Journal Pre-proofs Constructing a liquid-metal based self-healing artificial solid electrolyte interface layer for Li metal anode protection in lithium metal battery Guangzhou Zhang, Heming Deng, Runming Tao, Buqiong Xiao, Tainyu Hou, Song Yue, Nima Shida, Qi Cheng, Weixin Zhang, Jiyuan Liang PII: DOI: Reference:
S0167-577X(19)31826-9 https://doi.org/10.1016/j.matlet.2019.127194 MLBLUE 127194
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20 November 2019 17 December 2019 17 December 2019
Please cite this article as: G. Zhang, H. Deng, R. Tao, B. Xiao, T. Hou, S. Yue, N. Shida, Q. Cheng, W. Zhang, J. Liang, Constructing a liquid-metal based self-healing artificial solid electrolyte interface layer for Li metal anode protection in lithium metal battery, Materials Letters (2019), doi: https://doi.org/10.1016/j.matlet.2019.127194
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Constructing a liquid-metal based self-healing artificial solid electrolyte interface layer for Li metal anode protection in lithium metal battery Guangzhou Zhanga1, Heming Denga1, Runming Taod, Buqiong Xiaob, Tainyu Houb, Song Yueb, Nima Shidab, Qi Chengc, Weixin Zhangc*, Jiyuan Liangd* a. State Grid Electric Power Research Institute, Wuhan 430074, China b. Electric Power Research Institute of Xizang electric power co. LTD, Lhasa 85000, China c. School of Electrical and Electronic Engineering, Huazhong University of Science and Technology, Wuhan 430074, China d. Department of Chemistry, University of Tennessee, Knoxville 37996, USA Corresponding authors: [email protected]
(J. Liang) [email protected]
(W. Zhang) 1These
two authors contributed equally to this work.
Abstract: Uncontrollable Li dendrite growth and unstable SEI during repetitive Li deposition–dissolution processes severely impede the practical application of lithium metal batteries (LMBs). Herein, we create a novel artificial SEI layer by using liquid metal with self-healing property. The liquid metal could effectively facilitate the stable SEI layer formation by virtue of its self-healing property and regulate Li ion flus and inhibit the Li dendrite growth in the deposition process of Li. Electrochemical studies show that the LMNP-Li|LTO full-cell exhibits a superb rate capability and an excellent long-term cycling stability. This work offers a novel approach to achieve a stable Li metal anode with long cycle life. 1
Keywords: Lithium dendrite; Artificial SEI layer; Liquid metal; Energy storage and conversion; Composite materials 1. Introduction As a type of advanced energy storage device, lithium ion batteries (LIBs) play an important role in our daily life, however, the capacity of commercial LIBs is still far from the satisfaction . Compared with conventional graphite anode, metallic lithium has the greatest theoretical specific capacity (3860 mAh/g) and the lowest electrochemical potential (-3.04 V vs standard hydrogen electrode) . Thus, by using lithium metal as anode material for LMBs could have high energy density and potential as a promising candidate for the next generation battery. Unfortunately, the safety and stability issues of lithium metal anode, such as the crazy arbitrary growth of lithium dendrite and low cycle life, seriously hinder its practical application [3,4]. Generally, the solid electrolyte interface (SEI) layers play an important role in preventing the side reactions between electrolyte and Li, and hence suppress lithium dendrite. Recently, some researches show that constructing an artificial SEI layer as a physical barrier could be an effective approach to suppress the direct contact between Li and electrolyte. To date, various metal compounds have been coated on the surface of Li metal, such as Al2O3 , Cu3N  and CuF2 . However, the mechanical strength of these artificial SEI layers is unable to undergo the seriously continuous volume fluctuation of metallic lithium during long cycle processes, which thus results in damage and detachment of the artificial SEI layer, and eventually causes poor electrochemical performance. Therefore, developing an effective and stable artificial SEI layer is highly imperative. Self-healing materials, such as self-healing binders or self-healing metals, can suffer from mechanical fracture induced by the large volume change . Recently, Wu et al.  prepared carbon
skeleton stabilized GaSn liquid metal (LM) as self-healing anode, leading to an ultra-long cycle life. Benefiting from the fluidity and surface tension of LM, the expansion/contraction-induced cracking of the Li-active materials can be alleviated during cycling. If the LM can be coated on the Li metal, a stable artificial SEI layer and the dendrite-free Li metal can be therefore achieved. In this work, we successfully construct a novel self-healing artificial SEI layer to protect Li anode using a room-temperature GaSn LM alloy. In this artificial SEI layer, LM not only can regulate the Li+ flux uniform deposition but also can avoid the volume fluctuation induced cracking of SEI layer upon long-term cycling, hence achieves excellent full-cell cycling performance. This work demonstrates that employing LM alloy self-healing artificial SEI is a promising strategy for developing high energy density batteries, and it opens a new avenue toward achieving a long cycle life for LMBs. 2. Experimental The fabrication process of GaSn LM artificial SEI layer is schematically shown in Fig. 1a. Briefly, GaSn LMs were firstly prepared into nanoparticles (LMNPs) through ultrasound emulsification assisted by 1-Dodecanethiol. The LMNPs were then supported in carbon nanotubes (CNTs) skeleton to avoid their sedimentation in the SEI coating slurry. For the SEI coating preparation, LMNPs-CNTs and styrene butadiene rubber (SBR) were sufficient blended in the THF solution and then coated onto the surface of Li metal through doctor-blade method in an argon-filled glove box. After the THF solvent evaporation, the LM based artificial SEI with dark color coated Li metal was obtained (LMNP-Li), as shown in Fig.S1. The LMNP-Li anode was assembled with Li4Ti5O12 (LTO) cathode into full battery to evaluate its electrochemical performance. More details are in the Supplementary file. 3. Results and Discussion Fig. 1b shows the digital photo of the as-prepared GaSn LM. It demonstrates bright silver color and in 3
the liquid state at room temperature. After dropping on the flat substrate, GaSn LM tends to form into ball like due to its high surface tension. Obviously, this character makes LM difficult to coat onto the Li foil surface (Fig. S2). Hence, proper treatment method should be adopted to solve this problem. After modified with 1-Dodecanethiol, LM was prepared into about 200 nm LMNPs, as shown in Fig. 1c. Fig. 1d shows the SEM image of LMNPs supported on the CNTs. It can be observed that CNTs can interconnect into a robust 3D conductive structure, which favors the distribution of Li+ flux during charge and discharge processes. Fig. 1e-f presents the cross sectional SEM images of LMNP-Li. It can be seen that a dense and uniform composite coating is tightly adhered on the Li foil surface and the thickness of Li metal and artificial SEI layer is 600 μm and 50 μm, respectively. It should be noted that the thickness of the artificial SEI layer can be easily changed by adjusting the gap size of the doctor blade. Fig. 1g’s zoom-in SEM image of artificial SEI layer presents the GaSn LMNPs with spherical structure are uniformly dispersed in the artificial SEI layer matrix (indicated by the white arrows).
To evaluate the effectivity of self-healing artificial SEI layer in practical application, full-cell was assembled by using LMNP-Li as the anode and a LTO electrode as the cathode (denoted as LMNP-Li|LTO). For comparison, a pure Li foil and a LTO electrode constructed full-cell is also assembled (denoted as Li|LTO). Fig. 2a shows the compared galvanostatic charge-discharge curves of both cells at 1C. A plateau around 1.5 V can be observed in both cells, which attributes to the Ti4+/Ti3+ transformation during Li+ insertion and extraction . If examined closely, the polarization between the charge-discharge plateaus of Li|LTO is higher than that of LMNP-Li|LTO. These results are in accordance with the CV results (Fig. S3) and indicate that a smaller interfacial resistance in the LMNP-Li|LTO. Fig. 2b shows the both full cells’ rate performance at different current densities. Although there is no obvious capacity difference between both cells at low rate, their capacity gap 4
keeps growing along with the current density increasements. It can be conjectured that the kinetic of the full cell is significantly improved by using the artificial SEI layer modified Li foil. This is mainly due to the fact that a stable and uniform deposition behavior in artificial SEI layer can increase the reversibility of Li metal and promote faster ion transport kinetics. Moreover, Fig. 2c and 2d exhibit the cycling performance of the two cells at 1 C. The discharge capacity of Li|LTO is 125 mAh/g for the first cycle, and it reduces to 85 mAh/g after 350 cycles with capacity retention of 68%. In contrast, LMNP-Li|LTO cell shows a higher initial capacity of 140 mAh/g and better capacity retention with a capacity of 128 mAh/g after 350 cycles. These results further illustrate that the self-healing artificial SEI layer can effectively suppress the Li dendrites, and meanwhile, the lifespan of LMNP-Li|LTO cell is also optimized.
The surface morphology evolution of Li anode in the full-cell before and after cycling was further studied by SEM. For Li|LTO cell, without any protection, a large amount of bulk Li is consumed during the long-term cycling due to the repeated breakage/repair of the SEI layer, and thus the surface of the cycled Li metal presents a loose and porous structure (Fig. 3b), which is sharply contrast to the smooth surface of the original Li foil (Fig. 3a). However, for the LMNP-Li|LTO cell, with protection from the self-healing artificial SEI layer, the LMNP-Li electrode exhibits a smooth and compact interface without any obvious dendrite and crack after 350 cycles (Fig. 3c and 3d). Interestingly, it can be observed that the sphere-like LMNP still anchors on the artificial SEI layer after prolonged cycling (Fig. 3d inset), further revealing its structural stability. Meanwhile, elemental mapping of LMNP-Li (Fig. S4) shows that all of the elements, including carbon, gallium and tin are uniformly distributed on the surface of the LMNP-Li metal anode before and after cycling. There is no different between before and after cycling. Thus, the LMNP-Li metal anode has a stable and uniform interface. In addition, 5
electrochemical impedance spectra (EIS) were conducted to investigate the interface stability of batteries. As shown in Fig. S5, the interface resistance of Li|LTO cell with 10 days’ storage is twice that of storing for 5 days. By strong contrast, the interface resistance of LMNP-Li|LTO is not increased much after 10 days’ storage, indicates that the self-healing artificial SEI layer can effectively suppress the side reaction between Li metal and the organic electrolyte. The above results directly demonstrate the stability of the self-healing artificial SEI layer. 4. Conclusions In summary, a self-healing artificial SEI layer was prepared and coated onto the Li foil surface by using LM. When coupled with LTO cathode, the LMNP-Li|LTO full-cell exhibits smaller polarization, higher rate performance and better cycling performance. The superb electrochemical performances are attributed to the self-healing property of LM, which can assist the formation of stable artificial SEI layer to avoid cracking, regulate uniform Li+ flus deposition and restrain the dendrite formation. This work provides a promising way to tackle the problem of Li metal anode, and pushes LMBs one step closer towards the practical for the next-generation rechargeable battery. Acknowledgements This work is supported by the Natural Science Foundation of China (51802122, 51703081), Frontier Application Research Foundation of Wuhan (2018010401011285), 4th Yellow Crane Talent Programme (08010004), Achievements Transformation Project of Academicians in Wuhan (2018010403011341). Reference  M. Winter, B. Barnett, K. Xu. Chem. Rev. 118(23) (2018) 11433-11456.  D. Lin, Y. Liu, Y. Cui. Nat. Nanotechnol. 12 (2017) 194-206  L. Xu, S. Tang, Y. Cheng, et al. Joule 2(10) (2019) 1991-2015  X.B. Cheng, R. Zhang, C.Z. Zhao, et al. 117 (2017) 10403-10473. 6
 L. Wang, L. Zhang, Q. Wang, et al. 10 (2018) 16-23.  Y. Liu, D. Lin, P. Y. Yuen, et al. Adv. Mater. 29(10) (2017) 1605531.  C. Yan, X.B. Cheng, Y.X. Yao, et al. Adv. Mater. 30 (2018) 1804461-1804469.  Y. Liu, L. P. Yue, P. Lou, et al. Mater. Lett. 258(2020) 126803.  Y. Wu, L. Huang, X. Huang, et al. Energy Environ. Sci. 10 (2017) 1854-1861.  Q. Cheng, S. Tang, C. Liu, et al. J. Alloys Compd. 722 (2017) 229-234.
Fig. 1 (a) Schematic illustration of the fabrication of LMNP-Li anode. (b) Digital photo of GaSn LM alloy at room temperature. (c) SEM image of LMNP. (d) SEM image of CNTs skeleton supported the LMNP. (e-f) Cross sectional SEM images of LMNP-Li metal anode at different magnification.
Fig. 2 Electrochemical performance of Li|LTO and LMNP-Li|LTO full-cells. (a) Galvanostatic charge/discharge voltage profiles. Inset is the local enlarged curves. (b) Cycling Rate performance. Cycling performance of (c) Li|LTO cell and (d) LMNP-Li|LTO cell at 1 C.
Fig. 3 SEM images of Li metal anodes (a) before and (b) after cycling of Li|LTO cells. SEM images of LMNP-Li anodes (c) before and (d) after cycling of Li-LMNP|LTO cells. Inset shows locally enlarged SEM image. 8
Table of Contents
Conflict of Interest
The authors declare no competing financial interest. Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
A novel self-healing artificial SEI layer using liquid metal is uniformly coated on the surface of Li foil. The self-healing artificial SEI layer can efficiently suppress the Li dendrite. The LMNP-Li|LTO full cell exhibits excellent rate and cycling performance.
Jiyuan Liang and Weixin Zhang: Conceptualization, Methodology, Resources,Supervision. Guangzhou Zhang and Heming Deng: Writing-Original draft preparation, Investigation. Buqiong Hou, Song Yue, Qi Cheng and Nima Shjda: Investigation. Heming Deng and Runming Tao: Writing- Reviewing and Editing.