmetric cells: (a) bare Li, (b) Li(LiNO3), and (c) Li(PECA+LiNO3). (d) Cycling performance of three different samples cycled in LiFePO4|Li cells for 500 cycles at 2C (current density: 2.08 mA cm−2).

increases continuously during the whole test process, whereas cells of Li(LiNO3) and Li(PECA+LiNO3) possess stable interfacial impedance with a slight increase from the 1st to 7th days. For bare lithium anodes, the outermost layer of lithium metal reacts with the electrolyte due to its high activity21 and results in a continuously thickened SEI layer, which contributes to growing impedance values7,17 and irreversible consumption of lithium metal. However, the PECA coating and LiNO3-induced SEI layer provide effective segregation of the electrolyte and lithium anode, resulting in a stable interface and corresponding relatively constant impedance values (Figure S2b,c). Electrochemical Performance. To further confirm the interfacial stability provided by PECA-based coating, electrochemical properties of the Li plating/stripping process were also demonstrated by comparing the galvanostatic discharge/ charge voltage profiles of three different samples. The symmetric cells of bare lithium, Li(LiNO3), and Li(PECA+ LiNO3) were cycled under a current density of 1 mA cm−2, and the result is shown in Figure 3a−c. The cell with bare lithium electrodes shows random voltage oscillation and gets shortcircuited around 100 cycles (Figure 3a), whereas the other samples (Figure 3b,c) maintain stable Li plating/stripping during the entire process. We found that the single use of LiNO3 plays a certain role in stabilizing the film−solution interface but cannot endure a long cycle due to the fragility or the component changes of the LiNO3-induced SEI layer caused by the exhaustion of LiNO3, which leads to increasing polarization voltage and the deterioration of lithium metal anodes. In sharp contrast, for cells with Li(PECA+LiNO3)

measure the morphology, and it turns out that the PECA-based SEI layer is even with slight fluctuation (Figure 2c,d). In addition, the average Young’s modulus of this artificial coating is higher than 25 GPa, which is sufficient to suppress the lithium dendrite growth.19 In order to prove the excellent protective effect of the artificial SEI layer, three different samples have been investigated, respectively. For convenient writing, Li anodes with PECA-based SEI film and LiNO3containing electrolyte are hereafter denoted as Li(PECA+ LiNO3) and Li(LiNO3), respectively. The corrosive effect to lithium anodes with or without PECA-based coating caused by the electrolyte of 1 M LiPF6 and EC/DMC was studied, and the result is shown in Figure S1. Fresh bare lithium and Li(PECA+LiNO3) anodes were immersed in electrolyte for 7 days and then tested under a scanning electron microscope (SEM). The surface of bare lithium metal is rugged with many pits, which is attributed to the adverse reactions between lithium metal and the electrolyte. On the contrary, the surface of the Li(PECA+LiNO3) anode is compact and even with few scallops. This polymer coating exists steady in 1 M LiPF6 and EC/DMC electrolyte and presents an effective protection to the lithium anode, alleviating the corrosion effect of electrolyte effectively. The relationship of interface impedance and the time evolution in coin cells with different Li anodes has also been carried out (Figure S2). All of these AC impedance spectra consist of two partially overlapping semicircles in high and low frequency regions which are related to the SEI layer on the lithium anode and the charge transfer process, respectively.20 Interfacial resistance value of cells with bare Li electrodes (Figure S2a) is unstable and 4684

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Figure 4. Top-view and side-view SEM images of (a, b) bare Li anode, (c, d) Li(LiNO3) anode, and (e, f) Li(PECA+LiNO3) anode harvested from LiFePO4|Li cells after 150 cycles at a current rate of 1C (current density: 1.04 mA cm−2).

Figure 5. Schematic diagram of Li deposition on the surface of (a) bare lithium, (b) Li(LiNO3), and (c) Li(PECA+LiNO3) anode.

metal and continuously increased impedance,7,12,22 resulting in huge capacity loss. The capacity degradation of the Li(LiNO3) sample is so slight after 150 cycles (Figure S3), and its anode displays a relative rough surface (better than bare lithium, Figure 4c,d). It is well-established that LiNO3, working as an additive, can improve the interface stability to a certain extent.20,23−26 Unfortunately, the single use of LiNO3 cannot ensure a stable SEI layer in the long circulations due to the fragility of the inorganic layer and the corresponding growth of dendritic lithium.27 The capacity retention of the Li(LiNO3) sample in the LiFePO4|Li cell can reach only 43% after 500 cycles at a rate of 2C (current density: 2.08 mA cm−2) (Figure 3d), which reveals the break of the LiNO3-induced SEI layer and the corresponding growth of polarization (Figure S7). On the contrary, the Li(PECA+LiNO3) sample can reach a capacity retention of 93% even after 500 cycles at a rate of 2C (current density: 2.08 mA cm−2) (Figure 3d). The polymer coating exists steady on the surface of the lithium anode (Figure S8), and it still remains integrated for long cycles,

anodes, the PECA-based artificial SEI layer gives rise to an excellent stable lithium plating/stripping process with consistent polarization voltage. In addition, the PECA-based artificial SEI layer reacts with metal lithium and the reaction products facilitate the interface stability and homogeneous lithium deposition further. Long cycling performance of three samples in LiFePO4|Li cells was carried out, and the result is summarized in Table S1. The cell with a bare lithium anode exhibits high initial discharge capacity, but it fades to about 115 mAh g−1 after 150 cycles (Figure S3). Even worse, the capacity retention can only maintain 5% after 500 cycles at 2C (current density: 2.08 mA cm−2) (Figure 3d). SEM images reveal that the bare lithium anode after 150 cycles displays a rough surface morphology with obvious cracks (Figure 4a,b), and the elemental mapping (Figure S6) also confirms the generation of a large amount of byproducts. During the long cycling, bare lithium foils suffer from various side reactions with the electrolyte, which contributes to the accumulation of loose and porous lithium 4685

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Chemistry of Materials which has been proved by SEM and XPS spectra (Figures S9− S11). In order to detect the surface morphology information on lithium metal under the PECA-based SEI film, the Li(PECA+ LiNO3) anode was immersed in anhydrous 1,2-dimethoxyethane (DME) to remove the polymer coating. SEM images suggest that metal lithium exhibits a smooth and compact surface without cracks and dendrite structure even after 150 cycles at 1C (Figure 4e,f). Elemental mapping of N demonstrates the uniform distribution of the in situ generated interface layer composed of the reaction products between lithium and the PECA-based coating (Figure S11). The AC impedance spectra (Figure S12) also give the consistent results, confirming the excellent interfacial stability provided by this artificial SEI layer. A schematic of how the Li+ cations are accommodated on the surface of three different samples is depicted in Figure 5. During the charge and discharge process, the formation and partial dissolution of the SEI layer results in inhomogeneous lithium deposition and heterogeneous distribution of space charge for bare lithium.28−30 Active sites with protuberances possess a large number of electrons, and Li+ ions near these active sites deposit rapidly, resulting in the formation of dendritic lithium and an unstable SEI layer.7 These defects give rise to a series of security issues and shortened cycling life. The addition of LiNO3 plays a certain role in stabilizing the interface by building an inorganic SEI layer which is fragile and deteriorates seriously, accompanied by the growth of dendritic lithium in the long cycling.27,31 The existence of PECA-based SEI film prohibits the contact of fresh metal lithium and the electrolyte, decreasing the consumption of lithium metal. Meanwhile, it can be inferred from the even and compact morphology that the PECA-based artificial SEI layer stands in the diffusion pathway of Li+ and prohibits the local rapid deposition of dissociative Li+, contributing to a homogeneous and integrated surface of lithium foils. In addition, PECA and LiNO3 are easily reduced by Li metal at the interface, forming a more stable in situ interface layer. The polymer coating with superior flexibility can inhibit the smashing of this in situ interface layer in turn. Therefore, the synergy effect of the PECA layer and LiNO3 gives lithium metal an improved electrochemical property. Interface Investigation. To better elucidate the interface stability enhanced by this PECA-based artificial SEI layer, X-ray photoelectron spectroscopy (XPS) was employed to detect the surface chemical components of a bare lithium anode, Li(LiNO3), and the Li(PECA+LiNO3) anode after 10 and 150 cycles. The C 1s spectra of the bare Li anode (Figure S13) reveal that only C-H (284.6 eV, C 1s), C-C (285.2 eV, C 1s), and C-C-O (286.7 eV, C 1s) are detected on the surface for 10 cycles. However, more products such as Li2CO3 (289.8 eV, C 1s) and ROCO2Li (290.2 eV, C 1s) are formed during the subsequent cycles due to the side reactions of lithium metal and the electrolyte.12,32 Meanwhile, the byproducts such as LiF (685.1 eV, F 1s), P-F (686 eV, F 1s),33,34 pyrophosphates (133.3 eV, P 2p), and phosphates (133.9 eV, P 2p)35−37 are also generated in the subsequent 140 cycles, which are related to the reactions between LiPF6 salt and the lithium metal. Combined with the SEM images above, it can be concluded that the native SEI film of bare lithium metal is not stable for repeated cycling, causing a continuous consumption of lithium metal and a severe polarization. XPS spectra of Li(LiNO3) anodes (Figure 6) indicate that the surface of the Li metal contains primarily Li3PO4 (134.2 eV,

Figure 6. (a) C 1s, (b) N 1s, (c) P 2p, (d) F 1s, and (e) Li 1s XPS spectra of Li(LiNO3) anode after 10 and 150 cycles at 1C (current density: 1.04 mA cm−2) in LiFePO4|Li cells and (f) the corresponding histogram of element contents.

P 2p), Li3N (398.5 eV, N 1s), LiF (685.7 eV, F 1s), LiNO2 (56.1 eV, Li 1s), and residual LiPF6 (137.7 eV, P 2p)33,36,38 after 10 cycles, constituting the pristine native SEI film and preventing the lithium anode from being corroded effectively. However, this SEI layer is not stable enough to bear long circulations as mentioned above. XPS spectra confirm that there are various byproducts being generated or accumulating in the subsequent 140 cycles, such as LixPOyFz (136.8 eV, P 2p and 687.1 eV, F 1s), Li2N2O2 (399.5 eV, N 1s), imido group (397.3 eV, N 1s), R-CH2OCO2Li (289.1 eV, C 1s), and Li2CO3 (290.01 eV, C 1s and 55.5 eV, Li 1s).39,40 The histogram (Figure 6f) also indicates the increase of various elements content including P, N, F, Li, and O after 150 cycles, which confirms the continuous reactions of lithium anode with the electrolyte and the Li salt. It is noted that the Li 1s peak attributed to LiNO2 (reduction product of LiNO3) disappears in the 150th cycle and the amount of Li3N (reduction product of LiNO3 and LiNO2) accumulates from the 10th to 150th cycles. The result suggests that the LiNO3 additive has been exhausted in the 150th cycle. Hence, there will be no more Li3N precursor for the reparation of the continuously damaged SEI layer, resulting in successive consumption and heterogeneous deposition of metal lithium. The stability of this polymer film on the surface of the Li(PECA+LiNO3) anode has been proved by SEM and XPS test. To further demonstrate the stability and integrity of the in 4686

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areas. The average value is calculated and shown in Figure 8. Figure 8a reveals that the Li(PECA+LiNO3) anode enables

situ generated interface layer induced by PECA and LiNO3, the polymer coating was peeled by anhydrous DME in advance. In the XPS spectra of the Li(PECA+LiNO3) anode (Figure 7 and

Figure 8. Element content of (a) N and (b) F on the surface of different samples (Li(PECA+LiNO3), Li(LiNO3), and bare Li) probed via SIMS test.

stable existence of N and F even after 150 cycles, leading to excellent performance of metal lithium. On the other hand, samples of Li(LiNO3) and bare Li suffer from an unstable SEI layer, which can be inferred from the decreasing amount of element N and F during cycling. Therefore, the artificial SEI layer offers lithium metal effective protection and endows the lithium metal anode with superior cycling stability with high capacity retention. Our experimental results demonstrate an effective strategy to suppress the growth of lithium dendrites and decrease the side reactions between lithium metal and the electrolyte. The synergetic effect of PECA film and LiNO3 facilitates a stable SEI layer and high capacity retention. The PECA-based artificial SEI layer has the following outstanding properties on lithium metal anodes: (1) Suppressing corrosion to Li anode: The PECA-based SEI film provides an isolation effect and hinders the side reactions of lithium anode, resulting in less consumption of metal lithium and lower polarizing voltage. (2) Stabilizing the interface layer: The LiNO3 and PECA molecules react with lithium metal at the interface, forming an in situ generated protective layer. The flexible PECA polymer film can accommodate the volume change, guaranteeing the integrity of this interface layer during the charge/discharge process. (3) Homogeneous distribution of Li ions: The synergistic effect of the PECA-based artificial SEI film and the in situ generated nitrogenous interface layer facilitates homogeneous distribution of Li ions, which inhibits the growth of dendrite lithium by a large margin. (4) Excellent mechanical properties: The high Young’s modulus of the PECA-based film (about 25 GPa) can suppress the growth of dendritic lithium and decreases the risk of short circuit. In addition, the strong adhesion between lithium metal and the PECA coating can significantly improve the interface stability.

Figure 7. (a) C 1s, (b) N 1s, and (c) Li 1s XPS spectra of Li(PECA+ LiNO3) anode harvested from LiFePO4|Li cell after 150 cycles at 1C (current density: 1.04 mA cm−2).

Figure S14), the products such as C-H (284.6 eV, C 1s), C-C (285.2 eV, C 1s), C-O (285.8 eV, C 1s), O-CO (286.5 and 288.5 eV, C 1s), OC-O-C (289.6 eV, C 1s), Li-N− (400 eV, N 1s), and Li-C− (54.5 eV, Li 1s) are all assigned to the reactions between Li metal and the PECA film around the interface.24,32,33,36,41,42 LiNO2 (56.2 eV, Li 1s), Li3N (55.1 eV, Li 1s and 398.5 eV N 1s), and Li2N2O2 (399.5 eV, N 1s) are considered as the reduction products from LiNO3 additive.24,33 These reaction products compose the in situ interface layer. It is worth mentioning that the chemical constituents of the in situ interface layer with different cycles (10th and 150th cycles) are identical, which confirms its excellent stability. Hence, the compact and in situ generated interface layer renders lithium metal anodes better performance due to the effective protection. To further confirm the interface stability of the artificial SEI layer, secondary ion mass spectroscopy (SIMS) was used to investigate the element content of different samples quantificationally. Each sample was detected for 20 times with different

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CONCLUSIONS In conclusion, we have demonstrated an artificial SEI layer which guarantees the interface stability and homogeneous deposition of lithium metal, resulting in high capacity retention, dendrite free morphology, and long cycle life. The reaction products of the CN− functional group and NO3− with Li metal compose an in situ interface inorganic layer, offering the interface stability. The toughness of this polymer coating can 4687

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(7) Xu, W.; Wang, J.; Ding, F.; Chen, X.; Nasybulin, E.; Zhang, Y.; Zhang, J.-G. Lithium metal anodes for rechargeable batteries. Energy Environ. Sci. 2014, 7, 513−537. (8) Dupre, N.; Moreau, P.; De Vito, E.; Quazuguel, L.; Boniface, M.; Bordes, A.; Rudisch, C.; Bayle-Guillemaud, P.; Guyomard, D. Multiprobe Study of the Solid Electrolyte Interphase on SiliconBased Electrodes in Full-Cell Configuration. Chem. Mater. 2016, 28, 2557−2572. (9) Yan, K.; Lee, H. W.; Gao, T.; Zheng, G.; Yao, H.; Wang, H.; Lu, Z.; Zhou, Y.; Liang, Z.; Liu, Z.; Chu, S.; Cui, Y. Ultrathin twodimensional atomic crystals as stable interfacial layer for improvement of lithium metal anode. Nano Lett. 2014, 14, 6016−22. (10) Qian, J.; Henderson, W. A.; Xu, W.; Bhattacharya, P.; Engelhard, M.; Borodin, O.; Zhang, J. G. High rate and stable cycling of lithium metal anode. Nat. Commun. 2015, 6, 6362. (11) Hu, P.; Duan, Y.; Hu, D.; Qin, B.; Zhang, J.; Wang, Q.; Liu, Z.; Cui, G.; Chen, L. Rigid-flexible coupling high ionic conductivity polymer electrolyte for an enhanced performance of LiMn2O4/ graphite battery at elevated temperature. ACS Appl. Mater. Interfaces 2015, 7, 4720−7. (12) 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, 1853−1858. (13) Thompson, R. S.; Schroeder, D. J.; López, C. M.; Neuhold, S.; Vaughey, J. T. Stabilization of lithium metal anodes using silane-based coatings. Electrochem. Commun. 2011, 13, 1369−1372. (14) Marchioni, F.; Star, K.; Menke, E.; Buffeteau, T.; Servant, L.; Dunn, B.; Wudl, F. Protection of lithium metal surfaces using chlorosilanes. Langmuir 2007, 23, 11597−11602. (15) Umeda, G. A.; Menke, E.; Richard, M.; Stamm, K. L.; Wudl, F.; Dunn, B. Protection of lithium metal surfaces using tetraethoxysilane. J. Mater. Chem. 2011, 21, 1593−1599. (16) Thompson, R. S.; Schroeder, D. J.; López, C. M.; Neuhold, S.; Vaughey, J. T. Stabilization of lithium metal anodes using silane-based coatings. Electrochem. Commun. 2011, 13, 1369−1372. (17) Neuhold, S.; Schroeder, D. J.; Vaughey, J. T. Effect of surface preparation and R-group size on the stabilization of lithium metal anodes with silanes. J. Power Sources 2012, 206, 295−300. (18) Hu, P.; Duan, Y.; Hu, D.; Qin, B.; Zhang, J.; Wang, Q.; Liu, Z.; Cui, G.; Chen, L. Rigid−Flexible Coupling High Ionic Conductivity Polymer Electrolyte for an Enhanced Performance of LiMn2O4/ Graphite Battery at Elevated Temperature. ACS Appl. Mater. Interfaces 2015, 7, 4720−4727. (19) Stone, G.; Mullin, S.; Teran, A.; Hallinan, D.; Minor, A.; Hexemer, A.; Balsara, N. Resolution of the modulus versus adhesion dilemma in solid polymer electrolytes for rechargeable lithium metal batteries. J. Electrochem. Soc. 2012, 159, A222−A227. (20) Zhang, S. S. Role of LiNO3 in rechargeable lithium/sulfur battery. Electrochim. Acta 2012, 70, 344−348. (21) Wu, M.; Wen, Z.; Liu, Y.; Wang, X.; Huang, L. Electrochemical behaviors of a Li3N modified Li metal electrode in secondary lithium batteries. J. Power Sources 2011, 196, 8091−8097. (22) Pan, H.; Wei, X.; Henderson, W. A.; Shao, Y.; Chen, J.; Bhattacharya, P.; Xiao, J.; Liu, J. On the Way Toward Understanding Solution Chemistry of Lithium Polysulfides for High Energy Li−S Redox Flow Batteries. Adv. Energy Mater. 2015, 5, 1500113. (23) Aurbach, D.; Pollak, E.; Elazari, R.; Salitra, G.; Kelley, C. S.; Affinito, J. On the Surface Chemical Aspects of Very High Energy Density, Rechargeable Li−Sulfur Batteries. J. Electrochem. Soc. 2009, 156, A694−A702. (24) Xiong, S.; Xie, K.; Diao, Y.; Hong, X. Properties of surface film on lithium anode with LiNO3 as lithium salt in electrolyte solution for lithium−sulfur batteries. Electrochim. Acta 2012, 83, 78−86. (25) Zhang, S. S. Effect of Discharge Cutoff Voltage on Reversibility of Lithium/Sulfur Batteries with LiNO3-Contained Electrolyte. J. Electrochem. Soc. 2012, 159, A920−A923. (26) Liang, X.; Wen, Z.; Liu, Y.; Wu, M.; Jin, J.; Zhang, H.; Wu, X. Improved cycling performances of lithium sulfur batteries with LiNO3modified electrolyte. J. Power Sources 2011, 196, 9839−9843.

release the volume change of the Li anode and guarantee the integrity of the in situ interface layer. In addition, the high Young’s modulus of this polymer film can also suppress the dendritic lithium effectively. Experiment result reveals the stable existence of this artificial SEI layer during long cycling, and the strategy we described above is a powerful route to address the intrinsic problems of Li metal anodes.

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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.chemmater.7b00091. Interfacial study of different lithium anodes without cycling. Electrochemical cycling of LiFePO4|Li cells with different lithium anodes. Investigation of interfacial components (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (S.D.). *E-mail: [email protected] (G.C.). ORCID

Hong Li: 0000-0002-8659-086X Guanglei Cui: 0000-0002-8008-7673 Author Contributions

Z. Hu and S. Zhang contributed equally to this work. All authors have given approval to the final version of the manuscript. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank Qingdao Key Lab of Solar Energy Utilization and Energy Storage Technology, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao 266101, P. R. China, for fruitful help. This original research was supported by funding from the project supported by the National Natural Science Foundation for Distinguished Young Scholars of China (Grant No. 51625204), “135” Projects Fund of CAS-QIBEBT Director Innovation Foundation, the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDA09010105), and the Youth Innovation Promotion Association of CAS (2016193).

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