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Enhanced Electrochemical and Safety performance of Lithium Metal Batteries Enabled by the Atom Layer Deposition on PVDF-HFP Separator Wei Wang, Yao Yuan, Junling Wang, Yan Zhang, Can Liao, Xiaowei Mu, Haibo Sheng, Yongchun Kan, Lei Song, and Yuan Hu ACS Appl. Energy Mater., Just Accepted Manuscript • DOI: 10.1021/acsaem.9b00383 • Publication Date (Web): 30 May 2019 Downloaded from http://pubs.acs.org on May 30, 2019
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ACS Applied Energy Materials
Enhanced Electrochemical and Safety performance of Lithium Metal Batteries Enabled by the Atom Layer Deposition on PVDF-HFP Separator Wei Wang, Yao Yuan, Junling Wang, Yan Zhang, Can Liao, Xiaowei Mu, Haibo Sheng, Yongchun Kan*, Lei Song, and Yuan Hu* State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei, Anhui 230026, P. R. China * Corresponding authors E-mail:
[email protected] (Y. C. Kan);
[email protected] (Y. Hu)
Key words: ALD technique; PVDF-HFP; Safety; Lithium dendrites; Lithium metal batteries.
Abstract: Lithium metal batteries, due to its unique advantages such as light weight, the lowest anode potential and the highest theoretical specific capacity, have been regarded as the promising candidate for next-generation electrical energy storage. Nevertheless, the development and practical application of lithium metal batteries has been seriously hindered by the safety issue induced by lithium dendrites. Here the atom layer deposition (ALD) technique is introduced to fabricate the Al2O3 on the surface of PVDF-HFP membrane to endow it with higher thermal stability, great affinity with electrolytes, improved ion conductivity and higher Young’s modulus. Employing LiFePO4|Li cells, ALD100/PH separator imparts batteries with the best cycling performances and rate capacity among various separators. The SEM images of
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morphology after cycled indicate that ALD100/PH separators with extremely high Young’s modulus and ion conductivity can suppress the growth of lithium dendrites. Moreover, the ALD100/PH separator shows more than 1300 h of stable operation at current density of 0.5 mA cm-2, exhibiting the capability against metallic lithium and the potential for application in the field of lithium metal batteries. Thus, this interesting ALD technique capable of feasible fabrication procedure and desirable advantages maybe make commercial or as-prepared separators more advanced and potential candidates for the future rechargeable battery systems including Li-S, Li-O2 and other metal batteries. Introduction Nowadays, lithium metal has been recognized as the most promising one for the next generation of lithium-ion batteries1-3. Lithium metal as an ideal anode material in terms of energy density can deliver a high theoretical capacity (3860 mAh g-1) and possess a lowest redox potential of -3.04V vs H+/H and gravimetric density (0.53 g cm-3). Nevertheless, the further practical application of lithium metal-based batteries has been hindered by the fatal flaw of the dentritic and mossy lithium and low coulombic efficiency, leading to the unsatisfied electrochemical performance and safety concerns4. Usually, lithium dendrites are more likely to grow at the surface position where the current density is locally concentrated, meanwhile with the generation of SEI layer. The reduplicative broken and formation of SEI membrane may cause the constant consumption of electrolytes and salts, which make the capacity fade and Coulombic efficiency low. Furthermore, the repeated growth of lithium dendrites will eventually
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ACS Applied Energy Materials
pierce through the separator and cause the internal short circuits4-5. Up to now, extensive efforts have been devoted to improving safety and electrochemical capability of lithium ion batteries6-10, especially for lithium metal batteries11-12. In the case of suppression of lithium dendrites, the previous work reported that electrolytes with high ionic conductivity and stable anion mobility can prevent anion depletion and slow down the generation of lithium dendrites13. Moreover, adequate Young’s modulus of membranes, separators and protective layers can mechanically suppress the uncontrollable growth of dendritic lithium14-16. Therefore, fabricating advanced separators capable of high ion conductivity and Young’s modulus can be regarded as an efficient way to achieve safer lithium metal batteries. Actually, the mostly widen employed separators are polyolefin-based separators including polypropylene and polyethylene, which exhibit high flammability and low thermal stability. Once under high temperature condition, polyolefin separators will heat shrink and may result the direct contact of cathodes and anodes, which may lead to the internal short circuit and even explosion17-20. Moreover, other properties of separators such as poor wettability, low electrolyte uptake capability and ion conductivity would also effectively damage the electrochemical properties of LIBs2122. Therefore, it is of great importance to develop advanced separators with high thermal
stability and great affinity with polar electrolyte for lithium metal batteries. Several works such as modification of novel polymer separators and ceramic separators are proposed to enable state of the art lithium-ion batteries or lithium metal batteries with great electrochemical capacity and high safety23-24. Among these, inorganic materials,
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for instance, SiO225, TiO226, Al2O327, and MgO28, are also well-studied routes to enhance the thermal stability and wettability of polymer-based separators. Some advanced techniques such as atom layered deposition (ALD) are also used to fabricate novel separators with high safety. Jung prepared the Al2O3 coated PP separators with a low thickness of
