Inorganic-Rich SEI Derived from Electrochemically Deposited [Cu(TU)n]Cl Nanowires for Highly Stable Lithium Metal Batteries
Authors: Lee Changhyeon , Eom Kwang Sup 
Published: December 2024

Li metal batteries (LMBs) are promising next-generation energy storage systems because of the low electrode potential (-3.04 V vs. S.H.E) and high capacity (3,860 mAh g-1) of lithium metal anodes (LMAs). However, LMAs suffer from unavoidable dendrites and huge volume expansion of lithium resulting from unstable solid electrolyte interface (SEI) which has poor ion conductivity and mechanical strength [1]. To address these issues, artificial SEI is one of the most efficient methods to enhance its stability and hence prolong the lifespan of LMAs by modifying the electrode surface with metal compounds like copper sulfides [2] and halides [3]. In particular, inorganic materials derived from the metal compounds such as Li2S, LiCl, and Li3N have been widely known as high-quality SEI components. Li2S and Li3N have high Young’s modulus of 82.6 [4] and 150 GPa [5] respectively. Also, LiCl (0.05 eV) have a lower Li-ion diffusion barrier compared with LiF (0.28 eV) [6]. However, the existing methods for coating metal compounds on substrates such as hydrothermal, CVD, and sputtering have drawbacks requiring high temperature and high vacuum systems.
In this work, we introduce a facile electrochemical deposition method for fabricating [Cu(CH4N2S)n]Cl nanowires (CTC NWs) resulting in inorganic-rich SEI layers. The Cl- and thiourea (TU) in CTC NWs were converted to LiCl and Li2S respectively. Additionally, the residual TU catalyzes the formation of Li3N-rich SEI layer promoting decomposition of LiNO3 additive.
The bare Cu and CTC NWs surfaces after 10th cycle were investigated by XPS to study the chemical composition of the inorganic SEI layers (Fig. 1). For the S 2p spectra (Fig. 1a, d), the peaks at 160.5 and 162.5 eV were assigned to Li2S and Li2S2, which have higher intensity in CTC NWs. Additionally, the presence of new peak at 161.9 eV indicates Li2Sx (Fig. 1a). these lithium sulfides in the CTC NWs were induced by decomposition of TU. The signals in S 2p spectra of sulfone, SO3- and SO2- were originated from the decomposition of lithium salts (LiTFSI) in the electrolyte, which were confirmed in the all samples (Fig. 1a, d). The Cl 2p XPS spectrum shows only a peak of LiCl (198.7 and 200.3 eV) in the CTC NWs (Fig. 1b). As shown in N 1s spectra (Fig. 1c, f), the peak at 397.5 eV is Li3N, indicating the decomposition of LiNO3 which could result in the formation of Li3N. Meanwhile, the observed signal of LixN and pyrrolic N (C-N-H) was only detected at 398.5 and 399.6 eV in the CTC NWs, resulting from the residual TU (Fig. 1c).
The Nyquist plots were employed to compare the interfacial resistance change of the Li||Cu and Li||CTC NWs half-cell after a certain number of cycles (Fig. 2). After 60th cycle, the interfacial resistance of CTC NWs cell decreased much lower than the bare Cu cell, which demonstrate that inorganic-rich SEI layers derived from CTC NWs is more favorable to rapid charge transfer.
To further investigate the effect of the CTC NWs, we evaluated the electrochemical performance of Li plating/stripping behavior. The Li||CTC NWs exhibits enhanced cyclability, demonstrating a higher average coulombic efficiency (CE) of 96.2% over 100 cycles compared to Li||Cu. (Fig. 3). Furthermore, a comprehensive analysis of the morphological and chemical attributes of the inorganic-rich SEI layers induced by CTC NWs will be discussed in this presentation.
References
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Figure 1