Sequence-Defined Peptoids with -OH and -COOH Groups As Binders to Reduce Cracks of Si Nanoparticles of Lithium-Ion Batteries

Nanostructured Porous Polymer with Low Volume Expansion, Structural Distortion, and Gradual Activation for High and Durable Lithium Storage

Organic compounds exhibit great potential as sustainable, tailorable, and environmentally friendly electrode materials for rechargeable batteries. However, the intrinsic defects of organic electrodes, including solubility, low ionic conductivity, and restricted electroactivity sites, will inevitably decrease the cycling life and capacity. We herein designed and prepared nanostructured porous polymers (NPP) with a simple one-pot method to overcome the above defects. Theoretical calculations and experimental results demonstrate that the as-synthesized NPP exhibited low volume expansion, molecular-structural distortion, and a gradual function activation process during cycling, thus exhibiting superior, high, and durable lithium storage. The gradual molecular distortion during the lithium storage processes provides more redox-active sites for Li storage, increasing the Li-storage capacity. Ex situ spectrum studies reveal the redox reaction mechanism of Li storage and demonstrate a gradual activation process during the repeated charging/discharging until the full storage of 18 Li ions is achieved. Additionally, a real-time observation on the NPP anode by in situ transmission electron microscope reveals a slight volume expansion during the repeating lithiation and delithiation processes, ensuring its structural integrity during cycling. This quantitative work for high-durability lithium storage could be of immediate benefit for designing organic electrode materials.

Constructing practical micron silicon anodes via a homogeneous and robust network binder induced by a strong-affinity inorganic oligomer

Designing robust binders has been demonstrated to be an effective and facile strategy to stabilize Si anodes. However, the binders that performed well for Si nanoparticles are not applicable for low-cost and accessible Si micron-powders. Hence, a novel binder design strategy is still greatly required for practical micron-Si anodes. Herein, a robust water-based network binder (named as c-PTP-Alg) has been designed via coupling potassium tripolyphosphate (PTP) inorganic oligomer with alginic acid (Alg) organic macromolecule. Owing to the unique structure of PTP, a network with high mechanical resistance can be constructed in c-PTP-Alg binder via strong ion-dipole interactions. Moreover, the highly soluble and dispersed PTP inorganic oligomer in water prevents the organic macromolecule from aggregation. This induces a homogeneous texture in the c-PTP-Alg binder, which enables the polar groups in the composite binder to anchor micron-Si particles efficiently. Therefore, by simply applying the c-PTP-Alg binder, a significantly improved electrochemical performance of micron-Si anode with a high reversible capacity of 1599.9 mAh g^-1 after 100 cycles at 3000 mA g^-1 has been obtained. More specially, the high-energy-density Si||S-PAN full cells have also been constructed, showing the practical application prospect of the c-PTP-Alg binder.

An Energy Dissipative Binder for Self-Tuning Silicon Anodes in Lithium-Ion Batteries

The volume change of the silicon anode seriously affects the electrode integrity and cycle stability. Herein, a binder, GCA13, with energy dissipation function and surface stability effect is proposed to enhance the cycle life and specific capacity. Unlike traditional binders that protect silicon electrodes through long-chain networks, GCA13 introduces citric acid molecules with short-range functions on the long-chain guar gum through weak interconnection. This short-range action is similar to the function of a spring, which can effectively buffer the silicon particle pulverization caused by the volume change. Therefore, the electrode can effectively maintain structural integration with ignorable cracks and alleviated thickness swelling. Thus, the Si@GCA13 anode exhibits a high reversible capacity of 1184 mAh g^-1 under 2 A g^-1 after 740 cycles with a latter coulombic efficiency of 99.9%. Extraordinarily, benefiting from the superior properties of the GCA13 binder, the electrode shows remarkable cycling stability under low (-15 and 0 °C) and high temperatures (60 °C). The work demonstrates the great potential of this binder design strategy to achieve the overall property promotion of Si anodes for practical application even under harsh service conditions.

Hierarchical Materials from High Information Content Macromolecular Building Blocks: Construction, Dynamic Interventions, and Prediction

Hierarchical materials that exhibit order over multiple length scales are ubiquitous in nature. Because hierarchy gives rise to unique properties and functions, many have sought inspiration from nature when designing and fabricating hierarchical matter. More and more, however, nature's own high-information content building blocks, proteins, peptides, and peptidomimetics, are being coopted to build hierarchy because the information that determines structure, function, and interfacial interactions can be readily encoded in these versatile macromolecules. Here, we take stock of recent progress in the rational design and characterization of hierarchical materials produced from high-information content blocks with a focus on stimuli-responsive and "smart" architectures. We also review advances in the use of computational simulations and data-driven predictions to shed light on how the side chain chemistry and conformational flexibility of macromolecular blocks drive the emergence of order and the acquisition of hierarchy and also on how ionic, solvent, and surface effects influence the outcomes of assembly. Continued progress in the above areas will ultimately usher in an era where an understanding of designed interactions, surface effects, and solution conditions can be harnessed to achieve predictive materials synthesis across scale and drive emergent phenomena in the self-assembly and reconfiguration of high-information content building blocks.

Effect of Oxygen Plasma Pre-Treatment on the Surface Properties of Si-Modified Cotton Membranes for Oil/Water Separations

Hydrophobic and oleophilic Si-based cotton fabrics have recently gained a lot of attention in oil/water separation due to their high efficiency. In this study, we present the effect of O₂ plasma pre-treatment on the final properties of two Si-based cotton membranes obtained from dip coating and plasma polymerization, using polydimethylsiloxane (PDMS) as starting polymeric precursor. The structural characterizations indicate the presence of Si bond on both the modified cotton surfaces, with an increase of the carbon bond, assuring the success in surface modification. On the other hand, employing O₂ plasma strongly changes the cotton morphology, inducing specific roughness and affecting the hydrophobicity durability and separation efficiency. In particular, the wettability has been retained after 20 laundry tests at 40 °C and 80 °C, and, for separation efficiency, even after 30 cycles, an improvement in the range of 10-15%, both at room temperature and at 90 °C can be observed. These results clearly demonstrate that O₂ plasma pre-treatment, an eco-friendly, non-toxic, solvent-free, and one-step method for inducing specific functionalities on surfaces, is very effective in enhancing the oil/water separation properties for Si-based cotton membranes, especially in combination with plasma polymerization procedure for Si-based deposition.

Radical-Scavenging Activatable and Robust Polymeric Binder Based on Poly(acrylic acid) Cross-Linked with Tannic Acid for Silicon Anode of Lithium Storage System

The design of a novel binder is required for high-capacity silicon anodes, which typically undergo significant changes during charge/discharge cycling. Hence, in this study, a stable network structure was formed by combining tannic acid (TAc), which can be cross-linked, and poly(acrylic acid)(PAA) as an effective binder for a silicon (Si) anode. TAc is a phenolic compound and representative substance with antioxidant properties. Owing to the antioxidant ability of the C-PAA/TAc binder, side reactions during the cycling were suppressed during the formation of an appropriate solid-electrolyte interface layer. The results showed that the expansion of a silicon anode was suppressed compared with that of a conventional PAA binder. This study demonstrates that cross-linking and antioxidant capability facilitate binding and provides insights into the behavior of binders for silicon anodes. The Si anode with the C-PAA/TAc binder exhibited significantly improved cycle stability and higher Coulombic efficiency in comparison to the Si anode with well-established PAA binders. The C-PAA/TAc binder demonstrated a capacity of 1833 mA h g^-1_Si for 100 cycles, which is higher than that of electrodes fabricated using the conventional PAA binder. Therefore, the C-PAA/TAc binder offers better electrochemical performance.

Cross-Linked γ-Polyglutamic Acid as an Aqueous SiOx Anode Binder for Long-Term Lithium-Ion Batteries

Silicon oxide (SiO_x) has outstanding capacity and stable lithium-ion uptake/removal electrochemistry as a lithium-ion anode material; however, its practical massive commercialization is encumbered by unavoidable challenges, such as dynamic volume changes during cycling and inherently inferior ionic conductivities. Recent literature has offered a consensus that binders play a critical role in affecting the electrochemical performance of Si-based electrodes. Herein, we report an aqueous binder, γ-polyglutamic acid cross-linked by epichlorohydrin (PGA-ECH), that guarantees enhanced properties for SiO_x anodes to implement long-term cycling stability. The abundant amide, carboxyl, and hydroxyl groups in the binder structure form strong interactions with the SiO_x surface, which contribute strong interfacial adhesion. The robust covalent interactions and strong supramolecular interactions in the binder ensure mechanical strength and elasticity. Additionally, the interactions between lithium ions and oxygen (nitrogen) atoms of carboxylate (peptide) bonds, which serve as a Lewis base, facilitate the diffusion of lithium ions. A SiO_x anode using this PGA-ECH binder exhibits an impressive initial discharge capacity of 1962 mA h g^-1 and maintains a high capacity of 900 mA h g^-1 after 500 cycles at 500 mA g^-1. Meanwhile, the assembled SiO_x||LiNi_0.6Co_0.2MnO_0.2 full cell shows a reversible capacity of 155 mA g^-1 and displays 73% capacity retention after 100 cycles.

High-Performance Microsized Si Anodes for Lithium-Ion Batteries: Insights into the Polymer Configuration Conversion Mechanism

Microsized silicon particles are desirable Si anodes because of their low price and abundant sources. However, it is challenging to achieve stable electrochemical performances using a traditional microsized silicon anode due to the poor electrical conductivity, serious volume expansion, and unstable solid electrolyte interface. Herein, a composite microsized Si anode is designed and synthesized by constructing a unique polymer, poly(hexaazatrinaphthalene) (PHATN), at a Si/C surface (PCSi). The Li⁺ transport mechanism of the PCSi is elucidated by using in situ characterization and theoretical simulation. During the lithiation of the PCSi anode, CN groups with high electron density in the PHATN first coordinate Li⁺ to form CNLi bonds on both sides of the PHATN molecule plane. Consequently, the original benzene rings in the PHATN become active centers to accept lithium and form stable Li-rich PHATN coatings. PHATN molecules expand due to the change of molecular configuration during the consecutive lithiation process, which provides controllable space for the volume expansion of the Si particles. The PCSi composite anode exhibits a specific capacity of 1129.6 mAh g^-1 after 500 cycles at 1 A g^-1 , and exhibits compelling rate performance, maintaining 417.9 mAh g^-1 at 16.5 A g^-1 .

In Situ Construction of a Multifunctional Interface Regulator with Amino-Modified Conjugated Diene toward High-Rate and Long-Cycle Silicon Anodes

Silicon (Si) is deemed to be the next-generation lithium-ion battery anode. However, on account of the poor electronic conductivity of Si materials and the instability of the solid electrolyte interphase layer, the electrochemical performance of Si anodes is far from reaching the application level. In this work, a multifunctional poly(propargylamine) (PPA) interlayer is constructed on the Si surface via a simple in situ polymerization method. Benefiting from the electronic conductivity, ionic conductivity, robust interphase interactions for hydrogen bonding, and stability of multifunctional PPA, the optimized Si@PPA-7% electrode shows improved lithium storage capability. A high capacity of 1316.3 mAh g^-1 is retained after 500 cycles at 2.1 A g^-1, and 2370.3 mAh g^-1 can be delivered at 42 A g^-1, which are in stark contrast to the unmodified Si electrode. Furthermore, the rate and cycle capabilities of the LiFePO₄//Si@PPA-7% full cell are also obviously better than those of LiFePO₄//Si.

Dealloying Synthesis of Silicon Nanotubes for High-performance Lithium Ion Batteries

Practical applications of silicon based anodes in lithium ion batteries have attracted unprecedented attentions due to the merits of extraordinary energy density, high safety and low cost. Nevertheless, the inevitable huge volume change upon lithiation and delithiation brings about silicon electrode integrity damage and fast capacity fading, hampering the large-scale application. Herein, a novel one-dimensional tubular silicon-nitrogen doped carbon composite (Si@NC) with a core-shell structure has been fabricated using silicon magnesium alloy and polydopamine as a template and precursor. The as-obtained composite exhibits remarkable specific capacity and ultrafast redox kinetics, an outstanding cycling stability with fine capacity of 583.6 mAh g-1 at 0.5 A g-1 over 200 cycles is delivered. Moreover, a full cell matched with LiFePO4 cathode has demonstrated a reversible capacity of 148.8 mAh g-1 with high Coulombic efficiency as well as an excellent energy density of 396 Wh kg-1. The nanotube structure engineering and silicon confined in nitrogen doped carbon effectively alleviate the volume expansion and endow the composite with superior stability. The robust strategy developed here gives a new insight into designing silicon anodes for enhanced lithium storage properties.

Lithium Storage Mechanism and Application of Micron-Sized Lattice-Reversible Binary Intermetallic Compounds as High-Performance Flexible Lithium-Ion Battery Anodes

A strategy of lattice-reversible binary intermetallic compounds of metallic elements is proposed for applications in flexible lithium-ion battery (LIB) anode with high capacity and cycling stability. First, the use of metallic elements can ensure excellent electronic conductivity and high capacity of the active anode substance. Second, binary intermetallic compounds possess a larger initial lattice volume than metallic monomers, so that the problem of volume expansion can be alleviated. Finally, the design of binary intermetallic compounds with lattice reversibility further improves the cycle stability. In this work, the feasibility of this strategy is verified using an indium antimonide (InSb) system. The volumetric expansion and lithium storage mechanism of InSb are investigated by in situ Raman characterization and theoretical calculations. The active material utilization is significantly improved and the growth of In whiskers is inhibited in the micron-sized ball-milled and carbon coated InSb (bInSb@C) anode, which exhibits a reversible capacity of 733.8 mAh g^-1 at 0.2 C, and provides a capacity of 411.5 mAh g^-1 after 200 cycles at 3 C with an average Coulombic efficiency of 99.95%. This strategy is validated in pouch cells, illustrating the great potential of lattice-reversible binary intermetallic compounds for use as commercial flexible LIB anodes.

Suppressing Polysulfide Shuttling in Lithium-Sulfur Batteries via a Multifunctional Conductive Binder

Exhibiting high specific energy and low cost, lithium-sulfur batteries are considered promising candidates for the next-generation battery. However, its wide applications are limited by the insulating nature of the sulfur, dissolution of polysulfide species, and large volume change of the sulfur cathode. In this work, a conductive binder, crosslinked polyfluorene (C-PF) is synthesized and employed in Li-S batteries to enhance the overall electrochemical performance from the following three aspects: 1) possessing high electronic conductivity, C-PF facilitates lowered areal resistance for the sulfur electrode and leads to an improved rate capability; 2) owing to the cross-linked polymer structure, favorable mechanical properties of the electrode can be achieved, hence the well-preserved electrode integrity; 3) forming strong binding with various polysulfide species, C-PF manages to trap them from diffusing to the Li anode, which greatly improves the cycling stability of Li-S cells. Through designing a multifunctional binder to comprehensively enhance the Li-S cathode, this proposed approach could be broadly applied to fully harness the energy from S redox in addition to cathode material modifications.

Conjugated Porous Polydiaminophenylsulfone-Triazine Polymer-A High-Performance Anode for Li-Ion Batteries

Organic compounds are promising electrode materials because of their resource sustainability, environmental friendliness, and highly tailorable properties. The porous conjugated polymer shows great potential as an electrode material for its tunable redox nature, conjugated skeleton, and porous structure. Herein, a novel conjugated porous polymer, polydiaminophenylsulfone-triazine, was synthesized by a simple nucleophilic substitution reaction. The conjugated structure and triazine ring can improve the conductivity, charge-transfer efficiency, and physicochemical stability. Also, the porous polymeric framework shows a large specific surface area and high porosity, providing a large contact area with electrolytes and reducing diffusion distance. The polymer demonstrates highly stable cycling performance and good rate capability as an anode for lithium-ion batteries, suggesting a promising strategy to design a competitive electrode material.

Interface Engineering of Silicon and Carbon by Forming a Graded Protective Sheath for High-Capacity and Long-Durable Lithium-Ion Batteries

Silicon is one of the most promising anode materials for lithium-ion batteries, whereas its low electronic conductivity and huge volumetric expansion upon lithiation strongly influence its prospective applications. Herein, we develop a facile method to introduce a graded protective sheath onto the surface of Si nanoparticles by utilizing lignin as the carbon source and Ni(NO₃)₂ as the auxiliary agent. Interestingly, the protective sheath is composed of NiSi₂, SiC, and C from the interior to the exterior, thereby guaranteeing excellent compatibility between the neighboring components. Thanks to this unique coating layer, the obtained nanocomposite delivers a large reversible specific capacity (1586.3 mAh g^-1 at 0.2 A g^-1), excellent rate capability (879.4 mAh g^-1 at 5 A g^-1), and superior cyclability (88.2% capacity retention after 500 cycles at 1 A g^-1). Such great performances are found to derive from a slight volumetric expansion, high Li⁺ ion diffusion coefficients, good interface stability, and fast electrochemical kinetics. These properties are obviously superior to those of their counterparts, benefiting from the interface engineering. This study offers new insights into constructing high-capacity and long-durable electrode materials for energy storage.