Titanium Monoxide-Stabilized Silicon Nanoparticles with a Litchi-like Structure as an Advanced Anode for Li-ion Batteries

Stress-Relief Engineering in a N-Doped C-Modified Hierarchical Nanoporous Si Anode with a Microcurved Pore Wall Structure for Enhanced Lithium Storage

The commercialization of alloy-type anodes has been hindered by rapid capacity degradation due to volume fluctuations. To address this issue, stress-relief engineering is proposed for Si anodes that combines hierarchical nanoporous structures and modified layers, inspired by the phenomenon in which structures with continuous changes in curvature can reduce stress concentration. The N-doped C-modified hierarchical nanoporous Si anode with a microcurved pore wall (N-C@m-HNP Si) is prepared from inexpensive Mg-55Si alloys using a simple chemical etching and heat treatment process. When used as the anode for lithium-ion batteries, the N-C@m-HNP Si anode exhibits initial charge/discharge specific capacities of 1092.93 and 2636.32 mAh g-1 at 0.1 C (1 C = 3579 mA g-1), respectively, and a stable reversible specific capacity of 1071.84 mAh g-1 after 200 cycles. The synergy of the hierarchical porous structure with a microcurved pore wall and the N-doped C-modified layer effectively improves the electrochemical performance of N-C@m-HNP Si, and the effectiveness of stress-relief engineering is quantitatively analyzed through the theory of elastic bending of thin plates. Moreover, the formation process of Li15Si4 crystals, which causes substantial mechanical stress, is investigated using first-principles molecular dynamic simulations to reveal their tendency to occur at different scales. The results demonstrate that the hierarchical nanoporous structure helps to inhibit the transformation of amorphous LixSi into metastable Li15Si4 crystals during lithiation.

Preparation of Buffered Nano-Submicron Hierarchical Structure Hollow SiOx @C Anodes for Lithium-Ion Battery Materials with Carboxymethyl Chitosan

Silicon-based materials are among the most promising anode materials for next-generation lithium-ion batteries. However, the volume expansion and poor conductivity of silicon-based materials during the charge and discharge process seriously hinder their practical application in the field of anodes. Here, we choose carboxymethyl chitosan (CMCS) as the carbon source coating and binding on the surface of nano silicon and hollow silicon dioxide (H-SiO2 ) to form a hierarchical buffered structure of nano-hollow SiOx @C. The hollow H-SiO2 can alleviate the volume expansion of nano silicon during the lithiation process under continuous cycling. Meanwhile, the carbon layer carbonized by CMCS containing N-doping further regulates the silicon's expansion and improves the conductivity of the active materials. The as- prepared SiOx @C material exhibits an initial discharge capacity of 985.4 mAh g-1 with the decay rate of 0.27 % per cycle in 150 cycles under the current density of 0.2 A g-1 . It is proved that the hierarchical buffer structure nano-hollow SiOx @C anode material has practical application potential.

Engineering High-Performance SiOx Anode Materials with a Titanium Oxynitride Coating for Lithium-Ion Batteries

Micron-sized silicon oxide (SiOx) has been regarded as a promising anode material for new-generation lithium-ion batteries due to its high capacity and low cost. However, the distinct volume expansion during the repeated (de)lithiation process and poor conductivity can lead to structural collapse of the electrode and capacity fading. In this study, SiOx anode materials coated with TiO0.6N0.4 layers are fabricated by a facile solvothermal and thermal reduction technique. The TiO0.6N0.4 layers are homogeneously dispersed on SiOx particles and form an intimate contact. The TiO0.6N0.4 layers can enhance the conductivity and suppress volume expansion of the SiOx anode, which facilitate ion/electron transport and maintain the integrity of the overall electrode structure. The as-prepared SiOx-TiON-200 composites demonstrate a high reversible capacity of 854 mAh g-1 at 0.5 A g-1 with a mass loading of 2.0 mg cm-2 after 250 cycles. This surface modification technique could be extended to other anodes with low conductivity and large volume expansion for lithium-ion batteries.

Hydrophilic and Conductive Carbon Nanotube Fibers for High-Performance Lithium-Ion Batteries

Carbon nanotube fiber (CNTF) is a highly conductive and porous platform to grow active materials of lithium-ion batteries (LIB). Here, we prepared SnO₂@CNTF based on sulfonic acid-functionalized CNTF to be used in LIB anodes without binder, conductive agent, and current collector. The SnO₂ nanoparticles were grown on the CNTF in an aqueous system without a hydrothermal method. The functionalized CNTF exhibited higher conductivity and effective water infiltration compared to the raw CNTF. Due to the enhanced water infiltration, the functionalized CNTF became SnO₂@CNTF with an ideal core-shell structure coated with a thin SnO₂ layer. The specific capacity and rate capability of SnO₂@-functionalized CNTF were superior to those of SnO₂@raw CNTF. Since the SnO₂@CNTF-based anode was free of a binder, conductive agent, and current collector, the specific capacity of the anode studied in this work was higher than that of conventional anodes.