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

A Mechanically Robust In-Situ Solidified Polymer Electrolyte for SiOx-Based Anodes Toward High-Energy Lithium Batteries

Silicon suboxide (SiOx, 0 < x < 2) is an appealing anode material to replace traditional graphite owing to its much higher theoretical specific capacity enabling higher-energy-density lithium batteries. Nevertheless, the huge volume change and rapid capacity decay of SiOx electrodes during cycling pose huge challenges to their large-scale practical applications. To eliminate this bottleneck, a dragonfly wing microstructure-inspired polymer electrolyte (denoted as PPM-PE) is developed based on in-situ polymerization of bicyclic phosphate ester- and urethane motif-containing monomer and methyl methacrylate in traditional liquid electrolyte. PPM-PE delivers excellent mechanical properties, highly correlated with the formation of a micro-phase separation structure similar with dragonfly wings. By virtue of superior mechanical properties and the in-situ solidified preparation method, PPM-PE can form a 3D polymer network buffer against stress within the electrode particles gap, enabling much suppressed electrode volume expansion and more stabilized solid electrolyte interface along with evidently decreased electrolyte decomposition. Resultantly, PPM-PE shows significant improvements in both cycling and rate performance in button and soft package batteries with SiOx-based electrodes, compared with the liquid electrolyte counterpart. Such a dragonfly wing microstructure-inspired design philosophy of in-situ solidified polymer electrolytes helps facilitate the practical implementation of high-energy lithium batteries with SiOx-based anodes.

Accurate prelithiation of lithium ion battery SiOx anodes towards improved initial coulombic efficiency

We propose an accurate prelithiation method for SiOx anodes using ball-milling with LiF. The formation of a LiF-rich SEI layer reduces active lithium loss, resulting in excellent electrochemical performance. This study provides a new approach for developing high-performance silicon-based anodes for lithium-ion batteries.

A Robust Network Sodium Carboxymethyl Cellulose-Epichlorohydrin Binder for Silicon Anodes in Lithium-Ion Batteries

Silicon (Si), as an ideal anode component for lithium-ion batteries, is susceptible to substantial volume changes, leading to pulverization and excessive electrolyte consumption, ultimately resulting in a rapid decline in the cycle stability. Herein, a new sodium carboxymethyl cellulose-epichlorohydrin (CMC-ECH) binder featuring a three-dimensional (3D) network cross-linked structure is synthesized by a simple ring-opening reaction, which can effectively bond the Si anode through abundant covalent and hydrogen bonds to mitigate its pulverization. Benefitting from the merits of the CMC-ECH binder, the electrochemical performance is significantly enhanced compared to the CMC binder. The CMC-ECH binder is applied to Si anodes, a specific capacity of 1054.2 mAh g-1 can be maintained at 0.2 C following 200 cycles under an elevated Si mass loading of around 1.0 mg cm-2, and the corresponding capacity retention is 65.6%. In the case of the LiFePO4//Si@CMC-ECH full battery, the cycle stability exhibits a substantial enhancement compared with the LiFePO4//Si@CMC full battery. Furthermore, the CMC-ECH binder demonstrates compatibility with micron-Si anode materials. Based on the above, we have successfully developed a facilely prepared water-based CMC-ECH binder that is suitable for Si and micron-Si anodes in lithium-ion batteries.

Achievements, challenges, and perspectives in the design of polymer binders for advanced lithium-ion batteries

Energy storage devices with high power and energy density are in demand owing to the rapidly growing population, and lithium-ion batteries (LIBs) are promising rechargeable energy storage devices. However, there are many issues associated with the development of electrode materials with a high theoretical capacity, which need to be addressed before their commercialization. Extensive research has focused on the modification and structural design of electrode materials, which are usually expensive and sophisticated. Besides, polymer binders are pivotal components for maintaining the structural integrity and stability of electrodes in LIBs. Polyvinylidene difluoride (PVDF) is a commercial binder with superior electrochemical stability, but its poor adhesion, insufficient mechanical properties, and low electronic and ionic conductivity hinder its wide application as a high-capacity electrode material. In this review, we highlight the recent progress in developing different polymeric materials (based on natural polymers and synthetic non-conductive and electronically conductive polymers) as binders for the anodes and cathodes in LIBs. The influence of the mechanical, adhesion, and self-healing properties as well as electronic and ionic conductivity of polymers on the capacity, capacity retention, rate performance and cycling life of batteries is discussed. Firstly, we analyze the failure mechanisms of binders based on the operation principle of lithium-ion batteries, introducing two models of "interface failure" and "degradation failure". More importantly, we propose several binder parameters applicable to most lithium-ion batteries and systematically consider and summarize the relationships between the chemical structure and properties of the binder at the molecular level. Subsequently, we select silicon and sulfur active electrode materials as examples to discuss the design principles of the binder from a molecular structure point of view. Finally, we present our perspectives on the development directions of binders for next-generation high-energy-density lithium-ion batteries. We hope that this review will guide researchers in the further design of novel efficient binders for lithium-ion batteries at the molecular level, especially for high energy density electrode materials.

Simultaneous Presentation of Dexamethasone and Nerve Growth Factor via Layered Carbon Nanotubes and Polypyrrole to Interface Neural Cells

The implantation of neural electrodes usually induces acute and chronic inflammation, which can result in the formation of glial scars encapsulating the implanted electrodes and the loss of neurons near the active electrode sites. Local presentation of anti-inflammatory drugs or neural protective factors has been evidenced as an effective strategy to modulate inflammatory responses and promote electrode-neuron integration. Here, a novel delivery system for the simultaneous presentation of both anti-inflammatory drugs (dexamethasone, Dex) and nerve-growth-promoting factors (nerve growth factor, NGF) from the electrode sites was developed via layer-structured carbon nanotubes and conductive polymers. The modified electrodes exhibited higher charge storage capacitance and lower electrochemical impedance compared to unmodified electrodes and electrodes coated with polypyrrole/Dex. Dex released from the functional coating under controlled electrochemical stimulation was able to inhibit the lipopolysaccharide-induced secretion or mRNA transcription of inflammatory cytokines, including nitric oxide, TNF-α, and IL-6 in RAW264.7 cells, and control the activation of cultured astrocytes. In addition, the functional coatings did not show a toxic effect on PC12 cells and primary neural cells but exhibited promoted activities on the adhesion, growth, and neurite extension of neural cells.

Water-Soluble Polyamide Acid Binder with Fast Li+ Transfer Kinetics for Silicon Suboxide Anodes in Lithium-Ion Batteries

Silicon suboxide (SiOx) anodes have attracted considerable attention owing to their excellent cycling performance and rate capability compared to silicon (Si) anodes. However, SiOx anodes suffer from high volume expansion similar to Si anodes, which has been a challenge in developing suitable commercial binders. In this study, a water-soluble polyamide acid (WS-PAA) binder with ionic bonds was synthesized. The amide bonds inherent in the WS-PAA binder form a stable hydrogen bond with the SiOx anode and provide sufficient mechanical strength for the prepared electrodes. In addition, the ionic bonds introduced by triethylamine (TEA) induce water solubility and new Li+ transport channels to the binder, achieving enhanced electrochemical properties for the resulting SiOx electrodes, such as cycling and rate capability. The SiOx anode with the WS-PAA binder exhibited a high initial capacity of 1004.7 mAh·g-1 at a current density of 0.8 A·g-1 and a capacity retention of 84.9% after 200 cycles. Therefore, WS-PAA is a promising binder for SiOx anodes compared with CMC and SA.

In Situ Prepared Three-Dimensional Covalent and Hydrogen Bond Synergistic Binder to Boost the Performance of SiOx Anodes for Lithium-Ion Batteries

Polymer binders play an important role in enhancing the electrochemical performance of silicon-based anodes to alleviate the volume expansion for lithium-ion batteries. It is difficult for common one-dimensional (1D) linear binders to limit the volume expansion of a silicon-based electrode when combined with silicon-based particles with scant binding points. Therefore, it is necessary to design a three-dimensional (3D) network structure, which has multiple binding points with the silicon particles to dissipate the mechanical stress in the continuous charge and discharge circulation. Here, a covalent and hydrogen bond synergist 3D network green binder (poly(acrylic acid) (PAA)-dextrin 9 (Dex₉)) was prepared by the simple in situ thermal condensation of a one-dimensional liner binder PAA and Dex in the electrode fabrication process. The optimized SiO_x@PAA-Dex₉ electrode exhibits an initial Coulombic efficiency (ICE) of 82.4% at a current density of 0.2 A g^-1. At a high current density of 1 A g^-1, it retains a capacity of 607 mAh g^-1 after 300 cycles, which is approximately twice as high as that of the SiO_x@PAA electrode. Furthermore, the results of in situ electrochemical dilatometry (ECD) and characterization of electrode structures demonstrate that the PAA-Dex₉ binder can effectively buffer the huge volume change and maintain the integrity of the SiO_x electrodes. The research overcomes the low electrochemical stability difficulty of the 3D binder and sheds light on developing the simple fabrication procedure of an electrode.

Engineering of a newly isolated Bacillus tequilensis BL01 for poly-γ-glutamic acid production from citric acid

BACKGROUND

Poly γ-glutamic acid (γ-PGA) is a promising biopolymer for various applications. For glutamic acid-independent strains, the titer of γ-PGA is too low to meet the industrial demand. In this study, we isolated a novel γ-PGA-producing strain, Bacillus tequilensis BL01, and multiple genetic engineering strategies were implemented to improve γ-PGA production.

RESULTS

First, the one-factor-at-a-time method was used to investigate the influence of carbon and nitrogen sources and temperature on γ-PGA production. The optimal sources of carbon and nitrogen were sucrose and (NH₄)₂SO₄ at 37 °C, respectively. Second, the sucA, gudB, pgdS, and ggt genes were knocked out simultaneously, which increased the titer of γ-PGA by 1.75 times. Then, the titer of γ-PGA increased to 18.0 ± 0.3 g/L by co-overexpression of the citZ and pyk genes in the mutant strain. Furthermore, the γ-PGA titer reached 25.3 ± 0.8 g/L with a productivity of 0.84 g/L/h and a yield of 1.50 g of γ-PGA/g of citric acid in fed-batch fermentation. It should be noted that this study enables the synthesis of low (1.84 × 10⁵ Da) and high (2.06 × 10⁶ Da) molecular weight of γ-PGA by BL01 and the engineering strain.

CONCLUSION

The application of recently published strategies to successfully improve γ-PGA production for the new strain B. tequilensis BL01 is reported. The titer of γ-PGA increased 2.17-fold and 1.32-fold compared with that of the wild type strain in the flask and 5 L fermenter. The strain shows excellent promise as a γ-PGA producer compared with previous studies. Meanwhile, different molecular weights of γ-PGA were obtained, enhancing the scope of application in industry.

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.

Random Copolymer Hydrogel as Elastic Binder for the SiOx Microparticle Anode in Lithium-Ion Batteries

Silicon suboxides (SiO_x) have been widely concerned as a practical anode material for the next-generation lithium-ion batteries due to their relatively high theoretical capacity and lower volume change compared to silicon (Si). Nevertheless, traditional binder poly(vinylidene difluoride) (PVDF) still cannot hold the integrity of the SiO_x particle due to its weak van der Waals force. Herein, a copolymer binder for SiO_x microparticles is synthesized through a facile method of free radical polymerization between acrylamide (AM) and acrylic acid (AA). By adjusting the mass ratio of the AM/AA monomer, the copolymer binder can generate a covalent-noncovalent network with superior elastic properties from the synergistic effect. During electrochemical testing, the SiO_x anode with the optimal copolymer binder (AM/AA = 3:1) delivered a reversible capacity of 734 mAh g^-1 (two times that of commercial graphite) at 0.5C after 300 cycles. Thus, this work developed a green and effective strategy for synthesizing a water-soluble binder for Si-based anodes.