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

Reduced graphene oxide-encaged submicron-silicon anode interfacially stabilized by Al2O3 nanoparticles for efficient lithium-ion batteries

Silicon-carbon composites have been recognized as some of the most promising anode candidates for advancing new-generation lithium-ion batteries (LIBs). The development of high-efficiency silicon/graphene anodes through a simple and cost-effective preparation route is significant. Herein, by using micron silicon as raw material, we designed a mesoporous composite of silicon/alumina/reduced graphene oxide (Si/Al2O3/RGO) via a two-step ball milling combined annealing process. Commercial Al2O3 nanoparticles are introduced as an interlayer due to the toughening effect, while RGO nanosheets serve as a conductive and elastic coating to protect active submicron silicon particles during lithium alloying/dealloying reactions. Owing to the rational porous structure and dual protection strategy, the core/shell structured Si/Al2O3/RGO composite is efficient for Li+ storage and demonstrates improved electrical conductivity, accelerated charge transfer and electrolyte diffusion, and especially high structural stability upon charge/discharge cycling. As a consequence, Si/Al2O3/RGO yields a high discharge capacity of 852 mA h g-1 under a current density of 500 mA g-1 even after 200 cycles, exhibiting a high capacity retention of ∼85%. Besides, Si/Al2O3/RGO achieves excellent cycling reversibility and superb high-rate capability with a stable specific capacity of 405 mA h g-1 at 3000 mA g-1. Results demonstrate that the Al2O3 interlayer is synergistic with the indispensable RGO nanosheet shells, affording more buffer space for silicon cores to alleviate the mechanical expansion and thus stabilizing active silicon species during charge/discharge cycles. This work provides an alternative low-cost approach to achieving high-capacity silicon/carbon composites for high-performance LIBs.

Novel Terahertz Spectroscopy Analysis for the Electrode with Carbon Nanotubes (CNTs) in Lithium-Ion Batteries

In this study, to use carbon nanotubes (CNTs) as a conductive material instead of carbon black in cathode electrodes, their dispersions were prepared in 1-Methyl-2-pyrrolidinone (NMP) solvent by using an ultrasonic horn, and their dispersion stability was analyzed using CNTs on the formation of the network between cathode electrode constituent materials comprised of cathode material, CNTs, and current collectors, and their correlation with electrochemical performance results were investigated using various analytical techniques. Particularly, in the analysis, terahertz time domain spectroscopy (THz-TDS), a new non-destructive analysis method, was used to analyze and compare the various optical properties of the cathode’s slurries that co-existed with CNTs and cathode material, suggesting the suitability of its analytical use in the field of materials dispersion and the slurry manufacturing process for lithium-ion batteries (LIBs). In the investigated results, the sample with the highest dispersion stability of CNTs uniformly formed the networks of CNTs and cathode material in the electrode, which results in the highest electrical conductivity among all samples, and as a result, the best performance in electrochemical evaluations.

Mechanical Stirring Synthesis of 1D Electrode Materials and Designing of Pyramid/Inverted Pyramid Interlocking for Highly Flexible and Foldable Li-Ion Batteries with High Mass Loading

Flexible and foldable Li-ion batteries (LIBs) are presently attracting immense research interest for their potential use in wearable electronics but are still limited to electrodes with very small mass loading, low bending/folding endurance, and poor electrochemical stability during repeated bending and folding movements. Moreover, one-dimensional (1D) structured electrode materials have shown excellent electrochemical performance but are still restricted by the high cost and complicated fabrication process. Here, we present a very simple yet novel approach for fabricating extra-long Li₄Ti₅O₁₂ (LTO) and LiCoO₂ (LCO) nanofiber precursors by directly stirring the reagents in an atmospheric vessel. In addition, we present multilayer pyramid/inverted pyramid interlocking inside the LTO and LCO nanofiber films as well as between films and current collectors, which can create strengthened interfacial bonding like a zipper and tangentially disperse the strains generated during folding through the pyramidal planes and edges, leading to the realization of thick-film electrodes with outstanding electrochemical stability during folding movements. The foldable LIBs that are assembled with LTO and LCO nanofiber electrodes at a practical level of mass loading (14.9-19.4 mg cm^-2) can maintain 102% of the initial capacity after 15 000 times of fully folding (180°) motions.

Facile and Efficient Fabrication of Branched Si@C Anode with Superior Electrochemical Performance in LIBs

One-dimensional Si nanostructures with carbon coating (1D Si@C) show great potential in lithium ion batteries (LIBs) due to small volume expansion and efficient electron transport. However, 1D Si@C anode with large area capacity still suffers from limited cycling stability. Herein, a novel branched Si architecture is fabricated through laser processing and dealloying. The branched Si, composed of both primary and interspaced secondary dendrites with diameters under 100 nm, leads to improved area capacity and cycling stability. By coating a carbon layer, the branched Si@C anode shows gravimetric capacity of 3059 mAh g^-1 (1.14 mAh cm^-2 ). At a higher rate of 3 C, the capacity is 813 mAh g^-1 , which retained 759 mAh g^-1 after 1000 cycles at 1 C. The area capacity is further improved to 1.93 mAh cm^-2 and remained over 92% after 100 cycles with a mass loading of 0.78 mg cm^-2 . Furthermore, the full-cell configuration exhibits energy density of 405 Wh kg^-1 and capacity retention of 91% after 200 cycles. The present study demonstrates that laser-produced dendritic microstructure plays a critical role in the fabrication of the branched Si and the proposed method provides new insights into the fabrication of Si nanostructures with facility and efficiency.

Multifunctional Batteries: Flexible, Transient, and Transparent

The primary task of a battery is to store energy and to power electronic devices. This has hardly changed over the years despite all the progress made in improving their electrochemical performance. In comparison to batteries, electronic devices are continuously equipped with new functions, and they also change their physical appearance, becoming flexible, rollable, stretchable, or maybe transparent or even transient or degradable. Mechanical flexibility makes them attractive for wearable electronics or for electronic paper; transparency is desired for transparent screens or smart windows, and degradability or transient properties have the potential to reduce electronic waste. For fully integrated and self-sufficient systems, these devices have to be powered by batteries with similar physical characteristics. To make the currently used rigid and heavy batteries flexible, transparent, and degradable, the whole battery architecture including active materials, current collectors, electrolyte/separator, and packaging has to be redesigned. This requires a fundamental paradigm change in battery research, moving away from exclusively addressing the electrochemical aspects toward an interdisciplinary approach involving chemists, materials scientists, and engineers. This Outlook provides an overview of the different activities in the field of flexible, transient, and transparent batteries with a focus on the challenges that have to be faced toward the development of such multifunctional energy storage devices.

In Situ Construction of High-Performing Compact Si-SiOx-CNx Composites from Polyaminosiloxane for Li-Ion Batteries

Great efforts have been made to design high-performing Si/C composite anodes for Li-ion batteries to improve their energy density and cycling life. However, challenges remain in achieving fast electrical conductivity while accommodating significant electrode volumetric changes. Here, we report a unique Si/C-based anode architecture, a Si-SiO_x-CN_x composite, which is simultaneously constructed via the pyrolysis of a polyaminosiloxane precursor. The obtained structure features high-purity Si nanocrystals embedded in an amorphous silica matrix and then embraced by N-doped carbon layers. Notably, in this structure, all three components derived from the polyaminosiloxane precursor are linked by chemical bonding, forming a compact Si-SiO_x-CN_x triple heterostructure. Because of the improvement in the volumetric efficiency for accommodating Si active materials and electrical properties, this anode design enables promising electrochemical performance, including excellent cycle performance (830 mAh g^-1 after 100 cycles at 0.1 A g^-1) and outstanding rate performance (400 mAh g^-1 at 5 A g^-1). Moreover, this composite anode demonstrates great potential for high-energy Li-ion batteries, where a Si-SiO_x-CN_x//LiNi_0.9Co_0.1O₂ full-cell shows a high capacity of 180 mAh g^-1 as well as stable cycle performance (150 mAh g^-1 after 200 cycles at 0.19 A g^-1).

Porous Si/Cu Anode with High Initial Coulombic Efficiency and Volumetric Capacity by Comprehensive Utilization of Laser Additive Manufacturing-Chemical Dealloying

Si has been extensively investigated as an anode material for lithium-ion batteries because of its superior theoretical capacity. However, a scalable fabrication method for a Si-based anode with high initial coulombic efficiency (ICE) and large volumetric capacity remains a critical challenge. Herein, we proposed a novel porous Si/Cu anode in which planar Si islands were embedded in the porous Cu matrix through combined laser additive manufacturing and chemical dealloying. The compositions and dimensions of the structure were controlled by metallurgical and chemical reactions during comprehensive interaction. Such a structure has the advantages of micro-sized Si and porous architecture. The planar Si islands decreased the surface area and thus increased ICE. The porous Cu matrix, which acted as both an adhesive-free binder and a conductive network, provided enough access for electrolyte and accommodated volume expansion. The anode structure was well maintained without observable mechanical damage after cycling, demonstrating the high structure stability and integrity. The porous Si/Cu anode showed a high ICE of 93.4% and an initial volumetric capacity of 2131 mAh cm^-3, which retained 1697 mAh cm^-3 after 100 cycles at 0.20 mA cm^-2. Furthermore, the full-cell configuration (porous Si/Cu //LiFePO₄) exhibited a high energy density of 464.9 Wh kg^-1 and a capacity retention of 84.2% after 100 cycles.

Three-Dimensional Hierarchical Porous Structures Constructed by Two-Stage MXene-Wrapped Si Nanoparticles for Li-Ion Batteries

As the demand for batteries increases with the development of electric vehicles, the energy density of lithium-ion batteries (LIBs) should be continuously enhanced. Due to the excellent theoretical specific capacity, silicon (Si) is the most promising anode material for LIBs. Nevertheless, the application of Si-based anodes is constrained by critical problems such as low conductivity and extreme volume change. Herein, we demonstrate an effective strategy for the fabrication of a three-dimensional (3D) hierarchical porous-structured Si-based anode with dual MXene protection (namely, SiNP@MX1/MX2). By electrostatic force induced self-assembly between modified Si with a positive charge and MXene nanosheets with a negative charge on the surface, Si nanoparticles are riveted to the MXene nanosheets (namely, SiNP@MX1), and then embedded into the 3D MXene skeleton (MX2) via a hydrothermal reaction and freeze-drying. Through the tailored and reasonable design, the internal MX1 coating can accommodate the volume expansion and avoid particle aggregation. The external MX2 allows for rapid electron transport and ion transfer while further buffering volume changes. Most importantly, by preventing Si from directly contacting the electrolyte, the double MXene-wrapped protection design benefits from the formation of a stable solid electrolyte interphase (SEI) film. The SiNP@MX1/MX2 anode material has a high capacity of 1422 mA h g^-1 at a current density of 0.5 A g^-1 after 200 cycles, excellent cycle stability, and good rate performance. At the same time, the method proposed in this study is expected to be applied to the preparation of other alloy anodes/MXene hybrids for storage batteries.

A novel silicon nanoparticles-infilled capsule prepared by an oil-in-water emulsion strategy for high-performance Li-ion battery anodes

Conventional approaches for preparing yolk-shell nanostructures require complicated procedures such as multi-step coatings and template removal. Herein, we present a new and general strategy for making yolk-shell nanocomposites based on an oil-in-water emulsion system. As a demonstrating case, silicon nanoparticles were dispersed in an oil phase which was in an oil-in-water emulsion; then the oil/water interface was in-situ polymerized to form microcapsules. After carbonization, the shell of microcapsules was formed. The Li-ion battery anodes based on the microcapsules exhibit a good electrochemical performance including stable capacity and high rate-performance. The capacity remains 1100 mAh g^-1 after 500 cycles at a current density of 1.9 A g^-1, along with a Coulombic efficiency of ≈ 99.9%. In addition, the method presented here is general, which is applicable for the synthesis of many yolk shell-structured nanocomposites.

Covalently Bonded Silicon/Carbon Nanocomposites as Cycle-Stable Anodes for Li-Ion Batteries

Carbon coating is a popular strategy to boost the cyclability of Si anodes for Li-ion batteries. However, most of the Si/C nanocomposite anodes fail to achieve stable cycling due to the easy separation and peeling off of the carbon layer from the Si surface during extended cycles. To overcome this problem, we develop a covalent modification strategy by chemically bonding a large conjugated polymer, poly-peri-naphthalene (PPN), on the surfaces of nano-Si particles through a mechanochemical method, followed by a carbonization reaction to convert the PPN polymer into carbon, thus forming a Si/C composite with a carbon coating layer tightly bonded on the Si surface. Due to the strong covalent bonding interaction of the Si surface with the PPN-derived carbon coating layer, the Si/C composite can keep its structural integrity and provide an effective surface protection during the fluctuating volume changes of the nano-Si cores. As a consequence, the thus-prepared Si/C composite anode demonstrates a reversible capacity of 1512.6 mA h g^-1, a stable cyclability over 500 cycles with a capacity retention of 74.2%, and a high cycling Coulombic efficiency of 99.5%, providing a novel insight for designing highly cyclable silicon anodes for new-generation Li-ion batteries.

Bio-inspired fabrication of Ester-functionalized imprinted composite membrane for rapid and high-efficient recovery of lithium ion from seawater

Lithium ion (Li⁺) is one of the important sustainable resource and it's urgently demanded to develop high-selectivity and high-efficient method to extract of Li⁺ from seawater. Hence, we propose the ester-functionalized ion-imprinted membrane (IIMs) with high selectivity and stability for the rebinding and separation of Li⁺ in aqueous medium via ion imprinted technology and membrane separation technology. In this work, the hydrophilic polydimethylsiloxane membranes (PDMS) are synthesized by self-polymerization of dopamine (DA) in aqueous solution, resulting in the fabrication of dense poly-dopamine (PDA) layer on the surface of PDMS (PDMS-PDA). In view of weak bonding forces (such as hydrogen bond, ionic bond and Van der Waals' force) between traditional imprinted polymer and ligand, the ester groups are formed between modified PDMS-PDA and ligand by surface grafting. The obtained Li⁺ imprinted membranes (Li-IIMs) have a suitable cavity and high adsorption capacity toward Li⁺ which reveal a high rebinding capacity (50.872 mg g^-1) toward Li⁺ based on ample rebinding sites and strong affinity force. The superior relative selectivity coefficients (α_Na/Li, α_K/Li and α_Rb/Li are 1.71, 4.56 and 3.80, respectively) can be also achieved. The selectivity factors of Li-IIMs for Na⁺, K⁺ and Rb⁺ are estimated to be 2.52, 2.8 and 3.03 times larger than Li⁺ non-imprinted membranes (Li-NIMs), which imply the superior selectivity of Li-IIMs toward Li⁺. The regeneration ability of Li-IIMs is observed by systematic batch experiments. In summary, it can be concluded that the rebinding capacities of Li-IIMs is slightly decrease after eluting process, owing to the Li-IIMs with outstanding stability performance. Presentation of the method pave a fine prospect for coming true the long-term use of imprinted membrane.

Ultrahigh and Durable Volumetric Lithium/Sodium Storage Enabled by a Highly Dense Graphene-Encapsulated Nitrogen-Doped Carbon@Sn Compact Monolith

Tin-based composites hold promise as anodes for high-capacity lithium/sodium-ion batteries (LIBs/SIBs); however, it is necessary to use carbon coated nanosized tin to solve the issues related to large volume changes during electrochemical cycling, thus leading to the low volumetric capacity for tin-based composites due to their low packing density. Herein, we design a highly dense graphene-encapsulated nitrogen-doped carbon@Sn (HD N-C@Sn/G) compact monolith with Sn nanoparticles double-encapsulated by N-C and graphene, which exhibits a high density of 2.6 g cm^-3 and a high conductivity of 212 S m^-1. The as-obtained HD N-C@Sn/G monolith anode exhibits ultrahigh and durable volumetric lithium/sodium storage. Specifically, it delivers a high volumetric capacity of 2692 mAh cm^-3 after 100 cycles at 0.1 A g^-1 and an ultralong cycling stability exceeding 1500 cycles at 1.0 A g^-1 with only 0.019% capacity decay per cycle in lithium-ion batteries. Besides, in situ TEM and ex situ SEM have revealed that the unique double-encapsulated structure effectively mitigates drastic volume variation of the tin nanoparticles during electrode cycling. Furthermore, the full cell using HD N-C@Sn/G as an anode and LiCoO₂ as a cathode displays a superior cycling stability. This work provides a new avenue and deep insight into the design of high-volumetric-capacity alloy-based anodes with ultralong cycle life.

CNT-Intertwined Polymer Electrode toward the Practical Application of Wearable Devices

One of the greatest challenges for wearable electronics is the lack of virtually flexible electrodes with satisfactory electrochemical performance, and there is always a "softness vs effective capacity" dilemma. Herein, a polymer electrode is proposed. The carefully chosen and partially conjugated polyimide realizes the dual function of a flexible agent and an active agent. The softness of the electrode is rendered by the polymer, while the carbon nanotube ensures electron transfer (ET) within the polymer. A modified electrospinning method has been used in the preparation of a carbon nanotube (CNT)-intertwined polyimide (PI) film. The binder-free and current collector-free polymer electrode has as high as 80% active phase and releases near-theoretical capacity accompanied by very stable cycling up to 200 cycles. Owing to the dual role of the polymer component, the softness vs effective capacity dilemma has been well addressed. Aiming at the practical application, a fatigue test has been first conducted in a practical mode and the well-reserved electrochemical activity under extreme stress change as well as in plenty of electrolyte has been revealed. The work realizes that the flexible electrode well fulfills the requirement and sheds more light on the application of the polymer electrode materials.

New insights into Li diffusion in Li-Si alloys for Si anode materials: role of Si microstructures

Li ion transport is very important to the rate capability of electrode materials in Li ion batteries. For Si anodes, due to huge structural changes of Si structures during the process of charging and discharging, Li ion transport is essentially affected by the Si internal microstructures. Herein, we studied the effect of Si microstructures on Li ion diffusion in Li-Si alloys using first-principles molecular dynamics calculations. Our results demonstrate that the Li diffusion coefficients are closely related to the aggregation degree of Si atoms, regardless of whether it is the low Li concentration phase LiSi or the high Li concentration phase Li₂Si under consideration. Furthermore, through counting the number of Si microstructures, such as rings, chains and small clusters, the relationship between the aggregation degree of Si atoms and the number of Si microstructures is established. A large number of Si microstructures corresponds to the low aggregation degree of Si atoms, thus resulting in small Li diffusion coefficients due to the strong interaction between Li and Si atoms. Conversely, a small number of Si microstructures originates from the high aggregation degree of Si atoms, consequently leading to large Li diffusion coefficients. Our study provides a deep insight into the relationship between the Li ion diffusion and the Si distribution, which facilitates the performance improvement of future Si anode materials.

Green Synthesis of Dual Carbon Conductive Network-Encapsulated Hollow SiO x Spheres for Superior Lithium-Ion Batteries

Designing hollow/porous structure is regarded as an effective approach to address the dramatic volumetric variation issue for Si-based anode materials in Li-ion batteries (LIBs). Pioneer studies mainly focused on acid/alkali etching to create hollow/porous structures, which are, however, highly corrosive and may lead to a complicated synthetic process. In this paper, a dual carbon conductive network-encapsulated hollow SiO _x (DC-HSiO _x) is fabricated through a green route, where polyacrylic acid is adopted as an eco-friendly soft template. Low electrical resistance and integrated electrode structure can be maintained during cycles because of the dual carbon conductive networks distributed both on the surface of single particles formed by amorphous carbon and among particles constructed by reduced graphene oxide. Importantly, the hollow space is reserved within SiO _x spheres to accommodate the huge volumetric variation and shorten the transport pathway of Li⁺ ions. As a result, the DC-HSiO _x composite delivers a large reversible capacity of 1113 mA h g^-1 at 0.1 A g^-1, an excellent cycling performance up to 300 cycles with a capacity retention of 92.5% at 0.5 A g^-1, and a good rate capability. Furthermore, the DC-HSiO _x//LiNi_0.8Co_0.1Mn_0.1O₂ full cell exhibits high energy density (419 W h kg^-1) and superior cycling performance. These results render an opportunity for the unique DC-HSiO _x composite as a potential anode material for use in high-performance LIBs.