Defect-repaired reduced graphene oxide caging silicon nanoparticles for lithium-ion anodes with enhanced reversible capacity and cyclic performance

Design of dual carbon encapsulated porous micron silicon composite with compact surface for enhanced reaction kinetics of lithium-ion battery anodes

Developing high-performance composites with fast charging and superior cycle life is paramount for lithium-ion batteries (LIBs). Herein, we synthesized a double-shell carbon-coated porous structure composite with a compact surface (P-Si@rGO@C) using low-cost commercial micron-sized silicon (Si) instead of nanoscale silicon. Results reveal that the unique P-Si@rGO@C features high adaptability to volume expansion, accelerates electron/ion transmission rate, and forms a stable solid electrolyte interphase (SEI) film. This phenomenon arises from the synergistic effect of abundant internal voids and an external double-layer carbon shell with a dense surface. Specifically, the P-Si@rGO@C anode exhibits a high initial coulombic efficiency (ICE) (88.0 %), impressive rate-capability (612.1 mAh/g at 2C), and exceptional long-term cyclability (972.2 mAh/g over 500 cycles at 0.5C). Further kinetic studies elucidate the diffusion-capacitance hybrid energy storage mechanism and reveal an improved Li+ diffusion coefficient (from 3.47 × 10-11 to 2.85 × 10-9 cm2 s-1). Ex-situ characterization confirms the crystal phase change of micron-sized Si and the formation of a stable LiF-rich SEI. Theoretical calculations support these findings by demonstrating an enhancement in the adsorption ability of Si to Li+ (from -0.89 to -0.97 eV) and a reduction in the energy migration barrier (from 0.35 to 0.18 eV). Additionally, practical LixSi powder is shown to increase the ICE of full cells from 67.4 % to 87.9 %. Furthermore, a pouch cell utilizing the prelithiated P-Si@rGO@C anode paired with LiNi1/3Co1/3Mn1/3O2 (NCM111) cathode delivers a high initial reversible capacity of 7.2 mAh and 76.8 % capacity retention after 100 cycles. This work provides insights into the application of commercial silicon-aluminum alloy powder in the anode of high-energy LIBs.

A Rapid, Scalable Laser-Scribing Process to Prepare Si/Graphene Composites for Lithium-Ion Batteries

Silicon has gained significant attention as a lithium-ion battery anode material due to its high theoretical capacity compared to conventional graphite. Unfortunately, silicon anodes suffer from poor cycling performance caused by their extreme volume change during lithiation and de-lithiation. Compositing silicon particles with 2D carbon materials, such as graphene, can help mitigate this problem. However, an unaddressed challenge remains: a simple, inexpensive synthesis of Si/graphene composites. Here, a one-step laser-scribing method is proposed as a straightforward, rapid (≈3 min), scalable, and less-energy-consuming (≈5 W for a few minutes under air) process to prepare Si/laser-scribed graphene (LSG) composites. In this research, two types of Si particles, Si nanoparticles (SiNPs) and Si microparticles (SiMPs), are used. The rate performance is improved after laser scribing: SiNP/LSG retains 827.6 mAh g-1 at 2.0 A gSi+C -1, while SiNP/GO (before laser scribing) retains only 463.8 mAh g-1. This can be attributed to the fast ion transport within the well-exfoliated 3D graphene network formed by laser scribing. The cyclability is also improved: SiNP/LSG retains 88.3% capacity after 100 cycles at 2.0 A gSi+C -1, while SiNP/GO retains only 57.0%. The same trend is found for SiMPs: the SiMP/LSG shows better rate and cycling performance than SiMP/GO composites.

Scalable engineering of hierarchical layered micro-sized silicon/graphene hybrids via direct foaming for lithium storage

Low-cost micro-sized silicon is an attractive replacement for commercial graphite anodes in advanced lithium-ion batteries (LIBs) but suffers from particle fracture during cycling. Hybridizing micro-sized silicon with conductive carbon materials, especially graphene, is a practical approach to overcome the volume change issue. However, micro-sized silicon/graphene anodes prepared via the conventional technique encounter sluggish Li+ transport due to the lack of efficient electrolyte diffusion channels. Here, we present a facile and scalable method to establish efficient Li+ transport channels through direct foaming from the laminated graphene oxide/micro-sized silicon membrane followed by annealing. The conductive graphene layers and the Li+ transport channels endow the composite material with excellent electronic and ionic conductivity. Moreover, the interconnected graphene layers provide a robust framework for micro-sized silicon particles, allowing them to transform decently in the graphene layer space. Consequently, the prepared hybrid material, namely foamed graphene/micro-sized Si (f-G-Si), can work as a binder-free and free-standing anode without additives and deliver remarkable electrochemical performance. Compared with the control samples, micro-sized silicon wrapped by laminated graphene layers (G-Si) and commercial micro-sized Si, f-G-Si maximizes the utilization of silicon and demonstrates superior performance, disclosing the role of Li+ diffusion channels. This study sheds light on the rational design and manufacture of silicon anodes and beyond.

High-performance cellulose acetate-based gas barrier films via tailoring reduced graphene oxide nanosheets

Improving the gas molecule barrier performance and structural stability of bio-plastic films dramatically contribute to packaging and protective fields. Herein, we proposed a novel nanocomposite film consisting of cellulose acetate (CA)/polyethyleneimine (PEI)/reduced graphene oxide (rGO)-NiCoFeO_x) with high gas barrier property by applying "molecular glue" and "nano-patching" strategies. Systematical investigations demonstrated that the CA/rGO interfacial interaction was effectively enhanced due to the "molecular glue" role of PEI chains via physical/chemical bonds and the defective regions in rGO plane were nano-patched through hydrophilic interactions between edged oxygen-containing functional groups and ultrafine NiCoFeO_x nanoparticles (~3 nm). As a result, the oxygen and moisture transmission rates of the prepared CA/PEI/rGO-NPs hybrid film were significantly reduced to 0.31 cm³ ∗ μm/(m² ∗ d ∗ kPa) and 314.23 g/m² ∗ 24 h, respectively, which were 99.60% and 54.69% lower than pristine CA films. Meanwhile, the tensile strength of hybrid film was increased from 25.90 MPa to 40.67 MPa. More importantly, the designed nanocomposite film possesses excellent structural stability without obvious GO layer shedding and hydrophobicity attenuation after persistent bending at least 100 times. The exceptional robust and high gas barrier film displays great promising application in food, agriculture, pharmaceuticals and electronic instruments packaging industry.