Journal
ACS NANO
Volume 12, Issue 12, Pages 12255-12268Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsnano.8b06051
Keywords
liquid phase exfoliation (LPE); lithium metal battery (LMB); carbon host; carbon template; carbon support; dendrite; additive; fluoroethyelene carbonate (FEC)
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Funding
- National Science Foundation of China [51702223]
- China Postdoctoral Science Foundation [2017M623028]
- Young Scholar Start-up Grant of SCU [2017SCU12026]
- U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering [DE-SC0018074]
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We report a directional flow-aided sonochemistry exfoliation technique that allows for unparalleled control of graphene structural order and chemical uniformity. Depending on the orientation of the shockwave relative to the flow-aligned graphite flakes, the resultant bilayer and trilayer graphene is nearly defect free (at-edge sonication graphene AES-G) or is highly defective (in-plane sonication graphene IPS-G). AES-G has a Raman G/D band intensity ratio of 14.3 and an XPS-derived O content of 1.3 at. %, while IPS-G has an I-G/D of 1.6 and 6.2 at. % O. AES-G and IPS-G are then employed to understand the role of carbon support structure and chemistry in Na metal plating/stripping for sodium metal battery anodes. The presence of graphene defects and oxygen groups is highly deleterious: In a standard carbonate solution (1 M NaClO4, 1:1 EC-DEC, 5 vol % FEC), AES-G gives stable cycling at 2 mA/cm(2) with 100% Coulombic efficiency (CE) (within instrument accuracy) and an area capacity of 1 mAh/cm(2). Meanwhile IPS-G performs on-par with the baseline Cu support in terms of poor CE, severe mossy metal dendrites, and periodic electrical shorts. We argue that solid electrolyte interface (SEI) stability is the key for stable cycling, with defects of IPS-G being catalytic toward SEI formation. For IPS-G, the SEI layer also shows F-rich hot spots due to accelerated decomposition of FEC additive in localized regions.
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