Roll-Pressed Silicon Anodes with High Reversible Volumetric Capacity Achieved by Interfacial Stabilization and Mechanical Strengthening of a Silicon/Graphene Hybrid Assembly.

Application of Si anodes is hindered by severe capacity fading due to pulverization of Si particles during the large volume changes of Si during charge/discharge and repeated formation of the solid-electrolyte interphase. To address these issues, considerable efforts have been devoted to the development of Si composites with conductive carbons (Si/C composites). However, Si/C composites with high C content inevitably show low volumetric capacity because of low electrode density. For practical applications, the volumetric capacity of a Si/C composite electrode is more important than gravimetric capacity, but volumetric capacity in pressed electrodes is rarely reported. Herein, a novel synthesis strategy is demonstrate for a compact Si nanoparticle/graphene microspherical assembly with interfacial stability and mechanical strength achieved by consecutively formed chemical bonds using 3-aminopropyltriethoxysilane and sucrose. The unpressed electrode (density: 0.71 g cm-3 ) shows a reversible specific capacity of 1470 mAh g-1 with a high initial coulombic efficiency of 83.7% at a current density of 1 C-rate. The corresponding pressed electrode (density: 1.32 g cm-3 ) exhibits high reversible volumetric capacity of 1405 mAh cm-3 and gravimetric capacity of 1520 mAh g-1 with a high initial coulombic efficiency of 80.4% and excellent cycling stability of 83% over 100 cycles at 1 C-rate.

In Situ Synthesis of Amorphous GeSe/CNT Composite via Defective-carbon-mediated Chemical Bonding for Ultrastable Na Ion Storage.

Herein, we report the in-situ synthesis of amorphous GeSe/CNT composite via defective-carbon-mediated chemical bonding for ultrastable Na-ion storage. Structural defects in CNTs play a crucial role in the chemical bonding and bonding strength in GeSe/CNTs composites. Specifically, the bonding strength tends to increase with increasing defect concentrations of CNTs. Remarkably, the strong chemical bonding between GeSe and CNTs significantly weakens Ge-Se bonds and promotes amorphization of GeSe, thus facilitating a reversible conversion reaction and enhancing Na-ion diffusion. Consequently, GeSe/CNTs composite exhibits outstanding cyclability of 87.9% even after 1000 cycles at 1 A g-1 and a high-rate capability of 288.3 mA h g-1 at 10 A g-1 . Our work presents a promising approach for the amorphization of electrode materials enabled by the defective-carbon-mediated strong chemical bonding for Li-, Na-, and K-ion batteries.