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1. Vertically Aligned Carbon Nanofibers on Cu Foil as a 3D Current Collector for Reversible Li Plating/Stripping toward High‐Performance Li–S Batteries

   https://doi.org/10.1002/adfm.201906444  

   Chen, Yazhou; Elangovan, Ayyappan; Zeng, Danli; Zhang, Yunfeng; Ke, Hanzhong; Li, Jun; Sun, Yubao; Cheng, Hansong (November 2019, Advanced Functional Materials)

   Abstract A vertically aligned carbon nanofiber (VACNF) array with unique conically stacked graphitic structure directly grown on a planar Cu current collector (denoted as VACNF/Cu) is used as a high‐porosity 3D host to overcome the commonly encountered issues of Li metal anodes. The excellent electrical conductivity and highly active lithiophilic graphitic edge sites facilitate homogenous coaxial Li plating/stripping around each VACNF and forming a uniform solid electrolyte interphase. The high specific surface area effectively reduces the local current density and suppresses dendrite growth during the charging/discharging processes. Meanwhile, this open nanoscale vertical 3D structure eliminates the volume changes during Li plating/stripping. As a result, highly reversible Li plating/stripping with high coulombic efficiency is achieved at various current densities. A low voltage hysteresis of 35 mV over 500 h in symmetric cells is achieved at 1 mA cm⁻²with an areal Li plating capacity of 2 mAh cm⁻², which is far superior to the planar Cu current collector. Furthermore, a Li–S battery using a S@PAN cathode and a lithium‐plated VACNF/Cu (VACNF/Cu@Li) anode with slightly higher capacity (2 mAh cm⁻²) exhibits an excellent rate capability and high cycling stability with no capacity fading over 600 cycles. 

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2. A Systematic Electrochemical Investigation of a Dimethylamine Cosolvent-Assisted Nonaqueous Zinc(II) Bis(trifluoromethylsulfonyl)imide Electrolyte

   https://doi.org/10.1149/1945-7111/abe9cb  

   Asselin, Genevieve M.; Paden, Olivia; Qiu, Weiqi; Yang, Zicheng; Sa, Niya (March 2021, Journal of The Electrochemical Society)

   The development of the multivalent electrolytes is a critical component to advance polyvalent energy storage technology. In this work, a new and simple nonaqueous zinc electrolyte is developed and investigated where a secondary amine is introduced as a cosolvent. The addition of dimethylamine (DMA) as a cosolvent in THF facilitates the solubilization of Zinc (II) bis(trifluoromethanesulfonyl)imde (Zn(TFSI)₂) and results in a homogeneous electrolyte with reversible plating of zinc achieved at high coulombic efficiencies. The electrochemical properties of the developed electrolyte and the effects of the cosolvent and salt concentrations are systematically investigated. It was found that increasing the ratio of the cosolvent DMA in THF for a Zn(TFSI)₂electrolyte leads to more facile kinetics, better ion solubilization, and higher ion mobility evidenced by up a significant increase in conductivity as well as the plating/stripping current densities. Increased Zn(TFSI)₂salt concentration in a 2.0 M DMA in THF solvent mixture not only leads to a higher current density and conductivity, but also a higher molar conductivity due to a redissociation mechanism. The findings in this study are relevant and important to further understand and characterize multivalent electrolytes from a simple and effective electrolyte design strategy. 

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3. Chaotropic Salt‐Aided “Water‐In‐Organic” Electrolyte for Highly Reversible Zinc‐Ion Batteries Across a Wide Temperature Range

   https://doi.org/10.1002/adfm.202311271  

   Wang, Ziqing; Diao, Jiefeng; Burrow, James_N; Brotherton, Zachary_W; Lynd, Nathaniel_A; Henkelman, Graeme; Mullins, Charles_Buddie (November 2023, Advanced Functional Materials)

   Abstract Aqueous zinc‐ion batteries are promising alternatives to lithium‐ion batteries due to their cost‐effectiveness and improved safety. However, several challenges, including corrosion, dendrites, and water decomposition at the Zn anode, hinder their performance. Herein, an approach is proposed, that deviates from the conventional design by adding water into a propylene carbonate‐based organic electrolyte to prepare a non‐flammable “water‐in‐organic” electrolyte. The chaotropic salt Zn(ClO₄)₂exploits the Hofmeister effect to promote the miscibility of immiscible liquid phases. Interactions between propylene carbonate and water restrict water activity and mitigate unfavorable reactions. This electrolyte facilitates preferential Zn (002) deposition and the formation of solid electrolyte interphase. Consequently, the “water‐in‐organic” electrolyte achieves a 99.5% Coulombic efficiency at 1 mA cm⁻²over 1000 cycles in Zn/Cu cells, and constant cycling over 1000 h in Zn/Zn symmetric cells. A Na_0.33V₂O₅/Zn battery exhibits impressive cycling stability with a capacity of 175 mAh g⁻¹for 800 cycles at 2 A g⁻¹. Additionally, this electrolyte enables sustainable cycling across a wide temperature range from −20 to 50 °C. The design of a “water‐in‐organic” electrolyte employing a chaotropic salt presents a potential strategy for high‐performance electrolytes in zinc‐ion batteries with a large stability window and a wide temperature range. 

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4. Vanillin: An Effective Additive to Improve the Longevity of Zn Metal Anode in a 30 m ZnCl ₂ Electrolyte

   https://doi.org/10.1002/aenm.202301712  

   Hoang, David; Li, Yaqiong; Jung, Min_Soo; Sandstrom, Sean_K; Scida, Alexis_M; Jiang, Heng; Gallagher, Trenton_C; Pollard, Brenden_A; Jensen, Rachel; Chiu, Nan‐Chieh; et al (September 2023, Advanced Energy Materials)

   Abstract It remains a challenge to design aqueous electrolytes to secure the complete reversibility of zinc metal anodes. The concentrated water‐in‐salt electrolytes, e.g., 30 m ZnCl₂, are promising candidates to address the challenges of the Zn metal anode. However, the pure 30 m ZnCl₂electrolyte fails to deliver a smooth surface morphology and a practically relevant Coulombic efficiency. Herein, it is reported that a small concentration of vanillin, 5 mg mL_water⁻¹, added to 30 m ZnCl₂transforms the reversibility of Zn metal anode by eliminating dendrites, lowering the Hammett acidity, and forming an effective solid electrolyte interphase. The presence of vanillin in the electrolyte enables the Zn metal anode to exhibit a high Coulombic efficiency of 99.34% at a low current density of 0.2 mA cm⁻², at which the impacts of the hydrogen evolution reaction are allowed to play out. Using this new electrolyte, a full cell Zn metal battery with an anode/cathode capacity (N/P) ratio of 2:1 demonstrates no capacity fading over 800 cycles. 

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5. 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_Yoong; Niu, Junjie (December 2022, Advanced Materials)

   Abstract A dual‐layer interphase that consists of an in‐situ‐formed lithium carboxylate organic layer and a thin BF₃‐doped monolayer Ti₃C₂MXene 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 BF₃‐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 BF₃ 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⁻¹at 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⁻¹with 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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