A dual-layered artificial solid electrolyte interphase formed by controlled electrochemical reduction of LiTFSI/DME-LiNO3 for dendrite-free lithium metal anode

In Situ Formation of an Artificial Lithium Oxalate-Rich Solid Electrolyte Interphase on 3D Ni Host for Highly Stable Lithium Metal Batteries

Li metal, with a high theoretical capacity, is considered the most promising anode for next-generation high-energy-density batteries. However, the commercialization of the Li metal anode is limited owing to its high reactivity, significant volume expansion, continuous solid electrolyte interphase (SEI) layer degradation caused by undesirable Li deposition, and uncontrollable dendrite growth. This study demonstrates the in situ construction of a Li2C2O4-enriched SEI layer from NiC2O4 nanowires on three-dimensional Ni foam. The lithiophilic Li2C2O4-enriched SEI layer provides a uniform distribution of the electrical field and sufficient nucleation and deposition sites for Li without dendrite formation. Consequently, the stable Li2C2O4-enriched SEI layer successfully inhibits the formation of lithium dendrites, resulting in reversible Li stripping/plating behavior, maintained over an extended period of 5000 h with a deposition capacity of 1 mAh cm-2 at 1 mA cm-2. Additionally, a high cycling stability is observed in the full cell test with ∼70% capacity retention after 1300 cycles at 3 C. This approach offers a large-scale and facile synthesis process via the in situ precipitation growth of NiC2O4 followed by lithiation to form Li2C2O4. Furthermore, the significant stability of the Li2C2O4-enriched SEI layer aids the design of in situ-constructed SEI layers for highly stable Li metal batteries.

The lasting impact of formation cycling on the Li-ion kinetics between SEI and the Li-metal anode and its correlation with efficiency

Formation cycling is a critical process aimed at improving the performance of lithium ion (Li-ion) batteries during subsequent use. Achieving highly reversible Li-metal anodes, which would boost battery energy density, is a formidable challenge. Here, formation cycling and its impact on the subsequent cycling are largely unexplored. Through solid-state nuclear magnetic resonance (ssNMR) spectroscopy experiments, we reveal the critical role of the Li-ion diffusion dynamics between the electrodeposited Li-metal (ED-Li) and the as-formed solid electrolyte interphase (SEI). The most stable cycling performance is realized after formation cycling at a relatively high current density, causing an optimum in Li-ion diffusion over the Li-metal-SEI interface. We can relate this to a specific balance in the SEI chemistry, explaining the lasting impact of formation cycling. Thereby, this work highlights the importance and opportunities of regulating initial electrochemical conditions for improving the stability and life cycle of lithium metal batteries.

Synergistically Stabilizing Thin Li Metal through the Formation of a Stable and Highly Conductive Solid Electrolyte Interface and Silver-Lithium Alloy

In this study, a stable solid electrolyte interface (SEI) and a Ag-Li alloy were formed through a simple slurry coating of silver (Ag) nanoparticles and Li nitrate (LiNO3) on a Li metal surface (AgLN-coated Li). The Ag-Li alloy has a high Li diffusion coefficient, which allowed the inward transfer of Li atoms, thus allowing Li to be deposited below the alloy. Moreover, the highly conductive SEI enabled the fast diffusion of Li ions corresponding to the alloy. This inward transfer resulted in dendrite suppression and improved the Coulombic efficiency (CE). The AgLN-coated Li exhibited an initial capacity retention >81% and CE > 99.7 ± 0.2% over 500 cycles at a discharge capacity of 2.3 mA h cm-2.

An Inorganic-Rich SEI Layer by the Catalyzed Reduction of LiNO3 Enabled by Surface-Abundant Hydrogen Bonding for Stable Lithium Metal Batteries

Lithium (Li) metal anodes (LMAs) are promising anode candidates for realizing high-energy-density batteries. However, the formation of unstable solid electrolyte interphase (SEI) layers on Li metal is harmful for stable Li cycling; hence, enhancing the physical/chemical properties of SEI layers is important for stabilizing LMAs. Herein, thiourea (TU, CH₄ N₂ S) is introduced as a new catalyzing agent for LiNO₃ reduction to form robust inorganic-rich SEI layers containing abundant Li₃ N. Due to the unique molecular structure of TU, the TU molecules adsorb on the Cu electrode by forming CuS bond and simultaneously form hydrogen bonding with other hydrogen bonds accepting species such as NO₃ ^- and TFSI^- through its NH bonds, leading to their catalyzed reduction and hence the formation of inorganic-rich SEI layer with abundant Li₃ N, LiF, and Li₂ S/Li₂ S₂ . Particularly, this TU-modified SEI layer shows a lower film resistance and better uniformity compared to the electrochemically and naturally formed SEI layers, enabling planar Li growth without any other material treatments and hence improving the cyclic stability in Li/Cu half-cells and Li@Cu/LiFePO₄  full-cells.

Synergistic Effect of a Dual-Salt Liquid Electrolyte with a LiNO3 Functional Additive toward Stabilizing Thin-Film Li Metal Electrodes for Li Secondary Batteries

Li metal thickness has been considered a key factor in determining the electrochemical performance of Li metal anodes. The use of thin Li metal anodes is a prerequisite for increasing the energy density of Li secondary batteries intended for emerging large-scale electrical applications, such as electric vehicles and energy storage systems. To utilize thin (20 μm thick) Li metal anodes in Li metal secondary batteries, we investigated the synergistic effect of a functional additive (Li nitrate, LiNO₃) and a dual-salt electrolyte (DSE) system composed of Li bis(fluorosulfonyl)imide (LiTFSI) and Li bis(oxalate)borate (LiBOB). By controlling the amount of LiNO₃ in DSE, we found that DSE containing 0.05 M LiNO₃ (DSE-0.05 M LiNO₃) significantly improved the electrochemical performance of Li metal anodes. DSE-0.05 M LiNO₃ increased the cycling performance by 146.3% [under the conditions of a 1C rate (2.0 mA cm^-2), DSE alone maintained 80% of the initial discharge capacity up to the 205th cycle, whereas DSE-0.05 M LiNO₃ maintained 80% up to the 300th cycle] and increased the rate capability by 128.2% compared with DSE alone [the rate capability of DSE-0.05 M LiNO₃ = 50.4 mAh g^-1, and DSE = 39.3 mAh g^-1 under 7C rate conditions (14.0 mA cm^-2)]. After analyzing the Li metal surface using scanning electron microscopy and X-ray photoelectron spectroscopy, we were able to infer that the stabilized solid electrolyte interphase layer formed by the combination of LiNO₃ and the dual salt resulted in a uniform Li deposition during repeated Li plating/stripping processes.

Rational design of MXene@TiO2 nanoarray enabling dual lithium polysulfide chemisorption towards high-performance lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries face a few vital issues, including poor conductivity, severe volume expansion/contraction, and especially the detrimental shuttle effect during the long-term electrochemical process. Herein, we designed a hierarchical MXene@TiO2 nanoarray via in situ solvothermal strategies followed by heat treatment. The MXene@TiO2 heterostructure achieves superior charge transfer and sulfur encapsulation. Based on the polar-polar and Lewis acid-base mechanism, the robust dual chemisorption capability to trap polysulfides can be synergistically realized through the intense polarity of TiO2 and the abundant acid metal sites of MXene. Hence, the MXene@TiO2 nanoarray as a sulfur host retains a substantially stable discharge capacity of 612.7 mA h g-1 after 500 cycles at a rate of 2 C, which represents a low fading rate of 0.058% per cycle.