Robust, Ultrasmooth Fluorinated Lithium Metal Interphase Feasible via Lithiophilic Graphene Quantum Dots for Dendrite-Less Batteries.

Dendrite growth and in-homogeneous solid electrolyte interphase (SEI) buildup of Li metal anodes hinder the longtime discharge-charge cycling and safety in secondary metal batteries. Here, the authors report an in-situ restructured artificial lithium/electrolyte SEI exposing an ultrasmooth and thin layer mediated through graphene quantum dots (GQDs). The reformed artificial interphase comprises a mixture of organic/inorganic-rich compositions alike as mosaic interphase, albeit the synergistic effect mediated via hydroxylated GQDs involving redeposition-borne lithium, and its accumulated salts, facilitate a homogeneous and ultrasmooth near fluorine-rich interfacial environment ensuring a facile lithium-ion (Li-ion) diffusion and dendritic-free nature. As a result, symmetrical graphene dots-lithium cells enable a dendrite-less operation up to 2000 h with good cycling stability and capacity retention at current densities 1 and 5 mA cm-2 compared to bare lithium. The well-established fluorinated interface engenders a high reversible capacity and stable performance during the initial and long-term cycles upon configuring in lithium-sulfur (Li-S) cells. Thus, the authors' work illuminates the direction toward achieving dendritic-free smooth and robust metal anodes through manipulating and restructuring the critical SEI chemical components.

Flame retardant high-power Li-S flexible batteries enabled by bio-macromolecular binder integrating conformal fractions.

Polymer binders for sulfur cathodes play a very critical role as they prerequisites for an in-situ immobilization against polysulfide shuttle and volume change, while ensuring good adhesion within active materials for ion conduction along with robust mechanical and chemical stability. Here, we demonstrate anionic surface charge facilitated bio-polymer binder for sulfur cathodes enabling excellent performance and fire safety improvement. The aqueous-processable tragacanth gum-based binder is adjusted to house high sulfur loading over 12 mg cm-2 without compromising the sulfur utility and reversibility, imparting high accessibility for Li-ions to sulfur particles about 80%. The intrinsic rod and sphere-like saccharidic conformal fraction's multifunctional polar units act as active channels to reach the sulfur particles. As a result, the binder entraps polysulfides with 46% improvement and restrains the volume changes within 16 % even at 4 C. Moreover, the flexible Li-S battery delivers a stack gravimetric energy density of 243 Wh kg-1, demonstrating high reactivity of sulfur along with good shape conformality, which would open an avenue for the potential development of the compact and flexible high-power device.

Unlocking Rapid Charging and Extended Lifetimes for Li-Ion Batteries Using Freestanding Quantum Conversion-Type Aerofilm Anode.

Batteries capable of quick charging as fast as fossil fuel vehicles are becoming a vital issue in the electric vehicle market. However, conversion-type materials promising as a next-generation anode have many problems to satisfy fast charging and long-term cycles due to their low conductivity and large irreversibility despite a high theoretical capacity. Here, we report effective strategies for a SnO2-based anode to enable rapid-charging, long-cycle, and high reversible capacity. The quantum size of SnO2 nanoparticles uniformly embedded within a 3D conductive carbon matrix as a prerequisite for high reversible capacity increases the interdiffusion layer and facilitates a highly reversible conversion reaction between Li2O/Sn and SnO2. In particular, the Sn-C chemical bond achieves ion-site control and direct electron transfer, enabling boost charging. Further, the robust and porous structure of the binder-free three-dimensional electrode buffers the massive volume expansion during Li insertion/desertion and allows for multidimensional rapid-ion diffusion. As a result, our quantum SnO2 anode delivers a high reversible capacity of about 753 mAh g-1 with a 468% capacity increase after 4000 cycles at 10 C. It also presents a gradually increasing capacity up to 548 mAh g-1 even at 20 C and superior cyclability over 20 000 cycles in capacity stabilization. This study will contribute to designing aerofilm-based conversion-type electrodes for fast charging devices.

Understanding Excess Li Storage beyond LiC6 in Reduced Dimensional Scale Graphene.

A phenomenon is observed in which the electrochemical performances of porous graphene electrodes show unexpectedly increasing capacities in the Li storage devices. However, despite many studies, the cause is still unclear. Here, we systematically present the reason for the capacity enhancements of the pristine graphene anode under functional group exclusion through morphological control and crystal structure transformation. The electrochemical synergy of both the edge effect and surface effect of the reduced dimensional scale graphene in an open-porous structure facilitates significantly enhanced capacity through multidimensional Li-ion accessibility and accumulation of Li atoms. Furthermore, the Stone-Wales defects boosted during Li insertion and extraction promote a capacity elevation beyond the theoretical capacity of the carbon electrode even after long-term cycles at high C-rates. As a result, the morphologically controlled graphene anode delivers the highest reversible capacity of 3074 mA h g-1 with a 163% capacity increase after 2000 cycles at 5 C. It also presents a gradually increasing capacity up to 1102 mA h g-1 even at 50 C without an evident capacity fading tendency. This study provides valuable information into the practical design of ultralight and high-rate energy storage devices.