Self-assembly silicon/porous reduced graphene oxide composite film as a binder-free and flexible anode for lithium-ion batteries

Investigation of Fast-Charging and Degradation Processes in 3D Silicon-Graphite Anodes

The 3D battery concept applied on silicon-graphite electrodes (Si/C) has revealed a significant improvement of battery performances, including high-rate capability, cycle stability, and cell lifetime. 3D architectures provide free spaces for volume expansion as well as additional lithium diffusion pathways into the electrodes. Therefore, the cell degradation induced by the volume change of silicon as active material can be significantly reduced, and the high-rate capability can be achieved. In order to better understand the impact of 3D electrode architectures on rate capability and degradation process of the thick film silicon-graphite electrodes, we applied laser-induced breakdown spectroscopy (LIBS). A calibration curve was established that enables the quantitative determination of the elemental concentrations in the electrodes. The structured silicon-graphite electrode, which was lithiated by 1C, revealed a homogeneous lithium distribution within the entire electrode. In contrast, a lithium concentration gradient was observed on the unstructured electrode. The lithium concentration was reduced gradually from the top to the button of the electrode, which indicated an inhibited diffusion kinetic at high C-rates. In addition, the LIBS applied on a model electrode with micropillars revealed that the lithium-ions principally diffused along the contour of laser-generated structures into the electrodes at elevated C-rates. The rate capability and electrochemical degradation observed in lithium-ion cells can be correlated to lithium concentration profiles in the electrodes measured by LIBS.

Graphene-Based Nanomaterials for Flexible and Stretchable Batteries

Recently, as flexible and wearable electronic devices have become widely popular, research on light weight and large-capacity batteries suitable for powering such devices has been actively conducted. In particular, graphene has attracted considerable attention from researchers in the battery field owing to its good mechanical properties and its applicability in various processes to fabricate electrodes for batteries. Graphene is classified into two types: flake-type, fabricated from graphite, and film-type, synthesized using chemical vapor deposition. The unique processes involved in these two types enable the fabrication of flexible and stretchable batteries with various shapes and functions. In this article, the recent progress in the development of flexible and stretchable batteries based on graphene, as well as its important technical issues are reviewed.

In Situ Formed Weave Cage-Like Nanostructure Wrapped Mesoporous Micron Silicon Anode for Enhanced Stable Lithium-Ion Battery

The low-cost and high-capacity micron silicon is identified as the suitable anode material for high-performance lithium-ion batteries (LIBs). However, the particle fracture and severe capacity fading during electrochemical cycling greatly impede the practical application of LIBs. Herein, we first proposed an in situ reduction and template assembly strategy to attain a weave cage-like carbon nanostructure, composed of short carbon nanotubes and small graphene flakes, as a flexible nanotemplate that closely wrapped micron-sized mesoporous silicon (PSi) to form a robust composite construction. The in situ formed weave cage-like carbon nanostructure can remarkably improve the electrochemical property and structural stability of micron-sized PSi during deep galvanostatic cycling and high electric current density owing to multiple attractive advantages. As a result, the rechargeable LIB applying this anode material exhibits improved initial Coulombic efficiency (ICE), excellent rate performance, and cyclic stability in the existing micron-sized PSi/nanocarbon system. Moreover, this anode reached an approximation of 100% ICE after only three cycles and maintains this level in subsequent cycles. This design of flexible nanotemplated platform wrapped micron-sized PSi anode provides a steerable nanoengineering strategy toward conquering the challenge of long-term reliable LIB application.

Facile Fabrication of High-Performance Si/C Anode Materials via AlCl3-Assisted Magnesiothermic Reduction of Phenyl-Rich Polyhedral Silsesquioxanes

Si/C composites, combining the advantages of both carbon materials and Si materials, have been proposed as the promising material in lithium-ion storage. However, up to now, the most common fabrication methods of Si/C composites are too complicated for practical application. Here, we first use phenyl-substituted cagelike polyhedral silsesquioxane (T_n-Ph, n = 8, 12) as both carbon and silicon precursors to prepare the high-performance Si/C anode materials via a low-temperature and simple AlCl₃-assisted magnesiothermic reduction. AlCl₃ plays two roles in the reduction process, on the one hand, it acts as liquid medium to promote the reduction of siloxane core in such a mild condition (200 °C), and on the other hand, it act as catalyst for phenyl groups polycondensation into carbon materials, which makes the procedure of fabrication feasible and controllable. Impressively, T₁₂-Si/C exhibits an excellent lithium anodic performance with a reversible capacity of 1449.2 mA h g^-1 with a low volume expansion of 16.3% after 100 cycles. Such superior electrochemical performance makes the Si/C composites alternative anode materials for lithium-ion batteries.

Engineering of a bowl-like Si@rGO architecture for an improved lithium ion battery via a synergistic effect

In this work we propose a facile template-sacrificing method to prepare bowl-like silicon@reduced graphene oxide (Si@rGO) hybrids as a high-performance anode for lithium ion batteries (LIBs). Uniform SiO₂ spheres were initially synthesized and wrapped by GO, forming a three-dimensional (3D) skeleton. After reduction and etching, Si nanoparticles were obtained and evenly distributed on the flexible rGO layer, resulting in a bowl-like nanoarchitecture. A benefit of this novel structure is that the volume change of Si can be confined during the charge-discharge process. As a result, the Si@rGO anode exhibited a high first discharge capacity of ∼1890 mAh  g^-1 with a Coulombic efficiency of 90.79% at a current density of 0.1 A  g^-1. After 100 cycles, a stable specific capacity of 450 mAh  g^-1 was achieved, which is twice that of pure Si nanospheres (208 mAh  g^-1) and rGO (260 mAh  g^-1). Moreover, when the current density increased to 1 A g^-1, the specific capacity of Si@rGO was 100 mAh  g^-1, whereas it was 34 mAh  g^-1 for Si nanospheres, demonstrating the advantage of Si@rGO. By analyzing the electrochemical behavior, it is found that the outstanding LIB performance of Si@rGO can be ascribed to the involvement of rGO which constructs the 3D nanoarchitecture that acts as a buffer layer to stabilize the Si and promotes Li⁺ diffusion as well as the conductivity of the electrodes. This work highlights the significance of the microstructure for lithium ion storage performance of Si-based nanocomposites.

Silicon Nanoparticles Embedded in N-Doped Few-Layered Graphene: Facile Synthesis and Application as an Effective Anode for Lithium Ion Batteries

A fast one-step arc discharge exfoliation method is employed to synthesize Si/graphene composites by using a graphite rod filled with a mixture of Si powder and urea as a cathode. During the arc discharge process, the use of urea allows both the introduction of nitrogen atoms into the graphene and the uniform sealing of Si nanoparticles between the thin graphene sheets to occur simultaneously. The resulting N-doped graphene nanosheets embedded with Si (Si@NG) can act as an electrode material for lithium-ion batteries and delivers the reversible capacity of 1030 mAh g^-1 with a current density of 200 mA g^-1 over 100 cycles along with an outstanding coulombic efficiency of 96.84 %. The remarkable electrochemical rate capability performance can be owed to the multiple role of NG, which not only serves as a three-dimensional conductive support, but also effectively limits the volume variation of Si nanoparticles. The approach proposed here is expected to be extended to the preparation of other alloy anode/graphene hybrids for lithium ion batteries.

Dual Carbonaceous Materials Synergetic Protection Silicon as a High-Performance Free-Standing Anode for Lithium-Ion Battery

Silicon is the one of the most promising anode material alternatives for next-generation lithium-ion batteries. However, the low electronic conductivity, unstable formation of solid electrolyte interphase, and the extremely high volume expansion (up to 300%) which results in pulverization of Si and rapid fading of its capacity have been identified as primary reasons for hindering its application. In this work, we put forward to introduce dual carbonaceous materials synergetic protection to overcome the drawbacks of the silicon anode. The silicon nanoparticle was coated by pyrolysed carbon, and meanwhile anchored on the surface of reduced graphene oxide, to form a self-standing film composite (C@Si/rGO). The C@Si/rGO film electrode displays high flexibility and an ordered porous structure, which could not only buffer the Si nanoparticle expansion during lithiation/delithiation processes, but also provides the channels for fast electron transfer and lithium ion transport. Therefore, the self-standing C@Si/rGO film electrode shows a high reversible capacity of 1002 mAh g-1 over 100 cycles and exhibits much better rate capability, validating it as a promising anode for constructing high performance lithium-ion batteries.

Simultaneous Encapsulation of Nano-Si in Redox Assembled rGO Film as Binder-Free Anode for Flexible/Bendable Lithium-Ion Batteries

The emerging ubiquitous flexible/wearable electronics are in high demand for compatible flexible/high-energy rechargeable batteries, which set a collaborative goal to promote the electrochemical performance and the mechanical strength of the fundamental flexible electrodes involved. Herein, freestanding flexible electrode of Si/graphene films is proposed, which is fabricated through a scalable, zinc-driven redox layer-by-layer assembly process. In the hybrid films, silicon nanoparticles are intimately encapsulated and confined in multilayered reduced graphene oxide (rGO) nanosheet films. The designed monolithic rGO/Si film possesses several structural benefits such as high mechanical integrity and three-dimensional conductive framework for accessible charge transport and Li⁺ diffusion upon cycling. When adopted as binder-free electrode in half-cells, the optimized hybrid rGO/Si film delivers high gravimetric capacity (981 mA h g^-1 at 200 mA g^-1 with respect to the total weight of the electrode) and exceptional cycling stability (0.057% decay per cycle over 1000 cycles at 1000 mA g^-1). Besides, the binder-free rGO/Si film anode is further combined with a commercial LiCoO₂ foil cathode for completely flexible full cell/battery, which exhibits excellent cycling performance and a high capacity retention of over 95% after 30 cycles under continuous bending. This solution-processable, elaborately engineered, and robust Si/graphene films will further harness the potential of silicon-carbon composites for advanced flexible/wearable energy storage.

Si nanoparticles embedded in 3D carbon framework constructed by sulfur-doped carbon fibers and graphene for anode in lithium-ion battery

3D conductive network constructed with sulfur doped nanofibers and graphene that co-enhance the lithium storage property of the Si anode.

In situ mass change and gas analysis of 3D manganese oxide/graphene aerogel for supercapacitors

Manganese oxide nanoparticles decorated on 3D reduced graphene oxide aerogels (3D MnO_x/rGO_ae) for neutral electrochemical capacitors were successfully produced by a rapid microwave reduction process within 20 s.

Graphene Oxides Used as a New "Dual Role" Binder for Stabilizing Silicon Nanoparticles in Lithium-Ion Battery

For the first time, we report that graphene oxide (GO) can be used as a new "dual-role" binder for Si nanoparticles (SiNPs)-based lithium-ion batteries (LIBs). GO not only provides a graphene-like porous 3D framework for accommodating the volume changes of SiNPs during charging/discharging cycles, but also acts as a polymer-like binder that forms strong chemical bonds with SiNPs through its Si-OH functional groups to trap and stabilize SiNPs inside the electrode. Leveraging this unique dual-role of GO binder, we fabricated GO/SiNPs electrodes with remarkably improved performances as compared to using the conventional polyvinylidene fluoride (PVDF) binder. Specifically, the GO/SiNPs electrode showed a specific capacity of 2400 mA h g^-1 at the 50th cycle and 2000 mA h g^-1 at the 100th cycle, whereas the SiNPs/PVDF electrode only showed 456 mAh g^-1 at the 50th cycle and 100 mAh g^-1 at 100th cycle. Moreover, the GO/SiNPs film maintained its structural integrity and formed a stable solid-electrolyte interphase (SEI) film after 100 cycles. These results, combined with the well-established facile synthesis of GO, indicate that GO can be an excellent binder for developing high performance Si-based LIBs.

Confined silicon nanospheres by biomass lignin for stable lithium ion battery

Biomass lignin, as a significant renewable resource, is one of the most abundant natural polymers in the world. Here, we report a novel silicon-based material, in which lignin-derived functional conformal network crosslinks the silicon nanoparticles via self-assembly. This newly-developed material could greatly solve the problems of large volume change during lithiation/delithiation process and the formation of unstable solid electrolyte interphase layers on the silicon surface. With this anode, the battery demonstrates a high capacity of ∼3000 mA h g^-1, a highly stable cycling retention (∼89% after 100 cycles at 300 mA g^-1) and an excellent rate capability (∼800 mA h g^-1 at 9 A g^-1). Moreover, the feasibility of full lithium-ion batteries with the novel silicon-based material would provide wide range of applications in the field of flexible energy storage systems for wearable electronic devices.

Fabrication of a Nondegradable Si@SiO x /n-Carbon Crystallite Composite Anode for Lithium-Ion Batteries

A Si-based anode maintaining its high electrochemical performance with cycles was prepared for the nondegradable lithium-ion battery. Nanoscaled Si particles were mechanochemically coupled with approximately 3 nm thick oxide layer and n-carbon (nanoscaled carbon) crystallites to overcome silicon's inherent problems of poor electronic conductivity and severe volume change during lithiation and delithiation cycling. The oxide layer of SiO _x was chemically formed via a controlled oxygen environment during the process; meanwhile, the n-carbon crystallites were obtained by mechanical fragmentation from ∼70 μm sized multilayered graphene powders with a low degree of agglomeration. The Si-based composite anode, processed by the above-mentioned mechanochemical coupling, maintained a superior discharge capacity of 1767 mA h/g through 100 cycles with a Coulombic efficiency exceeding 98% at a current density of 100 mA/g. According to our current study, the coupling of the Si particles with oxide layer and n-carbon crystallites was found to be a significantly efficient way to prevent the performance degradation of the Si-based anode.

An in situ iodine-doped graphene/silicon composite paper as a highly conductive and self-supporting electrode for lithium-ion batteries

A highly conductive, highly flexible, self-supporting, and binder-free rGO/Si composite paper with superior electrochemical performance was obtainedvia in situiodine doping and used as electrodes for flexible LIBs.

Structure-preserved 3D porous silicon/reduced graphene oxide materials as anodes for Li-ion batteries

3D porous networks are subject to be destroyed during electrode preparation. Structure-preserved 3D porous Si/rGO anode materials were synthesized by tuning pore size distribution and performed superior electrochemical properties.

Silicon-Reduced Graphene Oxide Self-Standing Composites Suitable as Binder-Free Anodes for Lithium-Ion Batteries

Silicon-reduced graphene oxide (Si-rGO) composites processed as self-standing aerogels (0.2 g cm^-3) and films (1.5 g cm^-3) have been prepared by the thermal reduction of composites formed between silicon nanoparticles and a suspension of graphene oxide (GO) in ethanol. The characterization of the samples by different techniques (X-ray diffraction, Raman, thermogravimetric analysis, and scanning electron microscopy) show that in both cases the composites are formed by rGO sheets homogeneously decorated with 50 nm silicon nanoparticles with silicon contents of ∼40% wt. The performances of these self-standing materials were tested as binder-free anodes in lithium-ion batteries (LIBs) in a half cell configuration under two different galvanostatic charge-discharge cutoff voltages (75 and 50 mV). The results show that the formation of a solid electrolyte interphase (SEI) is favored in composites processed as aerogels due to its large exposed surface, which prevents the activation of silicon when they are cycled within the 2 to 0.075 V voltage windows. It is also found that the composites processed in the form of self-standing films exhibit good stability over the first 100 cycles, high reversible specific capacity per mass of electrode (∼750 mAh g^-1), areal capacities that reach 0.7 mAh cm^-2, and high Coulombic efficiencies (80% for the first charge-discharge cycle and over 99% in the subsequent cycles).

One-Step Formation of Silicon-Graphene Composites from Silicon Sludge Waste and Graphene Oxide via Aerosol Process for Lithium Ion Batteries

Over 40% of high-purity silicon (Si) is consumed as sludge waste consisting of Si, silicon carbide (SiC) particles and metal impurities from the fragments of cutting wire mixed in ethylene glycol based cutting fluid during Si wafer slicing in semiconductor fabrication. Recovery of Si from the waste Si sludge has been a great concern because Si particles are promising high-capacity anode materials for Li ion batteries. In this study, we report a novel one-step aerosol process that not only extracts Si particles but also generates Si-graphene (GR) composites from the colloidal mixture of waste Si sludge and graphene oxide (GO) at the same time by ultrasonic atomization-assisted spray pyrolysis. This process supports many advantages such as eco-friendly, low-energy, rapid, and simple method for forming Si-GR composite. The morphology of the as-formed Si-GR composites looked like a crumpled paper ball and the average size of the composites varied from 0.6 to 0.8 μm with variation of the process variables. The electrochemical performance was then conducted with the Si-GR composites for Lithium Ion Batteries (LIBs). The Si-GR composites exhibited very high performance as Li ion battery anodes in terms of capacity, cycling stability, and Coulombic efficiency.

Integrated reduced graphene oxide multilayer/Li composite anode for rechargeable lithium metal batteries

The rGO/Li composite electrode is constructed by combining rGO film with Li metal. The interconnected rGO layers not only help to suppress the formation of dendritic Li, but also store the dead Li and restrain the uneven surface potential.

A self-assembled Si/SWNT 3D-composite-nanonetwork as a high-performance lithium ion battery anode

A Si/SWNT 3D-composite-nanonetwork integrated anode for high-performance lithium storage, through a combined process of electrostatic induced self-assembly and film transfer.