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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)

   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. Accelerated Short Circuiting in Anode‐Free Solid‐State Batteries Driven by Local Lithium Depletion

   https://doi.org/10.1002/aenm.202204186  

   Lewis, John A. ; Sandoval, Stephanie E. ; Liu, Yuhgene ; Nelson, Douglas Lars ; Yoon, Sun Geun ; Wang, Runzi ; Zhao, Ying ; Tian, Mengkun ; Shevchenko, Pavel ; Martínez‐Pañeda, Emilio ; et al ( February 2023 , Advanced Energy Materials)

   “Anode‐free” solid‐state batteries (SSBs), which have no anode active material, can exhibit extremely high energy density (≈1500 Wh L⁻¹). However, there is a lack of understanding of the lithium plating/stripping mechanisms at initially lithium‐free solid‐state electrolyte (SSE) interfaces because excess lithium metal is often used. Here, it is demonstrated that commercially relevant quantities of lithium (>5 mAh cm⁻²) can be reliably plated at moderate current densities (1 mA cm⁻²) using the sulfide SSE Li₆PS₅Cl. Investigations of lithium plating/stripping mechanisms, in conjunction with cryo‐focused ion beam (FIB) imaging, synchrotron tomography, and phase‐field modeling, reveal that the cycling stability of these cells is fundamentally limited by the nonuniform presence of lithium during stripping. Local lithium depletion causes isolated lithium regions toward the end of stripping, decreasing electrochemically active area and resulting in high local current densities and void formation. This accelerates subsequent filament growth and short circuiting compared to lithium‐excess cells. Despite this degradation mode, it is shown that anode‐free cells exhibit comparable Coulombic efficiency to lithium‐excess cells, and improved resistance to short circuiting is achieved by avoiding local lithium depletion through retention of thicker lithium at the interface. These new insights provide a foundation for engineering future high‐energy anode‐free SSBs.

    

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3. Enabling High-Rate Long-lifespan Lithium-Sulfur Batteries via Stereolithography Technique and Oxidative Chemical Vapor Deposition

   Zhang, Yuxuan ; Lee, Sunghwan ( June 2022 , 64th Electronic Materials Conference)

   Enhancing battery energy storage capability and reducing the cost per average energy capacity is urgent to satisfy the increasing energy demand in modern society. The lithium-sulfur (Li-S) battery is especially attractive because of its high theoretical specific energy (around 2600 W h kg-1), low cost, and low toxicity.1 Despite these advantages, the practical utilization of lithium-sulfur (Li-S) batteries to date has been hindered by a series of obstacles, including low active material loading, shuttle effects, and sluggish sulfur conversion kinetics.2 The traditional 2D planer thick electrode is considered as a general approach to enhance the mass loading of the Li-S battery.3 However, the longer diffusion length of lithium ions, which resulted in high tortuosity in the compact stacking thick electrode, decreases the penetration ability of the electrolyte into the entire cathode.4 Although an effort to induce catalysts in the cathode was made to promote sulfur conversion kinetic conditions, catalysts based on transition metals suffered from the low electronic conductivity, and some elements (i.e.: Co, Mn) may even absorb and restrict polysulfides for further reaction. 5 To mitigate the issues listed above, herein we propose a novel sulfur cathode design strategy enabled by additive manufacturing and oxidative chemical vapor deposition (oCVD). 6,7 Specifically, the cathode is designed to have a hierarchal hollow structure via a stereolithography technique to increase sulfur usage. Microchannels are constructed on the tailored sulfur cathode to further fortify the wettability of the electrolyte. The as-printed cathode is then sintered at 700 °C in an N2 atmosphere in order to generate a carbon skeleton (i.e.: carbonization of resin) with intrinsic carbon defects. The intrinsic carbon defects are expected to create favorable sulfur conversion conditions with sufficient electronic conductivity. In this study, the oCVD technique is leveraged to produce a conformal coating layer to eliminate shuttle effects. Identified by scanning electron microscopy and energy-dispersive X-ray spectroscopy mapping characterizations, the oCVD PEDOT is not only covered on the surface of the cathode but also on the inner surface of the microchannels. High-resolution x-ray photoelectron spectroscopy analyses (C 1s and S 2p orbitals) between pristine and modified samples demonstrate that a high concentration of the defects has been produced on the sulfur matrix after sintering and posttreatment. In-operando XRD diffractograms show that the Li2S is generated in the oCVD PEDOT-coated sample during the charge and discharge process even with a high current density, confirming an eminent sulfur conversion kinetic condition. In addition, ICP-OES results of lithium metal anode at different states of charge (SoC) verify that the shuttle effects are excellently restricted by oCVD PEDOT. Overall, the high mass loading (> 5 mg cm-2) with an elevated sulfur utilization ratio, accelerated reaction kinetics and stabilized electrochemical process have been achieved on the sulfur cathode by implementing this innovative cathode design strategy. The results of this study demonstrate significant promises of employing pure sulfur powder with high electrochemical performance and suggest a pathway to the higher energy and power density battery. References: 1 Chen, Y. Adv Mater 33, e2003666. 2 Bhargav, A. Joule 4, 285-291. 3 Liu, S. Nano Energy 63, 103894. 4 Chu, T. Carbon Energy 3. 5 Li, Y. Matter 4, 1142-1188. 6 John P. Lock. Macromolecules 39, 4 (2006). 7 Zekoll, S. Energy & Environmental Science 11, 185-201. 

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4. A Rechargeable Battery with an Iron Metal Anode

   https://doi.org/10.1002/adfm.201900911  

   Wu, Xianyong ; Markir, Aaron ; Xu, Yunkai ; Zhang, Chong ; Leonard, Daniel P. ; Shin, Woochul ; Ji, Xiulei ( March 2019 , Advanced Functional Materials)

   To date, tremendous efforts of the battery community are devoted to batteries that employ Li⁺, Na⁺, and K⁺as charge carriers and nonaqueous electrolytes. However, aqueous batteries hold great promise for stationary energy storage due to their inherent low cost and high safety. Among metal batteries that use aqueous electrolytes, zinc metal batteries are the focus of attention. In this study, iron as an anode candidate in aqueous batteries is investigated because iron is undoubtedly the most earth‐abundant and cost‐effective metal anode. Reversible iron plating/stripping in a FeSO₄electrolyte is demonstrated on the anode side and reversible topotactic (de)insertion of Fe²⁺in a Prussian blue analogue cathode is showcased. Furthermore, it is revealed that LiFePO₄can pair up with the iron metal anode in a hybrid cell, delivering stable performance as well.

    

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5. Dual‐Solvent Li‐Ion Solvation Enables High‐Performance Li‐Metal Batteries

   https://doi.org/10.1002/adma.202008619  

   Wang, Hansen ; Yu, Zhiao ; Kong, Xian ; Huang, William ; Zhang, Zewen ; Mackanic, David G. ; Huang, Xinyi ; Qin, Jian ; Bao, Zhenan ; Cui, Yi ( May 2021 , Advanced Materials)

   Novel electrolyte designs to further enhance the lithium (Li) metal battery cyclability are highly desirable. Here, fluorinated 1,6‐dimethoxyhexane (FDMH) is designed and synthesized as the solvent molecule to promote electrolyte stability with its prolonged –CF₂– backbone. Meanwhile, 1,2‐dimethoxyethane is used as a co‐solvent to enable higher ionic conductivity and much reduced interfacial resistance. Combining the dual‐solvent system with 1mlithium bis(fluorosulfonyl)imide (LiFSI), high Li‐metal Coulombic efficiency (99.5%) and oxidative stability (6 V) are achieved. Using this electrolyte, 20 µm Li||NMC batteries are able to retain≈80% capacity after 250 cycles and Cu||NMC anode‐free pouch cells last 120 cycles with 75% capacity retention under≈2.1 µL mAh⁻¹lean electrolyte conditions. Such high performances are attributed to the anion‐derived solid‐electrolyte interphase, originating from the coordination of Li‐ions to the highly stable FDMH and multiple anions in their solvation environments. This work demonstrates a new electrolyte design strategy that enables high‐performance Li‐metal batteries with multisolvent Li‐ion solvation with rationally optimized molecular structure and ratio.

    

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