The Effect of Surface-Abundant Hydrogen Bonding on the Electrolyte Reduction for the Stable SEI in Lithium Metal Batteries

Media type: E-Article
Title: The Effect of Surface-Abundant Hydrogen Bonding on the Electrolyte Reduction for the Stable SEI in Lithium Metal Batteries
Contributor: Kim, Subin; Eom, Kwang Sup
imprint: The Electrochemical Society, 2022
Published in: ECS Meeting Abstracts
Language: Not determined
DOI: 10.1149/ma2022-02642318mtgabs
ISSN: 2151-2043
Keywords: General Medicine
Origination:
Footnote:
Description: <jats:p> Lithium (Li) metal anodes (LMAs) have been attracted world-wide attention as an ideal anode because of its extra-high theoretical capacity (3860 mAh g<jats:sup>-1</jats:sup>) and low electrode potential (-3.04 V vs S.H.E.). However, the dendritic growth of Li and low Coulombic efficiency (CE) are still hindering their practical uses [1]. To date, numerous methods such as construction of artificial solid electrolyte layer (ASEI) [2], adoption of 3D current collector [3], and tuning of the electrolyte composition [4] have been proposed to prevent Li dendrite growth and increase the CE. Among them, introducing functional additives is one of the most efficient approaches for practical application considering its cost-effectiveness. Until now, various functional additives were introduced to form stable and robust SEI layer in LMBs [4]. Among them, lithium nitrate (LiNO<jats:sub>3</jats:sub>) is considered as the most efficient electrolyte additive, ensuring high coulombic efficiency (CE) as well as long lifespan of LMBs. When LiNO<jats:sub>3</jats:sub> is dissolved in the electrolyte, NO<jats:sub>3</jats:sub> <jats:sup>-</jats:sup> anions are mainly reduced to form inorganic species such as Li<jats:sub>3</jats:sub>N, which has a high ionic conductivity and mechanical strength. As such species contribute to the construction of the robust and ionic-conductive SEI layer, and hence the reduction of NO<jats:sub>3</jats:sub> <jats:sup>-</jats:sup> is important for stable Li cycling. In this regard, many researchers have focused on increasing reduction of NO<jats:sub>3</jats:sub> <jats:sup>-</jats:sup> by using high-concentration LiNO<jats:sub>3</jats:sub> [4], or adding solubilizer to increase more NO<jats:sub>3</jats:sub> <jats:sup>-</jats:sup> in the electrolyte [5]. However, those remedies are still insufficient because most of them increase the viscosity of electrolyte leading to low kinetics, hence a novel and more efficient way to increase NO<jats:sub>3</jats:sub> <jats:sup>-</jats:sup> reduction is needed for practical application.</jats:p> <jats:p>On the other hand, recent researches have reported that the preferential reduction of specific anions is possible by regulation of inner Helmholtz plane (IHP) structure [6]. For instance, Huang et al. reported that intermolecular force between PF<jats:sub>6</jats:sub> <jats:sup>- </jats:sup>anions and surface adsorbent tris(trimethylsilyl) borate could derive in PF<jats:sub>6</jats:sub> <jats:sup>-</jats:sup>-abundant IHP, successfully resulted in LiF-rich SEI layer to increase the stability of LMA [6]. Inspired by those works, we expected that NO<jats:sub>3</jats:sub> <jats:sup>-</jats:sup>-derived SEI layer would be achieved by using surface adsorbent showing strong intermolecular interaction with NO<jats:sub>3</jats:sub> <jats:sup>-</jats:sup>.</jats:p> <jats:p>In this context, we introduce the adoption of thiourea (TU) as a catalytic additive for the LiNO<jats:sub>3</jats:sub> reduction during the SEI formation. Due to its unique molecular structure, addition of TU could induce NO<jats:sub>3</jats:sub> <jats:sup>-</jats:sup> <jats:sub> </jats:sub>derived SEI layer. Firstly, TU could adsorb onto metallic surface by its S atom. Meanwhile, thiourea could form hydrogen bonding with NO<jats:sub>3</jats:sub> <jats:sup>-</jats:sup> anion by its N-H bonds [7]. Hence in the presence of TU, we suggest that NO<jats:sub>3</jats:sub> <jats:sup>-</jats:sup>-abundant electrode surface would be achieved by interaction between TU-NO<jats:sub>3</jats:sub> <jats:sup>-</jats:sup>, resulting in Li<jats:sub>3</jats:sub>N-rich SEI layer.</jats:p> <jats:p>The adsorption behavior of TU on the Cu electrode was investigated by potential of zero charge (PZC) measurement (<jats:bold>Figure 1(a))</jats:bold>. As the TU concentration increases, PZC decreases, indicating more surface coverage by TU. <jats:bold>Figure 1(b) </jats:bold>shows <jats:sup>1</jats:sup>H NMR spectra of electrolytes with different components. Upshift displacement of N-H bond of TU were detected after addition of DME and LiTFSI, indicating that intramolecular H-bond of TU were weakened. By contrast, downshift displacement appeared when LiNO<jats:sub>3</jats:sub> was added, which means NO<jats:sub>3</jats:sub> <jats:sup>-</jats:sup> would form strong hydrogen bonding with TU. Furthermore, linear scanning voltammetry (LSV) curves at different concentration of TU were measured to investigate the effect of TU on electrolyte reduction (<jats:bold>Figure 1(c)</jats:bold>). The distinct peaks at 1.6 V and 1.3 V in the cell with 5 wt% LiNO<jats:sub>3</jats:sub> indicate reduction of LiNO<jats:sub>3</jats:sub> and LiTFSI, respectively. Interestingly, in the presence of TU, negative potential shift and increased current of those redox peaks were shown, indicating that the TU significantly increases the LiNO<jats:sub>3</jats:sub> reduction.</jats:p> <jats:p>Importantly, from the XPS analysis, it was found that more abundant Li<jats:sub>3</jats:sub>N components are in the ASEI layer with TU than that without TU, implying that TU accelerates the reduction of LiNO<jats:sub>3 </jats:sub>(<jats:bold>Figure 2(a-b)).</jats:bold> As a result, Li|Cu@ASEI with TU shows better cyclability and higher average CE of 96.44% during 80 cycles compared to Li|Cu@NSEI and Li|Cu@ASEI w/o TU (<jats:bold>Figure 3</jats:bold>). In addition, morphological and chemical investigation on the favorable ASEI layers assisted by TU, and its electrochemical performance in LMBs will be discussed in this presentation.</jats:p> <jats:p>[1] Cheng et al, <jats:italic>Chem. Rev</jats:italic>, <jats:bold>117</jats:bold>, 10403, 2017.</jats:p> <jats:p>[2] Lopez Jeffrey, et al. <jats:italic>JACS</jats:italic> 140.37 (2018): 11735-11744.</jats:p> <jats:p>[3] Yang Chun-Peng et al. Nature communications 6.1 (2015): 1-9.</jats:p> <jats:p>[4] Kang et al. <jats:italic>Journal of Power Sources</jats:italic> 490 (2021): 229504.</jats:p> <jats:p>[5] Zhang et al. <jats:italic>Advanced Materials</jats:italic> 32.24 (2020): 2001740.</jats:p> <jats:p>[6] Huang et al. <jats:italic>Angewandte Chemie. </jats:italic>60.35 (2021): 19232-19240.</jats:p> <jats:p>[7] Nishizawa et al. <jats:italic>Tetrahedron letters</jats:italic> 36.36 (1995): 6483-6486.</jats:p> <jats:p> <jats:inline-formula> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="2318fig1.jpg" xlink:type="simple" /> </jats:inline-formula> </jats:p> <jats:p>Figure 1</jats:p> <jats:p />
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