Breathing silicon anodes for durable high-power operations

Silicon anode materials have been developed to achieve high capacity lithium ion batteries for operating smart phones and driving electric vehicles for longer time. Serious volume expansion induced by lithiation, which is the main drawback of silicon, has been challenged by multi-faceted approaches. Mechanically rigid and stiff polymers (e.g. alginate and carboxymethyl cellulose) were considered as the good choices of binders for silicon because they grab silicon particles in a tight and rigid way so that pulverization and then break-away of the active mass from electric pathways are suppressed. Contrary to the public wisdom, in this work, we demonstrate that electrochemical performances are secured better by letting silicon electrodes breathe in and out lithium ions with volume change rather than by fixing their dimensions. The breathing electrodes were achieved by using a polysaccharide (pullulan), the conformation of which is modulated from chair to boat during elongation. The conformational transition of pullulan was originated from its a glycosidic linkages while the conventional rigid polysaccharide binders have beta linkagesopen1

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School of Energy and Chemical Engineering (Energy Engineering)ope

A4 Paper Chemistry: Synthesis of a Versatile and Chemically Modifiable Cellulose Membrane

Multifunctional cellulose membranes were developed from A4-sized printing paper via chemical modification. A4 paper is a widely used and easily accessible product with high cellulose content. Inspired by cellulose chemistry, we report a simple modification of the A4 paper, converting it from a common office supply to a user-modifiable functionalized cellulose membrane for practical applications. The hydroxyl groups of cellulose enable a facile tuning of its internal structure and polarity via chemical modification. In addition, the functionalized cellulose membrane has more stable mechanical strength compared to commercial cellulose-based filtration membranes. As a proof-of-concept, we demonstrate the separation of a water/oil mixture using the functionalized A4 membrane; we have extended this idea to origami-assisted membrane applications. Finally, this versatile A4 paper chemistry may offer a promising strategy for the development of functional membranes

In situ visualization of zinc plating in gel polymer electrolyte

Uniform zinc metal plating has been raised as a critical issue in zinc-based batteries. Randomly localized ions lead to severe zinc dendrite formation in liquid electrolyte due to nonuniform ion flux caused by electroconvective flow. One of the mitigating approaches is to use gel polymer electrolyte to regulate the ion flux for suppressing zinc dendrites by imparting viscoelasticity to the electrolyte and improving the ion transport along charged functional groups of polymer chains. However, to this date, the effectiveness of gel polymer electrolyte has been visualized using ex situ methods (e.g., scanning electron microscopy) that requires cell disassembly. And the underlying mechanism is poorly understood. Herein, we applied in situ optical microscopy with dark-field illumination and a transparent glass slide cell to visualize zinc metal plating in the gel polymer electrolyte. At a given current density, the morphological differences of plated zinc metal between the liquid and gel polymer electrolytes were compared. Our in situ opti-cal microscopy platform successfully showed that the gel polymer electrolyte supported by cross-linked polyacrylic acid (PAA)/N,N'-methylenebisacrylamide (MBA) polymer framework significantly suppressed the dendrite formation in contrast to the liquid electrolyte during plating. In addition, at various current densities, the tendency of dendritic growth was observed and statistically compared in both electrolytes. The findings will be useful for future design of rechargeable zinc-based batteries. (c) 2021 Elsevier Ltd. All rights reserved

Argentophilic pyridinic nitrogen for embedding lithiophilic silver nanoparticles in a three-dimensional carbon scaffold for reversible lithium plating/stripping

Reversible lithium metal plating and stripping are required for the durable operation of lithium metal batteries. Three-dimensional architecture has been employed for accommodating volume change of lithium metal during repeated plating and stripping while lithiophilic materials have been utilized for the even plating of lithium metal. One of the best pictures would be a three-dimensional electrically conductive scaffold having a significant amount of lithiophilic sites homogenously distributed on its skeleton. To realize the ideal architecture for lithium metal anodes, herein, we embedded silver nanoparticles as lithiophile in a three-dimensional carbon scaffold. To overcome the limited loading amount of silver in the porous structure, melamine as an argentophile having argentophilic (silver-philic) pyridinic nitrogen was introduced into the carbon scaffold. Melamine as the argentophile increased the silver loading ten times in the three-dimensional scaffold via the strong interaction with silver cation. The heavy lithiophile (silver) loading increased the lithium storage capacity, guaranteeing uniform lithium distribution throughout the scaffold. The silver nanoparticles loaded in the scaffold were alloyed with lithium to be silver-lithium alloy (AgxLiy) during lithium metal plating. The alloy served as the lithiophilic nucleation sites for the dendrite-free growth of lithium metal. As a result, the strong lithiophilicity derived from the heavy-loading silver improved the reversibility of lithium plating and stripping. The cycling durability of lithium metal batteries with lithium-ion-battery cathode reaction and oxygen reduction reaction was twice improved by employing the lithium-metal-infused 3D scaffold anode having the highest lithiophile loading with internal space enough to accommodate the volume of lithium metal

The Pyridinic-to-Graphitic Conformational Change of Nitrogen of Graphitic Carbon Nitride on Lithium Coordination during Lithium Plating

The reversibility of lithium plating/stripping should be guaranteed in lithium metal batteries. Seriously polarized lithium growth during plating leads to the dendritic evolution of lithium metal due to the uneven current distribution on the electrically conductive surface. Artificial protective layers covering electrodes (e.g., polymer film on copper foil) have been used to narrow the gap of the current density between positions on the conductive surface. Herein, we incorporated an active ingredient to attract lithium ions into the dendrite-suppressing layer. Pyridinic nitrogen of graphitic carbon nitride (g-C3N4) served as the lithium ion affinity center. Conformation of the nitrogen was changed from pyridinic to graphitic in the presence of lithium ions, which confirms the coordination of lithium ion to the pyridinic nitrogen. Lithium metal was plated between the g-C3N4 layer and the copper current collector (or the lithium metal). The homogeneous lithium nucleation expected from the active role of the pyridinic nitrogen on regulating ionic pathways suppressed the dendritic growth of lithium metal and decreased the overpotential required for the initial metal nucleation. Due to the top-down ion flux regulation on the uppermost surface (or tip) of lithium metal, the reversibility of lithium plating/stripping was dramatically improved

A metal-ion-chelating organogel electrolyte for Le Chatelier depression of Mn3+ disproportionation of lithium manganese oxide spinel

We present a metal-ion-chelating organogel electrolyte, thermally gelated within cells, to solve the problems triggered by metal dissolution from cathodes of lithium ion batteries. The organogel significantly improved the capacity retention of lithium manganese oxide spinel during cycling. The organogel mitigated metal deposition on anodes by capturing metal ions (anode protection). Interestingly, the organogel inhibited metal dissolution by keeping dissolved metal ions highly concentrated around the cathode surface (cathode protection by Le Chatelier's principle)