Near zero-strain silicon oxycarbide interphases for stable Li-ion batteries.

We investigate silicon oxycarbide nanotubes that incorporate Si, SiC, and silicon oxycarbide phases, which exhibit near zero-strain volume expansion, leading to reduced electrolyte decomposition. The composite effectively accommodates the formation of c-Li15Si4, as validated by in situ TEM analyses and electrochemical tests, thereby proposing a promising solution for Li-ion battery anodes.

Temperature-Dependent Fracture Resistance of Silicon Nanopillars during Electrochemical Lithiation.

During the lithation of silicon anodes, the solid-state diffusion of lithium into LixSi follows the Arrhenius law, the resulting morphology and fracture behavior are determined by the silicon anode operation temperature. Here, we reveal the temperature dependence of the lithiation mechanics of crystalline silicon nanopillars (SiNPs) via microscopic observations of the anisotropic growth and fracture behavior. We fabricated 1D SiNP structures with various orientations (⟨100⟩, ⟨110⟩, and ⟨111⟩) as working electrodes and operated them at temperatures ranging from -20 to 40 °C. The lithiation of crystalline silicon at low temperatures exhibited preferential volume expansion along ⟨110⟩ and decreased fracture resistance. Furthermore, low temperatures caused the catastrophic fracture of amorphous silicon after the second lithiation. Our findings demonstrate the importance of silicon anode temperature control to prevent mechanical fracture during the cycle of lithium-ion batteries in harsh environments (e.g., electric vehicles in winter).

Universal Solution Synthesis of Sulfide Solid Electrolytes Using Alkahest for All-Solid-State Batteries.

The wet-chemical processability of sulfide solid electrolytes (SEs) provides intriguing opportunities for all-solid-state batteries. Thus far, sulfide SEs are wet-prepared either from solid precursors suspended in solvents (suspension synthesis) or from homogeneous solutions using SEs (solution process) with restricted composition spaces. Here, a universal solution synthesis method for preparing sulfide SEs from precursors, not only Li2 S, P2 S5 , LiCl, and Na2 S, but also metal sulfides (e.g., GeS2 and SnS2 ), fully dissolved in an alkahest: a mixture solvent of 1,2-ethylenediamine (EDA) and 1,2-ethanedithiol (EDT) (or ethanethiol). Raman spectroscopy and theoretical calculations reveal that the exceptional dissolving power of EDA-EDT toward GeS2 is due to the nucleophilicity of the thiolate anions that is strong enough to dissociate the GeS bonds. Solution-synthesized Li10 GeP2 S12 , Li6 PS5 Cl, and Na11 Sn2 PS12 exhibit high ionic conductivities (0.74, 1.3, and 0.10 mS cm-1 at 30 °C, respectively), and their application for all-solid-state batteries is successfully demonstrated.

Nitrogen Plasma-Assisted Functionalization of Silicon/Graphite Anodes to Enable Fast Kinetics.

The practical use of silicon anodes is interfered by the following key factors: volume expansion, slow kinetics, and low electrical and ionic conductivities. Many studies have focused on surface engineering from the particle to electrode level to achieve stability and energy density. Herein, simple nitrogen gas plasma is introduced as a surface treatment method for silicon-based electrodes to avoid the problems of material synthesis-based functionalizations (e.g., high cost, time consuming, and low quality). The introduction of activated nitrogen gas on electrode surfaces changes the binding energy and resistance of silicon, increasing the reversibility of the charge/discharge reaction of silicon-based anodes. In addition, such doping and dehydrogenation of the electrode surface improve reaction kinetics to 876 mA h g-1 specific capacity at 8.5 A g-1 in silicon/graphite anodes even with a high silicon content of 40%. The proposed strategy, through nitrogen plasma, offers advantages for direct functionalization on electrode surfaces by a simple method.

Side-View Operando Optical Microscopy Analysis of a Graphite Anode to Study Its Kinetic Hysteresis.

Operando analyses have provided several breakthroughs in the construction of high-performance materials and devices, including energy storage systems. However, despite the advances in electrode engineering, the formidable issues of lithium intercalation and deintercalation kinetics cannot be investigated by using planar observations. This study concerns side-view operando observation by optical microscopy of a graphite anode based on its color changes during electrochemical lithiation. Since the graphite color varies according to the optical energy gap during lithiation and delithiation, this technique can be used to study the corresponding charge-discharge kinetics. In addition, the cell configuration uses liquid electrolytes similar to commercial cells, allowing practical application. Furthermore, this side-view observation has shown that microscale spatial variations in rate and composition control the insertion and deinsertion, revealing the kinetics throughout the whole electrode. The results of this study could enhance the fundamental understanding of the kinetics of battery materials.

Native Void Space for Maximum Volumetric Capacity in Silicon-Based Anodes.

Volumetric energy density is considered a primary factor in developing high-energy batteries. Despite its significance, less efforts have been devoted to its improvement. Silicon-based materials have emerged as next-generation anodes for lithium-ion batteries due to their high specific capacity. However, their volumetric capacities are limited by the volume expansion rate of silicon, which restricts mass loading in the electrodes. To address this challenge, we introduce porous silicon templated from earth-abundant minerals with native internal voids, capable of alleviating volumetric expansion during repeated cycles. In situ transmission electron microscopy analysis allows the precise determination of the expansion rate of silicon, thus presenting an analytical model for finding the optimal content in silicon/graphite composites. The inner pores in silicon reduce problems associated with its expansion and allow higher silicon loading of 42% beyond the conventional limitations of 13-14%. Consequently, the anode designed in this work can deliver a volumetric capacity of 978 mAh cc-1. Thus, suppressing volume expansion with natural abundant template-assisted materials opens new avenues for cost-effective fabrication of high volumetric capacity batteries.