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1. Stable metal anodes enabled by a labile organic molecule bonded to a reduced graphene oxide aerogel

   https://doi.org/10.1073/pnas.2001837117  

   Gao, Yue; Wang, Daiwei; Shin, Yun Kyung; Yan, Zhifei; Han, Zhuo; Wang, Ke; Hossain, Md Jamil; Shen, Shuling; AlZahrani, Atif; van Duin, Adri C.; et al (December 2020, Proceedings of the National Academy of Sciences)

   null (Ed.)

   Metallic anodes (lithium, sodium, and zinc) are attractive for rechargeable battery technologies but are plagued by an unfavorable metal–electrolyte interface that leads to nonuniform metal deposition and an unstable solid–electrolyte interphase (SEI). Here we report the use of electrochemically labile molecules to regulate the electrochemical interface and guide even lithium deposition and a stable SEI. The molecule, benzenesulfonyl fluoride, was bonded to the surface of a reduced graphene oxide aerogel. During metal deposition, this labile molecule not only generates a metal-coordinating benzenesulfonate anion that guides homogeneous metal deposition but also contributes lithium fluoride to the SEI to improve Li surface passivation. Consequently, high-efficiency lithium deposition with a low nucleation overpotential was achieved at a high current density of 6.0 mA cm −2 . A Li|LiCoO 2 cell had a capacity retention of 85.3% after 400 cycles, and the cell also tolerated low-temperature (−10 °C) operation without additional capacity fading. This strategy was applied to sodium and zinc anodes as well. 

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2. A BF ₃ ‐Doped MXene Dual‐Layer Interphase for a Reliable Lithium‐Metal Anode

   https://doi.org/10.1002/adma.202210111  

   Shang, Mingwei; Shovon, Osman Goni; Wong, Francis En; Niu, Junjie (February 2023, Advanced Materials)

   Abstract A dual‐layer interphase that consists of an in‐situ‐formed lithium carboxylate organic layer and a thin BF 3 ‐doped monolayer Ti 3 C 2 MXene on Li metal is reported. The honeycomb‐structured organic layer increases the wetting of electrolyte, leading to a thin solid electrolyte interface (SEI). While the BF 3 ‐doped monolayer MXene provides abundant active sites for lithium homogeneous nucleation and growth, resulting in about 50% reduced thickness of inorganic‐rich components among the SEI layer. A low overpotential of less than 30 mV over 1000 h cycling in symmetric cells is received. The functional BF 3  groups, along with the excellent electronic conductivity and smooth surface of the MXene, greatly reduce the lithium plating/stripping energy barrier, enabling a dendrite‐free lithium‐metal anode. The battery with this dual‐layer coated lithium metal as the anode displays greatly improved electrochemical performance. A high capacity‐retention of 175.4 mAh g −1 at 1.0 C is achieved after 350 cycles. In a pouch cell with a capacity of 475 mAh, the battery still exhibits a high discharge capacity of 165.6 mAh g −1 with a capacity retention of 90.2% after 200 cycles. In contrast to the fast capacity decay of pure Li metal, the battery using NCA as the cathode also displays excellent capacity retention in both coin and pouch cells. The dual‐layer modified surface provides an effective approach in stabilizing the Li‐metal anode. 

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3. A Carboranyl Electrolyte Enabling Highly Reversible Sodium Metal Anodes via a “Fluorine‐Free” SEI

   https://doi.org/10.1002/anie.202208158  

   Tomich, Anton W.; Park, Jehee; Son, Seoung‐Bum; Kamphaus, Ethan P.; Lyu, Xingyi; Dogan, Fulya; Carta, Veronica; Gim, Jihyeon; Li, Tao; Cheng, Lei; et al (December 2022, Angewandte Chemie International Edition)

   Abstract Realization of practical sodium metal batteries (SMBs) is hindered due to lack of compatible electrolyte components, dendrite propagation, and poor understanding of anodic interphasial chemistries. Chemically robust liquid electrolytes that facilitate both favorable sodium metal deposition and a stable solid‐electrolyte interphase (SEI) are ideal to enable sodium metal and anode‐free cells. Herein we present advanced characterization of a novel fluorine‐free electrolyte utilizing the [HCB 11 H 11 ] 1− anion. Symmetrical Na cells operated with this electrolyte exhibit a remarkably low overpotential of 0.032 V at a current density of 2.0 mA cm −2 and a high coulombic efficiency of 99.5 % in half‐cell configurations. Surface characterization of electrodes post‐operation reveals the absence of dendritic sodium nucleation and a surprisingly stable fluorine‐free SEI. Furthermore, weak ion‐pairing is identified as key towards the successful development of fluorine‐free sodium electrolytes. 

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4. Concentrated ternary ether electrolyte allows for stable cycling of a lithium metal battery with commercial mass loading high‐nickel NMC and thin anodes

   https://doi.org/10.1002/cey2.275  

   Yang, Jun; Li, Xing; Qu, Ke; Wang, Yixian; Shen, Kangqi; Jiang, Changhuan; Yu, Bo; Luo, Pan; Li, Zhuangzhi; Chen, Mingyang; et al (March 2023, Carbon Energy)

   Abstract A new concentrated ternary salt ether‐based electrolyte enables stable cycling of lithium metal battery (LMB) cells with high‐mass‐loading (13.8 mg cm⁻², 2.5 mAh cm⁻²) NMC622 (LiNi_0.6Co_0.2Mn_0.2O₂) cathodes and 50 μm Li anodes. Termed “CETHER‐3,” this electrolyte is based on LiTFSI, LiDFOB, and LiBF₄with 5 vol% fluorinated ethylene carbonate in 1,2‐dimethoxyethane. Commercial carbonate and state‐of‐the‐art binary salt ether electrolytes were also tested as baselines. With CETHER‐3, the electrochemical performance of the full‐cell battery is among the most favorably reported in terms of high‐voltage cycling stability. For example, LiNi_xMn_yCo_1–x–yO₂(NMC)‐Li metal cells retain 80% capacity at 430 cycles with a 4.4 V cut‐off and 83% capacity at 100 cycles with a 4.5 V cut‐off (charge at C/5, discharge at C/2). According to simulation by density functional theory and molecular dynamics, this favorable performance is an outcome of enhanced coordination between Li⁺and the solvent/salt molecules. Combining advanced microscopy (high‐resolution transmission electron microscopy, scanning electron microscopy) and surface science (X‐ray photoelectron spectroscopy, time‐of‐fight secondary ion mass spectroscopy, Fourier‐transform infrared spectroscopy, Raman spectroscopy), it is demonstrated that a thinner and more stable cathode electrolyte interphase (CEI) and solid electrolyte interphase (SEI) are formed. The CEI is rich in lithium sulfide (Li₂SO₃), while the SEI is rich in Li₃N and LiF. During cycling, the CEI/SEI suppresses both the deleterious transformation of the cathode R‐3m layered near‐surface structure into disordered rock salt and the growth of lithium metal dendrites. 

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5. Lithium-activated SnS–graphene alternating nanolayers enable dendrite-free cycling of thin sodium metal anodes in carbonate electrolyte

   https://doi.org/10.1039/d0ee02423f  

   Liu, Wei; Chen, Zidong; Zhang, Zheng; Jiang, Pingxian; Chen, Yungui; Paek, Eunsu; Wang, Yixian; Mitlin, David (January 2021, Energy & Environmental Science)

   null (Ed.)

   Sodium metal battery (SMB, NMB) anodes can become dendritic due to an electrochemically unstable native Na-based solid electrolyte interphase (SEI). Herein Li-ion activated tin sulfide graphene nanocomposite membrane (A-SnS–G) is employed as an artificial SEI layer, allowing cyclability of record-thin 100 μm Na metal foils. The thin Na metal is prepared by a self-designed metallurgical rolling protocol. A-SnS–G is initially placed onto the polypropylene (PP) separator but becomes in situ transferred onto the Na metal surface. Symmetric metal cells protected by A-SnS–G achieve low-overpotential extended high-rate cycling in a standard carbonate electrolyte (EC : DEC = 1 : 1, 5% FEC). Accumulated capacity of 1000 mA h cm −2 is obtained after 500 cycles at 4 mA cm −2 , with accumulated capacity-to-foil capacity (A/F) ratio of 90.9. This is among the most favorable cycle life, accumulated capacity, and anode utilization combinations reported. Protection by non-activated SnS–G membrane yields significantly worse cycling, albeit still superior to the baseline unprotected sodium. Post-mortem and dedicated light optical analysis indicate that metal swelling, dendrite growth and dead metal formation is extensive for the unprotected sample, but is suppressed with A-SnS–G. Per XPS, post-100 cycles near-surface structure of A-SnS–G is rich in metallic Sn alloys and inorganic carbonate salts. Even after 300 cycles, Li-based SEI components ROCO 2 -Li, Li 2 CO 3 and LiF are detected with A-SnS–G. As a proof of principle, an SMB with a high mass loading (6 mg cm −2 ) NVP cathode and a A-SnS–G protected anode delivered extended cyclability, achieving 74 mA h g −1 after 400 cycles at 0.4C. 

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